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  • richardmitnick 12:58 pm on April 18, 2017 Permalink | Reply
    Tags: , , , , , , EarthSky   

    From EarthSky: “Who needs dark energy?” 



    April 17, 2017
    Brian Koberlein

    Dark energy is thought to be the driver for the expansion of the universe. But do we need dark energy to account for an expanding universe?

    Image via Brian Koberlein/ One Universe at a Time.

    Our universe is expanding. We’ve known this for nearly a century, and modern observations continue to support this. Not only is our universe expanding, it is doing so at an ever-increasing rate. But the question remains as to what drives this cosmic expansion. The most popular answer is what we call dark energy. But do we need dark energy to account for an expanding universe? Perhaps not.

    The idea of dark energy comes from a property of general relativity known as the cosmological constant. The basic idea of general relativity is that the presence of matter https://briankoberlein.com/2013/09/09/the-attraction-of-curves/. As a result, light and matter are deflected from simple straight paths in a way that resembles a gravitational force. The simplest mathematical model in relativity just describes this connection between matter and curvature, but it turns out that the equations also allow for an extra parameter, the cosmological constant, that can give space an overall rate of expansion. The cosmological constant perfectly describes the observed properties of dark energy, and it arises naturally in general relativity, so it’s a reasonable model to adopt.

    In classical relativity, the presence of a cosmological constant simply means that cosmic expansion is just a property of spacetime. But our universe is also governed by the quantum theory, and the quantum world doesn’t play well with the cosmological constant. One solution to this issue is that quantum vacuum energy might be driving cosmic expansion, but in quantum theory vacuum fluctuations would probably make the cosmological constant far larger than what we observe, so it isn’t a very satisfactory answer.

    Despite the unexplainable weirdness of dark energy, it matches observations so well that it has become part of the concordance model for cosmology, also known as the Lambda-CDM model. Here the Greek letter Lambda is the symbol for dark energy, and CDM stands for Cold Dark Matter.

    In this model there is a simple way to describe the overall shape of the cosmos, known as the Friedmann–Lemaître–Robertson–Walker (FLRW) metric. The only catch is that this assumes matter is distributed evenly throughout the universe. In the real universe matter is clumped together into clusters of galaxies, so the FLRW metric is only an approximation to the real shape of the universe. Since dark energy makes up about 70% of the mass/energy of the universe, the FLRW metric is generally thought to be a good approximation. But what if it isn’t?

    A new paper argues just that. Since matter clumps together, space would be more highly curved in those regions. In the large voids between the clusters of galaxies, there would be less space curvature. Relative to the clustered regions, the voids would appear to be expanding similarly to the appearance of dark energy. Using this idea the team ran computer simulations of a universe using this cluster effect rather than dark energy. They found that the overall structure evolved similarly to dark energy models.

    That would seem to support the idea that dark energy might be an effect of clustered galaxies.

    It’s an interesting idea, but there are reasons to be skeptical. While such clustering can have some effect on cosmic expansion, it wouldn’t be nearly as strong as we observe. While this particular model seems to explain the scale at which the clustering of galaxies occur, it doesn’t explain other effects, such as observations of distant supernovae which strongly support dark energy. Personally, I don’t find this new model very convincing, but I think ideas like this are certainly worth exploring. If the model can be further refined, it could be worth another look.

    Paper: Gabor Rácz, et al. Concordance cosmology without dark energy. Monthly Notices of the Royal Astronomical Society Letters: DOI: 10.1093/mnrasl/slx026 (2017)

    Dark Energy Camera [DECam], built at FNAL

    DECam at Cerro Tololo, Chile, housing DECam

    See the full article here .

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  • richardmitnick 12:38 pm on April 15, 2017 Permalink | Reply
    Tags: , , , , EarthSky, , Is there life on Saturn’s moon?,   

    From EarthSky: “Is there life on Saturn’s moon?” 


    April 15, 2017
    Daniela Breitman

    Enceladus, one of 62 moons in a confirmed orbit around Saturn, has been in the spotlight since the Cassini spacecraft began orbiting Saturn, weaving among its moons and rings, in 2004. It was only when Cassini turned its instruments toward Enceladus that we learned of the moon’s powerful geysers and subsurface saltwater ocean. This week, scientists made another fascinating announcement about this Saturn moon. They say they now have strong evidence for a habitable area on the floor of Enceladus’ ocean. Their paper on this subject was published in the peer-reviewed journal Science on April 13, 2017.

    The ocean of Enceladus is covered by a layer of surface ice. The moon’s geysers emerge from the subsurface ocean through cracks in the ice. When the Cassini spacecraft flew through plumes of gas and icy particles that make up Enceladus’ geysers on October 28, 2015, it detected a significant amount of molecular hydrogen. Scientists confirmed this week that the best explanation for this observation is that hydrothermal reactions occurring on Enceladus’ ocean floor. They may be similar to hydrogen-generating interactions taking place at Earth’s hydrothermal vents.

    This discovery means the small, icy moon Enceladus might have a source of chemical energy that could be useful for living microbes, if any exist there.

    Scientists have suggested that water interacts with the rocky core of Enceladus, thereby producing hydrogen. The detection of molecular hydrogen in the plumes of Enceladus supports this idea. Image via NASA.

    Hydrothermal vents are common on Earth. They are fissures in the ocean crust through which geothermally heated water escapes. In other words, they are regions where water interacts with Earth’s magma. Earthly hydrothermal vents are home to many fascinating bacteria. Yellowstone’s Grand Prismatic Spring is an example of a hydrothermal area with a rich bacterial life.

    Life has not been discovered beneath the icy crust of Enceladus. But the detection of hydrogen is strong evidence that all the necessary conditions for life are present. Hunter Waite of the Southwest Research Institute in San Antonio and lead author of the new Enceladus study, said in a statement:

    Although we can’t detect life, we’ve found that there’s a food source there for it. It would be like a candy store for microbes.

