16 Dec 2021

• Four cavities in the hot gas of a single galaxy cluster have been found.
• Astronomers found this quartet of X-ray cavities in the cluster located about 3.9 billion light years from Earth using Chandra.
• This suggests there is a pair of supermassive black holes, both of which erupted and generated jets at about the same time.
• If confirmed, the two supermassive black holes would be among the closest pair ever discovered, with a separation of about 250 light years.

Four enormous cavities, or bubbles, have been found at the center of a galaxy cluster using NASA's Chandra X-ray Observatory, as described in our latest press release. The left panel of this graphic shows an optical image of the galaxy cluster called RBS 797, from NASA's Hubble Space Telescope. Hot gas that envelopes the individual galaxies is invisible in optical light, but it is detected in X-rays by Chandra (right). One pair of cavities can be seen towards the left and right of center in the Chandra image as black oval-shaped regions. The other pair is less distinct, but can be found above and below the center of the image.

Scientists have seen these X-ray cavities before in other galaxy clusters. A pair of cavities is thought to be a byproduct of eruptions from a giant black hole in a large galaxy at the center of a cluster. The eruptions power jets in opposite directions, which push gas away to create a pair of cavities. However, to produce four cavities each roughly pointing 90 degrees away from one another, a more complex phenomenon must be at play.

A team of astronomers studying RBS 797 think the most likely answer is that the galaxy cluster contains a pair of supermassive black holes, each of which has launched jets in perpendicular directions at almost the same time. Another possible explanation for the four cavities seen in RBS 797 is that there is only one supermassive black hole — with jets that somehow manage to flip around in direction quite quickly. Analysis of the Chandra data shows that the age difference for the east-west and north-south cavities is less than 10 million years.

Previously, astronomers observed the pair of cavities in the east-west direction in RBS 797, but the pair in the north-south direction was only detected in a new, much longer Chandra observation. The deeper image uses almost five days of Chandra observing time, compared to about 14 hours for the original observation. The NSF's Karl G. Jansky Very Large Array had already observed evidence for two pairs of jets as radio emission, which line up with the cavities.