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January 24, 2016 at 3:52 pm #8770AnonymousGuest
The SOCIETY for POPULAR ASTRONOMY
ronic News Bulletin No. 414 2016 January 24
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 OF A REAL NINTH PLANET
California Institute of Technology
Caltech researchers have found evidence of a giant planet tracing a bizarre, highly elongated orbit in the outer Solar System. The object, which the researchers have nicknamed Planet Nine, is supposed to have a mass about 10 times that of the Earth and orbits about 20 times further from the Sun on average than Neptune (which does so at an average distance of 2800 million miles). In fact, it would take the (still-hypothetical) planet between 10,000 and 20,000 years to orbit round the Sun. The researchers' evidence for the planet's existence came through mathematical modelling and computer simulations; they have not observed the object directly. There have been only two true planets discovered since ancient times, and this would be a third. The putative ninth planet — at 5,000 times the mass of Pluto — is sufficiently large that there should be no debate about whether it is a true planet. Unlike the class of smaller objects now known as dwarf planets, Planet Nine gravitationally dominates its neighbourhood of the Solar System. In fact, it dominates a region larger than any of the known planets.
The road to the theoretical discovery was not straightforward. In 2014, astronomers noted that 13 of the most distant objects in the Kuiper Belt are similar with respect to an obscure orbital feature. To explain that similarity, they suggested the possible presence of a small planet. A year-and-a-half-long collaboration began to investigate the distant objects. Fairly quickly it was realized that the six most distant objects from the original 13 under study all follow elliptical orbits that point in the same direction in space. That is particularly surprising because the outermost points of their orbits move around the Solar System, and they travel at different rates. It is almost like having six hands on a clock all moving at different rates, and when you happen to look up, they're all in exactly the same place. The odds of having that happen are something like 1 in 100. But on top of that, the orbits of the six objects arealso all tilted in the same way — pointing about 30 degrees downward in the same direction relative to the plane of the eight known planets. The probability of that happening is about 0.007%. It could not happen randomly, so something must be shaping the orbits.
The first possibility investigated by astronomers was that perhaps there are enough distant Kuiper-Belt objects — some of which have not yet been discovered — to exert the gravity needed to keep that sub-population clustered together. The researchers quickly ruled that out when it turned out that such a possibility would require the Kuiper Belt to have about 100 times the mass that it actually has. That left them with the idea of a planet. Their first instinct was to run simulations involving a planet in a distant orbit that encircled the orbits of the six Kuiper-Belt objects, acting like a giant lassoo to wrangle them into their alignment. That almost works but does not provide the observed eccentricities precisely. Then, effectively by accident, the team noticed that if they ran their simulations with a massive planet in an anti-aligned orbit — an orbit in which the planet's closest approach to the Sun, or perihelion, is 180 degrees away from the perihelion of all the other objects and known planets — the distant Kuiper-Belt objects in the simulation assumed the alignment that is actually observed. Through a mechanism known as mean-motion resonance, the anti-aligned orbit of the ninth planet actually prevents the Kuiper-Belt objects from colliding with it and keeps them aligned. As orbiting objects approach each other they exchange energy. So, for example, for every four orbits Planet Nine makes, a distant Kuiper-Belt object might complete nine orbits. They never collide. Instead, like a parent maintaining the arc of a child's swing by periodic pushes, Planet Nine nudges the orbits of distant Kuiper-Belt objects such that their configuration with relation to the planet is preserved.
