In 2019, the first ever image of a black hole was taken using the Event Horizon Telescope (EHT). Gas has been seen swirling around the black hole at the center of the Messier 87 (M87) galaxy, among other features astronomers have theoretically predicted. While the image is being hailed as historic, it’s very blurry and doesn’t provide the intricate details of the black hole. Now, astronomers have recreated this image to reveal a previously unseen ring of photons from the black hole.
The black hole in the galaxy M87 receives light from nearby gas, which also includes radio light. When a beam of light passes close to a black hole, it tends to change direction due to the warping of space-time. This deflection of light has been observed in stars and galaxies, but in the case of black holes, the bending of light is even more dramatic.
As light passes through the vicinity of a black hole from all directions, only the light focused on us is visible. Astronomers have observed that black holes can act as powerful lenses that can focus light in our direction. According to this theory, when light hits us, we should see a thin halo called a halo.
However, this photon ring is not visible in the landmark photo. This may be due to the material blocking the light path. When light passes through regions of cold gas, it tends to scatter, which causes blurry images.
In the new study, the team realized that there were actually two photos in the EHT data. One is a ring of photons and the other is a blurred glow of the surrounding area. They used an algorithm to peel back the layers of the image and reveal the photon rings.
The new observations are published in a paper in The Astrophysical Journal.