“New Light on Dark Energy” is Dim
Changing careers to work with people who are studying the nature of dark energy has been one of the best decisions I’ve ever made. I have never been happier professionally, and I admit there is much I have to learn about exactly how we are characterizing the nature of dark energy.
The discovery that the expansion of the universe is accelerating implies one of two things:
- A repulsive force exists throughout the universe fueling the expansion, OR
- We don’t understand gravity like we thought we did, because if there is no force pushing the universe apart, everything should be slowing down to begin a cosmic contraction.
To find out which one of these it is, we need to take some observations, lots of large-scale, wide-angle, deep-field observations that look at the distribution of galaxies, the brightnesses of supernovae, the lensing of galaxies behind other galaxies, etc.
Imaging and measuring a variety of large-scale structures in the universe and see how they have changed at different times in its history is where the effort to characterize dark energy is focused.
These efforts are usually in the form of surveys, like the Sloan Digital Sky Survey, and more recently, the one I’m involved in: The Dark Energy Survey.
Ok, enough of a preamble and on to the point of my post. As you can imagine, I’m very interested in new research that comes out in this area and so I was reading this news release from EurekAlert and smiled to myself (and shook my head a little too).
Why?
The way the press release was written, I couldn’t understand what the results of the research were.
Here’s the buildup:
Astronomers have used ESO’s Very Large Telescope to measure the distribution and motions of thousands of galaxies in the distant Universe. This opens fascinating perspectives to better understand what drives the acceleration of the cosmic expansion and sheds new light on the mysterious dark energy that is thought to permeate the Universe.
“Explaining why the expansion of the Universe is currently accelerating is certainly the most fascinating question in modern cosmology,” says Luigi Guzzo, lead author of a paper in this week’s issue of Nature, in which the new results are presented. “We have been able to show that large surveys that measure the positions and velocities of distant galaxies provide us with a new powerful way to solve this mystery.”
Cool, I’m with you so far…
Next, referring to the two options I’ve outlined above about what the acceleration of the universe implies:
Current observations of the expansion rate of the Universe cannot distinguish between these two options, but the international team of 51 scientists from 24 institutions found a way that could help in tackling this problem. The technique is based on a well-known phenomenon, namely the fact that the apparent motion of distant galaxies results from two effects: the global expansion of the Universe that pushes the galaxies away from each other and the gravitational attraction of matter present in the galaxies’ neighbourhood that pulls them together, creating the cosmic web of large-scale structures.
“By measuring the apparent velocities of large samples of galaxies over the last thirty years, astronomers have been able to reconstruct a three-dimensional map of the distribution of galaxies over large volumes of the Universe. This map revealed large-scale structures such as clusters of galaxies and filamentary superclusters ”, says Olivier Le Fèvre, member of the team. “But the measured velocities also contain information about the local motions of galaxies; these introduce small but significant distortions in the reconstructed maps of the Universe. We have shown that measuring this distortion at different epochs of the Universe’s history is a way to test the nature of dark energy.”
All right, that’s really cool, now I’m interested… What did they find?
Within current uncertainties, the measurement of this effect provides an independent indication of the need for an unknown extra energy ingredient in the ‘cosmic soup’, supporting the simplest form of dark energy, the so-called cosmological constant, introduced originally by Albert Einstein. The large uncertainties do not yet exclude the other scenarios, though.
Huh?
I read this press release many times and I’m still not clear what they found. I guess I’ll wait for the Nature paper to come out.
Here’s the full release, maybe you can make some sense of it.
Technorati Tags: cosmology, dark energy, eurekalert
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