Birthplace of the Sun?

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In a preprint [pdf] posted today on the astro-ph website, astronomers outline the discovery of a star more like a twin of the Sun than any previously discovered. The star is located in the galactic star cluster M67, 3000 light years away. The similarity is so close that the scientists even speculate that the Sun itself might have formed in this same cluster, 4.5 billion years ago. Key quote from paper:

The similarity of the age and overall composition of the Sun with the corresponding data of M67, and in particular the agreement of the detailed chemical composition of the Sun with that of M67-1194, could suggest that the Sun has formed in this very cluster. According to the numerical simulations by Hurley et al. (2005) the cluster has lost more than 80% of its stars by tidal interaction with the Galaxy, in particular when passing the Galactic plane, and the Sun might be one of those. We note that the orbit of the cluster encloses, within its apocentre and pericentre, the solar orbit. However, the cluster has an orbit extending to much higher Galactic latitudes, presently it is close to its vertical apex at z = 0.41 kpc (Davenport & Sandquist 2010), while the Sun does not reach beyond z = 80 pc (Innanen, Patrick & Duley 1978). Thus, in order for this hypothesis of an M67 origin of the Sun to be valid, it must have been dispersed from the cluster into an orbit precisely in the plane of the Galactic disk, which seems improbable.

The last sentences above refer to the different orbital inclinations of the galactic orbits of both the Sun and M67. M67’s orbital inclination is far steeper. While M67 is presently about 1350 light years (410 parsecs) above the galactic plane, the Sun’s orbit never takes it more than 261 light years above the plane.

One more point of interest: M67 is a well known object to amateur astronomers, located in the constellation Cancer.


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