- The Event Horizon Telescope, which endeavours to photograph black holes, is making a “ground-breaking” announcement on Wednesday.
- Scientists expect the announcement will unveil the first-ever pictures of a black hole‘s “shadow” caused by its event horizon, or point-of-no-return for light.
- The images could be of the Milky Way’s supermassive black hole, called Sagittarius A*, or an even larger black hole at the center of galaxy M87.
- Computer-simulated images offer a clue as to what to expect.
- Visit BusinessInsider.com for more stories.
The first-ever pictures of a black hole will likely be unveiled on Wednesday night. If you’re anxious to know what those pictures might look like, astrophysicists say computer simulations offer a reasonable preview.
Since 2006, radio telescopes around the globe have worked together to resolve dark, hulking, and important beasts that lurk at the centres of two different galaxies.
Called the Event Horizon Telescope (EHT), the project’s ultimate goal is baked into its name: take pictures of the event horizon, or point-of-no-return for a black hole.
“Just the mere fact of being able to see such a thing is awesome,” Timothy Brandt, an astrophysicist at the University of California, Santa Barbara who studies black holes but is not part of the EHT collaboration, told Business Insider. “I think we’ll learn some things scientifically, and I think we’ll learn more and more as time goes on. But still, just seeing those images will be pretty cool.”
EHT is using observatories at 11 different locations to create a “virtual” radio telescope that’s about the size of planet Earth. This helps researchers make out the details of two nearby supermassive black holes, so named because they can be millions if not billions of times as massive as stars like the sun.
The first, called Sagittarius A* (pronounced “A-star”), is at the center of our Milky Way galaxy and is thought to be as massive as 3.5 to 4.7 million suns. It’s about 26,000 light-years from Earth, which is cosmically close and makes it a workable target for EHT.
The second supermassive black hole resides inside an extremely large galaxy called Messier 87 (M87), which is about 53.5 million light-years away from us. Although that’s 2,000 times as distant as our own supermassive black hole, M87’s is thought to be 2.7 to 7 billion solar masses in size. Because it’s so much bigger, its event horizon should be roughly as visible as that of the Milky Way‘s own supermassive black hole.
No images of either galaxy’s central and colossal black holes have yet been released, but that’s expected to happen for the first time on Wednesday night in Australia. The scale and hype of the announcement – six press conferences in multiple languages held simultaneously across Belgium, Chile, Shanghai, Japan, Taipei, and the US – strongly suggests that’s the case.
“The European Commission, the European Research Council, and the Event Horizon Telescope (EHT) project will hold a press conference to present a ground-breaking result from the EHT,” reads one press release for the announcement.
Until that result is made public, advanced computer models of supermassive black holes offer a tantalising glimpse at what we may see.
What the first Event Horizon Telescope images might look like
Above is a high-resolution simulation of a supermassive black hole by data scientist Hotaka Shiokawa at the Rakuten Institute of Technology in Japan. It shows what an observer with a clear view of one might expect to see.
Black holes are defined by an ultimate border called the event horizon: a region of space so dense with matter, not even light can travel fast enough to escape its gravity.
This creates a circular “shadow” – where all light and matter is gobbled up – that reveals the size of the black hole’s event horizon. This shadow is the feature that EHT scientists hope to clearly resolve in radio waves. (Though invisible to human eyes, such frequencies of light aren’t easily absorbed by the gas and dust that litters interstellar space between Earth and the center of a galaxy.)
Far away from the event horizon, on a scale roughly the size of the solar system, supermassive black holes usually have an accretion disk. Accretion disks are clouds of hot gases and dust trapped in orbit around a black hole, and the closest material moves at perhaps 50% of light-speed.
Such incredible velocities lead to a lopsided-looking accretion disk that defines a black hole’s shadow.
“Part of it’s going to be brighter and part of it’s going to be fainter,” Brandt said of the accretion disk. “Some of it’s coming towards you, and that’s going to be brighter because of relativistic beaming.”
Beaming is comparable to the Doppler effect, which is what makes an approaching ambulance’s siren sound higher-pitched and one driving away sound lower-pitched. At velocities close to light-speed, stuff that’s moving toward Earth will look brighter and bluer, while stuff that’s moving away from will appear dimmer and redder.
If you expect to see a crystal-clear view of a black hole’s shadow and accretion disk, though, you may be disappointed with EHT’s first images.
“One of the biggest differences I am expecting to see between the simulations and the image(s) released tomorrow is the level of detail,” Misty Bentz, an astrophysicist at Georgia State University, told Business Insider in an email.
She added: “We can run very high resolution simulations that show a great level of detail, but I’m expecting more of a ‘fuzzy blob’ tomorrow based on the very difficult technological requirements involved in this project. It’s important to remember that we’re talking about pictures of objects that are on the scale of our solar system, but we are viewing them from 26,000 light years (in the case of the Milky Way) or 54 million light years away (in the case of M87).”
By “fuzzy blob,” Bentz is referring to simulation images more akin to the ones below:
The central image is closest to the one predicted by Einstein’s general relativity. The exact mass, spin, orientation, and other qualities of a supermassive black hole will determine how it actually looks.
Bentz said the final appearance may also provide clues about the black hole’s eating patterns, as well as its relation to its host galaxy’s “archaeology” or historical structure.
“In a way, it’s a bit like meeting a pen pal in person for the first time,” Bentz said. “You have imagined what they are like based on the information available, but you won’t know if your picture is accurate or not until the real version is right there in front of you.”
Why the images took so long to create and may be ‘fuzzy’
The Event Horizon Telescope took more than a decade to reach this point in part because of physics, but also because of complexity and cost.
On the physics side, Brandt said the operation is akin to taking a clear photo of a distant object in the dark: the longer the exposure, the more light and signal a camera can record, leading to a crisper image. This also helps counteract noise introduced by hardware, which can drown out a tough-to-see object.
The EHT is seriously challenged in this regard, though. While the telescope is considered to be Earth-sized on a virtual level, its ability to gather radio waves from the center of the galaxy is limited. It’s akin to having a circular mirror with all but a handful of tiny reflective patches ground away – making it hard to quickly generate a clear image. Supermassive black holes are also located very far away, which doesn’t make matters easier.
EHT got around these and other issues by using Earth’s rotation and movement around the sun to get different views of a black hole, and by spending many years collecting data.
“We need to look again and again and again, and keep looking and looking, and averaging all of that together,” Brandt said. In effect, this takes many weak observations of what normally looks like a one-dimensional point of light and helps build out a clearly defined two-dimensional object.
In the future, radio telescopes launched into space could improve detail and speed up image creation, though at significant cost.
“To make this any bigger, you’d have to put telescopes on the moon or something,” Brandt said. “And that, of course, gets pretty expensive.”
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