Message in a Wobble: Black Holes Send Memos in Light

[/caption]

Imagine a spinning black hole so colossal and so powerful that it kicks photons, the basic units of light, and sends them careening thousands of light years through space. Some of the photons make it to Earth. Scientists are announcing in the journal Nature Physics today that those well-traveled photons still carry the signature of that colossal jolt, as a distortion in the way they move. The disruption is like a long-distance missive from the black hole itself, containing information about its size and the speed of its spin.

The researchers say the jostled photons are key to unraveling the theory that predicts black holes in the first place.

“It is rare in general-relativity research that a new phenomenon is discovered that allows us to test the theory further,” says Martin Bojowald, a Penn State physics professor and author of a News & Views article that accompanies the study.

Black holes are so gravitationally powerful that they distort nearby matter and even space and time. Called framedragging, the phenomenon can be detected by sensitive gyroscopes on satellites, Bojowald notes.

Lead study author Fabrizio Tamburini, an astronomer at the University of Padova (Padua) in Italy, and his colleagues have calculated that rotating spacetime can impart to light an intrinsic form of orbital angular momentum distinct from its spin. The authors suggest visualizing this as non-planar wavefronts of this twisted light like a cylindrical spiral staircase, centered around the light beam.

“The intensity pattern of twisted light transverse to the beam shows a dark spot in the middle — where no one would walk on the staircase — surrounded by concentric circles,” they write. “The twisting of a pure [orbital angular momentum] mode can be seen in interference patterns.” They say researchers need between 10,000 and 100,000 photons to piece a black hole’s story together.

And telescopes need some kind of 3D (or holographic) vision in order to see the corkscrews in the light waves they receive, Bojowald said: “If a telescope can zoom in sufficiently closely, one can be sure that all 10,000-100,000 photons come from the accretion disk rather than from other stars farther away. So the magnification of the telescope will be a crucial factor.”

He believes, based on a rough calculation, that “a star like the sun as far away as the center of the Milky Way would have to be observed for less than a year. So it is not going to be a direct image, but one would not have to wait very long.”

Study co-author Bo Thidé, a professor and program director at the Swedish Institute of Space Physics, said a year may be conservative, even in the case of a small rotation and a need for up to 100,000 photons.

“But who knows,” he said. “We will know more after we have made further detailed modelling – and observations, of course.  At this time we emphasize the discovery of a
new general relativity phenomenon that allows us to make observations, leaving precise quantitative predictions aside.”

Links: Nature Physics

Anne Minard

Anne Minard is a freelance science journalist with an academic background in biology and a fascination with outer space. Her first book, Pluto and Beyond, was published in 2007.

Recent Posts

Earth’s Old Trees Keep A Record of Powerful Solar Storms

Most of the time the Sun is pretty well-mannered, but occasionally it's downright unruly. It…

11 hours ago

New Supercomputer Simulation Explains How Mars Got Its Moons

One mystery in planetary science is a satisfying origin story for Mars's moons, Phobos and…

16 hours ago

The Early Universe May Have Had Giant Batteries of Dust

The largest magnetic fields in the universe may have found themselves charged up when the…

21 hours ago

The First Close-Up Picture of Star Outside the Milky Way

Like a performer preparing for their big finale, a distant star is shedding its outer…

1 day ago

Here’s What We Know About Earth’s Temporary Mini-Moon

For a little over a month now, the Earth has been joined by a new…

2 days ago

New Study Suggests Black Holes Get their “Hair” from their Mothers

Despite decades of study, black holes are still one of the most puzzling objects in…

2 days ago