• This artist's concept illustrates a supermassive black hole with millions to billions times the mass of our sun. Supermassive black holes are enormously dense objects buried at the hearts of galaxies. (Smaller black holes also exist throughout galaxies.) Image credit: NASA/JPL-Caltech.

Black holes: Space's Biggest Mystery

Looking for a true adventure? If you’re not worried about whether you’d return or not, I can suggest a very unique place: a black hole.  

Black holes are some of the most fascinating objects found in outer space. We have no idea what happens once you’re in one. We cannot directly see them. But if you ever had the chance to get close to one, you’d definitely feel it.

Black holes are regions of spacetime with incredibly strong gravitational effects. Their gravitational pull is so strong that any objects or particles--even light--cannot escape.  That’s why they are really, really black. So black no one actually knows what they look like!

We can observe how gases swirl around these regions at nearly the speed of light, giving off lots of high-energy radiation.  And any light passing close to them also bends. These observations helps us detect them. 

About 100 years ago, Albert Einstein first predicted black holes with his famous theory of general relativity. American astronomer John Wheeler coined the term “black hole” before the first black hole was discovered in early 70s.  

If you think of a normal hole in the ground, your mind probably focuses on its’ emptiness, or absence of matter. Black holes are, in fact, the opposite of empty.  They have more matter stuffed into less space than any other object in the universe. If our sun were somehow compressed enough to become a black hole, it would span fewer than 6 kilometers (3.7 miles) across.

So why even name them black holes if they’re actually extremely dense bodies of matter? Well, black holes act like holes in the sense that things around it, like stars, “fall” into them. 

With a crazy amount of gravitational force, black holes swallow dust and gas from the galaxy around them, growing in size.

Supermassive black holes are millions or even billions of times as massive as the sun, but have a radius similar to that of our sun. Such black holes are thought to lie at the center of pretty much every galaxy, including our own the Milky Way.

What actually happens when you actually fall into a black hole is still an interesting area of speculation and study. But don’t worry; no human is likely to fall into a black hole anytime soon. 

The closest black hole we know of is V616 Mon. It's located about 3,000 light years away, and has between 9-13 times the mass of the sun. For comparison, Voyager 1—the farthest human-built probe—is a less than 20 light-hours away. 

The closest supermassive blackhole is in the middle of our own Milky Way, located about 27,000 light-years away.  All supermassive black holes are really far away, so we don’t really have to worry. 

Regardless of how far away these mysterious objects are, the magic of space, of nature really, is that they still make us wonder: How does the universe work? What do these beautiful and distant objects tell us? One lesson black holes might offer: the most powerful forces in our universe are still cloaked in mystery.

(Dr. Yadav Pandit is an experimental nuclear physicist currently working at Allen Community College as a physical science instructor. He writes a column of general interest in science for The Register.)

All Image Credits: NASA.

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