Could the nearby star Sirius B explode as a type Ia supernova, like some other white dwarf stars in binary star systems have?
Bruce Mason
Encinitas, California
A type Ia supernova occurs when a white dwarf — the cooling remnant of an aging star — draws hydrogen from a companion sun. When the dwarf reaches 1.4 times the mass of the Sun, the star spontaneously detonates in a fantastically bright thermonuclear blast. Nothing remains of the dwarf except debris.
The Sirius system, about 8.6 light-years from us, does include a white dwarf star (Sirius B) orbiting a companion (Sirius A). However, Sirius B is not close enough to its companion to accrete hydrogen and reach the supernova threshold of 1.4 solar masses.
Sirius B takes roughly 50 years to orbit Sirius A. At their nearest approach, the stars are still some 7 astronomical units (AU) from each other, or seven times the Earth-Sun distance. (One AU is equal to the average Earth-Sun distance of 93 million miles [150 million km].) The separation is too wide for mass to cross between Sirius A and Sirius B.
For mass transfer to occur, the two stars would need to be within a few stellar radii of each other. At that distance, they would complete an orbit over a period of hours to days.
Liz Kruesi
Freelance Science Writer and Editor, Denver, Colorado
This question and answer originally appeared in the September 2009 issue.
