An exploding star, in nearby galaxy M51, shows signs of an unusual composition. The material thrown into space in the explosion contains a wide variety of elements -- a mix that is atypical of supernova events at such an early stage of the explosion, researchers say.
Exploding stars are the "factories" that produce all the heavy elements found, among other places, in our bodies. In this sense, we are all stardust. These exploding stars -- supernovae -- are highly energetic events that can occasionally light up the night sky. Such an explosion generally involves disruption in the balance between gravity -- which pulls the star's material inward -- and the thermonuclear reaction at the star's core -- which heats it and pushes it outward.
Certain types of stars that go in this way have a much bigger mass (10-100 times) and are much younger than our sun. In them, the nuclear reaction begins like that of our sun -- fusing hydrogen into helium -- but the fusion then continues, producing heavier and heavier elements. The nuclear reaction eventually stops with iron, as there is no energy benefit to the star to fuse the heavier atoms, and the balance between gravity and thermonuclear activity comes to a halt. Gravity then takes over, and the mass of the star collapses quickly, releasing so much energy in the process that the explosion ensues. The star hurls its outer layers into space, and a new "bright star" appears in the night sky where none was seen before. Just such a new star was observed in the night sky between May 31 and June 1 in a spiral arm of our galaxy's close neighbor, M51.
The first to identify the supernova were amateur astronomers in France, and soon after it was detected by the PTF Sky Survey, in which Weizmann Institute scientists participate. The phenomenon was also photographed in the new Martin Kraar Observatory at the Weizmann Institute, as well as in Tel Aviv University's Wise Observatory in Mitzpe Ramon. Israel's place on the globe enables its scientists to follow supernova events when it is daytime for many other observers, and thus to add significantly to the data collection.
The new supernova is being studied by an international team of researchers, including Dr. Avishay Gal-Yam and his research team, Drs. Ofer Yaron, David Polishook and Dong Xu, research students Iair Arcavi and Sagi Ben Ami and Director of the Kraar Observatory, Ilan Manulis, all of the Weizmann Institute's Particle Physics and Astrophysics Department, as well as scientists from the US, England, Canada and other countries. They have already noted that the material thrown into space in the explosion contains a wide variety of elements. The mix they observed is atypical of supernova events at such an early stage of the explosion, and they plan to investigate this phenomenon.
The last supernova observed in M51 (which is a mere 26 million light years away) occurred in 2005. Supernovae are thought to appear about once in 100 years in any given galaxy. The high occurrence in M51 can be explained by its interaction with another, very close galaxy, which causes the process of massive star formation to accelerate, thus increasing the rate of collapse and explosion, as well.
Gal-Yam: "We invite any amateur astronomers who may have viewed the event to send us their time-dated photos. Collaboration with amateurs is very important to us and, in this case, it might help us pinpoint the exact time of the explosion."
Dr. Avishay Gal-Yam's research is supported by the Nella and Leon Benoziyo Center for Astrophysics; the Yeda-Sela Center for Basic Research; the Legacy Heritage Fund Program of the Israel Science Foundation; the Peter and Patricia Gruber Awards; and The Lord Sieff of Brimpton Memorial Fund.
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