Astronomers have discovered more than a million young stars forming in a hot, dusty cloud of molecular gases in a tiny galaxy near Milky Way.
The star cluster is buried within a supernebula in a dwarf galaxy known as NGC 5253, in the constellation Centaurus.
The cluster has one billion times the luminosity of our Sun, but is invisible in ordinary light, hidden by its own hot gases, researchers said.
“We are stardust, and this cluster is a factory of stars and soot,” said Jean Turner, a professor of physics and astronomy in the University of California, Los Angeles (UCLA) College and lead author of the research.
“We are seeing the dust that the stars have created. Normally when we look at a star cluster, the stars long ago dispersed all their gas and dust, but in this cluster, we see the dust,” Turner said.
The amount of dust surrounding the stars is extraordinary – approximately 15,000 times the mass of our Sun in elements such as carbon and oxygen.
The cluster is about 3 million years old, which in astronomical terms, is remarkably young. It is likely to live for more than a billion years, Turner said.
The Milky Way has not formed gigantic star clusters for billions of years, Turner said. It is still forming new stars, but not in nearly such large numbers, she said.
Some astronomers had believed that such giant star clusters could form only in the early universe.
The Milky Way has gas clouds, but nothing comparable to this galaxy’s Cloud D which houses the enormous star cluster enshrouded in thick gas and dust, Turner said.
How much of a gas cloud gets turned into stars varies in different parts of the universe. In the Milky Way, the rate for gas clouds the size of Cloud D is less than 5 per cent. In Cloud D, the rate is at least 10 times higher, and perhaps much more.
NGC 5253 has hundreds of large star clusters, including at least several that are young, the astronomers report. The most spectacular is found within Cloud D.
“We’re catching this cluster at a special time. With a cluster this large, we would expect several thousand stars that would have become supernovae and exploded by now. We found no evidence of a supernova yet,” Turner said.
The cluster contains more than 7,000 massive “O” stars – the most luminous of all known stars, each a million times brighter than our Sun.
NGC 5253 has approximately nine times as much dark matter as visible matter – a much higher rate than the inner parts of the Milky Way, Turner said.
The research was published in the journal Nature.