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Early September Astronomy Bulletin
« on: September 16, 2018, 15:36 »
STUDY SHOWS EARTH’S INGREDIENTS ARE NORMAL
Goldschmidt Conference
 
 The Earth's building blocks seem to be built from 'pretty normal' ingredients, according to researchers working with the world's most powerful telescopes. Scientists have measured the compositions of 18 different planetary systems from up to 456 light years away and compared them to ours, and found that many elements are present in similar proportions to those found on Earth.  This is amongst the largest examinations to measure the general composition of materials in other planetary systems, and begins to allow scientists to draw more general conclusions on how they are forged, and what this might mean for finding Earth-like bodies elsewhere.  The first planets orbiting other stars were only found in 1992 (this was orbiting a pulsar), since then scientists have been trying to understand whether some of these stars and planets are similar to our own solar system. It is difficult to examine these remote bodies directly. Because of the huge distances involved, their nearby star tends to drown out any electromagnetic signal, such as light or radio waves.  Because of this, the team decided to look at how the planetary building blocks affect signals from white dwarf stars. These are stars which have burnt off most of their hydrogen and helium, and shrunk to be very small and dense -- it is anticipated that our Sun will become a white dwarf in around 5 billion years.  White dwarfs' atmospheres are composed of either hydrogen or helium, which give out a pretty clear and clean spectroscopic signal. However, as the star cools, it begins to pull in material from the planets, asteroids, comets and so on which had been orbiting it, with some forming a dust disk, a little like the rings of Saturn.  As this material approaches the star, it changes how we see the star. This change is measurable because it influences the star's spectroscopic signal, and allows us to identify the type and even the quantity of material surrounding the white dwarf. These measurements can be extremely sensitive, allowing bodies as small as an asteroid to be detected.

The team took measurements using spectrographs on the Keck telescope in Hawaii, the world's largest optical and infrared telescope, and on the Hubble Space Telescope.  In this study, the team focused on the sample of white dwarfs with dust disks.   Astronomers were able to measure calcium, magnesium, and silicon content in most of these stars, and a few more elements in some stars.  They may also have found water in one of the systems, but have not yet quantified it: it's likely that there will be a lot of water in some of these worlds. For example, the team previously identified one star system, 170 light years away in the constellation Boötes, which was rich in carbon, nitrogen and water, giving a composition similar to that of Halley's Comet. In general though, their composition looks very similar to bulk Earth.  This would mean that the chemical elements, the building blocks of Earth are common in other planetary systems. From what can be seen, in terms of the presence and proportion of these elements, we're normal, pretty normal. And that means that we can probably expect to find Earth-like planets elsewhere in our Galaxy.  This work is still on-going and the recent data release from the Gaia satellite, which so far has characterized 1.7 billion stars, has revolutionized the field. This means we will understand the white dwarfs a lot better.  The team hopes to determine the chemical compositions of extrasolar planetary material to a much higher precision. 




A GREEN COMET APPROACHES EARTH
Spaceweather.com

Comet 21P/Giacobini-Zinner is approaching Earth. On Sept. 10th, it will be 0.39 AU (58 million km) from our planet and almost bright enough to see with the naked eye. Already it is an easy target for amateur telescopes. This comet is relatively small--its nucleus is barely more than a mile in diameter--but it is bright and active, and a frequent visitor to the inner solar system as it orbits the Sun once every 6.6 years. On Sept. 10th, 21P/Giacobini-Zinner will not only be near Earth, but also at perihelion, its closest approach to the Sun. Solar heating will make it shine like a star of 6th to 7th magnitude, just below the threshold of naked-eye visibility and well within range of common binoculars. 21P/Giacobini-Zinner is the parent of the annual Draconid meteor shower, a bursty display that typically peaks on Oct. 8th. Will the shower will be extra-good this year? Maybe. Draconid outbursts do tend to occur in years near the comet's close approach to the sun. However, not every close approach brings a meteor shower. Forecasters say there are no known Draconid debris streams squarely crossing Earth's path this year, so we will have to wait and see.

