Closing in on gamma-ray bursts
Jun 29, 2000
Astronomers have obtained the first detailed images of a galaxy in which a gamma-ray burst has taken place. Stephen Holland of the Danish Centre for Astrophysics in Aarhus, and co-workers in Denmark, Iceland Norway and the UK, used the Hubble Space Telescope to obtain the high-resolution images of the galaxy in which a gamma-ray burst occurred on 25 April 1998. The gamma-ray burst has been located in a region of active star formation in a spiral galaxy. The results also add weight to the theory that gamma-ray bursts are related to supernovae explosions.
The origin of gamma-ray bursts is one of the biggest unsolved problems in astrophysics. Some 3000 of these short-lived bursts of intense gamma-rays have been detected in the last three decades, but it is only recently that astrophysicists have confirmed that they originate outside our galaxy.
The burst of 25 April 1998 surprised astronomers because it was between a thousand and a million times fainter than a typical burst. Moreover, it was also unusual in that is was from a galaxy "only" 125 million light years away. However, this proved to be an advantage as it allowed the galaxy, ESO 184-G82, to be imaged by the Space Telescope Imaging Spectrograph on Hubble. Although 20 other galaxies have been identified with gamma-ray bursts, they are all too far away to be imaged. The Hubble images show that the galaxy contains numerous clouds of hydrogen and regions containing hot young stars.
The fact that a supernova was observed at exactly the same location as gamma-ray burst less than 24 hours later is further evidence that these two types of highly energetic events are related, although this has still to be proved conclusively.