NGC 5253
The blue background is a Hubble Space Telescope image of galaxy NGC 5253; the white spots are young star clusters. Superimposed is the gas (fuzzy red to yellow) as seen by the Submillimeter Array. The brightest part of the image is Cloud D. Jean Turner

A million young stars are forming in a tiny galaxy near the Milky Way, well hidden in a dusty region containing matter approximately 15,000 times more than the mass of our sun.

Even the Milky Way which is still forming stars is far behind the dwarf galaxy in the number of stars being churned out.

The star cluster is buried in the supernebula hot, dusty cloud of molecular gases in the dwarf galaxy known as NGC 5253.

The galaxy has approximately nine times as much dark matter as visible matter, which is much higher than found in the inner parts of the Milky Way.

Unlike other star clusters where the star formation disperses all the gas and dust, this one has still a lot of dust, which has kept it hidden for long.

The star cluster is believed to be one billion times brighter than the sun but invisible because of the phenomenal amount of dust covering the region.

It contains more than 7,000 massive 'O' stars — the most luminous stars, each a million times brighter than our sun.

"We are stardust, and this cluster is a factory of stars and soot," said Jean Turner, a professor of physics and astronomy in the UCLA College and lead author of the research published in Nature.

The cluster is young at three million years old, and expected to live for more than a billion years, she said. Some astronomers had believed that such giant star clusters could form only in the early universe.

The Milky Way has not formed gigantic star clusters for billions of years, Turner said.

The dwarf galaxy's Cloud D region houses the enormous star cluster. NGC 5253 has hundreds of other large star clusters in other regions.

Unlike large clusters which usually have a few supernova or stellar deaths, this one has not revealed any. But soon the explosions from some stars could send the dust and gas packing away into interstellar space, the astronomers expect.

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 forming clusters as found in Cloud D is less than 5%.

The research was conducted using the Submillimeter Array, a joint project of the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics, on Hawaii's Mauna Kea.