The Sight of Twisted Light Could Reveal a Spinning Black Hole
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. ThidÃ© says that the second effectâ€”orbital angular momentumâ€”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 ThidÃ© 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 Earthâ€™s spin tows the fabric of space and time in circles. â€œIf 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?â€ said [ThidÃ©]. â€œThatâ€™s how we started.â€ [Wired]
The effect is slight, so it’s not clear whether existing telescopes will be able to pick it up. But ThidÃ© is ready to try.
â€œWhat is new and exciting is the proposal that the effect is actually measurable for the black hole at the center of our galaxy,â€ says Saul Teukolsky of Cornell University. ThidÃ© says his team will review radio telescope observations of the Milky Wayâ€™s supermassive black hole to see if the twisted light effect has already shown up. [Science News]
Image: Nature Physics