    Microbes on Enceladus could produce their energy through a chemical reaction known as methanogenesis, which consists of burning hydrogen and carbon dioxide dissolved in the ocean water to form methane and water.

    This reaction is at the core of the development of life on Earth.

    The so-called tiger stripes and geysers of Enceladus, photographed by the Cassini-Huygens probe in October, 2015. Image via NASA.

    NASA/ESA/ASI Cassini Spacecraft

    ESA Huygens Probe from Cassini landed on Titan

    This Cassini image from 2005 shows Enceladus’ geysers – backlit – spewing into space. By flying the craft through the plume from geysers like this one, scientists obtained evidence for molecular hydrogen, possibly produced via hydrothermal processes on the floor on Enceladus’ ocean. Image via NASA.

    Scientists considered other explanations for Cassini spacecraft’s 2015 detection of molecular hydrogen within Enceladus’ geysers, for example, hydrogen leaking from the moon’s rocky core in ways other than hydrothermal reactions. The scientists who’ve studied these observations most closely, however, now feel that hydrothermal reactions are the best explanation.

    Liquid water, an energy source, and the right chemicals (carbon, hydrogen, nitrogen, oxygen, phosphorus and sulphur) are the three main requirements for life as we know it. Now scientists discovered all of these life-ingrediants – except phosphorus and sulphur – on Enceladus.

    The paper published in Science presents a detailed analysis of the possibility of methanogenesis on Enceladus. The calculations are inconclusive as to whether methanogenesis is happening or not around the hydrothermal vents of Enceladus. Nevertheless, this discovery is a big step in characterising the habitability of the ocean of Enceladus.

    Bottom line: In April, 2017, scientists announced that molecular hydrogen in the plumes of Enceladus, one of Saturn’s moons, may be due to methanogenesis, a process that implies microbial life.

    See the full article here .

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  • richardmitnick 2:33 pm on April 11, 2017 Permalink | Reply
    Tags: , , EarthSky, , Molecular clocks track human evolution   

    From EarthSky: “Molecular clocks track human evolution” 



    April 9, 2017
    Bridget Alex, Harvard University
    Priya Moorjani, Columbia University

    Our cells have a built-in genetic clock, tracking time… but how accurately?. Image via http://www.shutterstock.com

    DNA holds the story of our ancestry – how we’re related to the familiar faces at family reunions as well as more ancient affairs: how we’re related to our closest nonhuman relatives, chimpanzees; how Homo sapiens mated with Neanderthals; and how people migrated out of Africa, adapting to new environments and lifestyles along the way. And our DNA also holds clues about the timing of these key events in human evolution. The Conversation

    When scientists say that modern humans emerged in Africa about 200,000 years ago and began their global spread about 60,000 years ago, how do they come up with those dates? Traditionally researchers built timelines of human prehistory based on fossils and artifacts, which can be directly dated with methods such as radiocarbon dating and Potassium-argon dating. However, these methods require ancient remains to have certain elements or preservation conditions, and that is not always the case. Moreover, relevant fossils or artifacts have not been discovered for all milestones in human evolution.

    Analyzing DNA from present-day and ancient genomes provides a complementary approach for dating evolutionary events. Because certain genetic changes occur at a steady rate per generation, they provide an estimate of the time elapsed. These changes accrue like the ticks on a stopwatch, providing a “molecular clock.” By comparing DNA sequences, geneticists can not only reconstruct relationships between different populations or species but also infer evolutionary history over deep timescales.

    Molecular clocks are becoming more sophisticated, thanks to improved DNA sequencing, analytical tools and a better understanding of the biological processes behind genetic changes. By applying these methods to the ever-growing database of DNA from diverse populations (both present-day and ancient), geneticists are helping to build a more refined timeline of human evolution.

    How DNA accumulates changes

    Molecular clocks are based on two key biological processes that are the source of all heritable variation: mutation and recombination.

    Mutations are changes to the DNA code, such as when one nucleotide base (A, T, G or C) is incorrectly subbed for another.. Image via http://www.shutterstock.com

    Mutations are changes to the letters of DNA’s genetic code – for instance, a nucleotide Guanine (G) becomes a Thymine (T). These changes will be inherited by future generations if they occur in eggs, sperm or their cellular precursors (the germline). Most result from mistakes when DNA copies itself during cell division, although other types of mutations occur spontaneously or from exposure to hazards like radiation and chemicals.

    In a single human genome, there are about 70 nucleotide changes per generation – minuscule in a genome made up of six billion letters. But in aggregate, over many generations, these changes lead to substantial evolutionary variation.

    Scientists can use mutations to estimate the timing of branches in our evolutionary tree. First they compare the DNA sequences of two individuals or species, counting the neutral differences that don’t alter one’s chances of survival and reproduction. Then, knowing the rate of these changes, they can calculate the time needed to accumulate that many differences. This tells them how long it’s been since the individuals shared ancestors.

    Comparison of DNA between you and your sibling would show relatively few mutational differences because you share ancestors – mom and dad – just one generation ago. However, there are millions of differences between humans and chimpanzees; our last common ancestor lived over six million years ago.

    Bits of the chromosomes from your mom and your dad recombine as your DNA prepares to be passed on. Chromosomes image via http://www.shutterstock.com.

    Recombination, also known as crossing-over, is the other main way DNA accumulates changes over time. It leads to shuffling of the two copies of the genome (one from each parent), which are bundled into chromosomes. During recombination, the corresponding (homologous) chromosomes line up and exchange segments, so the genome you pass on to your children is a mosaic of your parents’ DNA.

    In humans, about 36 recombination events occur per generation, one or two per chromosome. As this happens every generation, segments inherited from a particular individual get broken into smaller and smaller chunks. Based on the size of these chunks and frequency of crossovers, geneticists can estimate how long ago that individual was your ancestor.

    Gene flow between divergent populations leads to chromosomes with mosaic ancestry. As recombination occurs in each generation, the bits of Neanderthal ancestry in modern human genomes becomes smaller and smaller over time. Image via Bridget Alex.

