Black holes in the news again

M87 is one of those galaxies that always swans about being different. It is Dark Matter deficient, not having as much of the stuff as most galaxies. Its central black hole is twice the size once thought, and now it appears the black hole is displaced from the centre of the galaxy, but only by a little bit. The black hole has been measured as 71 light years from the expected position at the centre of M87, itself in the middle of the Virgo cluster. To get kicked out, the black hole needs to interact with something close to its own 6.4 million solar mass size. The combined globular star clusters would only get it spun away by about 0.3 light years and there’s no indication of a second black hole that might have swung it round leaving only one plausible explanation – the black hole has recently merged and the dynamics of the merger has left it hurtling one way or another. The team observing it have not yet taken velocity measurements, so they don’t know quite which way its going or how fast, meaning they haven’t traced the path back to get more information on where its coming from. But if it is a merger flung black hole, this is the smallest displacement of any seen, according to the report in Astronomy Now.

Meanwhile, it seems the black hole M31* in the heart of the Andromeda Galaxy has been snacking on something big. To date, the black hole has been considered the second quietest known (second to our own, Sagittarius A*), but observations with the Chandra X-ray Space Observatory have shown it suddenly became active in 2006, shining ten times brighter than normal. Whereas our own black hole undergoes steady rises and falls in luminosity, the brightness of M31* has erupted in fits and bursts. More in the Astronomy Now report.

On a related note, a cataloge of observations, charting every Active Galactic Nucleus within 650 million light years, performed by NASA’s Swift X-ray Satellite is believed to have provided the data required to confirm that these vast powerhouses, central black holes putting out jets of relativistic particles, are set off by galactic mergers as theorists predicted.


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