The canonical model for the formation of the Solar System involves the gravitational collapse of a nebula into (perhaps) several stars across several light years. Is it possible that two or more of the stars (or protostars) combined to form our Sun? Or would any stellar collision release so much energy that our Sun could not have formed the way we see it today? Have astronomers or astrophysicists created n-body orbital models that allow for a "soft" collision of two stars combined with the ejection of the other(s)?
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asked Mar 18, 2021 at 21:30
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2$\begingroup$ In your scenario, are the stars fully formed (and possibly already starting to fuse hydrogen), or are they still protostars in the process of condensing? I expect that protostar collisions would make a mess of their protoplanetary discs. $\endgroup$– PM 2RingCommented Mar 18, 2021 at 23:14
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$\begingroup$ @PM2Ring I edited the question to clarify I would be interested in either or both possibilities. $\endgroup$– Connor Garcia ♦Commented Mar 18, 2021 at 23:32
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2 Answers
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The dynamics of the Solar System and the chemistry of the Solar System bodies don't support a hypothesis of a stellar merger later than formation of the protoplanetary disk which would have mixed-up things considerably and heavily disrupt any circumstellar disk. Thus this basically excludes any collision after the time one can start talking about a protostar, way before it even entered main sequence (as that's already the end of planetesimal formation).
answered Mar 19, 2021 at 11:09
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Stellar mergers are certainly possible, but also relatively rare. Maybe protostars merging is a bit more common since they have less relative velocity.
However, unless the merger is straight it will typically deposit a lot of angular momentum. The sun seems to be a slow rotator for its spectral class. Hence it is not likely it was formed through a stellar merger.
answered Mar 19, 2021 at 10:23
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1$\begingroup$ We know almost nothing about the early rotation rate of the Sun The fact that it is an averagely rotating (not slow) star for its age now does not tell us how fast it rotated in the first 100 Myr of its life. $\endgroup$– ProfRobCommented Mar 19, 2021 at 12:06
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$\begingroup$ @ProfRob - Do you think a rapidly rotating post-merger star could have slowed down past normal star rotation rates, or that nearly all stars are merger products? The simplest explanation is that the sun started with low angular momentum compared to similar stars. $\endgroup$ Commented Mar 19, 2021 at 14:04
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$\begingroup$ The Sun is not slowly rotating compared to similar stars of its age. Stars are born with angular momenta which have almost a two order of magnitude range - rotation periods of about 0.3 to 15 days at 10 Myr. By the time they get to Hyades age (700 Myr) all the solar-type stars are rotating with periods within 10% of each other. $\endgroup$– ProfRobCommented Mar 19, 2021 at 17:41
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