Companion
Decades ago, it was not known with certainty whether the companion galaxy NGC 5195 was a true companion, or another galaxy passing at a distance. The advent of radio astronomy and subsequent radio images of M51 unequivocally demonstrated the reality of the interaction.
Recent simulations bear out that M51's spiral structure was caused by NGC 5195 passing through the main disk of M51 about 500 to 600 million years ago. In this model, NGC 5195 came from behind M51 through the disk towards the observer and made another disk crossing as recently as 50 to 100 million years ago until it is where we observe it to be now, slightly behind M51.
Read more about this topic: Whirlpool Galaxy
Famous quotes containing the word companion:
“Now I thought I would observe how he spent his Sunday. While I and my companion were looking about at the trees and river, he went to sleep. Indeed, he improved every opportunity to get a nap, whatever the day.”
—Henry David Thoreau (1817–1862)
“My companion assumes to know my mood and habit of thought, and we go on from explanation to explanation, until all is said that words can, and we leave matters just as they were at first, because of that vicious assumption.”
—Ralph Waldo Emerson (1803–1882)
“... they think that Miss America belongs to them! That they can touch her and give her a kiss on the cheek—or even on the lips!”
—Ellie Ross, Travelling companion for Miss Americas. As quoted in Miss America, ch. 17, by Ann-Marie Bivans (1991)