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May 24, 2015 at 3:53 pm #8500Anonymous
Here is the latest round-up of news from the Society for Popular Astronomy. The SPA is arguably Britain's liveliest astronomical society, with members all over the world. We accept subscription payments online at our secure site and can take credit and debit cards. You can join or renew via a secure server or just see how much we have to offer by visiting http://www.popastro.com/
EVIDENCE THAT WATER REACHED EARTH FROM ASTEROIDS
Astronomers have found evidence that numerous planetary bodies,including asteroids and comets, contain large amounts of water. The findings support the possibility that water can be delivered to Earth-like planets by such bodies and thereby help to create an environment suitable for the formation of life. The research has found that water-rich asteroids similar to those in the Solar System appear to be commonplace. Accordingly, many planets may contain, or have contained, a volume of water comparable to that on the Earth. It is believed that the Earth was initially dry, but research suggests that the water in the oceans that exist today arrived through impacts by water-rich comets or asteroids. In observations obtained with the William Herschel telescope in the Canary Islands, astronomers detected a large quantity of hydrogen and oxygen in the atmosphere of a white dwarf known as SDSS J1242+5226, the compact remnant of a Sun-like star at the end of its 'life'. That is indirect evidence that a water-rich exo-asteroid was disrupted and eventually delivered the water it contained onto the star. That asteroid, the researchers believe, was comparable in size with Ceres, which at 900 km across is the largest asteroid in the Solar System. The amount of water found in SDSS J1242+5226 is equivalent to 30-35% of the volume of the Earth's oceans.
The impact of water-rich asteroids or comets onto a planet or white dwarf results in the mixing of hydrogen and oxygen into their atmospheres. Both elements were detected in large amounts in SDSS J1242+5226. Oxygen, which is a relatively heavy element, will sink deep down into the white dwarf over time, and hence it will no longer be visible a long time after the disruption event occurred. In contrast, hydrogen is the lightest element; it will always remain floating near the surface of the white dwarf where it can easily be detected. There are many white dwarfs that hold large amounts of hydrogen in their atmospheres, and the new study claims that that is evidence that water-rich asteroids or comets are common around other stars. [Whoa! — hydrogen is by far the most abundant element in the Universe, and when stars first form they are very largely made of it. Might not even a white dwarf, which has run its evolutionary course, somehow contrive to retain a little of it? — ED]
AURORA ON MARS
In late December 2014, the MAVEN spacecraft detected evidence of widespread aurorae in Mars's northern hemisphere. The 'Christmas Lights', as the researchers called them, were in all longitudes and descended to latitudes around 25. That was not the first time that a spacecraft had detected aurorae on Mars. Ten years ago, Mars Express found an ultraviolet glow coming from 'magnetic umbrellas' in the southern hemisphere. Unlike the Earth, Mars has not got a global magnetic field that envelops the entire planet. Instead, Mars has umbrella-shaped magnetic fields that sprout out of the ground like mushrooms, here and there, but mainly in the southern hemisphere. The umbrellas are remnants of an ancient global field that decayed billions of years ago. Aurorae occur, both on the Earth and on Mars, when energetic particles from space rain down on the upper atmosphere. On the Earth, the particles are guided toward the poles by the global magnetic field, which is why aurorae are seen most often around the Arctic and Antarctic. On Mars, there is no organized planetary magnetic field to guide the particles north and south, so they can go anywhere. According to the MAVEN data, solar particles that caused the 'Christmas lights' penetrated deeply into the Martian atmosphere, causing aurorae less than 100 km from the surface. That is lower than aurorae on the Earth, which range from 100 km to 500 km high.
Like Mars Express 10 years ago, MAVEN has an ultraviolet camera, so it is not seeing the same thing as human eyes. Although the Martian atmosphere is primarily CO2, it does contain some oxygen — and that is the key to the colour of the aurorae. Excited oxygen atoms in the Martian atmosphere would be likely to produce green light. MAVEN arrived at Mars in September 2014 on a mission to investigate how the planet lost most of its atmosphere. Billions of years ago, Mars was blanketed by layer of air massive enough to warm the planet and allow liquid water to flow on its surface. Today, however, only a tiny fraction of that ancient air remains, leaving Mars a desiccated wasteland. Where did the Martian atmosphere go? A favourite theory is solar wind erosion. Because Mars no longer has a global magnetic field to protect it, solar wind might strip away material from the upper layers of the atmosphere. Watching the aurorae might help MAVEN scientists learn more about that process.
