SOME OF THE EARTH'S WATER IS PROBABLY OLDER THAN THE SUN
Carnegie Institution
Water was crucial to the rise of life on Earth and is also important
to evaluating the possibility of life on other planets. Identifying
the original source of the Earth's water could help us to understand
how life-fostering environments come into being and how likely they
are to be found elsewhere. New research has found that much of our
Solar System's water may have originated as ices that formed in
interstellar space. Water is found throughout the Solar System, not
just on Earth, but on icy comets and moons, and in the shadowed basins
of Mercury. Water has been found included in mineral samples from
meteorites, the Moon, and Mars. Comets and asteroids in particular,
being primitive objects, provide a natural 'time capsule' of the
conditions during the early days of the Solar System. Their ices can
tell scientists about the ice that encircled the Sun after its birth,
the origin of which was an unanswered question until now. In its
youth, the Sun was surrounded by a protoplanetary disc, the so-called
solar nebula, from which the planets were born. But it was not clear
to researchers whether the ice in that disc originated from the
interstellar molecular cloud from which the Sun was formed, or whether
that interstellar water had been destroyed and was re-formed by the
chemical reactions taking place in the solar nebula.
If water in the early Solar System were primarily inherited as ice
from interstellar space, then it is likely that similar ices, along
with the pre-biotic organic matter that they contain, are abundant in
most or all proto-planetary discs around forming stars. But if the
early Solar System's water were largely the result of local chemical
processing during the Sun's birth, then it is possible that the
abundance of water varies considerably among forming planetary
systems, which would obviously have implications for the potential for
the emergence of life elsewhere. In studying the history of the Solar
System's ices, the team focused on hydrogen and its heavier isotope
deuterium. Isotopes are atoms of the same element whose nuclei have
the same number of protons but different numbers of neutrons. The
difference in masses between isotopes results in subtle differences in
their chemical behaviour, so the ratio of deuterium to ordinary
hydrogen in water molecules can tell scientists something about the
conditions under which the molecules formed. For example, inter-
stellar water-ice has a high ratio of deuterium to hydrogen because of
the very low temperatures at which it forms. Until now, it was
unknown how much of the deuterium enrichment was removed by chemical
processing during the Sun's birth, or how much deuterium-rich
water-ice the newborn Solar System was capable of producing on its
own. So the team created models that simulated a proto-planetary disc
in which all the deuterium from space ice had already been eliminated
by chemical processing, and the system had to start again 'from
scratch' at producing ice with deuterium in it during a million-year
interval. They did that in order to see if the system could reach the
ratios of deuterium to hydrogen that are found in meteorite samples,
but it could not do so, which told them that at least some of the
water in the Solar System has an origin in interstellar space and
pre-dates the birth of the Sun. The findings show that a significant
fraction of the Solar System's water is older than the Sun, which
indicates that interstellar ices should probably be found in all young
planetary systems.
219 MILLION STARS IN MOST DETAILED CATALOGUE OF VISIBLE MILKY WAY
RAS
A new catalogue of the northern part of our Galaxy includes no fewer
than 219 million stars. It represents the fruit of a ten-year
programme with the Isaac Newton Telescope (INT) on La Palma. The
Milky Way is the disc of our own Galaxy, and contains the majority of
the stars in the Galaxy, including the Sun, and the densest concen-
trations of dust and gas. The INT programme charted all the stars
brighter than 20th magnitude in the zone within 5 degrees of the
Galactic equator. From the catalogue, scientists have made a map of
the disc of the Galaxy that shows how the density of stars varies.
The catalogue, IPHAS DR2 (the second release from the survey
programme, 'INT Photometric H-alpha Survey of the Northern Galactic
Plane' or 'IPHAS'), illustrates modern astronomy's exploitation of
'big data': information on each of the 219 million detected objects is
summarised in 99 attributes. There are magnitudes measured through
two broad-band filters in the red part of the visible spectrum, and in
a narrow band centred on H-alpha. The H-alpha band also maps the
emission nebulae that are so common in the plane of the Milky Way.