ICE CONFIRMED AT MOON’S POLES
NASA/Jet Propulsion Laboratory

In the darkest and coldest parts of its polar regions, a team of scientists has directly observed definitive evidence of water ice on the Moon's surface. These ice deposits are patchily distributed and could possibly be ancient. At the southern pole, most of the ice is concentrated at lunar craters, while the northern pole's ice is more widely, but sparsely spread.  A team of scientists used data from NASA's Moon Mineralogy Mapper (M3) instrument to identify three specific signatures that definitively prove there is water ice at the surface of the Moon.  M3, aboard the Chandrayaan-1 spacecraft, launched in 2008 by the Indian Space Research Organization, was equipped to confirm the presence of solid ice on the Moon. It collected data that not only picked up the reflective properties we'd expect from ice, but was able to directly measure the distinctive way its molecules absorb infrared light, so it can differentiate between liquid water or vapour and solid ice.  Most of the newfound water ice lies in the shadows of craters near the poles, where the warmest temperatures never reach above minus 157 Centigrade.  Because of the very small tilt of the Moon's rotation axis, sunlight never reaches these regions.  Previous observations indirectly found possible signs of surface ice at the lunar south pole, but these could have been explained by other phenomena, such as unusually reflective lunar soil.  With enough ice sitting at the surface -- within the top few millimetres -- water would possibly be accessible as a resource for future expeditions to explore and even stay on the Moon, and potentially easier to access than the water detected beneath the Moon's surface.

 
 

INSIGHT PASSES HALWAY POINT TO MARS
NASA
NASA's InSight spacecraft, en route to a Nov. 26 landing on Mars, passed the halfway mark on Aug. 6. All of its instruments have been tested and are working well.  The spacecraft has covered 300 million
kilometres since its launch.  It will touch down in Mars' Elysium Planitia region, where it will be the first mission to study the Red Planet's deep interior. InSight stands for Interior Exploration using Seismic Investigations, Geodesy and Heat Transport.  The InSight team is using the time before the spacecraft's arrival at Mars to not only plan and practice for that critical day, but also to activate and check spacecraft subsystems vital to cruise, landing and surface operations, including the highly sensitive science instruments.  InSight's seismometer, which will be used to detect quakes on Mars, received a clean bill of health on July 19. The SEIS instrument (Seismic Experiment for Interior Structure) is a six-sensor seismometer combining two types of sensors to measure ground motions over a wide range of frequencies. It will give scientists a window into Mars' internal activity.


STRUCTURALLY “INSIDE OUT” PLANETARY NEBULA DISCOVERED
The University of Hong Kong

Astronomers have discovered the unusual evolution of the central star of a planetary nebula in our Milky Way. This discovery sheds light on the future evolution, and more importantly, the ultimate fate of the Sun.  The research team believes this inverted ionization structure of the nebula is resulted from the central star undergoing a 'born-again' event, ejecting material from its surface and creating a shock that excites the nebular material. Planetary nebulae are ionized clouds of gas formed by the hydrogen-rich envelopes of low- and intermediate-mass stars ejected at late evolutionary stages. As these stars age, they typically strip their outer layers, forming a 'wind'. As the star transitions from its red giant phase to become a white dwarf, it becomes hotter, and starts ionizing the material in the surrounding wind. This causes the gaseous material closer to the star to become highly ionized, while the gas material further out is less so.  Studying the planetary nebula HuBi 1 (17,000 light years away and nearly 5 billion years ahead of our solar system in evolution), however, the team found the reverse: HuBi 1's inner regions are less ionized, while the outer regions more so. Analysing the central star, with the participation of top theoretical astrophysicists, the authors found that it is surprisingly cool and metal-rich, and is evolved from a low-mass progenitor star which has a mass 1.1 times of the Sun.  The authors suggest that the inner nebula was excited by the passage of a shockwave caused by the star ejecting matter unusually late in its evolution. The stellar material cooled to form circumstellar dust, obscuring the star; this well explains why the central star's optical brightness has diminished rapidly over the past 50 years. In the absence of ionizing photons from the central star, the outer nebula has begun recombining -- becoming neutral. The authors conclude that, as HuBi 1 was roughly the same mass as the Sun, this finding provides a glimpse of a potential future for our solar system.

