[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: Planets in Binary Systems
Dear Bernd and list,
Thank you, Bernd. I think you are right about how we are just getting
under way to understanding the majority-type of star systems (over 80%) are
binary or multiple. H. Apt in 1979 writing for Scientific American that
year, suggested that ALL main-sequence stars may have companions. They just
are too dim or far away to be detected. Well-done post!
Randy
Bernd Pauli HD wrote:
> jjswaim schrieb/wrote/a écrit:
>
> > I recall reading that the current view is that 'Life' could not exist
> > on planets in a multiple star system, only in a single star system.
>
> Hello Julia and List,
>
> BOSS A.P. (1999) The Birth of Binary Stars (Sky & Telescope, June 1999,
> pp. 32-38):
>
> Planets in Binary Systems, p. 38: Forging multiple suns is one thing,
> but what about planets? Most theoretical work on planet formation has
> been done in the context of explaining our own solar system, a
> single-star scenario. Very little is known about how planets would arise
> in a binary system. But they can and do occur, because about a third of
> all extrasolar planets found to date reside in binary systems. Evidently
> binary stars are quite hospitable to the formation of giant planets. The
> creation of planets probably doesn't occur during a cloud's collapse to
> protostars but rather somewhat later.
> Naturally, theorists have wondered for decades what life on a world with
> two suns would be like. (Science-fiction legends Isaac Asimov and Robert
> Silverberg took this multiple-star notion to the extreme - a planet in a
> six-sun system - in their classic, Nightfall.) We do know which
> planetary orbits would be stable, however, so we can rule out certain
> orbital configurations, such as those with radii comparable to the
> distance between the component stars.
> New computer simulations by Matthew J. Holman (Harvard-Smithsonian
> Center for Astrophysics) and Paul A. Wiegert (York University) have
> refined where planets should and should not be found in a binary system.
> As they report in the January 1999 issue of the Astronomical Journal,
> planets remain in long-term stable orbits if they either occupy an orbit
> close to one member of the binary or reside a great distance beyond the
> coupled suns (effectively orbiting their center of mass). The exact
> zones of orbital stability are defined by what Holman and Wiegert term a
> critical semimajor axis, which typically is 10 to 30 percent of the
> distance between the binary's stars. This value is relatively unaffected
> by the ratio of the stars' masses, but it varies dramatically if the
> stars orbit one another in circular or highly eccentric orbits.
> As an aside, Holman and Wiegert ask, "If our own solar system had a
> solar-mass companion in an eccentric orbit, how large would its
> semimajor axis need to be for the Sun's planets (excluding Pluto) to
> survive?" The answer, they find, depends on the companion's orbital
> inclination. A second sun orbiting near the ecliptic would have to
> remain at least 400 a.u. away on average. For an over-the-top orbit
> inclined 75° or more, the standoff distance is more like 1,000 a.u.
> Even though it's now relatively easy to simulate what can happen in a
> multiple-star system once it forms, our models have a way to go before
> we'll fully understand how planets get into a binary bind in the first
> place. But we theorists are not disheartened. To the contrary, we are
> ready to take up the challenge. Our exploration of the "binary universe"
> is just getting under way.
>
> Best wishes,
>
> Bernd
>
> ----------
> Archives located at:
> http://www.meteoritecentral.com/list_best.html
>
> For help, FAQ's and sub. info. visit:
> http://www.meteoritecentral.com/mailing_list.html
> ----------
----------
Archives located at:
http://www.meteoritecentral.com/list_best.html
For help, FAQ's and sub. info. visit:
http://www.meteoritecentral.com/mailing_list.html
----------
References: