Telescope picks up unexpected ‘luminous echoes’ – smaller, later and of different colour to bright flares

Key takeaways

  • Astronomers have observed light behind a black hole for the first time, confirming Einstein’s theory of general relativity.
  • Unexpected “luminous echoes” of different colors and timings were detected, apart from the usual bright X-ray flares.
  • This discovery shows how black holes warp space and bend light, giving scientists new insights into these cosmic phenomena.

Astronomers have spotted light from behind a supermassive black hole for the first time in history. The discovery demonstrates that Albert Einstein’s theory of general relativity was correct again.

Using the European satellite Agency’s XMM-Newton and NASA’s NuSTAR satellite telescopes, astronomers saw the black hole as it emitted X-rays into space. The black hole is approximately 10 million times more massive than our sun and is located in the heart of a neighboring spiral galaxy known as I Zwicky, 1,800 million light-years distant from Earth.

After seeing a succession of spectacular X-ray flares, something unexpected happened: other flashes that were smaller, later, and had different “colors” than their predecessors. According to a research published this week in the journal Nature, the “echoes” of light looked to be X-rays reflected from beyond the black hole, which is an unusual location for light to originate.

Black holes’ gravitational forces are so strong that light cannot escape them. However, light may “echo,” or wrap around the back of a celestial phenomena, allowing astronomers to observe it.

“Any light that goes into that black hole doesn’t come out, so we shouldn’t be able to see anything that’s behind the black hole,” said lead author Dan Wilkins. “The reason we can see that is because that black hole is warping space, bending light and twisting magnetic fields around itself.”

While Einstein predicted in 1916 that a black hole’s gravity might bend light around it, it was never proved – until now.

“Fifty years ago, when astrophysicists starting speculating about how the magnetic field might behave close to a black hole, they had no idea that one day we might have the techniques to observe this directly and see Einstein’s general theory of relativity in action,” according to Roger Blanford, a co-author.

Researchers were not even trying to confirm Einstein’s theory. They were originally aiming to solve the riddles of the corona, an unusual characteristic of black holes that produces dazzling X-ray radiation.

“I’ve been building theoretical predictions of how these echoes appear to us for a few years,” according to Wilkins. “I’d already seen them in the theory I’ve been developing, so once I saw them in the telescope observations, I could figure out the connection.”

The prevalent view is that the corona originates as gas flows constantly into the black hole, creating a spinning disk around it, “like water flushing down a drain.” The gas disk is then heated to millions of degrees, creating a distorted magnetic field that finally snaps, releasing energy and forming the corona.

“This magnetic field getting tied up and then snapping close to the black hole heats everything around it and produces these high energy electrons that then go on to produce the X-rays,” according to Wilkins.

From here, astronomers hope to use the various “colors” observed as the X-ray echoes travel around the black hole to create a 3D map of the black hole surroundings. They also hope to learn how the corona produces such bright flares.

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