Gravitational close encounter to test relativity theories
If Usain Bolt were a star of the astronomical type he’d be star S0-102, which sprints around the Milky Way’s central black hole with the fastest time yet. It takes just 11.5 years for S0-102 to orbit the supermassive cosmic drain, astronomers report in the Oct. 5 Science.
Not to worry — “it’s not in danger of being sucked in,” says astrophysicist and study coauthor Andrea Ghez of UCLA. “But it is getting close enough that in principle, we can see the impact of the curvature of spacetime on its orbit.”
Spotted using the Keck telescope in Hawaii, S0-102 dethrones another stellar sprinter called S0-2, which takes a comparatively pokey 16 years to orbit the black hole. For nearly two decades, Ghez and her colleagues have been searching for stars moving oddly in this region — first, as proof the black hole exists, and now, as tools to test Einstein’s theory of general relativity, which may not hold up in a supermassive black hole’s immediate neighborhood.
There’s no doubt the team’s observations are accurate — and impressive, says astronomer Stefan Gillessen of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany. Gillessen and his colleagues also observe the galactic center, which he says is a very confused and chaotic environment.
“The galactic center still holds many surprises,” he says.
Scientists will keep a close eye on the daredevil pair for years, and hope to make some crucial observations in 2018, when S0-2 is nearest the black hole. (S0-102 passes closest approach three years later.)
As the stars approach the black hole, astronomers will watch the light for any changes caused by spacetime curving around the black hole. To an observer on Earth, light escaping the extreme gravity will change its wavelength and appear to shift. The stars’ paths may also wobble a bit.
“We know Einstein’s theory breaks down when you get to the core, to the center of a black hole — the singularity,” says Ghez. “A black hole is, almost by definition, the breakdown of Einstein’s general relativity.”
What scientists don’t know is how close to a black hole one can get before the theory begins to disintegrate.
But it’s clear living near a black hole is not an environment that every star could tolerate, Ghez says. “You’ve gotta be a tough little dude.”
L. Meyer et al. The shortest-known-period star orbiting our galaxy’s supermassive black hole. Science, Vol. 338, October 5, 2012, p. 84.
R. Cowen. Milky Way’s black hole seen in new detail. Science News, Vol. 174, September 27, 2008. Available online: [Go to]
N. Drake. Team glimpses black hole’s secrets. Science News Online, September 27, 2012. [Go to]
N. Drake. A star is torn. Science News, Vol. 181, June 2, 2012, p. 8. Available online: [Go to]
A. Witze. At home in the universe. Science News, Vol. 181, June 16, 2012, p. 22. Available online: [Go to]