    Building timelines based on changes

    Genetic changes from mutation and recombination provide two distinct clocks, each suited for dating different evolutionary events and timescales.

    Because mutations accumulate so slowly, this clock works better for very ancient events, like evolutionary splits between species. The recombination clock, on the other hand, ticks at a rate appropriate for dates within the last 100,000 years. These “recent” events (in evolutionary time) include gene flow between distinct human populations, the rise of beneficial adaptations or the emergence of genetic diseases.

    The case of Neanderthals illustrates how the mutation and recombination clocks can be used together to help us untangle complicated ancestral relationships. Geneticists estimate that there are 1.5-2 million mutational differences between Neanderthals and modern humans. Applying the mutation clock to this count suggests the groups initially split between 750,000 and 550,000 years ago.

    At that time, a population – the common ancestors of both human groups – separated geographically and genetically. Some individuals of the group migrated to Eurasia and over time evolved into Neanderthals. Those who stayed in Africa became anatomically modern humans.

    An evolutionary tree displays the divergence and interbreeding dates that researchers estimated with molecular clock methods for these groups. Image via Bridget Alex.

    However, their interactions were not over: Modern humans eventually spread to Eurasia and mated with Neanderthals. Applying the recombination clock to Neanderthal DNA retained in present-day humans, researchers estimate that the groups interbred between 54,000 and 40,000 years ago. When scientists analyzed a Homo sapiens fossil, known as Oase 1, who lived around 40,000 years ago, they found large regions of Neanderthal ancestry embedded in the Oase genome, suggesting that Oase had a Neanderthal ancestor just four to six generations ago. In other words, Oase’s great-great-grandparent was a Neanderthal.

    Comparing chromosome 6 from the 40,000-year-old Oase fossil to a present-day human. The blue bands represent segments of Neanderthal DNA from past interbreeding. Oase’s segments are longer because he had a Neanderthal ancestor just 4–6 generations before he lived, based on estimates using the recombination clock. Image via Bridget Alex.

    The challenges of unsteady clocks

    Molecular clocks are a mainstay of evolutionary calculations, not just for humans but for all forms of living organisms. But there are some complicating factors.

    The main challenge arises from the fact that mutation and recombination rates have not remained constant over human evolution. The rates themselves are evolving, so they vary over time and may differ between species and even across human populations, albeit fairly slowly. It’s like trying to measure time with a clock that ticks at different speeds under different conditions.

    One issue relates to a gene called Prdm9, which determines the location of those DNA crossover events. Variation in this gene in humans, chimpanzees and mice has been shown to alter recombination hotspots – short regions of high recombination rates. Due to the evolution of Prdm9 and hotspots, the fine-scale recombination rates differ between humans and chimps, and possibly also between Africans and Europeans. This implies that over different timescales and across populations, the recombination clock ticks at slightly different rates as hotspots evolve.

    Another issue is that mutation rates vary by sex and age. As fathers get older, they transmit a couple extra mutations to their offspring per year. The sperm of older fathers has undergone more rounds of cell division, so more opportunities for mutations. Mothers, on the other hand, transmit fewer mutations (about 0.25 per year) as a female’s eggs are mostly formed all at the same time, before her own birth. Mutation rates also depend on factors like onset of puberty, age at reproduction and rate of sperm production. These life history traits vary across living primates and probably also differed between extinct species of human ancestors.

    Consequently, over the course of human evolution, the average mutation rate seems to have slowed significantly. The average rate over millions of years since the split of humans and chimpanzees has been estimated as about 1×10?? mutations per site per year – or roughly six altered DNA letters per year. This rate is determined by dividing the number of nucleotide differences between humans and other apes by the date of their evolutionary splits, as inferred from fossils. It’s like calculating your driving speed by dividing distance traveled by time passed. But when geneticists directly measure nucleotide differences between living parents and children (using human pedigrees), the mutation rate is half the other estimate: about 0.5×10?? per site per year, or only about three mutations per year.

    For the divergence between Neanderthals and modern humans, the slower rate provides an estimate between 765,000-550,000 years ago. The faster rate, however, would suggest half that age, or 380,000-275,000 years ago: a big difference.

    To resolve the question of which rates to use when and on whom, researchers have been developing new molecular clock methods, which address the challenges of evolving mutation and recombination rates.

    New approaches for better dating

    One approach is to focus on mutations that arise at a steady rate regardless of sex, age and species. This may be the case for a special type of mutation that geneticists call CpG transitions by which the C nucelotides spontaneously become T’s. Because CpG transitions mostly do not result from DNA copying errors during cell division, their rates should be mainly independent of life history variables – and presumably more uniform over time.

    Focusing on CpG transitions, geneticists recently estimated the split between humans and chimps to have occurred between 9.3 and 6.5 million years ago, which agrees with the age expected from fossils. While in comparisons across species, these mutations seem to happen more like clockwork than other types, they are still not completely steady.

    Another approach is to develop models that adjust molecular clock rates based on sex and other life history traits. Using this method, researchers calculated a chimp-human divergence consistent with the CpG estimate and fossil dates. The drawback here is that, when it comes to ancestral species, we can’t be sure of life history traits, like age at puberty or generation length, leading to some uncertainty in the estimates.

    The most direct solution comes from analyses of ancient DNA recovered from fossils. Because the fossil specimens are independently dated by geologic methods, geneticists can use them to calibrate the molecular clocks for a given time period or population.

    This strategy recently resolved the debate over the timing of our divergence with Neanderthals. In 2016, geneticists extracted ancient DNA from 430,000-year-old fossils that were Neanderthal ancestors, after their lineage split from Homo sapiens. Knowing where these fossils belong in the evolutionary tree, geneticists could confirm that for this period of human evolution, the slower molecular clock rate of 0.5×10?? provides accurate dates. That puts the Neanderthal-modern human split between 765,000 to 550,000 years ago.

    As geneticists sort out the intricacies of molecular clocks and sequence more genomes, we’re poised to learn more than ever about human evolution, directly from our DNA.