The discovery resolves a long-lasting question regarding the evolutionary path of metal-rich central stars of planetary nebulae.  The team has been observing the evolution of HuBi 1 since 2014 using the Spanish flagship telescope Nordic Optical Telescope and was among the first astrophysicists to discover its inverted ionization structure.  After noting HuBi 1's inverted ionization structure and the unusual nature of its central star, astronomers looked closer to find the reasons in collaboration with top theoretical astrophysicists in the world. They came to realize that they had caught HuBi 1 at the exact moment when its central star underwent a brief 'born-again' process to become a hydrogen-poor [WC] and metal-rich star, which is very rare in white dwarf stars evolution.  The findings suggest that the Sun may also experience a 'born-again' process while it is dying out in about 5 billion years from now; but way before that event, our Earth will be engulfed by the Sun when it turns into a superhot red giant and nothing living will survive. 


WATER WORLDS ARE COMMON
Goldschmidt Conference     
 
Scientists have shown that water is likely to be a major component of those exoplanets (planets orbiting other stars) which are between two to four times the size of Earth.  It will have implications for the search of life in our Galaxy. The 1992 discovery of exoplanets orbiting other stars has sparked interest in understanding the composition of these planets to determine, among other goals, whether they are suitable for the development of life. Now a new evaluation of data from the exoplanet-hunting Kepler Space Telescope and the Gaia mission indicates that many of the known planets may contain as much as 50% water. This is much more than the Earth's 0.02% (by weight) water content.  Scientists have found that many of the 4000 confirmed or candidate exoplanets discovered so far fall into two size categories: those with the planetary radius averaging around 1.5 that of the Earth, and those averaging around 2.5 times the radius of the Earth.  Now a group of scientists, after analyzing the exoplanets with mass measurements and recent radius measurements from the Gaia satellite, have developed a model of their internal structure.  The group has looked at how mass relates to radius, and developed a model which might explain the relationship.  The model indicates that those exoplanets which have a radius of around x1.5 Earth radius tend to be rocky planets (of typically x5 the mass of the Earth), while those with a radius of x2.5 Earth radius (with a mass around x10 that of the Earth) are probably water worlds.

This is water, but not as commonly found here on Earth.  Their surface temperature is expected to be in the 200 to 500 degree Celsius range. Their surface may be shrouded in a water-vapour-dominated atmosphere, with a liquid water layer underneath. Moving deeper, one would expect to find this water transforms into high-pressure ices before we reaching the solid rocky core. The beauty of the model is that it explains just how composition relates to the known facts about these planets.  The data indicate that about 35% of all known exoplanets which are bigger than Earth should be water-rich. These water worlds likely formed in similar ways to the giant planet cores (Jupiter, Saturn, Uranus, Neptune) which we find in our own solar system. The newly-launched TESS mission will find many more of them, with the help of ground-based spectroscopic follow-up.


GALAXY CLUSTER HIDING IN PLAIN SIGHT
Massachusetts Institute of Technology

MIT scientists have uncovered a sprawling new galaxy cluster hiding in plain sight. The cluster, which sits 2.4 billion light years from Earth, is made up of hundreds of individual galaxies and surrounds an extremely active supermassive black hole, or quasar.  The central quasar is called PKS1353-341 and is intensely bright -- so bright that for decades astronomers observing it in the night sky have assumed that the quasar was quite alone in its corner of the Universe, shining out as a solitary light source from the centre of a single galaxy.  The researchers estimate that the cluster is about as massive as 690 trillion suns. Our Milky Way galaxy, for comparison, weighs in at around 400 billion solar masses.  The team also calculates that the quasar at the centre of the cluster is 46 billion times brighter than the Sun. Its extreme luminosity is likely the result of a temporary feeding frenzy: As an immense disk of material swirls around the quasar, big chunks of matter from the disk are falling in and feeding it, causing the black hole to radiate huge amounts of energy out as light. This might be a short-lived phase that clusters go through, where the central black hole has a quick meal, gets bright, and then fades away again.  Astronomers believe the discovery of this hidden cluster shows there may be other similar galaxy clusters hiding behind extremely bright objects that astronomers have miscatalogued as single light sources. The researchers are now looking for more hidden galaxy clusters, which could be important clues to estimating how much matter there is in the Universe and how fast the Universe is expanding.

