November 1, 2006 | David F. Coppedge

Strange Exploding Star Continues to Puzzle Astronomers

The Hubble took another image of the expanding shell of star V838 Monocerotis (see ESA and Hubblesite).  Four years after the first dramatic sequence (see 05/29/2003), astronomers are still puzzled by this star, with the most dramatic light echo ever photographed.  Leading hypothesis now is that two stars collided before the outburst.  The image made Astronomy Picture of the Day for Nov 3.
    The new Hubble image made the Oct. 14 cover of Science News.1  Ron Cowen wrote that astronomers have never seen anything like it and are “stumped by its behavior.”  It rapidly brightened and dimmed and swelled up to a gargantuan size as big as the orbit of Saturn.  It grew 30 times brighter in a single day a month after the explosion was witnessed in 2002, and grew 500 times its original width in a month.  Then its temperature rapidly dropped from 6000K to 2000K.  It’s unlike a classical nova; it may be a prototype for a new class of star.  Did a “hot Jupiter” planet fall into it?  Did two stars collide?  Researchers are toying with various theories.  “In the meantime,” Cowen ended, “astronomers have some beautiful pictures adorning their walls—and an intriguing stellar mystery.”
    The Hubble also took a dramatic picture of a supernova remnant, Cassiopeia A, in August; see EurekAlert and Hubblesite.  The outward-expanding shell is still moving at 30 million kilometers per hour, 340 years after the explosion around 1667.  It may have been seen by John Flamsteed, Astronomer Royal in Britain.
  Speaking of anomalies, in late September, another “weird” supernova was described by Lawrence Berkeley National Laboratory, reported EurekAlert.  The fact that its mass is well over the Chandrasekhar Limit of 1.4 solar masses for supernovae, according to well-established theory, “opens up a Pandora’s box” for inferring distances to remote galaxies and the presence of dark matter.  Though it may be possible to distinguish these “super-Chandrasekhar-mass” cases from regular Type 1a supernovae by their spectra, it’s not easy to do.  Dark energy studies and cosmological distance probes have been made on the basis that Type 1a supernovae were all the same, providing “standard candles” for measurement.

1Ron Cowen, “Enigmatic eruption: the strange case of V838 Monocerotis,” Science News, Week of Oct. 14, 2006; Vol. 170, No. 16, p. 248.

Supernovae were thought to be standard candles, till they were found to fall into two classes dubbed Type I and II.  Then Type 1 supernovae were the standard candles, till varieties were found, named 1a, 1b, and 1c.  Now Type 1a supernovas include some fast-rotating types with masses above the Chandrasekhar Limit.  Then there are some Type II’s that can switch types, says Wikipedia.  The universe keeps throwing curve balls at simplistic theories.  This is something to tuck away in your back pocket when reading confident claims about the universe.
    The pictures from Hubble, as usual, are really striking – almost unreal.  One of the legacies of the Hubble Space Telescope has been its portrayal of astronomical objects as dynamic environments, where dramatic processes are at work.  The stars will never again look like static, twinkling, changeless ornaments in the sky.  V838 is a dramatic example of how quickly things can change in the celestial realm.  Sorry, Aristotle.

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Categories: Cosmology, Physics

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