Giant ring of black holes

Composite image of Arp 147

This image of galaxy pair Arp 147 combines X-ray and visible light data to reveal the presence of black holes. Gas being sucked into the black holes emits X-rays (shown as pink).

  • Arp 147 is a pair of galaxies that collided, triggering a wave of star formation
  • Many of the new stars exploded as supernovae, some forming black holes.
  • Ring of these black holes can be seen in Chandra X-ray Observatory images

JUST IN TIME FOR VALENTINE’S DAY comes a new image of a ring — not of jewels, but of black holes.

The image above shows Arp 147, a pair of interacting galaxies located about 430 million light-years from Earth. The image is a combination of X-rays from the NASA’s Chandra X-ray Observatory (pink) and optical data from the Hubble Space Telescope (red, green, blue).

Arp 147 contains the remnant of a spiral galaxy (right) that collided with the elliptical galaxy on the left. This collision produced an expanding wave of star formation that shows up as a blue ring containing in abundance of massive young stars. These stars race through their evolution in a few million years or less and explode as supernovae, leaving behind neutron stars and black holes.

A fraction of the neutron stars and black holes will have companion stars, and may become bright X-ray sources as they pull in gas from their companions.

The nine X-ray sources scattered around the ring in Arp 147 are so bright that they must be black holes, with masses that are likely 10 to 20 times that of the Sun.

An X-ray source is also detected in the nucleus of the red galaxy on the left and may be powered by a poorly fed supermassive black hole. This source is not obvious in the composite image but can easily be seen in the X-ray image.

Other objects unrelated to Arp 147 are also visible—a foreground star in the lower left of the image and a background quasar as the pink source above and to the left of the red galaxy.

Infrared observations with NASA’s Spitzer Space Telescope and ultraviolet observations with NASA’s Galaxy Evolution Explorer (GALEX) have enabled estimates to be made of the rate of star formation in the ring.

These estimates, combined with the use of models for the evolution of binary stars have enabled scientists to conclude that the most intense star formation may have ended some 15 million years ago, in Earth’s time frame.

The results were published in the October 1, 2010, issue of The Astrophysical Journal. The scientists involved were Saul Rappaport and Alan Levine from the Massachusetts Institute of Technology, David Pooley from Eureka Scientific, and Benjamin Steinhorn, also from MIT.

Adapted from information issued by the Chandra X-ray Centre. Image credits: X-ray, NASA / CXC / MIT / S. Rappaport et al; optical, NASA / STScI.

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