Astronomy - June 2015

(Jacob Rumans) #1


30 million x

Star Spica Venus Full Moon
Magnitude 6.
1 firefly

Magnitude 1.0 Magnitude – 4.4 Magnitude –12.
100 x 14,500 x






SATELLITE EXPLODES. A 20-year-old U.S. military weather forecasting satellite exploded for unknown reasons in
early February, breaking into 43 pieces that the Air Force is now tracking, the website confirmed.

Due to Titan’s thick atmosphere, scientists have used the Cassini
spacecraft’s radar instrument to reveal the saturnian moon’s sur-
face features. The resulting images have provided insights into the
large satellite’s sand dunes and methane lakes, but they still hide
small-scale features because with radar comes image “noise.”
But thanks to a new image-processing algorithm, some views
are coming in clearer than ever, as NASA announced February 11.
Antoine Lucas, a planetary geophysicist at CEA-Saclay in France
who worked with the Cassini radar team as a postdoc, looked
to the mathematics community for models to reduce the grainy
appearance and came up with “despeckling,” which successfully
modifies the noise without compromising the data.
The clearer images will provide Cassini scientists with fresh
views of surface features, but “despeckling” won’t be used on all
images just yet. “It takes a lot of computation, and at the moment
quite a bit of ‘fine-tuning’ to get the best results with each new
image,” says radar team member Randy Kirk of the U.S. Geological
Survey, “so for now we’ll likely be despeckling only the most
important — or most puzzling — images.” — K. F.

Titan comes in clearer than ever



Astronomers have found supermassive black
holes weighing a billion times more than the
Sun at the center of galaxies when the universe
was only 800 million years old. We know that
the material feeding these starving black holes
heats up and emits X-rays, while highly ener-
getic particles emitting radio waves are ejected
from the innermost regions of the black hole
in the form of collimated jets. However, how
these monsters have reached their mass and
become so powerful already in the early uni-
verse still puzzles astronomers. One possibil-
ity is that they grow from seed black holes of
lower mass, so-called intermediate-mass black
holes (IMBHs), weighing a thousand times
more than the Sun but a thousand times less
than supermassive black holes.
IMBHs have been long sought as the miss-
ing link between stellar-mass black holes,
formed from the death of a star, and super-
massive black holes; nevertheless, observa-
tional evidence for their existence remains

scant. Thanks to combined
X-ray and radio observations,
we have discovered an IMBH
of 50,000 solar masses wander-
ing in the arm of a spiral galaxy. The galaxy
seems to have undergone a merger with
another galaxy of lower mass, suggesting that
the IMBH is the nucleus of the dwarf galaxy
whose body has been stripped off during the
collision. The IMBH has a radio jet as power-
ful as those observed in supermassive black
holes, which are able to clear out a cavity and
suppress star formation.
We have thus learned that the spiral arms
of galaxies, especially those undergoing a
merger with a low-mass galaxy, are great
places to search for the seed IMBHs from
which supermassive black holes may form.
Ultimately, these IMBHs can have a large
impact on their surroundings, as supermassive
black holes do, which has strong implications
for studies of supermassive black hole growth.

Mar Mezcua
Postdoctoral researcher,
Harvard-Smithsonian Center
for Astrophysics, Cambridge,

“DESPECKLED” DATA. This before-and-after image shows Cassini
radar data of Titan’s surface with (right) and without an algorithm applied
to modify electronic noise. NASA/JPL-CALTECH/ASI

FIREFLY. Magnitudes can be difficult to understand. An increase of 1 magnitude means
a 2.5118865-fold increase in brightness. This chart shows a magnitude 6.0 star represented
by a single firefly. A star 5 magnitudes brighter, like Spica, would be 100 times as luminous.
Much brighter objects, like Venus and the Full Moon, reflect far more light than any star
produces because they lie closer. ASTRONOMY: MICHAEL E. BAKICH AND ROEN KELLY

Some version of the magnitude system
for stellar brightness has been in use for
more than 2,000 years. British astrono-
mer Norman Pogson standardized the
magnitude definitions in 1856.

The black hole Mar Mezcua and her team
discovered has traits similar to both stellar-
mass black holes and supermassive ones.
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