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  • richardmitnick 4:57 pm on April 24, 2017 Permalink | Reply
    Tags: , Astrophysics, , , , Where Is Spitzer Now?   

    From Spitzer: “Where Is Spitzer Now?” 

    NASA Spitzer Telescope

    Spitzer

    1

    Current Observation Details
    Target Name NGC1385
    RA 3:37:28.32
    Declination -24:30: 4.60
    Program Name SPIRITS1 1
    Principal Investigator Kasliwal
    AOT iracmapp
    Start Time 2017-04-24 21:43:34 UTC
    Duration of Observation 29.39

    How To Read The Details
    Target Name
    This is the name of the object being observed by Spitzer. The name appears as it was input by the observer, and will usually appear as a unique, universally accepted catalog designation rather than a “name” in the traditional sense of the word.
    RA
    These are the coordinates in the sky where the object is located. They work much like longitude and latitude on Earth. RA is the object’s position along the equator, and Declination is its position north or south (positive numbers are the northern sky, and negative numbers are the southern sky).
    Declination
    These are the coordinates in the sky where the object is located. They work much like longitude and latitude on Earth. RA is the object’s position along the equator, and Declination is its position north or south (positive numbers are the northern sky, and negative numbers are the southern sky).
    Program Name
    When astronomers are granted observing time on Spitzer, their planned observations are defined under a unique program name. Each program has specific goals and objectives, such as the various Legacy Science programs, whose objective is to create a substantial and coherent database of archived observations that can be used by subsequent Spitzer researchers.
    Principal Investigator
    This is the name of the scientist who leads the team of people who are making the observation on Spitzer.
    AOT
    This is the specific observing mode that Spitzer is using for its observation. Spitzer has three different instruments (IRAC – The Infrared Array Camera, IRS – The Infrared Spectrograph, and MIPS – The Multiband Imaging Photometer for Spitzer), all of which can be used in several different ways.
    Start Time
    The time that the observation began. The times are given in UTC (also known as Greenwich Mean Time), which is 8 hours ahead of Pacific Standard Time (7 hours ahead of Pacific Daylight Time).
    Duration of Observation

    Different observations require different amounts of time to gather all the data. Some observations can be quite quick, and some can take hours.

    See the full article here .

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    The Spitzer Space Telescope is a NASA mission managed by the Jet Propulsion Laboratory located on the campus of the California Institute of Technology and part of NASA’s Infrared Processing and Analysis Center.

    NASA image

    NASA JPL Icon

    Caltech Logo

     
  • richardmitnick 4:03 pm on April 24, 2017 Permalink | Reply
    Tags: , Astrophotography, Astrophysics, , ,   

    From Liverpool: “Shooting for the stars: capturing the beauty of science through astrophotography” 

    Liverpool John Moores University

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    Thor’s Helmet is a planetary nebula. Nothing to do with planets, it is actually a shell of gas being thrown off from an old star towards the end of its life cycle. Planetary nebulae are wonderfully varied in shape and colour. This image was originally obtained with the Liverpool Telescope for BBC Sky At Night.

    2-metre Liverpool Telescope at La Palma in the Canary Islands

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    Castell Alun High School captured the Messier 27 through the NSO.

    National Solar Observatory at Kitt Peak in Arizona

    One of the best planetary nebulae to observe on the NSO, it almost fills the field of view, providing a spectacular image with vast detail. The image was produced by combining observations in the blue, visual and red filters using NSO’s 3-colour image tool.

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    The Crab Nebula is a supernova remnant, the expanding cloud of gas and dust from a catastrophically exploding star. Chinese astronomers witnessed this explosion in 1054 and we still see the remnant cloud now. To the human eye, it would be faint pink. Scientific instruments do not necessarily ‘see’ colours the same way as our eyes and allow astronomers to bring out details that a true colour image might not reveal.

    When thinking about the types of photographs that capture the beauty of science, a stunning landscape or an animal in its natural habitat might come to mind. But when it comes to images from telescopes, we might not immediately consider these as anything more than the collection of scientific data. Beyond their significance in helping us to discover more about our universe, the images of galaxies, planets and stars are also appreciated purely for aesthetic reasons. For many amateur and professional astrophotographers capturing the shapes and colours of the universe is just as important as capturing scientific data. In fact, most astronomical images for general viewing have been modified from their original form. An astrophotographer’s goal in this case is to bring out the best of the image – to find the art within the science.

