Help me understand Supernovas

[Lukedanieljames]

Hi everyone.

I have been reading all night about supernova's and I realize that our star is not massive enough to create a supernova, so lets say that it was, say 20 times more massive than our current sun.

Say that it had already collapsed and now the star sends out its shockwave at 10e41 J.

Can you explain to me in detail what would happen to each of the planets in the solar system.

I just curious because the sun crusher was supposed to destroy a solar system, but I'm hearing contradicting reports here.

Sometimes articles are saying that if one 'detonated' closer than 3300 lightyears it would strip our planet of its ozone, you can find this on almost any astrological site.

However non talk about what happens to stellar bodies inside a solar system

like jupitar, would it go unscathed? or would it explode?

i can't understand whats happening to these planets, and why the sun crusher can 'destroy' a solar system
thanks guys

[Lukedanieljames]

actually this article states that a supernova would obliterate any planet in the solar system
http://www.space.com/searchforlife/seti ... 10719.html

[Durandal]

First lesson. It's "supernovae".

[Lord Zentei]

Supernovae come in two flavours, type I and type II (these can have further subclassifications).

A simplified overview:

Type I supernovae occour in binary (or larger) systems when a white dwarf star orbits a mainsequence companion. At times this orbit is tight enough that gas is pulled away from the companion onto the white dwarf. In such an event, the white dwarf gains huge ammounts of extra fuel that cause it to explode, provided the total mass goes beyond the Chandrasekhar limit.

Type II supernovae occour in supergiant stars when they have used up all the fuel in their cores. In such an event the energy production that used to push against the star's gravity (remember, it has no solid structure, so should compress under its own gravity) stops, and the star collapses. The core is crammed into either a neutron star or a black hole, while the outer layers recoil outwards in an explosion at a significant fraction of the speed of light.

In regular stars, the core collapses but not into a neutron star or a black hole; the outer layers puff out into a red giant. In later stages, the red giant gradually blows itself away in a stellar superwind (like the solar wind, only more vigorous), and the core remains as a white dwarf.


PS: if you want more details, the Wiki artcles on supernovae are actually quite decent.

[Lord Zentei]

actually this article states that a supernova would obliterate any planet in the solar system
http://www.space.com/searchforlife/seti ... 10719.html

However, any ol' stellar disruption is not neccesarily a supernova.

[Lukedanieljames]

I read the wikipedia already, however it doesn't say anything about what happens to planets that are in the solar system, or another close by solar system

[Lord Zentei]

I read the wikipedia already, however it doesn't say anything about what happens to planets that are in the solar system, or another close by solar system

It does in cact go into that, at the bottom of the page:

Possible threats to Earth

Several prominent stars within a few hundred light years from the Sun are candidates for becoming supernovae in a relatively short time, perhaps as little as 1000 years into the future. Speculations as to the effects of a nearby supernova on Earth often focus on these large stars, such as Betelgeuse, a red supergiant at a distance of about 400 light years from Earth. Of interest is the conclusion that Type Ia supernovae are the most potentially dangerous, if they occur close enough to the Earth. Since these supernovae are the result of accretion onto relatively dim, common, white dwarf stars, it is likely that a supernova that could affect the Earth will occur unpredictably, and take place in a star system that is not well studied. The predictable supernovae, such as Betelgeuse, while spectacular, will have little effect on Earth. There is an estimation that a Type Ia supernova would have to be closer than 1000 parsecs - roughly 3300 light years - to affect the Earth [1]. There are likely to be many Type Ia candidates within this distance. However the typical rate for Type Ia supernovae in a galaxy is about 1 per 1000 years[2], and therefore the probability of one occurring within 1000 parsecs of Earth, given that the Milky Way is about 30,000 parsecs in diameter and 1000 parsecs thick, is probably less than 1 per 1 million years. The probability of a Type Ia within 100 parsecs is about 1 per billion years or less. Thus it is likely that a nearby Type Ia about 100-1000 parsecs away has occurred several times within the history of life on Earth, about 500 million years ago, but is unlikely to occur anytime within the lifespan of the human species.

Recent estimates predict that a Type II supernova would have to be closer than 8 parsecs, which is about 26 light years, to destroy half of the Earth's protective ozone layer [3]. Such estimates are mostly concerned with atmospheric modelling and considered only the known radiation flux from SN 1987A, a Type II supernova in the Large Magellanic Cloud.

