Professor Katherine Blundell OBE
7th October 2020, Gresham College
Professor Blundell was appointed Gresham Professor of Astronomy in 2019. She is a Professor of Astrophysics at Oxford University and a Research Fellow at St John’s College. Before this she was one of the Royal Society’s University Research Fellows, a Research Fellow of the 1851 Royal Commission, and a Junior Research Fellow at Balliol College, Oxford.
Her research interests include the evolution of active galaxies and their life cycles, the accretion of material near black holes and the launch and propagation of relativistic jets (jets of plasma emitted by some black holes). In her research she uses electromagnetic imaging and spectroscopy, as well as computational techniques.
She is also a renowned science communicator and set up a worldwide network of five schools-based Global Jet Watch observatories, which collect data on evolving black hole systems and nova explosions in our Galaxy, helping to inspire the next generation of scientists in South Africa, Chile, Australia and India.
Her awards include a Philip Leverhulme Prize in Astrophysics, the Royal Society’s Rosalind Franklin Medal in 2010, the Institute of Physics Bragg Medal in 2012, the Royal Astronomical Society’s Darwin Lectureship in 2015 and an OBE for services to astronomy and the education of young people in 2017.
Blundell’s first lecture series for Gresham College is called Cosmic Concepts, starting 2 October 2019, and she will be looking at how concepts developed in physics and cosmology have led to some of our most surprising discoveries about the Universe.
Professor Blundell’s lecture series are as follows:
2020/21 Cosmic Vision
2019/20 Cosmic Concepts
All lectures by the Gresham Professors of Astronomy can be accessed here.
At longer wavelengths than the normal optical wavelengths to which human eyes are normally sensitive, is the radio part of the electromagnetic spectrum.
Radio astronomy can tell us about the distribution of magnetic fields in the Universe, and reveal striking structures which have no comparable counterpart at visible wavelengths.
The following are notes from the on-line lecture. Even though I could stop the video and go back over things there are likely to be mistakes because I haven’t heard things correctly or not understood them. I hope Professor Blundell and my readers will forgive any mistakes and let me know what I got wrong.
Early astronomy could only be done by eye.
Astronomy is the oldest of the natural sciences, dating back to antiquity, with its origins in the religious, mythological, cosmological, calendrical, and astrological beliefs and practices of prehistory.
Ancient astronomers were able to differentiate between stars and planets, as stars remain relatively fixed over the centuries while planets will move an appreciable amount during a comparatively short time.
Early cultures identified celestial objects with gods and spirits. They related these objects (and their movements) to phenomena such as rain, drought, seasons, and tides. It is generally believed that the first astronomers were priests, and that they understood celestial objects and events to be manifestations of the divine, hence early astronomy’s connection to what is now called astrology.
In the 17th century BCE, the Babylonians were recording the movements of Venus. Even earlier, the Egyptians used the regular movement of the stars to measure time and to devise a calendar of 365 days.
Babylonian tablet in the British Museum recording Halley’s comet in 164 BC.
The common modern calendar is based on the Roman calendar. Although originally a lunar calendar, it broke the traditional link of the month to the phases of the Moon and divided the year into twelve almost-equal months, that mostly alternated between thirty and thirty-one days
They did not have anything to aid their observations, but they didn’t have the problem of light pollution.
In 1609 Galileo Galilei improved by-eye astronomy by using a telescope. It is a common misconception that he invented it
The first record of a telescope comes from the Netherlands in 1608. It is in a patent filed by Middelburg spectacle-maker Hans Lippershey with the States General of the Netherlands on 2 October 1608 for his instrument “for seeing things far away as if they were nearby”
https://en.wikipedia.org/wiki/Galileo_Galilei (Below left)
Galileo di Vincenzo Bonaiuti de’ Galilei (15 February 1564 – 8 January 1642) was an Italian astronomer, physicist and engineer, sometimes described as a polymath, from Pisa. Galileo has been called the “father of observational astronomy”, the “father of modern physics”, the “father of the scientific method”, and the “father of modern science”.
https://en.wikipedia.org/wiki/Hans_Lipperhey (Above right)
Hans Lipperhey (1570 – buried 29 September 1619), also known as Johann Lippershey or Lippershey, was a German-Dutch spectacle-maker. He is commonly associated with the invention of the telescope, because he was the first one who tried to obtain a patent for it. It is, however, unclear if he was the first one to build a telescope.
Galileo’s “cannocchiali” telescopes at the Museo Galileo, Florence
Galileo made his telescope with about 3x magnification. He later made improved versions with up to about 30x magnification. With his telescope, he could see magnified, upright images on the Earth — it was what is commonly known as a terrestrial telescope or a spyglass. He could also use it to observe the sky. Initially he was one of the few people who could construct telescopes good enough for that purpose. On 25 August 1609, he demonstrated one of his early telescopes, with a magnification of about 8 or 9, to Venetian lawmakers. His telescopes were also a profitable sideline as he was able to sell them to merchants who found them useful both at sea and as items of trade. He published his initial telescopic astronomical observations in March 1610 in a brief treatise entitled Sidereus Nuncius (Starry Messenger).
On 30 November, 1609, Galileo aimed his telescope at the Moon. He wasn’t the first person to do this but he was the first to deduce the cause of the uneven waning as light occlusion from lunar mountains and craters.
An illustration of the Moon from Sidereus Nuncius, published in Venice, 1610.
On 7 January 1610, Galileo observed with his telescope what he described at the time as “three fixed stars, totally invisible by their smallness”, all close to Jupiter, and lying on a straight line through it. Observations on subsequent nights showed that the positions of these “stars” relative to Jupiter were changing in a way that would have been inexplicable if they had really been fixed stars. On 10 January, Galileo noted that one of them had disappeared, an observation which he attributed to its being hidden behind Jupiter. Within a few days, he concluded that they were orbiting Jupiter: he had discovered three of Jupiter’s four largest moons.
Galileo’s observations of the satellites of Jupiter caused a revolution in astronomy: a planet with smaller planets orbiting it did not conform to the principles of Aristotelian cosmology, which held that all heavenly bodies should circle the Earth, and many astronomers and philosophers initially refused to believe that Galileo could have discovered such a thing. His observations were confirmed by the observatory of Christopher Clavius and he received a hero’s welcome when he visited Rome in 1611. Galileo continued to observe the satellites over the next eighteen months, and by mid-1611, he had obtained remarkably accurate estimates for their periods, which other astronomers had believed impossible
It was on this page that Galileo first noted an observation of the moons of Jupiter. This observation upset the notion that all celestial bodies must revolve around the Earth. Galileo published a full description in Sidereus Nuncius in March 1610
Galileo also made observations of Venus, Saturn and Neptune (although he did not recognise Neptune as a planet). He made observations of sunspots and observed the Milky Way to be a multitude of stars packed so densely that they appeared from Earth to be clouds. He also located many other stars too distant to be visible with the naked eye and observed the double star Mizar in Ursa Major in 1617.
Now you don’t need a telescope to see the night sky (providing you are blessed with good eyesight and there are no clouds about) because it is possible to see the Moon, some of our closer neighbouring planets (Mars was very visible recently) and stars (and in non-urban areas, the Milky Way)
The Milky Way over Exmoor. Credit: Keith Trueman
Dark Skies over Arundel Park. Credit: Jamie Fielding
Now I am very interested in astronomy and I regularly watch a programme on BBC4 called “The sky at night”. It has excellent presenters in Professor Chris Lintott and Dr Maggie Aderin-Pocock
It has the added benefit of not having Professor Brian Cox in it.
