A computer simulation shows the expected appearance of the accretion disk surrounding a black hole, as seen in radio wavelengths. The left side of the image is brighter than the right side due to the Doppler beaming effect: Light emitted from material moving toward an observer is brighter than light from material moving away from the observer. (Event Horizon Telescope Graphic / Hotaka Shiokawa)

WASHINGTON — Scientists are sharing the first pictures to show the immediate surroundings of a supermassive black hole, captured by a network of radio telescopes that adds up to what could be considered the world’s widest observatory.

First results from the project, known as the Event Horizon Telescope, are being unveiled at 9 a.m. ET (6 a.m. PT) Wednesday during a global wave of briefings.

The National Science Foundation is providing streaming-video coverage of the big reveal here in Washington, at the National Press Club. Scientists in Europe and Japan are  streaming separate briefings in Brussels and Tokyo. Still more news conferences are happening in Chile, China and Taiwan.

The Event Horizon Telescope, or EHT, is actually an consortium of radio telescope facilities that are combining efforts to do what none of them could do on their own: Chart the bright halo of hot material that surrounds what would otherwise be an invisible black hole.

As any science-fiction fan knows, black holes are concentrated areas of gravitational collapse so massive that nothing — not even light — can escape their pull.

If a dying star is massive enough, on the order of 10 or 20 times as massive as our sun, it’s likely to collapse into a black hole when it dies. But the biggest black holes are the ones that form at the center of galaxies as they evolve. These supermassive monsters can weigh millions or even billions as much as our sun

Our own Milky Way galaxy has just such a black hole at its core. Fortunately, our galaxy’s supermassive black hole is on the quiet side.

In April 2017, eight telescope facilities that are participating in the Event Horizon Telescope project took a close look at our galaxy’s central region, known as Sagittarius A* (that is, Sagittarius A-star, abbreviated as Sgr A*). The facilities were in Arizona, Hawaii, Mexico, Chile, Spain and even the South Pole.

The results from any one of the telescopes wouldn’t have anywhere near the resolution to make out the hot surroundings of the black hole, which is thought to measure 27.3 million miles in diameter. That may sound big, but at a distance of 25,640 light-years, the observational challenge has been compared to counting the dimples on a golf ball in Los Angeles … from a viewing spot in New York.

To bring the picture into focus, the Event Horizon Telescope’s teammates had to combine their observations using a technique known as very long baseline interferometry, or VLBI. The technique for synchronizing observations effectively turns their network into a huge radio telescope almost as wide as our planet.

University of Washington astronomer Eric Agol played a key role in suggesting VLBI as a way to view the “shadows” of supermassive black holes back in 1999. In an email, Agol also noted that a colleague of his at UW, Bruce Balick, was in on the discovery of Sagittarius A* 45 years ago.

During the 2017 campaign, the team also tried capturing an image of the supermassive black hole at the center of an elliptical galaxy known as M87, more than 50 million light-years from Earth. Images showing the radio signatures of both galactic-scale black holes are likely to be released at Wednesday’s briefings.

“I am not involved in the EHT, so I haven’t seen any of the results, but I am excited to see them!” Agol said.

Based on computer simulations, the event horizon of each black hole — that is, the boundary within which light waves can’t escape — is expected to look like a circle of black, surrounded by bright streams of superheated material swirling around the shadow. But don’t expect the pictures to look as sharp as the depictions of black holes you’ve seen in movies such as “Interstellar.” With a limited number of participating telescopes, even VLBI can take you only so far.

Fortunately, more telescopes have joined the campaign over the past couple of years, and astronomers are working on ways to improve their data processing methods. These first images of a supermassive black hole almost certainly will be improved upon in years to come.


Source: geekwire