JUPITER'S FAINTEST KNOWN MOON
Phys.org
In 2010 September, two previously unknown distant satellites of
Jupiter were discovered during routine tracking observations of
already-known moons. They were re-observed several times during that
autumn, in order to see if they really were satellites of Jupiter,
leading to their obtaining MPC designations S/2010 J 1 and S/2010 J 2.
With Jupiter now having 67 known satellites, the discovery of two
additional tiny satellites does not have a large bearing on our
understanding of the system. S/2010 J 1 was discovered in images
taken at the Palomar 200-inch Hale Telescope and S/2010 J 2 was
discovered in ones taken with the MegaCam mosaic CCD camera at the
3.6-m CFHT. Upon later inspection, S/2010 J 2 was also weakly visible
in the images from Palomar. Observations in 2010 October and November
and 2011 January allowed the orbits to be determined well enough to
confirm that they are indeed satellites and not just nearby asteroids,
allowing IAU designations to be granted in 2011 June. Further follow-
up observations have refined the orbits sufficiently for the
satellites' positions to be reliably be predicted several years into
the future.
During 2003 the CFHT observed the entire region around Jupiter in a
search for moons. Several faint objects were detected that were never
classified as satellites because they were not recovered in follow-up
observations. However, with well determined orbits of S/2010 J 1 and
2, it was possible to extrapolate backwards in time to 2003, and J 1
was indeed found in several images, although J 2 could not be located
in any of them. That is, however, not surprising, as J 2 is the
faintest Jupiter satellite observed to date, and ideal conditions are
required to see it, even with the CFHT. On the basis of their
brightnesses, the diameters of the moons can be estimated at about
3 km for J 1 and 2 km for J 2 . It is believed that nearly all moons
the size of J 1 or larger have been discovered, but there must be
dozens of undiscovered satellites in the 1-3-km class. J 1 is in an
orbit with an average distance (semi-major axis) from Jupiter of 23.45
million km and orbital period of 2.02 years, while J 2 has a
semi-major axis of 21.01 million km and an orbital period of 1.69
years. The irregular satellites of the giant planets are clustered in
'families' with similar orbits and colours. The families are believed
to have formed as a result of collisions of passing comets or
asteroids with former larger moons long ago. J 1 appears to belong to
the Carme group, and J 2 appears to belong to the Ananke group.
FEW BROWN DWARFS CLOSE TO HOME
NASA/Jet Propulsion Laboratory
The Wide-field Infrared Survey Explorer (WISE) was launched in 2009
and surveyed the entire sky in infrared light in 2010. One of the
mission's main scientific goals was to survey the sky for brown
dwarfs. Those small bodies start their lives like stars, but lack the
mass required to burn nuclear fuel. With time, they cool and fade,
making them difficult to find. WISE has better sensitivity than
previous infrared missions and has been able to pick up many brown
dwarfs, but there seem to be far fewer of them than some 'eperts' had
predicted. In 2011 August, the mission announced the discovery of the
coolest brown dwarfs observed yet, a new class of stars called Y
dwarfs. One of the Y dwarfs has a temperature below 25°C, about room
temperature, making it the coldest star-like body known. Since then,
the WISE team has found 200 brown dwarfs, including 13 Y dwarfs.
Determining the distances to the objects is a key factor in estimating
their population density in our neighbourhood. After measuring the
distances to several of the coldest ones, the scientists fell back on
estimates of the distances to all the others. They concluded that
there are about 33 brown dwarfs within 8 parsecs of Sun. There are
211 stars known within that distance -- about six stars to every brown
dwarf. The results are still preliminary: it is likely that WISE will
discover additional Y dwarfs, but not in vast numbers.
SMALL PLANETS CAN FORM EVEN AROUND METAL-DEFICIENT STARS
NASA
The formation of planets has been thought to occur mostly around stars
rich in heavy elements such as iron and silicon. Astronomers refer to
all chemical elements heavier than hydrogen and helium as metals.
They define metallicity as the metal content of a star. Stars with a
higher fraction of heavy elements than the Sun are considered
metal-rich.
Planets are created in discs of gas and dust around new stars. The
metallicity of a disc mirrors the metallicity of the star. Planets
like the Earth are composed almost entirely of elements such as iron,
oxygen, silicon and magnesium. Astronomers have hypothesized that
large quantities of heavy elements in the disc would lead to more
efficient planet formation. It has been noted that giant planets with
short orbital periods tend to be associated with metal-rich stars, but
new ground-based observations, combined with data collected by the
Kepler space telescope, show that small planets form around stars with
a wide range of heavy-element content. An international research team
studied the elemental composition of more than 150 stars having 226
planet candidates smaller than Neptune, and found that small planets
form around stars with a wide range of heavy-metal content, including
stars with only 25% of the Sun's metallicity.