    Robert Smith, creator of the “Iridis” image which won the Robotic Scope Special Prize at the Insight Astronomy Photographer of the Year competition, sums up the concept of science as art/art as science:

    “We often hear about the idea of representing scientific data in an appealing way as an expression of art, but why not look at it the other way around; ‘art as science’? Astrophotography is not just a matter of making science look pretty, it shows us that beauty actually is science. The winners of this competition were obviously selected because they were beautiful, striking or interesting, but each and every one is also an expression of astrophysical processes and could be the basis of a science seminar in their own right. It is physics that creates that beauty. Looking at the swirling gas in a nebula or the aurorae, you are literally seeing maths and physics.”

    Robert is an astronomer at the Astrophysics Research Institute (ARI) at LJMU and captured the award-winning image from ARI’s very own Liverpool Telescope. As the world’s largest fully robotic telescope, the Liverpool Telescope is responsible for a wide range of images which, in addition to their obvious importance scientifically, are also interesting and beautiful as pieces of art in their own right.

    Astronomers were among the first to embrace photography, with the first images of the sun captured on daguerreotypes, an early photographic imaging process, in the 1840s.

    Users of the Liverpool Telescope not only include researchers at LJMU but because it is remotely operated, it is available to astronomers from around the world. Schools and colleges across the UK and Ireland also get involved in capturing astronomical images. As a part of ARI’s educational outreach programmes, the National Schools’ Observatory (NSO) makes it possible for schoolchildren to study the night sky for themselves via the Telescope. Almost 4,000 schools have already participated with students making well over 100,000 astronomical observations from the classroom. A couple examples of the photos from NSO can be found on this page, but feel free to take a look at more on the NSO website.

    ______________________________________________________________________

    How do you photograph a night sky?

    Make sure it’s a clear night and find a place as far away from light pollution as you can. With a manual camera, try setting 25 second exposure, f/2.8, ISO 1600 (you can experiment with these settings). You’ll need a tripod to keep your camera stable during the exposure. Modern smartphones can produce impressive results as well. There are free apps available to download that automatically take a series of short exposures for you and add them together to create a long night-time photo.

    If you have access to a telescope, you can hold your smartphone up to the eyepiece of the telescope and take your shot, this is known as afocal photography – where the lens takes the place of the human eye.

    There are plenty of tips for getting started in astrophotography, just do a search online and you’ll be exposed to a wealth of information.
    ______________________________________________________________________

    See the full article here .

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    Liverpool John Moores University is a public research university[6] in the city of Liverpool, England. It has 21,875 students, of which 18,375 are undergraduate students and 3,500 are postgraduate, making it the 33rd largest university in the UK by total student population.

    The university can trace its origins to the Liverpool Mechanics’ School of Arts, established in 1823 making it a contestant as the third-oldest university in England; this later merged to become Liverpool Polytechnic. In 1992, following an Act of Parliament the Liverpool Polytechnic became what is now Liverpool John Moores University.

    It is a member of the University Alliance, a mission group of British universities which was established in 2007.[9] and the European University Association.

     
  • richardmitnick 2:04 pm on April 24, 2017 Permalink | Reply
    Tags: , , Astrophysics, , , Is TRAPPIST-1 Really Moonless?, Worlds Without Moons   

    From AAS NOVA: ” Worlds Without Moons” 

    AASNOVA

    American Astronomical Society

    24 April 2017
    Susanna Kohler

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    Many exoplanets are expected to host moons — but can planets in compact systems orbiting close to their host stars do so? [NASA/JPL-Caltech]

    Many of the exoplanets that we’ve discovered lie in compact systems with orbits very close to their host star. These systems are especially interesting in the case of cool stars where planets lie in the star’s habitable zone — as is the case, for instance, for the headline-making TRAPPIST-1 system.

    But other factors go into determining potential habitability of a planet beyond the rough location where water can remain liquid. One possible consideration: whether the planets have moons.

    Supporting Habitability

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    Locations of equality between the Hill and Roche radius for five different potential moon densities. The phase space allows for planets of different semi-major axes and stellar host masses. Two example systems are shown, Kepler-80 and TRAPPIST-1, with dots representing the planets within them. [Kane 2017]

    Earth’s Moon is thought to have been a critical contributor to our planet’s habitability. The presence of a moon stabilizes its planet’s axial tilt, preventing wild swings in climate as the star’s radiation shifts between the planet’s poles and equator. But what determines if a planet can have a moon?

