Astronomers Discover Baby Clusters That Reveal More about Galaxy Evolution

Astronomers may have discovered baby galaxy clusters in our distant universe. By combining observations made with ESA's Herschel and Planck space observatories, scientists have found what could be the precursors of the vast clusters of galaxies that we see today. The findings could reveal a bit more about galaxy evolution and the role played by dark matter in shaping these clusters.

Galaxies like our Milky Way are usually not found in isolation. In fact, galaxies usually form dense clusters of tens or even hundreds of galaxies. However, these clusters have not always existed, and scientists have long wondered how such massive structures assembled in the early universe.

"Because we are looking so far back in time, and because the universe is assumed to be homogenous in all directions, we think it's very similar to looking at the equivalent of what a baby cluster might look like," said Brenda L. Frye, one of the researchers, in a news release. "In contrast to previous observations, for which the odd one or two baby clusters was found which one would put in a zoo, we now have found a real sample of 200 baby clusters."

Planck's short wavelength data first identified 234 bright sources with characteristics that suggested they were located in the distant, early universe. Then, Herschel observed these objects across the far-infrared to submillimeter wavelength range (just a bit shorter than microwaves), but with much higher sensitivity and angular resolution. Herschel revealed that the vast majority of the Planck-detected sources are consistent with dense concentrations of galaxies in the early universe, vigorously forming new stars.

What's interesting is that many single galaxies the researchers detected appear much brighter than they should. They're brightened by what is a natural telescope in space; individual far-away galaxies light up with star formation because they are situated along just at the right line of sight where their light passes through massive galaxy clusters close to our own planet. It's also possible that these "single" galaxies may be near others that researchers just haven't spotted yet.

The findings are the best candidates to date of proto-clusters, which are precursors of the large, mature galaxy clusters we see in the universe today.

"We still have a lot to learn about this new population, requiring further follow-up studies with other observatories," said Herve Dole, one of the researchers. "But we believe that they are a missing piece of cosmological structure formation."

The findings are published in the journal Astronomy & Astrophysics.

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