New Telescope to Take First-Ever Black Hole Photo

Tags

black hole, Event Horizon Telescope, radio telescope, telescope network

SPACE.com 18 January 2012

Simulated view of a black hole in front of the Large Magellanic Cloud.
CREDIT: Alain R. | Wikimedia Commons

A group of astronomers are meeting this week to plan out an ambitious and unprecedented project — capturing the first-ever image of a black hole.

The researchers want to create an Earth-size virtual instrument called the Event Horizon Telescope, a worldwide network of radio telescopes powerful enough to snap a picture of the supermassive black hole at the heart of our Milky Way galaxy.

“Nobody has ever taken a picture of a black hole,” Dimitrios Psaltis, of the University of Arizona’s Steward Observatory, said in a statement. Psaltis is a co-organizer of the conference, which began today (Jan. 18) in Tucson, Ariz. “We are going to do just that.”

An elusive target

Black holes are exotic structures whose gravitational fields are so powerful that they trap everything, even light. They were first postulated by Albert Einstein’s theory of general relativity.

Astronomers have detected plenty of black holes in our galaxy and beyond via indirect means. It’s thought that most, if not all, galaxies harbor a supermassive black hole at their cores.

However, scientists have yet to image a black hole. Researchers working on the Event Horizon Telescope — named after a black hole’s “point of no return,” beyond which nothing can escape — hope to change that.

“Even five years ago, such a proposal would not have seemed credible,” said Sheperd Doeleman of MIT, the project’s principal investigator. “Now we have the technological means to take a stab at it.”

Doeleman and his team want to create a network of up to 50 radio telescopes around the world, which will work in concert to get the job done.

“In essence, we are making a virtual telescope with a mirror that is as big as the Earth,” Doeleman said. “Each radio telescope we use can be thought of as a small silvered portion of a large mirror. With enough such silvered spots, one can start to make an image.”

This artist’s illustration depicts scientists’ new understanding of the giant black hole at the core of galaxy M87. The bright radio ‘core’ of the jet base is located very close to the central black hole no larger than about 10 times the size of the event horizon. CREDIT: NAOJ/AND You Inc.

Imaging a black hole’s ‘shadow’

The team plans to point the Event Horizon Telescope at the supermassive black hole at the Milky Way’s center, which is about 26,000 light-years away and is thought to hold as much mass as 4 million suns.

That’s pretty big, but picking the object out at such a great distance is equivalent to spotting a grapefruit on the surface of the moon, researchers said.

“To see something that small and that far away, you need a very big telescope, and the biggest telescope you can make on Earth is to turn the whole planet into a telescope,” said Dan Marrone of the Steward Observatory.

Researchers hope to get a picture of the black hole’s outline, or “shadow.”

“As dust and gas swirls around the black hole before it is drawn inside, a kind of cosmic traffic jam ensues,” Doeleman said. “Swirling around the black hole like water circling the drain in a bathtub, the matter compresses and the resulting friction turns it into plasma heated to a billion degrees or more, causing it to ‘glow’ — and radiate energy that we can detect here on Earth.”

General relativity predicts that the black hole’s shadow should be a perfect circle. So the Event Horizon Telescope’s observations could provide a test of Einstein’s venerable theory, researchers said.

“If we find the black hole’s shadow to be oblate instead of circular, it means Einstein’s theory of general relativity must be flawed,” Psaltis said. “But even if we find no deviation from general relativity, all these processes will help us understand the fundamental aspects of the theory much better.”

The team hopes to keep adding more instruments to the telescope over time, providing a sharper image of our galaxy’s central black hole as the months and years go by.

Each telescope in the network will record its observations onto hard drives, which will be physically shipped to a central processing center at MIT’s Haystack Observatory, researchers said.

Radio rather than optical telescopes are the right tool for the job, they added, since radio waves can penetrate the murk of stars, dust and gas between Earth and the galactic center.

http://www.space.com/14278-black-hole-photos-event-horizon-telescope.html

Scientists Closing in on Black Hole at Center of Our Galaxy

Tags

black hole, Milky Way, Sagittarius A*

I’ve been reading up on stars, galaxies, pulsars, quasars and black holes in the last week or so. A life-long interest in all things space was no doubt “inherited” (by osmosis, sort of) from my mother, who had purchased a telescope and spent many hours staring up at the sky. Here’s a timely, to me anyway, article about black holes from Space.com.

———————————–

Clara Moskowitz, Assistant Managing Editor
SPACE.com 05 April 2012

Though scientists have suspected for a while that a giant black hole lurks at the center of our galaxy, they still can’t say for sure it’s the explanation for the strange behavior observed there.

