A group of scientists, led by Dr Sjoert van Velzen of Johns Hopkins University, has observed a new way for plasma to escape the gravitational pull of a supermassive black hole.
This artist’s impression shows a supermassive black hole consuming a star that has been torn apart by the black hole’s gravity; as a result of this ‘meal’ the black hole begins to launch a powerful jet that astronomers can detect with radio telescopes. Image credit: NASA / Goddard Space Flight Center / Swift.
The results are based on radio observations tracking a star as it gets torn apart by the supermassive black hole – which is located in the center of PGC 43234, a galaxy approximately 290 million light-years away.
Such violent events yield a burst of light which is produced as the bits and pieces of the star fall into the supermassive black hole.
For the first time, astronomers were able to show that this burst is followed by a radio signal from the matter that was able to escape the black hole by traveling away in a jetted outflow at nearly the speed of light.
The discovery of the jet was made possible by an observational response after the stellar disruption – known as ASASSN-14li – was announced earlier this year.
“The event was first picked up by the All-sky Automated Survey for Supernovae (ASAS-SN), and followed up with the Arcminute Microkelvin Imager Large Array, located in Cambridge,” said team member Dr Gemma Anderson, of the International Centre for Radio Astronomy Research.
Jets are often observed in association with black holes, but their launch mechanism remains a puzzle. Most supermassive black hole are fed a steady diet of gas, leading to jets that live for millions of years and change little on a human timescale.
However, the jet from PGC 43234’s black hole behaved very differently: the observations show that following a brief injection of energy, it produced short but spectacular radio fireworks.
The observed jet was anticipated by the so-called scale-invariant model of accretion. It predicts that all compact objects that accrete matter behave and look the same after a simple correction based on solely the mass of the object.
“I always liked the elegant nature of the scale-invariant theory, but previous observations never found evidence for the new type of jet it predicted,” Dr van Velzen said.
The new findings, which appear today in the journal Science, suggest that such jets could be common and previous observations were simply not sensitive enough to detect them.
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Van Velzen, S. et al. A radio jet from the optical and X-ray bright stellar tidal disruption flare ASASSN-14li. Science, published online November 26, 2015; doi: 10.1126/science.aad1182