DUST FROM COMET WILD 2 ANALYSED
University of Hawaii at Manoa
Our Solar System, and other planetary systems, started as a disc of microscopic dust grains, gas and ice around the young Sun. The amazing diversity of objects in the Solar System today — the planets, moons, asteroids and comets — was made from that primitive material. The 'Stardust' mission returned to Earth with samples of comet Wild 2, a comet that originated outside the orbit of Neptune and subsequently came closer to the Earth's orbit in 1974, when Jupiter's gravity altered Wild 2's orbit. Before Stardust returned, scientists thoughtthat everything it brought back from the comet would be either the primitive dust or circumstellar grains — rocks and minerals that formed around other stars. But that was not the case. A team of scientists has now investigated the oxygen-isotope and mineral composition of the comet dust returned from Wild 2 and discovered that the larger-sized dust appears to be similar to rocks found in primitive meteorites called chondrites. The smaller-sized dust, on the other hand, displays the entire range of known oxygen isotopic compositions that have been measured for objects from the inner Solar System (from the Sun to the asteroid belt). That unexpected combination of materials has deepened the uncertainties over Wild 2's past.
It would be interesting to know whether the fine-grained dust from comet Wild 2 represents a diverse sampling of many inner-Solar-Systemobjects that were transported to the outer Solar System, or whether it is in fact the raw starting material of the Solar System. The team thinks it has a method to address that question. Processing of material in the inner Solar System should alter the abundance of circumstellar grains and volatile elements in the fine-grained dust. If the fine-grained material is enriched in circumstellar grains and not depleted in volatiles, we can say with some assurance that we are looking at primitive Solar-System dust. If circumstellar grains are not over-abundant compared to meteorites, and volatiles are depleted, we can be reasonably sure that we are looking at a very diverse sample of fine-grained inner-Solar-System material in the comet. Reflecting on the complex life history of comet Wild 2's constituent material, the team notes that the comet's nucleus today is made up of small rocks and ice, separated by fractions of an inch, that originally formed billions of miles apart. Some rocks have seen temperatures above 1400C, but adjacent ice has been kept close to absolute zero for billions of years.
NEW TYPE OF GLOBULAR CLUSTER
Observations with the Very Large Telescope in Chile have discovered a new class of 'dark' globular star clusters around the giant galaxy Centaurus A. The objects look similar to normal clusters, but contain much more mass and may either harbour unexpected amounts of dark matter, or contain massive black holes — neither of which was expected nor is understood. Globular star clusters are huge balls of thousands of stars that orbit most galaxies. They are among the oldest known stellar systems in the Universe and have survived through almost the entire span of galaxy growth and evolution. The elliptical galaxy Centaurus A (also known as NGC 5128) is the closest giant galaxy to the Milky Way and is suspected to have as many as 2000 globular clusters. Many of them are brighter and more massive than the 150 or so that orbit the Milky Way.
Astronomers studied a sample of 125 of the clusters around Centaurus A with the FLAMES instrument on the VLT at Paranal in Chile. They deduced the masses of the clusters and compared them with their magnitudes. For most of the clusters in the new survey, the brighter ones had more mass in the way that was expected — if a cluster contains more stars it naturally has greater total brightness and more total mass. But some of the clusters were many times more massive than they looked. Also, the more massive those unusual clusters were, the greater the fraction of their material was dark. Something in the clusters was dark, hidden and massive. There were several possibilities. Perhaps the dark clusters contain black holes, or other dark stellar remnants in their cores. That may be a factor that explains some of the hidden mass, but the team concludes that it cannot be the whole story. What about dark matter? Globular clusters are normally considered to be almost devoid of that mysterious substance, but perhaps, for some unknown reason, some clusters have retained significant dark-matter clumps in their cores. That would 'explain' the observations but does not fit into conventional theory. The team is also engaged in a wider survey of other globular clusters in other galaxies.
GIANT HALO AROUND ANDROMEDA GALAXY
Space Telescope Science Institute (STScI)
Scientists using the Hubble telescope have discovered that the immense halo of gas enveloping the Andromeda galaxy, our nearest massive galactic neighbour, is about six times larger and 1,000 times more massive than was previously supposed. The dark, nearly invisible halo stretches about a million light-years from its galaxy, halfway to our own Milky Way galaxy. That finding promises to tell astronomers more about the evolution and structure of giant spirals, one of the most common types of galaxies. Haloes are the gaseous atmospheres of galaxies. The properties of the haloes control the rate at which stars form in galaxies, according to models of galaxy formation. The gargantuan halo of the Andromeda galaxy is estimated to contain half the mass of the stars in the galaxy itself, in the form of a hot, diffuse gas. If it could be viewed with the naked eye, the halo would be 100 times the diameter of the Full Moon in the sky. The Andromeda galaxy lies 2.5 million light-years away and looks like a faint spindle, with a longth of about 6 times the diameter of the Full Moon. It is considered to be a near-twin of the Milky Way galaxy. Because the gas in Andromeda's halo is dark, it does not emit a spectrum itself, so the team had to look at bright background objects through the gas and observe the extra absorption features imposed on their spectra. Available background 'lights' for such a study are quasars. The team used 18 quasars that exist far behind Andromeda to see how material is distributed well beyond the visible disc of the galaxy.
