ASTEROID-HUNTING SPACECRAFT SUCCESS
NASA
The Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE)
mission has released its third year of survey data, with the space-
craft discovering 97 previously unknown celestial objects in the
last year. Of those, 28 were near-Earth objects, 64 were main-belt
asteroids, and five were comets. The spacecraft has now characterized
a total of 693 near-Earth objects since the mission was re-started in
2013 December. Of those, 114 are new. NEOWISE is not only discovering
previously uncharted asteroids and comets, but it is providing
excellent data on many of those already known. Near-Earth objects
(NEOs) are comets and asteroids that have been nudged by the
gravitational attraction of the planets in the Solar System into
orbits that cause them to enter the Earth's neighbourhood. Ten of the
objects discovered by NEOWISE in the past year have been classified as
potentially hazardous asteroids, on the basis of their sizes and orbits.
More than 2.6 million infrared images of the sky were collected in the
third year of operations by NEOWISE. Those data are combined with the
first two years' NEOWISE data into a single archive that contains
approximately 7.7 million sets of images and a data base of more than
57.7 (US-)billion source detections extracted from those images. The
NEOWISE images also contain glimpses of rare objects, like comet
C/2010 L5 WISE. A new technique of modelling comet behaviour, called
tail-fitting, showed that that particular comet experienced a brief
outburst as it swept through the inner Solar System. The tail-
fitting technique identifies the size and quantity of dust particles
in the vicinity of the comet, and when they were ejected from the
comet's nucleus, revealing the history of the comet's activity. With
tail-fitting, future all-sky surveys may be able to find and collect
data on more cometary-outburst activity when it happens.
Originally called the Wide-field Infrared Survey Explorer (WISE), the
spacecraft was launched in 2009 December. It was placed in hiber-
nation in 2011 after its primary astrophysical mission was completed.
In 2013 September it was re-activated, re-named NEOWISE and assigned
a new mission: to assist NASA's efforts to identify the population of
potentially hazardous near-Earth objects. NEOWISE is also character-
izing more distant populations of asteroids and comets to provide
information about their sizes and compositions.
ENCELADUS MAY HAVE TIPPED OVER
NASA
Saturn's icy, ocean-bearing moon Enceladus may have tipped over in the
distant past, according to recent research from the Cassini mission.
Researchers found evidence that the moon's spin axis -- the line
through the north and south poles -- has re-oriented, possibly owing
to a collision with a smaller body, such as an asteroid. Examining
the moon's features, the team showed that Enceladus appears to have
tipped away from its original axis by about 55 degrees -- more than
halfway toward rolling completely onto its side. Cassini found a
chain of low areas, or basins, that trace a belt across the moon's
surface that researchers believe are the fossil remnants of an earlier
equator and poles. The area around the icy moon's current south pole
is an active region where long, linear fractures referred to as 'tiger
stripes' slice across the surface. Scientists speculate that an
asteroid may have struck the region in the past when it was closer to
the equator.
In 2005, Cassini discovered that jets of water vapour and icy
particles spray from the tiger-stripe fractures -- evidence that an
underground ocean is venting directly into space from beneath the
active south-polar surface. Whether it was caused by an impact or
some other process, astronomers think that the disruption and creation
of the tiger-stripe landform caused some of Enceladus' mass to be
redistributed, making the moon's rotation unsteady and wobbly. The
rotation would eventually have stabilized, probably taking more than a
million years to do so. By the time that the rotation settled down,
the north-south axis would have re-oriented to pass through different
points on the surface -- a mechanism researchers call 'true polar
wander'. The polar-wander idea could explain why Enceladus' modern-
day north and south poles appear quite different. The south is active
and topographically young, while the north is covered in craters and
appears much older. The moon's original poles would have looked more
alike before the event that caused Enceladus to tip over and relocate
the disrupted tiger-stripe landform to the moon's south-polar region.
INGREDIENT OF LIFE FOUND AROUND SUN-LIKE STARS
RAS
Using the Atacama Large Millimetre / submillimetre Array (ALMA),
astronomers have observed stars like the Sun at very early stages in
their formation and found traces of methyl isocyanate -- a chemical
building-block of life. This is the first-ever detection of that
pre-biotic molecule towards solar-type proto-stars, the sort from
which our Solar System evolved. The discovery could help scientists
understand how life arose on Earth. Two teams of astronomers detected
the methyl isocyanate in the multiple-star system IRAS 16293-2422.
ALMA's capabilities allowed both teams to observe the molecule at
several different and characteristic wavelengths across the radio
spectrum. They found the unique chemical fingerprints located in the
warm, dense inner regions of the cocoon of dust and gas surrounding
young stars in their earliest stages of evolution. Each team
identified and isolated the signatures of methyl isocyanate. They
followed that up with computer chemical modelling and laboratory
experiments to refine their understanding of the molecule's origin.
IRAS 16293-2422 is a multiple system of very young stars, around 400
light-years away, in a large star-forming region called Rho Ophiuchi.
The new results from ALMA show that methyl isocyanate gas surrounds
each of the young stars. The Earth and the other planets in the Solar
System formed from the material left over after the formation of the
Sun. Studying solar-type proto-stars can therefore open a window to
the past for astronomers and allow them to observe conditions similar
to those that led to the formation of our Solar System over 4.5 billion years
ago.
