Thursday 13 February 2014

Talk : Building Galaxies in the Office

A recent Cafe Sci Event featured a fascinating talk by Dr Mark Wilkinson (Dept. of Physics and Astronomy, University of Leicester). The talk was entitled "Building Galaxies in the Office" and gave an insight into what current research is telling us about how galaxies are formed and interact, and the role that black holes play within them.

To start with, Dr Wilkinson, showed a picture of the M83 galaxy, which has a structure similar to our own. It is beautiful...


He then gave some idea of the sheer number of galaxies in the Universe by showing the Hubble eXtreme Deep Field Image. This was generated by programming the Hubble telecope to spend 23 days staring at a particular region of space. In the image, shown below, almost everything you can see is a galaxy in its own right, with some of these being the earlies galaxies formed in the Universe.

Hubble eXtreme Deep Field Image...

And here is a image showing the area of sky scanned by the XDF compared to the size of the Moon

... from just this tiny part of sky

Dr Wilkinson also showed an image of the M87 elliptical galaxy, which has a prominent gas plume indicating the presence of a supermassive black hole at its centre. The plume, incidentally, is around 5000 light years in length (!)

M87 Jet, 5 thousand light years long...

Also presented was a Hubble image of ARP148, which is a collision between two galaxies in progress.


And also of ARP87, which is two gorgeous galaxies that are, almost lovingly, reaching out to each other under the forces of gravity as as they pass each other by


Other examples of interacting galalxies shown were NGC6050 and the beautiful "antennae galaxies" of NGC4038/4039, who are colliding in a way similar to how the Milky Way may collide with Andromeda in the distant future.

Anteannae Galaxies

Dr Wilkinson then moved on to discuss what the Universe was made of, which turns out to be :

Dark Energy : 71%
Dark Matter : 24%
Atoms : 5%

And just to give a feel for how fast things can change in physics, back in 1996, almost no-one thought that dark energy was a significant part of the universe!

Dr Wilkinson also talked about efforts to improve our understanding of the structure of our own galalxy. One example of this is the Gaia spacecraft that was lunched in late 2013. Gaia aims to produce a 6D space catalogue (3 position axes and 3 direction axes) of approximately 1 billion stars and objects (which represents around 1% of the Milky Way). It will do this by imaging each object around 70 times over 5 years. This BBC article explains how the spacecraft determines the distance of the objects it images.

There is also the Fermi probe, which has discovered two huge lobes of plasma above and below the milky way.

Fermi lobes

Dr Wilkinson explained how recent research suggested that massive black holes were not only a feature at the centre of many galaxies, but also controlled the size of the galaxy itself. The central black holes are able to do this because, above a certain size, the radiation emitted from a massive black hole is sufficient to disrupt the gas clouds in the galaxy as a whole, thus stopping the star formation mechanism.

Dr Wilkinson also looked at how the Milky way might have formed, noting that it appears to have grown in large part by eating up smaller galaxies. Incredibly, the remnants of these can still be seen (see here)

One example of these remnants of a gobbled up galaxy is the "Aquarius Stream" that was identified using the RAVE survey. Researchers commented that "...The comparison of the [meaasured] star parameters with simulations showed that those stars form part of a larger stream of stars originating from a smaller neighbouring galaxy which was attracted by the Milky Way. This galaxy finally met the Milky Way and was pulled apart by it about 700 million of years ago..." You can read more in their paper entitled "The Dawning of the Stream of Aquarius in Rave" (did you see what they did there?) and a list of other such streams can be found here

The Aquarius Stream

A particularly awesome stream/galaxy thing is the Sagittarius Dwarf Spheroidal Galaxy which has passed around and through the Milky Way several times.

To close out this report, it is perhaps appropriate to mention the discussion on what would happen when, in a few billion years time, the Milky Way collides with the Andromeda galaxy. You can see a beautiful computer simulation of the collision at this Hubble page., together with images of how the collision might look from earth here ... well, how they would look if there was anyone left to watch them, as the earths oceans would have boiled off long ago...

Related Content:
Fee- An Autobiography
Curiosity, Twitter and the British Connection
Interview with Prof Aragon-Salamanca
Interview with Prof Chris Lintott
Some background to the Space Shuttle
Lecture by Chris Lintott on 2011 Astronomy highlights

Image Sources
M83, XDF, XDF(Moon), M87, ARP 148, ARP87, Antennae, Stream,Fermi

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