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Supernovae ejecta from SN1987A have finally begun to collide with a shell of gas blown out by the star some 30,000 years earlier. We are about to see, for the first time in history, a supernova remnant in the making. A team at the National Science Foundation's Cerro Tololo Inter-American Observatory led by Patrice Bouchet of CTIO used this coutour plot of emission brightness to discover the new impact sites.
The most intense of their newly discovered "hot spots" is south-east of the first hot spot, on the north side of the ring. Other possible impact sites (colored red) are found distributed around the ring.
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The Crab Nebula, the most famous supernova remnant.
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Image credit: AURA/NOAO/National Science Foundation
Ejecta From Supernova 1987a Lights Up Circumstellar Ring
Astronomers using the National Science Foundation's Cerro Tololo Inter-American Observatory (CTIO) have discovered a new brightening of the circumstellar ring around Supernova 1987A in the Large Magellanic Cloud. This activity indicates that supernova ejecta have finally begun to collide with this shell of gas blown out by the star earlier in its lifetime. We are about to see a supernova remnant in the making, for the first time in history.
A "hot spot" that appeared in the circumstellar ring around SN1987A in 1997 was believed to be the first impact of supernova ejecta. But no other active sites had been observed until December 25th, 1999, when a team led by Patrice Bouchet of CTIO discovered the first new hot spot. Other members of the team included Stephen Lawrence, Arlin Crotts, Ben Sugerman, and Robert Uglesich of Columbia University, and Stephen Heathcote, also of CTIO. The new hot spot is about the same brightness as the first was when it was originally found. Other, fainter impact sites are present in their observations. They also found that the original hot spot had brightened significantly since their last observation over a year ago.
The CTIO observations used an innovative imaging system on the NSF's Blanco 4-m telescope that allowed them to achieve better spatial resolution than is commonly possible from ground-based observatories. The CTIO system tips and tilts a mirror to take the "twinkle" out of starlight, producing steadier, sharper images. Two novel image processing techniques developed by Columbia University and Cerro Tololo members of the team clearly show the new hot spot, and reveal fainter, possible new hot spots.
The significance of the newly discovered hot spots is that they are not confined to a single location, but are distributed around the circumstellar ring. The distribution around the ring indicates that a large fraction of the material ejected from the supernova is finally colliding with the circumstellar ring, instead of a fast moving "bullet" of ejecta making a single hot spot. If so, this is the beginning the long awaited formation of a supernova remnant around SN1987A. Other teams making follow-up observations with the Hubble Space Telescope in late January and early February have confirmed the new hot spot and found a number of other fainter new impact sites, some of which are present in the CTIO data at a more subtle level.
Background: Supernova 1987A occurred when the star known as Sanduleak -69o 202 ended its life in a gigantic explosion, which was observed on Earth on February 23rd, 1987 and was designated SN1987A. While news of that explosion traveled out at the speed of light, material from the star itself was ejected at a much lower speed, some tens of millions of miles per hour. This material is now beginning to catch up and collide with material blown out some twenty thousand years earlier by Sk -69o 202 in a relatively gentle, slow, cool stellar wind. The collision of supernova ejecta with the wind material, now forming the circumstellar shell, was predicted to occur sometime between 1995 and 2010. We are watching that prediction come true.
The first collision of ejecta may have been a fast moving jet of material striking the circumstellar ring, shocking the gas into emission, much like bullets hitting a target. The impact of the supernova ejecta with gas in the cool ring heats the gas from approximately 5,000 degrees to 25,000, producing the emission detected by the Bouchet et al. observations.
Now the entire ring is beginning to be engulfed with shocked material from the supernova, lighting up the ejecta and circumstellar material as a supernova remnant. We have observed many examples of supernova remnants - for example, the Crab Nebula - but all were formed long ago. We have never seen one in the making.
Supernova 1987A is located in the Large Magellanic Cloud (LMC), a dwarf galaxy that is a satellite to our Milky Way Galaxy, and is located at a distance of some 167,000 light years. The LMC is only observable from the Southern Hemisphere.
For more information:
Dr. Patrice Brouchet
Cerro Tololo Inter-American Observatory
La Serena, Chile
Dr. Arlin Crotts
New York, New York
Telephone: (212) 854-7899
Dr. Steve Lawrence
New York, New York
Telephone: (212) 854-4451
Dr. Bruce Bohanon
National Optical Astronomy Observatories
Telephone: (520) 318-8701