    A planet can retain a moon in a stable orbit anywhere between an outer boundary of the Hill radius (beyond which the planet’s gravity is too weak to retain the moon) and an inner boundary of the Roche radius (inside which the moon would be torn apart by tidal forces). The locations of these boundaries depend on both the planet’s and moon’s properties, and they can be modified by additional perturbative forces from the host star and other planets in the system.

    In a new study, San Francisco State University scientist Stephen R. Kane modeled these boundaries for planets specifically in compact systems, to determine whether such planets can host moons to boost their likelihood of habitability.

    3
    Allowed moon density as a function of semimajor axis for the TRAPPIST-1 system, for two different scenarios with different levels of perturbations. The vertical dotted lines show the locations of the six innermost TRAPPIST-1 planets. [Kane 2017]

    Challenge of Moons in Compact Systems

    Kane found that compact systems have a harder time supporting stable moons; the range of radii at which their moons can orbit is greatly reduced relative to spread-out systems like our own. As an example, Kane calculates that if the Earth were in a compact planetary system with a semimajor axis of 0.05 AU, its Hill radius would shrink from being 78.5 times to just 4.5 times its Roche radius — greatly narrowing the region in which our Moon would be able to reside.

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    Image of the Moon as it transits across the face of the Sun, as viewed from the Stereo-B spacecraft (which is in an Earth-trailing orbit). [NASA]

    Kane applied his models to the TRAPPIST-1 system as an example, demonstrating that it’s very unlikely that many — if any — of the system’s seven planets would be able to retain a stable moon unless that moon were unreasonably dense.

    Is TRAPPIST-1 Really Moonless?

    The TRAPPIST-1 star, an ultracool dwarf, is orbited by seven Earth-size planets (NASA).

    ESO Belgian robotic Trappist National Telescope at Cerro La Silla, Chile

    ESO Belgian robotic Trappist National Telescope at Cerro La Silla, Chile interior

    How do these results fit with other observations of TRAPPIST-1? Kane uses our Moon as an example again: if we were watching a transit of the Earth and Moon in front of the Sun from a distance, the Moon’s transit depth would be 7.4% as deep as Earth’s. A transit of this depth in the TRAPPIST-1 system would have been detectable in Spitzer photometry of the system — so the fact that we didn’t see anything like this supports the idea that the TRAPPIST-1 planets don’t have large moons.

    On the other hand, smaller moons (perhaps no more than 200–300 km in radius) would have escaped detection. Future long-term monitoring of TRAPPIST-1 with observatories like the James Webb Space Telescope or 30-meter-class ground-based telescopes will help constrain this possibility, however.

    Citation

    Stephen R. Kane 2017 ApJL 839 L19. doi:10.3847/2041-8213/aa6bf2

    There are further referenced articles of interest on the full article.

    See the full article here .

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  • richardmitnick 10:08 am on April 24, 2017 Permalink | Reply
    Tags: , Astrophysics, , , , What's The Largest Planet In The Universe?, What's the upper limit to planetary size?   

    From Ethan Siegel: “What’s The Largest Planet In The Universe?” 

    Ethan Siegel
    Apr 24, 2017

    1
    ATG medialab, ESA

    There’s a large difference between a planet and a star, but some planets can be significantly larger than anything we find in our own Solar System.

    In our Solar System, Jupiter is the largest planet we have, but what’s the upper limit to planetary size?

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    Lunar and Planetary Institute

    Jupiter may be the largest and most massive planet in the Solar System, but adding more mass to it would only make it smaller.

    If you get too much mass together in a single object, its core will fuse lighter elements into heavier ones.

    3
    NASA, ESA, and G. Bacon (STScI)

    It takes about 75-80 times as much mass as Jupiter to initiate hydrogen burning in the core of an object, but the line between a planet and a star is not so simple.

    At about eighty times the mass of Jupiter, you’ll have a true star, burning hydrogen into helium.

    4
    NASA/JPL-Caltech/UCB

    Brown dwarfs, between about 13-80 solar masses, will fuse deuterium+deuterium into helium-3 or tritium, remaining at the same approximate size as Jupiter but achieving much greater masses. Note the Sun is not to scale and would be many times larger.

    5

    Gliese 229 is a red dwarf star, and is orbited by Gliese 229b, a brown dwarf, that fuses deuterium only. Although Gliese 229b is about 20 times the mass of Jupiter, it’s only about 47% of its radius.

    This line — between a gas giant and a brown dwarf — defines the most massive planet.

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    Chen and Kipping, 2016, via https://arxiv.org/pdf/1603.08614v2.pdf

    Planetary size peaks at a mass between that of Saturn and Jupiter, with heavier and heavier worlds getting smaller until true nuclear fusion ignites and a star is born.

