Science and Exploration

3C 75 in Abell 400: Black Holes Determined To Be Bound

By Keith Cowing
Press Release
September 21, 2021
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3C 75 in Abell 400: Black Holes Determined To Be Bound
3C 75 in Abell 400

This composite X-ray (blue)/radio (pink) image of the galaxy cluster Abell 400 shows radio jets immersed in a vast cloud of multimillion degree X-ray emitting gas that pervades the cluster.
The jets emanate from the vicinity of two supermassive black holes (bright spots in the image). These black holes are in the dumbbell galaxy NGC 1128 (see optical image), which has produced the giant radio source, 3C 75.

The peculiar dumbbell structure of this galaxy is thought to be due to two large galaxies that are in the process of merging. Such mergers are common in the relatively congested environment of galaxy clusters. An alternative hypothesis is that the apparent structure is the result of a coincidence in time when the two galaxies are passing one another, like ships in the cosmic sea.

Careful analysis of the recent Chandra and radio data on 3C 75 indicates that the galaxies and their supermassive black holes are indeed bound together by their mutual gravity. By using the shape and direction of the radio jets, astronomers were able to determine the direction of 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 that a motorcyclist’s scarf is swept back while speeding down the road.

Image credit: X-ray: NASA/CXC/AIfA/D.Hudson & T.Reiprich et al.; Radio: NRAO/VLA/NRL larger image

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