The arrow shows where the star exploded: in one of the galaxy's spiral arms. Image: Johan Fynbo
Reading An international team of astronomers believes that they have discovered a new type of star death: The star simply collapses, causing its matter to condense into a black hole. Until now, astronomers only knew death in a supernova in heavy stars, where in a huge explosion large amounts of material are thrown into space and the star briefly shines as brightly as an entire galaxy. On the trail of unspectacular star death without supernova came the more than thirty scientists by photographs of the research satellite "Swift". The satellite launched two so-called gamma-ray bursts in two galaxies more than a billion light-years away in May and June this year. During these few seconds to several minutes of lightning, huge amounts of high-energy gamma radiation are emitted into space. The exact causes of these flashes are not yet known. However, they occur in connection with supernova events and thus with the death of stars and the formation of black holes.

Even after the two gamma-ray flashes observed, the scientists therefore searched for evidence of a supernova. But as carefully as they searched the sky region with the Keck Telescope in Hawaii and the Very Large Telescope of the European Southern Observatory (ESO), there were no traces of such a spectacular explosion.

After the gamma-ray flashes came from a dwarf galaxy teeming with heavy stars, the researchers believe in lightning the consequences of a relatively silent death of such a star. The black hole created by the collapse of the star produced the high-energy radiation as it absorbed the remaining matter of the star, the scientists said. However, how this quiet collapse happens exactly is still unclear. "Any previously unknown process is at work, " explains Italian astrophysicist Massimo Della Valle, one of the scientists involved. Now the researchers want to search for more gamma-ray flashes to find out the background of the unspectacular death of heavy stars.

Neil Gehrels (NASA Goddard Spaceflight Center, Greenbelt) et al: Nature, Vol. 444, p. 1044 Massimo Della Valle (Astrophysical Observatory, Firenze) et al .: Nature, Vol. 444, p.1050 Johan Fynbo (University of Copenhagen, Dark Cosmology Center, ) et al .: Nature, Vol. 444, p. 1047 Avishay Gal-Yam (California Institute of Technology, Pasadena) et a .: Nature, Vol. 444, p. 1053 ddp / science.de? Ulrich Dewald ad

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