Topic: Late February Astronomy Bulletin

[Clive]

POSSIBLE NAKED-EYE COMET IN MARCH
NASA

Comet Pan-STARRS (C/2011 L4) was discovered by the Panoramic Survey
Telescope & Rapid Response System on the Haleakala volcano in Hawaii,
a 1.8-m telescope that is used to watch for Earth-approaching objects
that might pose a danger.  In 2011 it noticed a comet, that was named
"Pan-STARRS" after it.  In early March, the comet will pass about the
same distance from us as the Sun is, as it briefly dips inside the
orbit of Mercury.  It may become a naked-eye object, perhaps about as
bright as the stars of the Plough.  However, a new comet is always an
unknown quantity, just as capable of being a dismal failure as giving
a spectacular display.  Unaltered by warmth and sunlight, distant
comets are like time capsules, harbouring frozen gases and primitive,
dusty material drawn from the original solar nebula 4.5 billion years
ago.  When such comets occasionally fall towards the Sun they bring
their virgin ices with them.  This is thought to be Comet Pan-STARRS'
first visit to the inner Solar System, so it has never been assailed
before by the fierce heat and gravitational pull of the Sun.  On the
one hand, the comet could fall apart without much of a show, but on
the other it might throw off a lot of material and embellish our
night sky substantially.

Because it will go nearer to the Sun than Mercury, Pan-STARRS could
be quite active, but could still be difficult to see.  From here the
comet will appear very close to the Sun, only observable in twilight
when the sky is not fully dark.  The best dates to look may be March
12 and 13 when Pan-STARRS emerges into the western sunset sky not far
from the crescent Moon.  A comet and the Moon, together, framed by
twilight-blue, is a rare sight.  The primary feature visible to the
naked eye may be the gaseous coma around the head of the comet, but
any tail will probably require binoculars or a small telescope.

Comet Pan-STARRS should not be confused with another, even more
promising, comet coming in November, Comet ISON.


THERE MAY BE EARTH-SIZE PLANETS NEARBY
Harvard-Smithsonian Center for Astrophysics

On the basis of a wild extrapolation from publicly available data from
the Kepler space telescope, some astronomers have asserted that 6% of
red-dwarf stars may have Earth-sized planets.  Since red dwarfs are
the most common stars in our galaxy, there could be Earth-like planets
quite 'nearby'.  An average red dwarf is only one-third as large and
one-thousandth as bright as the Sun; none is visible to the naked eye.
Despite their dimness, such stars are good places to look for
Earth-like planets.  A transiting planet gives a larger photometric
signal (light dip) if the star is small, as the planet blocks more of
the star's disc.  The Kepler catalogue of 158,000 stars was used to
identify all the red dwarfs, which were then re-analysed to calculate
more accurate sizes and temperatures.  95 planet candidates were
identified orbiting them.  That was claimed to imply that at least 60%
of such stars have planets smaller than Neptune.  [60% of 158,000 is
95 THOUSAND! -- ED]  However, most of the 95 weren't the right size or
temperature to be considered Earth-like.  Just three planetary
candidates were both warm and approximately Earth-sized.


RARE EXPLOSION MAY HAVE CREATED OUR GALAXY'S YOUNGEST BLACK HOLE
Chandra X-ray Observatory

New data suggest that a highly distorted supernova remnant may contain
the black hole formed most recently in the our galaxy.  The remnant
appears to be the product of a rare explosion in which matter is
ejected at high speeds along the polar axis of a rotating star.  The
remnant, called W49B, is about a thousand years old as seen from the
Earth and located about 26,000 light-years away.  W49B is the first of
its kind to be discovered in the Galaxy, and it appears that its
parent star ended its life in a way that most others don't.  Usually
when a massive star runs out of fuel, the central region of the star
collapses, triggering a chain of events that quickly culminate in a
supernova explosion.  Most such explosions are fairly symmetrical,
with the stellar material blasting away more or less evenly in all
directions.  However, in the W49B supernova, material near the poles
of the rotating star was ejected at a much higher speed than material
emanating from its equator.  Jets shooting away from the star's poles
mainly shaped the supernova explosion and its aftermath.  The remnant
now glows brightly in X-rays and at other wavelengths, offering the
evidence for a peculiar explosion.  By tracing the distribution and
amounts of different elements in the stellar debris field, researchers
were able to compare X-ray data from the Chandra satellite to
theoretical models of how a star explodes.  For example, they found
iron in only half of the remnant while other elements such as suphur
and silicon were spread throughout.  That matches predictions for an
asymmetrical explosion.  In addition to its unusual signature of
elements, W49B also is much more elongated and elliptical than most
other remnants.

The authors tried to discover what sort of compact object the
supernova explosion left behind.  Most massive stars that collapse as
supernovae leave dense, spinning cores -- neutron stars.  Astronomers
can often detect neutron stars through their X-ray or radio pulses,
although sometimes an X-ray source is seen without pulsations.  A
search of the Chandra data revealed no evidence for a neutron star in
W49B.  The lack of such evidence may imply that a black hole formed.
Because supernova explosions are not well understood, astronomers are
keen to study extreme cases like the one that produced W49B.  The
relative proximity of W49B makes it relatively accessible for detailed
study.


CLUES TO THE ORIGIN OF COSMIC RAYS
ESO

In the year 1006 a new star was seen in the southern skies and widely
recorded around the world.  It was much brighter than Venus and may
even have rivalled the brightness of the Moon.  It was so bright at
maximum that it cast shadows and was visible during the day.
Astronomers have identified the site of that supernova and named it
SN 1006. They have also found in the southern constellation Lupus a
glowing and expanding ring of material that constitutes the remains of
the explosion.  It has long been suspected that such supernova
remnants may also be where some cosmic rays -- very-high-energy
particles originating outside the Solar System and travelling at close
to the speed of light -- originate, but until now the way that that
might happen has been unknown.

A team of the Max Planck Institute for Astronomy has now used the VLT
to look at the SN 1006 remnant to try to see what is happening where
high-speed material ejected by the supernova is ploughing into
quasi-stationary interstellar matter -- the shock front.  The shock
front is analogous to the sonic boom produced by an aircraft going
supersonic and is a natural candidate for a cosmic particle
accelerator.  There appear to be many very rapidly moving protons in
the gas in the shock region.  While the protons are not themselves the
sought-for high-energy cosmic rays, they could be the necessary 'seed
particles', which then go on to interact with the shock-front material
to reach the extremely high energies required and fly off into space
as cosmic rays.  There is evidence that there is a region that is
being heated in just the way that would be expected if there were
protons carrying away energy from directly behind the shock front.