(November 23, 2018 at 12:16 am)Paleophyte Wrote: One of the more interesting anomalies about Oumuamua is that it had a very low velocity relative to the Local Standard of Rest prior to entering our solar system. That might suggest that it wasn't pulled free of another star but formed in interstellar space. I don't know how that might happen but it could very well give rise to something that is neither the asteroids nor comets that we are familiar with. That might account for some of Oumuamua's unusual characteristics.
I disagree. It seems to me that based on our current knowledge, we should expect extra-solar object ejected from other star systems to commonly possess low relative velocities to local standard of rest.
Here in our solar system a major means to eject an object formed around the sun from the sun’s gravitational influence is through close gravitational interaction between the object and a gas giant, primarily Jupiter, after the object has been initially perturbed into a gas giant crossing elliptical orbit. A number of comets that have been observed to follow hyperbolic heliocentric trajectories (e>1) due to encounters with Jupiter and Saturn. Although Jupiter’s gravity is powerful enough to slingshot small objects approaching with appropriate encounter geometry to solar escape velocity, it is not powerful enough to do this with any significant margin to spare (e>1, but just barely). This means as these object follow their Jupiter given escape trajectories, the sun would claw back almost all the extra heliocentric orbital energy imparted by Jupiter before the object can finally escape the sun’s gravity well for good. So the object will leave with almost zero surplus kinetic energy, and thus very minimal relative velocity with respect to the sun. So these objects will end up more or less fly in lose formation with the sun in their independent orbits around the Milky Way rather than just zip off at high speed in random directions never to be seen again.
I believe numerical simulation has shown that for a Star such as the sun, it is not difficult to come up with combinations of mass and orbits of gas giant planets that would enable the gas giant to pump other objects in the system up to stellar escape velocity. But it is much more difficult to come up with plausible combinations of mass and orbits that would enable the gas giant to impart a large amount of surplus kinetic energy to a small object in system beyond what is needed to escape. So objects thrown out with very little surplus energy should be common. Objects thrown out with lots of surplus energy sufficient to support galactic orbital vectors substantially different from the parent star would be comparatively uncommon.
The local standard of rest is nothing more than the average velocity of the stars in the broad galactic neighborhood around the sun. If the escape mechanism powered by a massive planet deep in a star’s gravity well is typical of the star systems in the sun’s neighborhood, then we would expect many of the ejected objects from these systems would end up with very little relative motion to their parent systems. In other words, we would expect the mean velocity of these interstallar objects to be essentially the same as the local standard of rest.
