<p>tl;dr: I think your question is still open and we don't have an answer yet</p>
<p>Regarding the fact that most massive stars are in binary or multiple systems, that has been known for a long time (I saw papers from the seventies already stating it, although I can't find the reference right now).</p>
<p>More recently, the community has started to realize that not only they are in binaries/multiples, but that they are often close enough to interact during their life, so that if you see a massive star that is single, there is a good chance it is the result of the merger of a binary.</p>
<p>An important milestone in this understanding is the paper by <a href="https://www.science.org/doi/10.1126/science.1223344" rel="nofollow noreferrer">Sana et al. 2012</a> with the famous pie chart showing the fraction of interacting binaries.</p>
<p><a href="https://i.sstatic.net/TRwTf.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/TRwTf.png" alt="Sana et al. 2012, fig. 2" /></a></p>
<p>As for triple, or quadruple systems, there is another famous plot, from <a href="https://ui.adsabs.harvard.edu/abs/2017ApJS..230...15M" rel="nofollow noreferrer">Moe &amp; Di Stefano 2017</a> that shows how the multiple systems become more and more common with higher mass.</p>
<p><a href="https://i.sstatic.net/pLQ05.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/pLQ05.png" alt="Moe &amp; Di Stefano 2017, fig. 39" /></a></p>
<p>In section 10 of this same paper you can find a nice discussion on why we observe these distributions.</p>
<p>Are the stars in a binary forming together at close distance (in situ)? Or are they forming separately and are then brought together by some mechanism like interaction with the gas, or with other stars?
Maybe the lower mass stars also form commonly in binaries, but being low mass they are easier to be flung away by the same interactions that bring together the massive ones?</p>
<p>These are all open problems in a very active research field. There is not a definitive answer to your question, yet.</p>
<p>As for the last part of your question, no, stars with different mass don't form in different places. From a given star-forming molecular cloud, all kind of stars will come out: from red dwarfs and solar-like stars, to O and B stars that are very massive. They all form in the same places, but with different fraction of multiplicity.</p>
<p>PS: just to be clear. I am not saying that <em>most</em> stars are in binaries/multiples. Most <em>massive stars</em> are in binaries/multiples, but the more massive is a star, the less common it is. The vast majority of stars have a mass <span class="math-container">$\le 1 M_\odot$</span>, and, as you can see from Moe &amp; Di Stefano's plot, those stars are usually single.</p>
<hr />
<p>EDIT: as suggested by <a href="https://astronomy.stackexchange.com/questions/52031/why-are-the-largest-stars-such-as-o-type-or-b-type-most-likely-to-be-in-multi/52039?noredirect=1#comment117117_52039">ProfRob</a>, it is also worth looking at the review by <a href="https://www.annualreviews.org/doi/full/10.1146/annurev-astro-081710-102602" rel="nofollow noreferrer">Duchêne &amp; Kraus (2013)</a> and their figure 1 that shows how the companion fraction (CF) and multiplicity fraction (MF) are higher the more massive the stars are.</p>
<p><a href="https://i.sstatic.net/2N8Fy.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/2N8Fy.png" alt="Duchêne &amp; Kraus (2013) fig. 1" /></a></p>

CC BY-SA 4.0
2023-02-28T17:03:05.813Z
Also worth citing Duchene & Kraus (2013). https://www.annualreviews.org/doi/full/10.1146/annurev-astro-081710-102602 and this image https://www.annualreviews.org/na101/home/literatum/publisher/ar/journals/content/astro/2013/astro.2013.51.issue-1/annurev-astro-081710-102602/20130808/images/medium/aa510269.f1.gif
ProfRob
CC BY-SA 4.0
2023-03-01T11:02:31.217Z
It might be worth provided a non-paywalled link for the Duchene & Krauss review (e.g., https://arxiv.org/abs/1303.3028) and an explanation of what the different symbols in the plot are (and maybe even a brief definition of "multiplicity fraction" and "companion fraction").
Peter Erwin
CC BY-SA 4.0
2023-02-28T09:17:02.983Z
2023-03-01T08:48:56.210Z
2023-03-01T08:48:56.210Z
Prallax
<p>I was just reading about what percentage of stars in our galaxy and, perhaps, other galaxies are in binary systems (or trinary... etc.).</p>
<p>Researchers keep going back and forth about whether or not most stars are in multiple-star systems are not....</p>
<p>But what recently caught my attention was a statement, repeated elsewhere, that 80% to 85% or so of the largest stars are in multi-star systems, while only maybe 25% (at best) of red dwarfs, the smallest true stars, are companions....</p>
<p>Why would this be?</p>
<p>The only reason I can think of is that large stars are in such gas-and-dust crowded areas that the same surplus of material that creates the gigantic stars in the first place also creates companions, while red dwarfs are in lonelier places....</p>
<p>Is that true?  Are red dwarfs usually found on the outskirts of galaxies?</p>

CC BY-SA 4.0
2023-02-27T22:30:15.557Z
"Researchers keep going back and forth about whether or not most stars are in multiple-star systems are not..." Pretty sure that's only your interpretation of some space.com articles, which are not written by researchers. Cite your sources instead of "..."
AtmosphericPrisonEscape
CC BY-SA 4.0
2023-02-27T23:31:27.000Z
Both can be true at the same time: most stars are in multiple systems and most systems are single-star systems
planetmaker
<astrophysics><stellar-evolution><binary-star><star-systems><red-dwarf>
Why are the largest stars, such as O-type or B-type, most likely to be in multi-star systems; while red dwarfs are least likely?
Kurt Hikes
# Why are the largest stars, such as O-type or B-type, most likely to be in multi-star systems; while red dwarfs are least likely?

