In Brief
  • Astronomers have found a white dwarf moving at 1% the speed of light (or..crazy fast) orbiting a black hole.
  • The star is far enough away so it is not completely pulled in, but it is close enough that material is pulled away from the star in small bits.

Living on the Edge

Some just enjoy living life dangerously. Apparently, this includes stars.

Astronomers have discovered a star that is whipping its way through space, orbiting a black hole at breakneck speeds. The star is only separated from the black hole by a distance of about 2.5 times the distance between the Earth and our moon. Members of the team studying this binary system have stated that it is the tightest orbit ever observed around a black hole.

The lead author of the study, Arash Bahramian, stated, “This white dwarf is so close to the black hole that material is being pulled away from the star and dumped onto a disk of matter around the black hole before falling in. Luckily for this star, we don’t think it will follow this path into oblivion, but instead will stay in orbit.” That means that this star isn’t likely to be overcome by the black hole’s gravity, it’ll continue spinning while losing mass until it eventually just disappears. As the black hole continues to strip gasses from the star, it will lose mass and move further from it.

Credit: X-ray: NASA/CXC/University of Alberta/A.Bahramian et al.; Illustration: NASA/CXC/M.Weiss
Image Credit – X-ray: NASA/CXC/University of Alberta/A.Bahramian et al.; Illustration: NASA/CXC/M.Weiss

Just…So Fast

In order to complete such an orbit, the star has to be traveling at a pretty impressive speed. The researchers calculated the speed of the white dwarf to be about 12,600,000 km/hr (8,000,000 miles/hr) or about 1 percent of the speed of light.

Black holes are among the most extreme objects in the universe. They are truly massive objects with gravity so strong that nothing can escape their pull. The “point of no return” that this star is flirting with is called a black hole’s event horizon. Black holes are surrounded by a disc of gas, dust, stars, planets and other celestial objects, called an accretion disk, that feed the black hole. Once these objects cross that event horizon, there is no going back. The gravity at that point is so strong that it will pull in anything. And so, while these scientists don’t think that this star is close enough to be pulled in, it sure is flirting with danger.