Guide to the Cosmos
Making the Wonders of our Universe Accessible to Everyone

Earth-Sized Telescope to Spy Black Hole

 

Astronomers are busy assembling a global array of radio telescopes to probe our galaxy’s supermassive black hole.

 

Supermassive black holes occupy the centers of nearly every major galaxy. The black hole at the center of the Milky Way, Sagittarius A* (“A-Star”) is 4 million times more massive than our Sun. Since some of its supermassive brethren are more massive than 10 billion suns, Sag A* is relatively puny. Compared with other galactic monsters, Sag A* has devoured a thousandth as many stars, gas, and the odd planet, and has emitted a thousandth as much radiation. This is one reason our galaxy is more habitable than many others.

 

Sag A* has been quite peaceful since its discovery 40 years ago, apparently due to a paucity of snacks.  But this is likely only an intermission. Radiation flares hundreds of light-years away indicate Sag A* ate well in the past, perhaps devouring an entire star and perhaps becoming one million times today’s brightness. Recently a gas cloud has approached Sag A*. The black hole and astronomers are licking their chops, preparing for the beast’s next feast.

 

While we frequently see radiation emitted by matter falling into black holes, no one has ever imaged the black hole itself. That image would put Einstein’s theory of General Relativity to its most stringent test. Despite being 26,000 light-years away, Sag A* is astronomers’ best hope of imaging a black hole’s event horizon, its point of no return.

 

That’s much easier said than done. From Earth, resolving Sag A*’s 12M km-wide event horizon is like resolving the tread pattern of Neil Armstrong’s footprints on the Moon. Earth’s largest telescope can’t do that, but a telescope as large as Earth could.

 

Congress isn’t likely to fund an 8000-mile-wide telescope, but radio astronomers can approach that performance by linking up telescopes across the globe. This technique, known as Very Long Baseline Interferometry (VLBI), has been employed since the 1970’s. Data from far-flung radio telescopes are recorded, precisely time-stamped, and then sent to a central processor, which combines the detected radio waves in proper phase.

 

The largest-ever international consortium will push the limits of VLBI with the latest electronics, supercomputers, and atomic clocks. Nearly 100 radio telescopes will participate, from Hawaii, California, Arizona, Mexico, Chile, Spain, France, and even the South Pole. Receivers are being upgraded to 450 GHz, about a million times the frequency of your favorite AM station. Astronomers will take advantage of Earth’s daily rotation, which carries all our telescopes across the full range viewing angles. Each telescope effectively becomes a narrow mirror thousands of miles long.

 

By recording all the data, from all the telescopes, around the clock, astronomers will amass immense data streams, from which supercomputers will produce previously unimaginable pictures. We might capture Sag A*’s dark central disk surrounded by a bright ring, remote starlight focused by the black hole’s immense gravity. That is the unique signature of a black hole’s event horizon, predicted by General Relativity.

 

Will Einstein be vindicated again, or will new physics be discovered?

 

 

Best Regards,

Robert

 

 

 

 

website: Guide to the Costmos

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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