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Durham University News

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Massive black hole causes storm in “Teacup” galaxy

(11 February 2015)

New evidence that the largest black holes can have a catastrophic effect on their surrounding galaxies has been discovered by an international team of astronomers led by Durham University.

Using the National Science Foundation's Very Large Array of 27 radio telescopes in New Mexico, they found surprisingly energetic activity in what they otherwise considered a "boring" galaxy.

The astronomers saw the galaxy as it was 1.1 billion years ago – the time it takes for light and radio waves emitted from it to reach the Earth.

Lead-author Chris Harrison, of the Centre for Extragalactic Astronomy at Durham University said: "It appears that a supermassive black hole is explosively heating and blasting around the gas in this galaxy and is transforming it from an actively star-forming galaxy into one devoid of gas that can no longer form stars.”

The discovery may help to explain the difference between two types of galaxy - spirals, like our own Milky Way, which are rich in gas and actively forming stars, and ellipticals, which are gas-poor and have very little star formation.

The massive ellipticals, astronomers think, started life as actively star forming galaxies. Powerful jets and winds of material, powered by supermassive black holes at the galaxies' centres, are believed to remove or destroy the raw material needed for continued star formation.

"For many years we've seen direct evidence of this happening in galaxies that are extremely bright when viewed through radio telescopes. These, rare, radio-bright galaxies harbour powerful jets, launched from the black hole that plough into the surrounding gas," Harrison said.

"However, to understand how all of the galaxies in our Universe formed, we needed to know if these same processes occur in less extreme galaxies that better represent the majority. This was the focus of our study."

This latest insight into supermassive black holes was the result of observations of a galaxy labelled J1430+1339, also known as the "Teacup", because of its appearance. The galaxy had been identified as having characteristics typical of galaxies with a central black hole actively consuming material.

Follow-on observations with NASA's Hubble Space Telescope also revealed evidence that the Teacup has the appearance of an elliptical-type galaxy, but surrounded by gas, suggesting that it is still in the process of transforming from a star-forming galaxy.

The observations showed that the galaxy has "bubbles" extending from 30,000 to 40,000 light-years on each side of its core, along with smaller jet-like structures, about 2,000 light-years in size. These jet-like structures are located at the position where visible-light observations indicate gas is being accelerated to speeds up to about 1,000 kilometres per second.

Co-author Dr Alasdair Thomson, a member of the Centre for Extragalactic Astronomy at Durham University, said: "These radio observations have revealed that the central black hole is whipping up a storm at the centre of this galaxy, by launching powerful jets that are accelerating the gas in the host galaxy and are colliding with the gas on larger-scales. This is the same kind of powerful process we'd previously seen in rare, extremely radio luminous galaxies. The incredible capabilities of the VLA telescope have allowed us to discover that these processes can occur in the more-common, radio-faint galaxies, as long as you look hard enough".

"This 'storm' in the 'Teacup' means that the jet-driven process in which a black hole is removing or destroying star-forming material may be much more typical than we knew before, and could be a crucial piece in the puzzle of understanding how the galaxies we see around us were formed" Harrison said. Harrison and his collaborators now have observed eight more such objects with the VLA and are analysing their data to see if the others show similar characteristics.

Harrison worked with a team of astronomers from the UK, the USA, and Chile. Their findings are published in The Astrophysical Journal. The research was funded in the UK by the Science and Technology Facilities Council and The Leverhulme Trust.

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