I need a formula!

[nomercy745]

I have a theroy i need to prove. In order to do it i need the formula that calculates the resulting mass of a star after 2 stars collide. If you have it I like to have it.

[UncleAl]

Mass is conserved. Calculating splatter and combined remnant is something very different. It requires discrete hydrodynamic simulation and it is intensely sensitive to starting conditions like spins and angle of attack. We're talking months in a supercomputer.

 

Star collision movies

Stellar Collisions and Cosmic Catastrophes

 

--

Uncle Al

UNDER SATAN'S LEFT FOOT

Vote a 10 for doing the experiments!

[freeztar]

Assuming both stars are either matter-matter or antimatter-antimatter, UncleAl is right, mass is conserved. The resultant mass is simply the mass of star 1 plus the mass of star 2.

[modest]

I agree that invariant mass is conserved. But, the invariant mass of more than one particle is not equal to each of their individual invariant masses added together unless they are all at rest to one another, so the question does get a little complicated.

 

Before and after the collision, I think this should hold:

 

[math]m = \frac {\sqrt{E^2 - (pc)^2}}{c^2}[/math]

 

where E is the sum of the energy of each star and p is the sum of the momentum of each star.

 

Mass in special relativity - Wikipedia, the free encyclopedia

 

~modest

[nomercy745]

thk u modest

[Qfwfq]

the invariant mass of more than one particle is not equal to each of their individual invariant masses added together unless they are all at rest to one another,

In the case of two stars, the kinetic and potential energies would be unimportant. Long before they do becomes important, you would have certainty of relevant quantities of matter being ejected with positive total energy. There probably are few cases in which this wouldn't occur. The pair would almost have to be in a bound state with dissipative effects bringing them gradually closer and with spins and orbits arranged so that surfaces meet without too much velocity difference.

[modest]

Yeah, I was just talking about that with Freeztar in a PM. I am assuming (perhaps incorrectly) that the OP is not really curious about stars, but more in lines with what happens relativistically when ideal objects collide. I probably said it better in the PM...

 

But, I'm not entirely sure about the OP in that thread. It's not very specific and we didnt't really ask for clarification. Your link ignores any contribution form special relativity, and that's only normal because no star in the real world would be traveling relativistic speeds relative to another. I don't know if the OP was wanting to take relativity into consideration or not. I assumed that he didn't so much care that the masses were stars but was just wondering what happened relativistically with masses when they collide.

 

I could be wrong about that though. His question might have been more along the lines of what really happens when actual stars collide in which case your link would probably be very helpful.

 

 

Nomercy, if you would like to ignore the effects of special relativity then the mass of the resulting star would simply be the rest mass of each colliding star summed. You could then, if you wanted to be a bit more exact, subtract the energy released in the collision (a nova, supernova, or GRB) divided by the speed of light squared.

 

~modest