Supermassive black hole in center of galaxy

By Casey Frye, CCNN Writer

Milky way
The Milky Way.

Recently, researchers from the University of Massachusetts Amherst made a breakthrough discovery: they figured out why the supermassive black hole in the center of the Milky Way – the Sagittarius A – spits out around 99% of the matter it eats! I couldn’t really understand why this was such big news, so I did a little research on black holes.

First, I had to learn about gravity! Hey, isn’t that the force that pulls you to the Earth and keeps you from floating away? It is, and in fact, all matter in space exerts this same pull effect. However, the more dense the mass, the stronger that gravitational pull. As for black holes, they are regions in space where the gravity is so strong, not even light can escape from its clutches (hence the name black hole)!

They tend to form where a lot of matter is crammed into a tiny space, becoming incredibly, super-duper dense! Sometimes, black holes form when a star runs out of energy, and can no longer keep itself hot. So, instead of twinkling brightly in the night sky, it sort of collapses on itself and becomes dense enough to make a black hole. Other times, black holes are formed in the center of a galaxy where there is a ton of material collapsing together, and they create what is known as supermassive black holes.

As you can imagine, it’s pretty difficult to see something black in the sky, so how do astronomers detect them? Well, gas in the surrounding area gets funneled into a disk around the black hole by gravity. The gas molecules spin faster and faster around it, until finally, they start to heat up! They get so hot, in fact, that they produce X-rays, which can be detected from Earth.

black hole sun
Black hole slurps up a delicious star.

Now, here’s where it gets strange. Astronomers were led to believe that black holes devour all gas and matter that cross their paths, but researchers recently discovered quite the opposite: black holes spit out 99% of the matter that flows towards them! In fact, the X-rays given off by the gas around the black hole was very faint, as if there was no gas spinning. This left astronomers wondering: why?

A team of researchers from the University of Massachusetts Amherst used NASA’s Chandra X-ray Observatory to crack the mystery. “Less than 1% of matter will be actually sacrificed for the freedom of 99% of gas,” said  Q. Daniel Wang, astrophysicist at the University of Massachusetts Amherst. “So, 99% of gas can escape from the capture of the black hole.” And why does this happen?

Well, apparently it has to do with the massive stars around the black hole and the fact that the starry material creates an atmosphere that’s too hot. Just think about the black hole as a sink and gas as water. When the water is cold, it just goes straight into the sink and down the drain. When the water is ultra hot, however, it becomes steam, and some of it escapes into the kitchen air instead of going down the drain.

Now, imagine water so hot that 99% of it escapes! That’s kind of what happens in the black hole. “The massive stars [around black holes] have extremely high winds associated with them and the winds are colliding and swirling at very high speeds, which make the gases in this environment very hot.” explained Wang.

black hole pic
Black holes spit out 99% of the materials they consume.

He’s basically saying that the colliding winds around black holes generate a ton of heat that makes gas really hot! What does this mean for the supermassive black hole in the center of our Milky Way? “We found that first, [Sagittarius A has trouble collecting] such gases. Second, the gases are too hot for the black hole to swallow. Instead it rejects about 99 percent of this super hot material, only letting a small amount in. This makes sense because the hotter the gases, the more difficult it is for the black hole to pull them in.”

This is kind of like the steam rising out of the sink instead of going into the drain! According to the astronomers, this phenomenon not only happens to the black holes in our galaxy, it might be going on with all black holes in the universe!

And that’s the whole mystery in a nutshell. Wow, I knew space was a strange celestial place, but who would have thought that there was extremely hot gas escaping the grasp of a supermassive black hole that light can’t even fight?

Images courtesy of NASA and Wikipedia.