BLACK HOLES 'CHANGE GEAR'
RAS
Black holes are extremely powerful and efficient engines that not only
swallow matter, but also return a lot of energy to the Universe in
exchange for the mass they consume. When black holes attract mass
they also trigger the release of intense X-ray radiation and power
strong jets. Black-hole jets -- lighthouse-like beams of material
ejected at close to the speed of light -- can have a major impact on
the evolution of their environment. For example, jets from the
super-massive black holes found at the centres of galaxies can blow
huge bubbles in clusters of galaxies, and heat the gas in them.
Another example of what black-hole jets can do is known as Hanny's
Voorwerp, a cloud of gas where stars started forming after it was hit
by the jet of a black hole in a neighbouring galaxy. Those phenomena
aroused interest in the way black holes produce and distribute energy.
In 2003 it became clear that there is a relationship between the X-ray
emission from a black hole and its jet outflow, which needs to be
explained if we want to understand how the black-hole engine works.
At first it seemed that the relationship was the same for all feeding
black holes, but counter-examples were soon found. They still showed
a connection between the energy released in the X-ray emission and
that put in the jet ejection, but the proportion differed from that in
the 'standard' black holes. As the number of such examples grew, it
started to appear that there were two groups of black-hole engines
working in slightly different ways.
Recently a team of astronomers found a black hole that seemed to
switch between the two regimes of X-ray/jet proportion, depending on
how its brightness changed. That suggested that black holes do not
necessarily come with two different engines, but that each black hole
can run in two different regimes. Then two more examples were found
of black holes that could 'change gear', suggesting that changing gear
might be a common property of black holes. The switch happens at a
similar X-ray luminosity for all three of the black holes. Those
discoveries provide new input to theoretical models that hope to
explain both the functioning of the black-hole engine itself and its
impact on the surrounding environment.
FIRST OBJECTS BURNED FURIOUSLY
ScienceDaily
The faint, lumpy glow given off by the very first objects in the
Universe may have been detected, with the best precision yet, by the
Spitzer space telescope. Those faint objects might be very massive
stars or voracious black holes. They are too far away to be seen
individually, but Spitzer has captured rather convincing evidence of
what appears to be the collective pattern of their infrared light.
The observations help to confirm that the first objects were numerous
in quantity and furiously burned cosmic fuel, and would have been
tremendously bright. Astronomers cannot yet directly rule out other,
more mundane, sources for that light, but it is becoming increasingly
likely that they are catching a glimpse of an ancient epoch.
Spitzer first caught hints of that remote pattern of light, known as
the cosmic infrared background, in 2005, and again with more precision
in 2007. Now, Spitzer is in the extended phase of its mission, during
which it performs more in-depth studies on specific patches of the
sky. Astronomers used Spitzer to look at two patches of sky for more
than 400 hours each. The team then carefully subtracted all the known
stars and galaxies in the images. Rather than being left with a
black, empty patch of sky, they found faint patterns of light with
several telltale characteristics of the cosmic infrared background.
The lumps in the observed pattern are consistent with the way the very
distant objects are thought to be clustered together. The Universe
formed 13.7 billion years ago in an, explosive Big Bang. With time,
it cooled, and after about 500 million years the first stars, galaxies
and black holes began to take shape. Astronomers say that Spitzer may
be seeing some of that 'first light'. It would have originated at
visible or even ultraviolet wavelengths and then, because of the
expansion of the Universe, stretched out to the longer, infrared
wavelengths observed by Spitzer. The new study improves on previous
observations by measuring that cosmic infrared background at angular
scales of up to 1° -- significantly larger than before.
PLAN APPROVED FOR BIGGEST TELESCOPE
ESO
ESO is to build the largest optical/infrared telescope in the world.
At its meeting in Garching earlier this month, the ESO Council
approved the European Extremely Large Telescope (E-ELT), subject to
confirmation by the authorities in four of the member countries. The
E-ELT will be a 39.3-m segmented-mirror telescope sited on Cerro
Armazones in northern Chile, close to the Paranal Observatory, and
will start operations early in the next decade. Spending on elements
of the project other than the initial civil works will not commence,
however, until the contributions pledged by the member states, as
agreed in funding principles approved by the Council in late 2011,
exceed 90% of the 1083-million-euro cost (at 2012 prices). Early
contracts for the project have already been placed. Shortly before
the Council meeting, a contract was signed to begin a detailed design
study for the very challenging adaptive mirror of the telescope. That
has one of the longest lead-times in the E-ELT programme, and an early
start was essential. Civil works that are expected to begin this year
include preparation of the access road to the summit of Cerro
Armazones and the levelling of the summit itself.
The year 2012 marks the 50th anniversary of the founding of the
European Southern Observatory. ESO is supported by 15 countries:
Austria, Belgium, Brazil, the Czech Republic, Denmark, France,
Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden,
Switzerland and the United Kingdom. It operates on three sites in
Chile -- La Silla, Paranal and (in partnership) Chajnantor.
Topic: Late June Astronomy Bulletin (Read 1294 times)