Super Star Cluster Hiding in Bubble
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Pseudo-color image of dwarf galaxy NGC 5253. Blue channel: Hubble Space Telescope image [courtesy of Daniela Calzetti (STScI)], in optical light; red: infrared image from the Keck Telescope.
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PASADENA, CA (JUNE 5, 2001) --
An international team of astronomers yesterday
reported the discovery of an "amazing" super star cluster hidden at the
center of the dwarf galaxy NGC 5253, 12 million light-years away in the
southern hemisphere constellation Centaurus. At around 15,000 years old,
this cluster may be the youngest ever discovered, said Jean Turner, an
astronomer at the University of California, Los Angeles.
The cluster is not visible to optical telescopes because the young stars
are cocooned deep in a nebula of gas. The astronomers used radio and
infrared telescopes too peer inside the nebula. They estimate that it
contains about a million hot, bright young stars within a tiny volume of
space. These million stars give off as much light as one billion Suns,
but they are squeezed into a volume of about six light-years (roughly
about the distance from our Sun to the nearest star). Fully one-quarter
of all the light coming from the galaxy comes from this super star
cluster. About 4,000 of the young stars in the cluster are extremely
massive, the astronomers said.
The young stars are trying to blast their way out of their cocoon by
giving off supersonic stellar winds, the astronomers said. They found
that gas in the nebula is moving at about 3,000 miles per hour, creating
a bubble around the star cluster. "We know of smaller wind bubbles
around young stars in our own Milky Way," Turner said, "but this wind is
far more powerful, with the potential to seriously disrupt its parent
galaxy."
Studies of this super star cluster should help astronomers to understand
how massive clusters affect the evolution of galaxies, Turner said. The
super star clusters in our own Milky Way galaxy formed billions of years
ago. According to Sara Beck of Tel Aviv University, a member of Turner's
team, "we've known for some time that galaxies undergoing bursts of star
formation make super star clusters and we've suspected that the winds of
these clusters could affect the evolution of the parent galaxies. But
this is a short-lived phase in the life of the cluster so it's hard to
catch one in the act. We are lucky that NGC 5253 is at the right place
and the right time for us to detect this extraordinary wind bubble."
Rebecca Johnson
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