Topic: Late October Astronomy Bulletin

[Clive]

AMATEUR RE-DISCOVERS LOST ASTEROID
ESA

A German amateur astronomer, Erwin Schwab, has re-discovered a
'potentially hazardous' asteroid that had been 'lost'.  The asteroid,
known by its catalogue name as 2008SE85, was discovered in 2008
September by the Catalina Sky Survey, and seen by a few observatories
into the next month, but noone had observed it since then and
predictions for its current position had become so inaccurate that the
object was considered lost.  In September, Schwab, using the 1-m
telescope at the Optical Ground Station in Tenerife, looked for the
object within the area of uncertainty of its predicted position, and
after only a few hours he found it about 2° away from its predicted
position.  Its recovery will allow a much more accurate determination
to be made of its orbit and help to confirm that it does not pose any
threat to the Earth.


TITAN SHOWS SURPRISING SEASONAL CHANGES
RAS

Detailed observations of Saturn's moon Titan from spacecraft have now
spanned 30 years, covering an entire Saturnian 'year'.  Dr. Coustenis
of the Meudon Observatory in Paris has found that the changing seasons
of Titan affect it more than has been supposed.  There are differences
in atmospheric temperatures, chemical composition and circulation
patterns, especially at the poles.  For example, hydrocarbon lakes
form around the north polar region of Titan during winter, owing to
colder temperatures and condensation.  Also, a haze layer surrounding
Titan at the north pole is significantly reduced near the equinox
because of changes in the atmospheric circulation patterns.  The main
cause of the cycles is solar radiation, which is naturally the
dominant energy source for Titan's atmosphere, dissociating the
nitrogen and methane molecules to create more complex ones, such as
ethane, and acting as the driving force for chemical changes.  Titan's
axial inclination is about 27°, so there are seasons much like those
of the Earth except that they are 30 times as long (and of course the
sunlight is much weaker so much further from the Sun).


PLUTO'S MOONS MAY BE HAZARDS TO NEW HORIZONS SPACECRAFT
Southwest Research Institute

The 'New Horizons' spacecraft is now almost seven years into its
9.5-year journey to explore Pluto and its system of moons.  Just over
two years from now, in 2015 January, New Horizons will begin
'encounter operations', which will culminate in a close approach to
Pluto on 2015 July 14.  While the spacecraft has been on its way,
evidence has accumulated of the possibility that debris that could
represent a threat to the craft may be orbiting in the Pluto system.
Astronomers have found more moons orbiting near Pluto -- the count is
now up to five.  Those moons, and perhaps others not yet discovered,
may act as debris generators, populating the Pluto system with shards
from collisions between them and smaller Kuiper-Belt objects.  Because
the spacecraft is travelling so fast -- more than 8 km/s -- a
collision with even a millimetre-sized grain could damage or destroy
it.  The New Horizons team is already using every available tool --
including computer simulations, ground-based telescopes, stellar
occultations by Pluto, and even the Hubble telescope -- to search for
debris in orbit.  At the same time, the team is plotting alternative,
more distant, courses through the Pluto system that would preserve
most of the scientific objectives but might be less of a risk if the
current plan is judged to be too hazardous.


PLANET FOUND IN NEAREST STAR SYSTEM
ESO

European astronomers have discovered a planet with about the mass of
the Earth orbiting a star in the Alpha Centauri system.  Alpha
Centauri is one of the brightest stars in the southern skies and is
the nearest stellar system to us -- only 4.3 light-years away.  It is
actually a triple star -- a system consisting of two stars rather
similar to the Sun, designated Alpha Centauri A and B and orbiting at
a mean separation of about 17 AU (about the distance of Uranus from
the Sun), and a much more distant faint red component known as Proxima
Centauri.  Radial-velocity measurements made over four years with the
HARPS instrument on the 3.6-m telescope at La Silla in Chile showed a
tiny, but real, reflex motion of the star from the motion of a planet
orbiting Alpha Centauri B every 3.2 days.  The effect is minute -- it
causes the star to move back and forth at little more than 1 mph.
Alpha Centauri B is very similar to the Sun but slightly smaller and
less bright. The newly discovered planet, with a mass little more than
that of the Earth, is orbiting only about six million km away from the
star, much closer than Mercury is to the Sun.  The orbit of the other
bright component of the double star, Alpha Centauri A, keeps it
hundreds of times further away, but it would still be a very brilliant
object in the planet's skies.


