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Posts Tagged ‘event horizon telescope’

Sagittarius A*: A Star (figuratively) of the Milky Way Gets Its Close-up 

Monday, June 6th, 2022
The first image of Sagittarius A*, the supermassive black hole at the center of the galaxy. Credit: © EHT Collaboration

The first image of Sagittarius A*, the supermassive black hole at the center of our galaxy.
Credit: © EHT Collaboration

Finally, the faceless monster lurking at the center of our galaxy has been photographed. Sounds like science fiction? It’s true! On Thursday, May 12, scientists with the Event Horizon Telescope (EHT) team published a photograph of Sagittarius A* (saj uh TAIR eeuhs AY star). Sagittarius A* is a supermassive (huge) black hole in the center of our galaxy, the Milky Way.

A black hole is a region of space whose gravitational force is so strong that nothing can escape from it, not even light. The event horizon is the “point of no return” for a black hole: Anything that crosses this horizon is sucked into the black hole forever. Supermassive black holes at least a million times more massive than the sun lurk at the center of many galaxies.

The EHT is a global network of ground-based telescopes that use a technique called radio interferometry to produce images of black hole event horizons. The collection of radio telescopes participating in the EHT project stretches from Hawaii to Europe and all the way south to Antarctica. Several dozen of the world’s leading observatories and universities contribute to the project. Supercomputers process the image data using special algorithms in a process called correlation.

Astronomers began using the EHT to make observations of Sagittarius A* in 2017. In 2019, the EHT released an image it had captured of the event horizon surrounding the supermassive black hole at the center of the Messier 87 galaxy (M87*). It was the first time an event horizon had been photographed.

If light can’t escape a black hole, how did EHT photograph M87* or Sagittarius A*? Technically, it didn’t: all black holes are invisible and cannot be directly photographed. But matter trapped in orbit near the event horizon is extremely energized and emits large amounts of light. The black hole lurks in the circular “shadow” within the halo of high-energy matter. Thus, the EHT can take a picture of a black hole much as we can take a picture of a doughnut hole.

Despite being closer to Earth, Sagittarius A* was still harder to image than M87*. Sagittarius A* is still 27,000 light-years from Earth. It’s also more than 1,000 times smaller and less massive than M87*. So, although the high-energy matter is orbiting both black holes at about the same speed, the matter completes an orbit around Sagittarius A* in a matter of minutes. Furthermore, Sagittarius A* is “quieter”: it emits far less energy than M87*. All these factors made it difficult for EHT to capture an image of it.

Now that EHT has imaged two black holes, astronomers can compare them. Both look remarkably similar, despite their differing sizes. Both confirm what was predicted by Einstein’s theory of relativity. But plenty of questions remain. For example, are the “blobs” in the picture actual elements, or are they artifact of the correlating process? The EHT is also considering the feasibility of creating a short video of Sagittarius A* by stringing together multiple consecutive images. And plenty more supermassive black holes are waiting for their photographic debut. A major observation campaign that concluded earlier this year featured even more telescopes. Expect more exciting results soon regarding these most extreme objects in the universe.

Tags: astronomy, black hole, event horizon telescope, galaxy, milky way, photograph, sagittarius A*, space, supermassive black hole
Posted in Current Events, Space | Comments Off

The Black Hole Event

Friday, April 12th, 2019

April 12, 2019

On Wednesday, April 10, scientists with the Event Horizon Telescope (EHT) team published a photograph of the invisible—or at least the area around the invisible. The EHT captured an image of an event horizon (the surface of a black hole) for the first time. The EHT is a global collection of radio telescopes that work together as one giant telescope. As its name implies, the EHT was created to observe an event horizon, a mission that has at last been accomplished. The EHT began its quest in 2006, and has since greatly expanded its network.

