NASA announced in a press release yesterday, that astronomers using Hubble’s wide field camera discovered a cluster of galaxies at the beginning stages of development. This is the farthest away that a cluster such as this has ever been observed in the early Universe. Michele Trenti, of the University of Colorado at Boulder and the Institute of Astronomy at the University of Cambridge in the United Kingdom, presented the results to the American Astronomical Society.
Early Cosmic Get-Together
Hubble was used to do a random sky survey when it came across these five small, but bright, galaxies clustered together in the farthest reaches of space. It is estimated that these galaxies were formed just 600 million years after the big bang. Clusters are the largest objects observed in our universe. They are usually comprised of hundreds of thousands of galaxies that are bound to each other by gravity. It’s sort of like a cosmic game of Pac-Man. These galaxies collide and swallow each other up to form larger galaxies. The galaxies observed in the image above are smaller than our own; however, they match ours in brightness.
“These galaxies formed during the earliest stages of galaxy assembly, when galaxies had just started to cluster together,” said Trenti. “The result confirms our theoretical understanding of the buildup of galaxy clusters. And, Hubble is just powerful enough to find the first examples of them at this distance.”
Long Distance Challenge
One of the biggest challenges is finding clusters bright enough to be seen 13 billion light-years away. Finding galaxy clusters this far back is challenging because they are so dim and scattered across the sky. Trenti expressed the need to examine many different areas as she said, “the search is hit and miss. Typically, a region has nothing, but if we hit the right spot, we can find multiple galaxies.”
Because the systems were so dim, the astronomers honed in on the brightest galaxies. The brighter the galaxy, the more mass it has which, in turn, marks a spot where cluster construction is most likely to occur. Astronomers use computer simulations to determine the way that these clusters likely formed. It is likely that there are many other galaxies in the same region that are just too dim to see. Based on the simulations, astronomers suspect that these bright galaxies form the central core of the cluster and will eventually form an elliptical giant similar to a closer cluster nearby, Virgo Cluster’s M87.
There is still some work to be done. The distances were measured based on color and the team will soon use spectroscopic observations, which measure the expansion of space. This will help astronomers precisely calculate the cluster’s distance and the velocity of the galaxies, which will show whether they are gravitationally bound to each other.