Weird Extragalactic X-Ray Flares Baffle Astronomers

And as you know, we love all things weird, extragalactic, and x-ray!


This image shows the elliptical galaxy Centaurus, where a strange source nearby dramatically flares X-rays unlike any ever seen. Credit: NASA, CXC, UA, J.Irwin et al.


Astronomers are baffled by two mysterious objects in space that blast superbright, superfast X-ray flares and could represent a brand new type of astrophysical phenomenon.

When these weird X-ray sources flare up, they become 100 times brighter in less than a minute. About an hour after a flare, the brightness returns back to normal. Jimmy Irwin of the University of Alabama, who led the study, said scientists have never seen anything like this, and they may be examples of a completely new phenomenon.

Other objects in the universe, known as ultraluminous X-ray sources (ULXs) that typically stem from black holes or neutron stars, can also create bright X-rays. But according to researchers, the newly discovered sources are hundreds to thousands of times brighter than typical ULXs.

“These flares are extraordinary,” Peter Maksym, a study co-author from the Harvard-Smithsonian Center for Astrophysics, said. “For a brief period, one of the sources became one of the brightest ULX to ever be seen in an elliptical galaxy.”

“When not flaring, the sources appear to be normal neutron-star or black-hole X-ray binaries,” in which another star orbits a dead neutron star or a black hole, the authors wrote, “but they are located in old stellar populations,” unlike other known objects that have repetitive flares as bright as the mystery objects.


Another ultrabright and inexplicably fast X-ray flare observed in 2005 inspired the researchers to search for additional mysterious X-ray sources. The scientists looked through archival X-ray observation data of 70 different galaxies from NASA’s Chandra X-ray Observatory and the European Space Agency’s XMM-Newton Observatory dating back to 1999 and found two more strange X-ray sources.

One of the unidentifiable objects in this study lies just outside Centaurus A, an elliptical galaxy located about 13 million light-years from Earth. The other is in a globular cluster of stars located just outside NGC 4636, another elliptical galaxy located 47 million light-years from Earth in the constellation Virgo. According to the study, the source in Centaurus A usually flares once every 1.8 days. Due to limited observation data, the researchers could determine only that the object in NGC 4636 flares at a minimum of every four days.

“Now that we’ve discovered these flaring objects, observational astronomers and theorists alike are going to be working hard to figure out what’s happening,” said co-author Gregory Sivakoff of the University of Alberta in Canada.


Read more from Scientific American.

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