Watching this wonderful programme means that I don’t have to go out in the cold and look at things myself.
It is possible, if there is no bright Moon, light pollution, clouds, and your eyes have adapted to the dark, to see that stars come in different colours (unless you are colour blind).
Stars exist in a range of colours: red, orange, yellow, green, white and blue with red being the coolest and blue being the hottest.
A star’s colour indicates it’s temperature, composition and relative distance from earth. Its luminosity indicates its size, the brighter it is, the larger it is.
Image credit: NASA/JPL-Caltech/2MASS
Rigel in Orion is a blue-white supergiant 900 light-years distant.
Procyon in Canis Minor is a yellow-white star 11.4 light years away.
Capella in Auriga is a yellow giant 42.2 light-years from Earth.
Arcturus in Bootes is an orange giant found 34 light years distant.
Castor (white) and Pollux (orange) in Gemini lie 33.7 light-years and 52 light-years away from Earth.
Aldebaran in Taurus is an orange-red giant 65 light-years from our solar system.
Betelgeuse in Orion is a red supergiant located 1400 light years away.
Another thing you can see in the sky without a telescope is s telescope is a rainbow.
A rainbow is a meteorological phenomenon that is caused by reflection, refraction and dispersion of light in water droplets resulting in a spectrum of light appearing in the sky. It takes the form of a multicoloured circular arc. Rainbows caused by sunlight always appear in the section of sky directly opposite the sun.
In a primary rainbow, the arc shows red (refracted the least) on the outer part and violet (refracted the most) on the inner side. This rainbow is caused by light being refracted when entering a droplet of water, then reflected inside on the back of the droplet and refracted again when leaving it.
Light is refracted (like all waves) because its speed changes when it moves from one medium to another.
A consequence of dispersion is the change in the angle of refraction of different colours of light, which is why you get a rainbow.
What is absolutely fascinating is that your eyes (providing you are not colour blind) are only capable of distinguishing three colours, red, blue and green.
Perception of colour begins with specialised retinal cells containing pigments with different spectral sensitivities, known as cone cells. In humans, there are three types of cones sensitive to three different spectra, resulting in trichromatic colour vision.
A range of wavelengths of light stimulates each of these receptor types to varying degrees. The brain combines the information from each type of receptor to give rise to different perceptions of different wavelengths of light.
There is a phenomenal number of colours and the wonderful thing is that because we all have different brains you won’t see a colour in the same way as somebody else.
A friend and colleague of professor Blundell, Andrew Steele, decided to take a picture of a rainbow.
Then he decided to take a picture with a UV (ultraviolet) filter. This blocked out all wavelengths of light except UV.
He then used an IR (infra-red) filter
Andrew Steel’s images show there is more out there than you can see with your eyes. There is a whole spectrum of electromagnic radiation
The electromagnetic spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies.
The electromagnetic spectrum covers electromagnetic waves with frequencies ranging from below one hertz to above 1025 hertz, corresponding to wavelengths from thousands of kilometres down to a fraction of the size of an atomic nucleus. This frequency range is divided into separate bands, and the electromagnetic waves within each frequency band are called by different names; beginning at the low frequency (long wavelength) end of the spectrum these are: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays at the high-frequency (short wavelength) end. The electromagnetic waves in each of these bands have different characteristics, such as how they are produced, how they interact with matter, and their practical applications. The limit for long wavelengths is the size of the universe itself, while it is thought that the short wavelength limit is in the vicinity of the Planck length. Gamma rays, X-rays, and high ultraviolet are classified as ionizing radiation as their photons have enough energy to ionize atoms, causing chemical reactions.
In most of the frequency bands above, a technique called spectroscopy can be used to physically separate waves of different frequencies, producing a spectrum showing the constituent frequencies. Spectroscopy is used to study the interactions of electromagnetic waves with matter. Other technological uses are described under electromagnetic radiation.
A small part of the electromagnetic spectrum that includes its visible components. The divisions between infrared, visible, and ultraviolet are not perfectly distinct, nor are those between the seven rainbow colours.
The electromagnetic waves are transverse waves and travel at the same speed in a vacuum, 3 x 108ms-1.
The electromagnetic spectrum is continuous so there is no break between each type of wave. In fact, there is an overlap. For instance, X-rays and gamma rays can have overlapping wavelengths/frequencies and it is how they are formed which determines which is which. In fact, it is just the wavelength/frequency which is different for each member of the electromagnetic spectrum and this causes them to have different energies.
In physics, a transverse wave is a moving wave whose oscillations are perpendicular to the propagation direction (direction of energy travel).
Although visible light is convenient for us, because we use it to see. It can’t pass through dust (shame as I hate dusting) any more than UB light can get through sunscreen.
If you want to look deeply into space and look past the dust in the centre of our galaxy, you need to use the longer wavelengths, at least into the Infra-red region.
The infra-red allows us to see right into the centre of the Milky Way
The Milky Way is the galaxy that contains our Solar System, with the name describing the galaxy’s appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye.
The Milky Way is a barred spiral galaxy with an estimated visible diameter between 170,000 and 200,000 light-years (ly). It is estimated to contain 100–400 billion stars and at least that number of planets. The dark matter halo around the Milky Way may span as much as 2 million light years. The Solar System is located at a radius of about 27,000 light-years from the Galactic Centre, on the inner edge of the Orion Arm, one of the spiral-shaped concentrations of gas and dust. The stars in the innermost 10,000 light-years form a bulge and one or more bars that radiate from the bulge. The galactic centre is an intense radio source known as Sagittarius A*, a supermassive black hole of 4.100 (± 0.034) million solar masses.
Increasing the resolution can even allow you to make out in detail the paths of stars very close to the galactic centre.
This is what Reinhard Genzel and Andrea Ghez did.
Reinhard Genzel ForMemRS (born 24 March 1952) is a German astrophysicist, co-director of the Max Planck Institute for Extraterrestrial Physics, a professor at LMU and an emeritus professor at the University of California, Berkeley. He was awarded the 2020 Nobel Prize for physics “for the discovery of a supermassive compact object at the centre of our galaxy”, which he shared with Andrea Ghez and Roger Penrose.
Andrea Mia Ghez (born June 16, 1965) is an American astronomer and professor in the Department of Physics and Astronomy at the University of California, Los Angeles. Her research focuses on the centre of the Milky Way galaxy. In 2020, she became the fourth woman to be awarded the Nobel Prize in Physics, sharing one half of the prize with Reinhard Genzel (the other half of the prize being awarded to Roger Penrose). The Nobel Prize was awarded to Ghez and Genzel for their discovery of a supermassive compact object, now generally recognized to be a black hole, in the Milky Way’s galactic centre.
This simulation shows the orbits of a tight group of stars close to the supermassive blackhole at the heart of the Milky Way. During 2018 one of these stars, S2, passed very close to the black hole and was the subject of intense scrutiny with ESO telescope. Its behaviour matched the predictions of Einstein’s general relativity and was inconsistent with simpler Newtonian gravity. More information and download options: http://www.eso.org/public/videos/eso1…
An image showing the orbits of stars extremely close to the supermassive black hole at the Milky Way’s core. The star S2, which orbits every 16 years, passed very close to the black hole in May 2018, letting astronomers examine the extreme effects of relativity. (Image credit: ESO/L. Calçada/spaceengine.org)
Reinhard Genzel and Andrea Ghez studied the galactic centre and tracked the paths of the stars and calculated their orbits. This enabled them to locate a seemingly dark point at the centre of our galaxy.
Their work identified a black hole at the centre of our galaxy which provides a focus the orbits of those stars. They were also able to determine that this black hole has a mass that is 4 million times the mass of our Sun.
