Benjamin Williams studies stars outside galaxies

The year 2006 brought some news about the origin of intergalactic stars. These are stars that don’t belong to any galaxy.

Most stars reside in one galaxy or another. For example, our sun belongs to the Milky Way galaxy. But in the 1990s, astronomers discovered stars between the galaxies of the nearby Virgo and Fornax galaxy clusters.

In 2006, Benjamin Williams of Pennsylvania State University and his colleagues used the Hubble Space Telescope to study over 5,000 stars in the intergalactic space between galaxies in the Virgo cluster. The new work provides a clue to the origin of these mysterious stars.

The clue comes from the quantity of iron and other heavy elements in the stars. Stars themselves create iron. That’s why big galaxies, like our Milky Way, have lots of iron – because they have lots of stars that forge iron. In contrast, little galaxies don’t have many stars, and they don’t have much iron.

The stars between galaxies have very little iron. They may come from small galaxies that got ripped apart when they passed too close to the big ones. The outskirts of big galaxies don’t have much iron, either. Galactic collisions may strip the big galaxies of their outermost stars, spilling them into the space between the galaxies.

Our thanks today to Research Corporation, a foundation for the advancement of science.

Our thanks to:
Benjamin Williams
Pennsylvania State University

December 29, 2006

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