Three-fourths of the universe's matter and energy is thought to be dark energy, the mysterious thing that is causing universal expansion to accelerate. A new way of mapping huge cosmic structures might finally shed some light on this dark energy.

The universe's accelerating expansion was first discovered in 1998, and astrophysicists have spent the last twelve years trying to figure out what could possibly be causing it. We don't know what dark energy is, but we do know that, for it to have the observed effect on cosmic expansion, it would have to account for three times the amount of matter and energy we've actually been able to observe.


At this point, there are a few competing explanations for what dark energy could be, and even better there's a way to experimentally test which is most accurate. We can test the various theories by precisely mapping the distribution of galaxies and groups of galaxies throughout the universe, and then figure out how this distribution has changed. The nature of the change will hopefully line up with what one of the theories predicts should happen, lending that theory strong experimental support.

In order to figure out how galaxies were distributed billions of years ago, we can focus in on sound waves found in the matter-energy soup of the most ancient universe. These sound waves are thought to leave imprints of galactic distribution patterns, and it's possible to measure these imprints by detecting radio emissions from hydrogen gas.

This technique is known as intensity mapping, and the goal of this new project is to try it on far vaster scales than ever before, as astronomer Tzu-Ching Chang explains:

Our project mapped hydrogen gas to greater cosmic distances than ever before, and shows that the techniques we developed can be used to map huge volumes of the Universe in three dimensions and to test the competing theories of dark energy."


The current study looks at parts of the sky that have already been mapped in extreme detail, and then recorded the total amount of hydrogen gas coming from large groups of galaxies within that region. They are currently gathering radio emissions from thousands of galaxies at a time, detecting more hydrogen gas than all that had ever been detected previously. Now the challenge is putting this massive amount of new data to good use in figuring out the nature of dark energy.



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