Earlier research from Hubble's 'Cosmic Origins' programme studied 44 distant galaxies and found haloes like Andromeda's, but such a massive halo has not previously been seen in a neighboring galaxy. Because the previously studied galaxies were much further away, they appeared much smaller on the sky. Only one quasar could be detected behind each faraway galaxy, providing only one sight-line to assess the halo size and structure. With its relative proximity and its correspondingly large extent on the sky, Andromeda provides a far better sampling of background quasars. As the light from one of the quasars travels through the halo, the gas there impresses extra absorption lines on it, enabling us to estimate how much Andromeda-halo gas there is between us and that quasar. The scientists used Hubble to study the ultraviolet light from the quasars. The team drew from about 5 years' worth of observations stored in the Hubble data archive to conduct the research. Many previous Hubble campaigns have used quasars to study gas much farther away than — but in the general direction of — Andromeda, so a treasure trove of data already existed.
Simulations of galaxies suggest that the halo formed at the same time as the rest of Andromeda. The team also discovered that it is enriched in elements much heavier than hydrogen and helium, and the only way to get the heavy elements is from supernovae, which form the heavy elements and then violently blow them out into space. Over Andromeda's existence, nearly half of all the heavy elements made by its stars have been expelled far beyond the galaxy's 200,000-light-year-diameter stellar disc. Because we live inside the Milky Way, scientists cannot determine whether or not such an equally massive and extended halo exists around our galaxy — a case of not being able to see the wood for the trees. If the Milky Way does possess a similarly huge halo, the two galaxies' haloes may be nearly touching already and quiescently merging long before the two massive galaxies collide, as they appeared destined to do in the far future.. Hubble observations indicate that the Andromeda and Milky Way galaxies will merge to form a giant elliptical galaxy, beginning about 4 billion years from now.
ASTRONOMERS UNVEIL FARTHEST GALAXY
A team of astronomers has pushed back the cosmic frontier of galaxy exploration to a time when the Universe was only 5% of its present age. The team discovered an exceptionally luminous galaxy more than 13 billion years in the past and determined its distance with the 'MOSFIRE' instrument on the Keck 10-m telescope in Hawaii. It is the most distant galaxy currently measured. The galaxy, EGS-zs8-1, was originally identified in images from the Hubble and Spitzer space telescopes. It is one of the brightest and most massive objects in the early Universe. Age and distance are vitally connected in any discussion of the Universe. The light we see from the Sun takes just eight minutes to reach us, while the light from the distant galaxies that we can see in large telescopes travels for billions of years before it reaches us — so we are seeing what those galaxies looked like billions of years ago. At the time that its light started out towards us, the distant galaxy has already built up more than 15% of the present-day mass of the Milky Way, but it had had 'only' 670 million years to do so. The astronomers also found that EGS-zs8-1 was still forming stars rapidly, about 80 times faster than our galaxy is doing now.
The MOSFIRE instrument allows astronomers to study several galaxies at the same time. Measuring galaxies at extreme distances and characterizing their properties will be a major goal of astronomy over the next decade. The new observations establish EGS-zs8-1 at a time when the Universe was undergoing an important change — the hydrogen between galaxies was becoming ionized. It appears that the young stars in the early galaxies like EGS-zs8-1 were the main drivers for that transition, called re-ionization. Taken together, the new observations also pose new questions. They confirm that massive galaxies already existed early in the history of the Universe, but they also show that those galaxies had very different physical properties from those of the galaxies seen around us today. Astronomers now have strong evidence that the peculiar colours of early galaxies — seen in the Spitzer images — originate from a rapid formation of massive, young stars, which interacted with the primordial gas in the galaxies. The researchers say that their observations presage discoveries that may become possible when the James Webb space telescope is launched in 2018. In addition to pushing back the 'cosmic frontier' to even earlier times, the telescope should be able to obtain spectra of EGS-zs8-1 and provide astronomers with more detailed insights into properties of its gas.
