Using NASA’s Chandra X-ray Observatory and the International Gemini Observatory, astronomers identified a distant and lonely galaxy about 9.2 billion light-years from Earth. This surprisingly solitary galaxy has drawn in and assimilated all of its former companion galaxies.
Known as 3C 297, the galaxy contains a quasar, a supermassive black hole that attracts gas at the galaxy’s center and propels powerful jets of matter that can be seen in radio waves. It has features of a galaxy cluster, huge structures that usually contain hundreds or even thousands of galaxies. Yet 3C 297 stands alone.
Valentina Missaglia of the University of Turin in Italy, who led the study, said: “It looks like we have a cluster of galaxies that is missing almost all of its galaxies. We expected to see at least a dozen galaxies the size of the Milky Way, but we only see one.”
Missaglia and her colleagues see two critical features of a galaxy cluster in the Chandra X-ray data:
A significant amount of gas surrounds the lone galaxy with temperatures reaching tens of millions of degrees, which is commonly seen in galaxy clusters, according to the X-ray data.
Second, the powerful X-rays produced by the jet from the supermassive black hole, 140,000 light-years away, suggest that the jet may have impacted gas encircling the galaxy.
A third feature of galaxy clusters shown by 3C 297 is that one of the radio jets has rotated, indicating that it has been interacting with its environment. This feature was previously discovered in Karl G. Jansky Very Large Array data.
The data from Missaglia’s team at the Gemini Observatory in Hawaii showed that none of the 19 galaxies that appear close to 3C 297 in a Gemini optical image and have accurate distance measurements are actually at the same distance as the lone galaxy, despite these crucial features of a cluster of galaxies.
Co-author Juan Madrid of the University of Texas, Rio Grande Valley, said: “What happened to all these galaxies? We think that the gravitational pull of the one large galaxy combined with interactions between the galaxies was too strong, and they merged with the large galaxy. For these galaxies, resistance was apparently pointless.”
Astronomers say 3C 297 is now a “fossil group” rather than a galactic cluster. At this point in the process, a galaxy intrudes and merges with several other galaxies. While other groups of fossils have already been found, this one is unusually distant at 9.2 billion light-years.
Co-author Mischa Schirmer of the Max Planck Institute for Astronomy said: “It can be challenging to explain how the universe can create this system just 4.6 billion years after the Big Bang. This doesn’t break our ideas about cosmology, but it does begin to push the boundaries of how quickly both galaxies and clusters of galaxies must have formed.”
While the authors cannot completely rule out the possibility of dwarf galaxies in 3C 297, their existence would still not account for the absence of larger galaxies such as the Milky Way. Nearby examples include M87 in the Virgo Cluster, which has massive galactic neighbors and has existed for billions of years. Nevertheless, 3C 297 will, in fact, be alone for billions of years.
- Valentina Missaglia, Juan Madrid et al. Powerful yet lonely: Is 3C 297 a high redshift fossil group? The Astrophysical Journal. DOI 10.3847/1538-4365/ac9f3e