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Thread: dead stars

  1. #1 dead stars 
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    I already asked this question somewhere within another thread, but now I have no idea where that thread is, so I'll ask it again here in its own thread... Is there any way that we can tell if a star has died and all we're seeing is its old photons that it sent out years and years ago? Just like the "if the sun 'went out' we wouldn't know it for 8 minutes" thing...


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    That is true (i think) yes, many stars in the sky today may actually be dead, and some are, but the light is still travelling to us as we're a few million lightyears behind on the whole star-death concept. also, if the sun died, we'd have 8 minutes to get somewhere safe from cold before the disastrous effects reached us.


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  4. #3 Re: dead stars 
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    Quote Originally Posted by Chemboy
    I already asked this question somewhere within another thread, but now I have no idea where that thread is, so I'll ask it again here in its own thread... Is there any way that we can tell if a star has died and all we're seeing is its old photons that it sent out years and years ago? Just like the "if the sun 'went out' we wouldn't know it for 8 minutes" thing...
    No, there's no way to tell. We cannot get information of any kind faster than the speed of light, so we have to wait for that last group of photons to arrive before we can know it's the last.
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    exactly. If the sun just dissapeared without doing the hundreds of years of red giant thing, then the first you'd know about it would be 8 minutes after it happened. The sun would be in the sky giving off warmth, and we'd still even be orbiting it... then 8 minutes later. *poof* the earth's orbit would straight-line and the sky would go dark.
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    Quote Originally Posted by musicalaviator
    exactly. If the sun just dissapeared without doing the hundreds of years of red giant thing, then the first you'd know about it would be 8 minutes after it happened. The sun would be in the sky giving off warmth, and we'd still even be orbiting it... then 8 minutes later. *poof* the earth's orbit would straight-line and the sky would go dark.
    actually, wouldn't we feel the effects of not being affected by gravitational force between the sun and the earth as soon as it happened?
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    gravity is instananeos. Wouldn't we be killed by the immense G-forces involved as well?
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    Quote Originally Posted by Nevyn
    gravity is instananeos. Wouldn't we be killed by the immense G-forces involved as well?
    No, it isn't instantaneous. Gravitational effects travel at the speed of light.

    I'm not sure what immense G-forces you mean. The loss of the Sun would not effect the gravity the Earth produces. In that regard, we wouldn't even notice a change.
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    without the sun we would not go round in circles. The Earth would change to a straight line tragectary. G forces are acceleration of velocity acting on the body. Seem as though the earth is changing velocity it is therefore accelerating
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    Quote Originally Posted by Nevyn
    without the sun we would not go round in circles. The Earth would change to a straight line tragectary. G forces are acceleration of velocity acting on the body. Seem as though the earth is changing velocity it is therefore accelerating
    The first part is correct, the second is not. There would be nothing to change the velocity and therefore add acceleration. The Earth would move away from it's original position in a straight line at exactly the same speed with which it orbited the Sun.

    (All of this, of course is based on supposing the Sun had simply vanished. If it had somehow "died" without going through the red dwarf stage, we'd be left in the dark and the Earth would continue to revolve around the mass of what was the Sun just as it does now.)
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    Quote Originally Posted by Old Geezer
    No, it isn't instantaneous. Gravitational effects travel at the speed of light.
    Do/does you/anyone have proof of that? And what connection is there between that and considering what the mediator of the gravitational force is?
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    1: Gravity must propegate at the speed of light since 'nothing' can propegate faster than light. Gravity is a force which obeys laws inside or own universe just as light does.

    2: As I discribed in the ISS thread, Earth's gravity's effect on us and anything orbiting itself (moon, ISS, satellite, space shuttle) is for the most part entirely independant of the outside effects of it's own motion, and the influence from the sun, The effect of this is that the earth 'appears' to be the centre of all gravitational influence until you move off to a distance where the influence of another body (moon or sun) becomes more dominant (greater than 50% of the gravitational pull) than the earth's gravity.

    For any spacecraft in orbit around the earth, is in a freefall path around the earth. as shown in this diagram:



    During this freefall, the effect is 'no acceleration off the orbital path'.

