Galaxy Collisions Unveil Star Clusters

Photo byCourtesy of NASA

Long Trail of Clumpy Stars Follows Galaxy Interactions

When galaxies collide, they create new generations of stars that might have never been born otherwise.

Close encounters between galaxies cause a gravitational tug-of-war. Gas and dust are drawn out into large streamers. The Hubble Space Telescope's vision is so sharp that it can see clusters of newborn stars strung along these tidal tails.

Photo byCourtesy of NASA

They form when knots of gas gravitationally collapse to create about 1 million newborn stars per cluster. String of pearls features were more common in our early universe when galaxies collided frequently.

It's a surprise to see many young objects in the tails. It tells us a lot about cluster formation efficiency. With tidal tails, you will build up new generations of stars that otherwise might not have existed.- author Michael Rodruck of Randolph-Macon College in Ashland, Virginia.

Galaxy collisions do not destroy stars. The rough-and-tumble dynamics trigger new stars and accompanying planets.

NASA's Hubble Space Telescope has homed in on 12 interacting galaxies with long, tadpole-like tidal tails of gas, dust, and many stars.

Hubble's exquisite sharpness and sensitivity to ultraviolet light have uncovered 425 clusters of newborn stars along these tails, looking like strings of holiday lights. Each cluster contains as many as 1 million blue, newborn stars.

Photo byCourtesy of NASA

When galaxies interact, gravitational tidal forces pull out long streamers of gas and dust. Two famous examples are the Antennae and Mice galaxies with long, narrow, finger-like projections. Clusters in tidal tails have been known about for decades.

A team of astronomers used a combination of new observations and archival data to get ages and masses of tidal tail star clusters. They found that these clusters are very young — only 10 million years old. And they seem to form at the same rate along tails stretching for thousands of light-years.

Photo byCourtesy of NASA

The tails look like they are taking a galaxy's spiral arm and stretching it into space. The exterior part of the arm gets pulled like taffy from the gravitational tug-of-war between a pair of interacting galaxies.

Before the mergers, the galaxies were rich in dusty clouds of molecular hydrogen that may have remained inert. But the clouds got jostled and bumped into each other during the encounters. This compressed the hydrogen to the point where it precipitated a firestorm of star birth.

The fate of these strung-out star clusters is uncertain. They may stay gravitationally intact and evolve into globular star clusters — like those that orbit outside the plane of our Milky Way galaxy. Or they may disperse to form a halo of stars around their host galaxy or get cast off to become wandering intergalactic stars.

Photo byCourtesy of NASA

This string-of-pearls star formation may have been more common in the early universe when galaxies collided with each other more frequently. These nearby galaxies observed by Hubble are a proxy for what happened long ago and, therefore, are laboratories for looking into the distant past.

About the Hubble Space Telescope

The NASA Hubble Space Telescope is an international cooperation project between NASA and the ESA. The telescope is managed by Goddard Space Flight Center in Greenbelt, Maryland. STScI conducts Hubble and Webb science operations in Baltimore.

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