Astronomy Questions

[Coyote]

I'd originally planned on directing this at Borodog, but it looks like he's got enough questions to deal with at the moment. Besides, I know there are some folks here who know a good deal about the subject, so I'll open this up to anyone who might like to have a go at it.

The Oort Cloud
I once heard a YEC* claim that there's no real evidence for the Oort Cloud, and that it was just something made up by scientists to explain how there could still be comets in an 'old' solar system. Is this true? (I mean its strictly theoretical status). How do we know there's an Oort Cloud? Is it a by-product of stellar formation, or a bunch of 'outside' junk that wanders into the Sun's gravitational influence? Do all stars have Oort Clouds?
* Young-Earth Creationist

Speed of Gravity
I can't seem to come up with a good way to phrase this question, so I hope this isn't too confusing:
Is gravitational attraction instantaneous, or does it travel at the speed of light (or slower)? For instance, if we could somehow strap some big Acme rockets onto the moon and move it away from earth, would the earth immediately experience the change in gravitational attraction or would it take a second or two for the 'signal' to reach it? Would weird things happen to the gravitational attraction between two objects passing at near-light speed?

Hubble Deep-Space Field
I hope I got the name of that right. I'm talking about the picture that shows scores of galaxies strewn about like so much confetti. I've seen it posted a couple of times here in the labyrinth as well as a few other sites I visit, and it's quite a memorable image. It looks huge, but just how large a section of our sky would it cover? Is it a particularly dense packing or would we see pretty much the same thing no matter which direction we look? Just thinking about that boggles my mind.

I know that's quite a few questions, but I've had a big surge of curiousity lately.



[This message has been edited by Coyote (edited 03-15-2004 04:53 AM).]

[d8P]

Oort Cloud
The Oort cloud is only a working hypothesis.

Speed of Gravity
Gravitational attraction is instantaneous. Earth would experience the change instantly. Anything with mass curves the fabric of spacetime around it (it is thought), like a marble on a sheet. Move the marble, the curvature moves with it.

[Dr. Borodog]

quote:

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The Oort Cloud

I once heard a YEC* claim that there's no real evidence for the Oort Cloud, and that it was just something made up by scientists to explain how there could still be comets in an 'old' solar system. Is this true? (I mean its strictly theoretical status). How do we know there's an Oort Cloud? Is it a by-product of stellar formation, or a bunch of 'outside' junk that wanders into the Sun's gravitational influence? Do all stars have Oort Clouds?
* Young-Earth Creationist

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The Oort cloud cannot be directly observed, however indirect evidence for its existence grows yearly. Such evidence includes:

- There are no comets observed to have orbits indicating extra-solar origin
- The long term comets (200+ years) exhibit a strong trend towards an apastron centered at 4.5 trillion miles from the sun
- There is no preferred direction from which comets originate
- There is an approximately 30 million year mass-extinction cycle in the fossil record that matches the 30 million year period of the sun's oscillation through the galactic disk

Unless you're a goofy nuthatch that believes the Universe is only 6000 years old, there must be an Oort cloud.

quote:

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Speed of Gravity

I can't seem to come up with a good way to phrase this question, so I hope this isn't too confusing:

Is gravitational attraction instantaneous, or does it travel at the speed of light (or slower)? For instance, if we could somehow strap some big Acme rockets onto the moon and move it away from earth, would the earth immediately experience the change in gravitational attraction or would it take a second or two for the 'signal' to reach it? Would weird things happen to the gravitational attraction between two objects passing at near-light speed?

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Gravity travels at the speed of light. The previous answer you received is incorrect. "Weird" things always happen at near the speed of light. For example, coalescing orbiting black holes would send out particular gravity wave signals; these are the kinds of signals scientists hope to detect with the upcoming generation of gravity-wave observatories.

quote:

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Hubble Deep-Space Field

I hope I got the name of that right. I'm talking about the picture that shows scores of galaxies strewn about like so much confetti. I've seen it posted a couple of times here in the labyrinth as well as a few other sites I visit, and it's quite a memorable image. It looks huge, but just how large a section of our sky would it cover? Is it a particularly dense packing or would we see pretty much the same thing no matter which direction we look? Just thinking about that boggles my mind.

