Pudd's Questions On Everything Beyond The Atmosphere

[blackpudd1n]

So things just look like stars until they realise that they've moved? How do they take these photographs? And how do they know that we haven't moved, and not the other thing? 'Cause if we're always moving, then it'd be hard to take the picture in the same spot, right?

 

So things just look like stars until they realise that they've moved? Yes.

 

How do they take these photographs? Pretty much exactly how you would think: a camera (or light-sensitive CCD plate, like a big digital camera) hooked up to the end of a big-ass telescope.

 

And how do they know that we haven't moved, and not the other thing? They compensate for the motion of the earth around the sun and the rotation of the earth when they take the photographs to make sure that the stars in each exposure are in the same spot.

 

Thanks for the answers in both of the posts above- I think I need to chew on them for a bit. It sounds like a lot of maths, doing this stuff!

[darwinfish]

If you have some time, this is great: http://webcast.berkeley.edu/playlist#c,d,Astronomy,2AC754AEB6E21150

[Thurisaz]

I can't help wondering how every planet ended up suspended in their particular orbit. How did the planets come to be?

 

You know, this might sound silly, but I still have a little trouble with the concept of the planets and our entire solar system just being suspended in space. It's the sun that keeps them in that spot, right? Its gravitational pull? Its hard for me to understand, because the idea is like a different type of gravity to here on earth. On earth, if it goes up, it comes down again. But in my head the sun's gravitational pull is like sideways or something.

 

...Anyway, back to stars. Normally, atoms don't fuse (we do have fission nuclear reactors that rip big atoms apart, but haven't managed to make any usable fusion reactors that combine little atoms into bigger atoms), but with all that energy around in the early stars, they were doing plenty of that. Now, the activation energy required to start the process is pretty big, but the energy released is also huge. That's why stars give off light; that light is some of the energy given off as light elements fuze into bigger elements....

 

Some more things...:

 

As it seems, the orbital distances of the planets are not random (at least not in our solar system, we ca n't know for sure about others). It's about the time the planets take to orbit their star... you find they commonly have quite whole-number relations there. Wikipedia has a page on this principle which is called orbital resonance: http://en.wikipedia.org/wiki/Orbital_resonance

 

As for what keeps the planets in orbit around stars, it's gravitation indeed; the orbital speeds and distances are in equilibrium with the star's gravity. Consider: If you throw a stone, it flies in a distinct arc until it hits the ground again. The harder you throw it, the farther it goes. If you can reach the right amount of power, you accelerate that rock to what is called the escape velocity and you catapult it into orbit. Well of course you'd need much more power than your arms can provide

 

It's the same with planets. They orbit with the escape velocity that fits their orbital speeds and distances in relation to their stars' gravity. Any faster and they'd start to leave the solar system, any slower and the star would pull them in with fatal consequences.

[Thought2Much]

http://www.csmonitor...th-s-atmosphere

 

something fun.

 

 

82%

 

I never took a physics class, so I was unaware of some of the terms for that (such as "mu"). I totally botched the question about the most abundant element in the earth's crust (oxygen), and I didn't know that "nimbus" meant "precipitating."

 

Pretty good for a guy with an art degree, I'd say.

[Thought2Much]

The bad astronomer has to say on that one:

 

"...it turns out there is a lower limit to that mass; if you don't have enough, then you don't get the high temperatures and pressures necessary to ignite fusion. That mass is about 0.077 times the mass of the Sun, or 80 times Jupiter's mass. In other words, Jupiter is 1/80^th the mass it needs to turn into a star. Some people call Jupiter a failed star, but in reality it ain't even close."

 

(Source: http://www.badastron...er_galileo.html)

 

I think he's referring to hydrogen fusion in his article, while I was referring to the lower mass for deuterium fusion (the value for which I pulled from Wikipedia; the article on brown dwarfs gives values for both, as well as for lithium fusion), which isn't sustainable for very long anyway.

[Thought2Much]

To expound on the life cycle of a supernova, which VacuumFlux started:

 

As noted, within the cores of stars, the great pressure and heat causes fusion to occur. Atomic fusion means that you slam two atoms together, and you get one atom of a heavier element, plus a release of energy and some other subatomic particles (such as neutrinos). This is how our sun works, and what enables us to live on earth today. In our sun, hydrogen atoms are smashing together to form the next element in the periodic table, which is helium.

 

If a star is really large, you also have hydrogen fusing into helium. When you get enough helium in the core, that helium starts to fuse to become lithium, and so on down the periodic table. The star actually becomes stratified into layers, until you wind up with a core that is composed of iron. Here is where things get all explody.

