Galaxy AM 1054-325 has been distorted into an S-shape from a normal pancake-like spiral shape by the gravitational pull of a neighboring galaxy, seen in this NASA Hubble Space Telescope image. A consequence of this is that newborn clusters of stars form along a stretched-out tidal tail for thousands of light-years, resembling a string of pearls. They form when knots of gas gravitationally collapse to create about 1 million newborn stars per cluster. NASA, ESA, STScI, Jayanne English (University of Manitoba)
Contrary to what you might think,
galaxy collisions do not destroy stars. In fact, the rough-and-tumble dynamics
trigger new generations of stars, and presumably accompanying planets.
Now NASA's Hubble
Space Telescope has homed in on 12 interacting galaxies that have long, tadpole-like
tidal tails of gas, dust, and a plethora of 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.
Clusters in tidal tails have been
known about for decades. When galaxies interact, gravitational tidal forces
pull out long streamers of gas and dust. Two popular examples are the Antennae
and Mice galaxies with their long, narrow, finger-like projections.
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 be forming at the same rate along tails
stretching for thousands of light-years.
"It's a surprise to see lots
of the young objects in the tails. It tells us a lot about cluster formation
efficiency," said lead author Michael Rodruck of Randolph-Macon College in Ashland, Virginia. "With tidal tails,
you will build up new generations of stars that otherwise might not have
existed."
The tails look like they are taking
a galaxy's spiral arm and stretching it out 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 simply 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.
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.
The Hubble Space Telescope is a
project of international cooperation between NASA and ESA. NASA's Goddard Space
Flight Center in Greenbelt, Maryland, manages the telescope. The Space
Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble and
Webb science operations. STScI is operated for NASA by the Association of
Universities for Research in Astronomy, in Washington, D.C.
LEARN MORE:
Scientific Paper: Star Clusters in
Tidal Debris
Hubble Science: Galaxy Details and
Mergers
Source: NASA's Hubble Traces 'String of Pearls' Star Clusters in Galaxy Collisions - NASA Science
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