Milky Way’s Black Hole, Sag A*, revealed in new image

Pamela L. Gay, Ph.D.
9 min readMay 13, 2022

Three hours before we were scheduled to record today’s episode of the Daily Space, the Event Horizon Telescope collaboration held a press conference with their latest results related to the super massive black hole in the center of our galaxy. Seven minutes later a slate of ten journal articles was published on these findings in the Astrophysical Journal Letters.

I am now going to try to summarize what I have so far been able to unpack from this trove of data, modeling, and interpretations.

First off — I want to say these results do not fundamentally change our understanding of anything. In the most assuring of ways, what was seen matched with what was expected.

Let’s start with some background.

When you go out and look at the night sky from a dark location, the sweep of the Milky Way passes through the now visible summer triangle of Cygnus, Lyra, and Aquila, and sweeps toward the equatorial constellation Sagittarius. If you have good skies and good eyes, you’ll see the band of the Milky Way thicken as it approaches Sagittarius’s teapot of stars, and that region where the Milky Way bulges out is the center of our galaxy.

Location of the galactic center in Sagittarius, using the Summer Triangle aphorism as a finding guide. Credit: Beth Johnson/Stellarium

The dust and gas that fills our galaxy’s disk forms nebula and star-forming regions that are stunning to explore with binoculars; but the same features that make this region beautiful also block our ability to see the center of our galaxy in the colors we can see with our eyes.

Going to either much longer or much shorter wavelengths allows us to pierce through this dust, and astronomers in the last century noticed a single point from which both high-energy X rays and low-energy radio waves were emitting. Following our tradition of naming things poorly, this object was cataloged as Sagittarius A* and over the decades, people have speculated that this monster in the Milky Way is everything from a swarm of dense objects to a singular massive black hole. As recently as the early 1990s, professors would simply sketch their favorite monster when they marked Sag A*s place in or galaxy on an overhead sheet.

In the 1990s, researchers Andrea Ghez and Reinhard Genzel led teams that combined high-speed (for astronomy) infrared images of the galactic center with a technique…

--

--

Pamela L. Gay, Ph.D.

Astronomer, technologist, & creative focused on using new media to engage people in learning and doing science. Opinions & typos my own.