 

The big problem with iron fusion is that, unlike the other kinds of fusion that lead up to it, it is an endothermic reaction. In other words, the reaction pulls energy from around it as it occurs instead of releasing it. When the fusion in the core of the star stops as a result, something amazing happens. The outward pressure exerted by the energy created by the fusion reactions stops,* and all of the layers of the star collapse in at once, like when a building is demolished with explosives. The incredible amount of energy of the collapse basically tells the iron, "FUCK YOU! YOU'RE GOING TO FUSE, DAMMIT!" With all of this extra energy, the iron gets fused into even heavier elements, and as this happens, the mass of the star actually rebounds outward with unbelievable force, splattering all of the elements that exist in nature everywhere.

 

In other words, we are all literally stardust.

 

 

 

*Stars are as big as they are because the energy from fusion puffs them up. Without the fusion, they would be much smaller.

[blackpudd1n]

Ooh, that sounds like story time! I like telling stories! Here's my very rough story about how this stuff works. Hopefully I won't get too much wrong.

 

Thanks for the story, VF! I think I got the gist of it. Basically, the whole universe in motion, right?

 

What's inside these black holes? Is it true that they're sucking everything into them?

[Ouroboros]

What's inside these black holes? Is it true that they're sucking everything into them?

Black holes suck, but space is cool.

[blackpudd1n]

Wow, just saw the rest of the responses on here. This is awesome! I'm totally in over my head, but I'm having fun

 

I really appreciate all of the responses you guys have given- it really helps me to start laying a foundation. Things don't click into place straight away, but it helps me not get discouraged and overwhelmed when I start like this on a science topic.

 

You all rock!

[blackpudd1n]

What's inside these black holes? Is it true that they're sucking everything into them?

Black holes suck, but space is cool.

 

But does that mean they'll start the next explosion all over again? Is that possibly how this cycle keeps going?

[Thought2Much]

What's inside these black holes? Is it true that they're sucking everything into them?

 

Not really, no. If you were to replace our sun with a black hole of the same mass, the orbits of the planets wouldn't change a bit as a result.

 

Matter loses its identity and differentiation inside a black hole; you no longer have elements and molecules; it's now just "stuff."

 

Do you remember the bit about escape velocity that Thurisaz posted? Every astronomical body has a speed that is required in order to escape its gravity. For earth, it's 7 miles per second. For Jupiter, it's a lot higher. For the sun, it's even higher still. What happens when the escape velocity gets so high that it's greater than the speed of light? In other words, even light doesn't have enough energy to escape a black hole, which is why they're black, and nothing comes out, which is why they're holes. Well, kinda sorta, anyway.

 

How are black holes created? Well, the objects called stellar mass black holes are formed from the supernovas that were mentioned earlier. Once they've blown a bunch of their mass off, if there's enough mass left over, then that mass collapses back in on itself, except now there isn't any kind of fusion going on anymore to puff itself back out. It just continues to collapse, until the radius of the star is so small compared to its mass that the escape velocity exceeds the speed of light.

 

Isn't it neat how all of this is connected?

[Thought2Much]

But does that mean they'll start the next explosion all over again? Is that possibly how this cycle keeps going?

 

No. Once black holes collapse in on themselves, that's it. Nothing gets out again.

 

"But, how do we know they're there, if nothing gets out, not even light?" I hear you ask.

 

Good question! If a black hole is close enough to another star, it can pull gas off of that star and into itself. As the gas gets pulled into a tighter and tighter orbit around the black hole, it forms a flattened disk; the gas becomes more energetic the faster it goes as it gets closer to the black hole, and puts out x-rays. We've actually observed stars with invisible companions that put out huge amounts of x-rays (such as Cygnus X-1), and we've concluded that this is why. Once the stuff falls into what's called the event horizon, nothing comes back out of the black hole; we can only see the stuff that's just outside of that edge.

 

There are actually objects called supermassive black holes, which reside in the centers of galaxies, including our own, but it isn't thought that these formed from stars, like the stellar mass black holes do.

[blackpudd1n]

But does that mean they'll start the next explosion all over again? Is that possibly how this cycle keeps going?

 

No. Once black holes collapse in on themselves, that's it. Nothing gets out again.

 

"But, how do we know they're there, if nothing gets out, not even light?" I hear you ask.

 

Good question! If a black hole is close enough to another star, it can pull gas off of that star and into itself. As the gas gets pulled into a tighter and tighter orbit around the black hole, it forms a flattened disk; the gas becomes more energetic the faster it goes as it gets closer to the black hole, and puts out x-rays. We've actually observed stars with invisible companions that put out huge amounts of x-rays (such as Cygnus X-1), and we've concluded that this is why. Once the stuff falls into what's called the event horizon, nothing comes back out of the black hole; we can only see the stuff that's just outside of that edge.

 

There are actually objects called supermassive black holes, which reside in the centers of galaxies, including our own, but it isn't thought that these formed from stars, like the stellar mass black holes do.

 

LOL I must ask a lot of questions if you're starting to see a common thread to them in order to start anticipating them

 

So, are you saying that black holes won't suck the universe in on itself?

[Ouroboros]

But does that mean they'll start the next explosion all over again? Is that possibly how this cycle keeps going?

