MilkyWay Eats Galaxy

[supernova1965]

http://www.space.com/scienceastronomy/closest_galaxy_031104.html


Look at this:tasdevil:

[DavidU]

Thats a neat find. Very interesting.

[Robh]

Fascinating. With the Canis Major dwarf of a billion stars and assuming the Milky Way has 100 billion stars, I can see where the extra 1% mass comes from. However, the Milky Way could have up to 400 billion stars.
Assuming a collision of stars occurred, what is the outcome if two Sun-like stars collide? Supernova?

Regards, Rob.

[mithrandir]

Think this is right, but stellar physics isn't my strong point.

Supernovas are caused when a large star suffers gravitational collapse after the internal fusion reactions stop producing enough energy to prevent the collapse.

Sun-like stars don't have enough mass to go supernova. They go through a red "giant" phase and finally collapse into a white dwarf.

Now if two of these Sun-like stars collided and merged, the resultant star might be big enough to eventually go supernova, but it wouldn't be the collision that did it. Maybe if they were already white dwarfs before the collision you might get your supernova.

[dpastern]

My stellar physics isn't strong either, but my understanding of stellar evolution is that stars with less than 1.4 solar masses after they have collapsed at the end of their lives and thus have lost solar mass to atmospheric ejections, etc can become white dwarfs.

Those above that cannot become a white dwarf unless they are rotating version (I'm not entirely sure of the physics of this aspect). White dwarf stars that have more than 1.4 solar masses after collapsing and ejecting material etc, are not possible (Chandrasekhar limit). I believe stars up to 8 solar masses pre collapse are under this limit, as the material at their core is not sufficient to be burnt and it's only the solar mass left after all fusionable materials have been burnt that really counts.

Anything above 8 solar masses is doomed to become a supernova, and eventually a neutron star or black hole, depending upon the original solar mass.

That's my basic understanding of it all.

2 solar masses (merged) wouldn't be sufficient to cause a supernova. More likely, the larger of the 2 would win out (due to gravity/mass relations) and draw material from the smaller of the 2 stars, probably stripping the 2nd star to the point where it becomes a white dwarf.

Dave

[Robh]

Yes, in terms of all up mass (2 solar masses) there wouldn't be enough for an evolutionary supernova.
But there must be some immediate effect of the collision.
I was thinking that there would be an enormous amount of added energy due to the momentum of the two colliding stars. Would this act to increase the temperature of the merged stars and cause a blow out of super-heated gases into space? :shrug:

Regards, Rob.

[renormalised]

They won't collide....the stars are that far apart that the chances of them colliding are vanishingly small. The average star in our part of the galaxy is roughly 10 light years apart, and for the galaxy overall about 4 light years. Either distance is about 6-7 orders of magnitude larger than most stars and even 4-5 orders larger than the largest stars. You can see from this how unlikely a collision is.

Even on the off chance two stars did collide, they'd just eventually merge into a larger star. So long as the collision's dynamics were right.