Changing face of infant stars

XZ Tau ejects gas into space

By BBC News Online science editor Dr David Whitehouse

New images captured by the Hubble Space Telescope have documented the dramatic changes that can take place in very young stars over just weeks or months.

Astronomers were amazed to see the double star system called XZ Tauri throw off a hot bubble of expanding gas.

The progression of the cloud away from the system and into space was followed through observations that were made over five years.

The event has given researchers new information about the early stages of stellar evolution.

Although scientists are puzzled by the ejection, they say that they have seen the beginnings of a so-called cooling zone - a region where the expanding gas bubble cools by emitting light.

XZ Tau is composed of two very young stars separated by roughly the same distance as between our Sun and Pluto (about six billion kilometres or four billion miles).

Fiery outflows

The bubble has been expanding over the past 30 years and now extends to nearly 15 times the distance between the stars.

Material is ejected along the magnetic poles of HH30

Time-lapse movies show jets of gas ploughing into space at hundreds of thousands of kilometres per hour, as well as moving shadows billions of kilometres in size.

The outflow from XZ Tau extends nearly 96 billion kilometres (60 billion miles).

Hubble has observed similar things in another star system called HH 30. Like XZ Tau, it is 500 light-years from Earth in the Taurus-Auriga molecular cloud, one of the nearest stellar nurseries to our planet.

Both star systems are probably less than a million years old, making them relative newborns.

Movies of HH 30 show a pair of thin jets streaming away from the centre of a dusty disc.

Astronomers are interested in the disk because it is probably similar to the one from which the Sun and the planets in our Solar System formed.