Planet Nine's existence helps to explain more than just the alignment of the distant Kuiper-Belt objects. It also provides an explanation for the curious orbits that two of them trace. The first of those objects, dubbed Sedna, was discovered in 2003. Unlike standard-variety Kuiper-Belt objects, which can get gravitationally 'kicked out' by Neptune but can then return back to it, Sedna never gets very close to Neptune. A second object like Sedna, known as 2012 VP113, was announced in 2014. The presence of Planet Nine in its proposed orbit naturally produces Sedna-like objects by taking a standard Kuiper-Belt object and slowly pulling it away into an orbit less connected to Neptune. But the real clincher for the researchers was the fact that their simulations also predicted that there would be objects in the Kuiper Belt on orbits inclined perpendicularly to the plane of the planets. In the last three years, observers have identified four objects tracing orbits roughly along one perpendicular line from Neptune and one object along another. Where did Planet Nine come from and how did it end up in the outer Solar System? Scientists have long believed that the early Solar System began with four planetary cores that went on to grab all of the gas around them, forming the four gas planets — Jupiter, Saturn, Uranus, and Neptune. Over time, collisions and ejections shaped them and moved them out to their present locations. But there is no reason why there could not have been five cores, rather than four. Planet Nine could represent that fifth core, and if it got too close to Jupiter or Saturn, it could have been ejected into its distant, eccentric orbit. Researchers continue to refine their simulations and learn more about the planet's orbit and its influence on the distant Solar System. Meanwhile, astronomers have begun searching the skies for it. Only a rough orbit is indicated, not the precise location of the planet. If the planet happens to be close to its perihelion, astronomers should be able to find it in images captured by previous surveys. If it is in the most distant part of its orbit, the world's largest telescopes will be needed to see it. If, however, Planet Nine is now located anywhere in between, many telescopes might have a shot at finding it.
ETA CARINAE 'TWINS' FOUND IN OTHER GALAXIES
Space Telescope Science Institute (STScI)
Eta Carinae, the most luminous and massive stellar system within 10,000 light-years of us, is best known for an enormous eruption seen in 1843 that ejected an amount of material at least 10 times the Sun's mass into space. That expanding veil of gas and dust, which still shrouds Eta Carinae, makes it the only object of its kind known in our Galaxy. Now a study using archival data from the Spitzer and Hubble space telescopes has found five similar objects in other galaxies. The most massive stars are always rare, but they have tremendous impact on the chemical and physical evolution of their host galaxy. Such stars produce and distribute large amounts of different chemical elements and eventually explode as supernovae. Located about 7,500 light-years away in the southern constellation of Carina, Eta Carinae outshines the Sun by 5 million times. It is a binary system that consists of two massive stars in a 5.5-year orbit. Astronomers estimate that the more massive star has about 90 times the Sun's mass, while the smaller companion may exceed 30 solar masses. As one of the nearest laboratories for studying high-mass stars, Eta Carinae has been a unique astronomical touchstone since its eruption in 1843. To try to understand why the eruption occurred and how it relates to the evolution of massive stars, astronomers needed to see additional examples. Catching rare stars during the short-lived aftermath of a major outburst approaches needle-in-a-haystack levels of difficulty, and nothing matching Eta Carinae had been found previously. Astronomers felt sure that others must be out there, it was really a matter of deciding what to look for and of being persistent.
The researchers developed an optical and infrared fingerprint for identifying possible Eta Carinae twins. Dust forms in gas ejected by a massive star. The dust dims the star's ultraviolet and visible light, but it absorbs and re-radiates that energy as heat at longer, mid-infrared wavelengths. With Spitzer, a steady increase in brightness starting at around 3 microns and peaking between 8 and 24 microns could be seen. By comparing that emission to the dimming seen in Hubble's optical images, it could be determined how much dust was present and compare it to the amount seen around Eta Carinae. An initial survey of seven galaxies from 2012 to 2014 did not turn up any Eta twins, underlining their rarity. It did, however, identify a class of less-massive and less-luminous stars of scientific interest, demonstrating that the search was sensitive enough to find Eta-like stars had they been present. In a follow-up survey in 2015, the team found two candidate Eta twins in the galaxy M83, located 15 million light-years away, and one each in NGC 6946, M101, and M51, between 18 and 26 million light-years away. Those five objects mimic the optical and infrared properties of Eta Carinae, indicating that each very likely contains a high-mass star buried in five to 10 solar masses of gas and dust. Further study should enable astronomers to estimate more precisely their physical properties.
