High-energy X-rays coming from the center of our Milky Way galaxy home may be the "screams" of dead stars feeding on companion stars in a vast cosmic graveyard, astronomers say.
NASA's NuSTAR space telescope has detected X-rays emanating from an area about 100 light years from the massive central black hole lurking in the heart of our galaxy, a hole that is 4.3 million times the mass of our sun, they said.
"We can see a completely new component of the center of our galaxy with NuSTAR's images," says Kerstin Perez from Columbia University in New York. "We can't definitively explain the X-ray signal yet - it's a mystery. More work needs to be done." NASA's NuSTAR telescope, or Nuclear Spectroscopic Telescope Array, captures clear images of the center of the Milky Way in high-energy X-rays since its launch in 2012.
One leading candidate for the X-rays is dead or dying stars, which can sometimes be paired in a binary system with another star from which they siphon off matter in a zombie-like frenzy of feeding that can result in eruptions of X-rays.
A particular kind of stellar "zombie" known as a pulsar might also be involved, researchers say.
Pulsars are formed when stars that have exploded in a supernova then collapse in on themselves, spinning extremely fast while sending out intense, narrow beams of X-ray radiation.
The beams flare out across the cosmos, like a lighthouse beacon, something intercepting the Earth where they can be recorded.
"We may be witnessing the beacons of a hitherto hidden population of pulsars in the galactic center," says study co-author and NuSTAR principle Fiona Harrison of the California Institute of Technology. "This would mean there is something special about the environment in the very center of our galaxy."
In addition to "zombie" stars and pulsars, the mysterious X-ray signals could be coming from white dwarfs, extremely dense burned-out remnants of stars with insufficient mass to have ended their lives in a supernova explosion, the astronomers say.
They can, however, become so dense that their extreme gravity can produce very strong X-ray emissions, they explain.
Previous research hasn't provided enough data to confirm any of these speculations, leaving the astronomers mulling a cosmic puzzle and considering more observations.
"This new result just reminds us that the galactic center is a bizarre place," says study co-author Chuck Hailey from Columbia University. "In the same way people behave differently walking on the street instead of jammed on a crowded rush-hour subway, stellar objects exhibit weird behavior when crammed in close quarters near the supermassive black hole."
The findings were reported in the journal Nature.
