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Tuesday, 6 June, 2000, 11:51 GMT 12:51 UK
Black holes blow as well as suck
STSCI
Bubbles of hot gas shoot from a giant black hole
By BBC News Online science editor Dr David Whitehouse

Astronomers have seen a giant black hole blowing huge bubbles of hot gas.

The supermassive black hole resides in what has long been considered a peculiar galaxy because of its unusual shape. Given the designation NGC 4438, the galaxy is in the Virgo cluster, 50 million light-years from Earth.

Hubble Space Telescope (HST) images of the galaxy's central region show a bubble rising from a dark band of dust. Another bubble comes from below the dust band and is just visible as dim red blobs in the close-up picture of the galaxy's core.

The bubbles are made of hot gas. They are caused when material, initially drawn towards the black hole, is blown out again in opposite directions. The twin jets of matter sweep away all material in their paths.

The jets eventually collide with a wall of dense, slow-moving gas. The collision produces the glowing material.

The bubbles will continue to expand and will eventually dissipate. Compared with the life of the galaxy, this bubble-blowing phase is a short-lived event. In the image, the bubble is 800 light-years high and 800 light-years across.

And how they feed

Another series of Hubble observations are leading astronomers to conclude that black holes grow inside galaxies feeding on a diet of gas and stars.


STSCI
Hubble peers into the core of a distant galaxy
An initial look at the pictures favours the idea that titanic black holes at the centres of galaxies did not exist before the galaxy was born but evolved within the galaxy by swallowing stars and gas.

How big the black hole becomes depends upon the food supply that in turn depends upon the size of the galaxy.

Astronomers believe that black holes in small galaxies went relatively undernourished, weighing in at a mere few million solar masses.

Formation and growth

Black holes in the centres of giant galaxies however, some over one billion solar masses, were so engorged with gas they once blazed as quasars, the brightest objects in the cosmos.

"This supports the original theory of how black holes got their masses. It suggests that the major events that made a galaxy and the ones that made its black hole shine as a quasar were the same events," says John Kormendy of the University of Texas at Austin.

Though this secret relationship between a black hole and its host galaxy has been suspected for the past several years, it is bolstered by the Hubble discovery of 10 more supermassive black holes in galaxy centres, raising the total to more than 30 black holes now available for study.

"For the first time we can put strong constraints on the relationship between galaxy formation and black hole formation and growth," says Kormendy.

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See also:

01 Jun 00 | Sci/Tech
Hubble catches the Crab
26 May 00 | Sci/Tech
Chandra homes in on a black hole
20 Mar 00 | Sci/Tech
Black Holes put on weight
04 May 00 | Sci/Tech
Hubble finds missing hydrogen
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