SOHO DISCOVERS 2,000th COMET
ScienceDaily
Drawing on help from citizen-scientists around the world, SOHO is by
far the greatest comet-finder of all time. Its performance is all the
more impressive because SOHO was not designed to find comets but to
monitor the Sun. Since it was launched on 1995 December 2, SOHO has
more than doubled the number of comets for which orbits have been
determined. Of course, it is not SOHO itself that discovers the
comets -- that is the province of the amateur-astronomer volunteers
who examine the pictures produced by SOHO's 'LASCO' (Large-Angle and
Spectrometric Coronagraph) cameras. Over 70 people representing 18
different countries have helped to find comets in the last 15 years
by searching through the publicly available SOHO images on-line.
It took SOHO ten years to spot its first thousand comets, but only
five more to find the next thousand. That is due partly to increased
participation from comet-hunters and work done to optimize the images
for comet-sighting, but also partly to an unexplained systematic
increase in the actual number of comets around the Sun. Indeed,
December alone saw an unprecedented 37 new comets, a number high
enough to be called a 'comet storm'.
LASCO is actually a set of three 'coronagraphic' cameras that view
successively larger annular areas around the Sun's bright disc, which
itself is occulted by the optical systems to enable them to observe
the Sun's faint outer atmosphere, the corona. Its comet-finding
ability is a natural side-effect. The reason that it sees so many
comets that are not discovered from the ground is of course that it
can observe them when they are very close to the Sun; from the ground
the part of the sky within 15° (and in many cases much more) of the
Sun is always either in daylight or in bright twilight and almost on
the horizon. The brightness of a comet typically rises inversely as a
very high (often about the fourth, sometimes even the sixth) power of
its distance from the Sun, so comets are enormously brighter when seen
in the LASCO fields than they could ever be when seen from the ground.
Many of the SOHO/LASCO comets have similar orbits that point to a
common origin. Indeed, 85% of them belong to a single group known as
the Kreutz family, believed to be remnants of a single large comet
that broke up several hundred years ago. The Kreutz comets are
'sungrazers'; they pass so near to the Sun that most of them -- very
small bodies -- are vaporized within hours of discovery. Many of the
others, however, that pass less desperately close, survive their
passages around the Sun and return periodically. One such is Comet
96P Machholz: orbiting the Sun approximately every six years, it has
now been seen by SOHO three times.
ASTEROID MAY BE EXTINCT COMET
University of Arizona. Tucson
New observations suggest that an asteroid discovered more than 100
years ago may not be a true asteroid at all, but may instead be a
supposedly extinct comet that is coming back to life. An astronomer
of the Catalina Sky Survey at the University of Arizona was searching
for 'potentially hazardous asteroids' when he came across what looked
like a comet -- a faint, wispy tail surrounding a bright star-like
core. Four images taken over the course of 30 minutes showed that the
object was moving with respect to the background stars. Its
brightness, magnitude 13.4, led him to suspect that it was a known
comet, but it turned out to be asteroid (596) Scheila, discovered in
1906.
The team checked previous images in the Survey's archives but found no
activity until December 3. Then, the object appeared brighter and
slightly diffuse. Previous analysis of (596) Scheila's colour
indicated that it is composed of primitive carbonaceous material left
over from the formation of the Solar System and might be an extinct
comet. After the discovery was announced, other observers obtained
images and spectra of the object to determine whether its tail
consists of ice and gases that it is emitting or if it is dust
resulting from a collision with another asteroid. A preliminary
conclusion is that the coma surrounding the asteroid is composed of
dust, but more observations will be needed to understand just what is
happening to (596) Scheila. Most asteroids are collision fragments
from larger asteroids and display a range of mineral compositions, but
some are thought to be former comets whose volatile ices have been
driven off by the Sun. If the activity recently observed proves to be
cometary in nature, Scheila will be only the sixth-known, and by far
the largest, main-belt comet.