MISSING ANTIMATTER EXPLAINED
The discovery of a 'left-handed' magnetic field that pervades the Universe may suggest a solution to a long standing problem — the absence of cosmic anti-matter. Planets, stars, gas and dust are almost entirely made up of 'normal' matter of the kind with which we are familiar on Earth. But theory suggests that there could also be anti-matter, like normal matter but with the opposite charge. For example, an anti-electron or positron has the same mass as its conventional counterpart, but a positive rather than negative charge. In 2001 theoretical models were published to try to solve the problem, asserting that the entire Universe is filled with helical magnetic fields. Researchers were inspired to search for evidence of such fields in data from the Fermi Gamma-ray space telescope (FGST), which was launched in 2008 and observes gamma rays from very distant sources, such as the super-massive black holes found in many large galaxies. The gamma rays are sensitive to effects of the magnetic field they travel through on their long journey to the Earth. If the field is helical, it will imprint a spiral pattern on the distribution of gamma rays.
The team sees that effect in the FGST data, allowing it not only to detect the magnetic field but to measure its properties. The data show a helical field with an excess of left-handedness — a discovery that suggests the actual mechanism that led to the absence of antimatter. Both the planet we live on and the star we orbit are made up of 'normal' matter, and though it features in many science-fiction stories anti-matter seems to be absent in nature. In the new result we have one of the first hints that we might be able to solve that problem. The discovery has wide ramifications, as a cosmological magnetic field could play an important role in the formation of the first stars and could seed the stronger field seen in galaxies and clusters of galaxies at the present day.
LHC DETECTS RARE PARTICLE DECAYS
Scientists at the Large Hadron Collider have announced the detection of a rare particle decay which was harder to find than the famous Higgs particle. The 'strange B meson' is certainly a lot less famous than the Higgs boson, but it also has an important role to play in the 'Standard Model' of particle physics. For the past several decades, particle physics has been governed by the Standard Model, which allows physicists to classify all sub-atomic particles and make predictions about particles and processes not yet observed. Its predictions are thus far borne out — the existence of the Higgs boson being the most famous example. Mesons are other sub-atomic particles. Now, scientists have detected the decay of strange B mesons for the first time, which qualitatively is in accord with the Standard Model. However, the rate of decay of 'non-strange B mesons' was four times the Standard Model's prediction. That is not entirely bad news, though. Physicists have long known that the Standard Model is incomplete. For example, it does not explain dark energy or dark matter. Data that deviate from the Standard Model could in fact point the way forward toward a better theory.
RUSSIAN ROCKET BURNS UP OVER SIBERIA
A Russian Proton-M carrier rocket carrying a Mexican satellite has malfunctioned and burnt up over Siberia soon after launch. Russia's space programme has experienced a series of embarrassing mishaps in recent months. A week previously, Russia was forced to delay the return of three astronauts on board the International Space Station (ISS) after an out-of-control unmanned cargo ship also burnt up as it re-entered the Earth's atmosphere on April 28. Russia used to be a byword in reliability for space technology, but its reputation has declined recently. Proton rockets now fail with alarming regularity. Confidence is waning, and many commercial satellite operators have already started to take their business elsewhere. For those who still have contracts with Proton, the new failure is a major headache, in particular for London-based Inmarsat. The world's largest mobile satellite services operator is in the midst of rolling out Global Xpress, its next-generation constellation of satellites. That is the largest single commercial space project in Britain, worth more than £1000 m, and will provide enhanced communications to ships, planes, the armed forces and broadcasting companies. Two of the three satellites in Global Xpress have been launched successfully on Protons. The third was due to be launched next month. That will not happen now, and the anticipated September inauguration of services on the new constellation may be put back several months as a consequence.
Industry sources say that the Mexican satellite has not been found, and launches of Proton-type rockets will wait until the reason for the malfunction is established. Roscosmos said in a statement that the communications satellite, booster and third stage burnt up almost entirely in the atmosphere, with no evidence of anything falling to Earth. Sources say that communications were lost with the Proton-M rocket shortly before it was supposed to separate from the third-stage rocket. The engine of the third stage accidentally switched off, Russian news agencies reported, citing space industry sources. Russia earns large amounts of foreign exchange from the launches of Western and Asian commercial satellites. The Proton-M carrier rocket is Russia's main vehicle for commercial satellite launches, but in recent years has been repeatedly grounded because of mechanical difficulties. Russia has been using Proton carriers since the Soviet era, and has had a monopoly on sending astronauts to the ISS since the mothballing of the US space shuttle programme.
SKA HEADQUARTERS WILL BE IN UK
A decision has been taken to site the permanent headquarters of the Square Kilometre Array (SKA) in the UK. The array is expected to cost £475 million. The first phase will consist of some 200 dishes in South Africa and 130,000 antennae in Australia. Last year the UK government made a full commitment to the SKA project, announcing funding of £100m in addition to existing support from the Science and Technology Facilities Council. The SKA HQ will be at Jodrell Bank in Cheshire, the home of a major radio observatory since 1945.
Bulletin compiled by Clive Down
(c) 2015 the Society for Popular Astronomy
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