    So if the sun (or in this diagram earth) suddenly dissapeared (beamed away like star trek dissapear) the 'freefall' non-acceleration line would be a straight line... assuming no other nearby objects are going to be orbited (ie moon, sun, jupiter etc)

    the apparent G-Force inside the spacecraft would not change from weightlessness in this situation at all. The change in direction is not a change in acceleration forces. The object was following a balance between Inertia (Straight line) and Gravity's 'curve of space' to start with, and now that the influencing gravitational body has gone, the same balance results in a different location... but no acceleration. The only way that bodys can experience G-force is to increase their kinetic energy directly - by using rockets to accelerate or through collisions with other bodys. Gravity just converts *potential* energy into a direction change or apparent acceleration... however as orbits prove, this impartation of energy is only apprent - it would be more accurate to discribe the process as a curving of the straight line in space. ie "Straight ahead" is around a curve when inside a gravity well.
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    Quote Originally Posted by Chemboy
    Quote Originally Posted by Old Geezer
    No, it isn't instantaneous. Gravitational effects travel at the speed of light.
    Do/does you/anyone have proof of that? And what connection is there between that and considering what the mediator of the gravitational force is?
    What are you calling "mediator of the gravitational force?" I'm fairly well educated in this field but I've never seen that term before.
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    It also makes sense that gravity can't travel instantaneously. Otherwise when that Quasar 40 million light years away explodes into little bitty pieces, suddenly it effects everything everywhere, and a tiny perturbtion of a 0.0000000000000000000000000001% of a degree in our orbit cannot be explained... until 40 million years later a quasar flares up and breaks up into dust in the night sky.

    If nothing can go faster than the speed of light, why can gravity do so?

    Mr Einstein Considered this idea and came up with the idea that gravity would effect an object only at the same time that the object's location was able to see the event which the gravity caused it. Thus if the sun was beamed out of the solar system... 8 minutes after that occurance, people on earth would both see it occur and at the same instant, earth's trajectory would change into a straight line through space instead of the orbit around the COG of the sun.
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    As far as I understand it, if a body such as the sun were to suddenly disappear, it would send out gravitational waves that would propagate at the speed of light, therefore Earth's orbit would not be affected for another 8 minutes. Its the same if you were to move a large mass suddenly. There are attempts to actually detect gravitational waves coming from binary pulsars or black holes in orbit around each other.
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    Quote Originally Posted by Corona
    As far as I understand it, if a body such as the sun were to suddenly disappear, it would send out gravitational waves that would propagate at the speed of light, therefore Earth's orbit would not be affected for another 8 minutes. Its the same if you were to move a large mass suddenly. There are attempts to actually detect gravitational waves coming from binary pulsars or black holes in orbit around each other.
    Very close but worded a little incorrectly. :wink:

    Assuming that gravity waves do exist (and they might), the Sun would STOP sending them out (not the other way around) :wink: thus releasing the Earth from it's orbit.
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    Quote Originally Posted by "Old Geezer"[/quote

    Very close but worded a little incorrectly. :wink:

    Assuming that gravity waves do exist (and they might), the Sun would STOP sending them out (not the other way around) :wink: thus releasing the Earth from it's orbit.

    Whoops! My bad. Guess you're prone to do that after watching too much Nova .
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    Quote Originally Posted by Corona
    Quote Originally Posted by "Old Geezer"[quote

    Very close but worded a little incorrectly. :wink:

    Assuming that gravity waves do exist (and they might), the Sun would STOP sending them out (not the other way around) :wink: thus releasing the Earth from it's orbit.

