Astronomers watch a black hole eating a star

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For the first time, astronomers have directly imaged the jet of material ejected when a black hole eats a star.

The rapid jet of particles is caused when a supermassive black hole rips apart a star that comes too close to its event horizon.

Astronomical imaging is the process of collecting electromagnetic radiation using telescopes, and although it can involve photography in this instance it did not.

Using radio and infrared telescopes the team studied a pair of galaxies colliding with each other nearly 150 million light-years from Earth.

A black hole at the centre of one of the galaxies – which is 20 million times bigger than our sun – was seen gobbling a star twice the size of the sun.

With the US National Science Foundation’s Very Long Baseline Array (VLBA) the team captured the rare stellar death, known as titdal disruption events, or TDEs.

Despite how rare they are, scientists have hypothesised that TDEs occur quite frequently within the universe.

Theoretical astrophysicists believe that material pulled from the doomed stars forms a rotating disk around the black hole, emitting intense radiation and shoots powerful jets of material from the poles of the disk, close to the speed of light.

“Never before have we been able to directly observe the formation and evolution of a jet from one of these events,” said Dr Miguel Perez-Torres, of the Astrophysical Institute of Andalusia in Granada, Spain.

Astronomers first caught a sign about the ejection back in 2005, when astronomers detected a powerful blast of infrared light coming from the centre of a pair of colliding galaxies called Arp 299.

“As time passed, the new object stayed bright at infrared and radio wavelengths, but not in visible light and X-rays,” said Dr Seppo Mattila, of the University of Turku in Finland.

“The most likely explanation is that thick interstellar gas and dust near the galaxy’s center absorbed the X-rays and visible light, then re-radiated it as infrared,” he added.

Artist conception of a tidal disruption event (TDE) that happens when a star passes fatally close to a supermassive black hole, which reacts by launching a relativistic jet. It zooms out of the central region of its host galaxy, Arp299B, which is undergoing a merging process with Arp299A (the galaxy to the left). Credit: Sophia Dagnello, NRAO/AUI/NSF; NASA, STScI astronomers Astronomers watch a black hole eating a star skynews black hole star 4336694
Image:
An srtiat’s impression of a tidal disruption event (TDE). Pic: Sophia Dagnello, NRAO/AUI/NSF

Using the Nordic Optical Telescope on the Canary Islands alongside NASA’s Spitzer space telescope, the researchers closely recorded and analysed this infrared emission.

Over a decade their continued observations with a range of telescopes revealed that the source of the radio emission appeared to be expanding in one direction.

Their measurements of the expansion suggested it was moving at 25% of the speed of light.

Radio waves from it were not absorbed by the galaxy but managed to reach the Earth.

After years of patient data-collection using a numbers of telescopes across the globe, the researchers were able to build up a picture of what was happening.

“Much of the time, however, supermassive black holes are not actively devouring anything, so they are in a quiet state,” Dr Perez-Torres explained.

“Tidal disruption events can provide us with a unique opportunity to advance our understanding of the formation and evolution of jets in the vicinities of these powerful objects,” he added.

“Because of the dust that absorbed any visible light, this particular tidal disruption event may be just the tip of the iceberg of what until now has been a hidden population,” Dr Mattila said.

“By looking for these events with infrared and radio telescopes, we may be able to discover many more, and learn from them,” he added.

The pair led a team of 36 scientists from 26 institutions from across the world in the observations of Arp 299.

They published their findings in the 14 June online issue of the journal Science.



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