The Sight of Twisted Light Could Reveal a Spinning Black Hole

By Andrew Moseman | February 14, 2011 12:10 pm

No, you can’t see a black hole. What you might be able to see, though, is the way in which relativity predicts a spinning black hole will bend space, time, and light around it. Scientists say in a new study in Nature Physics that they are closer than ever to being able to see this effect in faraway black holes from our vantage point here on Earth.

Galaxies probably have spinning, supermassive black holes at their center, and spinning black holes possess two types of angular momentum, study coauthor Bo Thide explains. There’s spin angular momentum, which is analogous to what the Earth creates as it spins on its axis, and there’s orbital angular momentum, which is analogous to what the Earth creates as it orbits the sun. Thidé says that the second effect—orbital angular momentum—distorts light in a way that scientists who know what to look for might be able to see it from here.

“Around a spinning black hole, space and time behave in such an odd way; space becomes time, time becomes space, and the whole space-time is actually dragged around the black hole, becomes twisted around the black hole,” Professor Thidé explained. “If you have radiation source… it will then sense this twisting of spacetime itself. The light ray may think that ‘I’m propagating in a straight line’, but if you look at it from the outside, you see it’s propagating along a spiral line. That’s relativity for you.” [BBC News]

Physicists call this effect “frame-dragging,” and they’re seen it even close to our home planet.

Observations of two Earth-orbiting satellites over the last few decades show that the satellites drag by several feet per year as Earth’s spin tows the fabric of space and time in circles. “If you can see it, such a tiny little effect from this minute mass that the Earth has compared to a black hole, how much easier would it be to see it around a black hole?” said [Thidé]. “That’s how we started.” [Wired]

The effect is slight, so it’s not clear whether existing telescopes will be able to pick it up. But Thidé is ready to try.

“What is new and exciting is the proposal that the effect is actually measurable for the black hole at the center of our galaxy,” says Saul Teukolsky of Cornell University. Thidé says his team will review radio telescope observations of the Milky Way’s supermassive black hole to see if the twisted light effect has already shown up. [Science News]

Related Content:
80beats: Itty Bitty Galaxy Home to Gargantuan Supermassive Black Hole
80beats: Study: Hyperactive Black Holes Aren’t Caused by Galactic Smash-ups
DISCOVER: 20 Things You Didn’t Know About… Light
DISCOVER: 20 Things You Didn’t Know About… Time

Image: Nature Physics

CATEGORIZED UNDER: Physics & Math, Space
  • giovanni

    oh my god!!

  • Crow

    It’s physics like this that will lead to breakthroughs like this:

  • Bo Thidé

    Well, we have not got 125 billion USF for our research. In fact, we have got nothing at all. When we presented a proposal to make this study, our (small) grants were immediately cut to zero – nada! That’t the hard fact for breakthrough physics research these days… Any benevolent sponsors out there? :-)

    (co-author of the paper)

  • nick

    Wow, that shows just how awesome the grant writing process is:

    Scientist – “we’ve figured out a way to look at existing data to see if it shows the effects of black holes so we can prove once and for all they exist!”

    Grant writers – “That’s awesome! The data already exists, so you obviously don’t need any money for your experiment! Later!!”

  • Bo Thide

    Even if the black-hole signatures should be there in the data (a remote possibility) it will of course cost money to find out and to analyse this data. We cannot possibly work on the data analysis without pay. Where should the asalary for me and my colleagues come from during the months that we do this work?? It the data is not there, we need to desigtn, set up and run a new experiment. Then we need to cover also costs for tavels, accommodation, computers, phone calls etc etc. With no research grants coming our way we will not be able to do it!

  • Sven

    How is this experiment any different than what whoever proved Special Relativity did? The positions of stars appeared altered against the backdrop of the sun. Would this experiment be a repetition of the same, only against ‘known’ positions of black holes such as galactic centers, or are we looking for polarized light, or something else entirely?


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