SCIENTISTS MONITOR COMET BREAK-UP
NASA
Amateur and professional astronomers alike have been following Comet
168P/Hergenrother, which has been traversing the constellations of
Andromeda and Lacerta. Over the past several weeks it has produced a
series of outbursts of dusty material. Now the comet's nucleus has
taken another step in its fragmentation: it has separated into at
least four distinct pieces, resulting in a large increase in dust
material in its coma. With more material to reflect the Sun's rays,
the coma has brightened considerably. The fragments are considerably
fainter than the nucleus. The fragmentation event was initially
detected on October 26 by observers using the Faulkes Telescope North
on Haleakala, Hawaii.
MARS ROVER FINDS SOIL SIMILAR TO HAWAII'S
NASA
The Curiosity rover has made its first analysis of soil on Mars.
A preliminary operation served to 'cleanse the palate' of the rover's
sample-collection systems, which may have brought contaminants from
the Earth. With that out of the way, Curiosity used a technique
called X-ray diffraction, in which X-rays are shot into samples that
include crystalline materials. The precise ways in which the X-rays
scatter off the crystals gives clear information as to their chemical
makeup, and hints as to their structure. The 'CheMin' experiment
first sieves a soil sample, separating out the components smaller than
150 microns. It then gives the sifted soil a shake while firing
X-rays at it. The sample was found to contain the minerals feldspar,
olivine and pyroxene, such as might be found in weathered basaltic
materials of volcanic origin, like those in Hawaii. So far, the
materials that Curiosity has analyzed are consistent with initial
ideas of the deposits in Gale Crater (the large equatorial crater
where it landed in August), recording a transition through time from a
wet to a dry environment. In the weeks since its arrival on Mars, the
rover has already examined some larger rocks. The ancient rocks, such
as the conglomerates, suggest flowing water, while the minerals in the
younger soil are consistent with limited interaction with water. The
next step is to deliver soil samples into another experiment within
the rover ('Sam', or 'Sample Analysis at Mars') instrument, which will
look for the presence of carbon-containing molecules.
DOUBTED EXO-PLANET MAY EXIST AFTER ALL
NASA/Goddard Space Flight Center.
A second look at data from the Hubble telescope is reviving the claim
(reported in ENB 256, 2008 November 30) that the 'nearby' star
Fomalhaut hosts a massive planet. The study suggests that the planet,
named Fomalhaut b, is completely shrouded by dust. Fomalhaut is the
brightest star in the constellation Piscis Austrinus and lies 25
light-years away. In 2008, Hubble astronomers announced the
exo-planet as the first one ever directly imaged in visible light
around another star. The object was imaged just inside a ring of
debris surrounding but offset from the host star. The planet's
location and mass -- no more than three times Jupiter's -- seemed just
right for its gravity to explain the ring's appearance. Recent
studies have claimed that that planetary interpretation is incorrect.
On the basis of the object's apparent motion and the lack of an
infrared detection by the Spitzer space telescope, the studies have
suggested that the object is a short-lived dust cloud unrelated to any
planet. A new analysis, however, brings the planet conclusion back to
life. Although the results seriously challenge the original discovery
paper, they do so in a way that actually makes the object's
interpretation much cleaner and leaves intact the core conclusion,
that Fomalhaut b is indeed a massive planet. The discovery study
reported that Fomalhaut b's brightness varied by about a factor of two
and cited that as evidence that the planet was accreting gas. Follow-
up studies then interpreted the variability as evidence that the
object actually was a transient dust cloud instead. In the new study,
astronomers re-analyzed Hubble observations of the star from 2004 and
2006. They easily recovered the planet in observations taken in red
light, and made a new detection in violet light. In contrast to the
earlier research, the team found that the planet remained at constant
brightness.
The team attempted to detect Fomalhaut b in the infrared with the
Subaru telescope in Hawaii, but was unable to do so. The non-
detections with Subaru and Spitzer imply that Fomalhaut b must be less
than twice the size of Jupiter. Another contentious issue has been
the object's orbit. If Fomalhaut b is responsible for the ring's
offset and sharp interior edge, then it must follow an orbit aligned
with the ring and must now be moving at its slowest speed. The speed
implied by the original study appeared to be too fast. Additionally,
some researchers argued that Fomalhaut b follows a tilted orbit that
passes through the ring plane. Using the Hubble data, the team
established that Fomalhaut b is moving with a speed and direction
consistent with the original idea that the planet's gravity is
modifying the ring. The team also addressed studies that interpret
Fomalhaut b as a compact dust cloud not gravitationally bound to a
planet. Near Fomalhaut's ring, orbital dynamics would spread out or
completely dissipate such a cloud in as little as 60,000 years. The
dust grains experience additional forces, which operate on much faster
time-scales, as they interact with the star's light. Given what we
know about the behaviour of dust and the environment where the planet
is located, scientists think that they are seeing a planetary object
that is completely embedded in dust rather than a free-floating dust
cloud. Because astronomers detect Fomalhaut b by the light of
surrounding dust and not by light or heat emitted by its atmosphere,
it no longer ranks as a 'directly imaged exo-planet'. But because it
has the right mass and is in the right place to affect the ring, it
could perhaps be allowed the weasel-worded claim to be a 'planet
identified from direct imaging'!
