Astronomers have found a pair of extraordinary objects that dramatically burst in X-rays. This discovery, made using data from NASA's Chandra X-ray Observatory and ESA's XMM-Newton observatory, may represent a new class of explosive events. The mysterious sources flare up and become about a hundred times brighter in X-rays in less than a minute, before returning to the original X-ray levels after about an hour. One of the sources, located near and presumably associated with the galaxy NGC 4636 at a distance of 47 million light years, was observed to flare once. Five flares were detected from the other source, which is located near the galaxy NGC 5128 at a distance of 12 million light years. What could these objects be? Probably not magnetars, which are young neutron stars with powerful magnetic fields. Magnetars are also known to have giant X-ray flares, but they are different from these newly discovered objects in a few different ways including how long they flare and where they are found. While the nature of these flares is unknown, researchers have begun to search for answers. One idea is that the flares represent episodes when matter being pulled away from a companion star falls rapidly onto a black hole or neutron star. This could happen when the companion makes its closest approach to the compact object in an eccentric orbit. Another explanation could involve matter falling onto an intermediate-mass black hole, with a mass of about 800 times that of the Sun for one source and 80 times that of the Sun for the other. These new flaring objects will likely keep both observational and theoretical astrophysicists busy for quite some time. Using telescopes like Chandra and XMM-Newton, they undoubtedly hope to come up with more answers soon. More information at http://chandra.harvard.edu/photo/2016/ngc5128/
