When a planetary star goes poof...

Factual Questions
1

So when a star goes supernova, the Science Channel usually shows planets at first orbiting a star, and then leading out into space in a straight line after the star explosion. Is this really what happens to planets of a dead star? If so, does the speed of said planets increase, slow down, or what? For example, Earth, which is currently orbiting at about 65,000mph… will this speed remain constant or increase significantly? *For the sake of argument, let’s say the Sun dies before engulfing the Earth into its self via a red giant.

Which then leads me to ask, how likely is it that we have giant rocky balls the size of earth and larger just hurtling in space with no orbit? I here a lot about 6 mile wide comets that we should worry about, but how about 8000 mile wide planetary objects just cruising along? 'Cuz that would hurt.

2

Maybe I’m just wrong about this, but if a star goes supernova, I wouldn’t have expected anything to continue resembling a planet for more than a very short period of time. Wouldn’t they just be blown into vapour?

3

I guess that would depend on how far the effects of a supernova will reach. What if it just missed Uranus?

4

I would imagine Earth would continue to travel in a straight line at a constant rate of speed until captured in the gravitational ‘well’ of a significantly influential body within its path. Its speed and trajectory would then be somewhat altered.

5

[QUOTE=ParentalAdvisory]
*For the sake of argument, let’s say the Sun dies before engulfing the Earth into its self via a red giant.

[/QUOTE]

Given my knowledge of astronomy, this is getting very close to a meaningless assumption. “Dies” how? We’re pretty sure that the lifetime of a star the sun’s size and class involves first growing into a red giant when it’s expended its hydrogen fuel, and then shrinking into a massive white dwarf. It’s not like a star can ‘die of accidental causes’ before its lifetime is up.

And… I don’t see how the earth could suddenly start moving in a straight line. The sun’s mass has to be SOMEWHERE. Either it remains more or less within the earth’s orbit, in which case we continue moving in a circle… or just maybe it’s possible that the sun could explode with enough force to spread its mass over an astronomically significant volume of space as a nebula of some sort. Or it expands just large enough to ‘swallow’ certain planets before contracting again.

In the second case (nebula explosion,) I don’t see how any of the planets could survive.

6

[QUOTE=ParentalAdvisory]
I guess that would depend on how far the effects of a supernova will reach. What if it just missed Uranus?
[/QUOTE]

If a star went poof, wouldn’t you hope it would miss Uranus?

At all events, its planets would certainly be in queer street.

7

[QUOTE=chrisk]
Given my knowledge of astronomy, this is getting very close to a meaningless assumption. “Dies” how? We’re pretty sure that the lifetime of a star the sun’s size and class involves first growing into a red giant when it’s expended its hydrogen fuel…
[/QUOTE]

I’ve heard that the sun will eventually encompass the Earth, and that the Earth’s speed will be reduced by friction with the gasses of the red giant and the planet will spiral in until it is destroyed.

The OP mentions our system, but I think the actual question is if there is a star that has planets around it, and the star goes nova, then what happens to the planets?

8

ParentalAdvisory writes:

> So when a star goes supernova, the Science Channel usually shows planets at
> first orbiting a star, and then leading out into space in a straight line after the
> star explosion. Is this really what happens to planets of a dead star?

You shouldn’t take the pictures shown in a science program as being anything except the fantasies of an artist. The gravitational attraction of the mass of the star doesn’t disappear. The planets will continue to orbit the remains of the star. The planets may get heated up slightly or they may be vaporized, depending on how much heat that hits them, but gravity doesn’t disappear because the star blows up. There’s still as much mass as before.

9

[QUOTE=Wendell Wagner]
ParentalAdvisory writes:

> So when a star goes supernova, the Science Channel usually shows planets at
> first orbiting a star, and then leading out into space in a straight line after the
> star explosion. Is this really what happens to planets of a dead star?

You shouldn’t take the pictures shown in a science program as being anything except the fantasies of an artist.
[/quote]

That’s why I’m asking.

