Topic: Mid March Astronomy Bulletin

[Clive]

LUNAR IMPACT OBSERVED
RAS

A meteorite with the mass of a small car crashed into the Moon last
September, according to Spanish astronomers. The impact, the biggest
seen to date, produced a bright flash and would have been easy to
detect from the Earth.  The Earth's atmosphere prevents small rocks
from space from reaching the surface, and geological activity and
weathering processes tend in time to efface the evidence of even major
impacts.  The Moon has no such atmosphere, and the record of the
collisions that span the 4.5 billion years' history of the Solar
System is plain to see on its surface, in the form of the vast numbers
of craters large and small that cover it.  Although there is little
likelihood now of a very large object striking the Moon or planets,
collisions with smaller objects are very common even today.  The odds
of seeing one of them by chance are very poor, so scientists have set
up networks of telescopes that can detect them automatically.

On 2013 September 11, Prof. Jose M. Madiedo was operating two such
telescopes in the south of Spain.  At 2007 UT he witnessed an
unusually long and bright flash in Mare Nubium, one of the ancient
lava-filled 'seas' of the Moon.  The flash occurred in the
un-illuminated part of the Moon's disc (it was shortly before First
Quarter) and might well have been visible to anyone who happened to be
looking at the Moon at that moment.  It was no doubt the result of a
rock crashing into the lunar surface and was briefly almost as bright
as the Pole Star.  In the video recording made by Prof. Madiedo, an
afterglow remained visible for a further eight seconds.  The event is
the longest and brightest confirmed impact flash ever observed on the
Moon.  It was probably produced by an impactor whose size was of the
order of a metre, and created a new crater with a diameter of around
40 metres.  The impact energy was equivalent to an explosion of
roughly 15 tons of TNT, at least three times higher than the largest
previously seen event observed in March last year.


PLANETS ORBITING 'NEARBY' RED-DWARF STARS
RAS

A group of astronomers from the UK and Chile reports the discovery of
eight small planets orbiting 'nearby' red-dwarf stars.  By way of a
rashly extreme extrapolation from that small sample, the scientists
estimate that a large fraction of red dwarfs, which make up at least
three-quarters of the stars in the Universe (or at least in our
Galaxy -- they are too faint to see in other galaxies) has associated
low-mass planets.  The researchers found the planets by analysing
archival data from two high-precision planet surveys made with the
Ultraviolet and Visual Echelle Spectrograph (UVES) and High-Accuracy
Radial-velocity Planet Searcher (HARPS), both operated by the European
Southern Observatory in Chile.  The two instruments are used to
measure how much a star is affected by the gravity of a planet in
orbit around it.  As an unseen planet orbits a distant star, the star
itself moves (though in a much smaller orbit than the planet) around
their common centre of gravity.  A small periodic variation in the
radial velocity of the star demonstrates the existence of the planet
that is causing it.  By combining the data from UVES and HARPS, the
team reckoned to be able to detect signals that were not strong enough
to be seen in the data from either instrument alone.

The astronomers thereby considered that they had discovered the eight
planets, three of which are in the so-called 'habitable zones' (which
merely means that the temperatures there are usually between freezing
and boiling) of their respective stars and are only a little more
massive than the Earth.  All the newly discovered planets orbit
red-dwarf stars between 15 and 80 light years away.  They take between
two weeks and nine years to complete each orbit, placing them at
distances from their stars of between 6 and 600 million km (equivalent
to between 0.04 and 4 times the distance from the Earth to the Sun).
The team used novel (cynics might say dodgy) analysis techniques to
squeeze the planetary signals out of the data, which did not
obviously exhibit them.  The discoveries add eight new exo-planet
signals to the previous total of 17 already known around such low-mass
stars.  The team also plans to follow up a further ten even weaker
signals.


A BREAKTHROUGH IN PLANET DISCOVERIES
NASA

The Kepler team has now discovered 715 new planets.  Kepler works by
looking for the slight dimming of starlight caused when a distant
planet transits its parent star.  Any dip in stellar brightness
attracts the attention of the Kepler team, and can prompt it to
declare a planet candidate.  Verification of candidates can be a
laborious process, proceeding slowly, planet by planet.  Now, however,
researchers have thought up a way to cut corners on the procedure by a
technique they call 'verification by multiplicity'; it relies in part
on the logic of probability, which a cynic might think less trust-
worthy than actual evidence of the planets.  Out of the 160,000 stars
Kepler has observed, a few thousand have planet candidates.  But not
all candidate systems are equal.  A subset of the total, numbering in
the hundreds, has not just one but multiple candidates.  By
concentrating on those systems, the team found 715 planets orbiting
305 stars.  All of the newly-discovered ones are located in
multi-planet systems.  Nearly 95% of the planets are smaller than
Neptune, that is, less than four times the size of the Earth.  That is
a marked increase in the known number of relatively small planets.
The study suggests that planets in multi-systems tend to be small and
their orbits tend to be circular, much like the inner part of our own
Solar System.  Four of the new planets are less than 2.5 times the
diameter of the Earth.


