KEPLER DISCOVERS FIVE NEW EXOPLANETS
Science Daily
The Kepler space telescope, intended to find Earth-size planets in the
`habitable zones' of Sun-like stars, was launched in 2009 March. It
continuously and simultaneously observes more than 150,000 stars, and
has already measured hundreds of possible planet signatures that are
being analyzed. Kepler looks for the signatures of planets by
measuring dips in the brightness of stars. When planets cross in
front of, or transit, their stars, they periodically block part of the
starlight. The size of the planet can be derived from the size of the
dip, and the temperature can be estimated from the characteristics of
the star it orbits and the planet's orbital period.
Now Kepler has discovered its first five new exo-planets, which have
been named Kepler 4b, 5b, 6b, 7b and 8b. [That begs the question why
the numbers did not start at 1!] The five planets are all much larger
than the Earth. Known as 'hot Jupiters', they range in size from
similar to Neptune to larger than Jupiter. They have orbital periods
ranging from 3.3 to 4.9 days. Estimated temperatures range from 1200
to 1600 degrees C. NOT very Earth-like! As the mission proceeds and
Kepler has time to gather more data, smaller and cooler planets should
be found. While many of the signatures detected so far are likely to
be caused by things other than planets, such as small stars orbiting
larger stars, ground-based observatories have confirmed the existence
of the five exo-planets. Kepler is expected to continue operations
until at least 2012 November.
INTERGALACTIC GAS STREAM LONGER THAN THOUGHT
NRAO
A stream of gas flowing from the Magellanic Clouds around our own
Milky Way is much longer and older than previously thought. The
Magellanic Clouds are the Milky Way's two nearest neighbour galaxies,
about 150,000 to 200,000 light-years away, and are deep in the
Southern Hemisphere; they are much smaller than our Galaxy and may
have been distorted by its gravity.
The first evidence of the gas stream, named the Magellanic Stream, was
discovered more than 30 years ago, and subsequent observations added
tantalizing suggestions that there was more. However, until now it
was not clear that all the gas was part of the same system. Now,
astronomers have used the Green Bank radio telescope to fill important
gaps in the picture of gas streaming outward from the Magellanic
Clouds. They combined their data with those from earlier studies with
other radio telescopes, including those at Arecibo in Puerto Rico,
Parkes in Australia, and Westerbork in the Netherlands. The result
shows that the stream is more than 40% longer than was previously
known with certainty.
One consequence of the added length of the gas stream is that it must
be older. Its age is now estimated at 2.5 billion years. The revised
size and age of the Magellanic Stream also provides a new possible
explanation for how the flow got started. The new age of the stream
puts its beginning near a time when the two Magellanic Clouds may have
passed close to each other, triggering massive bursts of star-
formation. The strong stellar winds and supernova explosions from
that burst of star-formation might have blown out the gas and started
it flowing toward the Milky Way. Earlier hypotheses for the stream's
cause required the Magellanic Clouds to pass much closer to the Milky
Way, but recent orbital simulations have cast doubt on such
mechanisms.
LESS ORDINARY MATTER THAN OTHERS SUPPOSED
University of Maryland
An international team of scientists has found that individual galactic
objects have less ordinary matter, relative to dark matter, than does
the Universe as a whole. Some scientists believe all ordinary matter,
the protons and neutrons that make up people, planets, stars, and all
that we can see, is a mere fraction (some say 17%) of the total
matter in the Universe. The protons & neutrons of ordinary matter are
referred to as baryons by devotees of particle physics and cosmology.
The remaining 83% is attributed to mysterious 'dark matter', the
existence of which is inferred largely from its gravitational pull on
visible matter. Dark matter is presumed to be some new form of
non-baryonic particle -- the stuff scientists hope the Large Hadron
Collider at CERN will create in high-energy collisions between
protons. The team posed the question of whether the 'universal' ratio
of baryonic matter to dark matter holds on the scales of individual
structures like galaxies. One might expect galaxies and clusters of
galaxies to be made of the same stuff as the Universe as a whole, so
if you were naive enough you might think that if you made an
accounting of the normal matter in each object, and its total mass,
you ought to get the same 17%.
