Making of the image of the black hole at the center of the Milky Way

The Event Horizon Telescope (EHT) Collaboration has created a single image (top frame) of the supermassive black hole at the center of the galaxy, called Sagittarius A* (or Sgr A* for short), by combining images extracted from the EHT observations.

The main image was produced by averaging together thousands of images created using different computational methods—all of which accurately fit the EHT data. This averaged image retains features more commonly seen in the varied images, and it suppresses features that appear infrequently.

The images can also be clustered into four groups based on similar features. An averaged, representative image for each of the four clusters is shown in the bottom row. Three of the clusters show a ring structure but with differently distributed brightness around the ring. The fourth cluster contains images that also fit the data but do not appear ring-like. 

The bar graphs show the relative number of images belonging to each cluster. Thousands of images fell into each of the first three clusters, while the fourth and smallest cluster contains only hundreds of images. The heights of the bars indicate the relative "weights," or contributions, of each cluster to the averaged image at top. 

SI-168-2022