    Bridget Alex, Postdoctoral College Fellow, Department of Human Evolutionary Biology, Harvard University and Priya Moorjani, Postdoctoral Research Fellow in Biological Sciences, Columbia University

    See the full article here .

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  • richardmitnick 8:54 am on April 8, 2017 Permalink | Reply
    Tags: , , , , , , EarthSky   

    From EarthSky: “Large asteroid coming close on April 19” 



    April 8, 2017
    Eddie Irizarry

    Asteroid 2014 JO25 will pass safely at 4.6 times the moon’s distance. It’s 60 times the diameter of the asteroid that penetrated the atmosphere over Chelyabinsk, Russia in 2013. People with small telescopes might be able to spot it.

    A big asteroid will have a safely sweep past Earth on April 19, 2017. It’ll come so close – and it’s known so far in advance – that scientists will be able to study the space rock using both radar and optical observations. The flyby should also be visible in amateur telescopes. Asteroid 2014 JO25 was discovered by astronomers at the Catalina Sky Survey near Tucson, Arizona in May 2014. It appears to be roughly 2,000 feet (650 meters) in size, with a surface about twice as reflective as that of Earth’s moon. The asteroid will safely pass at some 1,098,733 miles (1,768,239 km ) from our planet or about 4.6 times the distance from Earth to the moon.

    After analyzing the orbit of Asteroid 2014 JO25, astronomers have realized the April 19 encounter is the closest this asteroid has come to Earth for at least 400 years and will be its closest approach for at least the next 500 years. There is no danger as the space rock’s orbit is well known.

    2014 JO25 is classified as a Potentially Hazardous Asteroid by the Minor Planet Center. The asteroid will sweep close enough to allow good radar observations. NASA has said they will study this asteroid using the Goldstone Radar in California from April 16 to 21.

    NASA DSCC Goldstone Antenna in the Mojave Desert, California USA

    The Arecibo Observatory plans to do high resolution imaging using radar from April 15 to 20.

    NAIC/Arecibo Observatory, Puerto Rico, USA

    Radar observations will provide a better understanding of the space rock’s size and shape.

    Preliminary estimates indicate the asteroid’s size is about 60 times the diameter of the asteroid that penetrated the atmosphere over Chelyabinsk, Russia in February, 2013. NASA said:

    “There are no known future encounters by 2014 JO25 as close as the one in 2017 through 2500. It will be among the strongest asteroid radar targets of the year. The 2017 flyby is the closest by an asteroid at least this large since the encounter by 4179 Toutatis at four lunar distances in September 2004. The next known flyby by an object with a comparable or larger diameter will occur when 800-m-diameter asteroid 1999 AN10 approaches within one lunar distance in August 2027.”

    For backyard observers, the exciting news is that asteroid 2014 JO25 might be be visible moving across the stars though 8″-diameter and bigger telescopes. Can it be seen with smaller telescopes? Maybe, but in order to be able to detect its motion across the stars, at least an 8″ scope will be required. The asteroid will not be visible to the unaided eye, as it may show a brightness or magnitude between 10 and 11.

    The asteroid is currently located in the direction of the sun, but – during the first hours of April 19 – the space rock will come into view for telescopes as it crosses the constellation of Draco. Then, during the night of April 19, asteroid 2014 JO25 will seem to move across the skies covering the distance equivalent to the moon’s diameter in about 18 minutes.

    That’s fast enough for its motion to be detected though an amateur telescope. The best strategy to catch the space rock in your telescope is to observe a star known to be in the asteroid’s path, and wait for it.

    If you are looking at the correct time and direction, the asteroid will appear as a very slowly moving “star.” Although its distance from us will make the space rock appear to move slowly, it is in fact traveling though space at a speed of 75,072 mph (120,816 km/h)!

    Because it will appear to move very slowly, observers should take a good look at a reference star for a few minutes (not seconds) to detect the moving object.

    Although asteroid 2014 JO25 will be closest to Earth on the morning of Wednesday, April 19, 2017, (around 7:24 a.m. Central Time / 12:24 UTC) the space rock may look a bit brighter (but still only visible in telescopes) during the night of April 19, because the asteroid will be at a higher elevation in our skies.

    Will it be visible from both hemispheres? Yes. Observers in the Northern Hemisphere will be able to locate the asteroid both on the predawn hours and during the night of April 19. From South America, the space rock will only be visible during the night of April 19, at over 25 degrees above the northern horizon. Observers in Africa and Australia will also be able to spot the asteroid on April 19-20.

    The asteroid’s nearness to Earth at the time of closest approach might cause a slight parallax effect. That means the space rock’s apparent nearness on our sky’s dome to a fixed star might differ slightly, as seen from different locations across Earth. Thus, if you don’t see the asteroid at the expected time, scan one more field of view up and down from your reference star, that is, the star you are waiting to see the asteroid to pass by.

    At 3:40 a.m. Central Time on April 19, asteroid 2014 JO25 will be located in front of the constellation Draco the Dragon, as seen here. Illustration by Eddie Irizarry using Stellarium.

    A closer view of the space rock passing by the constellation Draco early on the morning April 19.

    Observers using a computerized “Go To” telescope can point the instrument at star HIP 87728 a few minutes before 3:40 a.m. Central Time on April 19, and watch the asteroid passing by the magnitude 5 star in Draco. Illustration by Eddie Irizarry using Stellarium.

    During the night of April 19, asteroid 2014 JO25 will pass though the constellations Canes Venatici and Coma Berenices. Illustration by Eddie Irizarry using Stellarium.

    The asteroid will be close to star 41 Comae, which is very close to Beta Comae. This star is magnitude 4 and thus visible to the unaided eye. Illustration by Eddie Irizarry using Stellarium.

    At around 9:30 p.m. Central Time on April 19, the space rock will be passing very close to 41 Comae Berenices (HIP 64022) a 4.8 magnitude star which is visible to the naked eye from suburban and dark skies. Illustration by Eddie Irizarry using Stellarium.

