Milky Way devours a newly discovered galaxy

THE Milky Way - the celestial star city in which our own sun and solar system reside - has been caught in an act of inter-galactic cannibalism.

Rodrigo Ibata, a research student at the Institute of Astronomy, Cambridge, has discovered a previously unknown 'dwarf spheroidal galaxy' on the outer fringes of the Milky Way. This galaxy, our closest neighbour in space, is being torn apart by the Milky Way's gravitational field and its millions of stars are being incorporated into our own galaxy.

The discovery was announced by Mr Ibata and his co-discoverers Dr Mike Irwin and Dr Gerry Gilmore, at the European and National Astronomy Meeting in Edinburgh yesterday. According to Dr Irwin, scientific protocol has given the galaxy 'a very boring name: Sagittarius Dwarf Spheroidal Galaxy. Rodrigo's Galaxy sounds best, but he'd never live it down.'

The evidence that the Milky Way is devouring another galaxy lay unnoticed in photographs taken nearly 20 years ago. The photographs contained so much information that no one knew where to look until Mr Ibata, his supervisor, Dr Gilmore, and Dr Irwin of the Royal Greenwich Observatory, analysed them this year.

In January, Mr Ibata found a group of anomalous stars in the course of analysing some of the 200 billion or so stars in the Milky Way. The anomaly puzzled his research supervisor Dr Gilmore, who called in Dr Irwin, a specialist in the study of 'satellite' galaxies.

The researchers analysed photographs of the southern night skies taken with the UK Schmidt telescope at the Anglo-Australian Observatory in Siding Springs, New South Wales. Many of the photographs had been taken in the 1970s but the new galaxy had not shown up because no one had realised that it might be there. To pick out the stars in the dwarf galaxy from the hundreds of thousands of others on the photographic plates, the astronomers employed computer-controlled techniques including the Automatic Plate Measuring facility at the Royal Greenwich Observatory.

The new galaxy is about 50,000 light years from the centre of the Milky Way, but is on the opposite side of the galaxy from the solar system, so is about 80,000 light years away from our sun. In contrast, the Large Magellanic Cloud, previously regarded as the nearest galaxy is some 170,000 light years away. (A light year is a measure of the distance that a beam of light travels in a year, approximately 10 million million kilometres.)

It is impossible by direct observation to distinguish the stars in the dwarf galaxy from the much more numerous foreground stars of the Milky Way, because it lies at the opposite side, almost across the centre of the Milky Way, from the Solar System. It thus appears to lie in a part of the sky near the galactic centre where there are vast star clouds.

(Graphic omitted)