# The Event Horizon and Black Holes in Space

## Black Hole Powered Spiral Galaxy

A black hole is a place in space where the gravitational field is so powerful that nothing, not even light, can escape. It's interior is invisible. The Hubble telescope in space took the pictures you find here. What is visible are the movements of the stars, spinning into the vortex that a black hole creates.

To give you an idea: a black hole's escape velocity exceeds the speed of light.

• 299,792 kilometers per second -or-
• 186,282 miles per second

That's how fast you would have to go in the direction of "UP!" in order to escape the gravitational pull of a black hole.

The earth's escape velocity is:

• 11 kilometers per second -or-
• 7 miles per second

One of the most fascinating aspects of a black hole and maybe its defining feature is THE EVENT HORIZON .

It is a boundary of space-time beyond which events can't affect an outside observer.

To understand this better: The presence of mass deforms space/time in such a way that the paths particles take is towards the mass.

At the event horizon of a black hole, this force, this deformation of the space-time continuum, is so great, so strong, that there are no more paths away from the black hole.

So once something is inside the event horizon of a black hole, moving into the hole is as inevitable as moving forward in time, and is, in some respects, the equivalent of doing so. To a far observer, a clock would appear to tick more and more slowly going towards a black hole. This effect, known as gravitational time dilution, causes the object to appear to slow down as it approaches the event horizon, until it is going infinitely slow. (Or, rather, time is going infinitely slow, approaching the event horizon of a black hole, because the object approaching the event horizon is approaching the speed of light. It goes faster and faster as the gravitional pull of the black hole becomes stronger and stronger, and as it approaches the speed of light, time appears to slow until it's stopped.)

We think of time as an absolute. So, imagine a clock, an alarm clock sitting on a dresser. This clock has a loud tick, at the rate of one tick per second. This clock decides to go out and explore space. It leaves the earth's gravity going along pretty quickly--at the rate of 7 miles per second. This is one speedy clock. But wait! The clock is approaching the center of the Milky Way Galaxy where there's a black hole! Uh-oh! The clock keeps going faster, and faster, approaching the speed of light, at 186,282 miles per second. It's approaching the event horizon of the black hole at the center of the galaxy. The ticks of the clock get slower, and slower, and slower...as it approaches the event horizon, but the whole clock itself is moving faster and faster, being sucked in by the black hole. We, observing from the outside, appear to see the clock stop.

That's because time is an artificial measurement created by human beings according to the earth's rotation towards, then away from, the sun. In the beginning, there were no hours, minutes, seconds...there were days, nights...changes of seasons, according to the earth's rotation on its axis and revolution around the sun--the giver of light. We measure time by light. When an object approaches the speed of light, time slows...time even appears to stop, at the event horizon of a black hole. The object appears to stop--but it hasn't. It is moving faster than the speed of light into the enormous field of gravity of the black hole.

## The Singularity

The center of a black hole is the most amazing feature of all: THE SINGULARITY .

This is where matter is crushed to an infinite density, the pull of gravity is infinitely strong, and space/time has infinite curvature. It means the black hole's mass has become entirely compressed into a region with zero volume. This zero-volume, infinitely compressed, infinitely dense region at the center of a black hole is called a gravitational singularity .

The mass of a black hole is not infinite. It is infinitely dense, infinitely compressed, but there is a determinate amount of mass.

Black holes found at the center of galaxies have a mass equal to several billion of our suns and are called supermassive black holes. The black hole singularity still has no volume, but it has a hugely (infinitely) dense mass that creates a gravitational field that sucks in surrounding stars. There is a black hole at the center of most galaxies, including ours, and there may be a black hole at the center of all galaxies. That fact has yet to be determined.

Stellar black holes are formed when a large star (20 or 30 times as large as our sun) undergoes gravitational collapse. This happens when the internal pressure of the star's core is insufficient to withstand the star's own gravity. The star goes out in a supernova blaze of glory, and what's left is a remnant, a compact star. The supernova state has burned off quite a bit of the mass, and if the remnant of the resulting compact star has a mass of three or four times that of our sun, not even the degeneracy pressure of neurons is sufficient to alter the continuous collapse of the matter of the star into becoming a black hole.

## Dust Disk around a black hole at Galaxy NGC 4261

Black holes can grow.  Once a black hole is formed, it can continue to grow, absorbing light, radiation, interstellar dust.  The supermassive black holes at the centers of most (or all) galaxies were formed from the accumulation of many galactic objects--stars, moons, planets, comets; anything that came within the growing range of the orginal collapsed star's EVENT HORIZON.

Black holes can shrink, at least according to Stephen Hawking.  He showed that black holes aren't entirely black.  They emit very small amounts of thermal radiation.  If Dr. Hawking's theory of black hole radiation is correct, then black holes will lose mass over time, in proportion to the energy released by the radiation.  (e=mc(sqared)).

