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Nova, Supernova, or Stellar Collision?

Nova, Supernova, or Stellar Collision?

"It may be that the remnant from the stellar merger is very unstable, closely resembling extremely young stars"

Dr. Joel Kastner, professor of imaging science and astronomical sciences and technology, and a team of astronomers from around the world are exploring a new corner of the galaxy, staring at a star about 20,000 light years away in the constellation Monoceros that exploded in 2002. The event has created a peculiar and spectacular flare—not quite as bright as a supernova, but more explosive than a nova.

Kastner and his colleague Dr. Noam Soker at the Israel Institute for Technology believe the object is a coalescence of two stars, one that is about 10 times the mass of the sun and the other about the same mass as the sun. According to a theory developed in part by Soker, the more massive star consumed the smaller star, releasing a huge amount of energy and causing it to spin rapidly, which over time—years—will create a strong magnetic field and generate significant X-rays.

While immediately following the event X-rays were not visible, in 2008 a long exposure by the European Space Agency's orbiting XMM-Newton X-ray Observatory detected the presence of X-rays. However, by the end of the 28-hour exposure the X-ray brightness already appeared to be dropping off. And to Kastner's team's surprise, in a recent follow-up exposure with NASA's orbiting Chandra X-ray Observatory in January 2010, the object had completely disappeared from view.

"It may be that the remnant from the stellar merger is very unstable, closely resembling extremely young stars, which are known to show huge spikes of X-rays. We hope to continue tracking the X-rays coming from the remnant star with Chandra and XMM, since this may be one of the few cases where we can prove stellar cannibalism actually happens," explains Kastner.

A paper on Kastner's team's discovery of X-rays from the possible stellar merger in Monoceros, lead-authored by astronomical sciences and technology graduate students Fabio Antonini and Rudy Montez, has been submitted to the Astrophysical Journal.

Sequence of satellite images

Now You See It, Now You Don't:

A sequence of images from two orbiting satellite X-ray observatories—NASA's Chandra and ESA's XMM-Newton. Click on the image to see a more detailed view.

Now You See It, Now You Don't:

A sequence of images from two orbiting satellite X-ray observatories—NASA's Chandra (left and right panels) and ESA's XMM-Newton (center panel)—shows a bright X-ray source appearing at the position of the exploding star in Monoceros (red arrow) in 2008. However, no source was present one year after the explosion (left) or earlier this year (right). The red and blue circles highlight sources that appear in all three X-ray images, demonstrating the exploding star in 2008 was not an artifact of the XMM telescope or detector. Instead, it appears stellar cannibalism has produced a "born-again" star, one that produces X-rays in violent bursts.