It has been argued that it is not possible to trace back the remains of the progenitor star of the Sun (sometimes called Coatlicue), which, being estimated in the mass range of 30 $M_{\odot}$, should have left a black hole after its explosion as a supernova, nor is it possible to find the sister stars formed from the compression of the same nebula:



because "[The Sun] has completed many Galactic orbits [since its formation]. Not only that, but it could have migrated in orbital radius as well." and "These twin stars did not influence its development nor that of its planets [and] are now dispersed in the Galaxy and cannot be identified".

Why did the supernova's remains and the sister stars not remain gravitationally bound together? Why did they not share the same angular momentum of revolution around the Galaxy?

Why did these massive bodies formed from the same nebula not become a bound system among them and with the supernova's remains, like the Sun and its planets in the Solar system?

  • $\begingroup$ I can't find a reliable site showing such a star existed (phys.org does not check what it publishes). news.nationalgeographic.com/news/2012/01/… suggests the Sun was ejected from stellar cluster M67, but not from a giant star. $\endgroup$
    – user21
    Oct 19 '18 at 20:59
  • $\begingroup$ @barrycarter The progenitor star named Coatlicue is cited also in an article appeared on Scientific American: scientificamerican.com/article/the-new-biography-of-the-sun Of course, alternative hypoteses exist too. $\endgroup$ Oct 21 '18 at 6:43
  • $\begingroup$ OK, most of the article is behind a paywall, so I can't see it. Google searches usually help with this sort of thing, but I can't see to find anything relevant. $\endgroup$
    – user21
    Oct 21 '18 at 17:53

Most stars are born in groups or clusters of anywhere between 100 and millions of stars. Most of these groups and clusters do not survive more than about 10 million years or so and the fraction that survive decreases further with time.

There are two basic reasons. First, it seems that most young clusters and associations may be born in an unbound state. Second, those that are gravitationally bound can become unbound through the expulsion of gas or through tidal interactions with the Galaxy, spiral arms and giant molecular fields. A supernova is one event that might be a culpable agent in expelling mass from a young cluster and consequently unbinding it.

It is therefore highly unlikely that a 4.5 billion year old star will be found in a cluster. There are very few examples of clusters at this age or older.

As an aside, the theory that the Sun was born from the debris of just one or even a few stars is totally false and easily disproved by looking at the isotopic composition of dust grains formed in other stars before the solar system was born. These can be found inside meteorites and demonstrate that the solar system contains debris from many, many stars; of both high and relatively low masses.

See How can there be 1,000 stellar ancestors before our Sun? and Parent stars of our Sun - Where are its remains?

Edit: It seems that you are just asking why we can't see siblings of the Sun, including this massive star that may have been involved in the formation of the solar system.

First - it isn't clear that the Sun was born in a cluster from material seeded by a supernova from another star in that cluster. There is a timing problem. The massive star that exploded would have to form more than 10 million years before the Sun. Clusters we see today do not seem to have such an extended star formation history.

Second - even if that weren't the case, a supernova very frequently gives rise to a "kick". The velocity dispersion of pulsars (recent supernova remnants) is exceedingly large (100s of km/s). Many remnants would escape the Galaxy and there is no chance of predicting where they would be in billions of years.

Thirdly - even if the first and second problems were not applicable, as I mentioned above, even bound clusters do disperse. Once free of any binding potential stars can undergo a process called "disc heating" - the action of encounters with spiral density waves and giant molecular clouds gradually increases their velocity dispersions (changing their kinetic energies and exerting torques that can change their angular momentum wrt the Galactic centre). This allows the solar siblings to go their separate ways. A Galactic orbit at the solar radius is more than 200 million years. A velocity difference of just 1 km/s (typical in a cluster even before it unbinds or is heated) could result in a separation by 200 pc in that time. The Sun has executed more than 20 such orbits.

  • $\begingroup$ I don't think that the authors of the article referenced in my post intended to state that the Sun was formed from the debris of a single star. Instead, the proposed mechanism (if I understood well) is that the explosion of a star named Coatlicue triggered the compression of the nebula that caused the formation of the star cluster comprising the Sun. Of course, the nebula contained debris of several previous stars. $\endgroup$ Oct 21 '18 at 6:47
  • $\begingroup$ @Stefano As Rob explains in his answer to the "1000 ancestors" question, a star-forming cloud is a mixture from a very large number of stars, from a huge volume of the galaxy; "several previous stars" is an extreme under-estimation. Sure, a supernova shockwave may trigger a region of a GMC to collapse, but SN explosions are often very asymmetrical, and the remnant may be ejected at a significant fraction of lightspeed. Good luck finding it 4.5G years later. ;) And of course, some SN explosions (pair-instability SN) don't leave a remnant. $\endgroup$
    – PM 2Ring
    Oct 21 '18 at 7:54
  • $\begingroup$ @stefanozunino It was the words "the progenitor star of the Sun" that were confusing, which you may wish to re-word. $\endgroup$
    – ProfRob
    Oct 21 '18 at 8:27
  • $\begingroup$ Coatlicue is not supposed to have formed in the star cluster of the Sun; it is assumed to have exploded near the nebula that as a consequence collapsed in a star cluster. So, it is a progenitor in this sense. However, I acknowledge that there is not a consensus about the formation of the cluster, nor about Coatlicue's remains (having read of a pulsar and a pair instability supernova). $\endgroup$ Oct 21 '18 at 13:15
  • $\begingroup$ @StefanoZunino Then why would you think it was in any sense gravitationally bound to the cluster of stars in which the Sun formed? Anyway - my answer now address all these points. $\endgroup$
    – ProfRob
    Oct 21 '18 at 13:48

In the article you link to, it suggests that the sun formed in a cluster of stars. There are many clusters, the most famous is the Pleiades, or 7-sisters. Clusters are formed of stars that were born at the same time, and share similar motions in space.

But the motions of the stars in a cluster are similar, not the same. Over time the stars in a cluster spread out, and over much more time can end up far far away. The stars in a cluster are not close enough to hold on to each other by gravity.

It is impossible to tell for certain which of the 100 billion stars in the galaxy were born at the same time as the sun. Nor is it possible to identify a particular black hole. Again the black hole may have had a similar, but not identical motion to the sun and would have drifted very far away over the course of 4.6 billion years.


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