The Event Horizon Telescope (EHT) — a planet-scale array of eight ground-based radio telescopes forged through international collaboration — was designed to capture images of a black hole. In coordinated press conferences across the globe, EHT researchers revealed that they succeeded, unveiling the first direct visual evidence of the supermassive black hole in the centre of Messier 87 and its shadow. The shadow of a black hole seen here is the closest we can come to an image of the black hole itself, a completely dark object from which light cannot escape. The black hole’s boundary — the event horizon from which the EHT takes its name — is around 2.5 times smaller than the shadow it casts and measures just under 40 billion km across. While this may sound large, this ring is only about 40 microarcseconds across — equivalent to measuring the length of a credit card on the surface of the Moon. Although the telescopes making up the EHT are not physically connected, they are able to synchronize their recorded data with atomic clocks — hydrogen masers — which precisely time their observations. These observations were collected at a wavelength of 1.3 mm during a 2017 global campaign. Each telescope of the EHT produced enormous amounts of data – roughly 350 terabytes per day – which was stored on high-performance helium-filled hard drives. These data were flown to highly specialised supercomputers — known as correlators — at the Max Planck Institute for Radio Astronomy and MIT Haystack Observatory to be combined. They were then painstakingly converted into an image using novel computational tools developed by the collaboration. Credit: EHT Collaboration/ESO

On April 10, 2019, scientists with the Event Horizon Telescope team released this first ever image of a black hole—or at least the event horizon surrounding a black hole. Credit: EHT Collaboration/ESO

A black hole is a region of space whose gravitational force is so strong that nothing can escape from it, not even light. The event horizon is the “point of no return” for a black hole: Anything that crosses this horizon is sucked into the black hole forever. Because light cannot escape a black hole, all black holes are invisible and cannot be directly photographed. But physicists predicted that an image of the area surrounding a black hole would reveal a halo of high-energy matter and radiation around a circular shadow.

Chandra X-ray Observatory close-up of the core of the M87 galaxy. Credit: NASA/CXC/Villanova University/J. Neilsen

The boxed area in this image shows the black hole at the core of the M87 galaxy.
Credit: NASA/CXC/Villanova University/J. Neilsen

Heino Falcke, a German astrophysicist now at Radboud University in the Netherlands, discovered that this halo would emit radio waves detectable on Earth. He helped found the EHT to photograph event horizons through these radio waves. The collection of ground-based radio telescopes participating in the EHT project stretches from Hawaii to Europe and all the way south to Antarctica. Several dozen of the world’s leading observatories and universities contribute to the project.

The EHT observed a supermassive black hole at the center of a huge galaxy called Messier 87, or M87, some 55 million lightyears from Earth. A supermassive black hole is a type of black hole with a mass from 1 million to billions of times the mass of our solar system’s  sun. Many galaxies have a supermassive black hole near their centers. The supermassive black hole at the center of M87 is one of the largest ever discovered, some 6.5 billion times the mass of our sun. The diameter of its event horizon is roughly the size of our entire solar system.

It took an enormous effort to produce the image released this April. Two years ago, in April 2017, eight radio telescopes of the EHT simultaneously observed the M87 black hole for 10 days. The observations had to be precisely synchronized (scheduled) by atomic clock to combine and match up their images. In total, the observatories collected more than 5 petabytes of data, equal to the text of 88 million print editions of the World Book Encyclopedia. (A petabyte is 1,000 terabytes. A terabyte is a measure of computer information or memory equal to about 1 trillion bytes). This was so much information that it was faster to fly the data by airplane between the laboratories that analyzed the data than to transfer it over the internet. An American computer scientist named Katie Bouman developed a special algorithm to combine the data from the eight telescopes into a single image.

Just like the detection of gravitational waves three years ago, this work promises to revolutionize astronomy. Each year, new observatories join the EHT, strengthening its resolution (image sharpness). The EHT has observed black holes other than the one at the core of M87, including the one at the center of our own Milky Way galaxy, Sagittarius A*. EHT scientists think they will be able to produce an image of that event horizon soon. Scientists might also be able to sharpen the image of the M87 black hole in the coming months.

Tags: black hole, event horizon telescope, space
Posted in Current Events, Education, People, Science, Space | Comments Off

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