The discovery of a rare celestial object located near the Milky Way's center could allow scientists to put Albert Einstein's theory of general relativity to the test. 

Presented at this year's meeting of the American Astronomical Society, the finding used new observations made with NASA's Swift Space Telescope to identify a little-seen subclass of neutron star. The images are a part of the telescope's seven-year mission to monitor the galaxy's heart, leading to the doubling of the number of pictures of the X-ray flares taking place at the black hole located there.

Known as Sagittarius A* (Sgr A*), the black hole is not nearly as bright as it would be if it were more active.

"Given its size, this supermassive black hole is about a billion times fainter than it could be," said Nathalie Degenaar, principal investigator on the Swift galactic center campaign and an astronomer at the University of Michigan in Ann Arbor. "Though it's sedate now, it was quite active in the past and still regularly produces brief X-ray flares today."

Sgr A* is expected to perk up later this year when a gas cloud three times Earth's mass will pass near it, though a good show is not a definite promise at this point.

"I would be delighted if Sagittarius A* suddenly became 10,000 times brighter. However it is possible that it will not react much - like a horse that won't drink when led to water," said Jon Miller, who also teaches astronomy at the University of Michigan.

In April, researchers thought things might have been picking up when Swift detected a high-energy burst and dramatic rise in X-ray brightness around the area where Sgr A* is located. Tracing it back to its source, the scientists discovered a magnetar, a neutron star with a magnetic field thousands of times stronger than average.

Because the magnetar emits regular X-ray and radio pulses as it spins, scientists now have the chance to look for small changes in its pulses' timing brought on by the black hole's gravitational field as it orbits Sgr A* - a prediction of Einstein's theory of general relativity,

"This long-term program has reaped many scientific rewards, and due to a combination of the spacecraft's flexibility and the sensitivity of its XRT, Swift is the only satellite that can carry out such a campaign," said Neil Gehrels, the mission's principal investigator at NASA's Goddard Space Flight Center in Greenbelt, Md.