Our galaxy's black hole was too active; the first image went to the more distant M87
The galactic center black hole has small mass with matter taking only half an hour to orbit, changing appearance within a single night; M87's black hole weighs 6 billion solar masses and appears nearly static over the same observation period, making it easier to image.
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The argument · tap a timestamp to hear it
Black holes are not passive; they shape galaxies
Black holes were once treated as isolated cosmic oddities—after confirmation of their existence, people thought they were just ‘also something in the universe,’ unremarkable. But the host shows the opposite is true: black holes regulate galaxy shape, size, and the distribution of habitable zones. Nearly certainly, over the long term all matter eventually falls into black holes; they have shaped galaxies' past and determine their future.
— Jana LevinBlack holes are too small; Earth must become the mirror
A telescope's angular resolution equals observation wavelength divided by mirror diameter; without a larger mirror, you must use shorter wavelengths. Black holes are the smallest objects predicted by Einstein's theory of gravity, so the team was forced to push observation frequency to 230 gigahertz—never before used—while making the ‘mirror’ Earth-sized. Both constraints simultaneously approached their limits; this is why the project took twenty years to break through.
— Shep DolemanNo new instruments built; instead, borrowed every major radio telescope
The Event Horizon Telescope built no new instruments—instead, it convinced existing radio observatories at the South Pole, two sites in Chile, Mexico, two in Hawaii, two in Arizona, Spain, and France to temporarily install its own recording equipment, operated in ways these facilities were not originally designed for. After collecting data, the team left with the hard drives and told the sites the results only months later. Over years of producing incremental results, they gradually convinced each observatory to hand over the keys.
— Shep DolemanMass and distance coincided to make two black holes equally visible
The galactic center black hole weighs about 4 million solar masses at 27,000 light-years away with an apparent diameter of roughly 50 microarcseconds—like reading the date on a coin a Los Angeles friend holds while you stand in New York. M87's black hole weighs 6 billion solar masses but sits about 2,000 times farther away; the two factors exactly cancel, giving it nearly identical apparent size, allowing the same ‘Earth telescope’ to resolve both.
— Shep DolemanHeavier black holes are actually easier to photograph
The press conference's first black hole image was not our galaxy's Sagittarius A*, but M87, 55 million light-years away—surprising the reporters. Sagittarius A* has only 4 million solar masses; matter orbits it in half an hour, so its appearance changes within a single night of observation. M87 weighs 6 billion solar masses; the same physics takes much longer, so over one night it's nearly static and easier to reconstruct into a clear image.
— Shep DolemanFour silent teams seeing the same ring proved it was real
The team feared everyone staring at one image and mutually convincing themselves they saw a ring, so they split data to four independent groups that didn't communicate, each using different algorithms to reconstruct images. In July 2018, all four appeared in the Harvard Black Hole Initiative basement with results—all rings. Then they spent six months deliberately training algorithms without ring structures; the algorithm still reconstructed a ring, confirming the ring was real signal, not algorithm bias or human expectation.
— Shep DolemanNext goal: turn still black hole photos into moving video
The next-generation project aims to turn black holes from still images to moving video; the key is adding a station atop Mount Kilimanjaro in Tanzania to the existing sites in Chile, Mexico, Wyoming, and the Canary Islands—each added telescope multiplies connections and speeds reconstruction. Funding for the Canary Islands site is in place, and the team has summited Kilimanjaro twice to scout; they state clearly: if any local community objects, the answer is no, period. This is a hard requirement; they expect true video around the 2030s.
— Shep DolemanEliminate ‘not a black hole’ by testing alternatives against data
Black hole video is worth more than the image: tracking polarized light reveals the magnetic fields around black holes, testing how they eject high-speed jets. More crucially, the team is already combining Event Horizon Telescope observations with infrared data to set exclusion limits on ‘black hole mimickers’—compact objects with surfaces slightly larger than the event horizon that would theoretically glow in infrared—gradually eliminating alternative explanations beyond general relativity.
— Shep DolemanIn their own words · checked verbatim
black holes are remarkably elegant, clean, simple systems.
Shep Doleman1:05
that they're the darkest phenomenon in the universe. They figure out a way to become the brightest beacons that we see on the edge of what's observable.
Jana Levin2:07
So we split our teams up into four groups. Each group had the data, but they could not talk to each other.
Shep Doleman38:19
And the four teams put up their images, and they were all rings. That was a moment where there was a lot of crying and screaming.
Shep Doleman39:20
I live for putting steel on mountaintops.
Shep Doleman45:51
no is an acceptable answer, full stop.
Shep Doleman46:52
If it's spinning maximally, the fastest it can ever spin, you see the same ring, but it's just about 4% smaller.
Shep Doleman47:55
the ability to coax this image from the black hole when it does everything in its nature not to be seen is really special
Shep Doleman54:08
Figures
| EHT formally established as institution | 2016 | 20:39 |
| Sagittarius A* mass | approximately 4 million solar masses | 26:52 |
| Sagittarius A* event horizon angular diameter | approximately 50 microarcseconds | 26:52 |
| M87 black hole mass | approximately 6 billion solar masses | 27:57 |
| M87 distance from Earth | 55 million light-years | 27:57 |
| Team size | 250 people | 36:11 |
| Sagittarius A* orbital period | approximately 30 minutes when not spinning; approximately 4 minutes at extreme spin | 48:56 |
Glossary
- VLBI (Very Long Baseline Interferometry)
- Using atomic clocks to synchronize signals from multiple global radio telescopes and synthesize them, equivalent to creating an Earth-sized telescope.
- event horizon
- The boundary around a black hole beyond which light cannot escape; the observable outline of a black hole.
- black hole mimicker
- A hypothetical compact object with a solid surface slightly larger than an event horizon that exhibits black-hole-like gravity but would theoretically glow in infrared.
- frame dragging
- The general-relativistic effect of a spinning black hole dragging the surrounding spacetime with it, used to measure black hole rotation.
How to listen
Astronomy enthusiasts interested in black hole imaging and large international research collaborations; scientific administrators; anyone curious about the next-generation ‘black hole movie’ project.
The first minute is an ad snippet from another podcast and can be skipped.