Chuck Bednar for redOrbit.com – @BednarChuck
A mysterious high-energy X-ray signal detected by the NASA Nuclear Spectroscopic Telescope Array (NuSTAR) could be the sounds of “zombie” stars feeding on the “brains” of nearby stellar companions, according to research published recently in the journal Nature.
“We can see a completely new component of the center of our galaxy with NuSTAR’s images,” lead author Kerstin Perez from Columbia University said in a statement earlier this week. “We can’t definitively explain the X-ray signal yet – it’s a mystery. More work needs to be done.”
Our galaxy, the Milky Way, is bustling with stars of all ages, smaller black holes, and a wide variety of stellar corpses, all of which surround a supermassive black hole called Sagittarius A*, the US space agency explained. In the new images, NuSTAR shows a 40 light-year across area around Sagittarius A* which had an unexpected haze of high-energy X-rays.
“Almost anything that can emit X-rays is in the galactic center,” Perez explained. “The area is crowded with low-energy X-ray sources, but their emission is very faint when you examine it at the energies that NuSTAR observes, so the new signal stands out.”
So what is causing this unusual X-ray glow?
Perez and her colleagues have come up with four potential explanations for this phenomenon, three of which center on different classes of stellar corpses. When a star dies, NASA explained, they don’t always simply fade away. Collapsed dead binary stars can feed on matter from the other member of their stellar pair, which could cause X-ray eruptions.
One of the theories involves a type of stellar zombie known as a pulsar, which is the collapsed remains of starts that explode as supernovae. Pulsars can spin with extreme velocity, emitting intense beams of radiation that can sweep throughout the sky. Those beams can intercept Earth on occasion, similar to a lighthouse beacon, the US space agency said.
“We may be witnessing the beacons of a hitherto hidden population of pulsars in the galactic center,” explained co-author Fiona Harrison of the California Institute of Technology (Caltech), principal investigator of the NuSTAR image. “This would mean there is something special about the environment in the very center of our galaxy.”
White dwarfs, the collapsed remains of stars not massive enough to explode in supernovae, may also be a potential source of these X-rays. A third theory suggests that small black holes that are feeding slowly off their companion stars are radiating X-rays as they swallow up matter.
The fourth hypothesis suggests that the source may not be a stellar corpse at all. Rather, cosmic rays coming from the supermassive black hole at the center of the galaxy could be emitting the X-rays as it devours material and interact with their surroundings. However, the researchers said that none of the theories are a perfect match for previous research findings.
“This new result just reminds us that the galactic center is a bizarre place,” said co-author Chuck Hailey of 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.”
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