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May 1, 2016 at 4:04 pm #8866Anonymous
Electronic News Bulletin No. 421 2016 May 1
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/
SUPERNOVA IRON FOUND ON MOON
Technical University of Munich (TUM)
In many cases, a 'dying' star ends its 'life' as a supernova, a cataclysmic explosion, shooting the majority of the star's material, primarily new chemical elements created during the explosion, out into space. At least one such supernova appears to have occurred 'close' to the Solar System approximately two million years ago. Evidence of that has been found on Earth in the form of increased concentrations of the iron isotope 60Fe detected in Pacific-Ocean deep-sea crusts and in ocean-floor sediment samples. That evidence is highly compelling: the radioactive 60Fe isotope is created almost exclusively in supernova explosions. It has a half-life of 2.62 million years, short compared to the age of the Solar System, so any radioactive 60Fe originating from the time of the Solar System's birth would long ago have decayed into stable elements and thus should no longer be found on Earth.
Samples of the surface of the Moon were gathered between 1969 and 1972 during Apollo lunar missions 12, 15 and 16, which brought the lunar material back to Earth. It is conceivable that 60Fe can occur on the Moon also as the result of bombardment by cosmic particles, since those particles do not break up there by colliding with air molecules, as is the case with the Earth's atmosphere. Instead they impact on the lunar surface directly and can thus result in transmutation of elements. But that can account for only a very small proportion of the 60Fe found. Since the Moon generally provides a better cosmic record than the Earth, scientists were also able to specify for the first time an upper limit for the flow of 60Fe that must have reached the Moon. Among other things that also made it possible for the researchers to infer the distance of the supernova event: the measured 60Fe flow corresponds to a supernova at a distance of about 300 light-years. The lunar samples were investigated with the high-sensitivity accelerator mass spectrometer of the Maier-Leibnitz Laboratory near Munich.
TRANSIT OF MERCURY
On May 9 there will be a transit of Mercury, when that planet will pass directly in front of the Sun. The last time that that happened was in 2006, and the next occasions will be in 2019 and 2032. During the transit, which takes place in the afternoon and early evening in the UK, Mercury will appear as a black dot silhouetted against the bright surface of the Sun. From the UK the transit begins at 12.12 BST, when the limb of Mercury appears first to touch the limb of the Sun, and ends at 19.42 BST when the limb of the silhouetted planet appears to leave the Sun. Observers in different locations will see the transit taking place at slightly different times. The entire event is visible from most of Western Europe, the western part of North and West Africa, the eastern part of North America and most of South America. Most of the transit (either ending with sunset or starting at sunrise) will be visible from the rest of North and South America, the eastern half of the Pacific, the rest of Africa and most of Asia. Observers in eastern Asia, south-eastern Asia and Australia will not be able to see the transit at all.
Mercury completes an orbit around the Sun every 88 days, and passes between the Earth and the Sun every 116 days. As the orbit of Mercury around the Sun is tilted with respect to that of the Earth, the planet usually appears to pass above or below the Sun. A transit can only take place when the Earth, Mercury and the Sun are exactly in line in three dimensions. There are 13 or 14 transits of Mercury each century, so they are fairly rare events, though each one can typically be seen from a large area of the Earth's surface. A transit was first seen in 1631, two decades after the invention of the telescope, by the French astronomer Pierre Gassendi. The most recent transit of Mercury visible in the UK was in 2003 (the 2006 event was visible in the western hemisphere). In transit, Mercury blocks out only a tiny part of the light from the Sun, so the event should NOT be viewed with the unaided eye. Looking at the Sun without appropriate protection, either during the transit or at any other time, can cause serious and permanent damage to the eyes.
CASSINI SAMPLES INTERSTELLAR DUST
The Cassini spacecraft has detected the faint but distinct signature of dust coming from beyond the Solar System. Cassini has been in orbit around Saturn since 2004, studying the planet, its rings and its moons. The spacecraft has also sampled millions of ice-rich dust grains with its cosmic-dust analyzer instrument. The vast majority of the sampled grains originate from active jets that spray from the surface of Saturn's tectonically active moon Enceladus. But among the myriad microscopic grains collected by Cassini, a special few — just 36 grains — stand out. Scientists conclude that those specks of material came from interstellar space — the space between the stars. Alien dust in the Solar System is not unanticipated. In the 1990s, the Ulysses mission made the first in-situ observations of such material, which were later confirmed by the Galileo spacecraft. The dust was traced back to the local interstellar cloud — a nearly empty bubble of gas and dust through which the Solar System is travelling with a distinct direction and speed. From that discovery, astronomers always hoped that they would be able to detect such interstellar interlopers at Saturn with Cassini. On average, a few such dust grains were captured per year, travelling at high speed and on a specific path quite different from that of the usual icy grains collected around Saturn. The dust grains were speeding through the Saturn system at over 72,000 km/h, fast enough to avoid being trapped inside the Solar System by the gravity of the Sun and its planets.
