# Accuracy of a stellar collision event

I'm in the process of writing a story and the first few thousand words take place near the head-on collision between a ten mile wide black hole and a really big star. I describe the star as big enough to swallow the sun and barely burp.

I'd like the events to be as close to accurate as possible, so this is the process that I describe:

• As the two objects approach each other, the star's shape becomes distorted and egg-like
• Upon impact, barely anything happens at all, the black hole burrows into the star (would you even see anything?)
• The black hole is much denser and flies through the star like it's barely there, eating as it goes
• When it reaches the core, it's been slowed down enough to really start feasting and it hollows out the core
• The hollow core collapses and bounces. A neutrino blast is instantly detected, but the surface of the star shows no disturbances as the shockwave has to propagate the plasma
• The black hole accelerates it feasting and creates a whirling mass inside the star, and the charged swirling plasma creates magnetic jets
• Jets erupt out of the both poles of the star in a gamma ray burst, releasing as much energy as everything else in the universe combined during the brief flash
• The erupting polar jets shred the star, causing it to detonate in a super (hyper?) nova

berkeman

mfb
Mentor
If it gets captured depends on the initial velocities. It might need several passes through the star to finally stay inside. It would disturb fusion, but a new equilibrium can be found. You get a quasi-star. With a neutron star core instead of a black hole, the Wikipedia article is more detailed.
No reason to explode.

newjerseyrunner
Interesting, I've never heard of such objects before. It looks like this type of objects is only stable of the outer layers contain enough material to absorb the initial collapse of the core. It has a minimum mass of 1000 suns in order to do so which is in the upper few percent of stars. So a star with 750 solar masses should not be able to withstand it and blow up? I'd still consider that large enough to swallow the sun with just a burp.

The quasi-star is interesting, wouldn't for such an object to exist the outward pressure have to be fairly uniform? Don't black holes tend to accrete matter in a spinning disc? Spinning plasma creates magnetic jets doesn't it? I was under the impression that the jets produce pressure several orders of magnitude higher at the poles than the equator. I thought that's what powered a gamma ray burst?

mfb
Mentor
1000 solar masses? At least as classical star, that is not stable, it would quickly lose a large fraction of its mass due to stellar winds.

Radiation from an accretion disk would be quite uniform.

Staff Emeritus
How fast is this black hole going, and what are you doing about conservation of momentum?

phyzguy
I think people underestimate how quickly this all happens. The final stages of core collapse in a massive star happens in miiliseconds. I suspect your whole scenario above happens too quickly for a human to perceive the various stages.

1000 solar masses? At least as classical star, that is not stable, it would quickly lose a large fraction of its mass due to stellar winds.

Radiation from an accretion disk would be quite uniform.
I had no plans of making the star so huge, you mentioned quasi-stars however, which seems to have a minimum size of that. This star should be stable, so it'd be below the limits of the quasi-star, so it wouldn't be possible for the black hole to get sucked in and somehow have the star stabilize after adjusting itself.

How fast is this black hole going, and what are you doing about conservation of momentum?
The two objects would be pulling each other in, so pretty quick. It doesn't have to settle in the core, just pass through it spending enough time there to destabilize the star. Would it be able to do that at a million km/hr?

I think people underestimate how quickly this all happens. The final stages of core collapse in a massive star happens in miiliseconds. I suspect your whole scenario above happens too quickly for a human to perceive the various stages.
In my story, the core collapses almost instantly. There is some build up as the hole and star approach each other and some time while the hole burrows through the mantle of the star. If it's going a million km/hr it'd take a good half an hour to get anywhere near the core after hitting the surface, the star wouldn't go catastrophic until the core collapses right?

Also, I was under the impression that there actually was some delay between core collapse and explosion. For Supernova 1987A, the neutrino blast arrive 3 hours ahead of the explosion because the explosion had all of that material to shock through. Do bigger stars have more umph and go instantly?

mfb
Mentor
The quasi-stars were probably large in the early universe, they can be smaller today.
In my story, the core collapses almost instantly.
I don't see how and why that should happen.
Also, I was under the impression that there actually was some delay between core collapse and explosion. For Supernova 1987A, the neutrino blast arrive 3 hours ahead of the explosion because the explosion had all of that material to shock through. Do bigger stars have more umph and go instantly?
The 3 hours is the shockwave traveling outwards through the outer star layers.

I don't see how and why that should happen.
Hmm, when I had originally had the idea, the black hole would be slowed down by the matter of the star enough to settle in it's core and start eating it. I didn't take into consideration that the black hole could probably punch through the star pretty easily. Would there be a way to get the black hole to stay near the center long enough for it to hollow out enough of the inside for it to collapse and bounce in the way I need for the explosion? How would I be able to determine about how much the black hole would decelerate after entering the plasma of the star?

The 3 hours is the shockwave traveling outwards through the outer star layers.
Right, so a research vessel in orbit with the ability to detect neutrinos would detect the explosion on the inside long before the star actually detonates, correct?

mfb
Mentor
Hmm, when I had originally had the idea, the black hole would be slowed down by the matter of the star enough to settle in it's core and start eating it. I didn't take into consideration that the black hole could probably punch through the star pretty easily. Would there be a way to get the black hole to stay near the center long enough for it to hollow out enough of the inside for it to collapse and bounce in the way I need for the explosion? How would I be able to determine about how much the black hole would decelerate after entering the plasma of the star?
I can see how the black hole will stay in the core after not too long, but I don't see how this would lead to a rapid core collapse. Estimating the drag will probably need some hydrodynamics. The moving black hole attracts matter, which then accumulates behind it (more than in front of it), which slows down the black hole. It will also consume some infalling matter, but that effect is probably smaller than the dynamic one.
Right, so a research vessel in orbit with the ability to detect neutrinos would detect the explosion on the inside long before the star actually detonates, correct?
If there is an explosion, yes. Of the order of hours.

newjerseyrunner