How We Know a Supermassive Black Hole Lurks in the Center of Our Galaxy

We live in a fairly massive galaxy called the Milky Way. Galaxies are collections of stars, gas, and dust. Our Sun, while very special to us, is just one of ~200 billion stars that make up our galaxy’s stellar collection. It’s a bit challenging to get a sense of what the Milky Way looks like. Why? Because we're sitting inside it. (Imagine trying to take a picture of your house from inside your bedroom.)

Our Sun, while very special to us, is just one of ~200 billion stars that make up our galaxy’s stellar collection.

But we think our galaxy is shaped like a disk or frisbee with what we call a "bulge of extra material" at the center. And lurking in the center of that bulge is what we believe to be a supermassive black hole.

What is a black hole?

A black hole is something so compact, so dense that not even light, the fastest-traveling thing we know of, can escape the pull of its gravity. Technically, anything can be a black hole as long as you compress it enough. That means you, your couch, and even your apartment would all become black holes if we squeezed them down small enough.

You, your couch, and even your apartment would all become black holes if we squeezed them down small enough.

The Earth, which is just shy of 8,000 miles across, would be a black hole if we compressed it to 1.8 centimeters across —about the size of a penny. To turn the Sun into a black hole, it would have to be compressed down to about 6 km. That’s an incredible amount of mass shoved into a space that's only a little more than half of that charity 10k race I ran pre-pandemic, which took only an hour to finish. 

Who discovered black holes?

In the 1700s, a man named John Michell theorized there could be dark stars, or stars so dense that even light could not escape them. Michell is described as a philosopher and a clergyman. The American Physical Society notes that he was "so far ahead of his scientific contemporaries that his ideas languished in obscurity until they were re-invented more than a century later.”

Now, haven’t we all felt like that at some point? No one seems to appreciate how brilliant my ideas are—I’m ahead of my time! 

How are black holes formed?

We now understand fairly well how some of these dark stars form: through the collapse of massive stars nearing the ends of their lives. A star that’s more than 20-30 times the mass of our Sun will spend tens of millions of years battling the crushing weight of its gravity, mostly by converting mass into energy through fusion. But eventually, gravity wins and the...

Keep reading on Quick and Dirty Tips