[QUOTE=Wendell Wagner]

The gravitational attraction of the mass of the star doesn’t disappear. The planets will continue to orbit the remains of the star. The planets may get heated up slightly or they may be vaporized, depending on how much heat that hits them, but gravity doesn’t disappear because the star blows up. There’s still as much mass as before.
[/QUOTE]

So a white dwarf, and its remaining material that’s left after going nova, is what has housed the systems gravity all along… and the mass leaving the star doesn’t reduce the systems over all gravity, so planets will stick around for a while. I’m not sure how that works, so I don’t know.
Okay, I’ll just ask a general question. Can a large rocky planet ever leave its solar system on a straight path to hell at insane speeds? :eek:

10

[QUOTE=Malacandra]
If a star went poof, wouldn’t you hope it would miss Uranus?

At all events, its planets would certainly be in queer street.
[/QUOTE]
Even if it hit Uranus, I’d still have

11

This is the only result I got when googling “planets orbiting supernova”:

12

[QUOTE=ParentalAdvisory]
That’s why I’m asking.
So a white dwarf, and its remaining material that’s left after going nova, is what has housed the systems gravity all along… and the mass leaving the star doesn’t reduce the systems over all gravity, so planets will stick around for a while. I’m not sure how that works, so I don’t know.
Okay, I’ll just ask a general question. Can a large rocky planet ever leave its solar system on a straight path to hell at insane speeds? :eek:
[/QUOTE]

Well, when the sun turns into a white dwarf it will have likely ejected quite a bit of its mass. So any remaining planets are going to have their orbits altered, especially for the few million years the sun is ejecting that mass…friction will slow the planets.

But the speed of a planet around the sun is very very small in astronomical terms. The sun is orbiting around the center of the galaxy, objects are zooming through interstellar space, probably lots of them. We just can’t see them unless they are massive enough to start fusion. There are lots of really small stars out there, red dwarfs, something like 100 times more red dwarf stars than main sequence stars like our sun. But it is very likely that there are even more smaller bodies out there, but we can’t detect them because they don’t shine.

So there are probably hundreds of trillions of planet sized objects out there in the galaxy that don’t orbit any star. And their movement relative to the earth will be many times larger than the earth’s velocity around the sun. So planets ejected from a solar system by a nova or some other method aren’t going to be traveling any faster than any other object floating around out there.

I guess the question you’re trying to ask is, we’re worried about asteroids hitting the earth, but why aren’t we worried about rogue planets zooming through our solar system and hitting the earth, or causing some other trouble.

And the answer is that sure, we could get rogue planets. But the distribution of objects is unequal. The solar system is filled with tiny little asteroids…specks of sand, pebbles, baseball sized rocks and iceballs. And these are much more comman than large asteroids…house sized asteroids. And house sized asteroids are much more common than dinosaur-killer mountain-sized asteroids. And there are only a few Texas-sized asteroids out there, I suppose Ceres could be described as Texas-sized. (I just visited Wikipedia. Ceres is 950 km in diameter. Texas is 1,200 km across. So Ceres is a bit smaller than Texas). But that’s the largest asteroid in the solar system, and it isn’t going anywhere.

Every day the earth gets hit by hundreds of sand-grain sized asteroids, meteor showers where dozens of larger meteors hit every minute happen now and then. But larger meteor strikes are rarer, because there just aren’t nearly as many large bodies in our solar system.

And an object ejected from another solar system is very unlikely to ever enter our solar system. As they say, space is really really big, and our solar system, large as it is, is really really tiny compared to the volume of interstellar space. And the earth is really really tiny compared to the volume of the solar system.

13

[QUOTE=ParentalAdvisory]
Can a large rocky planet ever leave its solar system on a straight path to hell at insane speeds? :eek:
[/QUOTE]

Oh, no doubt. Another massive body wandering in to the system would certainly do the trick quite nicely. (We’d likely see another conventional star coming, but a black hole, neutron star, or brown or white dwarf would be hard to impossible to see if it was headed our way.) A planet forming in a binary star system is likely to be ejected if it’s an intermediate distance from the two stars (not close enough to be orbiting one of them, and not far enough to be unaffected by the fact that there are two stars instead of one.) For that matter, a small planet can easily be ejected by a larger planet during the solar system’s formation, exactly like the probes that NASA has sent to fly by the outer planets (Voyager, Mariner, Pioneer, etc.)