If the latest evidence and math is correct, the universe will slowly disintegrate (in a sense--I know, not proper explanation, but anyway..). When the fabric of space expands, the force to break apart the particles, and even the quarks, will eventually just tear it all to pieces. Very depressing. But it's billions (if not trillions) of years away. So be glad for the moment here.

[Ouroboros]

No. Once black holes collapse in on themselves, that's it. Nothing gets out again.

Except quantum tunneling.

[VacuumFlux]

Basically, the whole universe in motion, right?

 

Yep. And there's no special, fixed reference frames that you can relate objects in the universe to; we can only describe where an object is by how it relates to other objects.

 

 

Once black holes collapse in on themselves, that's it. Nothing gets out again.

 

A very, very tiny bit gets back out through Hawking radiation. It's possible that over very, very long time periods the black holes that exist today may "evaporate".

 

So, are you saying that black holes won't suck the universe in on itself?

 

Yeah, they're not strong enough for that. We're orbiting a black hole right now and aren't in danger of falling in any time soon. That would only happen if we got knocked into it. Black holes do feed on nearby matter, and sometimes even other galaxies if they run into each other (that's going to happen around our solar system, eventually, when Andromeda gets close to the Milky Way). But the universe is also expanding, so many black holes are moving away from each other and will never have the chance to collide and feed.

 

One way to visualize gravity is that the universe is like a giant sheet (except in 3d). Mass makes a dent in the sheet. Imagine a lumpy sheet with stuff rolling around on the surface; if you roll a ball into a big hole, it falls down and stays there. That's what happens to dust when it becomes part of a planet, and what happens to light when it gets too close to a black hole. But if the ball is rolling fast enough near a dent, it can roll in and then right back out. The event horizon of a black hole is the line past which, if anything crosses that line, it won't have enough energy to roll back out. So the gravity around a black hole is just like the gravity around a planet; just the planet is light enough (or a shallow enough dent, in this analogy) that not everything that rolls through the dent gets stuck there.

[Thought2Much]

No. Once black holes collapse in on themselves, that's it. Nothing gets out again.

Except quantum tunneling.

 

You keep that quantum shit out of here!

 

(Of course, I only say that because I don't know a damn thing about quantum theory, except that it doesn't make any sense to me at all. I am staying out of the quantum theory thread for a reason.)

[Thought2Much]

A very, very tiny bit gets back out through Hawking radiation. It's possible that over very, very long time periods the black holes that exist today may "evaporate".

 

Yeah, I just didn't want to make things too complicated...yet.

[Thought2Much]

Black holes do feed on nearby matter, and sometimes even other galaxies if they run into each other (that's going to happen around our solar system, eventually, when Andromeda gets close to the Milky Way).

 

Some of the biggest releases of energy in the universe occur when two supermassive black holes collide, which sometimes happens when galaxies merge together.

[Ouroboros]

You keep that quantum shit out of here!

That's the problem. Quantum shit exists in two places at once. Even if you get it out of here, it will come back...

 

 

 

[stryper]

I just hate it when my shit keeps coming back.

[blackpudd1n]

Ever felt like your mind was going into spasms?

 

I just picked up Dawkins' The God Delusion to keep reading, and the section I'm in is on this stuff, and I think I can understand why a lot of people prefer to just say "god did it". It's an absolute mind-fuck trying to get your head around this stuff. Trying to understand how time began- what do you mean, time has a beginning?

 

And I'm alternating between extreme wonder and awe at it all, amazed by my very own existence, and struggling with the "it's too hard to comprehend, god must have dunnit".

 

I have to agree with Dawkins and any other scientist- the world and the universe is just too amazing, what little we know of it, and god looks really boring in comparison. "God did it" is easier, but far less satisfactory an answer for the wonder around us.

[Thurisaz]

One small bit about whether black holes could "start something new", in my own words...

 

...as stated previously, nothing that goes into a black hole (technically, nothing that crossed the event horizon - the distance where the escape velocity is exactly c, the speed of light) can come out. But... with nothing to stop the collapse anymore, the matter inside a black hole becomes smaller and denser and still smaller and still denser until density goes infinite and volume/radius approaches zero. Under such extreme circumstances all our deduced laws of nature, all our knowledge and understanding start to fail. In such a singularity, anythingcould possibly happen - which is why many scientists are glad that the singularity sits behind that event horizon. You just don't wanna know what weird impossible things might lurk behind it, now imagine they could come out to haunt you!

 

Of course if anything goes somewhere behind the event horizon then it's possible that the singularity might spawn a new spacetime, a new universe. If that wild speculation (one which the scifi authors really really love) should be true, we could say that black holes spawn the "next generation" of universes. Which is, if you ask me, a cool thought... whether it's true or not.

[blackpudd1n]

Which is, if you ask me, a cool thought... whether it's true or not.

 

lol dude, my head was already spasming!!!!!

[Thurisaz]

That proves you're normal