    In terms of physical size, however, brown dwarfs are actually smaller than the largest gas giants.

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    NASA Ames / W. Stenzel; Princeton University / T. Morton

    Jupiter may only be about 12 times Earth’s diameter, but the largest planets of all are actually less massive than Jupiter, with more massive ones shrinking as more mass is added.

    Above a certain mass, the atoms inside large planets will begin to compress so severely that adding more mass will actually shrink your planet.

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    Wikimedia Commons user MarioProtIV

    The exoplanet Kepler-39b is one of the most massive ones known, at 18 times the mass of Jupiter, placing it right on the border between planet and brown dwarf. In terms of radius, however, it’s only 22% larger than Jupiter.

    This happens in our Solar System, explaining why Jupiter is three times Saturn’s mass, but only 20% physically larger.

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    Wikimedia Commons user Kelvinsong

    A cutaway of Jupiter’s interior. If all the atmospheric layers were stripped away, the core would appear to be a rocky Super-Earth. Planets that formed with fewer heavy elements can be a lot larger and less dense than Jupiter.

    But many solar systems have planets made out of much lighter elements, without large, rocky cores inside.

    10
    NASA/ESA Hubble

    WASP-17b is one of the largest planets confirmed not to be a brown dwarf. Discovered in 2009, it is twice the radius of Jupiter, but only 48.6% of the mass. Many other ‘puffy’ planets are comparably large, but none are yet significantly larger.

    As a result, the largest planets can be up to twice as big as Jupiter before becoming stars.

    See the full article here .

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    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 9:23 am on April 24, 2017 Permalink | Reply
    Tags: , , Astrophysics, , Breaking Planet Chains and Cracking the Kepler Dichotomy, , Kepler Dichotomy, , Planetary migration   

    From astrobites: “Breaking Planet Chains and Cracking the Kepler Dichotomy” 

    Astrobites bloc

    Astrobites

    Apr 24, 2017
    Michael Hammer

    Title: Breaking the Chains: Hot Super-Earth systems from migration and disruption of compact resonant chains
    Authors: Andre Izidoro, Masahiro Ogihara, Sean N. Raymond, Alessandro Morbidelli, Arnaud Pierens, Bertram Bitsch, Christophe Cossou, Franck Hersant
    First Author’s Institution: Laboratoire d’astrophysique de Bordeaux, University of Bordeaux
    1
    3

    Status: Submitted to MNRAS [open access]

    To migrate, or not to migrate? That is the question. Of course, since planets are not Shakespearean characters, they should not have a choice! When a planet forms in a disk, it creates two spiral waves: a weaker one ahead of the planet that drags it forward (sending the planet outwards), and a stronger one behind the planet that pulls it backwards (sending the planet inwards). Ultimately, every planet should migrate inwards and in most cases, end up much closer to its star than where it formed.

    When planets in the outer disk migrate inwards faster than planets closer in, they start to catch up to each other. As these planets get closer together, they eventually become gravitationally locked into resonance: pairs of orbits where the outer planet takes exactly twice as long (or another integer ratio such as 3-to-2, etc.) to complete an orbit around its star as the inner one. Once this happens, the planets migrate together, maintaining that 2-to-1 ratio. In systems with many rocky planets, the third one will follow suit and fall into a resonance with the second planet, as will the fourth with the third, and so on. Eventually, the system will have a long chain of up to 10 resonant rocky planets tightly packed in the inner part of the disk!

    Yet even though migration is supposed to be inevitable, only about 5% of the planetary systems discovered by the Kepler mission are actually in this setup (TRAPPIST-1 is the most famous).

    The TRAPPIST-1 star, an ultracool dwarf, is orbited by seven Earth-size planets (NASA).

    The other 95% are not, many of which because they only have one planet. Today’s paper, led by Andre Izidoro, attempts to explain these discrepancies by suggesting that all systems migrate into resonant chains, but not all of them stay in resonant chains!

    Two-Phase Setup

    Izidoro et al. study this problem by conducting two-phase N-body simulations of 120 hypothetical planetary systems with 20 to 30 rocky planets for 100 Myr. These planets start out with 0.1 to 4.5 Earth masses and are spread out evenly in the outer disk beyond 5 AU.

    In phase one (0 to 5 Myr), the planets may migrate due to the presence of a gaseous protoplanetary disk. Meanwhile, the disk also keeps the planets on flat, circular orbits by damping the planets’ eccentricities and inclinations.
    In phase two (5 to 100 Myr), the planets can no longer migrate since the disk has dissipated away. However, they are free to develop eccentric and inclined orbits since they are now controlled by interactions with each other instead of interactions with the disk.

