Astronomers observe a lonely, distant galaxy that appears to have consumed all of its former companions

A galaxy far, far away ate all of its friends.  Now everything is on its own

Composite image of a lone galaxy containing a supermassive black hole, two jets, and an X-ray hotspot, all surrounded by hot gas. Credit: NASA MSFC/SAO/Chandra

More than 13 billion years ago, the first galaxies formed in the universe. They were elliptical, with intermediate black holes at their centers surrounded by a halo of stars, gas and dust. Over time, these galaxies evolved by flattening into disks with a large bulge in the middle. Then they were pulled together by mutual gravity to form galaxy clusters, huge clusters that make up the large-scale cosmic structure. This gravitational force also leads to mergers, as galaxies and their central black holes come together to form larger spiral galaxies with central supermassive black holes (SMBHs).

This merger and absorption process (and its role in galactic evolution) remains a mystery to astronomers today because most of it occurred during early universe, which is still very difficult to observe with existing telescopes. Using data from NASA’s Chandra X-ray Observatory and the International Gemini Observatory, an international team of astronomers has observed a lonely, distant galaxy that appears to have consumed all of its previous companions. Their findings, which appeared recently in Astrophysical Journalindicating that galaxies in the early universe grew faster than previously thought.

The research team was led by Valentina Missaglia, a postdoctoral astrophysicist at the University of Turin. She was joined by colleagues from the National Institute of Nuclear Physics (INFN), the Astrophysical Observatory of Turin, the University of Texas Rio Grande Valley, the Max Planck Institute for Astronomy (MPIA), and Brazil’s Ministry of Science, Technology and Innovation. Communications (MCTIC), the National Institute for Astrophysics (INPE), the Harvard and Smithsonian Center for Astrophysics, the Institute for Theoretical and Experimental Astronomy (IATE), and the National Institute of Astrophysics (INAF).

The team reports the unexpected discovery of a solitary galaxy (3C 297) about 9.2 billion light-years away. They also note that it has a quasar at its center and powerful jets (bright at radio spectrum) emanating from its electrodes. The environment of this galaxy appears to have several key features of a galaxy cluster; However, the galaxy seems to be alone. As Missaglia said in a Harvard-Chandra press release, “It appears that we have a galaxy cluster that is missing almost all of its galaxies,” she said. “We were expecting to see at least ten Milky Way-sized galaxies, and yet we only see one.”

Missaglia and her colleagues observed three features associated with galaxy clusters based on the Chandra data. First, the X-ray data revealed that 3C 297 is surrounded by large amounts of superheated gas (tens of millions of degrees) — something rarely seen outside galaxy clusters. Second, the SMBH’s relativistic jet stream created a bright source of X-rays about 140,000 light-years away, meaning it pushed through the gas surrounding the galaxy. Third, one of the radio planes appeared to curve, indicating that it was interacting with its surroundings.

This last result was previously observed based on data collected by Karl G. Jansky Very Large Array (VLA). But when the team consulted their data from the Gemini Observatory, they noticed that none of the 19 galaxies that appeared near 3C 297 were actually at the same distance. Co-author Juan Madrid, an assistant professor at the University of Texas Rio Grande Valley, said:

“The question is, what happened to all these galaxies? We think that the gravitational force of one large galaxy combined with the interactions between galaxies was very strong, and it merged with the large galaxy. For these galaxies, apparently, resistance was useless.”

While the authors cannot rule out the possibility of dwarf galaxies located around 3C 297, their presence does not explain why there are no larger galaxies nearby. In addition, they expect 3C 297 to spend several billion years on its own before it acquires any large galactic companions (such as M87 and the Virgo Cluster). While it’s not clear how galaxy 3C 297 ended up alone in a cluster-like environment, the team theorizes that it could be a “fossil cluster” – the final stage of a galaxy merging with several other galaxies.

While many other groups of fossils have been discovered before, 9.2 billion light-years away, this one is the farthest of all. The previous record holders for fossil groups were 4.9 and 7.9 billion light-years away (respectively). “It may be difficult to explain how the universe could have created this system just 4.6 billion years after the Big Bang,” said co-author Mischa Schirmer of MPIA. “This doesn’t break our ideas about cosmology, but it does start to push the speed limits of both galaxies And galaxy clusters It should have been formed.”

more information:
Valentina Messageglia et al., Strong but Lonely: Is 3C297 a fossil group with a high redshift?, The Astrophysical Journal Supplement Series (2022). DOI: 10.3847/1538-4365/ac9f3e

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