Fri, May 23, 2008 page2

• Scientists observe start of supernova for first time

  SENSATIONAL Albert Kong of National Tsing Hua University and a Princeton University researcher both watched the burst that confirmed a decades-old theory

  • By Meggie Lu / STAFF REPORTER
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  Although astronomers have long believed that extremely luminous X-ray outbursts (XRO) occur at the birth of a supernova, it was not until January that two scientists, including one sponsored by the National Science Council (NSC), observed the phenomenon by a stroke of luck, shedding new light on the evolution of the galaxy.

  Albert Kong (江國興), an associate professor at the Institute of Astronomy at National Tsing Hua University, and Princeton University researcher Alicia Soderberg simultaneously but separately witnessed the explosion transmitted by NASA’s SWIFT Ultraviolet/Optical Telescope.

  The supernova they observed was named “SN 2008D,” Kong said, adding that it had confirmed the four-decade old theory about XROs. The discovery was published in Nature magazine yesterday.

  “Upon the first glimpse of SN 2008D I knew that it was significant — the first thing that came into my mind was to inform astronomers around the world about it [so that everyone could work on its analysis together],” Kong said.

  A team of international astronomers formed almost instantly for the analysis, under the leadership of Soderberg, employing the aid of the most advanced telescopes in space, Kong said.

  “The analysis confirmed that the incident was indeed an XRO and not a gamma-ray burst, a related class of explosions,” he said.

  A supernova is a spectacular explosion in which a massive star about eight times the mass of the sun rapidly radiates as much energy as the sun will in its lifetime, expelling all or most of its stellar material.

  “In large stars, gravity and nuclear burning that occur in the stellar core are in equilibrium — until the core runs out of fuel for nuclear burning and collapses under its own gravity,” Kong said.

  “When the collapsing core rebounds, it generates a shock wave that causes the star to explode,” he said.

  The significance of this is that it enriched the intersteller medium with heavy elements, gives birth to neutron stars and black holes, and triggers the formation of other stars with their shockwaves, Kong said.

  “In the past, astronomers have generally accepted that at the birth of a supernova, an X-ray outburst that lasts several minutes would occur. But because of the limitations of [their] equipment, only the optical lights that occurred a day or two after an X-ray outburst could be observed,” Kong said.

  On Jan. 9, the SWIFT was observing the NGC2770 constellation, in which two supernova had previously been recorded, when the SN 2008D X-ray explosion was observed, he said.

  Kong attributed the spotting of the 400-second burst to luck. The support for the theory that every core-collapse supernova is marked by an XRO will drastically change the method of research in the field, Kong said.

  “In the future, an X-ray satellite with functions similar to the SWIFT telescopes we employed could detect hundreds of supernovas a year,” he said.

  “The universe is boundless — but thankfully, through collaboration between scientists across the globe, we can piece together the mechanisms of its inner workings,” he said.
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