A black hole is a region of spacetime where gravity is so strong that nothing—no particles or even electromagnetic radiation such as light—can escape from it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole.
For their work on black holes they shared the Nobel prize for physics in 2020 with Roger Penrose.
Sir Roger Penrose OM FRS (born 8 August 1931) is an English mathematical physicist, mathematician, philosopher of science and Nobel Laureate in Physics. He is Emeritus Rouse Ball Professor of Mathematics at the University of Oxford, an emeritus fellow of Wadham College, Oxford and an honorary fellow of St John’s College, Cambridge, and of University College London (UCL).
Penrose has made contributions to the mathematical physics of general relativity and cosmology. He has received several prizes and awards, including the 1988 Wolf Prize in Physics, which he shared with Stephen Hawking for the Penrose–Hawking singularity theorems, and one half of the 2020 Nobel Prize in Physics “for the discovery that black hole formation is a robust prediction of the general theory of relativity”.
“for the discovery that black hole formation is a robust prediction of the general theory of relativity”
“for the discovery of a supermassive compact object at the centre of our galaxy”
In 2019 Professor Blundell gave a lecture where she posed a question. Can anything go faster than light?
In it she described the work of James Clerk Maxwell
James Clerk Maxwell FRSE FRS (13 June 1831 – 5 November 1879) was a Scottish scientist in the field of mathematical physics. His most notable achievement was to formulate the classical theory of electromagnetic radiation, bringing together for the first time electricity, magnetism, and light as different manifestations of the same phenomenon. Maxwell’s equations for electromagnetism have been called the “second great unification in physics” after the first one realised by Isaac Newton.
Maxwell had studied and commented on electricity and magnetism as early as 1855 when his paper “On Faraday’s lines of force” was read to the Cambridge Philosophical Society.
Around 1862, while lecturing at King’s College, Maxwell calculated that the speed of propagation of an electromagnetic field is approximately that of the speed of light He considered this to be more than just a coincidence, commenting, “We can scarcely avoid the conclusion that light consists in the transverse undulations of the same medium which is the cause of electric and magnetic phenomena.”
Working on the problem further, Maxwell showed that the equations predict the existence of waves of oscillating electric and magnetic fields that travel through empty space at a speed that could be predicted from simple electrical experiments; using the data available at the time, Maxwell obtained a velocity of 310,740,000 metres per second. In his 1864 paper “A Dynamical Theory of the Electromagnetic Field”, Maxwell wrote, “The agreement of the results seems to show that light and magnetism are affections of the same substance, and that light is an electromagnetic disturbance propagated through the field according to electromagnetic laws”.
In other words, the speed of electromagnetic waves depends only on the electrical and magnetic properties of the space that they pass through.
The electric field (blue arrows) oscillates in the ±x-direction, and the orthogonal magnetic field (red arrows) oscillates in phase with the electric field, but in the ±y-direction.
Classically, electromagnetic radiation consists of electromagnetic waves, which are synchronized oscillations of electric and magnetic fields. In a vacuum, electromagnetic waves travel at the speed of light, commonly denoted c. In homogeneous, isotropic media, the oscillations of the two fields are perpendicular to each other and perpendicular to the direction of energy and wave propagation, forming a transverse wave.
Maxwell produced twenty equations, which in their modern form are four partial differential equations, in his textbook “A Treatise on Electricity and Magnetism” in 1873. He did most of this work at Glenlair during the period between holding his London Kings College post and his taking up the Cavendish chair at Cambridge. The complexity of his theory was reduced down to four differential equations, now known collectively as Maxwell’s Laws or Maxwell’s equations (the bane of my life as a physics undergraduate),
Once upon a time I could derive those equations ☹
Maxwell established there were no length limits to which his equations applied. In a way he predicted the existence of radio waves and X-rays, which are longer and shorter than visible light.
Heinrich Herts actually demonstrated existence of radio waves.
Heinrich Rudolf Hertz (22 February 1857 – 1 January 1894) was a German physicist who first conclusively proved the existence of the electromagnetic waves predicted by James Clerk Maxwell’s equations of electromagnetism. The unit of frequency, cycle per second, was named the “hertz” in his honour.
Above left: Early experimental Hertz radiator and resonator for creating and detecting Hertzian waves ~1890. Simple spark gap apparatus similar to this was the first ever built to produce and detect radio waves.
A high voltage produces a spark. The spark generated an electromagnetic wave which induced a current in the circular resonator. The current in the resonator causes a spark to jump across the little gap in it.
In that action at a distance Hertz had demonstrated the existence of electromagnetic waves with wavelengths greater than visible light, in values of centimetres and metres,
Hertz was able to demonstrate that these waves could be reflected and refracted in exactly the same way as visible light.
Thanks to the work of Maxwell and Herts it was found that visible light and radio waves were both parts of the electromagnetic spectrum.
This led to important developments in communication. Prior to this, communication over long distances had to take place by sending coded pulses of electric current through dedicated wires to transmit information.
Wireless telegraphy or radiotelegraphy is transmission of telegraph signals by radio waves.
Radiotelegraphy was the first means of radio communication. The first practical radio transmitters and receivers invented in 1894–1895 by Guglielmo Marconi used radiotelegraphy.
https://en.wikipedia.org/wiki/Guglielmo_Marconi (below left)
Guglielmo Giovanni Maria Marconi, 1st Marquis of Marconi FRSA (25 April 1874 – 20 July 1937) was an Italian inventor and electrical engineer, known for his pioneering work on long-distance radio transmission, development of Marconi’s law, and a radio telegraph system. He is credited as the inventor of radio, and he shared the 1909 Nobel Prize in Physics with Karl Ferdinand Braun “in recognition of their contributions to the development of wireless telegraphy”
https://en.wikipedia.org/wiki/Karl_Ferdinand_Braun (Above right)
Karl Ferdinand Braun (6 June 1850 – 20 April 1918) was a German electrical engineer, inventor, physicist and Nobel laureate in physics. Braun contributed significantly to the development of radio and television technology: he shared the 1909 Nobel Prize in Physics with Guglielmo Marconi “for their contributions to the development of wireless telegraphy”.
The Titanic disaster of 1912 would have been far worse without radio communication.
RMS Titanic was a British passenger liner operated by the White Star Line that sank in the North Atlantic Ocean in the early morning hours of 15 April 1912, after striking an iceberg during her maiden voyage from Southampton to New York City. Of the estimated 2,224 passengers and crew aboard, more than 1,500 died, making the sinking one of modern history’s deadliest peacetime commercial marine disasters.
Titanic’s radiotelegraph equipment (then known as wireless telegraphy) was leased to the White Star Line by the Marconi International Marine Communication Company, which also supplied two of its employees, Jack Phillips and Harold Bride, as operators. The service maintained a 24-hour schedule, primarily sending and receiving passenger telegrams, but also handling navigation messages including weather reports and ice warnings
The radio room was located on the Boat Deck, in the officers’ quarters. A soundproofed “Silent Room”, next to the operating room, housed loud equipment, including the transmitter and a motor-generator used for producing alternating currents. The operators’ living quarters were adjacent to the working office. The ship was equipped with a ‘state of the art’ 5 kilowatt rotary spark-gap transmitter, operating under the radio callsign MGY, and communication was conducted in Morse code. This transmitter was one of the first Marconi installations to use a rotary spark-gap, which gave Titanic a distinctive musical tone that could be readily distinguished from other signals. The transmitter was one of the most powerful in the world, and guaranteed to broadcast over a radius of 563 km. An elevated T-antenna that spanned the length of the ship was used for transmitting and receiving. The normal operating frequency was 500 kHz (600 m wavelength); however, the equipment could also operate on the “short” wavelength of 1,000 kHz (300 m wavelength) that was employed by smaller vessels with shorter antennas.
