Hubble Sheds light on Dark Matter (and neutrinos!)

There have been a flurry of press releases from NASA, ESA and other space organisations recently, announcing the results of their “ambitious surveys” covering issues such as dark matter, Antarctic ice, and even how the Earth’s oceans were initially formed! It is the new Hubble survey which provides a census on dark matter clusters that has piqued quite a lot of interest, and (perhaps more importantly) offers the chance to reproduce some wonderful Hubble photos! Check this one out…

Observations of this galaxy cluster, MACS J1206.2-0847, or MACS 1206 for short, will allow astronomers to construct the most detailed dark matter maps of more galaxy clusters than ever before. Credit: NASA, ESA, M. Postman (STScI), and the CLASH Team.

Where’s the Dark Matter in the photo?

Dark matter is often seen as a weakness in our current physical and astronomical theories; as all that can be said about it is that we cannot see it, experience it, measure it or even fully know how much of it there is! However, it has to be there, otherwise much of our observational data wouldn’t quite make sense.

The Hubble survey used the swirls and arcs formed by stretched starlight viewed in the images (like the one above) to determine the amount of dark matter present in galactic clusters. Dark matter has a gravitational influence on the matter around it and so it bends and distorts light via ‘gravitational lensing’ – thus acting as like a giant cosmic lens. It also plays a vital part in the early formation of galaxies, and so can also be an indicator of their age.

The results from the NASA survey were surprising – there appeared to be a more dark matter packed into galactic clusters than we believed. This result implies older galaxies, and alters the suspected amounts of dark matter, dark energy and baryonic mass (what makes up humans and everything we can see) present throughout the universe. (Follow the links to find out more)

A Small, Neutrino-Sized Issue

 Illustration of spacetime curvatureAlthough this may all seem quite abstract – and in a way, it is – these ongoing surveys are relevant now more than ever. With the scientific community in a panic over the as-yet unexplained faster-than-light neutrino, Einstein’s theory of relativity has been brought into question. Gravitational lensing and how all of how we interpret our astronomical observations relies heavily on this theory being correct.

For those who have been avidly following the neutrino drama, this blog post claims that the CERN observations are wrong, and explains away the anomalous result using special relativity. It is very well explained on the ArXiv blog:

“Although the speed of light is does not depend on the frame of reference, the time of flight does. In this case, there are two frames of reference: the experiment on the ground and the clocks in orbit. If these are moving relative to each other, then this needs to be factored in […] from the point of view of a clock on board a GPS satellite, the positions of the neutrino source and detector are changing.”

This minuscule, almost undetectable difference caused by the clocks being in orbit and not on the ground requires a neutrino travel time correction of 64 nanoseconds – almost exactly what was observed by the CERN team. While this is still unconfirmed and speculative, it makes a very convincing argument – and could resolve the dilemma once and for all…

Article by Nicola Guttridge

October 19, 2011

A recent Astrophysics graduate, now studying Science Communication in London. Anything Astronomy- or Physics-related is of guaranteed interest, as are most things to do with comedy, food, cute animals, writing, art and photography! Nicky tweets at @nickyguttridge and you can read her blog here. She also edits I, Science, the official science magazine of Imperial College London.

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