SECOND-LARGEST BLACK HOLE IN MILKY WAY
National Astronomical Observatory of Japan
Astronomers using the Nobeyama 45-m radio telescope have detected signs of an invisible black hole with a mass of 100,000 solar masses near the centre of the Milky Way. The team assumes that that possible 'intermediate-mass' black hole is a key to understanding the birth of the super-massive black holes located in the centres of galaxies. The observers found an enigmatic gas cloud, called CO-0.40-0.22, only 200 light-years away from the centre of the Milky Way. What makes CO-0.40-0.22 unusual is its surprisingly great velocity dispersion: the cloud contains gas with a very wide range of velocities. To investigate the detailed structure, the team observed CO-0.40-0.22 again to obtain 21 emission lines from 18 molecules. The results show that the cloud has an elliptical shape and consists of two components: a dense component extending 10 light-years with a small velocity dispersion, and a compact but low-density component with the very large velocity dispersion of 100 km/s. What makes that velocity dispersion so wide? There are no holes inside the cloud. Also, X-ray and infrared observations did not find any compact objects. Those features indicate that the velocity dispersion is not caused by a local energy input, such as supernova explosions. The team performed a simple simulation of gas clouds flung out by a strong-gravity source. In the simulation, the gas clouds are first attracted by the source and their speeds increase as they approach it, reaching maxima at the closest point to the object. After that the clouds continue past the object and their speeds decrease. The team found that a model using a gravity source with 100,000 times the mass of the Sun in a region with a radius of 0.3 light-years provided the best fit to the observed data. In view of the fact that no compact objects are seen in X-ray or infrared observations, the best candidate for the compact massive object seems to be a black hole.
If that is the case, this is the first detection of an intermediate-mass black hole. Astronomers already know about two sizes of black holes: stellar-mass black holes, formed after the explosions of very massive stars; and super-massive black holes (SMBH) often found at the centres of galaxies. The masses of SMBHs range from several million to billions of times the mass of the Sun. A number of SMBHs has been found, but no one knows how they are formed. One idea is that they are formed from mergers of many intermediate-mass black holes. But that raises a problem, because so far no firm observational evidence for intermediate-mass black holes has been found. If the cloud CO-0.40-0.22, located 'only' 200 light-years away from Sgr A* (the 400-million-solar-mass SMBH at the centre of the Milky Way), contains an intermediate-mass black hole, it might support the intermediate-mass-merger scenario of SMBH evolution. The results open a new way to search for black holes with radio telescopes. Recent observations have revealed that there is a number of wide-velocity-dispersion compact clouds similar to CO-0.40-0.22. The team proposes that some of those clouds might contain black holes. A study suggested that there are 100 million black holes in the Milky Way Galaxy, but X-ray observations have found only dozens so far. Most of the black holes may be 'dark' and very difficult to see directly at any wavelength. Investigations of gas motion with radio telescopes may provide a complementary way to search for dark black holes.
'GREEN PEA' GALAXIES AND EARLY UNIVERSE EVOLUTION
University of Virginia
Newly formed dwarf galaxies may have caused the Universe to heat up about 13 billion years ago, according to new work by an international team of scientists. The finding opens an avenue to better understanding of the early period of the Universe's 14-billion-year history. In the period of several hundred thousand years after the Big Bang, the Universe was so hot and dense that matter was ionized instead of being in a neutral form. But 380,000 years later, the expansion of the Universe had cooled it enough for matter to become neutral and for the first structures of the Universe to form — gas clouds of hydrogen and helium. Gravity then made such gas clouds grow in mass and collapse to form the first stars and galaxies. Then, about one billion years after the Big Bang, another important transformation occurred: the Universe re-heated, and hydrogen — the most abundant element — became ionized again, as it had been shortly after the Big Bang, an event which astronomers call 'cosmic re-ionization'. How that happened is still debated. Astronomers have long thought that galaxies were responsible for that transformation.
Using data from an ultraviolet spectrometer on the Hubble space telescope, the team discovered a 'nearby' compact dwarf galaxy emitting a large number of ionizing photons into the intergalactic medium (the space between galaxies). Scientists believe that such photons are responsible for the Universe's re-ionization. The galaxy appears to be an excellent local analogue of the numerous dwarf galaxies thought to be responsible for the re-ionization of the early Universe. The finding is significant, because it gives us a good idea of where to look to learn about the re-ionization phenomenon, which took place early in the formation of the universe that became the Universe we have today. Normal matter in the early Universe consisted mostly of gas. Stars and star clusters are born from clouds of gas, forming the first galaxies. Ultraviolet radiation emitted by those stars contains numerous ionizing photons. For that reason, scientists have long suspected that galaxies were responsible for cosmic re-ionization. However, for re-ionization to occur, galaxies must eject the photons into the intergalactic medium; otherwise, they are easily absorbed by the gas and dust in the galaxies where they originate before they can escape.