The radio operators were able to alert ships in the vicinity, who were able to locate where the ship was sinking, and come to the rescue. Some 700 people were saved thanks to radio, Hertz and Maxwell.
Radio communication was vital during the Second World War
Radio was how soldiers, sailors and pilots communicated with each other and their bases. It was how resistance fighters passed on information. It was how children, like my mum and dad, and their parents found out how the war was going (and how the poor people, whose country had been invaded by the Germans, could secretly get news).
Radio had another use during the war, radar.
Radar is a detection system that uses radio waves to determine the range, angle, or velocity of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. A radar system consists of a transmitter producing electromagnetic waves in the radio or microwaves domain, a transmitting antenna, a receiving antenna (often the same antenna is used for transmitting and receiving) and a receiver and processor to determine properties of the object(s). Radio waves (pulsed or continuous) from the transmitter reflect off the object and return to the receiver, giving information about the object’s location and speed.
Radar was developed secretly for military use by several nations in the period before and during World War II. A key development was the cavity magnetron in the United Kingdom, which allowed the creation of relatively small systems with sub-meter resolution. The term RADAR was coined in 1940 by the United States Navy as an acronym for “radio detection and ranging”. The term radar has since entered English and other languages as a common noun, losing all capitalisation.
Chain Home, or CH for short, was the codename for the ring of coastal Early Warning radar stations built by the Royal Air Force (RAF) before and during the Second World War to detect and track aircraft. Initially known as RDF, and given the official name Air Ministry Experimental Station Type 1 (AMES Type 1) in 1940, the radar units themselves were also known as Chain Home for most of their life. Chain Home was the first early warning radar network in the world, and the first military radar system to reach operational status. Its effect on the outcome of the war made it one of the most powerful weapons of what is today known as the “Wizard War”
Chain Home proved decisive during the Battle of Britain in 1940; CH systems could detect enemy aircraft while they were still forming up over France, giving RAF commanders ample time to marshal their entire force directly in the path of the raid. This had the effect of multiplying the effectiveness of the RAF to the point that it was as if they had three times as many fighters, allowing them to defeat the larger German force. With such high efficiency, it was no longer the case that “the bomber will always get through”
The Chain Home network was continually expanded, with over forty stations operational by the war’s end. Late in the war, when the threat of Luftwaffe bombing had ended, the CH systems were used to detect V2 missile launches.
Winston Churchill said that radar played a crucial role along with the brave pilots in winning the Battle of Britain.
Sir Winston Leonard Spencer Churchill, KG, OM, CH, TD, DL, FRS, RA (30 November 1874 – 24 January 1965) was a British statesman, army officer, and writer. He was Prime Minister of the United Kingdom from 1940 to 1945, when he led the country to victory in the Second World War, and again from 1951 to 1955
The Battle of Britain was a military campaign of the Second World War, in which the Royal Air Force (RAF) and Fleet Air Arm (FAA) of the Royal Navy defended the United Kingdom (UK) against large-scale attacks by Nazi Germany’s air force, the Luftwaffe. It has been described as the first major military campaign fought entirely by air forces. The British officially recognise the battle’s duration as being from 10 July until 31 October 1940, which overlaps the period of large-scale night attacks known as the Blitz, that lasted from 7 September 1940 to 11 May 1941. German historians do not accept this subdivision and regard the battle as a single campaign lasting from July 1940 to June 1941, including the Blitz.
The primary objective of the German forces was to compel Britain to agree to a negotiated peace settlement.
In 1933 Karl Jansky built equipment to study radio waves from different “viewing” angles. He recognised different sources of radio waves.
Karl Guthe Jansky (October 22, 1905 – February 14, 1950) was an American physicist and radio engineer who in August 1931 first discovered radio waves emanating from the Milky Way. He is considered one of the founding figures of radio astronomy.
He was a young engineer with Bell Laboratories and he was tasked with identifying sources of static for their overseas radio communications. He built this rotating antenna to get all-sky coverage at the chosen frequency of 20.5 MHz (wavelength about 14.5 meters), and it quickly got the nickname of “Jansky’s Merry-go-round.” With it, he picked up thunderstorms and a strange hiss that moved throughout the day. He eventually figured out that it was extra-terrestrial in origin, coming from the direction of Sagittarius, behind which lies the heart of our Galaxy.
The New York Times article stated that the radio waves had been traced to the centre of the Milky Way.
Jansky produced a paper about his findings but it took a while for radio astronomy to catch on because radio engineers knew nothing about astronomy and astronomers, at that time, knew nothing about engineering.
Grote Reber made progress.
Grote Reber (December 22, 1911 – December 20, 2002) was an American pioneer of radio astronomy, which combined his interests in amateur radio and amateur astronomy. He was instrumental in investigating and extending Karl Jansky’s pioneering work, and conducted the first sky survey in the radio frequencies.
In the summer of 1937, Reber decided to build his own radio telescope, in his back yard. It was considerably more advanced than Jansky’s, and consisted of a parabolic sheet metal dish 9 metres in diameter, focusing to a radio receiver 8 meters above the dish. The entire assembly was mounted on a tilting stand, allowing it to be pointed in various directions, though not turned. The telescope was completed in September 1937.
His 1937 radio antenna was the second ever to be used for astronomical purposes and the first parabolic reflecting antenna to be used as a radio telescope. For nearly a decade he was the world’s only radio astronomer.
Reber Radio Telescope in Wheaton, Illinois, 1937
His first receiver operated at 3300 MHz and failed to detect signals from outer space, as did his second, operating at 900 MHz. Finally, his third attempt, at 160 MHz, was successful in 1938, confirming Jansky’s discovery. In 1940, he achieved his first professional publication,
He turned his attention to making a radiofrequency sky map, which he completed in 1941 and extended in 1943.
You can see from the image above that Reber wrote a paper in 1944 where he pinpointed the area where the radio waves were coming from. This was the constellation Sagittarius, where the centre of our galaxy is known to exist.
Sagittarius is one of the constellations of the zodiac and is located in the Southern celestial hemisphere. It is one of the 48 constellations listed by the 2nd-century astronomer Ptolemy and remains one of the 88 modern constellations. Sagittarius is commonly represented as a centaur pulling back a bow. It lies between Scorpius and Ophiuchus to the west and Capricornus and Microscopium to the east.
The centre of the Milky Way lies in the westernmost part of Sagittarius
Reber’s data, published as contour maps showing the brightness of the sky in radio wavelengths, revealed the existence of radio sources such as Cygnus A and Cassiopeia A for the first time. As mentioned earlier he was the world’s only radio astronomer for nearly a decade from 1937. An area of research that only expanded after World War Two when scientists, who had gained a great deal of knowledge during the wartime expansion of RADAR, entered the field.
Grote Reber’s map (a projection of the sky) of the radio sky showing radiation concentration along the plane and centre of the Milky Way with a large maximum in Sagittarius (the centre of our galaxy) and smaller maxima in Cygnus. The map was made in 1944 at a wavelength of 1.9m.
The contour representation is a way of illustrating the bright and less bright signals being detected.
The more a contour is surrounded by other contours the brighter the region is. Professor Blundell is pointing to the region of Sagittarius, the centre of our galaxy, where the black hole is found. Radio signals beaming brightly.
