Help me understand Supernovas

[Kuroneko]

Thanks for the corrections.

You know what? We are both wrong. For some reason I expected the kinetic energy to double in order to preserve the total, but that is silly and actually checking this reveals an error. Let's say the new velocity is w. Then we have v²/2-μ/r = E = w²/2-2μ/r, i.e., initial = final, so that w² = v²+2μ/r, but since μ = v²r according to the assumption of an initially circular orbit, w² = 3v². What this means is that the kinetic energy triples, meaning that the eccentricity will be 2--a hyperbola! Since the resulting black hole would be small, this means that the Earth will escape solar system.

[Lord Zentei]

Thanks for the corrections.

You know what? We are both wrong. For some reason I expected the kinetic energy to double in order to preserve the total, but that is silly and actually checking this reveals an error. Let's say the new velocity is w. Then we have v²/2-μ/r = E = w²/2-2μ/r, i.e., initial = final, so that w² = v²+2μ/r, but since μ = v²r according to the assumption of an initially circular orbit, w² = 3v². What this means is that the kinetic energy triples, meaning that the eccentricity will be 2--a hyperbola! Since the resulting black hole would be small, this means that the Earth will escape solar system.

Ah, well. Happens to the best of us.

[Lukedanieljames]

You guys are really on the ball here, this is FANTASTIC!

so let me see, after the correction in math it is deemed that if a blackhole replaced our sun that the planets would actually float away into "outer space"

Ok another question, and i'm truely sorry for them all

what if a supermassive blackhole appeared in the middle of our solar system, replacing the sun

just for shits and giggles

would even the Kupler(sp?) belt be pulled in?

[Kuroneko]

so let me see, after the correction in math it is deemed that if a blackhole replaced our sun that the planets would actually float away into "outer space"

Only if the black hole had greater mass, but not great enough for the orbit to fall in, and if the operation conserves orbital energy. If only kinetic energy is conserved instead, then the orbits will elongate into high-eccentricity ellipses.

what if a supermassive blackhole appeared in the middle of our solar system, replacing the sun

Under the former scenario, the objects follow initially hyperbolic trajectories into the black hole.

[Lukedanieljames]

excellent info, excellent

i'm going to keep pounding away with questions right now, because i'm really close to getting all the answers I need.

I've read online on the nasa site I believe that if a large star ie 100 times the mass of the sun, decides to go supernova, that it can affect plantes up to 3300 lightyears away, and if it was class b or c up to 28 lightyears away, aslong as its a big enough star

Now here is the question, after the supernova, the star of that size would collapse down into a blackhole, although not a supermassive blackhole, smaller than the mass of the star itself, now....


If this star went supernova, and then the subsequent black hole appeared, I already know what happens when a blackhole like that appears, and I know what a supernova can do at distance if its big enough, so my question is

what would do more damage to planets and solar systems at a distance, (ie other solar systems)

a very large star going supernova and then turning into a blackhole, or a supermassive blackhole just appearing there, what would affect more of a region of space,

from what I understand, I believe the supermassive blackhole would do more damage, considering it is holding a galaxy together,

your thoughts?

[Lord Zentei]

excellent info, excellent

i'm going to keep pounding away with questions right now, because i'm really close to getting all the answers I need.

I've read online on the nasa site I believe that if a large star ie 100 times the mass of the sun, decides to go supernova, that it can affect plantes up to 3300 lightyears away, and if it was class b or c up to 28 lightyears away, aslong as its a big enough star

Now here is the question, after the supernova, the star of that size would collapse down into a blackhole, although not a supermassive blackhole, smaller than the mass of the star itself, now....


If this star went supernova, and then the subsequent black hole appeared, I already know what happens when a blackhole like that appears, and I know what a supernova can do at distance if its big enough, so my question is

what would do more damage to planets and solar systems at a distance, (ie other solar systems)

a very large star going supernova and then turning into a blackhole, or a supermassive blackhole just appearing there, what would affect more of a region of space,

from what I understand, I believe the supermassive blackhole would do more damage, considering it is holding a galaxy together,

your thoughts?

The appearance of the black hole due to the supernova is not what does damage in and of itself. It is the burst of radiation that is part and parcel of the supernova explosion. That is why type I supernovae (the exploding white dwarf kind) can cause damage even though they do not leave behind a black hole.

A miraculous appearance of a supermassive black hole would not immediately cause anything other than the orbits of nearby stars to be thrown into kilter. However, as the hole starts gobbling stuff up, an accretion disc would form around it, and this would irradiate nearby space. Just how soon this would occour, and the extent of the irradiation is a little hard to assess since it is dependant on a range of factors, but in the long term the supermassive black hole would cause more damage.

