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Old time science fiction stories often used the names of well known stars. Even though the few dozen stars which are well known to readers on Earth are only an extremely tiny fraction of all the billions of stars in our galaxy. And those stars were used without any care for their distances from our solar system or the various directions that they are seen in from Earth.

I was thinking recently of an old story by Edmund "world wrecker" Hamilton, "The Dead Planet" (1946).

https://www.isfdb.org/cgi-bin/title.cgi?69069

In that story our solar system is in "a thin region at the very edge of the galaxy" as seen from Rigel.

Of course the disc of the Milky Way Galaxy is about a hundred thousand light years in diameter, and and our solar system is about 27,000 light years from the center. And Rigel is about 800 to 1,000 lightyears from Earth, and as seen from Earth approximately in the opposite direction to the galactic center. Thus Rigel is approximately 800 to 1,000 light years farther from the center of the galaxy than the solar system is - about 4 percent farther than the solar system from the center of the galaxy.

That is the present situation, but can that change?

Rigel, the Sun, and every other star, star cluster, nebula, rogue planet, and other interstellar object all orbit around the center of mass of the Milky Way Galaxy.

I think that the Sun's orbit is nearly circular, but even a nearly circular orbit might take it thousands of light years closer to and farther from the center of the galaxy. Some stars - possibly including Rigel - have much more eccentric orbits.

So possibly someone with the right information might be able to calculate whether it would ever be possible for our solar system to be farther from the center of the galaxy than Rigel is - ignoring that Rigel is less than a billion years old and will probably be a neutron star or a black hole in just a few million years.

Can the Sun ever be farther than Rigel from the center of the galaxy?

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  • $\begingroup$ Are you asking "can it be" or "will it be"? $\endgroup$
    – ProfRob
    Sep 27, 2023 at 7:53

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I don't think it can, in the "near" future. The Sun has a velocity component of about 10 km/s towards the Galactic centre, but Rigel has a radial velocity of about 20 km/s away from the Sun.

That, and as you say, the short projected lifetime of Rigel means that the Sun won't be at a larger Galactocentric radius than Rigel while Rigel is still a "normal star".

However, all bets are off if you include Rigel as a neutron star remnant (or black hole). Neutron stars frequently have very high peculiar velocities of hundreds of km/s, as a result of "kicks" they receive during a supernova explosion. This can put them on highly non-circular orbits in the Galaxy, possibly leading to a much closer Galactic peri-centre. In addition, we cannot say that much about the solar position in hundreds of millions of years time. Its orbit could be perturbed (e.g. by an encounter with a giant molecular cloud) and it could end up considerably closer or further from the Galactic centre - radial migration of thousands of parsecs is possible in either direction.

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