Radio telescopes have advanced hugely over the years
In the left part of the above image you can see the Lovel telescope at Jodrell Bank.
The Jodrell Bank Observatory – originally the Jodrell Bank Experimental Station and from 1966 to 1999, the Nuffield Radio Astronomy Laboratories – hosts a number of radio telescopes, and is part of the Jodrell Bank Centre for Astrophysics at the University of Manchester. The observatory was established in 1945 by Bernard Lovell, a radio astronomer at the University of Manchester to investigate cosmic rays after his work on radar during the Second World War. It has since played an important role in the research of meteoroids, quasars, pulsars, masers and gravitational lenses, and was heavily involved with the tracking of space probes at the start of the Space Age.
Sir Alfred Charles Bernard Lovell OBE FRS (31 August 1913 – 6 August 2012) was a British physicist and radio astronomer. He was the first Director of Jodrell Bank Observatory, from 1945 to 1980
The Lovell Telescope is a radio telescope at Jodrell Bank Observatory, near Goostrey, Cheshire in the north-west of England. When construction was finished in 1957, the telescope was the largest steerable dish radio telescope in the world at 76.2 m diameter. It can produce very fine radio images
There are three other active telescopes at the observatory; the Mark II, and 13 m and 7 m diameter radio telescopes. Jodrell Bank Observatory is the base of the Multi-Element Radio Linked Interferometer Network (MERLIN), a National Facility run by the University of Manchester on behalf of the Science and Technology Facilities Council.
On 7 July 2019, the observatory became a UNESCO World Heritage Site.
The most famous radio observatory is the “Very Large Array”,
The Karl G. Jansky Very Large Array (VLA) is a centimetre-wavelength radio astronomy observatory located in central New Mexico on the Plains of San Agustin, between the towns of Magdalena and Datil, ~80 km west of Socorro. The VLA comprises twenty-eight 25-metre radio telescopes (27 of which are operational while one is always rotating through maintenance) deployed in a Y-shaped array and all the equipment, instrumentation, and computing power to function as an interferometer. Each of the massive telescopes is mounted on double parallel railway tracks, so the radius and density of the array can be transformed to adjust the balance between its angular resolution and its surface brightness sensitivity. Astronomers using the VLA have made key observations of black holes and protoplanetary disks around young stars, discovered magnetic filaments and traced complex gas motions at the Milky Way’s centre, probed the Universe’s cosmological parameters, and provided new knowledge about the physical mechanisms that produce radio emission.
The VLA stands at an elevation of 2124 m above sea level. It is a component of the National Radio Astronomy Observatory (NRAO). The NRAO is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
The VLA has appeared repeatedly in American popular culture since its construction:
The VLA is present in the 1984 movie 2010: The Year We Make Contact, as the location where Dr. Floyd and Dimitri Moiseyevich discuss the upcoming missions to Jupiter.
The VLA is present in the 1997 movie Contact, as the location where the alien signal is first detected.
Professor Blundell reminds us that you can’t actually radio waves
British artist Keith Tyson created a 300-piece sculpture called Large Field Array (2006–2007) named after the VLA.
In the 2009 science-fiction film Terminator Salvation, the VLA is the location of a Skynet facility. At the beginning of the film the site is attacked by Resistance forces
VLA is a range of different dishes collectively acting as one great big telescope giving fine detail even if the object is faint and/or far away
Drew Medlin’s images show that radio astronomy can give superior images to optical astronomy. With radio you can carry on when clouds are gathering as clouds are transparent to long wavelength radio waves.
Back to optical astronomy
An optical view of cygnus
Cygnus is a northern constellation lying on the plane of the Milky Way, deriving its name from the Latinized Greek word for swan. Cygnus is one of the most recognizable constellations of the northern summer and autumn, and it features a prominent asterism known as the Northern Cross (in contrast to the Southern Cross).
In the image below each dot of light is probably a star
The shining stars are telling us where nuclear fusion is taking place in the Universe
Nuclear fusion is a reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles (neutrons or protons). In main sequence stars (a continuous and distinctive band of stars that appear on plots of stellar colour versus brightness) and other high-magnitude stars the difference in mass between the reactants and products results in the release of energy which powers them.
Our Sun is a main-sequence star, and thus generates its energy by nuclear fusion of hydrogen nuclei into helium. In its core, the Sun fuses 500 million metric tons of hydrogen each second. The proton-proton chain reaction, branch I, dominates in stars the size of the Sun or smaller.
However, not all points of light in the optical view of Cygnus are stars
A fuzzy blob at the centre is a coagulation of many stars. The radio wave version of the image shows a completely different picture
It shows jets of radio emitting plasma being launched from central point, a black hole.
These jets transmit/transport extreme amounts of energy well beyond the confines of the galaxy that produced them into the galactic medium.
Professor Blundell pointing out the dot, that is a black hole, where the jets emanate from
The size scale is huge. The distance across the two plumes is more than 100 thousand lightyears across (a lightyear is the distance travelled by light in a year). This is a very big distance because the speed of light is large.
It took more than 100 million years for this region of space to reach this size. The central black hole has a mass equivalent to 1 billion times the mass of our Sun.
These plumes are readily detected at radio frequencies. The radio image shows evidence of energetic transport which impinges on the intergalactic medium, shocking it and giving rise to particle acceleration. It tells us about the presence of magnetic fields in the Universe and tells us about the highly energetic charged particles, electrons and protons, which are travelling at speeds close to that of the speed of light. The motion of these particles is characterised by the jets being expelled in opposite directions.
Huge amounts of energetic plasma are expelled in opposite directions from the host galaxy (blue in the above right image) to the intergalactic medium.
The brightness of the red indicates the brightness/luminosity of the emitted radio waves, which have a wavelength of about 6cm. This wavelength is much larger than the visible light wavelengths that make the galaxy visible to us.
Robert Lang has produced amazing images of the jets, showing the explosive and dynamic processes emanating from a black hole.
They move at great speeds close to the speed of light with a life cycle in millions of years. During this time they grow to huge sizes.
Quasar nuclei are very luminous
A quasar (also known as a quasi-stellar object, abbreviated QSO) is an extremely luminous active galactic nucleus (AGN), in which a supermassive black hole with mass ranging from millions to billions of times the mass of the Sun is surrounded by a gaseous accretion disk. As gas in the disk falls towards the black hole, energy is released in the form of electromagnetic radiation, which can be observed across the electromagnetic spectrum. The power radiated by quasars is enormous: the most powerful quasars have luminosities thousands of times greater than a galaxy such as the Milky Way. Usually, quasars are categorized as a subclass of the more general category of AGN. The redshifts of quasars are of cosmological origin.
The term quasar originated as a contraction of quasi-stellar [star-like] radio source because quasars were first identified during the 1950s as sources of radio-wave emission of unknown physical origin, and when identified in photographic images at visible wavelengths they resembled faint, star-like points of light. High-resolution images of quasars, particularly from the Hubble Space Telescope, have demonstrated that quasars occur in the centres of galaxies, and that some host galaxies are strongly interacting or merging galaxies. As with other categories of AGN, the observed properties of a quasar depend on many factors, including the mass of the black hole, the rate of gas accretion, the orientation of the accretion disk relative to the observer, the presence or absence of a jet, and the degree of obscuration by gas and dust within the host galaxy.
Quasars are found over a very broad range of distances, and quasar discovery surveys have demonstrated that quasar activity was more common in the distant past. The peak epoch of quasar activity was approximately 10 billion years ago. As of 2017, the most distant known quasar is ULAS J1342+0928 at redshift z = 7.54; light observed from this quasar was emitted when the universe was only 690 million years old. The supermassive black hole in this quasar, estimated at 800 million solar masses, is the most distant black hole identified to date. Recently, another quasar was detected from a time only 700 million years after the Big Bang, and with an estimated mass of 1.5 billion times the mass of our Sun.
