Monday, March 19, 2007

Wormhole

Anyone who has more than a passing interest in science fiction will be aware of "wormholes". They linked the Stargates in the series (and movie) of the same name. They sucked John Crichton and Farscape 1 through to some "distant galaxy". They even appeared in some of the eleventy-billion episodes of Star Trek, putting the Gamma Quadrant in Deep Space 9's back yard. In other words, they're a standard response to the problem of covering interstellar distances. Intriguingly, they may actually exist.

A black hole is a produced when a particularly heavy star runs out of fuel and collapses in on itself. Every object exerts a force, called gravity, on every other object in the universe (although because it follows an inverse square rule, unless the object is particularly massive, or you're very close to it, that force is essentially negligible). In order to escape from an object's gravity, you need to be going very fast - and that speed, called the "escape velocity", is a function of the size and gravity of an object.

A black hole is black because it is so small and heavy that the escape velocity required to escape its gravityish grasp exceeds the speed of light. Because Einstein's theory of General Relativity says that nothing can travel faster than the speed of light (299,792,458 m/s), it is impossible for anything to go fast enough to escape from a black hole. At the centre of the black hole is a singularity, but the distance at which the escape velocity equals the speed of light is called the event horizon (no, not the movie), and it's impossible to see past the event horizon.

No one has actually seen a black hole (because, like space, it's black), but there are plenty of spots where effects are seen which are consistent with the presence of a black hole. But the research linked above suggests that a wormhole may actually produce an effect similar to a black hole, so what we think are black holes may actually been wormholes.

Wormholes essentially punch a whole through space, and may link two distant bits of space (or even time), so they may be a way to explore the galaxy. Or they may just rip your atoms into bits and turn you into singularity soup. So they may one day aide space travel, but much like the first person to eat an oyster, the first person to attempt to travel through a wormhole is going to be taking one hell of a leap of faith.

The article linked above suggests that the new generation of particle accelerators may actually be able to create tiny little wormholes, which may be able to be distinguished from black holes by the absence of Hawking radiation. It's times like this that I wish I was good enough at maths to have contemplated following a career in physics - instead of sitting here at a boring desk I could be creating black holes and laying the foundations to future human exploration of the universe (or possibly destroying the world - either is cool with me).
Originaly posted at Anyone who has more than a passing interest in science fiction will be aware of "wormholes". They linked the Stargates in the series (and movie) of the same name. They sucked John Crichton and Farscape 1 through to some "distant galaxy". They even appeared in some of the eleventy-billion episodes of Star Trek, putting the Gamma Quadrant in Deep Space 9's back yard. In other words, they're a standard response to the problem of covering interstellar distances. Intriguingly, they may actually exist.

A black hole is a produced when a particularly heavy star runs out of fuel and collapses in on itself. Every object exerts a force, called gravity, on every other object in the universe (although because it follows an inverse square rule, unless the object is particularly massive, or you're very close to it, that force is essentially negligible). In order to escape from an object's gravity, you need to be going very fast - and that speed, called the "escape velocity", is a function of the size and gravity of an object.

A black hole is black because it is so small and heavy that the escape velocity required to escape its gravityish grasp exceeds the speed of light. Because Einstein's theory of General Relativity says that nothing can travel faster than the speed of light (299,792,458 m/s), it is impossible for anything to go fast enough to escape from a black hole. At the centre of the black hole is a singularity, but the distance at which the escape velocity equals the speed of light is called the event horizon (no, not the movie), and it's impossible to see past the event horizon.

No one has actually seen a black hole (because, like space, it's black), but there are plenty of spots where effects are seen which are consistent with the presence of a black hole. But the research linked above suggests that a wormhole may actually produce an effect similar to a black hole, so what we think are black holes may actually been wormholes.

Wormholes essentially punch a whole through space, and may link two distant bits of space (or even time), so they may be a way to explore the galaxy. Or they may just rip your atoms into bits and turn you into singularity soup. So they may one day aide space travel, but much like the first person to eat an oyster, the first person to attempt to travel through a wormhole is going to be taking one hell of a leap of faith.

The article linked above suggests that the new generation of particle accelerators may actually be able to create tiny little wormholes, which may be able to be distinguished from black holes by the absence of Hawking radiation. It's times like this that I wish I was good enough at maths to have contemplated following a career in physics - instead of sitting here at a boring desk I could be creating black holes and laying the foundations to future human exploration of the universe (or possibly destroying the world - either is cool with me).
Anyone who has more than a passing interest in science fiction will be aware of "wormholes". They linked the Stargates in the series (and movie) of the same name. They sucked John Crichton and Farscape 1 through to some "distant galaxy". They even appeared in some of the eleventy-billion episodes of Star Trek, putting the Gamma Quadrant in Deep Space 9's back yard. In other words, they're a standard response to the problem of covering interstellar distances. Intriguingly, they may actually exist.

A black hole is a produced when a particularly heavy star runs out of fuel and collapses in on itself. Every object exerts a force, called gravity, on every other object in the universe (although because it follows an inverse square rule, unless the object is particularly massive, or you're very close to it, that force is essentially negligible). In order to escape from an object's gravity, you need to be going very fast - and that speed, called the "escape velocity", is a function of the size and gravity of an object.

A black hole is black because it is so small and heavy that the escape velocity required to escape its gravityish grasp exceeds the speed of light. Because Einstein's theory of General Relativity says that nothing can travel faster than the speed of light (299,792,458 m/s), it is impossible for anything to go fast enough to escape from a black hole. At the centre of the black hole is a singularity, but the distance at which the escape velocity equals the speed of light is called the event horizon (no, not the movie), and it's impossible to see past the event horizon.

