# Merging of yellow dwarf stars (type G) - what will happen?



## matt-browne-sfw (Aug 1, 2007)

I know it's very unlikely that stars ever come too close to each other e.g. when two spiral galaxies merge. Well, Andromeda and the Milky Way will merge eventually.

There's a lot of speculation about merging of neutron stars or black holes. This event might trigger GRBs for example.

Let's take much smaller stars like our Sun. Suppose the path of another star of similar size crosses that of the Sun. Let's not consider what this will do with all of the planets in our solar system. Let's just look at the two yellow dwarfs.

What exactly will happen? Will they simply merge, eject a bit of mass, but basically the result is a merged star with say almost twice the weight of our Sun burning a bit faster? 

Or the other extrem: will they both be destoyed? No stars are left, only scattered fragments of stellar material? A kind of planetary nebula?

Can we simulate this with computer models? Can we predict the outcome?

I know the probability is virtually zero, but not equal zero. I meant this to be a thought experiment. 

Let's take two hypothetical yellow dwarfs and give them the cute little names A and B.

A is on a collision course with B. 

When they meet,  will they

1) merge or
2) be destroyed by an explosion (e.g. because of the high kinetic energy of A) ?
3) something else happens ?


----------



## Nik (Aug 18, 2007)

*Something else... ??*

Disclaimer: I'm no astrophysicist.

Um, the chances of a 1:1 collision are rather remote-- I'd say 'astronomical', but...

IMHO, you'd get a BIG SPLAT and a BIG Nova outburst. When the stardust settled, you'd probably have a slightly bigger star with a *very* odd spectrum due to mixing, plus a splendid 'planetary nebula' with the missing mass.

A close pass, though, is something different. It would certainly toss around Oort objects, could well slingshot planets hither & yon. Google etc for 'Nemesis'.

If you research close-binary stars and the ways they interact, exchange mass, mesh their magnetic fields etc, it would give you a better idea. IIRC, two similar stars could survive a pass to within a few diameters. The tidal and magnetic turbulence may even rejuvenate them to some extent by re-mixing their internals...

IIRC, exotic objects such as white dwarfs and neutron stars tend to sweep up any mass in their neighbourhood, flare Nova. Neutron stars also have **intense** magnetic fields, so have more reach than you'd expect, even after they've spun down from pulsar phase. Feeding one could spin it up again...


----------



## matt-browne-sfw (Sep 22, 2007)

Well, I posted this at Myspace as well. Folks there told me they will merge...


----------



## Sephiroth (Sep 23, 2007)

As I understand it, they _will _merge, after a violent period of interaction in which _a great deal _of ejecta is propelled outward into space 'Nova-style'. 

Such collisions must happen regularly near galactic centres, where the density of stars is at its greatest.


----------



## matt-browne-sfw (Sep 23, 2007)

Sephiroth said:


> As I understand it, they _will _merge, after a violent period of interaction in which _a great deal _of ejecta is propelled outward into space 'Nova-style'.
> 
> Such collisions must happen regularly near galactic centres, where the density of stars is at its greatest.



How much mass is lost by the two combined bodies?


----------



## Nik (Sep 24, 2007)

*Blue Straggler ??*

Blue straggler - Wikipedia, the free encyclopedia
SPACE.com -- Astronomers claim to have found proof of stellar collisions
Blue Stragglers
etc

Sorry, I don't have the reference but, IIRC, about 20% blows off before a compound star settles briefly to a shortened, exciting life.


----------



## Sephiroth (Sep 24, 2007)

I would go with Nik on that.  

The only other source I could find doesn't say, exactly, but in their small-scale simulation they get a 5% mass loss, and it is stated first that the mass loss in a 'tidal spin up' collision would be significantly greater than this, and then that this first assumption is slightly overestimated.  

(the bit in English is at the bottom)

Something in the region of 15-25% would seem reasonable.  The maths is impenetrable to me, however, so it's hardly an informed opinion.


----------



## matt-browne-sfw (Oct 3, 2007)

Those numbers sound reasonable. Thanks for that!


----------