[Lukedanieljames]

The appearance of the black hole due to the supernova is not what does damage in and of itself. It is the burst of radiation that is part and parcel of the supernova explosion. That is why type I supernovae (the exploding white dwarf kind) can cause damage even though they do not leave behind a black hole.

ah yes, i understand this, thats why i was wondering if a supernova or a supermassive blackhole does more damage in a given area of space, you know..say 3000 lightyears in diameter.

A miraculous appearance of a supermassive black hole would not immediately cause anything other than the orbits of nearby stars to be thrown into kilter. However, as the hole starts gobbling stuff up, an accretion disc would form around it, and this would irradiate nearby space. Just how soon this would occour, and the extent of the irradiation is a little hard to assess since it is dependant on a range of factors, but in the long term the supermassive black hole would cause more damage.

that was my feeling aswell, a supermassive blackhole a 100,000,000x more massive than a star is certainly going to start eating planets and stars, I was reading on i believe it was the harvard website that a blackhole ate an entire star in a matter of minutes once the star got close enough, scary thought

[Surlethe]

I was reading on i believe it was the harvard website that a blackhole ate an entire star in a matter of minutes once the star got close enough, scary thought

This is only natural. A black hole does damage through tidal forces; and for an object which close to the black hole's size, or bigger, there will be a significant differential in acceleration from one side of the object to the other. This, in turn, will stretch out the object and, eventually, tear it to shreds; a star, since it's so big compared to the average black hole, would be stretched out and torn up before it entered the black hole. To get a good mental image of a tidal force, think of what happens when you have a circle of soapsuds floating in the bathtub. When it approaches the drain, it will elongate and stretch out; this is because the part of the sud circle closest to the drain accelerates faster than the parts further away. When the difference in acceleration becomes large enough, the sud circle rips apart into a stream of bubbles.

[Kuroneko]

Like many questions, the answer is "it depends". If this is a galaxy like that of Star Wars, with inhabited systems just about everywhere and the timescale is millions of years, yes, the magically appearing supermassive black hole could do some major damage, particularly if it is spawned near the core worlds or with low enough angular momentum so that it eventually plunges into them.

The region of significant gravitational effect is usually quantified as the Hill-Roche sphere radius. Let's take the Milky Way with the Sun's orbit as a test case. The Sun has distance from galactic center about r = 2.5e20m and period of about T = 7.5e15s; we have standard gravitational parameter of the galactic mass within r as μ = 4π²r³/T² = 1.1e31m³/s². For a solar mass, we have Hill-Roche sphere radius R[GM☉/(3μ)]^{1/3} = 4.0e16m = 4.2ly; abitrary masses scale as the cube root. For example, the Sagittarius A* supermassive black hole has a mass of 2.6e6 solar masses, so if one like it appeared at Sun's orbit, it would have a Hill-Roche radius of 2.6e6^{1/3}*4.2ly = 580ly. A 1e8-solar mass black hole would have a H-R radius of almost two thousand lightyears.

Note that a star being within the H-R radius does not guarantee that the black hole will swallow it or even that it will force the star into orbit around it. It just puts an upper bound on anything substatinally interesting happening. Orbits usually occur at less than half this radius. If the black hole spawns somewhere other than at the radius of Sun's orbit for a Milky-Way-like galaxy, needless to say, the numbers change.

[Ma Deuce]

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.

It is also unlikely a biosphere would even form on a planet orbiting a star hot or massive enough to end it's life in a supernova; such stars tend to have lifespans of only a few hundred million years anyway. Come to think of it, in most cases that might not even be enough time for planetary bodies to form at all. I don't recall any extra-solar planets being discovered orbiting stars hotter than Class F.

[Lord Zentei]

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.

It is also unlikely a biosphere would even form on a planet orbiting a star hot or massive enough to end it's life in a supernova; such stars tend to have lifespans of only a few hundred million years anyway. Come to think of it, in most cases that might not even be enough time for planetary bodies to form at all. I don't recall any extra-solar planets being discovered orbiting stars hotter than Class F.

Indeed. If any life existed it would at most be of the bacterial level. In a Sci Fi verse, life might possibly have migrated there (though it would be a rather odd thing for a civilization to colonize any planets that might be found around O, B or A class stars - unless there were a resource not present elsewhere for instance).

As for the presence of planets, it is true that none have been found around stars larger than class F. Of course, by the very mass of the star, they would also be harder to detect, and there is still much to learn about planetary formation.

You might also be dealing with a "loose" multiple star a la Alpha and Proxima Centauri (where Proxima may have been captured by Alpha), which would solve both problems.