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There are two; the Hubble Deep Field (HDF), and the Hubble Ultra Deep Field (HUDF). The first is a tiny section of sky, the second is even smaller. If I remember correctly, the second image has either no local (in our galaxy) stars in the image, or just a handful of small dim ones. This tells you immediately that the image must be an incredibly tiny portion of the sky, since there are stars every where you look.

I don't recall off the top of my head the exact field of view, but trust me, it's very small.

However, you could NOT get a similar image from anywhere in the sky. Only by looking out of the plane of the galaxy can you see past the stars and dust of our galaxy itself.

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You will respect my philosophai.



[This message has been edited by Dr. Borodog (edited 03-15-2004 11:45 AM).]

[Quailman]

[Dr. Borodog]

[d8P]

Oops.

The good doctor is right, of course, about gravity travelling at the speed of light. That's what I get for not brushing up on my secondary school physics.

[extropalopakettle]

Do you think there are any stars that have planets with moons that themselves have moons (or whatever you'd call a body that orbits a moon)?

[Dr. Borodog]

Hmm. I've never thought about that.

At first blush I thought, why not? But actually, I'm pretty sure it would be difficult to arrange such a thing. The orbit of the "secondary" moon (the moon of the moon) would certainly be unstable; it would rapidly collide with the primary moon.

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You will respect my philosophai.

[Vinny]

Lookee what I found, Coyote!

http://www.greylabyrinth.com/Forums/Forum6/HTML/000091-5.html

Some good reading in there.

Originally posted by Reply 27 in linked thread, by Samadhi:

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Oh and here's a good one (seriously). What would you like to do with your PhD?
(Dr. Borodog. Hmmm.)

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Hahahahhaha!

[This message has been edited by Vinny (edited 03-15-2004 01:47 PM).]

[Samadhi]

What about a moon around two tidally locked massive bodies (Earth size+) orbiting around twin stars? That'd be interesting to see.

[Buzzsaw]

If Coyote doesn't mind, I would like to borrow this thread for a couple of my own astronomy questions.

My first question is: Do a Leo and a Pisces have any chance at all?

[Dr. Borodog]

No. Their child would become the Antichrist.

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You will respect my philosophai.

[Dr. Borodog]

[Samadhi]

Take out the stable caveat and it'd be very interesting indeed.

[Coyote]

Thanks for the input, everyone. My mind is properly boggled. Especially by the descriptions of just how small an area of the sky the Deep Field pictures take up. Makes me feel like I've been shoved into the Total Perspective Vortex.

Not to be ungrateful or anything, but a couple of the Oort questions remain unaddressed: even if it's existence is mainly theoretical, it would still have to jibe with current theories of stellar development, so I'm just wondering if it's thought that it formed along with the sun or developed later by slowy 'capturing' passing debris. d8P's link probably answered question about whether all stars have Oort Clouds. If the cloud is really at such a great distance I'd guess that binary stars and stars in clusters don't have such clouds, as constantly changing gravitational influences would have swept them clean fairly early on. Is this correct?

[Mr Nigma]

Well, obviously.

***wanders back into the labyrinth eating a fudge-sicle***

[pikachamp]

I have a question!
If two stars crashed into eachother (I'm guessing it's unlikely), what would happen? Would there be an explosion, or would they just merge together? Would the relative sizes make a difference?
Oh, and *steals Mr. Nigma's fudge-cicle.*

[This message has been edited by pikachamp (edited 03-15-2004 09:28 PM).]

[BigBenWD]

wow, makes you think. we could be like the size of a bug to some super race billions of feet tall. want to be put i nto perspective on how unimportant your like, the human race, the earth, the solar system, and even the galacy is? just think about how many more galaxies there are just like them, and how huge the universe is.

[Samadhi]

Coyote: Leftovers is the common theory. For the binary stars not necessarily. Two similar sized bodies orbiting around each other still have a center of mass. It's only when you get close to them that it would make a difference. (I believe).

[extropalopakettle]

OK, I think I knew this once, but let's refresh. Think of something like our solar system as a "first order cluster". Our galaxy would be, let's say, a "second order cluster". There are, I believe, clusters of galaxies - "third order clusters". Are there fourth order clusters? Fifth? What's the limit? Why?
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Actually, if I ever knew any of it, I'm pretty sure I didn't know the "why" part.

