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From: friesen@psivax.UUCP (Stanley Friesen)
Newsgroups: net.astro
Subject: Re: Question about Sirius
Message-ID: <900@psivax.UUCP>
Date: Fri, 13-Dec-85 13:55:10 EST
Article-I.D.: psivax.900
Posted: Fri Dec 13 13:55:10 1985
Date-Received: Wed, 18-Dec-85 06:51:26 EST
References: <283@infinet.UUCP>
Reply-To: friesen@psivax.UUCP (Stanley Friesen)
Distribution: net
Organization: Pacesetter Systems Inc., Sylmar, CA
Lines: 40

In article <283@infinet.UUCP> barnes@infinet.UUCP (Jim Barnes) writes:
>***
>
>In the Boston Globe today (December 9) there is an article about
>the dog star Sirius.  Sirius today is visible as a blue-white star
>but this article refers to historical accounts that refer to Sirius
>as a red star.  The speculation (theory?) presented in the article is
>that the white dwarf companion star of the visible blue-white star
>was a red giant in the recent past.  The question posed is whether a
>red giant star could collapse to a white dwarf star in 1500 years
>or so.  This seems to be much faster than what the current theory
>of stellar evolution would allow.
>
        Well, not by ordinary, simple collapse, but a supernove would
do it, assuming that some types of supernovas do not result in a
neutron star. There is in fact quite a problem with the dwarf
companion. According to standard stellar theory the lifetime of a star
is *inversely* proportional to its mass. That is in order for the
dwarf companion to have "died" before the currently visible member
even left the main sequence it must have been enormously more massive
than Sirius prime. It is now *less* massive. This certainly implies
something like a supernova, yet there is *no* trace of a supernova
remnant, nor of a planetary nebula, nor of any other sort of expelled
mass around Sirius. Also, a supernova that close would have all sorts
of bad side effects here on Earth, it would actually be brighter than
the Sun for months! And then there would be some really heavy radiation.
Yet a star as light as the current dwarf companion could *not* have
evolved into its current state that quickly, certainly not before the
more massive visible component achieved the same state. So the
question is even more puzzling. How could this configuration even come
about? At least unless it has been this way for enough millions of
years that the expelled mass has been dispursed. Anyone have a more
definitive answer??

--

                                Sarima (Stanley Friesen)

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