December 29, 2005 | David F. Coppedge

Echoes of Historic Supernovae Observed

Astronomers using telescopes at the Cerro-Tololo observatory in Chile were able to detect the faint light echoes of supernovae (see EurekAlert, and original paper in Nature1).  They found three light echoes for six of the smallest previously-catalogued supernova remnants (SNR) in the Large Magellanic Cloud (LMC), a small irregular galaxy visible from the southern hemisphere.  Assuming the shock wave moves out less than 10,000 km/sec, and calibrating against the echoes from the known 18-year old remnant of SN1987A, they estimated the ages of two of them at 410 and 610 years.  They believe surveys could uncover many more, now that they know what to look for.  The light echoes provide a method for fixing the ages of supernova remnants. 

1Armin Rest et al., “Light echoes from ancient supernovae in the Large Magellanic Cloud,” Nature 438, 1132-1134 (22 December 2005) | doi:10.1038/nature04365.

It’s interesting that there are no supernova remnants claimed to be tens or hundreds of thousands of years old or older.  One of the most distended SNR's in our galaxy, the Veil Nebula, is believed to be only 5,000 years old (see 02/16/2001).  Even so, all things being equal, the light from such an event would be expected to take some 160,000 years to arrive at earth.  Why are there no older remnants reported?  Is the same true for novae?  Here is a good research project for someone who likes to catalog things and think about their implications.

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Categories: Physical Science, Physics

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