M87 is a huge galaxy over 50 million light years away with approximately one trillion stars, but these facts are not the most interesting part about the galaxy. A photo taken through the 10” telescope in our observatory shows a jet surging out of the core of the galaxy. For years, astronomers have noticed the jet and theorized what might be causing it. The best guess was a black hole spewing out a supersonic jet of particles. In 2019, astronomers used large radio telescopes separated by thousands of miles to simultaneously look at the core of M87 where the jet appeared to be coming from. This super powerful combination of telescopes was named the Event Horizon Telescope (EHT). After observations that filled up a half ton of hard drives with about 5,000 terabytes of data, the most practical way to get the data to processing centers was definitely not e-mail, or the internet. The hard drives were shipped by plane, then the data extracted and processed into an image of unprecedented resolution. In the heart of it was what clearly appeared to be a black hole. It was named M87. This was the first photograph ever released of a black hole event horizon.
Our galaxy, the Milky Way, has its own peculiarities at its heart. Stars are orbiting around an area near the center, at unusually high speeds, with no visible anchor for their orbits. Astronomers were also noticing blasts of radio waves coming from the area. They presumed there must be a black hole there with a mass 4 million times greater than the Sun. They even gave it a name before they saw it, Sagittarius A. On May 12, 2022, the EHT astronomers released an image of Sagittarius A. It appears to be over 14 million miles in diameter, or 17 times the diameter of the Sun. It would be easy to see if it were close by. The problem is that it lies about 26,000 light years away. So, looking at it is the equivalent of seeing a donut on the Moon 240,000 miles away.
Getting a usable photo of the Milky Way black hole was more difficult than the process of getting a photo of M87. Gas orbits around the event horizon of a black hole at speeds close to the speed of light. M87* is large enough that it takes from days to weeks to orbit but the time it takes for gas to orbit Sagittarius A* is just minutes. The image was being blurred as it was being collected on the radio telescopes’ sensors. The final image is an average of what was seen during the imaging run.
The matter, or stuff, of the black hole itself is not seen in the image since it’s always cloaked in darkness. The size of a black hole is usually considered to be the area from which light cannot escape. Any light or piece of matter that falls inside this region is on an irreversible, one-way path to the center of the black hole. The edge of that region is called the event horizon. No one knows what happens inside that area. Despite the recent discoveries, the really interesting things are still cloaked in mystery.
Editor’s Note: In astronomy, a feature with* after the name is a black hole at the center of a galaxy and is pronounced “star.” e.g. “M87*” reads, “M87 star.”
