NASA's Hubble Space Telescope photographed a
100,000-light-year-long structure that looks like a string of pearls twisted
into a corkscrew shape winds around the cores of the two massive galaxies. The
“pearls” are superclusters of blazing, blue-white, newly born stars.
Image Credit: NASA/ESA
NASA's Hubble Space Telescope has photographed an unusual structure 100,000
light years long, which resembles a corkscrew-shaped string of pearls and winds
around the cores of two colliding galaxies.
The unique structure of the star spiral may yield new insights into the
formation of stellar superclusters that result from merging galaxies and gas
dynamics in this rarely seen process.
"We were surprised to find this stunning morphology. We've long known that
the 'beads on a string' phenomenon is seen in the arms of spiral galaxies and in
tidal bridges between interacting galaxies. However, this particular
supercluster arrangement has never been seen before in giant merging elliptical
galaxies," said Grant Tremblay of the European Southern Observatory in Garching,
Germany.
Young, blue super star clusters are evenly spaced along the chain through the
galaxies at separations of 3,000 light-years. The pair of elliptical galaxies is
embedded deep inside the dense galaxy cluster known as SDSS J1531+3414. The
cluster's powerful gravity warps the images of background galaxies into blue
streaks and arcs that give the illusion of being inside the cluster, an effect
known as gravitational lensing.
Observing astronomers first hypothesized that the "string of pearls" was
actually a lensed image from one of these background galaxies, but their recent
follow-up observations with the Nordic Optical Telescope in Santa Cruz de
Tenerife, Spain, ruled out this hypothesis.
The galaxy cluster is part of a Hubble program to observe 23 massive clusters
that create powerful gravitational lensing effects on the sky. The clusters were
first cataloged in the Sloan Digital Sky Survey (SDSS), a project to create the
most detailed three-dimensional maps ever made of the universe. Tremblay's team
discovered the bizarre string of stellar superclusters by chance, while
reviewing images as they came in from Hubble. Researchers were stunned by what
they saw in SDSS J1531+3414, and the unique nature of the source spurred the
team to do follow-up observations with both ground and space-based
telescopes.
The underlying physical processes that give rise to the "string of pearls"
structure are related to the Jeans instability, a physics phenomenon that occurs
when the internal pressure of an interstellar gas cloud is not strong enough to
prevent gravitational collapse of a region filled with matter, resulting in star
formation. This process is analogous to that which causes a column of water
falling from a rain cloud to disrupt, and rain to fall in drops rather than in
continuous streams.
Scientists currently are working on a better understanding of the star
chain's origin. One possibility is that the cold molecular gas fueling the burst
of star formation may have been native to the two merging galaxies. Another
possibility is a so-called "cooling flow" scenario, where gas cools from the
ultra-hot atmosphere of plasma that surrounds the galaxies, forming pools of
cold molecular gas that starts to form stars. The third possibility is that the
cold gas fueling the chain of star formation originates from a high-temperature
shock wave created when the two giant elliptical galaxies crash together. This
collision compresses the gas and creates a sheet of dense cooling plasma.
"Whatever the origin for this star-forming gas is, the result is awesome.
It's very exciting. You can't find a mundane explanation for this," Tremblay
said.
The Hubble Space Telescope is a project of international cooperation between
NASA and the European Space Agency. NASA's Goddard Space Flight Center in
Greenbelt, Maryland, manages the telescope. The Space Telescope Science
Institute (STScI) in Baltimore conducts Hubble science operations. STScI is
operated for NASA by the Association of Universities for Research in Astronomy,
Inc., in Washington.
For images and more information about Hubble, visit:
and
To learn more about gravitational lensing, visit:
NASA
Guillermo Gonzalo Sánchez Achutegui
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