    Bottom line: Asteroid 2014 JO25 will pass safely at 4.6 times the moon’s distance. People with small telescopes might be able to spot it. Charts here and other info on how to see it.

    See the full article here .

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  • richardmitnick 4:01 pm on April 7, 2017 Permalink | Reply
    Tags: , , , , , EarthSky   

    From EarthSky: “The Coma Cluster of galaxies” 



    April 7, 2017
    Larry Sessions

    The Coma Cluster is one of the richest galaxy clusters known. How many suns and how many worlds might be located in this direction of space?

    Almost every object you see in this photo is a galaxy. The Coma Cluster of galaxies contains as many as 10,000 galaxies, each housing billions of stars. Image via Justin Ng.

    The Coma Cluster is a group of galaxies in the faint constellation Coma Berenices, visible in medium to large amateur telescopes. Coma Berenices lies between Leo and Bootes, and as such is most conveniently viewed in the evening sky of spring and summer. The Coma Cluster is one of the richest galaxy clusters known. How many suns and how many worlds might be located in this direction of space? Follow the links below to learn more about the Coma Cluster of galaxies in the faint constellation Coma Berenices.

    The constellation Coma Berenices appears to the eye as a cluster of stars. But a telescope also reveals a vast region of distant galaxies in this part of the sky, which can be seen on this chart via SEDS

    This map shows both the Coma star cluster [Melotte 111] and the Coma galaxy cluster [(Abell 1656], in the tail end of Leo the Lion. Three stars outline a simple triangle that forms the constellation Coma Berenices.

    Coma Supercluster http://www.atlasoftheuniverse.com/superc/com.html

    How to see the Coma Cluster of galaxies. The constellation Coma Berenices lies between the constellations Leo the Lion and Bootes the Herdsman. This part of the sky is the site of a famous open star cluster, and also of the more distant galaxy cluster, visible through telescopes. Both the star cluster and the galaxy cluster need a dark sky to be seen.

    The galaxy cluster is is near the northern border of Coma Berenices, roughly midway a long a line drawn from Rho Bootes to Delta Leonis (Zosma), near the North Galactic Pole.

    The central part of Coma Cluster of galaxies covers a roughly circular area about a degree and a half across (9 times the area of a full moon), The full cluster may extend farther, and numerous other galaxy clusters are in the same area of sky. An old but beautiful name for this region of sky is the Realm of the Galaxies.

    Close-up on a majestic face-on spiral galaxy located deep within the Coma Cluster of galaxies. Image via NASA

    Science of the Coma Cluster

    The center of the Coma Cluster is about 320 million light years away, and it may stretch 20 million light years from side to side.

    This cluster as a whole is flying away from us at the rate of about 6,900 km/second (more than 15 million miles per hour!)

    One of the most populated galaxy clusters known, it contains as many as 10,000 or more members by some estimates. In any case there are more individual galaxies in this cluster than there are stars visible to the unaided human eye on a clear, dark night.

    Most galaxies in the cluster are elliptical, although there are a few spiral galaxies. The two brightest members are NGC 4889 and NGC 4874, both of which are giant ellipticals at least 2 to 3 times larger than our own Milky Way galaxy.

    Meanwhile, most galaxies in the Coma Cluster are dwarf galaxies, perhaps similar to the Milky Way’s companions, the Large and Small Magellanic Clouds.

    Coma Cluster in history

    Too faint to be seen by the human eye (or binoculars or even small telescopes), the ancients could not have seen the galaxy cluster and hence no mythology is associated with it. However, the Coma Cluster, also known as Abell 1656, is extremely interesting historically.

    Not only is it one of the largest and most densely populated clusters of galaxies known, it is also the source of our first ideas about the dark matter in our universe. Unseen and mysterious, this matter greatly increases the total mass and gravitational strength of the universe, further affecting its evolution and fate.

    Dark matter was unknown and unsuspected until Swiss-American astronomer Fritz Zwicky discovered it in the Coma Cluster in the 1930s. Zwicky tallied up the visible galaxies in the cluster and estimated its mass. Then he observed the motions of galaxies near the edge of the cluster, which are determined by the total gravity (and hence mass) of the cluster. Zwicky found that the mass derived from the latter method greatly exceeded that from visual inspection.

    Zwicky knew that if the law of gravity is correct — and there is no reason to doubt it — the only answer could be an additional source of mass, which he called Dunkle Materie in German.

    Today, the imprint of dark matter has been found throughout the universe, and is at least five times more prevalent than the more familiar visible matter, such as the stars and galaxies we can see.

    Bottom line: How to locate the Coma Cluster of galaxies, plus history and science surrounding this fascinating region of the night sky.

    The center of the Coma Cluster is approximately RA: 12h 59m, dec: +27° 59?

    See the full article here .

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  • richardmitnick 8:24 am on March 23, 2017 Permalink | Reply
    Tags: , , Colorado, , EarthSky, National Snow and Ice Data Center (NSIDC) in Boulder, Polar sea ice   

    From EarthSky: “Record low sea ice at both poles” 



    March 23, 2017
    Deborah Byrd

    Scientists at NASA and the National Snow and Ice Data Center (NSIDC) in Boulder, Colorado said on March 22, 2017 that Arctic sea ice probably reached its 2017 maximum extent on March 7, and that this year’s maximum represents another record low. Meanwhile, on the opposite side of the planet, on March 3 sea ice around Antarctica hit its lowest extent ever recorded by satellites at the end of summer in the Southern Hemisphere. NASA called it:

    ” … a surprising turn of events after decades of moderate sea ice expansion.”

    Walt Meier, a sea ice scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland said:

    “It is tempting to say that the record low we are seeing this year is global warming finally catching up with Antarctica. However, this might just be an extreme case of pushing the envelope of year-to-year variability. We’ll need to have several more years of data to be able to say there has been a significant change in the trend.”

    Satellites have been continuously measuring sea ice in 1979, NASA said, and on February 13, the combined Arctic and Antarctic sea ice numbers were at their lowest point since.

