27Mar2013

Black Hole Binary Star Orbits At Record Breaking Speed

Through the eyes of ESA’s XMM-Newton Space Telescope, astronomers have caught a black hole and star in the act… the act of orbiting each other at rate of once every 2.4 hours! It’s a pace which has broken the previous record by as much as 60 minutes. The black hole is recorded as MAXI J1659-152 and it’s three times more massive than our Sun with a red dwarf companion which weighs in about 20% solar mass. They’re pretty close companions, too. They are only separated by about a million kilometers. 

On September 25, 2010, NASA’s Swift Space Telescope thought it had captured a gamma ray burst. Hours later, Japan’s MAXI Telescope aboard the International Space Station picked up a bright X-ray source in the same place. The call went out to other space and ground telescopes, including the XMM-Newton, and what they found was the X-rays were the product of a black hole stripping material from a minuscule companion star.

As astronomers watched, they recorded several regularly spaced troughs in the incoming emissions. For fourteen and a half hours, they observed with the XMM-Newton with no breaks until they caught the event horizon of the black hole’s accretion disc. As the system rotated, the information “from the edge” momentarily obscured the X-rays as seen from the telescope’s line of sight. From these calculations, researchers were able to measure an orbital period of a scant 2.4 hours – setting a record for black hole X-ray binary systems.

The previous record-holder, Swift J1753.5–0127, was fast, but not fast enough. It took of 3.2 hours. Since the black hole and star orbit the same central point, the lighter star is furthest away and has to complete its longer orbit at the dizzying speed of 2,000,000 km/h – the fastest orbiting star ever observed in an X-ray binary system. And the black hole? Well, it might be slower, but even it is moving at an incredible 150,000 km/h!

“The companion star revolves around the common centre of mass at a dizzying rate, almost 20 times faster than Earth orbits the Sun. You really wouldn’t like to be on such a merry-go-round in this Galactic fair!” says lead author Erik Kuulkers of ESA’s European Space Astronomy Centre in Spain.

Image Credit: ESA

 According to the news release, his team also saw that they lie high above the Galactic plane, out of the main disc of our spiral Galaxy, an unusual characteristic shared only by two other black-hole binary systems, including Swift J1753.5–0127.

“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 Kuulkers.

Returning to MAXI J1659−152, the quick response of XMM-Newton was key in being able to measure the remarkably short orbital period of the system.

“Observations started at tea-time, just five hours after we received the request to begin taking measurements, and continued until breakfast the next day. Without this rapid response it would not have been possible to discover the fastest rotation yet known for any binary system with a black hole,” adds Norbert Schartel, ESA’s XMM-Newton project scientist.

Toast and jam anyone?

Original Story Source: ESA Space Science News Release. Submitted by Tammy Plotner for “Dave Reneke’s World of Space and Science News”.

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