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Friday, September 17, 1999 Published at 10:39 GMT 11:39 UK


Hubble's hot stuff

The Qunituplet cluster, few stars are brighter and hotter

By BBC News Online Science Editor Dr David Whitehouse

Peering through 25,000 light-years of obscuring dust and myriad stars, the Hubble Space Telescope has provided the clearest view yet of a pair of the young clusters of stars near the very centre of our Milky Way galaxy.

Located less than 100 light-years from heart of our galaxy, where astronomers believe lurks a supermassive black hole, these giant clusters have an excess of massive stars and offer new clues as to how such clusters form.

[ image: The Arches cluster]
The Arches cluster
The Hubble images reinforce the long-held view among astronomers that the galactic core is a unique place in our galaxy, where conditions under which stars form are completely different from elsewhere.

Observations made with many kinds of telescopes show that the core is a place of violent star formation. Clouds of hydrogen swirl around the centre of our galaxy under the gravitational influence of the central black hole.

Called the Arches and Quintuplet clusters, they are two and four million years old, respectively. Ripped apart The older cluster is more dispersed, and it has stars on the verge of blowing up as supernovae, such as the Pistol Star, the brightest known star in our galaxy.

[ image: The very heart of our galaxy is hidden behind stars, gas and dust]
The very heart of our galaxy is hidden behind stars, gas and dust
The Arches cluster is so dense, over 100,000 of its stars would fill a spherical region in space whose radius is the distance between the Sun and its nearest neighbour, the star Proximal Centauri, four light-years away.

Only one out of every 10,000,000 stars in the Galaxy is as luminous as the bright Arches cluster stars. This suggests that conditions are so extreme at the hot and dynamic hub of our galaxy, massive stars are favoured to form. At least a dozen of the stars weigh about 100 times more than our Sun.

Astronomers believe that both clusters might have formed when two giant clouds containing dust and hydrogen had a head-on collision. This precipitated the birth of thousands of stars.

Both clusters are destined to be ripped apart in just a few million years by gravitational tidal forces in the galaxy's core. But in the brief time they are around, they shine more brightly than any other star cluster in the Galaxy.

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