The green shapes on the image below correspond to the jets flowing from the host galaxy and affecting the intergalactic medium.
Zooming in on the lower region there is a hot spot where there is a great big shock due to the energetic jet impacting on the intergalactic medium. The blue pixels are radio waves and the fine resolution image was made with the Merlin network of telescopes including the Lovell telescope. The red pixels show information produced using the Chandra telescope, which is sensitive to the energetic short wavelength X-ray electromagnetic waves.
The Chandra X-ray Observatory (CXO), previously known as the Advanced X-ray Astrophysics Facility (AXAF), is a Flagship-class space telescope launched aboard the Space Shuttle Columbia during STS-93 by NASA on July 23, 1999. Chandra is sensitive to X-ray sources 100 times fainter than any previous X-ray telescope, enabled by the high angular resolution of its mirrors. Since the Earth’s atmosphere absorbs the vast majority of X-rays, they are not detectable from Earth-based telescopes; therefore space-based telescopes are required to make these observations. Chandra is an Earth satellite in a 64-hour orbit, and its mission is ongoing as of 2020.
Chandra is one of the Great Observatories, along with the Hubble Space Telescope, Compton Gamma Ray Observatory (1991-2000), and the Spitzer Space Telescope (2003-2020). Its mission is similar to that of ESA’s XMM-Newton spacecraft, also launched in 1999 but the two telescopes have different design foci; Chandra has much higher angular resolution.
Merlin and Chandra are able to investigate these very energetic quasar jets spurting out of a black hole and affecting the media outside the galaxy.
The image below left shows that the end to end length of the jets is 36 million light years across.
The image below right shows a distance of 65000 light years, equivalent to three Milky Ways sandwiched in sideways.
Just using visible light would mean missing out on seeing the detail and immensity of this structure.
The influence of these radio quasars is vastly in excess of the event horizon of the black hole which produced the jets. They redistribute energy to the intergalactic medium and affect the structure of galaxies.
Radio waves stream millions of light-years into space from the heart of the galaxy Centaurus A (Source: Ilana Feain, Tim Cornwell, Ron Ekers (CSIRO))
Particles emitting radio waves stream millions of light-years into space from the heart of the galaxy Centaurus A. Data for the image was gathered with CSIRO’s Australia Telescope Compact Array and Parkes radio telescope: the frequency of the radio waves was 1.4 GHz. The smallest structure visible in the image is 680 parsecs (210 light-years) across: the scale bar represents 50,000 parsecs (about 163,000 light-years). The white dots are not stars but background radio sources, each a huge galaxy like Centaurus A in the distant Universe. Image: Ilana Feain, Tim Cornwell and Ron Ekers (CSIRO/ATNF). ATCA northern middle lobe pointing courtesy R. Morganti (ASTRON), Parkes data courtesy N. Junkes (MPIfR).
Ronald David Ekers AO (born 18 September 1941) FRS FAA is an Australian radio astronomer. His fields of specialty include the study of active galactic nuclei, cosmology, and radio astronomy techniques.
The image below shows how big the streams of radio waves are by comparing them with a group of radio telescopes.
The jets can take millions of years to grow so we can’t see them evolve step-by-step because we don’t live long enough. We can’t follow their life cycles.
Deep hi-fidelity imaging with radio telescopes allows the study and examination of plasma physics processes as well as other astrophysical processes and how they effect the surroundings into which they expand and grow.
The MeerKAT image of the giant X-shaped radio galaxy PKS 2014-55. Courtesy of SARAO and Bill Cotton et al
Before the above image was taken astronomers wondered if the phenomenon was just a pair of jets which produced the other pair, and which was which.
The prominent X-shape of PKS 2014-55 is made up of two pairs of giant lobes consisting of hot jets of electrons. These jets spurt outwards from a supermassive black hole at the galaxy’s heart.
The image indicates that once a pair of jets blew out material, this material fell back and diverted because there was no other space for expansion. Lots more information could be found by examining the images in great detail and thinking about all the processes taking place
Hercules A is a bright astronomical radio source within the vicinity of the constellation Hercules corresponding to the galaxy 3C 348. Galaxy, 3C 348, is a supergiant elliptical galaxy.
The pink in the above image shows radio waves. The other parts of the image are seen using optical wavelengths by the Hubble space telescope.
The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versatile, well known both as a vital research tool and as a public relations boon for astronomy.
In the above image Professor Blundell is pointing out a galaxy
In the above left image Professor Blundell is pointing out how big the radio structure is and the black hole that produces it and indicating successive balloons of signals being blown.
Professor Blundell also pointed out a region in the top left of the image that showed the jet appeared to be wiggling about. The wiggling might be due to inhomogeneities in the densities of material through which the jet is trying to pass through as empty space isn’t really empty, or it could be due to processes happening in the event horizon of the Black Hole.
It isn’t clear what is going on with the radio plasma structure but astrophysicists are coming up with intelligent theories.
So, to our own galaxy, the Milky Way
Are their radio jet sources in our own galaxy?
Black holes in our galaxy provide a complementary way of studying radio jet phenomena.
The above image shows that black holes are not the end of the matter. The question is, how does the radio structure have that shape? Professor Blundell with Robert Laing were able to find out a lot more.
The different colours represent different brightnesses of the radio structure:
Blue is relatively faint; green is brighter; yellow is brighter still; red is brightest
The image shows that brightness fades as you get further from the central red point. The green and pale blue on the left show a prominent zig-zag and on the right show a corkscrew shape.
The curly and corkscrew shapes arise because of how the radio jets spurts changes with time. The motion is a bit like that of someone rowing a boat.
Pairs of hydrogen blobs are squirted in opposite directions
The various red and blue squiggles above are stills from an animation of the observed precession of blobs of plasma. Blue shows the material moving towards the viewer and the red shows the material moving towards the viewer.
Once the plasma is launched in anti-parallel directions (each direction is in a slightly different direction compared with its neighbour and with succeding plasma blobs) from the central point near the black hole it travels balistically, i.e. it suffers no acceleration or deceleration.
The speed that the plasma is launched affects the detailed appearance of the structure as shown in a previous image with the zigzag on the left and the corkscrew on the right.
If the speed at which the plasma is launched is at all comparable with the speed of light then there is a strong dependence of the structure with the speed the plasma is launched.
In other words if the speed of the jet is at all comparable with the speed of light then the appearance of the zigzag and corkscrew shape depends precisely on the speed.
The images above and below are stills from another animation showing the effect of changing the launch speed. The distance at which the object is from the Earth was changed to preserve the angular scale on the screen to get over the fact the speeds were increasing.
As the speed increase the asymmetries in the structure become more exaggerated and more profound. Material moving towards the Earth gets much closer, much more quickly. Material is also moving away from the Earth but all the light received from the corresponding points are received at the same telescope time. So, the details of the pattern we see depend crucially on light travel time effects, in a sense special relativity itself.
In physics, the special theory of relativity, or special relativity for short, is a scientific theory regarding the relationship between space and time.
So, back to the micro quasar
Cygnus A is an extra galactic radio source
Cygnus A (3C 405) is a radio galaxy, and one of the strongest radio sources in the sky. It was discovered by Grote Reber in 1939. In 1951, Cygnus A, along with Cassiopeia A, and Puppis A were the first “radio stars” identified with an optical source. Of these, Cygnus A became the first radio galaxy; the other two being nebulae inside the Milky Way. In 1953 Roger Jennison and M K Das Gupta showed it to be a double source. Like all radio galaxies, it contains an active galactic nucleus. The supermassive black hole at the core has a mass of (2.5 ± 0.7) x 109 times the mass of our Sun.