    On February 13, total polar sea ice covered 6.26 million square miles (16.21 million square km). That’s 790,000 square miles (2 million square km) less than the average global minimum extent for 1981-2010 – the equivalent of having lost a chunk of sea ice larger than Mexico.

    These line graphs plot monthly deviations and overall trends in polar sea ice from 1979 to 2017 as measured by satellites. The top line shows the Arctic; the middle shows Antarctica; and the third shows the global, combined total. The graphs depict how much the sea ice concentration moved above or below the long-term average. Arctic and global sea ice totals have moved consistently downward over 38 years. Antarctic trends are more muddled, but they do not offset the great losses in the Arctic. Image via Joshua Stevens/ NASA Earth Observatory.

    NASA explained the seasonal cycle of sea ice’s growth and shrinkage at Earth’s poles, and described specific weather events this year that led to the lower-than-average sea ice:

    The ice floating on top of the Arctic Ocean and surrounding seas shrinks in a seasonal cycle from mid-March until mid-September. As the Arctic temperatures drop in the autumn and winter, the ice cover grows again until it reaches its yearly maximum extent, typically in March. The ring of sea ice around the Antarctic continent behaves in a similar manner, with the calendar flipped: it usually reaches its maximum in September and its minimum in February.

    This winter, a combination of warmer-than-average temperatures, winds unfavorable to ice expansion, and a series of storms halted sea ice growth in the Arctic. This year’s maximum extent, reached on March 7 at 5.57 million square miles (14.42 million square km), is 37,000 square miles (97,00 square km) below the previous record low, which occurred in 2015, and 471,000 square miles (1.22 million square km) smaller than the average maximum extent for 1981-2010.

    Walt Meier added:

    “We started from a low September minimum extent. There was a lot of open ocean water and we saw periods of very slow ice growth in late October and into November, because the water had a lot of accumulated heat that had to be dissipated before ice could grow. The ice formation got a late start and everything lagged behind – it was hard for the sea ice cover to catch up.”

    NASA also said the Arctic’s sea ice maximum extent has dropped by an average of 2.8 percent per decade since 1979. The summertime minimum extent losses are nearly five times larger: 13.5 percent per decade. Besides shrinking in extent, the sea ice cap is also thinning and becoming more vulnerable to the action of ocean waters, winds and warmer temperatures.

    This year’s record low sea ice maximum extent might not necessarily lead to a new record low summertime minimum extent, since weather has a great impact on the melt season’s outcome, Meier said. But, he added:

    ” … it’s guaranteed to be below normal.”

    Meanwhile, in Antarctica, this year’s record low annual sea ice minimum of 815,000 square miles (2.11 million square km) was 71,000 square miles (184,000 square km) below the previous lowest minimum extent in the satellite record, which occurred in 1997. NASA explained:

    “Antarctic sea ice saw an early maximum extent in 2016, followed by a very rapid loss of ice starting in early September. Since November, daily Antarctic sea ice extent has continuously been at its lowest levels in the satellite record. The ice loss slowed down in February.”

    This year’s record low happened just two years after several monthly record high sea ice extents in Antarctica and decades of moderate sea ice growth. The Arctic and Antarctica are very different places; the Arctic is an ocean surrounded by northern continents, while Antarctica is a continent surrounded by ocean. In recent years, climage scientists have pointed to this difference to help explain why the poles were reacting to the trend of warming global temperatures differently.

    But many had said they expected sea ice to begin decreasing in Antarctica, as Earth’s temperatures continue to warm. Claire Parkinson, a senior sea ice researcher at Goddard, said on March 22:

    “There’s a lot of year-to-year variability in both Arctic and Antarctic sea ice, but overall, until last year, the trends in the Antarctic for every single month were toward more sea ice.

    Last year was stunningly different, with prominent sea ice decreases in the Antarctic.

    To think that now the Antarctic sea ice extent is actually reaching a record minimum, that’s definitely of interest.”

    There’s no real reason Earth’s poles should react in the same way, or at the same rate, to global warming. A fundamental difference between Arctic (left) and Antarctic (right) regions is that the Arctic is a frozen ocean surrounded by continents, while the Antarctic is a frozen continent surrounded by oceanic waters. Map via NOAA/ climate.gov/ researchgate.net.

    Bottom line: Considering both poles in February 2017, Earth essentially lost the equivalent of a chunk of sea ice larger than Mexico, in contrast to the average global minimum for 1981-2010.

    See the full article here .

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  • richardmitnick 8:42 am on March 22, 2017 Permalink | Reply
    Tags: , , , , EarthSky, , Star’s death spiral into black hole   

    From EarthSky: “Star’s death spiral into black hole” 



    March 22, 2017
    Eleanor Imster

    NASA said on March 20, 2017 that scientists used data from its Swift satellite to get a comprehensive look at a star’s death spiral into a black hole.

    NASA/SWIFT Telescope

    The star was much like our sun. The black hole contains some 3 million times the mass of our sun and lies at the center of a galaxy 290 million light-years away. As the black hole tore the star apart, it produced what scientists call a tidal disruption event. They’ve labeled this particular event – an eruption of optical, ultraviolet, and X-ray light, which began reaching Earth in 2014 – as ASASSN-14li.

    Astronomers report the detection of flows of hot, ionized gas in high-resolution X-ray spectra of a nearby tidal disruption event, ASASSN-14li in the galaxy PGC 43234. This artist’s impression shows a supermassive black hole at the center of PGC 43234 accreting mass from a star that dared to venture too close to the galaxy’s center. Image credit: ESA / C. Carreau.

    The scientists have now used Swift’s data to map out how and where these different wavelengths were produced, as the shattered star’s debris circled the black hole. The video animation above is an artist’s depiction of what these scientists believe happened. They said it took awhile for debris from the star to be swallowed up by the black hole.

    Dheeraj Pasham, an astrophysicist at the Massachusetts Institute of Technology (MIT) in Cambridge, Massachusetts, and the lead researcher of the study, said:

    “We discovered brightness changes in X-rays that occurred about a month after similar changes were observed in visible and UV light. We think this means the optical and UV emission arose far from the black hole, where elliptical streams of orbiting matter crashed into each other.”

