[extropy-chat] Most star systems are single

[Amara Graps]

There was a news item on pg. 17 in the May 2006 Sky and Telescope,
that blew me away when I read it.

Most star systems are single.

Charles Lada made this conclusion based on the Milky Way's most common
stars: red dwarfs (spectral class M), which comprise about 85% of the
total number of stars. Surveys of stars in our galaxy by others indicate
that very few have companions, therefore about 2/3 of star systems in
our galaxy are single star systems.

Here is his paper:

STELLAR MULTIPLICITY AND THE INITIAL MASS FUNCTION: MOST STARS ARE
SINGLE
Charles J. Lada
The Astrophysical Journal, 640: L63-L66, 2006 March 20 


ABSTRACT
In this Letter I compare recent findings suggesting a low binary star
fraction for late-type stars with knowledge concerning the forms of the
stellar initial and present-day mass functions for masses down to the
hydrogenburning limit. This comparison indicates that most stellar
systems formed in the Galaxy are likely single and not binary, as has
been often asserted. Indeed, in the current epoch two-thirds of all
main-sequence stellar systems in the Galactic disk are composed of
single stars. Some implications of this realization for understanding
the star and planet formation process are briefly mentioned.

which you can download here:

http://www.journals.uchicago.edu/ApJ/journal/issues/ApJL/v640n1/20200/20200.web.pdf

The implications for star formation is that the core mass of a molecular
cloud undergoing collapse to a protostar would have a 2-3 times higher
surface density. The angular momentum of the core body would be different
too.

For planet formation, the estimates of the number of planets around M
stars just increased:

(Lada)
"Finally, I note that the large fraction of single star systems in the
field is consistent with the idea that most stars could harbor planetary
systems unperturbed by binary companions, and thus extrasolar planetary
systems that are characterized by architectures and stabilities similar
to that of the solar system could be quite common around M stars,
provided planetary systems can form around M stars in the first place."


Amara
-- 

********************************************************************
Amara Graps, PhD          email: amara at amara.com
Computational Physics     vita:  ftp://ftp.amara.com/pub/resume.txt
Multiplex Answers         URL:   http://www.amara.com/
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"What I find most disheartening is the thought that somewhere out there
our galaxy has been deleted from somebody else's sample."
   -- Alec Boksenberg [on the occasion of his 60th birthday celebration]