Images of the galaxy in the radio portion of the electromagnetic spectrum show two jets protruding in opposite directions from the galaxy’s centre. These jets extend many times the width of the portion of the host galaxy which emits radiation at visible wavelengths. At the ends of the jets are two lobes with “hot spots” of more intense radiation at their edges. These hot spots are formed when material from the jets collides with the surrounding intergalactic medium.
In 2016, a radio transient was discovered 460 parsecs away from the centre of Cygnus A. Between 1989 and 2016, the object, cospatial with a previously-known infrared source, exhibited at least an eightfold increase in radio flux density, with comparable luminosity to the brightest known supernova. Due to the lack of measurements in the intervening years, the rate of brightening is unknown, but the object has remained at a relatively constant flux density since its discovery. The data are consistent with a second supermassive black hole orbiting the primary object, with the secondary having undergone a rapid accretion rate increase. The inferred orbital timescale is of the same order as the activity of the primary source, suggesting the secondary may be perturbing the primary and causing the outflows.
Alan R Duffy (born 1983) is a professional astronomer and science communicator.
The image below shows Cygnus A using radio and X-ray telescopes.
The blue parts of the image show dumbbell shapes of radio emitting plasma. The red-orange parts of the image are X-ray emitting plasma and are measured by the Chandra X-ray satellite operated out of Harvard.
Why does using X-rays and radio waves given different pictures for the same astrophysical phenomena?
Radio waves are associated with electrical and magnetic fields. So, the radio emitting part of the image is tracing where there are magnetic fields at the same time as moving, very energetic charged particles, such as protons and electrons (split up hydrogen atoms). These charged particles get accelerated to very high energies because of what happens when the jets blast out and crash into their surroundings, but at the same time there are a lot of heating processes taking place and they gives rise to some of the X-ray emissions. These X-ray emissions are much closer to the deep potential well, which is located at the heart of the black hole (mass is 1 billion times the mass of our Sun). A potential well is the region surrounding a local minimum of potential energy.
X-ray emission indicates the presence of gravitational forces attracting matter inwards. It traces very high temperatures and the regions indicated in red are at temperatures greater than a million degrees (at such high temperatures the choice of using kelvin or degree Celsius is irrelevant). The energies are calibrated in other ways.
Zooming into the radio “dumbbell on the right-hand side gives the images shown below. They are still showing radio emission with a wavelength of about 6cm.
The central nucleus of the host galaxy, the location of the Black Hole, is the little dot in the above image.
The brightness of the region between the Black Hole “dot” and the “ball of fire” is giving information about the jet that is curling around in the direction that ultimately leads to bright shock structures.
Looking at the “ball of fire” section more closely shows the jet waving around.
Katrien Steenbrugge and Professor Blundell fitted their model of precession to the jet in Cygnus A and found that it was a bit shorter than six months with a precession angle of 20o. In the case of Cygnus A the precession angle was just a degree and a half but the periodicity of the cycle was a little short of one million years.
It is believed that all galaxies contain a supermassive Black Hole, and they give rise to highly energetic structures.
The VLA is still important for understanding the radio Universe but new technologies are emerging.
MeerKAT, originally the Karoo Array Telescope, is a radio telescope consisting of 64 antennas in the Northern Cape of South Africa. In 2003, South Africa submitted an expression of interest to host the Square Kilometre Array (SKA) Radio Telescope in Africa, and the locally designed and built MeerKAT was incorporated into the first phase of the SKA.
The Square Kilometre Array (SKA) is an intergovernmental radio telescope project being planned to be built in Australia and South Africa. Conceived in the 1990s, and further developed and designed by the late-2010s, if built it will have a total collecting area of approximately one square kilometre sometime in the 2020s It would operate over a wide range of frequencies and its size would make it 50 times more sensitive than any other radio instrument. It would require very high-performance central computing engines and long-haul links with a capacity greater than the global Internet traffic as of 2013. Initial construction contracts began in 2018. Scientific observations of the fully completed array is not expected any earlier than 2027
The South African Radio Astronomy Observatory (SARAO), a facility of the National Research Foundation, is responsible for managing all radio astronomy initiatives and facilities in South Africa, including the MeerKAT Radio Telescope in the Karoo, and the Geodesy and VLBI activities at the HartRAO facility. SARAO also coordinates the African Very Long Baseline Interferometry Network (AVN) for the eight SKA partner countries in Africa, as well as South Africa’s contribution to the infrastructure and engineering planning for the Square Kilometre Array Radio Telescope.
The array of different radio telescopes all resemble the oldest dish that produced the early radio image of the Milky Way. The dishes all work together as one and give very sharp high-resolution images/views of the southern skies. Each white dot in the above image is one of 64 radio antennas – collectively called MeerKAT.
The array was inaugurated in 2018 and the image below uses a human scale to show how big the dishes are. The diameter is so large that it wouldn’t fit into the hall of Gresham College, where the lecture was taking place.
The 64 dishes give an excellent picture of the radio Universe.
The MeerKAT telescope isn’t just important for the fantastic images produced within the last two years but it is important as a pathfinder and prototype of the next generation of telescopes, the square kilometre array, partly based in South Africa and partly based in Australia
The image shown below was captured by MeerKAT and shows a double radio source of 20cm wavelength. Purple showed the least bright radio waves, orange showed the brighter radio waves and yellow showed the brightest radio waves.
The region that the jets are launched from, the Black Hole, can be clearly seen. They always flow in anti-parallel directions with plasma flowing back, sometimes in the familiar ring structures.
What is remarkable about the image is that linear streaks can be seen and they almost resemble lightning as charged particles streak across one part of space to another.
Data from MeerKAT was used by MPati Ramatsoku to produce the image below.
The image gives an insight into how the radio galaxies evolved
The multiple highly collimated linear threads show that the radio emitting lobes are connected by the presence of electric fields that would, perhaps, otherwise be unseen without a sensitive enough telescope.
The most prominent radio threads are a couple of hundred thousand light years across.
Space is a violent, dynamic and explosive place.
Returning to the Milky Way
What’s happening at the centre of our galaxy? It’s hard to tell with optical telescopes since visible light is blocked by intervening interstellar dust. In other bands of light, though, such as radio, the galactic centre can be imaged and shows itself to be quite an interesting and active place. The featured picture shows the inaugural image of the MeerKAT array of 64 radio dishes just completed in South Africa. Spanning four times the angular size of the Moon (2 degrees), the image is impressively vast, deep, and detailed. Many known sources are shown in clear detail, including many with a prefix of Sgr, since the Galactic Centre is in the direction of the constellation Sagittarius. In our Galaxy’s Centre lies Sgr A, found here just to the right of the image centre, which houses the Milky Way’s central supermassive black hole. Other sources in the image are not as well understood, including the Arc, just to the left of Sgr A, and numerous filamentary threads. Goals for MeerKAT include searching for radio emission from neutral hydrogen emitted in a much younger universe and brief but distant radio flashes.
The image corresponds to a specially resolved version of the cosmic static imaged by Reber 76 years ago.
Producing a wide field zoom shows lots of highly collimated streaks which emanate from the plane of the Milky Way at the same time as seeing lots of little loops or circles. These correspond to the remnants of supernova explosions
Zooming in a little bit allows some of the detail of the distribution of the radio emitting plasma that occurs at the centre of the Milky Way galaxy.