STREAM OF STARS BEING INGESTED BY MILKY WAY
Yale University
Researchers have discovered a band, or stream, of stars that they
believe to be the remnant of an ancient star cluster slowly being
ingested by the Milky Way galaxy. It was found by searching a region
recently surveyed by the Sloan Digital Sky Survey III (SDSS-III), an
international collaboration that is mapping the sky through wide-field
photometry. Galaxies are believed to form hierarchically through the
merger of smaller galaxies and still smaller star clusters, which are
disrupted by the gravitational force of the principal galaxy. That
process may be the primary way galaxies such as the Milky Way grow in
mass. The Milky Way is constantly accreting small galaxies and star
clusters, because the more powerful gravity of our Milky Way pulls
them apart and their stars then become part of the Milky Way itself.
Researchers have previously found evidence of the Milky Way
assimilating dwarf galaxies, but it is thought that the newly found
stellar stream, called the Triangulum stream, is the remnant of a star
cluster rather than of a larger galaxy, because the stream is very
narrow.
FIRST DIRECT DETECTION OF DARK GALAXIES
ScienceDaily
It has been suggested that most of such people as think about galaxies
at all picture them as huge islands of stars, gas and dust that
populate the Universe in visual splendour. Theory, however, has
allowed that there could be other types of galaxies that are devoid of
stars and are made predominantly of dense gas. Such 'dark' galaxies
would be unseen against the black backdrop of space. Some models have
proposed that dark galaxies were common in the early Universe when
galaxies had more difficulty forming stars -- partly because their
density of gas was not sufficient to form stars -- and only later did
they begin to ignite stars, becoming like the galaxies we see today.
According to a current theory of galaxy formation, big galaxies form
from the merger of smaller ones. Dark galaxies bring to big galaxies
a lot of gas, which then accelerates star formation in the bigger
galaxies. Now, an international team of astronomers has actually
detected several dark galaxies by observing the fluorescent glow of
their hydrogen gas, illuminated by the ultraviolet light of 'nearby'
quasars.
FERMI MEASURES COSMIC 'F0G' PRODUCED BY ANCIENT STARLIGHT
NASA
Astronomers using data from the Fermi gamma-ray space telescope have
made a measurement that enables them to estimate the total amount of
light from all of the stars that have ever shone, accomplishing a
primary mission goal. The optical and ultraviolet light from stars
continues to travel throughout the Universe even after the stars
themselves have ceased to shine, so it forms a sort of fossil
radiation field that can be explored by observations of gamma rays
from distant sources. Gamma rays are the most energetic form of
light. Since Fermi's launch in 2008, it has observed the entire sky
in high-energy gamma rays every three hours, creating a detailed map
of the Universe at those energies. The total sum of starlight in the
cosmos is known to astronomers as the extragalactic background light
(EBL). To gamma rays, the EBL functions as a kind of cosmic fog.
Astronomers investigated the EBL by studying gamma rays from 150
blazars, or galaxies powered by black holes, that were strongly
detected at energies greater than 3 billion electron volts (3 GeV), or
more than a billion times the energy of visible light. With more than
a thousand detected so far, blazars are the most common sources
detected by Fermi, but gamma rays at those energies are few and far
between, which is why it took four years of data to make the analysis.
As matter falls toward a galaxy's central super-massive black hole,
some of it is somehow accelerated outward at almost the speed of light
in jets pointed in opposite directions. When one of the jets happens
to be aimed in the direction of the Earth, the galaxy appears
especially bright and is classified as a blazar. During their
journey, which may be across billions of light-years, the gamma rays
pass through a sort of fog of visible and ultraviolet light emitted by
stars throughout the history of the Universe. Occasionally, a gamma
ray collides with starlight and transforms into a pair of particles --
an electron and its antimatter counterpart, a positron. Once that
occurs, the gamma-ray light is lost. In effect, the process dampens
the gamma-ray signal in much the same way as fog dims a distant light
source.
From studies of nearby blazars, scientists have determined how many
gamma rays should be emitted at different energies. More distant
blazars show fewer gamma rays at higher energies -- especially above
25 GeV -- thanks to absorption by the cosmic fog. Thus the farthest
blazars are missing most of their highest-energy gamma rays. The
researchers then determined the average gamma-ray attenuation across
three distance ranges between 9.6 billion years ago and today. From
that measurement, the scientists were able to estimate the fog's
thickness. To account for the observations, the average stellar
density in the cosmos has to be about 1.4 stars per 100 billion cubic
light-years, which implies that the average distance between stars in
the Universe is about 4000 light-years.
Topic: Mid November Astronomy Bulletin (Read 1392 times)