In 2012, the team discovered the Phoenix cluster, one of the most massive and luminous galaxy clusters in the Universe. The mystery was why this cluster, which was so intensely bright and in a region of the sky that is easily observable, hadn't been found before.  It's because astronomers had preconceived notions of what a cluster should look like. For the most part, astronomers have assumed that galaxy clusters look "fluffy," giving off a very diffuse signal in the X-ray band, unlike brighter, point-like sources, which have been interpreted as extremely active quasars or black holes.  The images are either all points, or fluffs, and the fluffs are these giant million-light-year balls of hot gas that we call clusters, and the points are black holes that are accreting gas and glowing as this gas spirals in. The Phoenix discovery proved that galaxy clusters could indeed host immensely active black holes, prompting astronomers to wonder: Could there be other nearby galaxy clusters that were simply misidentified?  To answer that question, the researchers set up a survey named CHiPS, for Clusters Hiding in Plain Sight, which is designed to reevaluate X-ray images taken in the past.  For every point source that was previously identified, the researchers noted their coordinates and then studied them more directly using the Magellan Telescope, a powerful optical telescope that sits in the mountains of Chile. If they observed a higher-than-expected number of galaxies surrounding the point source (a sign that the gas may stem from a cluster of galaxies), the researchers looked at the source again, using NASA's space-based Chandra X-Ray Observatory, to identify an extended, diffuse source around the main point source.  Some 90 percent of these sources turned out to not be clusters.   The team plans to comb through more X-ray data in search of galaxy clusters that might have been missed the first time around.


SOME OF THE OLDEST GALAXIES IN UNIVERSE
Durham University

Astronomers from the Institute for Computational Cosmology at Durham University and the Harvard-Smithsonian Center for Astrophysics, have found evidence that the faintest satellite galaxies orbiting our own Milky Way galaxy are amongst the very first galaxies that formed in our Universe.  Scientists working on this research have described the finding as "hugely exciting".  The research group's findings suggest that galaxies including Segue-1, Bootes I, Tucana II and Ursa Major I are in fact some of the first galaxies ever formed, thought to be over 13 billion years old. When the Universe was about 380,000 years old, the very first atoms formed. These were hydrogen atoms, the simplest element in the periodic table. These atoms collected into clouds and began to cool gradually and settle into the small clumps or "halos" of dark matter that emerged from the Big Bang.  This cooling phase, known as the "Cosmic dark ages," lasted about 100 million years. Eventually, the gas that had cooled inside the halos became unstable and began to form stars -- these objects are the very first galaxies ever to have formed.  With the formation of the first galaxies, the Universe burst into light, bringing the cosmic dark ages to an end.  The team identified two populations of satellite galaxies orbiting the Milky Way.

The first was a very faint population consisting of the galaxies that formed during the "cosmic dark ages." The second was a slightly brighter population consisting of galaxies that formed hundreds of millions of years later, once the hydrogen that had been ionized by the intense ultraviolet radiation emitted by the first stars was able to cool into more massive dark matter halos.  Remarkably, the team found that a model of galaxy formation that they had developed previously agreed perfectly with the data, allowing them to infer the formation times of the satellite galaxies.  The finding supports the current model for the evolution of our Universe, the 'Lambda-cold-dark-matter model' in which the elementary particles that make up the dark matter drive cosmic evolution.  The intense ultraviolet radiation emitted by the first galaxies destroyed the remaining hydrogen atoms by ionizing them (knocking out their electrons), making it difficult for this gas to cool and form new stars.  The process of galaxy formation ground to a halt and no new galaxies were able to form for the next billion years or so.  Eventually, the halos of dark matter became so massive that even ionized gas was able to cool. Galaxy formation resumed, culminating in the formation of spectacular bright galaxies like our own Milky Way.  A decade ago, the faintest galaxies in the vicinity of the Milky Way would have gone under the radar. With the increasing sensitivity of present and future galaxy censuses, a whole new trove of the tiniest galaxies has come into the light, allowing us to test theoretical models in new regimes.


