[Physics] It's the end of the world as we know it.

[Ragnarak]

When the sun eventually becomes a red giant, we're gonna die but i'm trying to make sure i understand exactly what would happen.

If it doesn't lose much mass it'll engulf the earth in it's photosphere. We'll all be dead by then but what happens to the earth? The orbit would decay and it'd spiral inwards right? Would the density of the photosphere would provide some 'drag' which would slow the decaying orbit down? That'd make sense but i'm not sure whether that density would be negligable.

Also if the sun did lose mass (in form of solar wind etc) when turning into a red giant what would happen? The solar wind forces may push the earth outwards and as the sun has less mass the orbital radius of the earth would increase? Would the earth move out to a new stable orbit further away from the sun (and outside of it's photosphere)?

I'm just trying to see if i've made any stupid asumptions or forgotten anything.

[Baron Morte]

Actually recent discoveries point out that galaxy clash that will take place somewhere in the next 4bi years will more likely be responsible for our solar´s system final disruption than an eventual sun burnout.
This galaxy, Andromeda, if memory serves, will be the resposible for our obliteration.

As far as this situation goes, I am under the impression that due to great reduction in our sun´s density, intwine with its mass dispersion nearer to the earth, our orbit will suffer minor effects.

Obviously this is a major toss because i am no astro·physi·cist .

Ps. Do you think the [physics] tag scared people away?

[JonnyBGood]

What are you talking about? The sun's just a bright light shone down my god to illuminate our miserable lives.

[MrL_JaKiri]

Originally Posted by Baron Morte

Actually recent discoveries point out that galaxy clash that will take place somewhere in the next 4bi years will more likely be responsible for our solar´s system final disruption than an eventual sun burnout.
This galaxy, Andromeda, if memory serves, will be the resposible for our obliteration.

Galaxies aren't exactly solid things that hit eachother, BOOM, duder.

ps.

Both these events are estimated for about 5bn years hence.

[Ragnarak]

Originally Posted by Baron Morte

Ps. Do you think the [physics] tag scared people away?

Yes, but i was hoping the REM reference in the title would get mark in here

[MrL_JaKiri]

Originally Posted by Ragnarak

Yes, but i was hoping the REM reference in the title would get mark in here

Hey duder wazzup

[Baron Morte]

Originally Posted by MrL_JaKiri

Galaxies aren't exactly solid things that hit eachother, BOOM, duder.

ps.

Both these events are estimated for about 5bn years hence.

It is obvious that I didnt mean "words colliding" kind of end. But the gravitatinal strength involved in such collisions, bearing in mind that galaxies do have black holes inside them, is more than enough to shatter our word into smithereens.

[Jennifer]

............are you a physicist?

[MrL_JaKiri]

Originally Posted by Ragnarak

If it doesn't lose much mass it'll engulf the earth in it's photosphere. We'll all be dead by then but what happens to the earth? The orbit would decay and it'd spiral inwards right? Would the density of the photosphere would provide some 'drag' which would slow the decaying orbit down? That'd make sense but i'm not sure whether that density would be negligable.

It depends of course whether we're talking about the end of the planet, or the end of life on the surface. The orbit can go **** itself as far as surface life is concerned, as we'll be dead either way. Furthermore, I'd suspect that the drag will be appreciable (as in 'non-negligable', rather than UUGE), however its only effect will be to cause the orbit to depreciate more quickly.

Originally Posted by Ragnarak

Also if the sun did lose mass (in form of solar wind etc) when turning into a red giant what would happen? The solar wind forces may push the earth outwards and as the sun has less mass the orbital radius of the earth would increase? Would the earth move out to a new stable orbit further away from the sun (and outside of it's photosphere)?

I don't see why we need to bring the solar wind into it; if the sun loses a significant amount of mass, the earth will move into a more distant orbit perfectly naturally (it'll be an ellipse with a more significant eccentricity, of course)

[Proteus]

By the time something threatens the Earth, we'll have invented planet-engines to move it somewhere else.

[MrL_JaKiri]

Originally Posted by Proteus

By the time something threatens the Earth, we'll have invented planet-engines to move it somewhere else.

Moving planets is fine. Don't try to move stars, they'll get annoyed at you.

[Proteus]

Originally Posted by MrL_JaKiri

Moving planets is fine. Don't try to move stars, they'll get annoyed at you.

I think a giant fan is in order.

[MrL_JaKiri]

Originally Posted by Proteus

I think a giant fan is in order.

Stars are great

[Ragnarak]

Originally Posted by MrL_JaKiri

It depends of course whether we're talking about the end of the planet

I was talking end of the planet.

I was trying to think how the drag affects the period/radius. Drag is dependant on velocity squared, so the slower you go the less drag. By the time the drag is negligable i'd assume that the earth would already be quickly spiralling inwards, but wanted to prove this numerically.

[MrL_JaKiri]

Originally Posted by Ragnarak

I was talking end of the planet.

I was trying to think how the drag affects the period/radius. Drag is dependant on velocity squared, so the slower you go the less drag. By the time the drag is negligable i'd assume that the earth would already be quickly spiralling inwards, but wanted to prove this numerically.

Remember also that the drag will increase the closer to the sun you get, because it'll go from rarified to thick (well, not quite that extreme, but you get the idea).

I was going to write some more, but I can't think how to word it, because my mind's working in 1930's detective slang.

[Ragnarak]

Originally Posted by MrL_JaKiri

Remember also that the drag will increase the closer to the sun you get, because it'll go from rarified to thick (well, not quite that extreme, but you get the idea).

I was going to write some more, but I can't think how to word it, because my mind's working in 1930's detective slang.

I was just going to assume an average density for the photosphere. Hmmm.

[MrL_JaKiri]

Originally Posted by Ragnarak

I was just going to assume an average density for the photosphere. Hmmm.

It should be possible to work out the rate of change of density of it wrt orbital distance

[Ragnarak]

Originally Posted by MrL_JaKiri

It should be possible to work out the rate of change of density of it wrt orbital distance

Yeah, cheers.

[MrL_JaKiri]

Originally Posted by Ragnarak

Yeah, cheers.

I don't think it matters that much; the effects of the solar wind and the drag on the planet (or, for both, on the planet's magnetosphere to be more accurate) will be tiny compared to gravity.

[Stew]

Wassit matter its 4bill yrs away, I wont be here, my kids wont be here, my grand kids wont be here, humans wont be here!

[Intrepid00]

What the hell do they care about, its an event like Stew said that will happen billions of years after you dead. You have any idea just how big 1 billion is. If you had 1 billion dollars and spent 1 dollar every second you wouldn't spend all of it by the time your dead.

[Ragnarak]

Originally Posted by Intrepid00

What the hell do they care about, its an event like Stew said that will happen billions of years after you dead. You have any idea just how big 1 billion is. If you had 1 billion dollars and spent 1 dollar every second you wouldn't spend all of it by the time your dead.

I study astrophysics*





















*kind of

[Ragnarak]

Originally Posted by Stew

my kids wont be here

something you ain't told me bout?

[MrL_JaKiri]

Originally Posted by Intrepid00

What the hell do they care about, its an event like Stew said that will happen billions of years after you dead. You have any idea just how big 1 billion is. If you had 1 billion dollars and spent 1 dollar every second you wouldn't spend all of it by the time your dead.

He's a phyicist (sort of). I think he knows about big numbers.

ps.

Rag, tell muslim that he's being a moron. (the buried thread)

[Ragnarak]

Originally Posted by MrL_JaKiri

He's a phyicist (sort of).

I'm offended

But fair enough.

[Deciduous]

I remember reading that the Earth's orbit would shift outwards (Sun's lower mass and all that jazz) and be outside the Sun's photosphere, so all that drag business doesn't seem appropriate.

[Ragnarak]

Originally Posted by Deciduous

I remember reading that the Earth's orbit would shift outwards (Sun's lower mass and all that jazz) and be outside the Sun's photosphere, so all that drag business doesn't seem appropriate.

There's 2 possibilities.

It depends on whether the sun retains it's mass as it tranforms into a red giant.

[Baron Morte]

Originally Posted by MrL_JaKiri

He's a phyicist (sort of). I think he knows about big numbers.

ps.

Rag, tell muslim that he's being a moron. (the buried thread)

Well i think you are the moron, considering that you think that a physics degree is enough to challange terms which were built by countless physics which were by far better than you.

[MrL_JaKiri]

Originally Posted by Baron Morte

Well i think you are the moron, considering that you think that a physics degree is enough to challange terms which were built by countless physics which were by far better than you.

1. I don't have a physics degree

2. I'm not disagreeing with either Physics, or the quoted dictionary definition. On the same page, there's a definition which is simpler and more accurate, for instance.

[MrL_JaKiri]

Originally Posted by Ragnarak

There's 2 possibilities.

It depends on whether the sun retains it's mass as it tranforms into a red giant.

It will lose quite a lot of mass (a nova, as opposed to a supernova)

[Tactitus]

Originally Posted by Ragnarak

There's 2 possibilities.

It depends on whether the sun retains it's mass as it tranforms into a red giant.

Stars can lose a significant percentage of their mass after they become red giants (see planetary nebulae).

[BeeKiller]

Originally Posted by Baron Morte

It is obvious that I didnt mean "words colliding" kind of end. But the gravitatinal strength involved in such collisions, bearing in mind that galaxies do have black holes inside them, is more than enough to shatter our word into smithereens.

