LMC X-1

LMC X-1 is one of the most distant stellar-mass black holes discovered to date, yet it is also one of the best understood. Observations by space-based ultraviolet and X-ray telescopes, as well as a large optical telescope on the ground, have helped astronomers compile a detailed dossier.

Like all the other known stellar-mass black holes, this one is a member of a binary system. The two stars orbit each other once every 3.9 days. From the orbital period and the distance to the system, astronomers can calculate the masses of the two stars. The black hole is 10.9 times the mass of the Sun, while the bright companion is 32 times the mass of the Sun.

The companion is a blue supergiant, cataloged as Star 32. It is classified as spectral type O7 or O8 (O stars are the hottest of all stars, with surface temperatures tens of thousands of degrees hotter than the surface of the Sun). The companion is 17 times the Sun's diameter, and it is only about five million years old.

The companion produces a strong "wind" of electrically charged particles. Although the wind is speeding outward at around 2 million mph (3.2 million kph), the black hole captures some of the particles, forming an accretion disk around the black hole. The superhot disk produces much of the X-ray energy observed by space-based telescopes.

Observations show that the companion puffs outward toward the black hole. In the next few hundred thousand years, it will reach a gravitational tipping point, in which a flood of its own gas pours onto the black hole. The gas may pile onto the black hole's accretion disk so rapidly that it will trigger a thermonuclear explosion known as a nova, which will make the system briefly shine millions of times brighter than it does today.

Eventually, the companion star may stage an even more spectacular explosion, blasting itself to bits as a supernova. Only the star's crushed core will remain -- either a neutron star or another black hole.

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This document was last modified: September 8, 2011.