COLLAPSING STAR GIVES BIRTH TO BLACK HOLE
NASA
Astronomers used the combined power of the Large Binocular Telescope
(LBT) and the Hubble and Spitzer space telescopes, to look for
remnants of a vanished star, only to find that it disappeared out of
sight. The star, which was 25 times the mass of the Sun, should have
exploded in a very bright supernova. Instead, it fizzled out -- and
then left behind a black hole. 'Massive fails', like that one in a
'nearby' galaxy, could explain why astronomers rarely see supernovae
from the most massive stars. As many as 30% of such stars, it seems,
may quietly collapse into black holes -- no supernova required. The
typical view is that a star can form a black hole only after it goes
supernova. If a star can fall short of a supernova and still make a
black hole, that would help to explain why we don't see supernovae
from the most massive stars. Among the galaxies that have been
watched is NGC 6946, a spiral galaxy 22 million light-years away that
is nicknamed the 'Fireworks Galaxy' because supernovae frequently
happen there -- indeed, one, SN 2017eaw, was discovered as recently as
May 14. Starting in 2009, one particular star, named N6946-BH1, began
to brighten weakly. By 2015, it appeared to have winked out of
existence. After the LBT survey for failed supernovae turned up the
star, astronomers aimed the Hubble and Spitzer space telescopes to see
if it was still there but merely dimmed. They also used Spitzer to
search for any infrared radiation emanating from the spot. That would
have been a sign that the star was still present, but perhaps just
hidden behind a dust cloud. All the tests came up negative. The star
was no longer there. By a process of elimination, the researchers
eventually concluded that the star must have become a black hole. It
is too early in the project to know how often stars experience massive
failures, but astronomers are able to make a preliminary estimate.
N6946-BH1 is the only probable failed supernova found in the first
seven years of the survey. During that time, six normal supernovae
have occurred within the galaxies monitored, suggesting that 10 to 30
per cent of massive stars die as failed supernovae. That is just the
fraction that would explain the very problem that motivated the
observers to start the survey, that is, that there are fewer observed
supernovae than should be occurring if all massive stars die that way.
The really interesting part of the discovery is the implications that
it holds for the origins of very massive black holes -- the kind that
the LIGO experiment* detected via gravitational waves. It does not
necessarily make sense that a massive star could become a supernova
-- a process which entails blowing off much of its outer layers -- and
still have enough mass left over to form a massive black hole on the
scale of those that LIGO detected. It may be much easier to under-
stand how a very massive black hole is made if there is no supernova.
*LIGO is the Laser Interferometer Gravitational-Wave Observatory.
GALAXY ALIGNMENTS TRACED BACK 10 BILLION YEARS
University of Turku
A new study reveals that the most massive galaxies in the Universe
have been aligned with their surroundings for at least ten billion years.
That discovery shows that galaxies, like people, are influenced by their
environment from a young age. Astronomers have long known that
galaxies cluster together into enormous systems -- the urban centres of
the cosmos -- and that the largest galaxies tend to 'point' towards their
neighbours. But how and when those alignments occur remains a mystery.
Using the Hubble Space Telescope, the international team of collaborators
observed 65 distant galaxy clusters whose light has taken billions of years to
reach the Earth. They showed for the first time that the largest galaxies in those systems
were already aligned with their surroundings when the Universe was
only 1/3 of its current age. Although clusters have hundreds or
thousands of member galaxies, most are randomly oriented in space.
Only the biggest galaxies are aligned with their surroundings, which
suggests that they are especially sensitive to their environment.
The team is eager to look further back in time by observing more
remote clusters, but studying galaxies at the dawn of time is not
easy, even with Hubble.
CONTRACTS FOR THE ELT'S GIANT MIRROR SIGNED
ESO
Contracts for the manufacture of the 39-metre primary mirror of ESO's
Extremely Large Telescope have been signed at the ESO headquarters
near Munich. The German company SCHOTT will produce the blanks of
the mirror segments, and the French company Safran Reosc will polish,
mount and test the segments. The contract to polish the mirror blanks
is the second-largest contract for the ELT construction and the third-
largest contract ESO has ever awarded. The unique optical system of
the Extremely Large Telescope consists of five mirrors, each of which
presents its own significant engineering challenge. The 39-metre-
diameter primary mirror, which will be made up of 798 individual
hexagonal segments each measuring 1.4 metres across, will be by far
the largest ever made for an optical telescope. Together, the
segments will collect tens of millions of times as much light as the
human eye. Once the mirror blanks are ready they will be passed to
Safran Reosc, who will design the mounting interfaces, polish and
figure the segments, integrate them into their support systems, and
perform optical tests before delivery. During the polishing process,
each segment will be polished until it has no surface irregularity
greater than about 10 nanometres. Both SCHOTT and Safran Reosc have
already had long and successful involvements with ESO. Together they
manufactured many optical components, including the 8.2-metre main
mirrors of the four Unit Telescopes of the ESO Very Large Telescope.
The ELT is currently under construction at Cerro Armazones near the
Paranal Observatory in northern Chile, and is scheduled to see first
light in 2024.
Topic: Late June Astronomy Bulletin (Read 2455 times)