[Lukedanieljames]

I read the wikipedia already, however it doesn't say anything about what happens to planets that are in the solar system, or another close by solar system

It does in cact go into that, at the bottom of the page:

Possible threats to Earth

Several prominent stars within a few hundred light years from the Sun are candidates for becoming supernovae in a relatively short time, perhaps as little as 1000 years into the future. Speculations as to the effects of a nearby supernova on Earth often focus on these large stars, such as Betelgeuse, a red supergiant at a distance of about 400 light years from Earth. Of interest is the conclusion that Type Ia supernovae are the most potentially dangerous, if they occur close enough to the Earth. Since these supernovae are the result of accretion onto relatively dim, common, white dwarf stars, it is likely that a supernova that could affect the Earth will occur unpredictably, and take place in a star system that is not well studied. The predictable supernovae, such as Betelgeuse, while spectacular, will have little effect on Earth. There is an estimation that a Type Ia supernova would have to be closer than 1000 parsecs - roughly 3300 light years - to affect the Earth [1]. There are likely to be many Type Ia candidates within this distance. However the typical rate for Type Ia supernovae in a galaxy is about 1 per 1000 years[2], and therefore the probability of one occurring within 1000 parsecs of Earth, given that the Milky Way is about 30,000 parsecs in diameter and 1000 parsecs thick, is probably less than 1 per 1 million years. The probability of a Type Ia within 100 parsecs is about 1 per billion years or less. Thus it is likely that a nearby Type Ia about 100-1000 parsecs away has occurred several times within the history of life on Earth, about 500 million years ago, but is unlikely to occur anytime within the lifespan of the human species.

Recent estimates predict that a Type II supernova would have to be closer than 8 parsecs, which is about 26 light years, to destroy half of the Earth's protective ozone layer [3]. Such estimates are mostly concerned with atmospheric modelling and considered only the known radiation flux from SN 1987A, a Type II supernova in the Large Magellanic Cloud.

it states it for both types, one is 26 lightyears, the other 3300 lightyears

but it doesn't say anything for planets within 1 light year or in a solar system

[Lord Zentei]

An explosion 100 billion times brighter than the Sun will appear as bright as the Sun at a range of 5 light years or so (note that this is for the visible band only). At a range of 1 light year it will appear 25 times brighter than the Sun, and 100 times brighter at half a light year.

This is from the inverse square law of flux, and the fact that there are ~65k astronomical units to a light year.

I imagine that surface biospheres within the range you specified will most likely be destroyed, though the planets themselves will survive (as long as the supernova does not occour within the actual system itself). Some things might survive in deep sea vents or deep underground, though don't quote me on that.

[Lord Zentei]

Mind, much of the energy is high yield radiation, not visible light.

[Manus Celer Dei]

So hang on, are black holes and neutron stars the only possible outcomes of a supernova? I though it was also possible for a white dwarf to be formed.

[Dooey Jo]

So hang on, are black holes and neutron stars the only possible outcomes of a supernova? I though it was also possible for a white dwarf to be formed.

No, white dwarves form from lower mass stars. White dwarves can however be caused to go supernova as explained by Lord Zentei above (type I supernovae).

[SirNitram]

it states it for both types, one is 26 lightyears, the other 3300 lightyears

but it doesn't say anything for planets within 1 light year or in a solar system

That's because you have to factor in a number of variables for that; there's no generic answer.

The size of the star is needed, to compute the energy it puts out.

The distance of the planet is needed, to work out how much energy reaches it's orbit.

The size of the planet's silhouette in regards to facing the star is needed, because stars are huge, the sphere of a supernova is many, many times that, and a planet is tiny. Most energy will never interact with the planet.

[Lord Zentei]

I imagine that surface biospheres within the range you specified will most likely be destroyed, though the planets themselves will survive (as long as the supernova does not occour within the actual system itself). Some things might survive in deep sea vents or deep underground, though don't quote me on that.

NOTE: It is highly unlikely that there is a biosphere in the same system as a star that is about to go supernova: such stars swell into red supergiants first, increasing in luminosity, so any life would presumably be fried already anyway.

[Lukedanieljames]

Here is a question, i read on the internet that if our sun was replaced with a blackhole of equal mass, that nothing would happen to our orbits, this makes sense, however, since the mass is actually at the singularity of the blackhole and not spreadout or relatively spreadout as in a star, would the earth's orbit move a bit closer to the blackhole, and then perhaps never stop moving forward until we were eaten?