EARLY OPAQUE UNIVERSE LINKED TO GALAXY SCARCITY:
University of California - Riverside

A team of astronomers has made a surprising discovery: 12.5 billion years ago, the most opaque place in the Universe contained relatively little matter.  It has long been known that the Universe is filled with a web-like network of dark matter and gas. This "cosmic web" accounts for most of the matter in the Universe, whereas galaxies like our own Milky Way make up only a small fraction. Today, the gas between galaxies is almost totally transparent because it is kept ionized -- electrons detached from their atoms -- by an energetic bath of ultraviolet radiation.  Over a decade ago, astronomers noticed that in the very distant past -- roughly 12.5 billion years ago, or about 1 billion years after the Big Bang -- the gas in deep space was not only highly opaque to ultraviolet light, but its transparency varied widely from place to place, obscuring much of the light emitted by distant galaxies.  Then a few years ago, a team at the University of Cambridge, found that these differences in opacity were so large that either the amount of gas itself, or more likely the radiation in which it is immersed, must vary substantially from place to place.  Today, we live in a fairly homogeneous Universe.  If you look in any direction you find, on average, roughly the same number of galaxies and similar properties for the gas between galaxies, the so-called intergalactic gas. At that early time, however, the gas in deep space looked very different from one region of the Universe to another.  To find out what created these differences, astronomers turned to one of the largest telescopes in the world: the Subaru telescope on the summit of Mauna Kea in Hawaii. Using its powerful camera, the team looked for galaxies in a vast region, roughly 300 million light years in size, where they knew the intergalactic gas was extremely opaque.

For the cosmic web more opacity normally means more gas, and hence more galaxies. But the team found the opposite: this region contained far fewer galaxies than average. Because the gas in deep space is kept transparent by the ultraviolet light from galaxies, fewer galaxies nearby might make it murkier.  Normally it doesn't matter how many galaxies are nearby; the ultraviolet light that keeps the gas in deep space transparent often comes from galaxies that are extremely far away. At this very early time, it looks like the UV light can't travel very far, and so a patch of the Universe with few galaxies in it will look much darker than one with plenty of galaxies around.  This discovery may eventually shed light on another phase in cosmic history. In the first billion years after the Big Bang, ultraviolet light from the first galaxies filled the Universe and permanently transformed the gas in deep space. Astronomers believe that this occurred earlier in regions with more galaxies, meaning the large fluctuations in intergalactic radiation may be a relic of this patchy process, and could offer clues to how and when it occurred.  By studying both galaxies and the gas in deep space, astronomers hope to get closer to understanding how this intergalactic ecosystem took shape in the early Universe.

 
ANCIENT QUASARS CONFIRM QUANTUM ENTANGLEMENT 
Massachusetts Institute of Technology

