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Breakneck star orbits black hole at record speed

Two million km/h SPEED DEMON

Vid The ESA's XMM-Newton has turned up a star and black hole, separated by around a million kilometres, orbiting each other in just 2.4 hours.

The pair outstrips the previous record of 3.2 hours for an orbit, held by Swift J1753.5-0127. The speed at which each of the two objects move is pretty impressive. Since they orbit a common centre of gravity, the star – with a mass of just 20 percent that of the sun – has the greater distance to travel. It rips along at more than two million km/h, the fastest star ever observed in an X-ray binary system, while the black hole, MAXI J1659-152, limps along at a mere 150,000 km/h.

MAX J1659-152 and its companion are part of the Milky Way, but have found themselves in a high orbital plane, out of the main disk of the galaxy.

“These high galactic latitude locations and short orbital periods are signatures of a potential new class of binary system, objects that may have been kicked out of the Galactic plane during the explosive formation of the black hole itself,” says Dr Erik Kuulkers of ESA’s European Space Astronomy Centre in Spain in the ESA's announcement.

ESA animation illustrating the high-speed orbit

The pair were first spotted on September 25, 2010 by NASA's Swift space telescope, in what was first thought to be a gamma ray burst. Japan's MAXI telescope on the ISS caught the same phenomenon later that day.

Other observations, including those made by XMM-Newton, revealed that the X-rays were emitted by matter the black hole is ripping from its companion. A 14.5 hour observation by XMM-Newton showed dips in the emission, caused by the black hole's accretion disk obscuring the X-rays during the system's rotation. Those dips set the orbital period at 2.4 hours.

Dr Kuulkers is lead author of a paper published in Astronomy & Astrophysics. The pre-press version was posted at Arxiv here. ®

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