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6 Jul 2022

Voracious Black Hole Slipped Through Our Fingers for 50 years, But SkyMapper Caught It

The most rapidly growing supermassive black hole in the last 9 billion years of cosmic history was serendipitously found in the SkyMapper Southern Survey, while looking for something completely different!

Dr. Adrian Lucy (Space Telescope Science Institute) was using the SMSS and other imaging surveys to search the Southern sky for symbiotic binary stars, pairs of stars that are so close that the outer layers of one star are flowing onto the other. After obtaining spectroscopy of the candidates at a telescope in South Africa, Dr. Lucy (then a PhD student at Columbia University) discovered that one object was unlike the rest: not a star at all, but a distant supermassive black hole. 

A more detailed study of the source, known as SMSS J114447.77-430859.3 or J1144 for short, was then initiated by A. Prof. Christian Wolf (ANU), who realised that a source so far away, and yet so apparently bright, must have an extraordinary intrinsic luminosity. Additional spectroscopy of J1144 was obtained with the ANU 2.3m telescope at Siding Spring Observatory (which is also home to SkyMapper), as well as the 4m Southern Astrophysical Research (SOAR) telescope in Chile.

What all those observations revealed was a supermassive black hole, 2.6 billion times as massive as the Sun, and more luminous than any others we know of in the last 9 billion years. J1144's enormous luminosity arises from its voracious appetite, eating nearly an Earth's mass of material every second. Such rapid growth was not unusual earlier in cosmic history, before the expansion of the Universe caused major galaxy collisions to become less and less common, but only future investigations will be able to determine why this black hole is such a late bloomer.

At a visual magnitude of 14.5, J1144 has been within reach of astronomers for a very long time, without its true nature having been discovered until now. In fact, J1144 has been showing up in images taken as long ago as 1901 (using an 8-inch telescope in Peru affiliated with Harvard College Observatory). When supermassive black hole studies were taking off in the 1960s, such a bright source would have been easily observable. However, J1144 is situated less than 20 degrees from the plane of the Milky Way, where the vast number of foreground stars make it incredibly difficult to stumble upon the rare objects in the distant Universe. And although J1144 has since been found to be bright in ultraviolet radiation, J1144's patch of sky fell into a small gap in the all-sky ultraviolet survey conducted by the GALEX satellite.

Much remains to be uncovered about the galaxy in which J1144 lives and the nature of the black hole and its growth, but background sources like J1144 are also extremely valuable for revealing the flows of gas around the Milky Way. The future for studies of J1144 is undoubtedly bright.

Unanticipated discoveries are a significant motivation to perform all-sky surveys like SkyMapper's, and thanks to the data interfaces supported by the National Computational Infrastructure, the wider astronomical community and the public at-large can utilise the SkyMapper Southern Survey data for their own investigations.

The discovery of J1144 was announced in a paper led by Dr. Christopher Onken (ANU) and submitted to the Publications of the Astronomical Society of Australia.