Sat, Jan 12, 2019 - Page 7 News List

First sighting of Milky Way black hole expected soon

The Guardian

Astronomers attempting to capture the first images of the black hole at the heart of the Milky Way have given early hints that the ambitious project has been successful.

The observations, by the Event Horizon Telescope (EHT), are expected to be unveiled in March in one of the most eagerly awaited scientific announcements of the year.

Now, a senior scientist on the project has said that “spectacular” data were gathered during observations of two black holes, including Sagittarius A* at the center of our own galaxy.

“We managed to get very high-quality data at the very high resolutions necessary to observe the [black hole’s] shadow, if it’s really there,” said Sera Markoff, a professor of theoretical astrophysics and astroparticle physics at the University of Amsterdam who coleads the EHT Multiwavelength Working Group.

The team is in the final phase of reviewing data that was gathered in 2017 and Markoff could not confirm yet whether the observations had produced the first direct image of a black hole’s silhouette.

Peter Galison, a professor in the department of the history of science at Harvard University and also involved in the project, said that, if successful, the EHT’s first image would become one of the most significant in the past 50 years of astronomy.

“If we get an image out of it, it will become one of the iconic images of science,” he said. “It’s an extraordinarily ambitious project.”

There is little doubt about the existence of black holes: The phenomenally dense objects distort the fabric of space-time in their vicinity, causing objects and light to appear to swerve off course. More recently, the gravitational wave observatory Ligo has detected ripples sent out across space-time when pairs of black holes collide.

However, until now, a black hole has never been directly observed. The main barrier is that black holes are so compact that a telescope roughly the size of Earth would be required to see even the nearest one.

The EHT gets around this by linking together 15 to 20 telescopes spanning the South Pole, Europe, South America, Africa, North America and Australia. Collectively, the array has a resolution equivalent to being able to see a drawing pin in New York from London.

The EHT uses a technique known as interferometry, in which astronomers at observatories on different continents simultaneously observe the same object and combine the collected data on a supercomputer.

This requires all the telescopes in the array to swivel toward the target black hole and measure every radio wave coming from its direction.

Coordinating this was a “huge accomplishment of diplomacy and organization,” Galison said.

The EHT has two primary targets: Sagittarius A*, at the center of the Milky Way, and a supermassive black hole called M87 in the Virgo cluster of galaxies. M87 is 50 million to 60 million light years away, but at more than 6 billion solar masses (1,000 times larger than our local black hole), astronomers hope that it should be visible.

No one is sure what the image will look like, but theoretical predictions show a black silhouette, set against a surrounding glow of radiation — not unlike the depiction in the film Interstellar.

“You’d imagine seeing a black shadow or depression,” Markoff said.

Beside telling us what black holes look like, the EHT could also reveal whether they have properties predicted by Einstein’s theory of general relativity and give insights into exotic processes that occur in the extreme environment close to the event horizon.

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