However, the team suggests that individual objects have less ordinary
matter, relative to dark matter, than they would expect from the
cosmic mix, sometimes a lot less. Just how much less depends
systematically on scale, according to the researchers. The smaller an
object, the further its ratio of ordinary matter to dark matter is
from the cosmic mix. The research indicates that the largest bound
structures, rich clusters of galaxies, have 14% of ordinary baryonic
matter, close to the 17% they expect. In smaller objects --
individual galaxies and satellite galaxies -- the normal matter
content gets steadily less. In the smallest dwarf satellite galaxies,
the content of normal matter is only about 1% of what they think it
should be. The variation of the baryon content is very systematic
with scale, so they say. The smaller the galaxy, the smaller is its
ratio of normal matter to dark matter. To put it another way, the
smallest galaxies are very dark-matter-dominated.
ASTRONOMERS TRY TO EXPLAIN HUBBLE SEQUENCE
RAS
Not for the first time, some astronomers have been trying to explain
the diversity of galaxy shapes. They tracked the evolution of
galaxies over the thirteen billion years from the early Universe to
the present day. Galaxies make up most of the visible component of
the cosmos. The smallest have a few million and the largest as many
as a million million stars. American astronomer Edwin Hubble
developed in the 1930s a taxonomy for galaxies that has since become
known as the 'Hubble Sequence'. There are three basic shapes: spiral,
where arms of material wind out in a disc from a small central bulge,
barred spirals, where the arms wind out in a disc from a larger bar of
material, and elliptical, where the galaxy's stars are distributed
more evenly in a bulge without arms or disc. For comparison, the
galaxy we live in has between two and four hundred thousand million
stars and is classified as a barred spiral.
Explaining the Hubble Sequence is complex. The different types
clearly result from different evolutionary paths but at least until
now a detailed explanation has eluded scientists. The team combined
data from the infrared Two-Micron All-Sky Survey (2MASS) with their
computer model to reproduce the evolutionary history of the Universe.
To their surprise, their computations reproduced not only the
different galaxy shapes but also their relative numbers. The
astronomers' model is underpinned by and endorses the 'Lambda Cold
Dark Matter' model of the Universe. Here 'Lambda' is the highly
mysterious 'dark energy' component that some astronomers now like to
believe makes up about 72% of the cosmos, with cold dark matter
making up another 23%. [It's not our fault if even the assertions,
let alone the numbers, in different items in these Bulletins don't
chime with one another!] Galaxies are thought to be embedded in very
large haloes of dark matter, and researchers believe that those may be
crucial to their evolution. Their model suggests that the number of
mergers between the haloes and their galaxies drives the final outcome
-- elliptical galaxies result from multiple mergers whereas disc
galaxies have seen none at all. Our Milky Way galaxy's barred-spiral
shape suggests that it has had a complex history, with only a few
minor collisions and at least one episode where the inner disc
collapsed to form the large central bar. The goal now is to compare
the model predictions with observations of more distant galaxies.
HST OBSERVES VERY DISTANT GALAXIES
STSI
The Hubble space telescope has observed galaxies even more distant
than before and uncovered a primordial population of compact and
ultra-blue galaxies that have never been seen before. The data come
from images taken on the 'Ultra-deep Field' last August with the new
'Wide-Field Camera 3', which are deep enough at near-infrared
wavelengths to show galaxies at redshifts from z=7 to beyond z=8.
The clear detection of galaxies between z=7 and z=8.5 corresponds to
look-back times of approximately 12.9 to 13.1 billion years ago. The
images have been discussed by astronomers who say that the faintest
galaxies show signs of linkage to their origins from the first stars.
They are so blue that they must be extremely deficient in heavy
elements, thus representing a population that has nearly primordial
characteristics.
The existence of such galaxies pushes back the time when galaxies
began to form to before 500-600 million years after the Big Bang.
The deep observations also demonstrate the progressive build-up of
galaxies and provide further support for the hierarchical model of
galaxy assembly whereby small objects accrete mass, or merge, to form
bigger objects by a process of collision and agglomeration. The
galaxies are as small as 1/20th the Milky Way's diameter and are
crucial to understanding the evolutionary link between the birth of
the first stars and the formation of the first galaxies. Astronomers
also combined the new Hubble data with observations from the Spitzer
space telescope to estimate the ages and masses of the primordial
galaxies. Their masses seem to be only 1% of that of the Milky Way
and show that the galaxies, seen at 700 million years after the Big
Bang, must have started forming stars hundreds of millions of years
earlier, pushing back the time of the earliest star-formation in the
Universe.
Topic: Mid January Astronomy Bulletin (Read 990 times)