Cannibalism among the stars.

• Author: Braffman-Miller, Judith
• Position: Science & Technology

WHEN A STAR like the sun perishes, it leaves behind a small, dense relic core called a white dwarf. However, our star, unlike many others of its kind, is a lonely one bereft of stellar companions. Thus, it is not fated to experience the circumstances that befall similar small stars when they dwell in close proximity to a companion star in a binary system. When such binary systems exist, the white dwarf can engage in some vampire-like behavior, stealing its companion star's material--and this can trigger very explosive stellar fireworks.

In May, a team of astronomers announced that they have discovered a small substellar "failure" called a brown dwarf that once had been a true star--before it was ravaged by its hungry white dwarf companion. Brown dwarfs usually are born, not made, and so this little stellar "failure" sheds new and important light on the existence of cannibalism among the stars.

Astronomers made this important discovery by observing a very dim binary system dubbed J1433, which is situated about 730 light-years from our solar system. This system is composed of a low-mass object--about 60 times the mass of our own solar system's gas-giant planet, Jupiter--in a much-too-close-for-comfort 78-minute orbit around a voracious white dwarf companion.

Because of their extremely close proximity, the white dwarf easily is able to slurp mass from its low-mass companion. This process has succeeded in removing approximately 90% of the small star's mass, forcing it to experience a sea change from a true star into a sub-stellar brown dwarf.

Most brown dwarfs are "failed stars" that were born with too little mass to sparkle brightly as a result of the process of stellar nucleosynthesis--the nuclear fusion of hydrogen atoms into progressively heavier and heavier atomic elements that occurs in the searing-hot and fiery furnaces of stars.

In dramatic contrast, the brown dwarf of the J1433 system was born a true, full-fledged, nuclear-fusing star, but has been stripped down to its current puny, substellar mass as the result of billions of years of cannibalism on the part of its companion white dwarf.

Brown dwarfs are genuine oddballs, bizarre objects whose very existence challenges the neat distinction between true stars and giant planets. Many astronomers long have proposed that those relatively cool, small inhabitants of the universe are born the same as true stars--within extremely dense blobs embedded within the swirling, whirling, billowing folds of one of the many frigid and gigantic dark molecular clouds that inhabit the Milky Way...