Hubble pinpoints farthest protocluster of galaxies
Washington: Astronomers have uncovered a cluster of galaxies in the initial stages of development – the most distant ever observed in the early universe – thanks to NASA’s Hubble Space Telescope.
In a random sky survey made in near-infrared light, Hubble found five tiny galaxies clustered together 13.1 billion light-years away. They are among the brightest galaxies at that epoch and very young existing just 600 million years after the big bang.
Galaxy clusters are the largest structures in the universe, comprising hundreds to thousands of galaxies bound together by gravity.
The developing cluster, or protocluster, is seen as it looked 13 billion years ago. Presumably, it has grown into one of today’s massive galactic cities, comparable to the nearby Virgo cluster of more than 2,000 galaxies.
“These galaxies formed during the earliest stages of galaxy assembly, when galaxies had just started to cluster together,” said Michele Trenti of the University of Colorado at Boulder and the Institute of Astronomy at the University of Cambridge in the United Kingdom.
“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,” she stated.
Trenti used Hubble’s sharp-eyed Wide Field Camera 3 (WFC3) to pinpoint the cluster galaxies and presented the results at the American Astronomical Society meeting in Austin, Texas.
The five bright galaxies spotted by Hubble are about one-half to one-tenth the size of our Milky Way, yet are comparable in brightness. The galaxies are bright and massive because they are being fed large amounts of gas through mergers with other galaxies.
The team’s simulations show that the galaxies eventually will merge and form the brightest central galaxy in the cluster, a giant elliptical similar to the Virgo Cluster''s M87.
The observations are part of the Brightest of Reionizing Galaxies survey, which uses Hubble’s WFC3 to search for the brightest galaxies around 13 billion years ago, when light from the first stars burned off a fog of cold hydrogen in a process called reionization.
The study will be published in an upcoming issue of The Astrophysical Journal.