CIRCUMBINARY PLANET FOUND IN QUADRUPLE STAR SYSTEM
Science Daily

A planet dubbed PH1 is the first to be identified by 'citizen
scientists' participating in a Yale-led programme that enlists members
of the public to review astronomical data, obtained from the Kepler
spacecraft and placed on  thePlanethunters.org  website, for signs of
planets.  The volunteers noticed slight dips in light caused by the
planet as it passed in front of its parent stars, a common method of
finding extra-solar planets.  Further observations from the Keck
telescopes in Hawaii indicate that PH1 is a gas giant with a radius
about 6.2 times that of the Earth, making it a bit bigger than
Neptune. It has turned out to be a 'circumbinary' planet, orbiting
outside the 20-day orbit of a pair of eclipsing stars that are 1.5 and
0.41 times the mass of the Sun.  It revolves around its host stars
roughly every 138 days.  Beyond the planet's orbit, at about 1000 AU,
is a second pair of stars orbiting the planetary system.  Circumbinary
planets are at one of the extremes of planet formation, and the
discovery of such systems is obliging astronomers to try to understand
how such planets can assemble and evolve in such dynamically
challenging environments.


STAR HAS 11-YEAR ORBIT AROUND BLACK HOLE AT GALACTIC CENTRE
University of California - Los Angeles

Astronomers report the discovery of a remarkable star that orbits the
black hole at the centre of our Milky Way galaxy in just 11.5 years.
It has been named S0-102 (the S is for Sagittarius, the constellation
containing the Galactic Centre).  Another star, S0-2, was already
known to be in orbit around the hole in a period as short as 16 years.
Most of the stars have orbits of 60 years or longer.

S0-102 and S0-2 are each in an elliptical orbit around the central
black hole.  The planetary motions in the Solar System demonstrated
Newton's gravitational theory 300 years ago; the motions of S0-102 and
S0-2 can be expected in due course to demonstrate an effect predicted
by Einstein's general theory of relativity, which describes gravity as
a consequence of the curvature of space and time.  The elliptical
orbits of the two stars tell us the mass of the black hole, but as we
improve the precision of the measurements and maintain them for a
longer time we will be able to see the relativistic deviations from
perfect ellipses.  They arise from the strong curvature of space-time
near the hole, as well as the apparent bending of the path of the
light as it comes from the stars to us.  The deviations from perfect
ellipses are very small and require very precise measurements, but
over the last 15 years researchers have dramatically improved their
ability to make such measurements.  S0-2, which is three magnitudes
brighter than S0-102, will make its closest approach to the hole in
2018.


SUPER-MASSIVE BLACK HOLES IN EARLY UNIVERSE
RAS

Infrared surveys of the sky have led to the discovery of a population
of rapidly-growing super-massive black holes in the early Universe.
The holes were previously undetected because they are obscured by
thick layers of dust.  A new study has shown that they are emitting
vast amounts of radiation through violent interactions with their
host galaxies.  The most extreme object in the study, called
ULASJ1234+0907, is in the constellation Virgo; the light from it has
taken 11 billion years to reach us, so we see it as it appeared in the
early Universe.  Its black hole has more than 10 billion times the
mass of the Sun.

Some astronomers are said to think that super-massive black holes
exist at the centres of all galaxies.  In the most massive galaxies,
they are thought to grow through violent collisions with other
galaxies, which trigger the formation of stars and provide material
for the black holes to accrete.  The collisions also produce dust
within the galaxies and thereby embed the black holes in dusty
envelopes.  A good example of a less-distant dusty, growing black hole
is in the well-studied galaxy Markarian 231, located a mere 600
million light-years away.  Observations made with the Hubble telescope
have shown evidence that it underwent a violent impact with another
galaxy in the 'recent' past.  ULASJ1234+0907 is a more extreme
analogue of Markarian 231, suggesting that conditions in the early
Universe were more turbulent than they are today.


SPITZER SPACE OBSERVATORY MEASURES HUBBLE CONSTANT
NASA

Astronomers using the Spitzer space telescope have made a fresh
measurement of the Hubble constant (the rate of expansion of the
Universe).  Determining the expansion rate is critical for
understanding the age and size of the Universe.  Spitzer operates in
infrared light; its new measurement is said to improve by a factor of
3 on a previous study made in visible light with the Hubble telescope,
and supposedly brings the uncertainty down to 3%.  The new value for
the constant is 74.3 ± 2.1 km/s per megaparsec (a megaparsec is
roughly 3 million light-years).  Infrared light penetrates dust and
provides better observations of the Cepheid variable stars that
represent an important rung in what astronomers call the cosmic
distance ladder.


PRECISE MEASUREMENTS OF THE GALAXY
National Astronomical Observatory of Japan

Very-long-baseline interferometry (VLBI) is a radio-astronomical
technique that integrates data from a number of mutually distant radio
telescopes and can determine the distances and proper motions of
Galactic objects.  The National Astronomical Observatory of Japan
operates such a system, called VERA (VLBI Exploration of Radio
Astrometry); it has found that the distance from the Sun to the
Galactic Centre is 26,100 light-years, and that the Galactic rotation
velocity of the Solar System is 240 km/s.  The latter value is higher
than the 220 km/s that was determined in 1986 and endorsed by the
International Astronomical Union.  There is an implication that the
mass of dark matter in the Galaxy may be about 20% larger than has
been supposed up till now.