Physics update course December 2012

Saturday 15th December

Astrophysics activities for the classroom


Dr Sian Owen

The activities focused on space science and astronomy, with links to current research. Topics covered included the Solar System, evolution of stars, galaxies and the expansion of the universe.

Transit activity

clip_image004 clip_image006

The above activity was a model to show how some of the exoplanets have been discovered. The central lamp represents the star (brightness can be altered).

clip_image008 clip_image010

Suspended around the lamp on fine twine are small black discs which act as the planets. A light dependent resistor (LDR) is placed level with the twin facing the lamp and is connected to an ohmmeter.

The black disc is moved along the twine at set distances and the resistance of the LDR is measured. A light curve can be plotted of resistance as a function of distance. The presence of the “planet” is indicated by a drop in light intensity and an increase in the resistance of the LDR.

clip_image012 clip_image014

An activity to get across the different sizes of objects in the universe.


Gas discharge tubes


Each tube contains a unique gas. When a high voltage is connected across the tube it produces light of distinct wavelengths. Using a diffraction grating or a spectrometer these wavelengths can be seen. Each element has its own distinct spectra. This is how hydrogen and helium were discovered in our Sun.


The above picture is the solar spectrum. Spectrum from other stars can be used to identify the elements present.

Sloan digital sky survey

Galaxy Zoo

Life cycle of stars using balloons.

clip_image022 clip_image024

Exploring the Zooinverse


Dr Chris Lintott Department of physics University of Oxford                                                                                                     

Dr Lintott (Oxford astrophysicist and BBC series The Sky at Night) runs the world’s largest collaboration, inviting more than 700,000 people of all ages and abilities to work with scientists to classify galaxies, hunt for planets, listen to Whales, and study cyclones.

All of this is possible via the website, and in this talk Dr Lintott gave an overview of the project’s history and its greatest discoveries (including a planet with four stars and the mysterious green pea galaxies).

clip_image028 clip_image030

The picture above right is a sketch by Lord Ross who discovered the spiral nature of some nebulas, today known to be spiral galaxies.,_3rd_Earl_of_Rosse

Fifty years later it was realised that these “nebulae” were made up of stars and the scale of the universe had expanded.

clip_image032 clip_image034

Sloan digital sky survey                                                                             

Over eight years of operation SDSS obtained deep-multi-coloured images covering more than a quarter of the sky and created 3-dimensional maps containing more than 930,000 galaxies and more than 120,000 quasars.

clip_image036 clip_image038

2.4m swing with precision SDSS has found 600 million objects and measured distances to galaxies. “Mapping the universe” showing the gaps between galaxies, largest images within the universe. Cosmic voids are seen and that the observable universe is clumpy. Stars, as seen from outside the Galaxy, appear to form the shape of a bow tie whose centre is at the Sun. These wedges describe the patches of sky observed by the telescope.

The Sloan Great Wall (SGW) is a cosmic structure formed by a giant wall of galaxies (a galactic filament). To date it is the largest known structure in the universe. Its discovery was announced from Princeton University on October 20, 2003, by J. Richard Gott III, Mario Jurić, and their colleagues, based on data from the Sloan Digital Sky Survey. The wall measures 1.38 billion light years (×1025 m) in length, which is approximately 1/60 of the diameter of the observable universe, and it is located approximately one billion light-years from Earth.

The Sloan Great Wall is 2.74 times longer than the CfA2 Great Wall of galaxies, which was discovered by Margaret Geller and John Huchra of Harvard in 1989. It contains several galactic superclusters, the largest and richest of which is named, SCl 126. This is located in the highest density region of the structure. It is followed in size by the supercluster, SCl 111.


The Sloan Great Wall in a DTFE reconstruction of the inner parts of the 2dF Galaxy Redshift Survey

Why is the universe lumpy?

Create a computer program to produce a universe as we know the physics ingredients. We can put ourselves on one of the galaxies.


Right recipe gives us the universe but it is nasty. Only 4% of the universe is ordinary matter. The picture below of an astronomer illustrates that you don’t need much of the image to see that the picture is of a head of a man, but that a lot of the image is hidden.


Similarly even though we can’t see it we need dark matter to produce the gravity to give the lumpiness in the universe. Sloan survey matches the theory but we don’t like the theory. We need new ways to compare theory and observations.

We can look at the different galaxy shapes.

clip_image045 clip_image047

Elliptical galaxies are crowded. Galaxies that appear blue are younger than other galaxies. Different gases are found in the different galaxies.

