Fairy-Tale Astronomy

Posted by jns on 12 October 2006

In a way it’s hardly worth the bother to describe the background to this tidbit, which is a headline to a “Search and Discovery” item in this month’s Physics Today.* The story concerns type Ia supernovae, which are white dwarf stars that make their startling brightness by accreting enough mass to ignite the fusion of carbon in their core, vaporizing the star. But, along the way, accreting mass may simply ignite in a smaller fusion explosion on the surface of the star and blow away from it — this is a plain nova, and they’re much more frequent occurences.

It might seem like a challenge for the white dwarf to find mass to swallow up, but it’s not so hard because many of them are in binary-star arrangements, and they can take mass from their companion star. One such nova outburst was seen recently. Here’s a bit of the background from the story:

Stargazers have noticed novae since antiquity. But only 10 novae, RS Ophiuchi among them [the interesting star system that's the subject of the article], have ever been caught in outburst more than once. RS Ophiuchi flared up in 1985, 1967, 1958, 1933, and 1898 and possibly in 1944 and 1902. Hiroaki Narumi and Kiyotaka Kanai of Japan spotted the new outburst on 12 February and promptly alerted their fellow astronomers.

From the previous outbursts, astronomers identified RS Ophiuchi as a symbiotic binary: a white dwarf and red giant orbiting their mutual center of mass. [...] The pairing is unusual. So far, only about 200 symbiotics have been cataloged in our galaxy.

What Narumi and Kanai witnessed was the thermonuclear explosion on the white dwarf surface. As the burning layer lifts off, it expands adiabatically and cools. By March, the ejecta’s optical flux had plunged to one thousandth of its 4.5-magnitude peak.

Anyway, the whole point of my mentioning it was to assert that — occasionally — even physicists display their sense of humor, although it might not always be recognizable to others. It was the title of the article that caused me to chortle:

White dwarf is caught hurling its outer layers at its red giant companion

Make of it what you will.
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^*Unfortunately it’s subscriber only, but for reference, here’s the link.