NGC 2207 - IC 2163

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• published: 16 Dec 2014
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At this time of year, there are lots of gatherings often decorated with festive lights. When galaxies get together, there is also the chance of a spectacular light show. Take, for example, NGC 2207 and IC 2163. Located about 130 million light years from Earth in the constellation of Canis Major in the southern hemisphere, this pair of spiral galaxies is caught in a grazing encounter. This system has hosted three supernova explosions in the past 15 years, which is quite a few in such a short time. This galactic pair has also produced one of the most bountiful collections of super bright X-ray lights known. These special objects - officially known as 'ultraluminous X-ray sources' or ULXs - have been found using data from NASA’s Chandra X-ray Observatory. As in our Milky Way galaxy, NGC 2207 and IC 2163 are sprinkled with many systems known as X-ray binaries, which consist of a star in a tight orbit around either a neutron star or a 'stellar-mass' black hole. The strong gravity of the neutron star or black hole pulls matter from the companion star. As this matter falls toward the neutron star or black hole, it is heated to millions of degrees and generates X-rays. ULXs are far brighter in X-rays than most 'normal' X-ray binaries. While the true nature of ULXs is still debated, they are likely an unusual type of X-ray binary. For example, some astronomers think that the black holes in some ULXs may be heavier than stellar mass black holes and could represent a hypothesized, but as yet unconfirmed, intermediate-mass category of black holes. Regardless of what they are, ULXs put on intriguing X-ray light displays no matter what the season.