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The Moon orbits the Earth.
The Earth orbits the Sun.

Does the Sun orbit another bigger star?
If so, does this star orbit, in turn, a very big star?
... etc ...

What are all the intermediate subsystems up to motion around the center of the Milky Way?

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The Sun is not within the gravitational sphere of influence of any other star. The centre of mass of the solar system (which is very close to the Sun) instead orbits in the general Galactic gravitational potential. Because this has a roughly cylindrical symmetry (the Galaxy is basically a disk with a bulge in the middle), this means that it executes a (roughly) circular orbit around the centre of the Galaxy, taking about 230 million years to do so. At the same time it is wobbling in the vertical plane of the Galactic disc, up and down with a cycle of about 70 million years (see How far is the Earth/Sun above/below the galactic plane, and is it heading toward/away from it? )

There is really nothing intermediate because the stars in the milky way form a "collisionless system" they don't really interact gravitationally on an individual basis. Stars can be influenced by perturbations in the smooth Galactic potential caused by massive star clusters, giant molecular clouds and spiral arms. This is thought to be why the velocity dispersions of stars around regular circular orbits increases with age.

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  • $\begingroup$ The 230 million year period - OK, orbit around the galactic barycenter. But what produces the 70 million year vertical movement? Is it an orbit around a mass concentration (one of the spiral arms)? $\endgroup$ – Anthony X Sep 1 '16 at 3:18
  • $\begingroup$ @AnthonyX See astronomy.stackexchange.com/questions/1997/… $\endgroup$ – Rob Jeffries Sep 1 '16 at 10:19
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Does the Sun turn around a big star?

No. Such a star, if it existed, would easily be the brightest star in the sky. You would have been taught about it early on in school if it existed. But it doesn't.

For a while it was conjectured that the Sun had a small companion star to explain a perceived periodicity in mass extinction events. This too has been ruled out by the Wide-field Infrared Survey Explorer.

What are all the intermediate subsystems up to motion around the center of the Milky Way?

Our Sun, being a single star, is a bit of an oddity. Most stars are members of multiple star systems, typically pairs.

Some stars occur in clusters. The Pleiades is a relativity nearby (440 light years) cluster of stars. Someone with extremely keen eyesight and exceptionally good viewing conditions, might be able to see 14 stars of the over 3,000 stars that form this cluster. Open clusters such as the Pleiades don't last long. The stars in an open cluster are only weakly bound to the cluster and are eventually dispersed.

A key feature of the Milky Way is its spiral arms. Our Sun is currently in a lesser arm of the Milky Way, the Orion Arm. Stars however are not gravitationally bound to spiral arms. One widely used explanation of the spiral arms is that they are gravitational traffic jams in space.

We could also ask the same beyond...

Our galaxy is a member of the Local Group, which in turn is a member of the Virgo Supercluster, which in turn is a part of the Laniakea Supercluster. Even larger scale objects include galaxy filaments. And that's where the hierarchy ends. The expansion of space overtakes gravity at such immense distances.

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No. The sun does not revolve around another big star.

It revolves around the center of our galaxy along with the whole solar system, including comets, asteroids, and a large amount of other stars and stellar systems.

As per some theories, however, at the center of our Milky Way galaxy lies a Super Massive black hole, which was essentially once a huge star, at least more than 10 times the mass of our sun, that had collapsed into itself due to its enormous gravity forming the black hole. So based on these theories, it wouldn't be technically incorrect to say that the sun revolves around a 'dead' star.

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Yes and no....

It is now thought that all galaxies have a super massive black hole at their center. In that sense each galaxy thus orbits around its central black hole. See: UCLA Article on galatic center

But a black hole isn't a "star" in the sense of emitting sunlight. A black hole is a "sun" which is so massive that it has collapsed into a singularity.

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  • $\begingroup$ That's what I wanted to say at first, then I wondered if Sgr A* is really the major source of gravity resulting in the rotation of the galaxy, or if it is only a small part of it. Also, supermassive black holes are not the result of the collapse of just one "sun"; Sgr A* has a mass of roughly 4 million solar masses! $\endgroup$ – uhoh Dec 4 '18 at 19:43
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The Sun does NOT revolve around an even bigger star. If it did, you'd see two stars, assuming the larger one didn't outshine the Sun. In that case, you'd only see one. Also, the earth would be a lot hotter, getting heat from two stars. We'd also be in danger of solar wind, more solar wind than we'd usually get from just the Sun.

So, because we don't see two stars and it isn't getting any hotter than it should and we don't get double the solar wind that we do, and add the presumed fact that you weren't taught that in school, it's safe to say that the Sun orbits around nothing.

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    $\begingroup$ Pluto turns around the Sun, but from Pluto the Sun is very small. Idem, the Sun could turn around a very big and very far star looking very small from the Earth. $\endgroup$ – Sebastien Palcoux Mar 1 '15 at 3:29
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    $\begingroup$ This answer would be true only for the closest of binaries. This answer is wrong for wide binaries. The binary companion would be a very bright star at night, and may even not be visible during the day. $\endgroup$ – David Hammen Mar 1 '15 at 7:31

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