MOST MASSIVE STARS CAN FORM IN ISOLATION
Science Daily
Observations made with the Space Telescope by University of Michigan
astronomers suggest that the most massive stars in the Universe could
form almost anywhere, including in near-isolation rather than in a
cluster. The scientists observed eight such stars in the Small
Magellanic Cloud, ones that they believe to range from 20 to 150 times
the mass of the Sun. Five of them had no neighbours bright enough to
discern; the other three appeared to be in small clusters of ten or
fewer stars. The researchers acknowledge the possibility that all of
the stars they studied may not still be located in the neighbourhoods
in which they were born. Two of them are known to be runaways that
have been kicked out of their clusters of origin, but in several cases
the astronomers found wisps of left-over gas nearby, strengthening the
possibility that the stars are still in the isolated places where they
were formed.
The most massive stars are of particular interest because to a
considerable extent they direct the evolution of their galaxies.
Their winds and radiation shape interstellar gas and promote the birth
of new stars, and their violent supernova explosions create heavy
elements.
RAPID STAR-FORMATION IN EARLY UNIVERSE
RAS
Astronomers using the Herschel infrared space telescope, a 3.5-m
instrument launched in 2009, have found evidence for a surge in star
birth in a newly discovered population of massive galaxies in the
early Universe. Their measurements suggest that stars formed most
rapidly about 11 billion years ago, or about three billion years after
the Big Bang. They saw evidence that the galaxies were forming stars
at a tremendous rate and had large reservoirs of gas that would power
the star-formation for hundreds of millions of years.
Those results stem from the recent discovery in the early Universe of
extremely luminous galaxies, in which the newly-formed stars are still
cocooned in the clouds of gas and dust within which they were born.
The dust has a temperature of around -240 C, at which it does not
shine in visible light but is bright at the far-infrared wavelengths
observed by Herschel. From the Herschel observations, focused on
about 70 galaxies in the constellation Ursa Major, the scientists
received the impression that such galaxies represent an important
episode in the build-up of present-day large galaxies such as our own
Milky Way. The Herschel galaxies have prodigious rates of star
formation, far higher than anything seen in the present Universe.
They probably developed through violent encounters between previously
undisturbed galaxies, after the first stars and galaxy fragments had
already formed.
TEN YEAR-OLD GIRL DISCOVERS SUPERNOVA
BBC News
A 10-year-old girl in Canada has become the youngest person to have
discovered a supernova. Kathryn Gray was studying images which had
been sent to her father from an amateur's observatory when she noticed
the magnitude-17 supernova in the galaxy UGC 3378, which is about 240
million light-years away in the constellation Camelopardus. Kathryn's
father, Paul Gray, himself an amateur astronomer, helped her by taking
steps to rule out asteroids and checking the list of currently known
supernovae. The discovery was then verified by an independent
astronomer and officially registered. The new supernova is named
SN 2010lt.
ODYSSEY SPACECRAFT SETS LONGEVITY RECORD
NASA/JPL
Mars Odyssey, which was launched in 2001, has broken the record for
longest-serving spacecraft at Mars. The probe began its 3,340th day
in Martian orbit on December 15, breaking the record set by the Mars
Global Surveyor, which orbited Mars from 1997 to 2006. Odyssey's
observations including the monitoring of seasonal changes on Mars from
year to year and the most detailed maps that have been made of most of
the planet. In 2002, the spacecraft detected hydrogen just below the
surface throughout Mars' high-latitude regions. The deduction that
the hydrogen is in frozen water prompted the Phoenix Mars Lander
mission, which confirmed that idea in 2008. Odyssey also carried the
first experiment sent to Mars specifically to prepare for manned
missions, and found that radiation levels from solar flares and cosmic
rays are 2 to 3 times higher there than around the Earth.
BRAZIL TO JOIN ESO
ESO
The Federative Republic of Brazil has signed the formal accession
agreement paving the way for it to become a Member State of the
European Southern Observatory. Following government ratification,
Brazil will become the fifteenth Member State and the first from
outside Europe.
The design phase of the European Extremely Large Telescope (E-ELT) was
recently completed, and a major review was conducted in which every
aspect of the project was scrutinised by an international panel of
independent experts. The panel found the project to be technically
ready to enter the construction phase. The go-ahead for construction
is planned for 2011, and when the telescope is useable, supposedly
early in the next decade, European, Brazilian and Chilean astronomers
will have access to it.
Topic: Early January Astronomy Bulletin (Read 820 times)