Strange cluster reveals star secrets

NGC 1850 is a strange stellar concoction

By BBC News Online science editor Dr David Whitehouse

The Hubble Space Telescope has focused on a peculiar stellar collection in a nearby galaxy, the like of which has never been seen in ours.

The unusual double cluster, designated NGC 1850, is situated in the Large Magellanic Cloud, some 179,000 light-years distant (1.7 million, million, million kilometres or one million, million, million miles).

Astronomers classify it as a "globular-like" star cluster - a type of object so far unknown in our own Milky Way Galaxy. It is surrounded by a filigree pattern of diffuse gas, which scientists believe was created by the explosion of massive stars.

The spectacular Hubble image is a mine of information for astronomers about the interactions of gas, dust and exploding stars. In particular, it shows how hot stars live brief lives and then explode, inducing the birth of other stars.

Stellar shockwaves

This Hubble image shows how, millions of years ago, massive stars in the cluster exploded as supernovae, forming the spectacular pattern of diffuse gas visible in the image.

NGC 1850 seen by the Paranal Observatory in South America

The shockwaves from the supernova explosions triggered the birth of new stars where they hit and compressed interstellar gas.

Detailed observations reveal two components of the cluster. There is a relatively young central region and an even younger, smaller cluster adjacent to it. The main cluster is about 50 million years old whilst the smaller one is only four million years old.

The two star clusters offer astronomers the chance to study the birth of stars at both ends of the stellar mass scale - from low-mass, so-called T-Tauri stars, to high-mass type OB stars.

Young and dim

T-Tauri stars are young, Sun-like stars that are still forming. They are so young that they may have not started converting hydrogen to helium, which is how our Sun and most other stars produce energy. Instead, they radiate energy released by their own gravitational contraction.

Astronomers have observed that T-Tauri stars tend to occur in crowded environments, but because they are inherently faint they are often difficult to distinguish with ground-based telescopes.

The new image shows that Hubble's fine angular resolution can pick out these stars, even in galaxies other than our own.

Hubble also has advantages when studying the very massive stars that can be found in NGC 1850 in abundance. These stars emit large amounts of ultraviolet radiation, which is absorbed by the Earth's atmosphere.

From its position in space, Hubble can detect this light. The data can then be analysed and used to determine the stars' properties.