NC State astrophysicist discovers youngest known supernova in Milky Way

May 14, 2008

A North Carolina State University researcher has discovered the youngest known supernova in our galaxy. Estimated at a mere 140 years old, this celestial whippersnapper is at least 200 years younger than the next oldest known supernova, and its discovery may pave the way to a greater understanding of exploding stars.

Dr. Stephen Reynolds, an astrophysicist at NC State, led a team of researchers who suspected that a celestial object known as G1.9+0.3 was a very young supernova remnant. They examined images of the object that were taken in 2007 by NASA's Chandra X-Ray Observatory and compared these images to those taken of the same object in 1985 by the National Radio Astronomy Observatory's Very Large Array radio telescope.

Not only did the Chandra images confirm Reynolds' suspicions that the object was a young supernova remnant, but the scientists discovered that the supernova had increased in size by 16 percent in just 22 years, suggesting that the initial explosion had occurred only 140 years ago - or less if the rate of explosion had been slowing.

The results will appear in the June 10 edition of Astrophysical Journal Letters.

Supernovae are exploding stars, and act as the "engines" that drive the life cycles of galaxies. A supernova explosion disperses heavy metals, cosmic rays, and high-energy particles throughout the galaxy, aiding in the formation of new stars. In fact, a supernova explosion may have helped prod our own solar system into existence.

The brightness of supernovae can easily be obscured from optical telescopes by large amounts of interstellar gas and dust, rendering them all but invisible to astronomers. X-ray and radio telescopes, however, can detect the radio waves and high energy X-rays that supernovae emit, enabling us to "see" even highly obscured explosions.

Reynolds says that the G1.9+0.3 supernova has the largest obscuration of any known galactic supernova object.

"If not for all the interstellar 'gunk' between us and this object, people would have seen this supernova as a new star in the constellation Sagittarius in the years around 1870 to 1900," Reynolds adds.

"Normally, we deal with older remnants and have to work very hard to see even tiny changes. This supernova is getting brighter, which means it's still on its way up -- studying it will go a long way toward filling in gaps in our knowledge of these events and their effect on galaxies."
Note to editors: An abstract of the paper follows.

"The Youngest Galactic Supernova Remnant G1.9+0.3"
Authors: Stephen Reynolds, Kazimierz Borkowski, North Carolina State University, et al.
Published: June 10, 2008 in Astrophysical Journal Letters


Our 50 ks Chandra observation of the small radio supernova remnant (SNR) G1.9+0.3 shows a complete shell structure with strong bilateral symmetry, about 10000 in diameter. The radio morphology is also shell-like, but only about 8400 in diameter, based on observations made in 1985. We attribute the size difference to expansion between 1985 and our Chandra observations of 2007. Expansion is confirmed in comparing radio images from 1985 and 2008. We deduce that G1.9+0.3 is of order 100 years old . the youngest supernova remnant in the Galaxy. Based on a very high absorbing column density of 5:5£1022 cm-2, we place G1.9+0.3 near the Galactic Center, at a distance of about 8.5 kpc, where the mean remnant radius would be about 2 pc, and the required expansion speed about 14;000 km s-1. The X-ray spectrum is featureless and well-described by the exponentially cut off synchrotron model srcut. With the radio flux at 1 GHz fixed at 0.9 Jy, we find a spectral index of 0:65 and a rolloff frequency of 1:4£1018 Hz. The implied characteristic rolloff electron energy of about 94(B=10 ¹G)-1=2 TeV is the highest ever reported for a shell supernova remnant. It can easily be reached by standard diffusive shock acceleration, given the very high shock velocities; it can be well described by either age-limited or synchrotron-loss-limited acceleration. Not only is G1.9+0.3 the youngest known Galactic remnant, it is also only the fourth Galactic X-ray synchrotron-dominated shell supernova remnant.

North Carolina State University

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