Yesterday, NuSTAR provided startling new data about the center of our galaxy that is challenging scientists’ understanding of black holes and the effects they can have on nearby celestial bodies.
NuSTAR and the Milky Way galaxy
The centers of galaxies are complex, turbulent places made all the more complex by the fact that almost all of them seem to be home to black holes. But these aren’t your average stellar black holes, which average a measly 10 to 24 times the mass of our sun. These monster black holes have masses that are billions of times larger than nearby suns, and given their size, are theorized to be the main power source of their respective galaxies.
NASA’s Nuclear Spectroscopic Telescope Array, aka NuSTAR, carries out a census of collapsed stars and black holes in the Milky Way. Unsurprisingly, one of the most interesting places to study black holes is in the center of the Milky Way, where the biggest one in our neighborhood resides.
Previous research has shown that the inner few parsecs (a parsec is about 3.26 light years) of the galactic center is mostly home to white dwarfs, which are roughly the mass of the sun and emit “soft” or lower energy X-rays. However, the NuSTAR team has announced in a recent press release that they have detected a mysterious glow of unexplained “hard” or high-energy X-rays near the center of the Milky Way galaxy.
“We can’t definitively explain the X-ray signal yet – it’s a mystery. More work needs to be done,” said lead study author Kerstin Perez in the press release.
Four possible explanations for the mysterious X-rays
Scientists plan to investigate at least four possible theories to explain this mysterious and unexpected surge of high-energy X-rays. One theory involves pulsars, which are the collapsed remains of stars whose lives ended in a supernova. Pulsars spin thousands of times a second and release intense radiation. “We may be witnessing the beacons of a hitherto hidden population of pulsars in the galactic center…this would mean that there is something special about the environment in the very center of our galaxy,” said study co-author Fiona Harrison.
A second theory supposes that some of the white dwarfs orbiting the galactic center have grown dense enough with age that they are able to produce these high-energy X-rays. A third theory attributes these X-rays to a cluster of smaller black holes that once belonged to binary star systems (a pair of stars that orbit each other). These small black holes may be radiating X-rays as they gobble up material from their former partner stars.
A final theory posits that the high-energy X-rays may be explained by the presence of cosmic rays. Cosmic rays are extremely high-energy radiation, which might have come in this case from the supermassive black hole at the galaxy’s center. The cosmic rays’ interaction with cosmic gases further out from the center might then explain the mysterious glow.
What all of these theories have in common, however, is that they all challenge scientists’ understanding of the galactic center:
“This new result just reminds us that the galactic center is a bizarre place…in the same way people behave differently [when]walking on the street [as opposed to] a crowded rush hour subway, stellar objects exhibit weird behavior when crammed in close quarters near the supermassive black hole,” said study co-author Chuck Hailey.
Thanks to NuSTAR, our understanding of galaxies, and the Milky Way galaxy in particular, just got significantly more intriguing.