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‘Arrested development’ at work in the Universe December 17, 2008

Posted by Sarah in science.
Tags: , , , ,

Left: Composite image of galaxy cluster Abell 85, using X-ray data (purple) from Chandra and optical image from the Sloan Digistal Sky Survey. Right: Snapshots of the Universe's evolution from a simulation by Volker Springel of MPA, at 0.9, 3.2 and 13.7 billion years.

A cross-continental team of astronomers led by Andrei Vikhlinin have used data from the American X-ray space telescope Chandra to help pin down the nature of the most enigmatic stuff in the Universe, dark energy. By observing clusters of galaxies over a range of different ages, the team were able to track how their masses have evolved over the history of the Universe. Using the statistics of this evolution and comparing them with results from several other complimentary studies, they have significantly narrowed the constraints on the precise nature of dark energy.

Dark energy is the slightly nebulous name given to the energy that causes the Universe’s expansion to accelerate, thought to represent almost three quarters of all mass-energy in the Universe. The term was first coined about 10 years ago, when distant supernovae were found to be further away than predicted, suggesting some unknown and invisible repulsive force. Using observations from several other studies, such as the cosmic microwave background results from WMAP, scientists have repeatedly confirmed the presence of this extra anti-gravitational push.

So in a way, this study tells us nothing new – only that we’re on the right track, and that our current if vague understanding is becoming increasingly plausible over other exotic theories. But the method Vikhlinin and his colleagues used is very neat, and the paper has a lot of very interesting information.  Clusters of galaxies are the largest gravitationally bound structures in the Universe, and without the gravity-opposing force of dark energy, we would expect bigger and bigger clusters to form as the Universe evolves. But as dark energy begins to win the fight with gravity, the formation of clusters gradually switches off. And that’s exactly what was observed.

Sean Carroll, a man who knows much more about it, gives a nice overview with some of the paper’s graphs, over on Cosmic Variance. CV has lots of posts about dark energy and the like, so go and link-hop to explore.

Phil Plait weighs in here.

The paper is here (access at your own peril, it’s pretty dense and no pretty pictures!) and will be published in ApJ in February 2009.

Update: Disco Dave has a nice compilation of blog posts and info sources on dark energy.

Image credit: X-ray (NASA/CXC/SAO/A.Vikhlinin et al.); Optical (SDSS); Illustration (MPE/V.Springel)



1. freidenker85 - December 17, 2008

Amazing! I used to think that Dark Energy is just some excuse for “I don’t know what’s causing the anomaly in the standard model”, and I’m delighted to read (also popped into CV to check some more) about evidence for Dark Energy. What I don’t realize is what exactly Dark Energy IS. The way it’s presented here and on CV makes it as if it’s a black box that has predictable behavior, but what black box? It’s “some mass, somewhere”? It obviously behaves like mass, and the observations confirm this, but do we know where is it? Is there any alternative explanation as to what can originate this amount of energy? Why “Dark Energy”, anyway?

2. Sarah - December 17, 2008

Yes I know what you mean, it’s hard to get your head round. In its simplest form you could consider dark energy to be a mathematical construct that explains the discrepancy in omega_matter, the matter density parameter, found from measurements of galaxy and cluster dynamics on the one hand, and supernova distance scales on the other. I don’t think you should think of it as “stuff”, certainly not as “matter” in any way that is familiar to us. It’s an energy phenomenon that we can’t explain from our current models of cosmology and particle physics. But much is happening in the realms where these two fields meet, such as the (now slightly delayed) advent of the LHC and recent results from dark matter experiments. I can’t wait 🙂

3. cormac - December 17, 2008

Hi Sarah, good post. Did you link with me? It’s showing up on my blog (http://coraifeartaigh.wordpress.com) but I don’t see the link. Good stuff anyway..

4. Sarah - December 18, 2008

Cormac – no I didn’t, but WordPress automatically adds links to similar stories from other blogs. I imagine that’s what happened.

5. SarahAskew » An Early Universe 101 - October 14, 2010

[…] rekindled my interest in fundamental physics and cosmology, which explains some recent posts (here, or here) on the […]

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