“If the speed of light is the highest attainable speed, why can’t it escape a black hole?”

First, a few words about the speed of light, which is indeed the fastest speed attainable through space.  How fast is it?

The speed of light: It's not just an engineering challenge - it's the law.

The speed of light is 299,792,458 meters per second.  That works out to about 186,000 miles per second.

Trying to go at or faster than light through space requires inventing exotic new mathematics that permit real number answers to equations that involve division by zero and square roots of negative numbers. If you can figure out how to do this sort of math, a Nobel prize is yours for the asking.

The speed of light is more than just a zillion times faster than we’ve ever been able to achieve with our technology, it’s also a fundamental constraint on everything – both matter and energy – in the universe.

So if nothing is faster than light, than how can a black hole “trap” light?

Light is trapped in black holes because black holes bend space itself.

All objects with mass curve the space around them.  Objects with little mass, such the Earth and Moon, only curve space a tiny amount, while objects with the mass of stars curve space a lot more. For a really massive object, like a black hole, the curvature of space they create in their vicinity is so severe that space is wrapped completely around itself.

Here’s a way to create a model of a black hole:

Take a sheet of paper.  That’s the universe.  To keep things simple, let’s declare that this is a one-dimensional universe, in that objects within this universe all exist along a single mathematical line and they can move in one direction only – left and right along that line.  In this 1-d universe there is no such thing as moving up and down on the paper, nor can you be anywhere except on the paper.

A one-dimensional universe. Everything exists on a straight line.

To get from the left side of the paper (we’ll call that point “A”) to the right side of the paper (we’ll call that point “B”) you have to move in a straight line on the surface of the paper.

Without massive objects being present, the 1-d universe lies completely flat, and the shortest route (indeed, the only route) between A and B is along that flat straight line.  So far so good.  The shortest path between two points in flat universe is along a straight line.

But what if you introduce a massive object, like a star, into your 1-d universe?

The mass of the star bends space itself.  You, living on the paper in this simplified universe, don’t see this curvature because your line of sight can only follow the line through space.  Seen with the benefit of having extra dimensions (as you are when you hold the paper) you see a straight line traveling on a curved piece of paper. Is the line still straight?  YES.  It’s the space itself that’s curved.

The line from A to B really is straight, it just travels through curved space.

In this 1-d universe imagining a jump from A to B without following the straight line is the equivalent of imagining a science-fiction jump through “hyperspace.”

What if the object on the line of your paper is so massive that it curves space completely around on top of itself?  What if point B were inside the region where the curvature of space exceeds 360 degrees?

Then you’d have a black hole.  Traveling along a straight line from A to B (as you must in this 1-d universe) you’d encounter a place where space had wrapped around itself and once you enter this region, no matter how fast you go, even at the speed of light, you can never leave.

That’s a 1-d black hole.

Once inside a black hole, you can't ever leave no matter how fast you're going.

Now try imagining a point in space where space itself has been curved on top of itself in all dimensions – left-right, up-down, forward-backward, and time itself.

Black holes capture light (thus making them “black”) because light is trapped within a region of infinitely inward-curving space.

In a real-world Black Hole, space curves on top of itself in all dimensions.

The term “mind-bending” seems appropriate, don’t you think?

I’ve heard that all galaxies have a black hole at the center. Does our galaxy have a black hole?

You heard correctly, Carina.  Astronomers have found evidence that all galaxies in the universe, including our own Milky Way galaxy, have Supermassive Black Holes at their centers.

A black hole of the type that most folks have heard about is the remains of a large star (considerably more massive than our Sun) that has reached the end of its life and has died in a spectacular explosion known as a supernova.

Black Holes come in a variety of sizes, including "Supermassive."

If the star-corpse that survives a supernova explosion has a mass greater than several times the mass of our Sun it will collapse under its own gravity and become a black hole. These “stellar” black holes have masses ranging anywhere from roughly four times the mass of our Sun up to about two dozen times the mass of our Sun.

Astronomers have directly observed large stars in high-speed (close to 1,000 miles per second) elliptical orbits swarming around an incredibly massive yet invisible object at the center of our Milky Way Galaxy that is closely associated with extremely powerful radio emissions – the classic hallmarks of a Supermassive Black Hole.

The Supermassive Black Hole at the center of our Milky Way galaxy has a mass that astronomers estimate to be about four million times greater than the mass of our Sun, but occupies a region of space smaller than our solar system.

A Supermassive Black Hole, as massive as 4 million Suns, sits in the star-packed center of our galaxy.

In galaxies where the Supermassive Black Hole is actively devouring stars and gas astronomers have found huge jets, hundreds of thousands of light-years long, of electrically charged subatomic particles that have been focused by the black hole’s powerful magnetic fields and blasted into space at a whisker less than the speed of light.  That’s right – Supermassive Black Holes are sloppy eaters – not everything that spirals toward the maw is swallowed. Some stuff headed for oblivion in a Supermassive Black Hole instead gets shredded into plasma, irradiated and then violently ejected from the galaxy.

Centraurus A (left) and M87 (right) are examples of galaxies displaying huge jets of subatomic particles that are being violently ejected from the Supermassive Black Holes at their centers.

Fortunately for us, the Supermassive Black Hole at the center of our galaxy, nearly 30,000 light-years from us, doesn’t appear to be gobbling stars at any great speed.

Not only have astronomers discovered that all galaxies appear to have Supermassive Black Holes at their centers, they’ve also discovered that these monster black holes are essential to galaxies taking the shapes that they do and being so good at making stars, which is a necessary first step in the creation of planets where folks like you and I can live.

Supermassive Black Holes: ubiquitous, mysterious, fantastically powerful, terrifying, and yet necessary (from a respectable distance) for life.