Two stars collide: Black Hole vs Supernova

[I like Chop Goblins.]

I know nothing about the science of astrophysics. I assumed black holes happen when a star gets too massive and ultimately collapses under its own gravity. So why does a supernova happen when colliding two stars together, instead of a black hole? Do black holes ONLY form out of "slow and steady" processes like a star slowly gobbling up non-star matter?

[76561198025051992]

The "fuel" in stars burn when it's compressed. If it's compressed all at once, it burns all at once, and this is a supernova. Black holes form when the core of a star is out of fuel and it collapses with nothing to burn. That's about as simple as I can make it.

[Wehr Wulf]

Originally posted by Holden Afart:

I know nothing about the science of astrophysics. I assumed black holes happen when a star gets too massive and ultimately collapses under its own gravity. So why does a supernova happen when colliding two stars together, instead of a black hole? Do black holes ONLY form out of "slow and steady" processes like a star slowly gobbling up non-star matter?

Youre talking about in the game vs IRL I assume? Because yea, the in game physics arent accurate in that scenario.

Black holes happen at the end of a stars life when it runs out of fuel ( only big stars, 8x more massive that our sun ).

IRL, 2 stars colliding or combining is not any different that 2 asteroids or 2 planets.... if they collide at high speed, itd be messy. If they slowly come into contact (decaying orbit) they would just merge, combine their mass into a larger star....

But either way, 2 stars coming together wouldnt cause a supernova or a black hole (like what you see happen in game) because that only happens when a massive star spends all its fuel.

[H54L]

Useful comment by Wotan. Only 1 change in wording I'd make, that while a stellar merger (in addition to being messy) would it seems likely *usually* result in a larger, hotter shorter lived star, such as because the cores of the stars would pretty much never hit straight on, it would be interesting to get a good simulation of sufficiently massive stars with a head on centered core to core collision, and something like an explosive event, even though not a supernova, seems a plausible aspect. This is of course still a variation of 'messy'.

[davidb11]

To be fair, we've determined in real life a bunch of Supernova are caused by the collision of Two White Dwarf stars, having gone past the Chandrasekhar limit from the impact merger.

So, uh, supernovas don't need to be done very slowly when a star burns out of fuel over millions of years. :P

[H54L]

:-) Yeah, that's fun. I'd love to see a lot of compact object merger stuff done in Universal Sandbox with realistic time scale of orbital decay (even though they could not reasonably today also get a lot of the actual merger detail in for abritary objects, I'd be satisfied with just a general category explosion (no calculation on our PCs needed), etc. (I'm assuming this gravitational decay stuff is not already done in USandbox. Is that right?)

Of course, while white dwarf mergers aren't one of the main types of supernova *that we've detected commonly* -- since they are less energetic (harder to find) than such as kilonova events -- I'd like to add one thing to answer a bit of the OP question about what results. (also you might like to see the article further below)

For the OP: For most white dwarf mergers we should not get black holes from them (since getting above 2.4 solar masses would be the less common outcome, usually it would not be enough mass to get a black hole then). Mostly we'd end up with heavy white dwarfs or neutron stars. This is since even for white dwarfs merging that together go past the Chandrasekhar limit, I'd expect even for most of those heavier mergers we'd still see more commonly a neutron star for these since very often the 2 white dwarfs together would still together mass less than 2.3 solar masses, as very many white dwarfs are much less than the most massive ones that approach 1.4 solar masses.

Also, I was just looking over this report, and you might like it also:

"...rare type of astronomical event—and may finally confirm the identity of a brilliant but short-lived star observed nearly 850 years ago. ...
"... Pa 30 appears to contain little to no hydrogen and helium but is instead rich in the elements of sulfur and argon.

"The nebula's unusual structure and characteristics match the predicted result of a collision between end-stage stars known as white dwarfs, Fesen said. White dwarfs are faint, extremely dense stars about the size of Earth that contain the mass of the Sun. The merger of two white dwarfs is one proposed explanation for a subclass of supernovae—or star explosions—called Iax events, in which the star is not completely destroyed, Fesen said."

"I have never seen any object—and certainly no supernova remnant in the Milky Way galaxy—that looks quite like this, and neither have any of my colleagues," Fesen said. "This remnant will allow astronomers to study a particularly interesting type of supernova that up to now they could only investigate from theoretical models and examples in distant galaxies."

"The study by Fesen and his co-authors built upon work published in 2019 by Russian researchers who found an extremely unusual star nearly in the dead center of Pa 30. That star exhibited several properties suggesting the collision of two white dwarfs, and it had a surface temperature of nearly 400,000 degrees Fahrenheit with an astounding outflowing wind velocity of about 35 million miles per hour."
(continues...))
https://phys.org/news/2023-01-images-capture-year-old-aftermath-stellar.html

It would be fun to see additional images of nublea from these.