New explanation offered for cosmic mystery explosions

<body leftmargin="0" bgcolor="#000060" text="#FFFFFF" link="#FFFF00" vlink="#FF9900"> <table border="0" cellpadding="0" cellspacing="0" width="95%" height="1"> <tr> <center> <td valign="top" width="33%" height="33"> <p class="MsoNormal"><b><font face="Arial" size="5">New explanation offered for cosmic mystery explosions</font></b></p> <p class="MsoNormal"><font size="1" face="Arial">Oct. 5</font><font face="Arial"><font size="1">, 2005<br> Courtesy California Institute of Technology<br> and World Science staff<br> </font> <br> </font> <b><font face="Arial" size="2">Astronomers announced last May that they had solved the mystery of huge explosions that go off every day or so in space. But now, researchers say there may be more than one explanation for the flashes, because the shortest of them seem to have a different source than longer ones.<br> <br> In a new set of published findings, a group of astronomers focused on these shortest explosions and said they occur when of two extremely compact stars that collide. </font></b> </p> <p class="MsoNormal"> <b><font face="Arial" size="2"> This is the origin of the bursts that last a few thousandths of a second, according to Penn State University astronomer Derek Fox and 32 other researchers who wrote the paper published in the Oct. 6 issue of the research journal <i>Nature</i>.<br> <br> Longer ones, which last a few seconds, were attributed to explosions of single stars in the paper of May 27. That paper was published in the journal <i>Science</i>.<br> <br> The explosions, whether short or long, are called gamma-ray bursts because they briefly flash tremendous amounts of gamma rays, a type of light much more energetic than visible light.<br> <br> The findings in <i> Nature </i> suggest the short version of the bursts are due to violent collisions between a black hole and a neutron star, or by collisions of two neutron stars. Black holes and neutron stars are both extremely dense remnants of stars that have exploded after burning out their fuel.<br> <br> The short gamma-ray bursts typically shine brighter than a billion suns during the short interval they are at peak power. <br> <br> Fox and colleagues wrote that their findings were based on detailed observations of short gamma-ray bursts that occurred on May 9 and July 9 of this year. <br> <br> The May 9 event was originally detected by NASA’s Swift Satellite, and the July 9 one by High-Energy Transient Explorer, another satellite of the space agency.<br> <br> Theorists had already suspected that the short bursts were caused by the extremely heavy black holes and/or neutron stars slamming together. The new observations back up that “coalescence model,” the astronomers said.<br> <br> “Our observations do not prove the coalescence model, but we surely have found a lady with a smoking gun next to a dead body,” said Shri Kulkarni of the California Institute of Technology, one of the researchers.<br> <br> The astronomers gathered evidence that they said led them to believe the July 9 event was too faint to be a supernova, or a single exploding star. It was fainter than any supernova that has ever been observed. </font></b> </p> <p class="MsoNormal"> <b><font face="Arial" size="2"> Further, the energies observed in both the July 9 and May 9 bursts are consistent with computer simulations for collisions of “compact object binaries”—that is, neutron stars and black holes, the researchers said.<br> <br> Also, the location of the May 9 burst on the outskirts of a star-forming galaxy is at a place where one would expect to see old stars that have collapsed into the extremely massive neutron stars and even more massive black holes. The July 9 burst appears to have come from deeper within the galaxy.<br> <br> “I am amazed that we have been able to make such great strides in the space of a few months.” Kulkarni added. “Now it is time to start addressing what beast lies at the heart of these explosions.”</font></b> </p> <p class="MsoNormal"> <b> <font face="Arial" size="2">* * *</font> </p> <p><font face="Arial" size="2" color="#FFFFFF">Send us a <a href="mailto:editor@world-science.net">comment</a> on this story, or <a href="mailto:?Body=http://www.world-science.net/othernews/051005_gammafrm.htm">send it to a friend</a></font> </p> <p>  </p> </b> </center> </td> </tr> </table> </body>