[Lord Zentei]

Here is a question, i read on the internet that if our sun was replaced with a blackhole of equal mass, that nothing would happen to our orbits, this makes sense, however, since the mass is actually at the singularity of the blackhole and not spreadout or relatively spreadout as in a star, would the earth's orbit move a bit closer to the blackhole, and then perhaps never stop moving forward until we were eaten?

Nope. If the Sun were magicaly turned into a black hole of equal mass, the orbits would not change.

For spherical objects like the Sun (and planets) the field of gravity above the surface is identical to what it would be if the mass were concentrated in the center. It is the distance as measured from the center that counts, not the distance from the surface.

Below the surface of a star or planet, however, the gravity does become different: specifically it gradually diminishes, until it becomes zero gravity at the center.

[Lukedanieljames]

Here is a question, i read on the internet that if our sun was replaced with a blackhole of equal mass, that nothing would happen to our orbits, this makes sense, however, since the mass is actually at the singularity of the blackhole and not spreadout or relatively spreadout as in a star, would the earth's orbit move a bit closer to the blackhole, and then perhaps never stop moving forward until we were eaten?

Nope. If the Sun were magicaly turned into a black hole of equal mass, the orbits would not change.

For spherical objects like the Sun (and planets) the field of gravity above the surface is identical to what it would be if the mass were concentrated in the center. It is the distance as measured from the center that counts, not the distance from the surface.

Below the surface of a star or planet, however, the gravity does become different: specifically it gradually diminishes, until it becomes zero gravity at the center.

Here is a followup question

say with a snap of Q's finger, that a blackhole replaces our sun, but Q decides to increase its mass 2 fold,

that is one thing, another is the same, except say its 50 times more massive,

what would happen to the planets?

would pluto eventually get sucked into the blackhole, or would it just orbit closer?

and how long would it take
!

[Lord Zentei]

Here is a followup question

say with a snap of Q's finger, that a blackhole replaces our sun, but Q decides to increase its mass 2 fold,

that is one thing, another is the same, except say its 50 times more massive,

what would happen to the planets?

would pluto eventually get sucked into the blackhole, or would it just orbit closer?

and how long would it take
!

It would simply orbit closer. The orbital energy of a planet is the kinetic energy plus its (negative) potential energy, and this is conserved. If anything does get sucked in, it would cause the black hole to spin (faster).

There is a good page on it here: Linka

The relevant bit:

Semi-major Axis and Total Energy

The relationship between these two can easily be derived for a circular orbit and also works for elliptical and hyperbolic orbits. As we see in the diagram: a = F/m = GM/r2 = v2/r. In the case of a circle e = 0 and r = a. So
v2 = GM/a and thus:
E = 1/2 m(GM/a) - m(GM)/a = m (GM)/(2a)
E/m = GM/(2a)

Given that the orbital energy of the planet is conserved, the semimajor axis would be reduced proportionally to the mass. So, the orbit would be 2x or 50x tighter, respectively.

The planet would start the new orbit as soon as it felt the new gravity field (the orbit would be much more elliptical than previously).

[Lord Zentei]

The planet would start the new orbit as soon as it felt the new gravity field (the orbit would be much more elliptical than previously).

Clarification: it would start accellerating due to the new gravitic field as soon as it felt its effects, if the current location of the planet is beyond what would be possible for its new orbit for the given stellar mass, it would spiral inwards towards the new orbit; I'm not entirely sure of the time taken, though I imagine it would be in the same ballpark as a Hochmann transfer; I imagine someone better versed than I (Kuroneko for instance) can give a better answer if I am mistaken in this.

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[This edit is brought to you by the letters, N and L.]

EDIT: Of course, the fact that we are dealing with a magical replacement scenario makes it a little hard to assess.

If we do not assume that the orbital energy is conserved, and instead assume that the kinetic energy alone is conserved, we need to recalculate the potential energy and hence the orbital energy of the planets.

[Lukedanieljames]

The planet would start the new orbit as soon as it felt the new gravity field (the orbit would be much more elliptical than previously).