Now researchers are closer than ever to being able to image this region and probe the physics at work – potentially shedding light on the great conflict between the theories of general relativity and quantum mechanics.

At the heart of the Milky Way astronomers see some wacky things. For example, about a dozen stars seem to be orbiting some invisible object. One star has been found to make a 16-year orbit around the unseen thing, moving at the hard-to-imagine speed of about 3,000 miles (5,000 kilometers) a second. By comparison, the sun moves through space at a comparatively glacial 137 miles (220 kilometers) a second.

Based on the laws of motion, these dozen stars’ orbits should be caused by the gravitational pull of some massive object in the center of the galaxy. Yet telescopes observe nothing there.

“The really important thing is that all the orbits have a common focus,” astrophysicist Mark Reidof the Harvard-Smithsonian Center for Astrophysics said during the recently concluded April 2012 meeting of the American Physical Society.”There’s one point on the sky, and there’s nothing you can see on images at this position.”

Plus, all this is happening in a region only about 100 times as wide as the distance between the Earth and the sun – very tiny in the galactic scheme of things. [Photos: Black Holes of the Universe]

There is, however, a very faint emission of radio waves coming from this area, which scientists call Sagittarius A* (pronounced “Sagittarius A-Star”). By comparing it against the sun’s movement around the Milky Way, researchers have been able to determine that this object is barely moving at all – less than 1 kilometer (0.62 miles) a second, much slower even than the rate that the Earth revolves around the sun.

If Sagittarius A* were any moderate-mass object, it likely would be pulled by the gravity of nearby objects and experience some motion.

Reid said of the object’s apparent stillness: “The only way that this can happen is if Sagittarius A* is tied to a very massive object. When you do the analysis, you get a lower limit of 4 million solar masses.”

The density limit of a black hole

Astronomers can’t see the galactic center well enough to measure exactly how large Sagittarius A* is, but they can say for sure that its radius is no larger than about two-tenths the distance between the Earth and the sun.

The means that in the center of the Milky Way, something packing about 4 million times the mass of the sun is sitting within an area that could fit inside the orbit of Mercury and is basically invisible, producing much less light than any of the stars orbiting it.

Right now, that puts this object’s density at about an eighth of the theoretical limit for a black hole. So while scientists can’t say for sure the object is a black hole, it’s looking mighty likely.

“Although there are alternative explanations, they would actually be even much more fantastic than the rather mundane supermassive black hole that almost certainly is there,” Reid said.

One of these other, exotic explanations is that there exists a ball made of an unidentified variety of heavy fermion particles. But even such a ball would be unlikely to have the density required to explain all the evidence.

Looking closer

To finally solve this riddle, astronomers yearn to image the center of the galaxy directly. Not only is it very distant and faint, this region is hard to see because of all the dust between it and Earth.

Astronomers have recently begun a project called the Event Horizon Telescope. This instrument would integrate many radio observatories around the world, turning them into a giant interferometer capable of very precise measurements. Ultimately, the resolution should be sharp enough to distinguish Sagittarius A*.

So far, the Event Horizon Telescope has integrated only three observatories, in Hawaii, California and Arizona, for an observing time of between 15 and 20 hours. But astronomers hope to add more locations and observing time soon.

“EHT is not a dream, it’s not on the drawing board,” said Avery Broderickof Canada’s University of Waterloo and the Perimeter Institute for Theoretical Physics.”It’s something that works.”

One of Broderick’s goals is not only determining once and for all if Sagittarius A* is a black hole, but probing the physics of the object.

Testing general relativity

Black holes straddle the two most successful theories of physics: one that describes the realm of the very large, and one that describes the province of the very small.

Black holes’ extremely large masses invoke Einstein’s general theory of relativity, which describes how mass warps the fabric of space and time to create gravity. But an explanation for black holes’ extremely small spatial dimensions also requires quantum mechanics. [Images: The Big Bang & Early Universe]

So far, quantum mechanics and general relativity are incompatible. When combined to describe black holes, the equations break down and suggest that the density of a black hole is infinite.

Though the Event Horizon Telescope has produced only very preliminary data so far, Broderick and his colleagues have used them to test the space-time predictions of general relativity.

“Even with existing data today we can say something interesting about the higher-order structure of astrophysical black holes,” Broderick said. “We will in principle be able to distinguish deviations from general relativity.

“General relativity is safe for right now, but it’s not going to be safe for much longer.”

http://www.space.com/15166-milky-center-black-hole-sagittariusastar.html