THIS SUPERNOVA JUST WON'T FADE AWAY


German Version Spanish Version For more information contact: Dr. Stefan Immler NASA/USRA Goddard Space Flight Center Greenbelt, MD 20771 USA Phone: +1-301-286-0072 immler@milkyway.gsfc.nasa.gov		July 21, 2005 THIS SUPERNOVA JUST WON'T FADE AWAY Scientists say that a star which exploded in 1979 still shines as brightly in X-rays today as it did when X-ray telescopes first observed it years ago. This is a surprise finding because such objects usually fade significantly after only a few months. The scientists could document a unique history of the star, both before and after the explosion, by studying rings of light leftover from the blast, similar to the way climate history is derived from analyzing rings in a tree trunk. Dr. Stefan Immler at NASA's Goddard Space Flight Center in Greenbelt, Md., led this observation using the European Space Agency's XMM-Newton observatory. The star explosion (supernova), called SN 1979C, shows no sign of letting up, he said.
Links to high-resolution images: Figure 1: JPG (455 kB) Figure 1: PS (14 MB) Figure 1: JPG (455 kB, no scalebar) Figure 1: PS (14 MB, no scalebar) Figure 2: JPG (139 kB) Figure 2: PS (12 MB) Figure 2: JPG (139 kB, no scalebar ) Figure 2: PS (12 MB, no scapebar)		Figure 1: XMM-Newton optical/UV image of the galaxy M100 and supernova SN 1979C obtained with the Optical Monitor in the B, U, and UVW1 filters. The position of SN 1979C is marked by a white circle. The streak across the image is from an artefact caused by a dead detector column. The scalebar is 2 arcmin, correspoding to 32,600 lightyears. Click on the image for a high-resolution version. Credit: NASA/ESA/Immler et al.
Link to the scientific publication: Late-time X-Ray, UV and Optical Monitoring of Supernova 1979C Link to the ESA press release: This Supernova Just Won't Fade Away		"This 25-year-old candle in the night has allowed us to study aspects of a star explosion never before seen in such detail," Immler said. "All the important information that usually fades away in a couple of months is still there." Among the many unique finds, Immler said, is the history of the star's stellar wind dating back 16,000 years before the explosion. Such a history is not even known about our Sun. Also, the scientists could measure the density of the material around the star, another first. The lingering mystery, though, is how this star could fade away in visible light yet remain so radiant in X-rays. The results appear in The Astrophysical Journal.
NASA home ESA portal		Figure 2: Composite XMM-Newton X-ray image of the galaxy M100 in soft (0.3-1.5 keV, red), medium (1.5-4 keV, green) and hard (4-10 keV, blue) X-rays. The image shows large amounts of diffuse X-ray emission from hot gas in the galaxy (red), various point-like X-ray sources and supernova SN 1979C south-east of the nucleus of M100 (marked by a white line). Same scale as Figure 1. The scalebar is 2 arcmin, correspoding to 32,600 lightyears. Click on the image for a high-resolution version. Credit: NASA/ESA/Immler et al.
		Stars explode when they run out of fuel to burn. Stars more than 10 times the mass of our Sun will explode in an event called a core-collapse supernova. Without fuel and thus energy to support its gravity, such stars first implode. The core reaches a critical density, and much of the infalling matter gets bounced back out violently into space by powerful shockwaves. Supernovae can outshine an entire galaxy and are often easily seen in neighboring galaxies with a backyard telescope. Supernovae are typically half as bright after about ten days and fade steadily after that, regardless of the wavelength. SN 1979C has in fact faded in optical light by a factor of 250 -- from a magnitude of 11.6 to 17.6, the latter of which is just barely visible with a good amateur telescope. In X-rays, however, this supernova is still the brightest object in its host galaxy, M100, in the direction of constellation Coma Berenices. Immler's team could identify the history of the star that created SN 1979C through a process analogous to counting rings in a tree trunk. This star, about 18 times more massive than our Sun, produced fierce stellar winds. That material was flung into space for millions of years, creating concentric rings around the star. The X-rays -- produced after the explosion when the supernova shock caught up with the stellar wind and heated it to a temperature of several million degrees -- illuminated 16,000 years' worth of stellar activity. "We can use the X-ray light from SN 1979C as a 'time machine' to study the life of a dead star long before it exploded," Immler said. The detailed analysis was only possible because SN 1979C hasn't yet faded away. Scientists have 25 years of data in a variety of wavelengths, from radio waves through the optical/ultraviolet to X-rays. Other recent supernovae have faded considerably. Immler speculates that the abundance of stellar wind has provided ample material to keep SN 1979C glowing so brightly. The team also captured a rare glimpse of the ultraviolet radiation from the supernova using the XMM-Newton observatory. The ultraviolet image independently confirms what the X-ray analysis found: that the circumstellar material -- encompassing a region 25 times larger than our Solar System -- has a relatively high density of 10,000 atoms per cubic centimeter, or about 1,000 times denser than the wind from our Sun. The ultraviolet image also shows galaxy M100 in detail never seen before. "XMM-Newton is known among scientists as a superior X-ray observatory, but the study of SN 1979C demonstrates the importance of the satellite's simultaneously observing UV and optical telescope," said Dr. Norbert Schartel, XMM-Newton Project Scientist at ESA's European Space Astronomy Centre (ESAC) in Madrid. Immler is a member of the XMM-Newton U.S. Guest Observer Facility, based at NASA Goddard, and teaches cosmology at the University of Maryland, College Park. He is funded at NASA Goddard through the Universities Space Research Association.

home

July 21, 2005