14

Actually we’ve discovered one pulsar (neutron star) with a whole family of planets.

(The page which was the source of that quote appears to be the work of proponents of the crackpot “electric sun” theory.)

15

[QUOTE=MEBuckner]
…the crackpot “electric sun” theory.)
[/QUOTE]

Wasn’t aware of that theory. Did some more reading. Here is a discussion where it doesn’t seem so crackpot.

16

I’d hate to see a discussion that did look crackpot to you. That page could almost be a textbook example of crackpottery.

And to nitpick Lemur866, red dwarfs are main sequence stars. It is accurate to say that they’re a lot more common than the larger, hotter main sequence stars, though. On my table of the closest stars, out of the 52 closest (including some in multiple-star systems), 36 are red dwarfs, and only 3 are G-type (the Sun, alpha Cen A, and tau Ceti).

17

[QUOTE=Lemur866]
…As they say, space is really really big, and our solar system, large as it is, is really really tiny compared to the volume of interstellar space. And the earth is really really tiny compared to the volume of the solar system.
[/QUOTE]
Really, [size=7]REALLY[size], big.

In the standard “get a picture of how big it is” analogy, we put a basketball at home plate on a baseball diamond.

Mercury is a pellet of birdseed 35’ away
Earth is a peanut 90’ away (first base)
Jupiter is a 1" marble 450’ away (over the fence!)
Pluto (no longer a planet) is a grain of pepper way past the parking lot–about 2/3 of a mile away

To make the picture “realistic,” you raise the whole thing up in the air, start the planets orbiting–adding Venus, Mars, etc. of course–throw in some orbiting sand between Mars & Jupiter, and some more out past Pluto. The nearest start will be, on this scale, some 5,000 miles away.

Now take one of your Earth-sized balls and toss it at the solar system. It’ll miss Uranus, and everything else, and pass right through…so to speak.

Converting to metric is left as an exercise for the student.

18

[QUOTE=Chronos]
I’d hate to see a discussion that did look crackpot to you. That page could almost be a textbook example of crackpottery.

And to nitpick Lemur866, red dwarfs are main sequence stars. It is accurate to say that they’re a lot more common than the larger, hotter main sequence stars, though. On my table of the closest stars, out of the 52 closest (including some in multiple-star systems), 36 are red dwarfs, and only 3 are G-type (the Sun, alpha Cen A, and tau Ceti).
[/QUOTE]

I think it’s evident from Lemur’s comments that he’s referring to “brown dwarfs,” i.e., Superjovian agglomerations of hydrogen, helium, and trace elements that are not large enough to begin core fusion. As you note, “red dwarfs” are the Class M (and late Class K?) stars that are the smallest, least massive, dimmest members of the Main Sequence (and also the most common stars, something like 70-80% of all stars).

19

Huh. I misremembered. Red dwarfs ARE main sequence stars.

I don’t know why I thought red dwarfs weren’t main sequence, it’s the red giants and white dwarfs that aren’t main sequence.

But I believe the point still stands…there is an inverse correlation between the mass of an object and the frequency of that object type. There are only a few really massive objects, a medium amount of medium objects, and a lot of small objects. Our galaxy contains on the order of 100 billion stars, according to Eric Idle. So there are probably thousands of billions of Ceres and Earth and Jupiter sized objects zooming around the galaxy but not orbiting any star…but these objects are not likely to enter our solar system.

20

What about black dwarfs? After a star becomes a white dwarf, and its energy disappears completely, except for the fact that it is spinning (1000 times faster then if it contained hydrogen and helium material in the original star (I read that somewhere, not sure if it’s true)). Of course our universe hasn’t been around long enough to form black dwarfs, but lets say another 20 billion years a solar system goes black (a white dwarf loses all energy and light and gets a subzero surface, as well as its planets). Now if a system like this does not get affected by external forces, is it possible for orbiting objects to just “fall out”? What would prevent a falling out? Could a potential black dwarf stop rotating on it’s own without external forces (ex, galaxy mergers, etc…)? I’m talking about eons into the future here, well after brown dwarfs.