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Astronomers study galactic ‘hailstorm’ in early universe

Astronomers have looked back nearly 13 billion years, when the universe was less than 10 percent its present age, to determine how quasars regulate the formation of stars and build-up of the most massive galaxies.

Quasars are extremely luminous objects powered by super-massive black holes with the mass of a billion suns.

A quasar spits out cold gas at speeds up to 2,000 km per second, and across distances of nearly 2,00,000 light years – much farther than has been observed before, found the authors.

How this cold gas – the raw material for star formation in galaxies – can be accelerated to such high speeds has remained a mystery.

“It is the first time that we have seen outflowing cold gas moving at these large speeds at such large distances from the supermassive black hole,” said Claudia Cicone, student at Cambridge University’s Cavendish Laboratory, lead author of the first paper.

galactic hailstorm
Illustration of the outflow (red) and gas flowing in to the quasar in the centre (blue). The cold clumps (shown in the inset image) embedded in the hot outflow are launched in a “galactic hailstorm”. Credit: Tiago Costa.
Cicone’s observations allowed the second team to develop a detailed theoretical model of the outflowing gas around a bright quasar.

“We found that while gas is launched out of the quasar at very high temperatures, there is enough time for some of it to cool through radiative cooling – similar to how the Earth cools down on a cloudless night,” said Tiago Costa, lead author of the second paper from Institute of Astronomy and the Kavli Institute for Cosmology.

Quasars are powered by supermassive black holes at the centre of galaxies, surrounded by a rapidly spinning disk-like region of gas.

As the black hole pulls in matter from its surroundings, huge amounts of energy are released.

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“The amazing thing is that in this distant galaxy in the young universe the conditions are just right for enough of the fast moving hot gas to cool to the low temperatures that Claudia and her team have found,” Costa said.

The two results appeared in the journals Monthly Notices of the Royal Astronomical Society and Astronomy & Astrophysics.


Claudia Cicone, Roberto Maiolino, Simona Gallerani, Roberto Neri, Andrea Ferrara, Eckhard Sturm, Fabrizio Fiore, Enrico Piconcelli and Chiara Feruglio. Very extended cold gas, star formation and outflows in the halo of a bright quasar at z > 6 Astronomy & Astrophysics DOI:10.1051/0004-6361/201424980

Tiago Costa, Debora Sijacki and Martin Haehnelt. Fast cold gas in hot AGN outflows.Monthly Notices of the Royal Astronomical Society. DOI:10.1093/mnrasl/slu193

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