As teased earlier this month, today the Event Horizon Telescope (EHT) project announced and presented the first ever photographs of a black hole — “the last photon orbit.” Another epic story of big science and an international team. The interplay of models and simulations, data capture, and complex processing. And funding.
Much news coverage. Here’s an article by Space.com: “Eureka! Black Hole Photographed for 1st Time.” I’ll add other articles later.
“We have seen what we thought was unseeable,” Sheperd Doeleman, of Harvard University and the Harvard-Smithsonian Center for Astrophysics, said today (April 10) during a press conference at the National Press Club in Washington, D.C.
Doeleman directs the Event Horizon Telescope (EHT) project, which captured the epic imagery. These four photos, which were unveiled today at press events around the world and in a series of published papers, outline the contours of the monster black hole lurking at the heart of the elliptical galaxy M87.
And in case you’re wondering about Sagittarius A*: The EHT team hopes to get imagery of that supermassive black hole soon, Doeleman said today. The researchers looked at M87 first, and it’s a bit easier to resolve than Sagittarius A* because it’s less variable over short timescales, he explained.
In addition, the shape of an event horizon can reveal whether a black hole is spinning, said Fiona Harrison of the California Institute of Technology, the principal investigator of NASA’s black-hole-studying Nuclear Spectroscopic Telescope Array (NuSTAR) mission.
The National Science Foundation (NSF) news has detailed coverage, including papers about the announcement which were published in a special issue of The Astrophysical Journal Letters. See their video “BRIEF, SELF-CONTAINED, NARRATED OVERVIEW of Event Horizon Telescope project and the first black hole.“
Here’s the NSF YouTube video of the press event:
Other YouTube videos
Perimeter Institute for Theoretical Physics (published on Apr 10, 2019)
Time – Scientists from The NSF Hold Conference on Results from The Event Horizon Telescope.
Veritasium (published on Apr 10, 2019) – which explains the 40 microarcsecond (μas) image, with links to additional information in the description.
TEDx Talks (published Dec 7, 2016) via Phys.org — Scientist superstar Katie Bouman designed algorithm for black hole image
“I’m so excited that we finally get to share what we have been working on for the past year!” the 29 year-old Bouman, a postdoctoral researcher at the Harvard-Smithsonian Center for Astrophysics …
In 2016, Bouman developed an algorithm named CHIRP to sift through a true mountain of data gathered by the Event Horizon Telescope project from telescopes around the world to create an image.
“No one algorithm or person made this image,” wrote Bouman, who in the fall will begin work as an assistant professor at the California Institute of Technology (Cal Tech).
“It required the amazing talent of a team of scientists from around the globe and years of hard work to develop the instrument, data processing, imaging methods, and analysis techniques that were necessary to pull off this seemingly impossible feat,” she said on Facebook.
SciShow Space Channel (published on Apr 19, 2019)
Host: Hank Green
Description: For the first time ever we have visual confirmation that black holes actually exist and we got it with a telescope the size of our planet.
In astronomy angular resolution refers to the ability to see two objects that appear close together in space as their own distinct sources. But it really just comes down to how much detail you get into an image, and there are really only two ways to improve it: One is to study light that has a shorter wavelength; the other is to make your telescope bigger — specifically increase its collection area or the size of whatever it uses to collect light.
So to study a black hole like this astronomers are interested in radio wavelengths of about one millimeter, but there’s a catch at those wavelengths — the telescope you need to resolve a black hole would have to be like as big as a planet.
So the EHT collaboration came up with one they turned the entire earth into a telescope …
Here’s a weird thing about telescopes — you could take a bunch of small ones spread them out and get computers to link them all up and pretend to have a telescope that’s as big as the distance between them and this actually works. You get gaps in the images but the same amount of resolution. This technique is called interferometry.
They collected petabytes worth of data which was flown on hard drives to supercomputers in the US and Germany to be processed into a picture, which requires the programs not to just stitch together separate images but eliminate all of the noise coming from stuff that’s not the black hole, and then to fill in all the gaps due to us not having a single telescope dish the size of a planet.
Filling in those gaps is kind of like inferring the melody of a well-known song when you can only hear some of the notes, but it might be difficult to narrow it down to just one song — that’s why the EHT didn’t produce just one image. Initially there were actually four. Four separate teams worked independently from one another to produce the first images to avoid potential bias. They used two different classes of algorithms, but in the end they all came out relatively the same. Most importantly you can see the shadow in the middle of all of them that proves their techniques were working.
After some more refinement the now-famous final image was made by averaging three different processing methods …
In the future there are several ways to improve images like these: 1. One is to simply look at the object for longer (the collaboration observed M87 star over four nights between seven and twenty five times each night collecting data for just three to seven minutes apiece). 2. Another is to collect data at other wavelengths of light which will require upgraded technology with faster processing speeds. 3. We could also add in more telescopes as well as add ones that have larger collecting dishes …
Example: Why is the image blurry?
With current technology, that’s the highest resolution achievable. The resolution of the Event Horizon Telescope is about 20 microarcseconds. (One microarcsecond is about the size of a period at the end of a sentence if you were looking at it from Earth and that period was in a leaflet left on the moon, according to the Journal of the Amateur Astronomers Association of New York.)
If you take an ordinary photo that contains millions of pixels, blow it up a few thousand times and smooth it out, you’ll see about the same resolution as seen in the black hole image, according to Geoffrey Crew, the vice chair of the Event Horizon Telescope.
TED.com Video: “Inside the black hole image that made history” — a conversation with Sheperd Doeleman, global team leader for the Event Horizon Telescope project.
Smithsonian Channel via Space.com: ” ‘Black Hole Hunters’ Shows Epic Chase to Capture First Images“
The one-hour documentary, called “Black Hole Hunters,” debuts today (April 12) at 9 p.m. EDT and at 9 p.m. PDT, depending on your time zone. It follows Harvard University astronomer Shep Doeleman and his team, which this week released the first images of a black hole, created using a networked set of telescopes called the Event Horizon Telescope (EHT).
“We can abstract away all of the astrophysics of the problem and really just think of it as a purely computational imaging problem. We have these sparse, noisy data, and our challenge is to find the image that actually caused it.” — Katie Bouman, Caltech Magazine, Summer 2019
Wiki: Photon sphere
A photon sphere is a spherical area or region of space where gravity is strong enough that photons are forced to travel in orbits. The radius of the photon sphere—which is also the lower bound for any stable orbit—is, for a Schwarzschild black hole …
Very-long-baseline interferometry (VLBI) is a type of astronomical interferometryused in radio astronomy. In VLBI a signal from an astronomical radio source, such as a quasar, is collected at multiple radio telescopes on Earth. The distance between the radio telescopes is then calculated using the time difference between the arrivals of the radio signal at different telescopes. This allows observations of an object that are made simultaneously by many radio telescopes to be combined, emulating a telescope with a size equal to the maximum separation between the telescopes.
Multi-messenger astronomy is astronomy based on the coordinated observation and interpretation of disparate “messenger” signals. Interplanetary probes can visit objects within the Solar System, but beyond that, information must rely on “extrasolar messengers”. The four extrasolar messengers are electromagnetic radiation, gravitational waves, neutrinos, and cosmic rays. They are created by different astrophysical processes, and thus reveal different information about their sources.