NASA Hubble Telescope confirms Iranian
ISNA - Tehran
TEHRAN (ISNA)-Data from NASA's Hubble Telescope
have confirmed findings of an Iranian astronomer Andisheh
Mahdavi who had discovered clump of dark matter five years ago.
Andisheh Mahdavi who had discovered clump of dark
matter five years ago.
The result could challenge current theories about dark matter
that predict galaxies should be anchored to the invisible
substance even during the shock of a collision.
Abell 520 is a gigantic merger of galaxy clusters located 2.4
billion light-years away. Dark matter is not visible, although
its presence and distribution is found indirectly through its
effects. Dark matter can act like a magnifying glass, bending
and distorting light from galaxies and clusters behind it.
Astronomers can use this effect, called gravitational lensing,
to infer the presence of dark matter in massive galaxy clusters.
Andisheh Mahdavi, Assistant Professor Department of Physics and
Astronomy San Francisco State University has observed an
unexpected dark core at the center of Abell 520, reaffirming a
mystery first noted in 2007, but it was called "unreal" by
scientists since there was no sufficient evidence and the dark
matter were anchored to other galaxies.
This technique revealed the dark matter in Abell 520 had
collected into a "dark core," containing far fewer galaxies than
would be expected if the dark matter and galaxies were anchored
together. Most of the galaxies apparently have sailed far away
from the collision.
Initial detections of dark matter in the cluster, made in 2007,
were so unusual that astronomers shrugged them off as unreal,
because of poor data. New results from NASA's Hubble Space
Telescope confirm that dark matter and galaxies separated in
One way to study the overall properties of dark matter is by
analyzing collisions between galaxy clusters, the largest
structures in the universe. When galaxy clusters crash,
astronomers expect galaxies to tag along with the dark matter,
like a dog on a leash. Clouds of hot, X-ray emitting
intergalactic gas, however, plow into one another, slow down,
and lag behind the impact.
That theory was supported by visible-light and X-ray
observations of a colossal collision between two galaxy clusters
called the Bullet Cluster. The galactic grouping has become an
example of how dark matter should behave.
Studies of Abell 520 showed that dark matter's behavior may not
be so simple. Using the original observations, astronomers found
the system's core was rich in dark matter and hot gas, but
contained no luminous galaxies, which normally would be seen in
the same location as the dark matter. NASA's Chandra X-ray
Observatory was used to detect the hot gas. Astronomers used the
Canada-France-Hawaii Telescope and Subaru Telescope atop Mauna
Kea to infer the location of dark matter by measuring the
gravitationally lensed light from more distant background
The astronomers then turned to the Hubble's Wide Field Planetary
Camera 2, which can detect subtle distortions in the images of
background galaxies and use this information to map dark matter.
To astronomers' surprise, the Hubble observations helped confirm
the 2007 findings.
The team proposed numerous explanations for the findings, but
each is unsettling for astronomers. In one scenario, which would
have staggering implications, some dark matter may be what
astronomers call "sticky." Like two snowballs smashing together,
normal matter slams together during a collision and slows down.
However, dark matter blobs are thought to pass through each
other during an encounter without slowing down. This scenario
proposes that some dark matter interacts with itself and stays
behind during an encounter.
Another possible explanation for the discrepancy is that Abell
520 has resulted from more complicated interaction than the
Bullet Cluster encounter. Abell 520 may have formed from a
collision between three galaxy clusters, instead of just two
colliding systems in the case of the Bullet Cluster.
A third possibility is that the core contained many galaxies,
but they were too dim to be seen, even by Hubble. Those galaxies
would have to have formed dramatically fewer stars than other
normal galaxies. Armed with the Hubble data, the group will try
to create a computer simulation to reconstruct the collision and
see if it yields some answers to dark matter's weird behavior.
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, Md., manages the
telescope. The Space Telescope Science Institute (STScI) in
Baltimore, Md., conducts Hubble science operations. STScI is
operated by the Association of Universities for Research in
Astronomy, Inc., in Washington, D.C.
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