No one has actually seen a black hole (because, like space, it's black), but there are plenty of spots where effects are seen which are consistent with the presence of a black hole. But the research linked above suggests that a wormhole may actually produce an effect similar to a black hole, so what we think are black holes may actually been wormholes.

Wormholes essentially punch a whole through space, and may link two distant bits of space (or even time), so they may be a way to explore the galaxy. Or they may just rip your atoms into bits and turn you into singularity soup. So they may one day aide space travel, but much like the first person to eat an oyster, the first person to attempt to travel through a wormhole is going to be taking one hell of a leap of faith.

The article linked above suggests that the new generation of particle accelerators may actually be able to create tiny little wormholes, which may be able to be distinguished from black holes by the absence of Hawking radiation. It's times like this that I wish I was good enough at maths to have contemplated following a career in physics - instead of sitting here at a boring desk I could be creating black holes and laying the foundations to future human exploration of the universe (or possibly destroying the world - either is cool with me).
originaly posted at
http://thekillfile.blogspot.com/2007/04/wormhole-extreme.html

Thursday, March 15, 2007

FALLING CLOUDS

Clouds are made of water droplets, and water is about 800 times denser than air. Why don't clouds fall like a rock to the ground?

Friday, March 9, 2007

Cup of tea

When you finish stirring sugar into your cup of tea the water comes to rest in a few seconds. Is the decay of the water's rotation caused primarily by the walls of the cup or by its bottom?

Sunday, March 4, 2007

1300 blackholes


Every dot of light in that image is a black hole, hundreds of millions and even billions of light years away. Before you say, "Say wha?", this will take some explanation.

The black holes themselves are black (duh). But as matter falls into them, it can settle into a disk, called an accretion disk. If you remember your college physics — you did take college physics, right? — as something falls into a black hole, it acquires a huge amount of kinetic energy (for you pedants, it actually converts gravitational potential energy to kinetic energy). Think of it this way: when you hold a rock up over the ground, it has potential energy– the potential to move due to gravity. When you let go, that potential energy becomes kinetic energy– the energy of motion. If you don’t think it has energy, then let it hit your toe. The kinetic energy will be converted to a loud crunching sound, and you will potentially have to go to the hospital.

So matter falling into gravity can gather energy, and matter falling into a black hole can get a lot of energy. This is converted to motion and heat, and as the matter piles up into the accretion disk it gets terribly, terribly hot: as hot as millions of degrees. There are also associated magnetic fields and other forces which can make the matter in the disk light up, getting it extremely bright. The bigger the black hole, the brighter this disk can get.

Astronomers think that in the center of every big galaxy there is black hole with millions or even billions of times the Sun’s mass. Guess how bright they can get?

Answer: pretty damn bright. In fact, as long as they are actively feeding, black holes like this are the brightest sustained objects it the Universe. We call them "active galaxies". They’re so bright they they can be spotted when they are billions of light years away. And hey, didn’t I say that the spots in the image above were at that distance?

Yes, good! You’re paying attention. The image at the top of this entry is from the orbiting Chandra X-ray Observatory — it’s only one part of a bigger image revealing 1300 black holes at the centers of galaxies.

When matter gets heated to millions of degrees, it gives off X-rays, so Chandra is a great telescope to spot black holes, especially the supermassive monsters in the centers of galaxies. We’re still trying to figure out just how many galaxies are active, and how many are quiescent like the Milky Way (our central black hole has 4 million times the mass of the Sun, but is not currently feeding, so it’s not active).

Also, we’re not completely sure what the structure of the accretion disk is like near a hole. The current theory is that near the black hole it’s very flat and thin, but farther out it puffs up into a torus or doughnut (or bagel if you’re from New York City). But think about this: imagine putting a pea in the center of a donut hole. From most viewing angles, the pea is hidden. If you view it face-on you can see the pea, but at an angle the donut blocks your view. From edge-on you’re looking through a lot of doughnut and can’t see the pea at all.

This model explains a lot about what we see with these active galaxies, but is it right?

Maybe. Maybe not.

The new observations from Chandra are very interesting. If we see a black hole torus face-on, we expect to see X-rays of all energies, since they are free to get to us. But if we see one edge-on, only the highest-energy X-rays can penetrate the obscuring torus, so we’d expect to see only those high-energy X-rays and no low energy ones. So, looking at 1300 black holes as Chandra did, you’d expect to see a few that are face-on, a few edge-on, and most ranging in between. In other words, the observations should show most black holes sending out a mix of high and low energy X-rays.

Oops. They didn’t. They reveal lots of high-energy-X-ray-emitting-galaxies, and lots of low-energy-X-ray-emitting-galaxies, but very few in between, the opposite of what the model predicted.

Does this mean the model is completely wrong? No, because in fact the model does very well predicting what we see from black holes in a whole bunch of other obsrevations, hundreds and even thousands of them. So what these new data really mean is that the details of the model need to be worked on more. Maybe in active galaxies the torus doesn’t puff up as much. Maybe the disks are bigger than we thought, or there isn’t as much dust in the torus, or a hundred other reasons.

The devil, that rascal, is always in the details. And if there is any actual place in the Universe that could be described as Hell, it’s the gaping maw of a black hole and the swirling maelstrom surrounding it. So there will always be devilish details to hammer out.

One final note: these active galaxies can pour out gamma rays as well– gamma rays have even higher energy than X-rays. NASA and the Department of Energy are building GLAST, an observatory whose main mission is to investigate these supermassive black holes (I’ve written about GLAST several times). It’s due for launch in November, so by this time next year we’ll have a lot more data, and a lot more answers. But we’ll have a lot more questions, too! This is truly the game that never ends, which is one reason it’s so much fun.

Originally posted at http://www.badastronomy.com/bablog/2007/03/12/1300-black-holes/