    Their study was published March 15, 2017 in the Astrophysical Journal Letters.

    A tidal disruption event happens when a star passes too close to a very massive black hole. ASASSN-14li is the closest tidal disruption discovered in 10 years, so of course astronomers are studying it as extensively as they can. During events like this, tidal forces from a black hole may convert the star into a stream of debris. Stellar debris falling toward the black hole doesn’t fall straight in, however, but instead collects into a spinning accretion disk, encircling the hole.

    The accretion disk is the source of all the action, as observed by earthly astronomers.

    Within the disk, star material becomes compressed and heated before eventually spilling over the black hole’s event horizon, the point beyond which nothing can escape and astronomers cannot observe.

    The animation above, from NASA’s Goddard Space Flight Center illustrates:

    … how debris from a tidally disrupted star collides with itself, creating shock waves that emit ultraviolet and optical light far from the black hole. According to Swift observations of ASASSN-14li, these clumps took about a month to fall back to the black hole, where they produced changes in the X-ray emission that correlated with the earlier UV and optical changes.

    According to the scientists, the ASASSN-14li black hole’s event horizon is typically about 13 times bigger in volume than our sun. Meanwhile, the accretion disk formed by the disrupted star might extend to more than twice Earth’s distance from the sun.

    Bottom line: A team of scientists used observations from NASA’s Swift satellite have mapped the death spiral of a star as it was destroyed by the black hole at the center of its galaxy.

    See the full article here .

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  • richardmitnick 8:38 am on March 19, 2017 Permalink | Reply
    Tags: , , , , EarthSky, , TDE's, When galaxies collide black holes eat   

    From EarthSky: “When galaxies collide, black holes eat” 



    March 12, 2017
    Deborah Byrd

    When our Milky Way galaxy and neighboring Andromeda galaxy collide, supermassive black holes will have a feast!

    Artist’s concept of a Tidal Disruption Event, in which a black hole eats a star, in the distant galaxy F01004-2237. As the black hole swallows the star, there’s a release of gravitational energy from the star’s debris. The result is a visible flare. Image via Mark Garlick.

    What’ll our sky look like 5 billion years from now, when our Milky Way galaxy merges with the nearby Andromeda galaxy? If there are any people left to look then [this is false, there will be no people, as our sun will hve in 3 billion years grown into a red giant, consumed Mercury and Venue, and at least fried Earth before eating it] they’ll be able to see flares about every 10 to 100 years, each time our Milky Way’s central supermassive black hole swallows a star. The flares will be visible to the unaided eye [forget it, but still you need to pay your taxes]. They’ll appear much brighter than any other star or planet in the night sky. That’s according to astronomers at the University of Sheffield in England, who say that central, supermassive black holes in colliding galaxies swallow stars some 100 times more often than previously thought.

    Their study was published March 1, 2017 in the peer-reviewed journal Nature Astronomy.

    The study is based on a survey of just 15 galaxies, a very small sample size by astronomical standards. However, in that small sample, the astronomers were surprised to see a black hole swallow a star. Astronomers call this sort of event a tidal distruption event, or TDE. They’d been only been only seen before in surveys of many thousands of galaxies, leading astronomers to believe they were exceptionally rare: only one event every 10,000 to 100,000 years per galaxy.

    Artist’s concept of Earth’s night sky in 3.75 billion years. The Andromeda galaxy (left) will fill our field of view then, astronomers say, as it heads toward a collision, or merger, with our Milky way galaxy. Image via NASA; ESA; Z. Levay and R. van der Marel, STScI; T. Hallas; and A. Mellinger.

    The 15 galaxies of the University of Sheffield study are doing something those other thousands of galaxies weren’t doing. They’re undergoing collisions with neighboring galaxies. Study co-author James Mullaney said in a statement:

    “Our surprising findings show that the rate of TDEs dramatically increases when galaxies collide. This is likely due to the fact that the collisions lead to large numbers of stars being formed close to the central supermassive black holes in the two galaxies as they merge together.”

    Another study co-author, Rob Spence, said:

    “Our team first observed the 15 colliding galaxies in the sample in 2005, during a previous project.

    However, when we observed the sample again in 2015, we noticed that one galaxy – F01004-2237 – appeared strikingly different. This led us to look at data from the Catalina Sky Survey, which monitors the brightness of objects in the sky over time. We found that in 2010, the brightness of F01004-2237 flared dramatically.”

    Galaxy F01004-2237 – which is 1.7 billion light years from Earth – had flared in a way characteristic of TDEs. These events are known to cause flaring due to energy release, as a star edges toward a galaxy’s central, supermassive black hole.

    NGC 2207 and IC 2163 are two spiral galaxies in the process of merging, or colliding. If the new study from University of Sheffield is correct, there is a much greater chance for stars to be eaten in these galaxies by their central, supermassive black holes.

    Bottom line: A study from the University of Sheffield shows that collisions – like that predicted for our Milky Way galaxy and neighboring Andromeda galaxy – cause black holes to eat stars some 100 times faster than previously thought.

    See the full article here .

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  • richardmitnick 11:42 am on March 16, 2017 Permalink | Reply
    Tags: , , , EarthSky, Great Barrier Reef is dying   

    From EarthSky: “Great Barrier Reef is dying” 



    March 16, 2017
    Deborah Byrd

    Bleached coral in 2016 on the northern Great Barrier Reef. Image via Terry Hughes et al./Nature.

    Great Barrier Reef – the world’s largest reef system – is being increasingly affected by climate change, according to the authors of a cover story in the March 15, 2017 issue of the peer-reviewed journal Nature. Large sections of the reef are now dead, these scientists report. Marine biologist Terry Hughes of the ARC Center of Excellence for Coral Reef Studies led a group that examined changes in the geographic footprint – that is, the area affected – of mass bleaching events on the Great Barrier Reef over the last two decades. They used aerial and underwater survey data combined with satellite-derived measurements of sea surface temperature. Editors at Nature reported:

    “They show that the cumulative footprint of multiple bleaching events has expanded to encompass virtually all of the Great Barrier Reef, reducing the number and size of potential refuges [for fish and other creatures that live in the reef]. The 2016 bleaching event proved the most severe, affecting 91% of individual reefs.”

