The Sun's speed and direction

[dougettinger]

Why do stars in our neighborhood like our Sun go at velocities like 220 km/s and in similar orbital directions around the center of the galaxy? If a typical star is formed by the random gravitational collapse of an IMC what gives the new star the impetus to go in a certain predicted direction at such large velocities? Is the aggregate cloud already moving in that direction and that velocity before star formation? This is not an April Fools question.

[neufer]

Why do stars in our neighborhood like our Sun go at velocities like 220 km/s and in similar orbital directions around the center of the galaxy? If a typical star is formed by the random gravitational collapse of an IMC what gives the new star the impetus to go in a certain predicted direction at such large velocities? Is the aggregate cloud already moving in that direction and that velocity before star formation? This is not an April Fools question.

How would a star stay in our neighborhood if it didn't have a similar velocity, dougettinger?

[The Code]

Why do stars in our neighborhood like our Sun go at velocities like 220 km/s and in similar orbital directions around the center of the galaxy? If a typical star is formed by the random gravitational collapse of an IMC what gives the new star the impetus to go in a certain predicted direction at such large velocities? Is the aggregate cloud already moving in that direction and that velocity before star formation? This is not an April Fools question.

Should we just go with the flow? What could stop it going with the flow? Smoke inside a car going at 70mph, only blows away when you open a window. There maybe a sort of glass bubble around our galaxy.

[Chris Peterson]

Why do stars in our neighborhood like our Sun go at velocities like 220 km/s and in similar orbital directions around the center of the galaxy? If a typical star is formed by the random gravitational collapse of an IMC what gives the new star the impetus to go in a certain predicted direction at such large velocities? Is the aggregate cloud already moving in that direction and that velocity before star formation? This is not an April Fools question.

Simple orbital mechanics. Everything in the galaxy is orbiting (approximately) around the center of mass of the galaxy. And the orbital velocity is determined by the distance from that center. It doesn't matter if we're talking stars or clouds of gas, the orbital dynamics are about the same. So yes, the cloud that a group of stars forms from will already be orbiting at the speed dictated by its position in the galactic disc, and the stars that form from it will have similar velocities. Of course, stars do perturb one another this far out, where the galaxy's gravity is fairly weak. As a consequence, there is quite a bit of variability in stellar orbits- many are much less circular than ours, for instance. You only have to wait a few tens of thousands of years for the appearance of the sky to change significantly.

[The Code]

Why do stars in our neighborhood like our Sun go at velocities like 220 km/s and in similar orbital directions around the center of the galaxy? If a typical star is formed by the random gravitational collapse of an IMC what gives the new star the impetus to go in a certain predicted direction at such large velocities? Is the aggregate cloud already moving in that direction and that velocity before star formation? This is not an April Fools question.

Oh dear. This has got me thinking. You know what i am going to say don't you?

How can Gas and dust, be affected by gravity, from 28 thousand light years away? Or is the space/time in our galaxy also spinning with us?

Mark

[Chris Peterson]

How can Gas and dust, be affected by gravity, from 28 thousand light years away?

The real question is, in the context of everything we know about gravity, how could gas and dust not be affected by gravity? Gas and dust have mass, and everything with mass is affected by gravity. Nobody has ever found an exception. You can look at the behavior of our galaxy in terms of Newtonian mechanics, where gravity is treated as a force, or in terms of GR, where the gravity is seen as distorting spacetime. Either way, the behavior predicted by these theories is precisely what we observe.

In the case of our galaxy, the dust and gas (or stars) are not being affected by gravity from 28 thousand light years away. They are being affected by the gravity of a distributed mass. There's nothing special about the center of the galaxy, or its center of mass, except as a mathematical abstraction. The actual force (or distortion of spacetime) doesn't come from a single point.

Or is the space/time in our galaxy also spinning with us?

No, it isn't (except for the predicted phenomenon of frame dragging, which is a much more subtle distortion of spacetime than I think you are referring to.)

[dougettinger]

How can Gas and dust, be affected by gravity, from 28 thousand light years away?

The real question is, in the context of everything we know about gravity, how could gas and dust not be affected by gravity? Gas and dust have mass, and everything with mass is affected by gravity. Nobody has ever found an exception. You can look at the behavior of our galaxy in terms of Newtonian mechanics, where gravity is treated as a force, or in terms of GR, where the gravity is seen as distorting spacetime. Either way, the behavior predicted by these theories is precisely what we observe.

In the case of our galaxy, the dust and gas (or stars) are not being affected by gravity from 28 thousand light years away. They are being affected by the gravity of a distributed mass. There's nothing special about the center of the galaxy, or its center of mass, except as a mathematical abstraction. The actual force (or distortion of spacetime) doesn't come from a single point.

Or is the space/time in our galaxy also spinning with us?

No, it isn't (except for the predicted phenomenon of frame dragging, which is a much more subtle distortion of spacetime than I think you are referring to.)

My question was well answered. Thank you. But the answer raises other questions. How does Newtonian mechanics and the observed distributed masses address the reason for globular star clusters that create a halo around galaxies? And do the stars in globular clusters and elliptical galaxies show any trend in directional velocities that would indicate some central distributed or concentrated mass?

[dougettinger]

Why do stars in our neighborhood like our Sun go at velocities like 220 km/s and in similar orbital directions around the center of the galaxy? If a typical star is formed by the random gravitational collapse of an IMC what gives the new star the impetus to go in a certain predicted direction at such large velocities? Is the aggregate cloud already moving in that direction and that velocity before star formation? This is not an April Fools question.

How would a star stay in our neighborhood if it didn't have a similar velocity, dougettinger?

My viewpoint and question comes from the nebula hypothesis that predicts the gravitational collapse of materials inward from all directions. I believe that Chris answered my question as well as it can be answered at this time.

[Chris Peterson]

My question was well answered. Thank you. But the answer raises other questions. How does Newtonian mechanics and the observed distributed masses address the reason for globular star clusters that create a halo around galaxies? And do the stars in globular clusters and elliptical galaxies show any trend in directional velocities that would indicate some central distributed or concentrated mass?

Galaxies do have a density distribution that results in a central mass concentration. And Newtonian mechanics is adequate for explaining the motion of all galactic components- stars, dust, gas, globulars- in the context of the distributed mass (with the assumption of dark matter being present).

Working backwards, however- asking how the entire structure came into being- is much more difficult. It is a problem that can only be addressed by a combination of cosmological theory describing the early Universe, and numerical simulation. People have proposed quite reasonable scenarios for galaxy formation, including the creation of globulars, but this matter is far from settled.

[dougettinger]

Does any recent publication exist that proposes a means and timeline for galaxy evolution including globular clusters?