Early January is the time when thousands of astronomers get together for the winter American Astronomical Society meeting. It’s a chance to catch up on the latest and greatest astronomy discoveries and talk shop about things like black holes and stars and galaxies. As a member since 1992, I’ve been happy to attend those meetings . I go to partake of what we often refer to as “the firehose of astronomy information.”

Well, as you might guess, the ongoing COVID-19 pandemic has put a stop to those meetings for the time being. We came this close to having an in-person meeting this week in Salt Lake City. However, the humongous rise of infections due to the omicron variant of COVID-19 (and the continuing wave of delta infections) forced the meeting’s cancellation. But, it hasn’t stopped the flow of information. And, for that, I’m grateful—because there’s a LOT out there to talk about! And, as usual, black holes take center stage for at least part of the meet ing.

Astronomy and its Changing View of Black Holes

Back when I first studied astronomy, these cosmic monsters were not yet observed. Sure, people thought they might exist; they had theoretical and mathematical underpinnings as far back as the early 20th century. But, for a long time, nobody found them.

In one of my oldest textbooks, the writer devoted only one or two paragraphs to the possibility of such things actually existing. And, that’s entirely understandable. There wasn’t evidence or data for black holes, and thus, not much to say.

Today, we find them across the universe. Astronomers have managed to get at least one very detailed image of the region around a distant supermassive black hole. And, they’ll get more.

So, we have a LOT to say about them. So, what changed? We got more data about them, from actual observations. However, it turns out that you don’t really look directly at a black hole and detect it through an optical telescope. Nope.

Astronomers have to find them using indirect means. They look for high-energy radiation (x-rays, radio waves) from the regions around black holes. Or, they look at the motions of stars and clouds of gas and dust in the region around a black hole. Or, they might also look for any gravitational lensing effect from the black hole.

Black Holes at AAS

One of the stories from the AAS press conferences (which are going on even though the meeting isn’t), is about the role that black holes played in a period of time called the Epoch of Reionization. This was an era when the infant universe was just starting to “light up”.

Prior to that the everything existed in a period called the “Dark Ages”. That’s when the universe was a dense “fog” of primordial gas (mostly hydrogen). As that gas began to clump together, the first galaxies formed and the first stars were born. But, their light had to get out through that fog. It turns out that the earliest black holes could have played in an import role in this reionization process. Their extreme radiation may have punched holes in the cosmic “fog” of hydrogen. That allowed ultraviolet light from the earliest stars and galaxies to travel across the universe.

Now, we can’t see those early black holes. Their galaxies are too far away. But, astronomers have found a supermassive black hole inside a galaxy similar to the early ones. This black hole is quite powerful. If ancient supermassive black holes were anything like this one, then they could be part of what triggered the Epoch of Reionization.

Our Own Black Hole

Black holes at the hearts of galaxies aren’t just limited to the long ago and far away. They’re now pretty commonly known throughout the modern universe. This includes our own Milky Way. Its central, supermassive black hole lies about 26,000 light-years away from us. The object is named Sagittarius A* (or, Sgr A*, pronounced “Sadge A-Star” for short). It’s relatively quiet these days, but in the past, Sgr A* was much more active. It periodically gets busy and lights up its neighborhood as it swallows up stars and other materials that stray too close.

The evidence for that activity is found in clouds of gas (called “molecular clouds”). They lie at various distances close to Sgr A* and often “glow” in x-rays, emitted as the clouds get heated up by radiation streaming away from Sgr A. Essentially, whenever the black hole gets more active, that affects the surrounding clouds and they glow.

Science Moves Forward

These two stories (out of several being released) are really good examples of a concept called “Follow the science”. We’ve all heard it in relation to the ongoing COVID-19 pandemic. It’s as true for the black holes as it is for the scientists studying the virus. The more data we get about black holes, the more we learn about them and their activities. Astronomers now know these cosmic monsters played (and are playing) an important role in the evolution of the universe itself.

The same is true for the pandemic virus. The more we know about it, the more we can develop vaccines to counter it. (And, perhaps also convince people to GET those vaccines, wear masks in public, etc. to prevent an even more catastrophic spread of the disease it causes.

In terms of black holes, what we used to think about black holes is no longer as important as what we know now. And, it will be truly interesting to see what else we learn about them as astronomy progresses. That’s the role of science, whether its viruses or black holes: to progress, to teach us more about the universe in which we live.