In spite of a strong interest in astronomy, I heard something on NPR last evening that was news to me.
Our Galaxy is large enough that it apparently has around two dozen smaller galaxies orbiting it. The large and small Magellanic clouds visible in southern latitudes being examples.
Question 1: How long has this been known?
Question 2: How well established is the number of satellite galaxies?
Question 3: As the story didn’t mention Andromeda, I am guessing it is massive enough that it is a peer of the Milky Way rather than a satellite. Is this correct? and if so, do the Milky Way Satellites also orbit Andromeda?
Apparently there is evidence that at least one of these galaxies is on a highly elliptic orbit (like a comet in our solar system) such that at perigee it passes INTO our galaxy, even closer to the center of the Milky Way than our own sun! This galaxy has not been directly observed and is thought to be currently hidden behind the dust of our own galaxy. The evidence for it’s existence was discribed as “ripples” or “waves” in our own galaxy.
Question 4: How strong is the evidence of this “comet” galaxy.
Question 5: What might the orbital period of the galaxy be? (order of magnitude answer would be fine)