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Date Posted: 20:44
Author: Eponymous - 19 Aug 2002
Subject: Re: Bynary Star
In reply to: ketch - 19 Aug 2002 's message, "Re: Bynary Star" on 20:42

I posted the following some time ago:

I asked several astrophysicists (including about 30 Indian astrophysics) specifically about the "24,000 year" hypothesis. All who have responded say the claim is implausible. The following excerpts give a flavor of the problems involved:

2.1 "No, the claim is not at all plausible. A stellar companion with 24000yr period would be at a distance of about 1000 AU****. At this distance even the faintest star would be about 10 times brighter than
Venus in our skies."

2.2 "There is no possibility that the Sun is in orbit 'about' a companion. The companion would have to be more massive than the sun. Even assuming the companion body is a black hole, it would still have obvious observational effects that even a good amateur astronomer today wouldn't likely miss."

2.3 "No, it is not feasable. There was a lot of interest some years ago in trying to identify an extended binary companion of the sun's in an effort to explain an apparent periodocity of something like 80 million years, but nothing turned up. Any companion with a period as short as 24,000 years would have been seen trivially as part of that search.
"There is no distinction between a dwarf orbiting the sun and the sun orbiting
a dwarf. Binary stars each orbit their common center of mass."

2.4 "I think its not possible. Here's why: From Kepler's laws, the orbital period P (in yrs) is given by
P = sqrt ( m /a^3); thats read as square root of m over a cubed, where a is the semi-major axis (or radius if it is a circle) of the orbit in units of the earth-sun distance (called astronomical unit, AU), and m is
the reduced mass in units of mass of the sun. Stated another way, a = P^(2/3) m^(1/3).
"Now plug in the numbers, the value of m is atmost 1, P=24000 yrs which implies a is atmost 832 AU. Given that the radius of pluto's orbit is only 40 AU, the gravity of this binary system would have caused observable perturbations to its orbit or other planets in the solar system. Furthermore, any star that close would have been extremely bright (only about a million times less brighter than the sun and brighter than the
brightest star on the night sky) even white dwarfs/black holes/neutron stars are ruled out as they would be detectable as well."

2.5 "No, this is not a plausible suggestion. First, we would see perturbations in the Sun's
motion relative to other stars, and we do not find
that. Second, any star that close to us, even if it were a
star of very faint absolute magnitude, would have been either a) very
bright in the sky, and hence obvious to us or
b) would have such a large proper motion that we would
have found it already, anyway."

2.6 "No. Given that period, even the faintest star would have been detected."

2.7 "[T]hat period works out to a semi major axis of about 850 AU's.
At that distance any companion would have to be of very low
mass - Jupiter or less. [Too small a mass to support the orbit of our solar system.] Otherwise it would have been picked up on various proper motion surveys."

2.8 "There was some recurring speculation that there might be a binary companion with a period on the order of tens of millions of years, although there really isn't any evidence that such a companion exists, and would most probably have been detected by now. But a companion with the period you specify really is not possible, since it would have to reside something like 800 AU or so away; even a black hole would be obvious at that distance."

2.9 "There is no evidence to hand that would agree with that idea."

2.10 "The suggestion is not plausible. Even the faintest star at that distance would be almost as bright as the moon. We would also have picked it up in proper motion surveys, or observed perturbations in the orbits of the outer planets."

**** AU = 'astronomical unit' = the distance from Earth to the sun. I made ad hoc use of the symbol '^' to mean "to the power of" (e.g., 2^2 = 2 squared.)

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