QZ Vulpeculae, Nova Vulpecula 1988
in the constellation Vulpecula
5 to 10 times the mass of the Sun
Diameter roughly 20-40 miles (32-65 km), equal to the size of a large city
A Japanese space telescope, Ginga, discovered this system in April 1988 when the system produced a massive outburst of X-rays, known as an X-ray nova. For a few days, the system produced roughly one million times more energy than in the days before the outburst.
The outburst likely was produced by an accretion disk around a black hole. The black hole "steals" gas from a close companion star. This hot gas encircles the black hole, becoming denser and hotter over the years. Eventually, the disk becomes so hot that it triggers a runaway nuclear explosion that blasts away much of its material.
To learn about GS 2000+25 (which is named for its sky coordinates), astronomers have conducted follow-up observations with ground-based telescopes. They have studied the spectrum of the system, which reveals the orbital motion of the two objects. They have also measured the brightness of the system to determine the size and orientation of the companion star, which puffs out toward the black hole. The brightness helps reveal the angle at which we view the system, which is important in determining the mass of the black hole and the companion star.
These studies have found that the companion is probably a class K dwarf -- a star that is cooler, smaller, and about half as massive as the Sun. It orbits the black hole once every 8.3 hours. The star is quite different from most stars of its class however, indicating that it probably was born with a much greater heft but has lost much of its original mass to the black hole, which is 5 to 10 times as massive as the Sun.
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This document was last modified: May 11, 2012.