The central part of the image is Sagittarius A*
Sagittarius A* (pronounced “Sagittarius A-Star”, abbreviated Sgr A*) is a bright and very compact astronomical radio source at the Galactic Centre of the Milky Way. It is located near the border of the constellations Sagittarius and Scorpius, about 5.6° south of the ecliptic. Sagittarius A* is the location of a supermassive black hole (4 million solar masses in size), similar to those at the centre of most, if not all, spiral galaxies and elliptical galaxies.
There are all sorts of radio fireworks going on in that region
The “Background” section that Professor Blundell is pointing to is a double radio source that is actually in the far background. Far away from the Milky Way that can be just discerned through all the radio emission spectra coming from the plane of the whole galaxy.
“The Mouse” seen above consists of two bulges that have their origins in the remnants of supernova explosions and some of the white streaks corresponds to stars that have a very significant proper motion
Zoom out further whilst still looking at the Milky Way. The bright orange/red emission from the very centre of our galaxy actually corresponds to a wide-angle view of the plane of our galaxy.
There is something of a bubble structure. The darkest region corresponds with an absence of radio emissions. There is a rim that delineates the shape of the seemingly opposite direction bubbles.
The stunning radio image obtained by MeerKAT shows the central portions of the Milky Way galaxy. Its plane, marked by a series of bright features, runs horizontally through the image, while the newly discovered radio bubbles extend vertically above and below. (Credit: SARAO. Adapted from results published in Heywood et al. 2019.)
The bubbles were caused by a phenomenally energetic burst that erupted near the Milky Way’s supermassive black hole a few million years ago. Until now, they have been hidden by the glare of extremely bright radio emission from the centre of the galaxy
It’s a characteristic signature of the fact that the jet ejector snowploughed out and cleared out gas from that region, energising the surrounding plasma as it did so.
It is a huge size. The image below indicates how large it is by comparing it to a large radio telescope dish
Modern technology can image these objects in the sky.
Astronomy using radio waves gives a new view of the Universe. It reveals dynamical structures, extreme energies and sometimes explosions, as indicated by supernova remnants.
Radio waves are used on Earth for communication and radar.
The persistence of radio engineers in Australia led by John O’Sullivan working with astrophysicists were pursuing of emerging black holes that we ended up with Wi-Fi. Thanks to him people can be connected together over the internet without having to resort to using wires.
John O’Sullivan is an Australian electrical engineer whose work in the application of Fourier transforms to radio astronomy led to his invention with colleagues of a core technology that made wireless LAN fast and reliable. This technology was in 1994 patented by CSIRO. That forms part of the 802.11a, 802.11g and 802.11n Wi-Fi standards and thus O’Sullivan is also credited with the invention of Wi-Fi.
The radio band of the electromagnetic spectrum is a wonderful space to study things beyond our plane and a fantastic means by which we communicate
“Immortal, Invisible, God Only Wise” is a Christian hymn and written two years after James Clerk Maxwell’s prediction of radio wave
“Immortal, invisible, God only wise,
In light inaccessible hid from our eyes,”
If we just rely on the visible, we miss out a lot.
Questions and answers
1) How do radio waves get converted in to coloured images?
Colour mapping is used. A colour scale is defined and a scheme for distinguishing brightness is produced.
The eyes/brain can recognise different colours but they can also work in monochrome. Brightness corresponds with increased greyness. Contours are also used to distinguish different brightnesses as not everyone can see colours. Lots of contour lines means a bright signal.
2) Where does the energy come from to produce the gigantic jets?
Mass near a black hole has a lot of gravitational potential energy. The gravitational attraction of the black hole sucks matter in, which moves at great speeds.
Conservation of angular momentum.
If the matter spins fast, but not fast enough, it spurts out. The energy associated with this gives rise to plasma and particle acceleration at the outermost edges of the jet. It links back to the compact region at the heart of it all, the black hole. It is gravitational activity.
3) What would the advantages of a radio telescope if it could be built on the dark (far) side of the Moon?
Less of a problem than what goes on, on the Earth.
Radio telescopes work when it is cloudy.
They struggle with the ionosphere and troposphere that surround the Earth
The ionosphere is the ionized part of Earth’s upper atmosphere, from about 60 km to 1,000 km altitude, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays an important role in atmospheric electricity and forms the inner edge of the magnetosphere. It has practical importance because, among other functions, it influences radio propagation to distant places on the Earth.
The troposphere is the lowest layer of Earth’s atmosphere, and is also where nearly all weather conditions take place.
The ionosphere and troposphere hinder the process of radio astronomy at very long wavelengths – 10s of metres.
The Moon has no atmosphere and probably has no magnetic field or ionosphere. Putting telescopes on the far side of the Moon would give fantastic observations as longer wavelengths could be seen
Some of the audience added comments
a) There is no such thing as the dark side of the Moon. All the lunar surface gets roughly equal light and dark as the Earth does. Putting a radio telescope on the far side of the Moon would help shield it from most human interference. But the difficulties of building it are high
b) As Professor Blundell has said, a radio telescope in space would solve the problem that some wavelengths do not get through the Earth’s atmosphere. Some radio telescopes have already been launched on satellites. However, a big collecting area is needed.
4) Wonderful images of rotating stars! Everything is rotating, but relative to what? What determines the fixed frame to measure it against? If it is the “distance stars”, how is that averaged? And if they weren’t there, if it was only the Sun and the Earth …?
The fixed frame is the plane of our galaxy. Whilst Sagittarius moves through the sky, telescopes track it only when it is close to the centre of our galaxy.
Stars whizzing around a fixed point, the black hole at the centre of the galaxy, are compared with the galactic plane when doing any observations.
You need to take into account things like how fast the Earth is moving along the line of sight to the particular target being studied.
5) How does a shock wave form when the density of interstellar matter is so low and particle separation so large?
A shock wave forms when you get discontinuities in the densities of the gases or the plasmas. Empty space isn’t actually empty but has a low density compared to the Earth’s atmosphere, but not so low that the laws of shock physics don’t apply in the same way as on Earth.
Size scales are much larger in space, 100 to 1000 light years plus. The density discontinuities are close enough to cause the shock physics that give rise to the particle acceleration seen in the Milky Way and others.
6) Compared to optical astronomy does radio astronomy allow us to look further back in time towards the “Big Bang”.
Radio waves can see through dust in a way that is superior to Infra-red and in a way that optical wavelengths can’t.
So very distant galaxies, that are very dusty, are visible to radio telescopes when they might not be visible to optical telescopes. So, in a sense radio telescopes can get closer to the Big Bang.
Radio telescopes are sensitive to the radio emissions from the cosmic microwave background
The cosmic microwave background (CMB, CMBR), in Big Bang cosmology, is electromagnetic radiation which is a remnant from an early stage of the universe. The CMB is faint cosmic background radiation filling all space. It is an important source of data on the early universe because it is the oldest electromagnetic radiation in the universe, dating to the epoch of recombination. With a traditional optical telescope, the space between stars and galaxies (the background) is completely dark. However, a sufficiently sensitive radio telescope shows a faint background noise, or glow, almost isotropic, that is not associated with any star, galaxy, or other object. This glow is strongest in the microwave region of the radio spectrum.
CMB radio signals have a shorter wavelength at the brightest points (in the mm wavelength range). Its origin is the Big Bang and the signals get us closer to it, but not close enough.
The CMB is only giving information about the characteristics and nature of events that occurred some 100000 years after the Big Bang,
Radio astronomy gets closer to the Big Bang than optical astronomy, but not close enough.