(Asked by: username_0 on 2023-02-27)

I was just reading about what percentage of stars in our galaxy and, perhaps, other galaxies are in binary systems (or trinary... etc.).

Researchers keep going back and forth about whether or not most stars are in multiple-star systems are not....

But what recently caught my attention was a statement, repeated elsewhere, that 80% to 85% or so of the largest stars are in multi-star systems, while only maybe 25% (at best) of red dwarfs, the smallest true stars, are companions....

Why would this be?

The only reason I can think of is that large stars are in such gas-and-dust crowded areas that the same surplus of material that creates the gigantic stars in the first place also creates companions, while red dwarfs are in lonelier places....

Is that true? Are red dwarfs usually found on the outskirts of galaxies?

**Tags:** astrophysics, stellar-evolution, binary-star, star-systems, red-dwarf
> **Comments:**
> **username_1**: "Researchers keep going back and forth about whether or not most stars are in multiple-star systems are not..." Pretty sure that's only your interpretation of some space.com articles, which are not written by researchers. Cite your sources instead of "..."  
> **username_2**: Both can be true at the same time: most stars are in multiple systems and most systems are single-star systems  

---

## 1 answers

### Answer by username_3 on 2023-02-28. Score: 1

tl;dr: I think your question is still open and we don't have an answer yet

Regarding the fact that most massive stars are in binary or multiple systems, that has been known for a long time (I saw papers from the seventies already stating it, although I can't find the reference right now).

More recently, the community has started to realize that not only they are in binaries/multiples, but that they are often close enough to interact during their life, so that if you see a massive star that is single, there is a good chance it is the result of the merger of a binary.

An important milestone in this understanding is the paper by [Sana et al. 2012](https://www.science.org/doi/10.1126/science.1223344) with the famous pie chart showing the fraction of interacting binaries.

[![Sana et al. 2012, fig. 2](https://i.sstatic.net/TRwTf.png)](https://i.sstatic.net/TRwTf.png)

As for triple, or quadruple systems, there is another famous plot, from [Moe & Di Stefano 2017](https://ui.adsabs.harvard.edu/abs/2017ApJS..230...15M) that shows how the multiple systems become more and more common with higher mass.

[![Moe & Di Stefano 2017, fig. 39](https://i.sstatic.net/pLQ05.png)](https://i.sstatic.net/pLQ05.png)

In section 10 of this same paper you can find a nice discussion on why we observe these distributions.

Are the stars in a binary forming together at close distance (in situ)? Or are they forming separately and are then brought together by some mechanism like interaction with the gas, or with other stars?
Maybe the lower mass stars also form commonly in binaries, but being low mass they are easier to be flung away by the same interactions that bring together the massive ones?

These are all open problems in a very active research field. There is not a definitive answer to your question, yet.

As for the last part of your question, no, stars with different mass don't form in different places. From a given star-forming molecular cloud, all kind of stars will come out: from red dwarfs and solar-like stars, to O and B stars that are very massive. They all form in the same places, but with different fraction of multiplicity.

PS: just to be clear. I am not saying that *most* stars are in binaries/multiples. Most *massive stars* are in binaries/multiples, but the more massive is a star, the less common it is. The vast majority of stars have a mass $\le 1 M\_\odot$, and, as you can see from Moe & Di Stefano's plot, those stars are usually single.

---

EDIT: as suggested by [ProfRob](https://astronomy.stackexchange.com/questions/52031/why-are-the-largest-stars-such-as-o-type-or-b-type-most-likely-to-be-in-multi/52039?noredirect=1#comment117117_52039), it is also worth looking at the review by [Duchêne & Kraus (2013)](https://www.annualreviews.org/doi/full/10.1146/annurev-astro-081710-102602) and their figure 1 that shows how the companion fraction (CF) and multiplicity fraction (MF) are higher the more massive the stars are.

[![Duchêne & Kraus (2013) fig. 1](https://i.sstatic.net/2N8Fy.png)](https://i.sstatic.net/2N8Fy.png)

> **Comments:**
> **username_4**: Also worth citing Duchene & Kraus (2013). https://www.annualreviews.org/doi/full/10.1146/annurev-astro-081710-102602 and this image https://www.annualreviews.org/na101/home/literatum/publisher/ar/journals/content/astro/2013/astro.2013.51.issue-1/annurev-astro-081710-102602/20130808/images/medium/aa510269.f1.gif  
> **username_5**: It might be worth provided a non-paywalled link for the Duchene & Krauss review (e.g., https://arxiv.org/abs/1303.3028) and an explanation of what the different symbols in the plot are (and maybe even a brief definition of "multiplicity fraction" and "companion fraction").  

---