Importantly, unlike Ulysses and Galileo, Cassini was able to analyze the composition of the dust, showing it to be made of a very specific mixture of minerals, not ice. The grains all had a surprisingly similar chemical make-up, containing major rock-forming elements like magnesium, silicon, iron and calcium in average cosmic proportions. Conversely, more reactive elements like sulphur and carbon were found to be less abundant compared to their average cosmic abundance. Cosmic dust is produced when stars die, but with the vast range of types of stars in the Universe, astronomers naturally expected to encounter a huge range of dust types over the period of the study. Stardust grains are found in some types of meteorites, which have preserved them since the birth of the Solar System. They are generally old, pristine and diverse in their composition. But surprisingly, the grains detected by Cassini are not like that. They have apparently been made rather uniform through some repetitive processing in the interstellar medium. Scientists speculate on how such processing of dust might take place. Dust in a star-forming region could be destroyed and re-condense multiple times as shock waves from dying stars passed through, resulting in grains like the ones Cassini observed streaming into the Solar System.
SMALL MOON ORBITING DWARF PLANET MAKEMAKE
NASA/Goddard Space Flight Center
Scientists using the Hubble telescope have discovered a small, dark moon orbiting Makemake, the second-brightest icy dwarf planet — after Pluto — in the Kuiper Belt. That planet, discovered in 2005, is named for a creation deity of the Rapa Nui people of Easter Island. The moon — provisionally designated S/2015 (136472) 1 and nicknamed MK 2 — is more than 1,300 times fainter than Makemake. MK 2 was seen approximately 13,000 miles from the planet, and its diameter is estimated to be 100 miles (Makemake itself is 870 miles). The Kuiper Belt is a vast reservoir of leftover frozen material from the construction of the Solar System 4500 million years ago and is home to several dwarf planets. Some of them have known satellites, but this is the first discovery of a companion object to Makemake. Makemake is one of five dwarf planets recognized by the International Astronomical Union. The observations were made in 2015 April with Hubble's 'Wide-Field Camera 3'. The observing team used the same Hubble technique to observe the moon as they did for finding the small satellites of Pluto in 2005, 2011, and 2012. Several previous searches around Makemake had turned up empty. Preliminary estimates show that the moon's orbit seems to be edge-on, so often the moon would be missed because it gets lost next to the relatively bright Makemake. A moon's discovery can provide valuable information on the dwarf-planet system. By measuring the moon's orbit, astronomers can calculate a mass for the system and gain insight into its evolution. Uncovering the moon also reinforces the idea that most dwarf planets have satellites.
Finding this moon increases the parallels between Pluto and Makemake. Both objects are already known to be covered in frozen methane. As was done with Pluto, further study of the satellite will easily reveal the density of Makemake, a key result that will indicate if the bulk compositions of Pluto and Makemake are also similar. The researchers will need more Hubble observations to make accurate measurements to determine if the moon's orbit is elliptical or circular. Preliminary estimates indicate that if the moon is in a circular orbit, it must complete a circuit around Makemake in 12 days or longer. Determining the shape of the moon's orbit will help settle the question of its origin. A tight circular orbit means that MK 2 is probably the product of a collision between Makemake and another Kuiper-Belt object. If the moon is in a large, elongated orbit, it is more likely to be an object captured from the Kuiper Belt. Either event would probably have occurred several thousand million years ago, when the Solar System was young. The discovery may have solved one mystery about Makemake. Previous infrared studies revealed that while Makemake's surface is almost entirely bright and very cold, some areas appear less cold than others. Astronomers had suggested that that discrepancy may be due to the Sun warming discrete dark patches on Makemake's surface. However, unless Makemake is in a special orientation, any dark patches should make its brightness vary substantially as it rotates, but little variability has ever been observed.
THE MISSING BROWN DWARFS
Leibniz-Institut fur Astrophysik Potsdam (AIP)
When re-analyzing catalogued and updated observational data of brown dwarfs in the solar neighbourhood, astronomers have found that a significant number of nearby brown dwarfs should still be out there, awaiting discovery. Brown dwarfs are objects that are too large to be called planets, yet too small to be stars. Having masses less than 7% of the mass of the Sun, they are unable to create sufficient pressure and heat in their interiors to ignite hydrogen-to-helium fusion, a fundamental physical mechanism by which stars generate radiation. In that sense brown dwarfs are 'failed stars'. It is therefore important to know how many brown dwarfs really exist in different regions of the sky in order to achieve a better understanding of star formation and of the motion of stars in the Milky Way. A team of astronomers has taken a careful look at the distribution of nearby known brown dwarfs from a point of view that was not looked from before. To their surprise they discovered a significant asymmetry in the spatial configuration, strongly deviating from the known distribution of stars. By projecting the nearby brown dwarfs onto the Galactic plane they realized that half of the sky is practically empty of them. That was an unexpected result, as they had been looking at an environment that ought to be homogeneous. The empty region overlaps with a large part of the northern sky.