    The NY Times published this map on March 15, 2017, based on information from the ARC Centre of Excellence for Coral Reef Studies. It shows that individual reefs in each region of the Great Barrier Reef lost different amounts of coral in 2016. Numbers show the range of loss for the middle 50% of observations in each region. Study authors told the NY Times this level of destruction wasn’t expected for another 30 years.

    Hughes and colleagues said in their study [Nature]:

    “During 2015–2016, record temperatures triggered a pan-tropical episode of coral bleaching, the third global-scale event since mass bleaching was first documented in the 1980s …

    The distinctive geographic footprints of recurrent bleaching on the Great Barrier Reef in 1998, 2002 and 2016 were determined by the spatial pattern of sea temperatures in each year. Water quality and fishing pressure had minimal effect on the unprecedented bleaching in 2016, suggesting that local protection of reefs affords little or no resistance to extreme heat. Similarly, past exposure to bleaching in 1998 and 2002 did not lessen the severity of bleaching in 2016.

    Consequently, immediate global action to curb future warming is essential to secure a future for coral reefs.”

    According to the website CoralWatch.org:

    Many stressful environmental conditions can lead to bleaching, however, elevated water temperatures due to global warming have been found to be the major cause of the massive bleaching events observed in recent years. As the sea temperatures cool during winter, corals that have not starved may overcome a bleaching event and recover their [symbiotic dinoflagellates (algae)].

    However, even if they survive, their reproductive capacity is reduced, leading to long-term damage to reef systems.

    In March 2016, researchers could see bleached coral in the northern Great Barrier Reef from the air. Image via James Kerry/ARC Center of Excellence for Coral Reef Studies.

    Bottom line: Authors of a cover story published on March 15, 2017 in the journal Nature called for action to curb warming, to help save coral reefs.

    See the full article here .

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  • richardmitnick 6:27 pm on February 19, 2017 Permalink | Reply
    Tags: , , , , , EarthSky, NAOJ Nobeyama Radio Observatory, Supernova Remnant W44   

    From EarthSky: “Hints of a quiet, stray black hole” 


    Via NAOJ Nobeyama Radio Observatory
    No writer credit

    Supernova Remnant W44. https://earthspacecircle.blogspot.com/2015/12/supernova-remnant-w44.html

    Graduate student Masaya Yamada and professor Tomoharu Oka, both of Keio University, led a research team that was surveying gas clouds around the supernova remnant W44, located 10,000 light-years away from us, when they noticed something unusual. Their statement explained:

    “During the survey, the team found a compact molecular cloud with enigmatic motion. This cloud, [nicknamed] the ‘Bullet,’ has a speed of more than 100 km/second [60 miles/second], which exceeds the speed of sound in interstellar space by more than two orders of magnitude. In addition, this cloud, with the size of two light-years, moves backward against the rotation of the Milky Way galaxy.”

    The energy of motion of the Bullet is many times larger than that injected by the original W44 supernova. The astronomers think this energy must come from a quiet, stray black hole, and they proposed two scenarios to explain the Bullet:

    ” In both cases, a dark and compact gravity source, possibly a black hole, has an important role. One scenario is the ‘explosion model’ in which an expanding gas shell of the supernova remnant passes by a static black hole. The black hole pulls the gas very close to it, giving rise to an explosion, which accelerates the gas toward us after the gas shell has passed the black hole. In this case, the astronomers estimated that the mass of the black hole would 3.5 times the solar mass or larger.

    The other scenario is the ‘irruption model’ in which a high speed black hole storms through a dense gas and the gas is dragged along by the strong gravity of the black hole to form a gas stream. In this case, researchers estimated the mass of the black hole would be 36 times the solar mass or larger. With the present dataset, it is difficult for the team to distinguish which scenario is more likely.”

    Via NAOJ Nobeyama Radio Observatory

    ASTE Atacama Submillimeter telescope
    ASTE Atacama Submillimeter telescope

    Nobeyama Radio Telescope - Copy
    Nobeyama Radio Telescope

    (a) CO (J=3-2) emissions (color) and 1.4 GHz radio continuum emissions (contours) around the supernova remnant W44. (b) Galactic longitude-velocity diagram of CO (J=3-2) emissions at the galactic latitude of -0.472 degrees. (c -f): Galactic longitude-velocity diagrams of the Bullet in CO (J=1-0), CO (J=3-2), CO (J=4-3), and HCO+ (J=1-0), from left to right. Galactic longitude-velocity diagrams show the speed of the gas at a specific position. Structures elongated in the vertical direction in the diagrams have a large velocity width. Credit: Yamada et al. (Keio University), NAOJ

    Schematic diagrams of two scenarios for the formation mechanism of the Bullet. (a) explosion model and (b) irruption model. Both diagrams show a part of the shock front produced by the expansion of the supernova remnant W44. The shock wave enters into quiescent gas and compresses it to form dense gas. The Bullet is located in the center of the diagram and has completely different motion compared to the surrounding gas. Credit: Yamada et al. (Keio University)

    These astronomers published their findings in January, 2017 in the peer-reviewed Astrophysical Journal Letters.

    A black hole is a place in space where matter is squeezed into a tiny space, and where gravity pulls so hard that even light can’t escape. Black holes are black. No light comes from them. Up to now, most known stellar black holes are those with companion stars. The black hole pulls gas from the companion, which piles up around it and forms a disk. The disk heats up due to the enormous gravitational pull by the black hole and emits intense radiation.

    On the other hand, if a black hole is floating alone in space – as many must be – its lack of light or any sort of emission would make it very, very hard to find.

    See the full article here .

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