Matter Rides Black Hole's Space-Time Wave
SAN DIEGO -- Armed with cosmic speed guns and other high-tech devices, astronomers have witnessed amazing speeds around one black hole and an exotic wave in space-time careening around another.
The findings are among the most convincing ever of the incredible velocities and distortions that occur very close to black holes, and they help provide better estimates of the masses of the black holes. They also showcase a new method for getting an even better handle on these gravitational behemoths.
In one finding, a spinning black hole appears to create an orbiting wave. In a gross oversimplification, the process is similar to the wobble of a spinning top. The other study found evidence of hotspots -- perhaps blobs of hot gas the size of the Sun, or maybe regions lit by magnetic energy -- travelling at 10 percent the speed of light.
The results were presented here Monday at a meeting of the American Astronomical Society.
Black hole basics
Black holes are so dense they can trap light. They can't be seen, but astronomers find them by noting their gravitational effect on surrounding objects or by seeing X-rays and other radiation kicked up in their vicinity when gas is superheated as it swirls in at phenomenal speeds.
The infalling gas forms a thin disk, theory says. From this accretion disk come the X-rays used in the new research.
Any object with mass warps the space and time around it, in much the same way a heavy object deforms a stretched elastic sheet. Light passing by a very massive star or galaxy can be noticeably bent, for example.
Einstein's work predicts all this. But beyond Einstein, even stranger things are predicted. If an object spins, it further distorts space-time; imagine the elastic sheet being twisted by a heavy, spinning heavy.
The effect is called frame dragging. It is a modification to the simpler aspects of gravity set out by Newton. Working from Einstein's relativity theory, Austrian physicists Joseph Lense and Hans Thirring predicted frame dragging in 1918. (It is also known as the Lense-Thirring effect.)
Other studies have found evidence for spinning black holes and the warping of space-time around them. Even the rotation of Earth has been shown to distort nearby space-time, causing satellites to be dragged by 6 feet (2 meters) every year.
Frame dragging may play an important role in the twisted physics that cause black holes not just to swallow light and matter, but to spit out tremendous amounts of hot gas in high-velocity jets seen in several studies.
In observations by NASA's orbiting Rossi X-ray Timing Explorer, scientists examined the energy given off by iron gas. The light waves were stretched as the light struggled to climb out of the black hole's gravitational clutches.
The data revealed matter orbiting the relatively small black hole hundreds of times per second, "glowing like light bulbs on a merry-go-round," said Jeroen Homan of MIT.
The effect seen can be described by frame dragging, said co-researcher Jon Miller of the Harvard-Smithsonian Center for Astrophysics. Confident in the finding, he still remains cautious.
"It may be that other explanations turn out to be better, "Miller told SPACE.com. "It is not a shut case."
The results will be published in the Astrophysical Journal Letters.
Blobs of gas
The other study, using the European Space Agency's XMM-Newton satellite, found three apparent blobs of hot gas flying around a different black hole at 20,000 miles per second (32,190 kilometers per second). That's 10 percent of light-speed. The blobs are very close to the black hole and allow astronomers to calculate a more precise mass and size of the object.
The black hole, anchoring a galaxy known as Markarian 766, contains about 100 million times the mass of the Sun.
The black hole encompasses a region just smaller than the orbit of Mercury. The blobs of iron gas are at a distance equal to the orbit of Jupiter. But unlike Jupiter's 12-year orbit, the blobs circle the black hole in a mere 27 hours.
The speed was measured using the Doppler technique, same as a cop's radar gun. It's also the phenomenon that makes an ambulance siren change pitch when heading toward you (the waves are compressed) versus away from you (the waves are stretched).
It is the first time material has been observed making a complete orbit so close to a black hole, said study member Lance Miller of Oxford University.
Miller and his colleague, study leader Jane Turner of NASA and the University of Maryland Baltimore County, acknowledged that similar but tentative results were announced in September by a European group. And other studies have seen evidence for matter near a black hole, even possibly sliding beyond the point of no return.
In an interview, Turner said the new results were "more clear" and "easy to interpret" compared to previous observations.
Both studies presented today are "pioneering results" that point the direction for future observations that could better pin down the physics of black holes, said Fred Lamb, a University of Illinois researcher who was not involved in the research.
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