SMALLEST KNOWN GALAXY WITH SUPERMASSIVE BLACK HOLE
University of Utah
Astronomers have discovered that an ultra-compact dwarf galaxy called
M60-UCD1 harbours a super-massive black hole -- the smallest galaxy
known to contain one. It is also one of the most black-hole-dominated
galaxies known. The team used observations from the Gemini North 8-m
telescope in Hawaii and the Hubble telescope, and discovered that
M60-UCD1 has a black hole with a mass of 21 million suns. The only
way that such a massive hole could arise in such a small galaxy seems
to be that the galaxy is the stripped remnant of an originally larger
one that was torn apart in a galactic collision. Super-massive black
holes, having masses of at least 1 million Suns, are thought to exist
at the centres of many galaxies. The one at the centre of our own
Galaxy has a mass of about 4 million Suns, but it is less than 0.01%
of the Galaxy's total mass; the one at the centre of M60-UCD1 is five
times more massive than the Milky Way's, and is 15% of the small
galaxy's total mass of about 140 million Suns.
Some scientists are reported to believe that M60-UCD1 once was a big
galaxy with perhaps 10 billion [U.S. billion, = 1000 million] stars in
it, but then it passed very close to the centre of the even larger
galaxy M 60, and in that process all the stars and dark matter in the
outer parts were torn away and became part of M 60, which is among the
largest galaxies in what some astronomers refer to as the 'local
universe'. M 60 appears also to be pulling in another galaxy, named
NGC 4647; M 60 is about 25 times the mass of NGC 4647. M60-UCD1 is
roughly 54 million light-years away from us, but 'only' 22,000 light-
years from the centre of M 60. Astronomers have debated whether such
dwarf galaxies are the nuclei of larger galaxies whose outer parts
were stripped away during collisions with other galaxies, or whether
they formed like globular clusters -- groups of perhaps 100,000 stars,
all born together. There are about 200 globular clusters in our Milky
Way, but some galaxies have thousands.
DISTANT GALAXY CONTAINS 3 CLOSELY ORBITING BLACK HOLES
Science Daily
A team of scientists has discovered a trio of super-massive black
holes, closely orbiting the centre of a distant galaxy more than four
billion light-years away. It is the tightest trio of black holes
known -- with two of them orbiting one another like binary stars. The
new discovery may help astronomers in their search for gravitational
waves, a phenomenon predicted by Einstein. The black holes are at the
very extreme of Einstein's theory of General Relativity. Some
scientists are said to believe that gravitational waves originate
among merging black holes, and the current study of the tightly-packed
black-hole trio may help or hinder that theory. The idea that we
might be able to find more potential sources of gravitational waves is
attractive, as knowing where such signals might originate could help
us to try to detect those 'ripples' in space-time as they warp the
Universe. Before we get too excited, however, we must notice that
just recently other observers have cast doubt on even the reality of
the announced trio of black holes.
MASSIVE GALAXIES GROW BY ABSORBING SMALLER NEIGHBOURS
RAS
Massive galaxies seem mostly to have stopped making their own stars
and are instead absorbing nearby galaxies. Australian astronomers
looked at more than 22,000 galaxies and found that while smaller
galaxies are very efficient at creating stars from gas, the most
massive galaxies are much less efficient, producing hardly any new
stars themselves, and instead grow by eating other galaxies. The
researchers said that our own Milky Way is at a tipping point and is
expected to grow mainly by incorporating smaller galaxies, rather than
by collecting gas. The Milky Way has not merged with another large
galaxy for a long time, but we can still see remnants of all the old
galaxies that it has cannibalised. It is likely to absorb two nearby
dwarf galaxies, the Large and Small Magellanic Clouds, in about four
billion years, and is eventually likely to merge with the 'nearby'
Andromeda Galaxy. Ultimately, gravity is expected to cause all the
galaxies in bound groups and clusters to merge into a few super-giant
galaxies, although it will be many billions of years before that
happens.
INTERSTELLAR MOLECULES FOUND AT GALACTIC CENTRE
Max-Planck-Gesellschaft
The search for molecules in interstellar space began in the 1960s, and
about 180 different molecular species have been discovered so far.