[This message has been edited by extropalopakettle (edited 03-15-2004 11:21 PM).]

[Dr. Borodog]

There are clusters of clusters, they are called superclusters. You can't get any bigger than superclusters, though, without running into the scale of the Universe. In other words, even though the Universe may be infinite in mass and extent, you still cannot create structures larger than the limit of causal connectivity.


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You will respect my philosophai.

[Dr. Borodog]

Coyote,

As to whether Oort objects formed with the Sun or were captured afterward, quite frankly, I'm not sure. It's not my field. Im not sure what Samadhi meant by "leftovers." The word doesn't answer the question for me. Personally, I'd imagine that the Oort cloud predates the majority of the solar system, much like globular clusters predate galactic disk stars. A spherically collapsing gas and dusk cloud will produce bodies in random orbits before the conservation of angular momentum flattens the remaining material into a protostellar disk, from which arises the sun and planets.

But that's pure speculation off the top of my head.




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You will respect my philosophai.

[Samadhi]

What I meant was the cloud or nursery that the star forms from would likely have matter "left over" at the outer edges of its gravitational influence. Barring nearby stars to grab that matter, I'd think it would coalesce into objects like comets. These objects once coalesced or while coalescing (depending on how much light presure would matter) ~shrug~ would drop towards sol like raindrops.

[Samadhi]

But that's pure speculation off the top of my head.

[Quailman]

Most Distant Object in Solar System Discovered

[zeek]

Far out.

[Samadhi]

Coyote: First step in the Perspective Vortex http://ipac.jpl.nasa.gov/media_images/ssc2004-05d1.jpg

[BigBenWD]

really REALLY far out.

[Courk]

I don't have time to re-read that article, but what I skimmed of it seems similar, if not identical, to the article I read in my paper this morning. And now for my questions:

If Sedna is not a planet, but a planetoid, that must mean it does not meet the criteria to be called a planet. What, then, is the criteria for planet-dom? Which of these does Sedna lack?

[Lucky Wizard]

There's no consensus on whether Sedna is a planet or a planetoid. The criteria for planet-dom are:

• the object has to orbit a star;
  
• the object doesn't have nuclear fusion going on in its core; and
  
• the object has to be of considerable mass.
  

Sedna pretty clearly fulfills the first two criteria. As for the last one... there has been a debate for some time about what constitutes "considerable mass". Some people might define it to include Sedna, whereas some might define it to exclude Sedna but include Pluto, and some might define it to exclude Pluto.

BTW, is this thread screwing up anyone else's browser?

[Coyote]

Yup, it messed up my browser as well. Weird.

[Dr. Borodog]

Neither Sedna nor pluto fit my personal criteria to be a planet. Pluto quite clearly did not form in the ecliptic with the rest of the planets; therefore, it ain't no planet.



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You will respect my philosophai.

[pikachamp]

My questions seem to have been ignored.

Originally posted by me:

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If two stars crashed into eachother (I'm guessing it's unlikely), what would happen? Would there be an explosion, or would they just merge together? Would the relative sizes make a difference?

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[Dr. Borodog]

Sorry, pika, I forgot about it.

I'm not sure the of the current theoretical answer to your question. If I get a chance, I'll try to look it up.


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You will respect my philosophai.

[Coyote]

Don't bother letting us know the answer unless it somehow requires the use of the word 'kaboom'. Astrophysics would be so much more popular if they would incorporate a few really cool sound effects into theories about the evolution of the cosmos.

*Bam!!* *Smack!* *Kablooie!* ... Now that's science!

[Dr. Borodog]

pika,

Try this article: http://www.space.com/scienceastronomy/astronomy/stars_collide_000531.html


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You will respect my philosophai.

[pikachamp]

(This is referring to brief discussion we had in GLC last night.)
So what does happen when neutron stars collide?

[Dr. Borodog]

Probably a Gamma Ray Burst, which briefly outshines the entire Universe in gamma rays. If one occurs within a few thousand lightyears of here, Earth would be sterilized. GRBs are like God's Own Autoclave.


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You will respect my philosophai.

[MacadamiamaN]