Peeking at Galaxies in the Early Universe

The only way we can understand the cosmos is to find new and innovative ways to interpret the light we capture from it.  Using the largest and most technologically advanced telescopes in the world, we peer deeper into space, further back in time, and see photons that have spent eons travelling to Earth.  If we can get rid of all of the other light from closer objects, and zero in on this distant light, we can begin to understand what was present at the beginning.

The three panels show different components of near-infrared background light detected by the Hubble Space Telescope in deep-sky surveys.  The middle one reveals “intrahalo light” from rogue stars torn from their host galaxies, and the panel on the right captures the signature of the first galaxies formed in the universe. Credit: Ketron Mitchell-Wynne / UCI

Using data from deep sky surveys conducted by the Hubble Space Telescope (HST), astronomers from UC Irvine and the Space Telescope Science Institute in Baltimore have peered beyond the foreground light to statistically map the number of primordial galaxies that existed as little as 500 Million years after the Big Bang.  They found that there are 10 times as many of these galaxies as was previously detected with Hubble surveys.

UCI Ph.D. student Ketron Mitchell-Wynne, lead author on the paper, said the time period under investigation is known as the “epoch of reionization.”  This is the period of time in the universe’s existence where it was large enough to be transparent, but still dominated by neutral Hydrogen.  As the first stars and galaxies formed, UV light ionized the Hydrogen all across the universe during this epoch.

“For this research, we had to look closely at what we call ’empty pixels,’ the pixels between galaxies and stars,” said UCI cosmologist Asantha Cooray, research project lead. “We can separate noise from the faint signal associated with first galaxies by looking at the variations in the intensity from one pixel to another. We pick out a statistical signal that says there is a population of faint objects. We do not see that signal in the optical [wavelengths], only in infrared. This is confirmation that the signal is from early times in the universe.”

Astronomers believe that the primordial galaxies were nothing like the spiral and elliptical galaxies we see today, and that they were much more diffuse and contained massive bright stars.  Until better data is obtained with the James Webb Space Telescope, Hubble’s Successor, we won’t be able to see exactly what they look like to verify this claim.

Cooray hopes to extend the deep sky surveys to include other wavelengths of light, such as X-Rays.  Are there primordial X-Ray sources out there waiting to be seen? If so, what is their origin? The latest technology brings us to a deeper probing of the early universe.


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