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The Space Telescope Science Institute (STScI) in Baltimore has released this remarkable image of a cosmic ring, a fitting pre-Valentine's day image.
The cause of this odd structure, 430 light years away, was a collision between an elliptical and a spiral galaxy. The catastrophic event resulted in two objects with unusual structures that dominate the above image, and this earned them a place in Arp's "Atlas of Peculiar Galaxies", where they are number 147.
The elliptical galaxy (the redder of the two) almost completely lost its original shape, and also developed a ring structure, that appears highly elliptical due to the viewing angle, while near the nucleus there appears to be either a spiral or concentric ring structure.
The spiral galaxy, on the other hand, has seen all its material transferred into an enormous ring, in which the compression of gas has triggered a rapid burst of massive star formation. These stars give the ring its blue colour.
From the abundance of gas in the ring, stars tens of times more massive than the Sun were formed, and many of these short lived giants have already ended their lives as supernovae, after only a few million years of life.
Because a fraction of these stars were certainly members of double systems, material from the surviving member began to fall onto the compact remnant left after the explosion (either a black hole or neutron star) and this generates X-rays. This X-ray emission, mapped by NASA's Chandra X-ray Observatory, is shown in pink in the figure, while red, green and blue are from a Hubble Space Telescope image.
In the star forming ring, at least 9 intense X-ray sources can be seen, and their luminosity suggests that they are powered by as many black holes, with masses between 10 and 20 solar masses. The nucleus of the elliptical galaxy is also associated with an X-ray source, although it's not so clear in the composite image. In this case, the emission is likely the result of a super-massive black hole with only a very limited supply of infalling material.
From a previous study of the blue star-forming ring, using the Spitzer Space Telescope and NASA's Galaxy Evolution Explorer (GALEX), we know that the epoch of maximum star formation occurred around 15 million years ago. It is therefore likely that more new black holes will "soon" be added to those already present.
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