Researchers have discovered an extremely bright galaxy cluster inconspicuously disguised as a single point of light in a region of space not far from the Milky Way.
The new discovery may potentially provide insight into how the supermassive black holes sitting at the heart of galaxy clusters affect formation and evolution of galaxies.
What Are Galaxy Clusters?
Galaxy clusters are groups of thousands of galaxies brought together by the inward pull of gravity. The galaxy cluster closest to the Milky Way is the Virgo Cluster, which comprises around 2,000 galaxies 60 million light-years away.
In 2010, astronomers manning the South Pole Telescope in Antarctica discovered a super-luminous object in the sky toward the Phoenix constellation, which they mistakenly thought to be a quasar. Quasars are the brightest objects in the universe. Scientists believe quasars are found at the center of galaxies, where they are fueled by a supermassive black hole.
However, a follow-up X-ray data obtained at the Chandra X-Ray Observatory showed that the quasar was not a quasar after all. It is a rich galaxy cluster sitting 7 billion light-years from Earth.
To date, the Phoenix cluster, named after the constellation where it resides, is the brightest galaxy cluster in the X-ray range. Its central galaxy is estimated to have 3 trillion stars and is actively forming 740 newborn stars every year.
The astonishing discovery led astronomers to ask if there were more galaxy clusters mistakenly thought to be singular points of light in the sky. The answer is yes.
New Galaxy Cluster Around A Quasar
Much closer to Earth is another galaxy cluster hiding in plain sight. Only 2.4 billion light-years from Earth, which is not far according to astronomical standards, is a galaxy cluster circling the quasar PKS1353-341.
Astrophysicists at the Massachusetts Institute of Technology have discovered the galaxy cluster among a pool of 22 possible candidates for the pilot study of the Clusters Hiding in Plain Sight or the CHiPS survey.
The yet unnamed galaxy cluster is 690 trillion times as massive as the sun. The Milky Way itself has a mass that is only 400 to 780 billion times more than the Sun. A key feature of this galaxy cluster is the central galaxy, which is particularly bright at a luminosity 46 billion times that of the Sun.
The researchers believe the light comes from a super-heated disk of matter circling the supermassive black hole at the heart of the central galaxy.
Spotting A Galaxy Cluster
The CHiPS researchers used data obtained from a wide range of all-sky surveys. These include X-ray data from the ROSAT, near-infrared from 2MASS, mid-infrared from WISE and SUMSS, and radio waves from NVSS.
The goal of the survey is to find galaxy clusters located close to the Milky Way that may have been mistaken for luminous X-ray objects.
The galaxy clusters found to have extreme central galaxies will be subjected to further study at Chandra.
"There might be many of these missing clusters in our local universe," says MIT astrophysicist and lead author Taweewat Somboonpanyakul, "We should have an answer of whether or not Phoenix represents the most extreme central cluster region in the universe within the next year or two."
The new research is detailed in a paper that has been accepted for publication in The Astrophysical Journal.