Vassar Today

Close Encounter with the Galactic Kind

Spiral galaxy NGC 2207 (left) and spiral galaxy IC 2163 do-si-do 114 million miles from Earth, in the constellation Canis Major. This image was created from three separate pointings of the Hubble Space Telescope. The observation team studying the galaxies is led by Professor Debra Elmegreen of Vassar College and her husband, Dr. Bruce Elmegreen, of the research division of IBM. They explain that their calculations indicate that IC 2163 is swinging past NGC 2207 in a counterclockwise direction, having made its closest approach 40 million years ago. However, IC 2163 does not have sufficient energy to escape the gravitational pull of NGC 2207 and is destined to be pulled back and swing past the larger galaxy again in the future.

Strong tidal forces from the larger galaxy on the left have distorted the shape of the smaller one on the right, which is flinging out stars and gas into long streamers stretching out a hundred thousand light-years toward the right-hand edge of the image.

Trapped in their mutual orbit around each other, these two galaxies will continue to distort and disrupt each other. Eventually, billions of years from now, they will merge into a single, more massive galaxy. It is believed that many present-day galaxies, including the Milky Way, were assembled from a similar process of coalescence of smaller galaxies occurring over billions of years.

For much more information about this image and Professor Elmegreen and her team, go to the Space Telescope Science Institute website: