Astronomy Picture of the Day
APOD: 2006 February 17 - Supernova Remnant and Shock Wave
Explanation: A massive star ends life as a supernova, blasting its outer layers back to interstellar space. The spectacular death explosion is initiated by the collapse of what has become an impossibly dense stellar core. Pictured is the expanding supernova remnant Puppis A - one of the brightest sources in the x-ray sky. Now seen to be about 10 light-years in diameter, light from the initial stellar explosion first reached Earth a few thousand years ago. Recorded by the Chandra Observatory's x-ray cameras, the inset view shows striking details of the strong shock wave disrupting an interstellar cloud as the shock sweeps through preexisting material. The larger field ROSAT image also captures a pinpoint source of x-rays near the remnant's center. The source is a young neutron star, the remnant of the collapsed stellar core kicked out by the explosion and moving away at about 1,000 kilometers per second.
APOD: 2005 December 2 - Crab Nebula Mosaic from HST
Explanation: The Crab Nebula is cataloged as M1, the first object on Charles Messier's famous list of things which are not comets. In fact, the cosmic Crab is now known to be a supernova remnant, an expanding cloud of debris from the death explosion of a massive star. Light from that stellar catastrophe was first witnessed by astronomers on planet Earth in the year 1054. Composed of 24 exposures taken in October 1999, January 2000, and December 2000, this Hubble Space Telescope mosaic spans about twelve light years. Colors in the intricate filaments trace the light emitted from atoms of hydrogen, oxygen, and sulfur in the debris cloud. The spooky blue interior glow is emitted by high-energy electrons accelerated by the Crab's central pulsar. One of the most exotic objects known to modern astronomers, the pulsar is a neutron star, the spinning remnant of the collapsed stellar core. The Crab Nebula lies about 6,500 light-years away in the constellation Taurus.
APOD: 2002 March 31 - The Mysterious Rings of Supernova 1987A
Explanation: What's causing those odd rings in supernova 1987A? In 1987, the brightestsupernova in recent history occurred in the Large Magellanic Clouds. At the center of the picture is an object central to the remains of the violent stellar explosion. When the Hubble Space Telescope was pointed at the supernova remnant in 1994, however, the existence of curious rings was confirmed. The origins of these rings still remains a mystery. Speculation into the cause of the rings includes beamed jets emanating from a dense star left over from the supernova, and a superposition of two stellar winds ionized by the supernova explosion.
APOD: 1999 March 7 - Tychos Supernova Remnant in X ray
Explanation: How often do stars explode? By looking at external galaxies, astronomers can guess that these events, known as a supernovae, should occur about once every 30 years in a typical spiral galaxy like our MilkyWay. However, the obscuring gas and dust in the disk of our galaxy probably prevents us from seeing many galactic supernovae -- making observations of these events in our own galaxy relatively rare. In fact, in 1572, the revered Danish astronomer, Tycho Brahe, witnessed one of the last to be seen. The remnant of this explosion is still visible today as the shockwave it generated continues to expand into the gas and dust between the stars.Above is an image of the X-rays emitted by this shockwave made by a telescope onboard the ROSAT spacecraft. The nebula is known as Tycho's Supernova Remnant.
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