TROJAN ASTEROID FOUND NEAR NEPTUNE
Subaru Telescope facility, Hawaii
Astronomers using the 8.2-m Subaru Telescope in Hawaii have discovered
the first Neptune Trojan asteroid, 2008 LC18, to be found near
Neptune's L5 Lagrangian point L5. Lagrangian points are five places
in space where the gravitational forces from two bodies of very
unequal mass, such as the Sun and a planet, are in balance such that
small bodies like asteroids can remain more or less fixed with respect
to the planet. The Lagrangian points L1, L2, and L3, which are
points along the direct line drawn through the two main bodies, are
unstable, so a slight displacement of an object there may result in
its permanent departure. The other points, L4 and L5, 60° ahead of
and behind the planet, are stable, so dust grains and other objects
remain in the vicinity and tend to collect there. Trojans share their
planet's orbit, but they do not collide with the planet because they
stay safely near the Lagrangian point ahead of or behind it. Neptune
was already known to be accompanied by six Trojan asteroids, but they
are all near the L4 point. It is more difficult to discover them near
L5, because that point is currently in Sagittarius, in a very rich
Milky-Way star field nearly in the line of sight to the Galactic
Centre. It is estimated that the 'new' Neptune Trojan has a diameter
of about 100 km.
RICHEST PLANETARY SYSTEM DISCOVERED
ESO
Astronomers have discovered a planetary system containing at least
five planets. They used the HARPS spectrograph, attached to ESO's
3.6-m telescope at La Silla, Chile, for a six-year study of the
Sun-like star HD 10180, located about 40 parsecs away in the southern
constellation Hydrus. From the 190 individual HARPS measurements, the
astronomers detected the tiny back and forth motions of the star
caused by the complex gravitational attractions from five or more
planets. The five strongest signals correspond to planets with
Neptune-like masses -- between 13 and 25 Earth masses -- which orbit
the star with periods ranging from about 6 to 600 days. They are
between 0.06 and 1.4 AU (Astronomical Units or Earth--Sun distances)
from their central star. There may be other planets present in the
system, but the evidence is inconclusive.
The newly discovered system of planets around HD 10180 differs from
the Solar System inasmuch as it has five Neptune-like planets all
lying within a distance equivalent to the orbit of Mars, but no
Jupiter-like giant. All the planets seem to have almost circular
orbits. So far, astronomers know of fifteen systems with at least
three planets. Using the new discovery as well as data for other
planetary systems, the astronomers found an equivalent of the
Titius-Bode law that exists in our Solar System: the distances of the
planets from their star seem to follow a regular pattern. Another
result found by astronomers studying such systems is that massive
planetary systems are found around relatively massive and metal-rich
stars, while the four lowest-mass systems belong to lower-mass and
metal-poor stars. Theoreticians have tried to develop models that
mimic that property.
'CITIZEN SCIENTISTS' DISCOVER NEW PULSAR
University of Wisconsin
Einstein@Home, based at the University of Wisconsin at Milwaukee and
at the Max-Planck-Institute in Germany, is a project that enlists the
aid of 250,000 volunteers from 192 countries, who donate time from
their home and office computers to search for signals from radio
pulsars in observations from Arecibo, the world's largest and most
sensitive radio telescope. More than a year after the project
started, the first deep-space discovery has been made by it, when
three lay people -- a German and an American couple -- have discovered
a new radio pulsar. The object, PSR J2007+2722, is a neutron star
that rotates 41 times per second. It is in the Milky Way, about 5000
parsecs away in the constellation Vulpecula. Unlike many pulsars that
spin as quickly and steadily, PSR J2007+2722 sits alone in space, and
has no orbiting companion star. Astronomers think it may be a
'recycled' pulsar that has lost its companion, but they can't rule
out that it may be a young pulsar born with a lower-than-usual
magnetic field.
GAMMA-RAY NOVA DISCOVERED
Space.com
A nova is a thermonuclear explosion on the surface of a white-dwarf
star. It is fuelled by hydrogen transferred from a companion star.
Novae emit X-rays, but until now they have not been known to emit
gamma-rays, a still more energetic form of radiation. Now researchers
using the orbiting Fermi telescope have discovered gamma-rays from a
nova called V407 Cygni, some 2700 parsecs away. It is a binary system
which consists of a white dwarf and a pulsating red giant. The
gamma-rays came after a nova explosion in the system, spotted by
Japanese amateur astronomers in March, which at its peak was just
below the level of naked-eye visibility, brighter than at any other
time in the 70-odd years that the system has been under observation.
The researchers suggest that the gamma-rays were generated when the
blast waves from the nova collided with the dense wind from the red
giant.
In most novae, the white dwarf's companion is a normal main-sequence
star, whose stellar wind is light compared with that of the red giant
in V407 Cygni, so there is far less material with which to generate
gamma-rays. Very few binary systems combine the kind of white-dwarf
stars that give rise to novae with red giant companions, so gamma-ray
novae are probably quite rare.
ACTIVE STAR FORMATION IN DISTANT CLUSTER OF GALAXIES
Texas A&M University
Images obtained with the Spitzer space telescope of an early, distant,
cluster of galaxies have revealed that a significant fraction of those
ancient galaxies were still actively forming stars. The images looked
back in time nearly 10 billion years at a high-redshift cluster known
as CLG J02182-05102. The cluster is 'modern' in its appearance and
size despite being observed 'only' 4 billion years after the Big Bang,
and is seen to be producing hundreds to thousands of new stars every
year, a higher birth-rate than that in present 'nearby' galaxies.
What is particularly striking is the fact that the stellar birth rate
is higher in the cluster's centre than at its edges, the exact
opposite of what happens in our part of the Universe where the cores
of galaxy clusters are known to be galactic graveyards full of massive
elliptical galaxies composed of old stars. A well-established
hallmark of galaxy evolution in action is how the fraction of
star-forming galaxies decreases with increasing galaxy density. In
other words, there are more star-forming galaxies in the field than in
the crowded cores of galaxy clusters. However, in the old cluster
there are many galaxies with star-formation rates comparable with
those of their cousins in the lower-density field environment.
Topic: Late August Astronomy Bulletin (Read 756 times)