Clarification: it would start accellerating due to the new gravitic field as soon as it felt its effects, if the current location of the planet is beyond what would be possible for its new orbit for the given stellar mass, it would spiral inwards towards the new orbit; I'm not entirely sure of the time taken, though I imagine it would be in the same ballpark as a Hochmann transfer; I imagine someone better versed than I (Kuroneko for instance) can give a better answer if I am mistaken in this.

-------------------------------

[This edit is brought to you by the letters, N and L.]

EDIT: Of course, the fact that we are dealing with a magical replacement scenario makes it a little hard to assess.

If we do not assume that the orbital energy is conserved, and instead assume that the kinetic energy alone is conserved, we need to recalculate the potential energy and hence the orbital energy of the planets.

I wonder how much larger the mass has to be until everything in the system is sucked into the blackhole
i know there are stars with masses 100x larger than our sun, maybe if one of those was put in our system that all the planets would get eaten

i doubt it would take a supermassive blackhole like something in the middle of a galaxy

[drachefly]

Well, how fast do you want it to be sucked in?

Once you get a couple of the hole's diameters away, it acts just like a normal heavy object.

So, to suck in the whole solar system, it would need to be about as big as the solar system. And then it would be about as heavy as the black hole at the center of the galaxy, after all.

[Lord Zentei]

Well, how fast do you want it to be sucked in?

Once you get a couple of the hole's diameters away, it acts just like a normal heavy object.

So, to suck in the whole solar system, it would need to be about as big as the solar system. And then it would be about as heavy as the black hole at the center of the galaxy, after all.

Not neccesarily: if you assume that the orbital energy of any given planet is conserved, they would presumably just move into a tighter orbit. In that case, a planet would only be sucked in if the new orbit was smaller than the black hole.

But if it is only kinetic energy that is conserved, the potential energy needs to be reassessed and the new orbital energy might drop far enough that the hole gobbles the planet much sooner.

[Kuroneko]

The question is inherently ambiguous. "Magically" doubling solar mass can be taken in a variety of ways, depending on just which conservation laws are violated (besides, of course, mass). (1) If mechanical energy is conserved, then the potential of every mass surrounding the Sun doubles, forcing kinetic energy to compensate. This accelerates the planet in a short time frame and kills all life on Earth from the stress. (2) Alternatively, if kinetic energy is conserved but potential is ignored (let's say the difference is blamed on subspace or some such babble), the result is more interesting.

Because the result of this event depends somewhat on the location of the Earth at the time it occurs, I'll assume for simplicity that the the Earth's orbit is circular with velocity v = 2.9783e4m/s at orbital radius r = 1.4961e11m (this reprsents the "typical" configuration). The eccentricity is the norm of the eccentricity vector (v×(r×v))/μ - r/|r|. Note that the assumption of circular orbit means v is normal to r, v×(r×v) is away from the origin, and μ = v²r exactly.

(1) Now, in the former scenario, kinetic energy (~v²) is tripled (see next post) when μ is doubled. Therefore, the new eccentricity is e = |3v²r/μ-1| = 2, a hyperbola. (2) In the latter scenario, everything stays the same except μ and gravitational potential, so the new eccentricity is then e = |1/2-1| = 1/2. If multiplied 50-fold, it is |1/50-1| = 49/50. In other words, the Earth's new orbit is elliptical (e<1) that still includes the point at which the event has occured (as it should). As the mass increases, the orbit becomes more and more 'squashed', with the major axis becoming much greater than the minor axis.

Edit: In the first scenario, incorrect reasoning fixed.

[Lord Zentei]

Thanks for the corrections.

(And of course, I neglected to consider the stress killing life on Earth in the event of mechanical energy being conserved).

[Dooey Jo]

I wonder how much larger the mass has to be until everything in the system is sucked into the blackhole
i know there are stars with masses 100x larger than our sun, maybe if one of those was put in our system that all the planets would get eaten

i doubt it would take a supermassive blackhole like something in the middle of a galaxy

You can have particles escaping from a black hole as long as they are not within the Schwarzchild radius (although circular orbits would be impossible before that). Of course, since planets are pretty big, one could probably say that it is definitely doomed if the distance is less than the Schwarzchild radius plus the planet's own radius. Depending on the black hole, the planet may begin breaking up before that (the gravitional stress on the planet could be too high, for instance).

So in order for your black hole to eat the planets, you would have to get them quite close. As drachefly said, a few radii away, a black hole will act just like any other point mass, so unless your scenario creates really elliptical orbits, you will need a huge black hole.