A distant — and lonely — galaxy appears to have pulled in and assimilated all of its former companion galaxies. This result made with NASA’s Chandra X-ray Observatory and the International Gemini Observatory may push the limits for how quickly astronomers expect galaxies to grow in the early universe.
The unexpectedly solo galaxy is located about 9.2 billion light-years from Earth and contains a quasar, a supermassive black hole pulling in gas at the center of the galaxy and driving powerful jets of matter seen in radio waves. The environment of this galaxy, known as 3C297, appears to have the key features of a galaxy cluster, enormous structures that usually contain hundreds or even thousands of galaxies. Yet 3C297 stands alone.
A team of researchers expected to see at least a dozen galaxies within 3C297, yet they found only one. Accurate distance measurements from Gemini data revealed that none of the 19 galaxies that appear close to 3C297 in the optical image are actually at the same distance as the lonely galaxy.
The question is, what happened to all of these galaxies in 3C297? The team thinks 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, apparently resistance was futile.
The researchers think 3C297 is no longer a galaxy cluster, but a “fossil group.” This is the end stage of a galaxy pulling in and merging with several other galaxies. While many other fossil groups have been detected before, this one is particularly distant, at 9.2 billion light-years away. (The previous record holders for fossil groups were at distances of 4.9 and 7.9 billion light-years.)
It may be challenging to explain how the Universe can create this system only 4.6 billion years after the Big Bang. This result doesn’t break the current ideas of cosmology, but it begins to push the limits on how quickly both galaxies and galaxy clusters must have formed.
Revised: March 29, 2023