Milky Way the dead centre

By Richard Macey
October 11, 2004

Life in the heart of a big city can be pretty cool. But astronomers have found that the centre of our city of stars, the Milky Way galaxy, is no place for intelligent beings to set up home.

They have discovered that the galaxy's middle is a turbulent place populated by bright stars that live fast and die young.

And when death comes, it is a violent event that devastates the neighbourhood. So violent, they say, that scientists hunting extra-terrestrial beings need not bother looking there.

"Life cannot exist at the centre of the galaxy," said one of the astronomers, Wilfred Walsh, of the University of NSW.

The researchers, led by Antony Stark, of the Harvard-Smithsonian Centre for Astrophysics, reached their conclusion after using a radio telescope at the South Pole to explore the Milky Way's heart. Dr Walsh said a black hole at the centre of the Milky Way was being circled by vast gas clouds.

The gas clouds were continually colliding, growing in density, and raining down on the black hole, about 500 light years away.

But so much gas would rush in at once that the black hole could not swallow it all. Much of the gas splashed back into space.

"It has been described as being like trying to fill a dog's dish with a fire hose," said Dr Walsh. The jettisoned gas then condensed into new stars.

"There could be thousands of stars formed. The stars that burn brightest burn for the shortest time. Some only live a few hundred thousand years or a million years. Then they die in spectacular explosions called supernovae."

The explosions swamp the inner galaxy with radiation lethal to any life. "It would be like living inside a nuclear reactor," said Dr Walsh. The process was a continual cycle, with stellar explosions happening every few million years - so regularly that life on any nearby planets could never get a foothold.

Fortunately, we reside in the Milky Way's middle-distance suburbs, about 25,000 light years from the centre and far from the deadly radiation, confirming the validity of the real estate agent's chant: position, position, position. Dr Walsh spent 2002 collecting the data, operating the radio telescope at the South Pole.

"It was an amazing experience," he said. "Every day I had to walk one kilometre to the telescope. The average temperature in winter was minus 60. You had to learn to dress properly and never get lost in the dark."

Their findings have been published in The Astrophysical Journal Letters.

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