    Whoops! My bad. Guess you're prone to do that after watching too much Nova .
    No problem at all, I knew exactly what you meant. But it's very possible that one or two others here might not so I thought it best to correct it - just in case.
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    Quote Originally Posted by Old Geezer
    Quote Originally Posted by Chemboy
    Quote Originally Posted by Old Geezer
    No, it isn't instantaneous. Gravitational effects travel at the speed of light.
    Do/does you/anyone have proof of that? And what connection is there between that and considering what the mediator of the gravitational force is?
    What are you calling "mediator of the gravitational force?" I'm fairly well educated in this field but I've never seen that term before.
    Something such as gravitons, but they're only theoretical particles. As far as I know, no one knows what the mediator that carries the gravitational force is exactly, for a fact.
    "There is a kind of lazy pleasure in useless and out-of-the-way erudition." -Jorge Luis Borges
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    Quote Originally Posted by Chemboy
    Quote Originally Posted by Old Geezer
    Quote Originally Posted by Chemboy
    Quote Originally Posted by Old Geezer
    No, it isn't instantaneous. Gravitational effects travel at the speed of light.
    Do/does you/anyone have proof of that? And what connection is there between that and considering what the mediator of the gravitational force is?
    What are you calling "mediator of the gravitational force?" I'm fairly well educated in this field but I've never seen that term before.
    Something such as gravitons, but they're only theoretical particles. As far as I know, no one knows what the mediator that carries the gravitational force is exactly, for a fact.
    Ah-ha, now I see what you mean - "medium" instead of "mediator."

    Why do you suppose a medium is even necessary? Light dosen't need one. And there's nothing to indicate that gravity does eother.
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    Quote Originally Posted by Old Geezer
    Ah-ha, now I see what you mean - "medium" instead of "mediator."

    Why do you suppose a medium is even necessary? Light dosen't need one. And there's nothing to indicate that gravity does eother.
    No, I don't mean medium. I said mediator and I mean mediator. I know that light doesn't need a medium and there's no reason for gravity to need one either necessarily. I mean mediator as in the photons that <u>mediate</u> the electromagnetic force, binding electrons to the nucleus of an atom, but for the gravitational force.
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    Quote Originally Posted by Chemboy
    Quote Originally Posted by Old Geezer
    Ah-ha, now I see what you mean - "medium" instead of "mediator."

    Why do you suppose a medium is even necessary? Light dosen't need one. And there's nothing to indicate that gravity does eother.
    No, I don't mean medium. I said mediator and I mean mediator. I know that light doesn't need a medium and there's no reason for gravity to need one either necessarily. I mean mediator as in the photons that <u>mediate</u> the electromagnetic force, binding electrons to the nucleus of an atom, but for the gravitational force.
    OK, now we're back to square one - or less. Because photons do not provide that function at all. it's done through the attraction between electrons and protons - there's no other "mediator" than that simple electrostatic force.

    And currently there's no indication of such a thing as a graviton - it's pure speculation at this point.
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  23. #22  
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    Quote Originally Posted by Old Geezer
    Quote Originally Posted by Chemboy
    Quote Originally Posted by Old Geezer
    Ah-ha, now I see what you mean - "medium" instead of "mediator."

    Why do you suppose a medium is even necessary? Light dosen't need one. And there's nothing to indicate that gravity does eother.
    No, I don't mean medium. I said mediator and I mean mediator. I know that light doesn't need a medium and there's no reason for gravity to need one either necessarily. I mean mediator as in the photons that <u>mediate</u> the electromagnetic force, binding electrons to the nucleus of an atom, but for the gravitational force.
    OK, now we're back to square one - or less. Because photons do not provide that function at all. it's done through the attraction between electrons and protons - there's no other "mediator" than that simple electrostatic force.

    And currently there's no indication of such a thing as a graviton - it's pure speculation at this point.
    Sorry to burst your bubble, but according to dictionary.com which I take to be a reliable source, and another website that I got under Google for 'carrier of electromagnetic force' and in a book that I am currently reading on particle physics, photons are the carriers of electromagnetic force, binding electrons to the nucleus of an atom.
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    Old Geezer, you said you were quite well versed in this field, yet are completely unaware of the use of the word mediator in relation to particles responsible for 'transmitting' forces. (That seems rather bizarre.)Photons do mediate the electromagentic force.

    Chemboy, Dictionary.com is fine for English usage, but I would not use it to justify/validate a scientific argument.

    There is a rather nice treatment of the issue of the speed of gravity here. Things are not as simple as they seem. (They are either much more complex, or even simpler.)
    http://metaresearch.org/cosmology/speed_of_gravity.asp
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