The Chandra Space Telescope captured this composite image of the galaxy cluster Abell 400, which shows microwave radio jets immersed in a vast cloud of multi-million-degree X-ray emitting gas that pervades the cluster.
The jets emanate from the vicinity of two supermassive black holes – the bright spots in the image. The black holes are located in galaxy NGC 1128 – also called the dumbbell galaxy – and together create a giant radio-emissions source known as 3C 75.
Astronomers think NGC 1128 exhibits its peculiar dumbbell structure because it actually comprises two galaxies in the process of merging. Such mergers are common within galaxy clusters, but the structure also might be the result of a coincidence, in which the two galaxies, instead of merging, are simply passing through each other in space.
Analysis of the recent Chandra and radio data on 3C 75 indicates the supermassive black holes are definitely bound together by their mutual gravity.
By using the shape and direction of the radio jets, astronomers were able to track the motion of the black holes. The swept-back appearance of the radio jets is produced by the rapid motion of the galaxy through the hot gas of the cluster, in much the same way a motorcyclist’s scarf is swept back by the wind while speeding down a road.
The binary black holes in 3C 75 are about 25,000 light-years apart, and astronomers think they are at an early stage in their evolution. Computer simulations indicate that binary supermassive black holes gradually spiral in toward each other until they coalesce to form a single and even more massive black hole.
That event, if and when it happens, would be accompanied by phenomena known as gravitational waves. The waves would spread across the universe and produce ripples in the fabric of space, which would appear as minute changes in the distance between any two points.
Sensitive gravitational wave detectors scheduled to be operational in the next decade could catch one of these events, estimated to occur several times each year within the observable universe.