The scientists concluded that there should be many more brown dwarfs in the solar neighbourhood that are yet to be discovered and that will fill the observed gap. If they are right, that would mean that star formation fails significantly more often than has been thought, producing one brown dwarf for every four stars. In any case, it appears that the established picture of the solar neighbourhood and of its brown-dwarf population will have to be re-thought. It is quite possible that not only are brown dwarfs still hiding in the observational data, but also other objects with even smaller, planet-like masses.
LARGE GALAXY ORBITING MILKY WAY
A large galaxy orbiting the Milky Way has seemingly appeared out of nowhere. The newly discovered dwarf galaxy, which has been named Crater 2, sits around 400,000 light-years away, and has already earned the title of the fourth-largest known galaxy circling our own. But how does a galaxy that big stay hidden for so long? Its stars are so diffuse that it is remarkably dark, and it has been masked until now by its brighter neighbours. In fact, it is one of the dimmest galaxies ever detected. As far as we know, the Milky Way is orbited by 49 other galaxies, but this research suggests that there may be other dark galaxies in our cosmic neighbourhood, that have remained hidden because of their diffuse, ghostly appearance. Crater 2 was first detected in January, when astronomers used a computer algorithm to study images taken by the Very Large Telescope in Chile, and then pinpoint regions where there might be unusual clustering of stars — one of those clusters turned out to be Crater 2.
Because galaxies do not tend to have defined edges, astronomers often describe them in terms of their 'half-light diameter', which basically means the diameter of the part of the galaxy that emits half its light. On the basis of such an analysis so far, the astronomers calculate that Crater 2 has a half-light diameter of around 7,000 light-years, which means if we could see it in the night sky, it would look twice as big as the full Moon — but also very diffuse, because of how far apart its stars are. In the last 10 years alone, the number of known satellite galaxies has doubled, which suggests we still have a lot to learn about the galaxies orbiting our own. In fact, there is evidence that Crater 2 itself might belong to a small group of galaxies that are falling into the Milky Way; it seems to be aligned with a number of other astronomically nearby objects.
ALIGNMENT OF BLACK HOLES
Deep radio imaging by researchers in the University of Cape Town and University of the Western Cape, in South Africa, has revealed that supermassive black holes in a region of the distant Universe are all spinning out radio jets in the same direction — most likely a result of primordial mass fluctuations in the early Universe. The new discovery is of an alignment of the jets of galaxies over a large volume of space, a finding made possible by a three-year deep imaging survey of the radio waves coming from a region called ELAIS-N1, with the Giant Metre-wave Radio Telescope (GMRT). The jets are produced by the super-massive black holes at the centres of the galaxies, and the only way for the alignment to exist is if the black holes are all spinning in the same direction. Since the black holes don't know about each other, or have any way of exchanging information or influencing each other directly over such vast scales, the spin alignment must have occurred during the formation of the galaxies in the early Universe. That implies that, in the structure of that volume of space, there is a coherent spin that arose from the primordial mass fluctuations that seeded the creation of the large-scale structure of the Universe.
The finding was not planned for: the initial investigation was to explore the faintest radio sources, using the best available telescopes — a first view into the kind of Universe that will be revealed by the South African MeerKAT radio telescope and the Square Kilometre Array (SKA), the world's most powerful radio telescope. Earlier observational studies had detected deviations from uniformity (so-called isotropy) in the orientations of galaxies. But the new radio images offer a first opportunity to use jets to reveal alignments of galaxies on physical scales up to 100 Mpc. And measurements of the total intensity of radio emission of galaxy jets have the advantage of not being affected by effects such as scattering, extinction and Faraday rotation, which may be an issue for other studies. The presence of alignments and certain preferred orientations can shed light on the orientation and evolution of the galaxies, in relation to large-scale structures, and the motions in the primordial matter fluctuations that gave rise to the structure of the Universe. What could those large-scale environmental influences during galaxy formation or evolution have been? There are several options: cosmic magnetic fields, fields associated with exotic particles (axions), and cosmic strings are only some of the possible candidates that could create an alignment in galaxies even on scales larger than galaxy clusters. A large-scale spin distribution has never been predicted by theories, and an unknown phenomenon like that presents a challenge that theories about the origins of the Universe need to account for.
