Topic: Mid September Astronomy Bulletin

[Clive]

ICE, AND PROBABLY METHANE, ON DISTANT DWARF PLANET
California Institute of Technology

Dwarf planet 2007 OR10 orbits the Sun far out in the Solar System and
is about half the size of Pluto, making it the fifth-largest dwarf
planet.  It is one of the reddest objects in the Solar System.  There
are a few other distant dwarf planets that also are red; they are
themselves part of the large group of icy bodies called Kuiper Belt
Objects (KBOs).  The spectrum of 2007 OR10 shows that the surface is
covered in water ice -- a surprise, because although ice is common in
the outer Solar System, it is almost always white, not red.

There is, however, one other dwarf planet that is both red and covered
with water ice: Quaoar, which was discovered in 2002 and is slightly
smaller than 2007 OR10.  Quaoar is big enough to have had an
atmosphere and a surface covered with volcanoes that spewed an icy
slush, which then froze solid as it flowed over the surface.  But
because Quaoar is not as big as dwarf planets like Pluto or Eris, it
could not hold onto volatile compounds like methane, carbon monoxide,
or nitrogen as long.  A couple of billion years after Quaoar formed,
it began to lose its atmosphere to space; now, all that remains is
some methane.  Over time, exposure to the radiation from space turned
that methane -- which consists of a carbon atom bonded to four
hydrogen atoms -- into long hydrocarbon chains, which look red.  The
irradiated methane sits on Quaoar's icy surface like frost, giving it
a rosy hue.  The spectrum of 2007 OR10 looks similar to Quaoar's,
suggesting that what happened on Quaoar also happened on 2007 OR10.
Although the latter's spectrum clearly shows the presence of water
ice, the evidence for methane is not definitive at present.


COLDEST STARS DISCOVERED
NASA

Scientists using the Wide-field Infrared Survey Explorer (WISE) have
discovered six 'Y dwarfs' -- star-like bodies with temperatures as
cool as the human body -- all within a distance of about 40 light-
years.  They are the coldest members of the brown-dwarf family,
objects that are sometimes referred to as 'failed stars' because they
are too low in mass to fuse atoms at their cores; instead, these
objects cool and fade with time, until what little light they do emit
is at infrared wavelengths.  Brown dwarfs have atmospheres that are
similar to those of gas giant planets like Jupiter, but they are
easier to observe because they are alone in space, away from the
relatively blinding light of a parent star.  The coldest of the six
Y dwarfs, called WISE 1828+2650, has an estimated atmospheric
temperature less than 25°C.  Another, WISE 1541-2250, is about nine
light-years away and may become recognized as the seventh-closest
star system, in place of Ross 154.


EXTREMELY METAL-POOR STAR
ESO

A faint star called SDSS J102915+172927, in the constellation Leo, has
been found to have the smallest abundance of elements heavier than
helium of all stars yet studied.  It has a mass less than that of the
Sun and is probably more than 13 billion years old.  Observers at the
VLT found that the proportion of metals in the SDSS star is more than
20,000 times smaller than in the Sun.  It is believed that the
lightest chemical elements -- hydrogen and helium -- were created
at the Big Bang, together with some lithium, while almost all other
elements were formed later in stars.  Supernova explosions spread the
stellar material into the interstellar medium, making it richer in
metals.  New stars formed from the enriched medium, so they had more
metals in their composition than the older stars.  The abundance of
metals is therefore a guide to the age of a star, so the SDSS object
could be one of the oldest stars ever found.  It has a surprising lack
of lithium.  It 'should' have a composition similar to that of the
Universe shortly after the Big Bang, with a few more metals in it.
But the proportion of lithium seems to be at least fifty times less
than expected in the material produced by the Big Bang.  The same
observers have identified several more candidate stars that may prove
to have metal levels similar to, or even lower than, those in SDSS
J102915+172927.


UNIFORMITY OF SUPERNOVAE INVESTIGATED
ScienceDaily

Type Ia supernovae are thought to occur when a white dwarf in a binary
star system receives additional material from its companion star,
until its mass exceeds a certain limit at which the star initially
collapses but then explodes.  There has recently been interest in
determining the nature of the mass 'donors', with the ultimate goal of
establishing whether supernovae everywhere evolve in the same manner,
having the same luminosity at various stages.  Estimating cosmological
distances depends largely on assumptions about the constancy of the
candle-power of such very luminous objects as supernovae, and the
assumptions need to be tested.  The research has indicated that in
about a quarter of the cases in spiral galaxies, and possibly more,
the companion star that donates mass to the white dwarf is probably an
ordinary medium-sized star, largely similar to the Sun.  [This item is
silent as to the nature of the other three-quarters of the cases, even
in spiral galaxies.]


