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:
“Religion which lays so many restraints upon us, is a troublesome companion to those who will lay no restraints upon themselves.”
—Laurence Sterne (1713–1768)
“Never make a companion equal to a brother.”
—Hesiod (c. 8th century B.C.)
“The companion of an evening, and the companion for life, require very different qualifications.”
—Samuel Richardson (1689–1761)