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Your Weight on a White Dwarf Star


A white dwarf star is a stellar corpse, a cinder that in time will cool off enough to become a black dwarf. According to theoreticians, however, our Galaxy - or for that matter: the universe - isn't yet old enough to accommodate black dwarf stars. In any event, I imagine the Milky Way Galaxy must be littered with millions if not billions of stellar corpses; but if astronomers have a hard time estimating the number of living stars in our Milky Way (300 billion perhaps), faint dead stars must pose even more of a challenge.

Astronomers tell us that white dwarfs are exceedingly small and dense. Sirius, the brightest star in the sky, has a white dwarf companion named Sirius B or "The Pup," said to have a mass roughly equaling the Sun's and a radius more or less equaling Earth's. Whether this figure is correct or not (I've read conflicting reports), we'll presume that it is, at least for the purpose of calculating our weight on the surface of this star.

If you had joined me to figure out your weight on Jupiter and the Moon, you'll find that the answer this time comes much more readily than it had before. Since the Sun is about 333,000 times more massive than Earth, that means you'd weigh 333,000 times more on a white dwarf having the Sun's mass but the Earth's size.

Actually it's more difficult to find out your weight on the surface on the Sun (that is, if you could stand on the surface of the Sun), but let's give it a go. The radius of the Sun is some 109 times greater than the Earth's. On the surface of the Sun, you'd be 109 times further away from the Sun's center of gravity than you are from the Earth's center of gravity (or a white dwarf's center of gravity, given the white dwarf is the size of Earth). Since gravity weakens with distance, we must square 109 (109 x 109 = 11881) to find out that it's 11,881 times weaker (or 1/11,881 times as strong -- known as the inverse-square law). Divide the Sun's mass 333,000 by 11,881 to find out that you'd weigh about 28 times more on the Sun than on Earth.

Next month, we'll figure your weight on a neutron star.


by Bruce McClure


Your Weight

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Burham's White Dwarf Puzzle

"Double stars with white dwarf components are of very great interest to the theoretical astrophysicists, since they often present the strange circumstance that the more massive star is still a main sequence object, while the less massive star has reached the white dwarf stage. If the two stars are of the same age, and have always been a physical pair, then the more massive star should evolve faster than the other. Both Sirius and Procyon present us with this puzzle." - pages 407-408, Burnham's Celestial Handbook