Actually galaxies colliding doesn't actually affect the individual stars anywear near as much as the shape of the overall galaxies themselves. The distances between stars/black holes/planets etc are so huge that they only have relatively minor influences over each other at these distances. Gravity is actually the weakest fundemental force (by far) from what i remember. O_O

[MrL_JaKiri]

Originally Posted by BeeKiller

Actually galaxies colliding doesn't actually affect the individual stars anywear near as much as the shape of the overall galaxies themselves. The distances between stars/black holes/planets etc are so huge that they only have relatively minor influences over each other at these distances. Gravity is actually the weakest fundemental force (by far) from what i remember. O_O

You were doing so well up until that final line.

Gravity is the weakest, yes, because the mass of a particle is (for all charged particles) relatively much less than its charge.

The weak and the strong nuclear forces are very short ranged, so we don't have to deal with them.

The thing is that there is no (significant, or existing beyond theory at least) antimass. Charge almost ALWAYS cancels itself out at long ranges. Gravity, because it's all positive, doesn't.

[Ragnarak]

Originally Posted by MrL_JaKiri + Tacitus

It will lose quite a lot of mass (a nova, as opposed to a supernova)

It can but it might not. I was hoping to take both eventualities into consideration.

ps. muslim, give up, please

[MrL_JaKiri]

Originally Posted by Ragnarak

It can but it might not. I was hoping to take both eventualities into consideration.

What I'd do if I wanted to calculate this was to rephrase the question.

1. How much mass will the star have to lose for the earth to be outside the photosphere?

2. Assuming a linear relationship between % distance inside the photosphere and retardation force, how fast will it spiral in (the force required to keep it in that orbit and the force from drag are both based on v^2, so the relationship will be (sort of) linear at this accuracy)?

Of course, 2 involves other problems; as a qualitiative statement 'If in the photosphere, the earth will fall into the sun' is fine, but it's the numbers that cause the problem.

[BeeKiller]

Originally Posted by MrL_JaKiri

You were doing so well up until that final line.

Gravity is the weakest, yes, because the mass of a particle is (for all charged particles) relatively much less than its charge.

The weak and the strong nuclear forces are very short ranged, so we don't have to deal with them.

The thing is that there is no (significant, or existing beyond theory at least) antimass. Charge almost ALWAYS cancels itself out at long ranges. Gravity, because it's all positive, doesn't.

ah good point, i forgot about how the other forces cancel out whereas gravity doesn't. I suppose even though the effect would be weak it could affect our orbit, which could, quite easily make the planet uninhabitable (too hot or cold). This could happen, although the overall effect on the solar system (on a more cosmic scale) would probably negligble.

[MrL_JaKiri]

Originally Posted by BeeKiller

ah good point, i forgot about how the other forces cancel out whereas gravity doesn't. I suppose even though the effect would be weak it could affect our orbit, which could, quite easily make the planet uninhabitable (too hot or cold). This could happen, although the overall effect on the solar system (on a more cosmic scale) would probably negligble.

If you want an example of the electromagnetic force being quite active on a large scale, look at this thread; the interaction between the planet and the photosphere is likely to be largely due to EM interactions, for instance.

[Tactitus]

Originally Posted by MrL_JaKiri

What I'd do if I wanted to calculate this was to rephrase the question.

1. How much mass will the star have to lose for the earth to be outside the photosphere?

Don't you need to know the size of the photosphere first though? I don't think anyone really knows how large the photosphere will get--I've seen estimates ranging from inside earth's orbit to outside Mars' orbit.

2. Assuming a linear relationship between % distance inside the photosphere and retardation force, how fast will it spiral in (the force required to keep it in that orbit and the force from drag are both based on v^2, so the relationship will be (sort of) linear at this accuracy)?

I don't think one can assume it will spiral in though. We've already discovered planets in orbits << 1 AU around stars that have already passed through the red giant phase. These are all jovian-sized planets, but still the outer photosphere of a red giant is quite tenuous (a good vacuum by terrestrial standards).

[MrL_JaKiri]

Originally Posted by Tactitus

Don't you need to know the size of the photosphere first though? I don't think anyone really knows how large the photosphere will get--I've seen estimates ranging from inside earth's orbit to outside Mars' orbit.

Obviously assumptions will have to be made, but you can estimate it.

Originally Posted by Tactitus

I don't think one can assume it will spiral in though. We've already discovered planets in orbits << 1 AU around stars that have already passed through the red giant phase. These are all jovian-sized planets, but still the outer photosphere of a red giant is quite tenuous (a good vacuum by terrestrial standards).

It's not a question of if though, which is the point I was making. It's a question of WHEN.

[Stew]

Originally Posted by Ragnarak

something you ain't told me bout?

I did think that when I put it! I should have said - the next generation. (not star trek..)