Astronomers have discovered hundreds of mysterious cosmic threads that point towards the supermassive black hole at the heart of the Milky Way, after a survey of the galaxy.
The strange filaments, each of which stretches five to 10 light years through space, resemble the dots and dashes of morse code on a vast scale. They spread out from the galactic centre 25,000 light years from Earth like fragmented spokes on an enormous wheel.
Farhad Yusef-Zadeh, an astronomer at Northwestern University in Evanston, Illinois, said he was “stunned” to discover the structures in data taken by the MeerKAT radio telescope in the Northern Cape of South Africa.
The observatory, the most sensitive radio telescope in the world, captured images of the threads during an unprecedented 200-hour survey of the galactic core. Yusef-Zadeh told the Guardian: “They all seem to trace back to the black hole. They are telling us something about the activity of the black hole itself.”
Four decades ago, Yusef-Zadeh found much larger, vertical filaments surrounding Sagittarius A*, the black hole at the centre of the Milky Way, in data gathered by another telescope called the Very Large Array in New Mexico. Those structures dangle perpendicular to the plane of the Milky Way disc and measure 150 light years from top to bottom.
What produced the more numerous vertical filaments is still unclear, but studies have found that they possess strong magnetic fields and emit radio waves as they accelerate particles in cosmic rays to the verge of light speed.
According to Yusef-Zadeh, researchers – himself included – have been so busy grappling with the nature of the giant vertical threads that the existence of the shorter, horizontal filaments which trace back to the centre of the Milky Way almost went unnoticed.
“The emphasis has been on understanding the vertical filaments. The horizontal structures somehow didn’t register,” Yusef-Zadeh said. “It was a surprise to suddenly find a new population of structures that seem to be pointing in the direction of the black hole. I was actually stunned when I saw these.”
“If it wasn’t for MeerKAT these wouldn’t have been detected,” he added. “We’ve never been able to dedicate that amount of time to the centre of the galaxy.
The shorter, horizontal threads that spread out from the centre of the Milky Way came into focus when the scientists removed the background and filtered noise from the MeerKAT images. Yusef-Zadeh believes the structures, described in the Astrophysical Journal Letters, formed through a different process to the larger, vertical filaments.
He suspects that an outburst of material from the black hole about 6m years ago slammed into surrounding stars and gas clouds, creating streaks of hot plasma that point back towards the black hole. The effect is akin to blowing blobs of paint across a canvas with a hairdryer.
“The outflow from the black hole interacts with the objects it meets and distorts their shape,” Yusef-Zadeh said. “It’s sufficient to blow everything in the same direction.”
By studying the cosmic threads, astronomers hope to understand more about the spin of the Milky Way’s central black hole and the accretion disc of infalling material that whirls around it.
“These are not going to be the last images of the centre of the galaxy,” said Yusef-Zadeh. “Our galaxy is rich in lots of structures that we can’t explain. There’s still a lot to be learned.”