NEW INSIGHT INTO HOW UNIVERSE WORKS
NASA/Goddard Space Flight Center
On Sept. 14, waves of energy travelling for more than a thousand million years gently rattled space-time in the vicinity of the Earth. The disturbance, produced by a pair of merging black holes, was captured by the Laser Interferometer Gravitational-Wave Observatory (LIGO) facilities in Hanford, Washington, and Livingston, Louisiana. The event marked the first-ever detection of gravitational waves and opens a new scientific window on how the Universe works. Less than half a second later, the Gamma-ray Burst Monitor (GBM) on the Fermi Gamma-ray Space Telescope picked up a brief, weak burst of high-energy light consistent with the same part of the sky. Analysis of the burst suggests just a 0.2% chance of its simply being a random coincidence. Gamma-rays arising from a black-hole merger would be a landmark finding because black holes are expected to merge 'cleanly', without producing any sort of light. Detecting light from a gravitational-wave source will enable a much deeper understanding of the event. Fermi's GBM sees the entire sky not blocked by the Earth and is sensitive to X-rays and gamma rays with energies between 8,000 and 40 million electron volts (eV). For comparison, the energy of visible light ranges between about 2 and 3 eV. With its wide energy range and large field of view, the GBM is the premier instrument for detecting light from short gamma-ray bursts (GRBs), which last less than two seconds. They are widely thought to occur when orbiting compact objects, like neutron stars and black holes, spiral inward and crash together. Those same systems also are suspected to be prime producers of gravitational waves.
Currently, gravitational-wave observatories possess relatively blurry vision. That will improve in time as more facilities begin operation, but for the September event, dubbed GW150914 after the date, LIGO scientists could only trace the source to an arc of sky spanning an area of about 600 square degrees. Less than half a second after LIGO detected gravitational waves, the GBM picked up a faint pulse of high-energy X-rays lasting only about a second. The burst effectively occurred beneath Fermi and at a high angle to the GBM detectors, a situation that limited their ability to establish a precise position. Fortunately, the Earth blocked a large swath of the burst's likely location as seen by Fermi at the time, allowing scientists to narrow down the burst's position. The GBM team calculates that there is less than a 0.2% chance that random fluctuations would have occurred in such close proximity to the merger. Assuming that the events are connected, the GBM localization and Fermi's view of the Earth combine to reduce the LIGO search area by about two-thirds, to 200 square degrees. With a burst better placed for the GBM's detectors, or one bright enough to be seen by Fermi's Large Area Telescope, even greater improvements are possible. The LIGO event was produced by the merger of two relatively large black holes, each about 30 times the mass of the Sun. Binary systems with black holes that big are not expected to be common, and many questions remain about the nature and origin of the system. Black-hole mergers were not expected to emit significant X-ray or gamma-ray signals because orbiting gas is needed to generate light. Theorists expected any gas around binary black holes would have been swept up long before their final plunge. For that reason, some astronomers view the GBM burst as most likely a coincidence and unrelated to GW150914. Others have developed alternative scenarios where merging black holes could create observable gamma-ray emission. It will take further detections to clarify what really happens when black holes collide.
MICE FLOWN IN SPACE SHOW LIVER DAMAGE
University of Colorado Anschutz Medical Campus
In a discovery with implications for long-term space flight and future missions to Mars, scientists have found that mice flown aboard the space shuttle Atlantis returned to Earth with early signs of liver disease. The mice studied spent 13.5 days aboard the space shuttle. When they returned, liver samples were collected. It was found that space flight appeared to activate specialized liver cells that may go on to induce scarring and cause long-term damage to the organ. The mice also lost lean muscle mass. For years scientists have studied the impact of space flight on human physiology but most of the research has focused on bone, muscle, brain and cardiovascular function. Yet studies suggesting that astronauts who spent time in space developed diabetes-like symptoms link microgravity with metabolism and point toward the liver, the major organ of metabolism, as a possible target of the space environment.
The team found that space flight resulted in increased fat storage in the liver, comparing pair-fed mice on Earth to those on the shuttle. That was accompanied by a loss of retinol, an animal form of Vitamin A, and changes to levels of genes responsible for breaking down fats. As a result, mice showed signs of non-alcoholic fatty liver disease (NAFLD) and potential early indicators for the beginnings of fibrosis, which can be one of the more progressive consequences of NAFLD. With NASA planning longer deep-space missions, including one to Mars which would take at least a year, the findings are significant. Whether or not this is a problem is an open question and scientists need to look at mice involved in longer-duration space flight to see if there are compensatory mechanisms that come into play that might protect them from serious damage. The stress of space flight and re-entry to Earth might have also played a role in the liver damage. Further study in this area is merited and analysis of tissues harvested in space from mice flown aboard the International Space Station for several months may help to determine whether long-term space flight might lead to more advanced hepatic injury and whether damage can be prevented.
Bulletin compiled by Clive Down
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