Professor's research on galaxy clusters submitted to The Astrophysical Journal

Like a snowball rolling downhill and getting larger and larger, galaxies in space form clusters that grow in size as they careen through the cosmos ­– and just how big they could grow and how long they’ll keep growing is the subject of a research team headed by Western Washington University’s Ken Rines.

“By measuring how much mass exists in and around clusters, it is possible to estimate how much they will grow in the future,” said Rines. “Historically, it has been nearly impossible to estimate how much mass lives in the outskirts of clusters because standard methods do not work in such low-density environments.”

Rines and his fellow researchers, Margaret Geller of the Smithsonian Astrophysical Observatory and Antonaldo Diaferio of the University of Torino in Italy, used the state-of-the-art MMT Telescope (located south of Tucson, Ariz., and jointly operated by the Smithsonian Institution and the University of Arizona) to observe thousands of galaxies and measure their velocities, which then gives a truer measurement of the cluster’s overall mass. The team used a new method that uses the galaxies’ velocities to determine how fast they must be moving to escape the gravitational pull of the cluster.

According to Rines and his team, these observations show that galaxy clusters will continue to grow between now and the far future as the clusters add new galaxies to their mass, assembling into huge virtual island universes isolated from any neighbors.

“Computer simulations predict that clusters will approximately double in mass before they become isolated, and our observations confirm this prediction. Our own Milky Way Galaxy will have a similar, lonely fate as all other galaxies rush away, leaving the stars to slowly die out over trillions of years,” said Rines.

Rines’ research was recently submitted to The Astrophysical Journal, and can be viewed at

For more information, contact Rines at (360) 650-7944, or