posted by anonymous on .
The average speed of stars relative to the Sun in the solar neighborhood is about 20 km/s (this is the speed at which we see stars moving toward or away from the Sun - NOT their orbital speed). Suppose you discover a star in a solar neighborhood that is moving at a much higher speed relative to the Sun, say at 200 km/s. What kind of orbit does this star probably have around the Milky Way? In what part of the Galaxy does it spend most of its time? Explain.
Most stars in the vicinity of the sun are going around the center of the Milky Way galaxy with an average speed of about 220 km/s. The 20 km/s typical relative speed of most nearby stars represents a random variation from the average orbital speed.
If some nearby star had a relative velocity of 200 km/s, it would be in a completely different type of orbit, and one that would not be as circular as our sun's (and NOT going around the center in the opposite direction). That means it would spend most of its time much farther away from the sun's position. It could be coming from the "outer halo" of stars that extends far above and below the galactic plane.