<p>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).</p>

CC BY-SA 4.0
2021-03-19T11:09:17.873Z
2021-03-19T11:09:17.873Z
planetmaker
<p><a href="https://astronomy.stackexchange.com/questions/41002/if-two-stars-collide-what-is-the-probability-that-they-merge-to-form-a-single-s/41016#41016">Stellar mergers are certainly possible</a>, but also relatively rare. Maybe protostars merging is a bit more common since they have less relative velocity.</p>
<p>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.</p>

CC BY-SA 4.0
2021-03-19T12:06:43.193Z
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.
ProfRob
CC BY-SA 4.0
2021-03-19T14:04:42.770Z
@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.
Anders Sandberg
CC BY-SA 4.0
2021-03-19T17:41:00.400Z
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.
ProfRob
CC BY-SA 4.0
2021-03-19T17:52:30.347Z
https://arxiv.org/abs/1502.06965
ProfRob
CC BY-SA 4.0
2021-03-19T10:23:41.813Z
2021-03-19T10:23:41.813Z
Anders Sandberg
<p>The <a href="https://en.wikipedia.org/wiki/Solar_System#Formation_and_evolution" rel="nofollow noreferrer">canonical model for the formation of the Solar System</a> 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 &quot;soft&quot; collision of two stars combined with the ejection of the other(s)?</p>

CC BY-SA 4.0
2021-03-18T23:14:16.853Z
In your scenario, are the stars fully formed (and possibly already starting to fuse hydrogen), or are they still [protostars](https://en.wikipedia.org/wiki/Protostar) in the process of condensing? I expect that protostar collisions would make a mess of their protoplanetary discs.
PM 2Ring
CC BY-SA 4.0
2021-03-18T23:32:30.087Z
@PM2Ring I edited the question to clarify I would be interested in either or both possibilities.
Connor Garcia
<star><solar-system><orbital-mechanics><star-formation><collision>
Could our Sun be the product of an ancient stellar collision?
Connor Garcia
# Could our Sun be the product of an ancient stellar collision?

(Asked by: username_0 on 2021-03-18)

The [canonical model for the formation of the Solar System](https://en.wikipedia.org/wiki/Solar_System#Formation_and_evolution) 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)?

**Tags:** star, solar-system, orbital-mechanics, star-formation, collision
> **Comments:**
> **username_1**: In your scenario, are the stars fully formed (and possibly already starting to fuse hydrogen), or are they still [protostars](https://en.wikipedia.org/wiki/Protostar) in the process of condensing? I expect that protostar collisions would make a mess of their protoplanetary discs.  
> **username_0**: @PM2Ring I edited the question to clarify I would be interested in either or both possibilities.  

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## 2 answers

### Answer by username_2 on 2021-03-19. Score: 3 | Accepted answer

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).


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### Answer by username_3 on 2021-03-19. Score: 1

[Stellar mergers are certainly possible](https://astronomy.stackexchange.com/questions/41002/if-two-stars-collide-what-is-the-probability-that-they-merge-to-form-a-single-s/41016#41016), 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.

> **Comments:**
> **username_4**: 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.  
> **username_3**: @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.  
> **username_4**: 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.  
> **username_4**: https://arxiv.org/abs/1502.06965  

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