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Our solar system and center of Milky way

  1. Oct 18, 2011 #1
    Hi !

    Somewhere I read about our solar system is going slowly out of our galaxy (moving backward from the center, but then I can also read our solar system is approaching center with sonic speed. So how is our solar system actually moving toward the centre of milky way (beside rotation around the galaxy orbit.
  2. jcsd
  3. Oct 18, 2011 #2


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    Our solar system is orbiting around the center of mass of the Milky Way galaxy. It is bound to the galaxy by the gravitational attraction, and is certainly not leaving. It takes about 200 million years to complete one orbit. I think the orbit is roughly circular, so it is neither moving significantly toward or away from the galactic center.
  4. Oct 18, 2011 #3
    I understand the orbiting, but still many of objects in orbit, they swing closer (or vice versa) to the gravitational mass in the center. In our center there is huge number of black holes including 4mio-sun-size one, thus attracting nearby objects, which further distract the orbiting of the others. For sure they are not strong to reach our solar system with their gravitational force, but I don't see any proof we are on the same spot when do one orbit (in hundreeds milion years).
  5. Oct 18, 2011 #4


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    According to science writer and physicist Nigel Calder, writing in the book "The Chilling Stars" coauthored by Henrik Svensmark, our solar system orbits the galaxy in 240 million years, and traverses each of the 4 major arms of the spiral as it does so.

    Calder claims that our proximity to various regions of birthing and dying stars in our journeying around the galaxy results in major effects on Earthly climate. The key is the flux of cosmic rays, he says. Recent results of the CERN CLOUD experiment tend to support this view, it is suggested.

  6. Oct 18, 2011 #5


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    You have a couple of misconceptions here:

    (1) The gravitational attraction of a given mass M is only determined by the mass. It makes no difference whether the mass is composed of black holes, stars, dark matter, or some mixture. As has been said before on this forum, if the sun suddenly turned into a 1 solar mass black hole, the Earth would continue on its orbit unchanged.

    (2) Gravitational attraction extends to infinity, falling off as 1/r^2. So the gravitational attraction of the central (4 Million Solar Mass) black hole does reach our solar system, and adds to the gravitational attraction of all of the other mass inside the solar systems' orbit. It is only a small part of the total, but it does contribute.

    (3) No one said that the solar system would return to the same spot. Orbits in a galaxy are different from orbits in the solar system, where the planets are essentially orbiting around a point mass (the sun). In a galaxy, everything is moving around, so the gravitational field is constantly changing. So the orbits do not close on themselves, and are only roughly 'orbits' in the conventional sense. Still, the sun basically circles around the center of the galaxy.
  7. Oct 18, 2011 #6
    I know 1 solar mass black hole would have small force (i've read somewhere 100sun-size black hole is similary gravity force than on the moon), but would change the orbits of the closest objects. A bit larger hole, like 100sun-size (using ncgs simulator) would change all orbits in our solar system, if would for example pass between mars and earth
    (with velocity 50km/s).

    And why then on Keppler's law outer orbits (like solar system) doesn't have smaller radian velocity as expected ? For 27000 light year distance, 250km/s is still pretty fast.
    (for comparision, S2 at a very close hole range orbits a 5000km/s).
    Why is then our solar system towards the Hercules with 20km/s ? The scientists say,
    we are moving out of the centre until we will do path 250light years, when the distance will reverse.

    Again, Im asking if our solar system is constantly on a same distance toward the milky way centre or it is changing (during a looooong period). There are so many documents saying diferently each one, so Im a bit confused.
  8. Oct 19, 2011 #7
    Sorry, I have to take issue with that claim. This is only true if you can ignore the effects of mass distribution within the object you are talking about. If you are close enough (or it's big or massive enough!) you may need to remembe dipole, quadro and so on effects.

    As I recall from history of the issue, Newton was quite worried about the question of whether or not you can replace a uniform spherical mass with an equal mass, dimensionless dot in its centre (for the purposes of his calculations). Since his times we know that yes, you can .... but only for the uniform masses. OR if you can afford to ignore the smaller contributing effects.
  9. Oct 20, 2011 #8
    Hi !

    I did some studies and now I can understand why despite of high radian velocity of our solar system, we are somehow sticking on a same distance from the milky way center.
    It ought to be dark matter, more detailed cold dark matter (they are two mores, with neutrinos etc. within), which is "transparent" to light but holds a gravitational force (already measured in experiments). So actually we are quite compact sitting in our orbit with unnumbered numbers of different size gravitational forces beside our sun an neighbour planets. Can this "theory" be confirmed ?
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