GALAXY WITH EPISODIC JETS
RAS

Certain galaxies exhibit jets that are shot out at nearly the speed
of light from the poles of discs of material that is thought to be
rotating round super-massive black holes at the galaxies' cores.
There is one spiral galaxy, nicknamed Speca, that shows evidence for
three distinct episodes of such activity.  It is about 1.7 billion
light-years away, and there are 60-odd other galaxies in a cluster
with it.  They may provide an analogy with what young galaxies and
clusters looked like when the Universe was much younger.  Galaxies in
such clusters would have been gathering up additional material,
colliding with each other, undergoing bursts of star formation, and
interacting with primordial material falling into the cluster from
outside; Speca is showing evidence for many of those phenomena.

Speca (an acronym) first came to light in an image that combined data
from the visible-light Sloan Digital Sky Survey with a survey from the
VLA radio telescope.  Images from various radio telescopes operating
at different wavelengths identified three separate pairs of radio-
emitting lobes, providing evidence for three distinct epochs of jet
activity.  The outermost lobes are old enough that their particles
should have lost most of their energy and ceased to produce radio
emission.  It is thought that those old, relic lobes have been
're-lit' by shock waves from rapidly-moving material falling into the
cluster of galaxies as the cluster continues to accrete matter.


PROPERTIES OF YOUNG GALAXIES
RAS

Scientists have discovered a distant galaxy that throws light on two
fundamental questions of galaxy formation -- how galaxies accrete
matter and how they give off energetic radiation.  It is believed
that, during the epoch when the first galaxies formed, their
ultraviolet light ionized surrounding neutral hydrogen atoms, i.e. it
stripped them of their electrons.  That was the origin of the ionized
plasma that today fills the Universe.  But there is a question as to
how the high-energy radiation was able to escape from the immediate
surroundings of a galaxy, known as the galactic halo.  The galaxies we
observe today tend to be completely surrounded by haloes of neutral
hydrogen, which absorb all the light capable of ionizing hydrogen
before it has a chance to escape into inter-galactic space.

The scientists, using the Magellan telescopes at Las Campanas and
archival images from the Hubble telescope, discovered a galaxy with an
extended patch of light surrounding it.  It appeared that roughly half
of the galaxy's radiation must be escaping and exciting hydrogen atoms
beyond its halo.  The key to the escape of radiation was found in the
unusual, distorted shape of the galaxy.  It appears that the object
had recently collided with another galaxy, creating a hole in its
halo, allowing radiation to pass through.  The escape of radiation
during such galactic interactions and collisions may be able to account
for the re-ionization of the Universe.  At early times, when the
Universe was much denser, collisions between galaxies would have been
much more common than they are today.

The new observation also demonstrates the flow of in-bound matter, from
which a galaxy initially forms.  In the present case, the escaping
ionizing radiation illuminates a long train of incoming gas, which is
feeding new matter into the galaxy.  The existence of such structures
had been suggested by theory, but they had not been seen previously
because they barely emit any light of their own.


PLUTO PROBE ON TRACK
NASA

One of the fastest spacecraft ever launched -- New Horizons -- is
heading for Pluto.  Launched in 2006, it has been going for longer
than some missions last, and still has four more years to go.  When it
reaches Pluto in 2015 it will have travelled for longer than any
spacecraft has previously flown to reach its main target, although
Voyager 2 had been going for more than 12 years when it had its final
and very successful rendezvous with Neptune in 1989.  To save power
and reduce wear, New Horizons hibernates much of the time.  The probe
is equipped with spectrometers and one of the largest and highest-
resolution interplanetary telescopes ever flown, called LORRI, short
for Long-Range Reconnaissance Imager.  At closest approach to Pluto,
about 10,000 km, LORRI should resolve details almost as well as a spy
camera.


PLAN TO REVIVE 1970s UK SATELLITE
BBC News

When the Prospero spacecraft was launched by a Black Arrow rocket on
1971 October 28, it marked the end of a very short era -- it was the
first UK satellite to be launched on a UK launch vehicle, and it would
also be the last, as Ministers had cancelled the rocket project in the
run-up to the flight.  However, as the Black Arrow was ready, the
programme team decided to fire it anyway.  Prospero was successfully
put into orbit from the remote Woomera base in the Australian desert,
and the satellite is still up there.

Carrying a series of experiments to investigate the effects of the
space environment, the satellite operated satisfactorily until 1973
and was contacted annually until 1996.  Now, scientists are hoping
to re-establish communications in time for the satellite's 40th
anniversary.  First, they have to re-engineer the 'ground segment',
but that is not easy because the satellite was built by the Space
Department at the Royal Aircraft Establishment in Farnborough and the
department was broken up long ago.  The codes to contact Prospero were
missing, and the technical reports made in the 1970s were also thought
to have been lost.  The codes were eventually discovered typed on a
piece of paper in the National Archives at Kew.  But even with the
codes, the engineers still have to build equipment to communicate with
the satellite, and to obtain approval from the broadcast regulator
Ofcom to use Prospero's radio frequencies, which are being employed
these days by other satellite operators.  Once that ground segment is
complete, then they will see if it is still possible to communicate
with Prospero.  If the satellite is still alive, some of the
experiments might even be working.