CLOUDS SEEN CIRCLING SUPERMASSIVE BLACK HOLES
RAS

Astronomers see clouds of gas orbiting supermassive black holes at the
centres of galaxies.  Once thought to be in relatively uniform,
fog-like rings, the accreting matter is now thought instead to form
clumps dense enough intermittently to dim the intense radiation
blazing from the vicinities of the holes.  Evidence for the clouds
comes from records collected over 16 years by the Rossi X-ray Timing
Explorer, a satellite in low Earth orbit equipped with instruments
that measure variations in X-ray sources.  Those sources include
active galactic nuclei, brilliantly luminous objects powered by
supermassive black holes as they gather and condense huge quantities
of dust and gas.

From records for 55 active galactic nuclei, astronomers found a dozen
instances where the X-ray signal dimmed for periods of time ranging
from hours to years, presumably when a cloud of dense gas passed
between the source and satellite.  The clouds they observed orbit a
few light-weeks to a few light-years from the centres of the nuclei.


FOUR NEW GALAXY CLUSTERS FURTHER BACK IN TIME
RAS

Four very distant galaxy clusters, each potentially containing
thousands of individual galaxies, have newly been discovered.
Astronomers used a new way of combining data from two ESA satellites,
Planck and Herschel, to identify more distant galaxy clusters than has
previously been possible.  The researchers believe up to 2000 further
clusters could be identified using that technique, helping to build a
more detailed time-line of how clusters are formed.  Galaxy clusters
are the most massive objects in the Universe, containing hundreds to
thousands of galaxies, bound together by gravity.  While astronomers
have identified many nearby clusters, they need to go further back in
time to understand how such structures are formed.  The light from the
most distant of the four new clusters identified by the team has taken
over 10 billion years to reach us, so the researchers are seeing what
the cluster looked like when the Universe was 'only' three billion
years old.

Although we are able to see individual galaxies that go further back
in time, up to now the most distant clusters found by astronomers date
back to when the universe was 4.5 billion years old.  Clusters can be
identified at such distances because they contain galaxies in which
huge amounts of dust and gas are being formed into stars.  Galaxies
are divided into two types: elliptical galaxies that have many stars,
but little dust and gas; and spiral galaxies like our own, which
contain lots of dust and gas.  Most clusters today are dominated by
giant elliptical galaxies in which the dust and gas has already been
formed into stars.  It is thought that what we are seeing in the
distant clusters are giant elliptical galaxies in the process of being
formed.

Observations were recorded by the Spectral and Photometric Imaging
Receiver (SPIRE) instrument as part of the Herschel Multi-tiered
Extragalactic Survey (HerMES).  The researchers are among the first to
combine data from two satellites both of which ended their operations
last year: Planck, which scanned the whole sky, and Herschel, which
surveyed certain sections in greater detail.  The researchers used
Planck data to find sources of far-infrared emission in areas covered
by the Herschel satellite, then cross-referenced with Herschel data to
look at those sources more closely.  Of sixteen sources identified by
the researchers, most were confirmed as single, nearby galaxies that
were already known.  However, four were shown by Herschel to be formed
of multiple, fainter sources, indicating previously unknown galaxy
clusters.  The team then used additional existing data and new
observations to estimate the distances of those clusters and to
determine which of the galaxies within them were forming stars.  The
researchers are now hoping to identify more clusters by that
technique, with the aim of looking further back in time to the
earliest stage of cluster formation.


FIRST LIGHT FOR MUSE
ESO

A new instrument called MUSE (Multi Unit Spectroscopic Explorer) has
been installed on ESO's Very Large Telescope (VLT) at the Paranal
Observatory in northern Chile.  MUSE's scientific goals include
looking at the mechanisms of galaxy formation in the early Universe,
and studying both the motions of material in nearby galaxies and their
chemical properties, but it will be able to do other things as well.
MUSE uses 24 spectrographs to create both images and spectra of
selected regions of the sky.  It creates 3D views of the Universe with
a spectrum for each pixel as the third dimension.  In the subsequent
analysis the astronomer can move through the data and study different
views of the object at different wavelengths.