Now a carbon-bearing molecule with a branched structure has for the
first time been detected. The molecule, iso-propyl cyanide
(i-C3H7CN), was discovered in a gas cloud called Sagittarius B2 (Sgr B2),
a region of star formation that is a favourite spot for molecule-hunting
astronomers, about 27,000 light-years away and close to the centre of
our Galaxy. The branched structure of the carbon atoms within the
iso-propyl cyanide molecule is unlike the straight-chain carbon backbone
of other molecules that have been detected so far, including its sister
molecule, normal propyl cyanide (n-C3H7CN). It is not just the
structure of the molecule that is a surprise -- it is also plentiful, at almost
half the abundance of its straight-chain sister molecule, which the team
had already detected with the single-dish radio telescope of the Institut
de Radioastronomie Millimetrique (IRAM) a few years ago. This time it
used the Atacama Large Mm/sub-mm Array (ALMA), in Chile, to
investigate anew the molecular content of Sgr B2, which is rich in
emission from complex interstellar molecules. As many as 50 individual
features for i-propyl cyanide and even 120 for n-propyl cyanide were
identified in the ALMA spectrum of Sgr B2. The two molecules, each
consisting of 12 atoms, are also the joint-largest molecules yet detected
in any star-forming region. The team constructed computational models
that simulate the chemistry of formation of the molecules detected in
Sgr B2. In common with many other complex molecules, both forms of
propyl cyanide were found to be efficiently formed on the surfaces of
interstellar dust grains. But the models indicate that for molecules
large enough to produce branched-chain structure, those may be the
prevalent forms. Any detection of the next member of the alkyl
cyanide series, n-butyl cyanide (n-C4H9CN), and its three branched
isomers would allow scientists to test that idea. Amino acids
identified in meteorites have a composition that suggests that they
originate in the interstellar medium. Although no interstellar amino
acids have yet been found, interstellar chemistry may be responsible
for the production of a wide range of important complex molecules that
eventually find their way to planetary surfaces.
ROSETTA COMET LANDING DATE
BBC
The date has been fixed for ESA's attempt to land on a comet:
Wednesday November 12. The date is actually a day later than the one
that had been discussed in provisional planning in recent months. It
will see the Rosetta satellite, which is currently orbiting the comet
known as 67P, drop a small robot from a height of 20km. If all goes
well, the lander will free-fall towards the comet, making contact with
the surface somewhere in a 1km-wide zone at roughly 15:35 GMT.
Because the event will be taking place so far away, radio signals will
take 28 minutes and 20 seconds to arrive here, so confirmation of
success or failure will not come until just after 16:00 GMT.
The chosen landing site is on the 'head' of the rubber-duck-shaped
comet and is currently referred to simply as 'J', the designation it
was given in a list of possible destinations in the selection process.
It is far from ideal: it contains some cliffs, but is the flattest,
most boulder-free location the mission team could find in its survey
of the comet. Mapping of J and a back-up site known as C is ongoing.
Rosetta has recently manoeuvred into an orbit just 20km from 67P,
enabling its camera system to see details that are less than a metre
across. For landing, such information has only limited utility,
however, as the automated touchdown can only be targeted to a
precision of hundreds of metres, and such an error is larger than any
of the apparently smooth areas in the J zone. The whole separation,
descent and landing (SDL) procedure is expected to take seven hours.
Philae will take a picture of Rosetta as it leaves its 'parent'. It
will also point a camera downwards so that we can see the surface as
it approaches -- not that that information can change anything, as
Philae has no thrusters to control or alter its descent trajectory.
It will land where it will land. But the images will help controllers
determine where the robot ended up after the event. If Philae gets
down successfully into a stable, operable configuration, it will fire
harpoons and deploy screws to try to hang on to the surface, since the
gravitational force of such a small body as the comet is tiny.
Already the main satellite has returned some astonishing pictures of
Comet 67P and the close-quarters observations it will conduct over the
next year will be very interesting..
Topic: Mid October Astronomy Bulletin (Read 1759 times)