In visible light, Markarian 739 resembles a smiling face, with a pair of bright cores underscored by an arcing spiral arm. This cheerful object is really a pair of merging galaxies.
Data from Swift and Chandra reveal the eastern core (left) to be a previously unknown supermassive black hole; past studies already had identified one in the western core. The two supermassive black holes are separated by about 11,000 light-years.
Astronomers refer to galaxy centers exhibiting such intense emission as active galactic nuclei (AGN). Yet as common as monster black holes are, only about one percent of them are currently powerful AGN. Binary AGN are rarer still: Markarian 739 is only the second identified within half a billion light-years.
For decades, astronomers have known that the eastern nucleus of Markarian 739 contains a black hole that is actively accreting matter and generating prodigious energy. The Chandra study shows that its western neighbor is too. This makes the galaxy one of the nearest and clearest cases of a binary AGN.
This happy little galaxy is 425 million light-years away. This goes to show anything is possible in our remarkable universe!
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