Despite 20 years of intensive searching, no galaxy emitting sufficient ionizing radiation had been found, and the mechanism by which the Universe became re-ionized remained a mystery. In an effort to solve that problem, the international research team proposed to observe 'green-pea' galaxies. Discovered in 2007, those galaxies represent a special and rare class in the nearby Universe. They appear green to light sensors, and are round and compact, like a pea. They are believed to host stellar explosions or winds strong enough to eject ionizing photons. The team examined data from the Sloan Digital Sky Survey — a data base of more than a million galaxies. From that survey, they identified approximately 5,000 galaxies that match their criteria: very compact galaxies emitting very intense UV radiation. Researchers selected five galaxies for observation with the Hubble telescope. Using Hubble's UV-radiation-detecting capabilities, the research team found that the 'green-pea' galaxy J0925+1403, located at a distance of three billion light-years, was ejecting ionizing photons with an intensity never seen before — about an 8% ejection. That fundamental discovery shows that galaxies of that type could explain cosmic re-ionization, supporting the most common hypothesis for that phenomenon.
COLOSSAL STAR EXPLOSION
Astronomers have seen what could be the most powerful supernova ever detected. The exploding star was first observed in June last year but is still radiating vast amounts of energy. At its peak, the event was 200 times more powerful than a typical supernova, making it shine with 570 billion times the brightness of the Sun (absolute magnitude about -20). Researchers think that the explosion and ongoing activity have been boosted by a very dense, very strongly magnetized, remnant object called a magnetar. That object, created as the supernova got going, is probably no bigger than a city such as London, and is probably spinning at a fantastic rate — perhaps a thousand times a second. But it probably also is slowing, and as it does so, it is dumping that rotational energy into the expanding shroud of gas and dust thrown off in the explosion. The super-luminous supernova was observed some 3.8 billion light-years away by the 'All-Sky Automated Survey for SuperNovae' (ASAS-SN). That uses a suite of camera lenses at Cerro Tololo, Chile, to sweep the sky for sudden brightenings. Follow-up observations with larger facilities are then used to investigate objects in more detail. The intention of ASAS-SN is to get better statistics on the different types of supernovae and where they are occurring in the cosmos.
Astronomers have long been fascinated by those monster explosions and have come to recognize just how important they are to the story of how the Universe has evolved. Not only do they forge the heavier chemical elements in nature but their shock waves disturb the space environment, stirring up the gas and dust from which the next generation of stars will be formed. The source star for the recent supernova must have been 50 to 100 times the mass of the Sun. Such stars begin very voluminous but then shed a lot of mass in great winds that blow out into space. So, by the time that star blew up, it was probably much reduced in size. It would have been very hot, however, about 100,000° at the surface. Basically, it would have got rid of all of its hydrogen and helium, leaving just the material that had been 'burnt' into carbon and oxygen. There are signs that the supernova may be about to fade, and the team has observing time on the Hubble telescope in the coming weeks to try to understand the mechanisms driving the supernova.
MOST DISTANT MASSIVE GALAXY CLUSTER
Massachusetts Institute of Technology
The early Universe was a chaotic mess of gas and matter that only began to coalesce into distinct galaxies hundreds of millions of years after the Big Bang. It would take several billion more years for such galaxies to assemble into massive galaxy clusters — or so scientists had thought. Now astronomers have detected a massive, sprawling, churning galaxy cluster that formed only 3.8 billion years after the Big Bang. Located in Bootes, 10 billion light years from us and potentially comprising thousands of individual galaxies, the megastructure is about 1,000 times more massive than the Milky Way galaxy. The cluster, named IDCS J1426.5+3508 (or IDCS 1426), is the most massive cluster of galaxies yet discovered in the first 4 billion years after the Big Bang. IDCS 1426 appears to be undergoing a substantial upheaval: the researchers observed a bright knot of X-rays, slightly off-centre in the cluster, indicating that the cluster's core may have shifted some hundred thousand light-years from its centre. The scientists surmise that the core may have been dislodged by a violent collision with another massive galaxy cluster, causing the gas within the cluster to slosh around. Such a collision may explain how IDCS 1426 formed so quickly in the early Universe, at a time when individual galaxies were only beginning to take shape. In the grand scheme of things, galaxies probably did not start forming until the Universe was relatively cool, and yet this cluster seems to have been formed 'shortly' after that.