Last year, physicists at MIT, the University of Vienna, and elsewhere provided strong support for quantum entanglement, the seemingly far-out idea that two particles, no matter how distant from each other in space and time, can be inextricably linked, in a way that defies the rules of classical physics.  Take, for instance, two particles sitting on opposite edges of the Universe. If they are truly entangled, then according to the theory of quantum mechanics their physical properties should be related in such a way that any measurement made on one particle should instantly convey information about any future measurement outcome of the other particle -- correlations that Einstein skeptically saw as "spooky action at a distance."  In the 1960s, the physicist John Bell calculated a theoretical limit beyond which such correlations must have a quantum, rather than a classical, explanation.  But what if such correlations were the result not of quantum entanglement, but of some other hidden, classical explanation? Such "what-ifs" are known to physicists as loopholes to tests of Bell's inequality, the most stubborn of which is the "freedom-of-choice" loophole: the possibility that some hidden, classical variable may influence the measurement that an experimenter chooses to perform on an entangled particle, making the outcome look quantumly correlated when in fact it isn't.  Last February, the MIT team and their colleagues significantly constrained the freedom-of-choice loophole, by using 600-year-old starlight to decide what properties of two entangled photons to measure. Their experiment proved that, if a classical mechanism caused the correlations they observed, it would have to have been set in motion more than 600 years ago, before the stars' light was first emitted and long before the actual experiment was even conceived.  Now, the same team has vastly extended the case for quantum entanglement and further restricted the options for the freedom-of-choice loophole. The researchers used distant quasars, one of which emitted its light 7.8 billion years ago and the other 12.2 billion years ago, to determine the measurements to be made on pairs of entangled photons. They found correlations among more than 30,000 pairs of photons, to a degree that far exceeded the limit that Bell originally calculated for a classically based mechanism.  If some conspiracy is happening to simulate quantum mechanics by a mechanism that is actually classical, that mechanism would have had to begin its operations -- somehow knowing exactly when, where, and how this experiment was going to be done -- at least 7.8 billion years ago. That seems incredibly implausible, so we have very strong evidence that quantum mechanics is the right explanation.  The Earth is about 4.5 billion years old, so any alternative mechanism -- different from quantum mechanics -- that might have produced our results by exploiting this loophole would've had to be in place long before even there was a planet Earth, let alone an MIT.  So we've pushed any alternative explanations back to very early in cosmic history.


15 YEARS IN SPACE FOR SPITZER SPACE TELESCOPE
NASA

Initially scheduled for a minimum 2.5-year primary mission, NASA's Spitzer Space Telescope has gone far beyond its expected lifetime -- and is still going strong after 15 years.  Launched into a solar orbit on Aug. 25, 2003, Spitzer was the final of NASA's four Great Observatories to reach space. The space telescope has illuminated some of the oldest galaxies in the Universe, revealed a new ring around Saturn, and peered through shrouds of dust to study newborn stars and black holes. Spitzer assisted in the discovery of planets beyond our solar system, including the detection of seven Earth-size planets orbiting the star TRAPPIST-1, among other accomplishments.  Spitzer detects infrared light -- most often heat radiation emitted by warm objects.  Each of the four Great Observatories collects light in a different wavelength range. By combining their observations of various objects and regions, scientists can gain a more complete picture of the Universe.  Spitzer has logged over 106,000 hours of observation time. Thousands of scientists around the world have utilized Spitzer data in their studies, and Spitzer data is cited in more than 8,000 published papers.

Spitzer's primary mission ended up lasting 5.5 years, during which time the spacecraft operated in a "cold phase," with a supply of liquid helium cooling three onboard instruments to just above absolute zero. The cooling system reduced excess heat from the instruments themselves that could contaminate their observations. This gave Spitzer very high sensitivity for "cold" objects.  In July 2009, after Spitzer's helium supply ran out, the spacecraft entered a so-called "warm phase." Spitzer's main instrument, called the Infrared Array Camera (IRAC), has four cameras, two of which continue to operate in the warm phase with the same sensitivity they maintained during the cold phase.  Spitzer orbits the Sun in an Earth-trailing orbit (meaning it literally trails behind Earth as the planet orbits the Sun) and has continued to fall farther and farther behind Earth during its lifetime. This now poses a challenge for the spacecraft, because while it is downloading data to Earth, its solar panels do not directly face the Sun. As a result, Spitzer must use battery power during data downloads. The batteries are then recharged between downloads.  In 2016, Spitzer entered an extended mission dubbed "Spitzer Beyond." The spacecraft is currently scheduled to continue operations into November 2019, more than 10 years after entering its warm phase.   
 
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