Virtual Telescope Readies to Image Black Hole's 'Ring of Fire'

With the addition of a telescope at the southern-most point of Earth, the Event Horizon Telescope (EHT) now spans the diameter of our planet and, when the vast project goes online, astronomers will get their first glimpse of the bright ring surrounding a supermassive black hole.

Using a method known as Very Long Baseline Interferometry, or VLBI, astronomers can combine the observing power of many telescopes situated at distant locations around the planet. The distance between those observatories, known as the “baseline,” then mimics a virtual telescope of that diameter. So, if you have telescopes dotted across one hemisphere of the globe, spanning 5,000 miles, you are, in effect, mimicking a giant telescope with a gargantuan diameter of 5,000 miles.

Of course, it isn’t a “simple” task of networking a bunch of telescopes and pointing them at a celestial object in the hope of gaining some usable data, but as interferometer communications hardware and computational software becomes more sophisticated, grand projects such as the EHT are starting to see the light of day. Or, in this case, the light generated by the invisible boundary surrounding a supermassive black hole.

Now, in an attempt to make direct observations of the supermassive black hole in the center of our galaxy, located at a powerful radio emission source called Sagittarius A*, the South Pole Telescope (SPT) at the National Science Foundation’s Amundsen-Scott South Pole Station has been linked to the EHT and the stage is set for a historic new era of exploring the most extreme objects in the known universe.

The SPT is a 10-meter telescope that is sensitive to millimeter wavelengths of radiation tasked with the day job of making high-resolution images of cosmic microwave background radiation, or CMB. By linking the observatory with the EHT, this telescope’s unique location will give the vast VLBI project a huge boost.

“Now that we’ve done VLBI with the SPT, the Event Horizon Telescope really does span the whole Earth, from the Submillimeter Telescope on Mount Graham in Arizona, to California, Hawaii, Chile, Mexico, Spain and the South Pole,” said Dan Marrone of the University of Arizona. “The baselines to SPT give us two to three times more resolution than our past arrays, which is absolutely crucial to the goals of the EHT. To verify the existence of an event horizon, the ‘edge’ of a black hole, and more generally to test Einstein’s theory of general relativity, we need a very detailed picture of a black hole. With the full EHT, we should be able to do this.”

It is predicted that when the EHT goes online, it will be 1,000 times more powerful than the Hubble Space Telescope and it will need all the power it can muster if we are to resolve the bright ring or crescent thought to surround the supermassive black hole in the Milky Way’s core. Although the supermassive black hole is 4 million times the mass of our sun, at a distance of 26,000 light-years, its predicted size will be tiny from our perspective.

“Because it is smaller than Mercury’s orbit around the sun, yet almost 26,000 light-years away, studying its event horizon in detail is equivalent to standing in California and reading the date on a penny in New York,” writes a University of Arizona press release.

But, should the EHT be able to achieve this monumental task, astrophysicists are getting excited for what we’ll see.

If our current understanding of how black holes work — and if some of the finer details of Einstein’s general theory of relativity holds up in the region immediately surrounding the black hole — we have a basic idea of what we’ll see. Although the event horizon is the point of no escape even for light and we shouldn’t see anything, just above the event horizon, extreme physics generate powerful radiation. In which case, the EHT should resolve a partial or full ring-like structure; energetic radiation glowing around a very definite dark shadow — this shadow being the event horizon.

And the best thing is, at that moment, when the event horizon ring is finally resolved, we’ll know whether or not black holes act as we expect. This will also be the first ever direct observations of the structure surrounding a black hole.

Read more at Discovery News