Galaxy clusters are conglomerations of hundreds to thousands of galaxies bound together by gravity. They are the most massive structures in the Universe, and those that are relatively 'nearby', such as the Virgo cluster, are extremely bright and easy to locate in the sky. However, finding galaxy clusters that are farther away in space — and further back in time — is a difficult and uncertain exercise. In 2012, scientists using the Spitzer space telescope first detected signs of IDCS 1426 and made some initial estimates of its mass. To get a more precise estimate of the mass, the team used data from several observatories: Hubble, Keck, and the Chandra X-ray observatory. Both the Hubble and Keck observatories recorded optical data from the cluster, which the researchers analyzed to determine the amount of bending of light round the cluster as a result ofgravitational lensing. They also examined X-ray data from the Chandra observatory to get a sense of the temperature of the cluster. High temperature objects give off X-rays, and the hotter a galaxy cluster,the more the gas within that cluster has been compressed, making the cluster more massive. From the X-ray data, astronomers could also calculate the amount of gas in the cluster, which can be an indication of the amount of matter (mass) in it. All three methods gave roughly the same mass — about 2.5 times 10 to the power 14 solar masses. Now, the team is looking for individual galaxies within the cluster to get a sense for how such mega-structures could form in the early Universe.
ANCIENT GAS CLOUD MAY BE RELIC FROM FIRST STARS
Researchers have discovered a distant, ancient cloud of gas that may contain the signature of the very first stars that formed in the Universe. The gas cloud has an extremely small percentage of heavy elements, such as carbon, oxygen and iron — less than a thousandth the fraction observed in the Sun. It is many billions of light-years away from the Earth, and is observed as it was just 1.8 billion years after the Big Bang. The observations were made by the Very Large Telescope in Chile. Heavy elements were not manufactured during the Big Bang; they were made later by stars. The first stars were made from completely pristine gas, and astronomers think that they formed quite differently from stars today. The researchers say that soon after forming, those first stars — known as Population III stars — exploded as powerful supernovae, spreading their heavy elements into the surrounding clouds of gas. Those clouds then carried a chemical record of the first stars and their deaths, and that record can be read like a fingerprint. Previous gas clouds found by astronomers show a higher enrichment level of heavy elements, so they were probably polluted by more recent generations of stars, obscuring any signature from the first stars. The newly observed cloud is the first one to show the tiny heavy-element fraction expected for a cloud enriched only by the first stars. The researchers hope to find more such systems, where they can measure the ratios of several different elements. By finding new clouds where more elements can be detected, astronomers may be able to test for the unique pattern of abundances expected for enrichment by the first stars.
FOUR NEW ELEMENTS FOR PERIODIC TABLE
Confirmation that four new elements — those with atomic numbers 113, 115, 117 and 118 — have been synthesized has come from the International Union of Pure and Applied Chemistry (IUPAC), completing the seventh row of the Periodic Table. The groups credited for creating them, in Japan, Russia and the US, have spent several years gathering enough evidence to convince experts from IUPAC and its physics equivalent, the International Union of Pure and Applied Physics, of the elements' existence. All four are highly unstable super-heavy metals that exist only for a fraction of a second. They are made by bombarding heavy-metal targets with beams of ions, and can usually only be detected by measuring the radiation and other nuclides produced as they decay. Element 113, currently known by its place-holder name ununtrium, is the first to be discovered in East Asia. It was created by firing a beam of zinc-70 at a target made of bismuth-209. Elements 115 (ununpentium) and 117 (ununseptium) were discovered by groups collaborating across institutions in the US and Russia. Element 118 (ununoctium) was discovered in the US. Now that the elements have been officially discovered, the institutions responsible will get to choose permanent names for them. But it will be a while before the textbooks and posters can be updated, as the new names and symbols will have to be approved by the inorganic chemistry division of IUPAC and submitted for public review. Various rules govern the names that can be given to new elements, which can be inspired by nature, mythology, people or places.
Bulletin compiled by Clive Down
(c) 2016 the Society for Popular Astronomy
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