article_snippet.sent: one of physics' greatest mysteries.
article_snippet.sent: It is a hypothesized form of matter particle that does not reflect or emit light and as a result it can't be seen or measured directly.
article_snippet.sent: Scientists have observed that galaxies move more than can be accounted for by the universe's expansion.
article_snippet.sent: Scientists are called peculiar velocities.
article_snippet.sent: For example, our own Milky Way galaxy and its neighbour Andromeda are moving with a speed of 2 million km/hr.
article_snippet.sent: Previous models haven't fully accounted for this observed motion.
article_snippet.sent: Hudson and Hudson team are interested in discovering what structures are responsible for the peculiar velocities.