Studying galaxy shapes is more difficult now because of the sheer number. One researcher, called Kevin, looked at 50,000 in one week. Humans do this task much better than computers. 250 million classifications have been done and discrepancies may show how dark matter may work.

clip_image049 clip_image051

clip_image053 clip_image055

clip_image057 clip_image059

There should be equal numbers of clockwise and anti-clockwise galaxies however one researcher, Michael, using Sloan found 3000 more anticlockwise galaxies. It turned out that humans have a bias for anticlockwise (known as the ballerina effect).

clip_image061 clip_image063

The Galactic Centre is the rotational centre of the Milky Way. There is strong evidence that there is a supermassive black hole at the centre of it. Stars are seen orbiting the centre and obeying Kepler’s laws.

Estimates for the mass of the Milky Way vary, depending upon the method and data used. At the low end of the estimate range, the mass of the Milky Way is 5.8xE11 solar masses and the supermassive black hole is believed to have a mass of 3 million solar masses.

In mid-2013 it is expected a large gas cloud will fall into the black hole causing causing increased radio emission etc.

Overfeeding of black holes is resisted as predicted by the Eddington limit due to magnetic fields (which means that astronomers don’t really know why).

clip_image065 clip_image067

The above picture on the left is a Hubble Space Telescope photograph showing the jet of matter ejected from M87 at nearly light speed, as it stretches 1.5 kpc (5 kly) from the galactic core.

clip_image069 clip_image071

M87 is a supergiant elliptical galaxy ten times more massive that the next massive galaxy.

Elliptical galaxies cannot form stars.

Dr Brian May (former member of Queen) is a self-funded post. doc,, whose PhD was on galactic dust, got his fans to work on Zooinverse. More people are required.

clip_image073 clip_image075

The picture above left is showing the number of people watch US TV compared to writing Wikipedia. If the people watching TV could be persuaded to go galaxy hunting a lot more could be discovered.’s_Voorwerp

One of Brian May’s fans, Hanny van Arkel discovered an astronomical object of unknown nature in 2007 while she was participating as an amateur volunteer in the Galaxy Zoon project. Photographically, it appears as a bright blob close to spiral galaxy IC 2497 in the constellation Leo Minor. The object is known as Hanny’s Voorwerp. It seems to consist of green gas (galaxy size) with no stars. There doesn’t appear to be an active black hole in it as X-rays should be produced at high temperatures and only three photons have been found. It may be a galaxy that we have caught in a sleeping state. 50,000 years ago it might have been active and it might switch back on in the future. Any light seen may be an echo of the past.

Hubble Andromeda project.

clip_image077 clip_image079

While the Milky Way is a great place to study stars, it’s often a confusing place to work — you don’t know exactly how far away any given star (we actually know the distances to other galaxies better than we know the distances between stars in our own galaxy) is and there’s lots of dust to get in your way. Instead, if we look at Andromeda, we know all the stars are at nearly the same distance, and we have much less dust to block our view.

Resolving one light year apart Star clusters can be picked out and stellar evolution can be observed. 80,000 classifications have been done and 1000 background galaxies found. 100 billion stars can be seen and almost all of them have planets.

The Kepler mission “specifically designed to survey a portion of our region of the Milky Way galaxy to discover dozens of Earth-size planets in or near the habitable zone and determine how many of the billions of stars in our galaxy have such planets.”Kepler’s only instrument is a photometer that continually monitors the brightness of over 145,000 main sequence stars in a fixed field of view. This data is transmitted to Earth, then analysed to detect periodic dimming caused by extrasolar planets that cross in front of their host star.

clip_image081 clip_image083

2.4 million stars have been seen. Every twenty nine minutes the brightness of the stars is measured looking for “transit”. Stars can have variable brightness and this can cause problems. High precision is required.

Some transits can be caused because of the presence of binary stars (eclipsing binary). Extra transits indicate the presence of planets (Neptune sized are most common).

clip_image085 clip_image087

All the information gained from the images can allow us to figure how planets are formed. One of the most peculiar things seen is a planet with four suns. This should have disrupted planet formation.

clip_image089 clip_image091

Often planets seem to be migrating inwards to a safe position and Neptune sized exoplanets seem to be most common. Why aren’t Neptune sized planets the norm in our Solar System?

Our Solar System may have suffered as a result of the late heavy bombardment eight hundred million years after the start of the Solar System.

Jupiter-Saturn resonance (“Nice” model) may show that there was a 1:3 chance that a fifth giant gas planet got thrown out.

clip_image093 clip_image095

Exoplanets can be distinguished by their gravitational lensing effect on light.

Many free floating Neptune-sized planets have been seen.

In our Solar System Jupiter changes the least.

The presence of Jupiter and Saturn in their current positions brings stability to the Solar System and prevents migration. This situation is likely to be rare in other solar systems. Our star, the Sun, is quieter than most which is why there is expected to be few Earths.

Dark energy is a very poor description. It can really be thought of an anti-gravity force or negative energy pressure.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s