If Dr. Hawking's theory, which is now accepted science, is correct, than a black hole the weight of an automobile (but remember, with NO VOLUME!) would only take a nanosecond to evaporate, during which time it would be 200 times brighter than our sun.

The large accretion disks and gas jets are evidence of the supermassive black holes at the center of the galaxies within our range.  The only mass large enough to power these enormous phenomena is a black hole.

## More by this Author

Paradise7 4 years ago from Upstate New York Author

Mine, too! thanks for the comment.

Caleb DRC 4 years ago

Your thorough and lucid writing made the understanding of Black Holes much easier. All this time I thought a Black Hole was my wallet, but now I know differently. GREAT JOB!

Paradise7 5 years ago from Upstate New York Author

Thanks for visiting this hub, DDS. It's one of my personal favorites. I thought I did a good job, putting a hard concept into fairly simple language. It is just a little creepy--it's hard to get your mind around!

DDS 5 years ago from Toronto

interesting, awes inspiring and just maybe a little creepy.

Tony L Smith 5 years ago from Macon

Nice study Paradise7, I'm probably going to have to read it again soon, kinda think there is golden truth nuggets that are parallels to this.

thanks for sharing

Paradise7 6 years ago from Upstate New York Author

Thank you, Sukhera and Sam for your comments. That's interesting, Sam, that you wrote a book on a science topic when you are a graphic artist. It must be the artistic imagination which makes these subjects so fascinating to us.

SamAntone 6 years ago

Wow! Did you say you were a bookkeeper? You sound like a rocket scientist! And a good writer, at that. I'm a graphic artist, but do physics from an arm-chair. In other words, I'm an armchair physicist. I wrote a book containing a description of how matter was created from nothing. Quite a feat for an artist, though I'm sure I took quite a few liberties.

sukhera143 7 years ago from Home

Nice sharing.

Paradise7 7 years ago from Upstate New York Author

Thank you, Info Help. I'm proud of this one. It was more engrossing, more intense, and a little more difficult to write, but I thought the effort was worth it.

Info Help 7 years ago from Chicago

This hub is fascinating! Great job on the thorough research, the pictures are amazing! I have heard of the event horizon but, never really understood it until now. Thanks!

Paradise7 7 years ago from Upstate New York Author

You're entirely welcome, myownworld, and thanks for reading!

myownworld 7 years ago from uk

Brilliant! you've explained the black hole phenomenon so well that I just wanted to go on reading...the pictures are fascinating too, so thank you for sharing!

Paradise7 7 years ago from Upstate New York Author

Thanks, Jaspal. I liked writing this. I think I should have named this hub, The Black Hole, or something like that. When I first got fascinated it was with the event horizon--the place where time stops!

Jaspal 7 years ago from New Delhi, India

Wow, you've explained the black hole so well and in fairly layman language. Great hub and super pics!

Paradise7 7 years ago from Upstate New York Author

Thank you all for your gracious comments, and I'm very glad you enjoyed this hub. I had quite a time writing it, but was pretty pleased with the final results--and here's the pay off, that you've come to visit and liked it, too!

creativeone59 7 years ago from Gold Canyon, Arizona

Wow, that was a very enlightening hub about the black hole, thank you for sharing it. creativeone59

Veronica Allen 7 years ago from Georgia

I'm with Catherine R, I have often found the detailed explanation of the black hole a little difficult to understand, but how you explained helped a little. I'll have to bookmark it and come back to read it. I do however appreciate how you compared the immense power the black hole has in comparison to earth,s most powerful star - the sun! That really helped explain the information much better. I love the pictures by the way, the visual helps as well.

dohn121 7 years ago from Hudson Valley, New York

I absolutely loved the photographs you posted here (you could say that they're out of this world?! = grandpa joke) I really learned a lot from reading this, including the speed in which you would need to be traveling in order to escape a black hole...I guess that only fictitious spacecraft would be able to escape one. Thanks, Paradise.

Oh, and congrats on Hub #50!!! That's quite an accomplishment! Have one on me :D

Paradise7 7 years ago from Upstate New York Author

Thank you both for the comments. I really had to bend my brain doing the research. I got a headache, even though it was all fascinating to me. I tried to boil it down without dumbing it down and think I did ok. I'm pretty proud of this baby. Thank you so much for reading it!

Catherine R 7 years ago from Melbourne, Australia

I think you have explained black holes brilliantly in this hub. I am no physicist and I can tell you that it it hard for my simple brain to grasp these concepts but I do feel that I am one step closer after reading this! Thank you so much.

lynnechandler 7 years ago

This is a really interesting hub. I love the pics especially the one of the cartwheel. You did a really good job on explaining the event horizon.