    Compact, but not too compact

    Izidoro et al. find that all of their planetary systems migrate into compact resonant chains within 1.5 Myr, safely less than the disk’s lifetime of 5 Myr. Many of these systems (40%) then survive as resonant chains for the entire 100 Myr simulation.

    However, some systems (60%) become too compact (see Figure 1). In particular, the ones that are too compact with higher mass planets become unstable after the disk fades away! The resonant chains then collapse as some of the planets eject and the rest spread farther apart. As they spread out, the surviving planets’ orbits also become more eccentric and inclined.

    2
    Figure 1. Two example resonant chains after phase one. The first system (left) will survive phase two (without the disk). The second system (right) will become unstable because it has more planets too close together. Some of the surviving planets will develop inclined orbits, making them less likely to transit. Adapted from Figs. 2 and 3 of the paper.

    Single-Planet Imposters

    In order to compare their results with actual exoplanet systems discovered by the Kepler Mission, Izidoro et al. must determine what fraction of their planets can transit (and be “detected” by Kepler).

    Planet transit. NASA/Ames

    NASA/Kepler Telescope

    They find that in the stable resonant chains, Kepler can detect 3 or more planets in 66% of these systems. On the other side in the unstable systems, the inclined orbits from the instabilities make it so that Kepler can only detect 1 planet in 78% of these systems, even though over 90% of the unstable systems still have multiple planets.

    Explaining the Kepler Dichotomy

    One of the defining features of Kepler’s planets is the large number of systems with only one transiting planet. Naturally, we expected that Kepler would not be able to find all of the planets in each of its systems since planets at large separations from their star that do not line up with our line-of-sight will not transit. However even with this bias, the fact that there are so many more single-planet systems than two-planet systems (see Figure 2) suggests that Kepler systems belong to a dichotomy: roughly 50% of all systems have just one planet (including non-transiting ones) and 50% have many planets (5+ for small stars). Such a high fraction of single-planet systems is a huge surprise, given how many planets exist in our own solar system.

    However, the two populations of planetary systems in this study offer an explanation for the Kepler dichotomy that would imply these single planets are not so lonely. Izidoro et al. calculate that if no more than 25% of all planetary systems are compact resonant chains (with the rest being unstable systems), this distribution of systems can match the high fraction of systems with just one transiting planet in the Kepler dichotomy — even though nearly all of these systems would have multiple planets.

    2
    Figure 2. Comparison of Kepler’s planetary systems to this paper’s planetary systems. In the Kepler sample (green), the vast majority of systems have only one transiting planet. The unstable systems in this paper (blue) would have even more single-transit systems, while the stable resonant chains (red) have a lot fewer. A proper balance between these two (90% unstable, 10% stable — gray) matches the Kepler dichotomy pretty well. Fig. 15 of the paper.

    Why so unstable?

    Izidoro et al. expect that in reality, roughly 5% of all planetary systems are stable resonant chains (since this is the fraction found by Kepler), which is consistent with their upper limit of 25% they need to explain the dichotomy. Even though the authors find that 40% remain stable in their study, they suspect that simulations with a more realistic protoplanetary disk would lead to many more systems going unstable. Nonetheless, the authors caution that their model remains incomplete until they find a reason for ~95% of Kepler’s systems becoming unstable at some point in their history.

    It may also be the case that not all systems migrate into resonant chains to begin with, or even that planets do not migrate as easily as this study presumes. For now, we can still take solace in knowing that at least some of Kepler’s single-planet systems have non-transiting companions that they can orbit with for billions of years.

    See the full article here .

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    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 9:54 am on April 23, 2017 Permalink | Reply
    Tags: , Astrophysics, , Computer modelling, , , , , Modified Newtonian Dynamics, or MOND, , Simulating galaxies,   

    From Durham: “Simulated galaxies provide fresh evidence of dark matter” 

    Durham U bloc

    Durham University

    21 April 2017
    No writer credit

    1
    A simulated galaxy is pictured, showing the main ingredients that make up a galaxy: the stars (blue), the gas from which the stars are born (red), and the dark matter halo that surrounds the galaxy (light grey). No image credit.

    Further evidence of the existence of dark matter – the mysterious substance that is believed to hold the Universe together – has been produced by Cosmologists at Durham University.

    Using sophisticated computer modelling techniques, the research team simulated the formation of galaxies in the presence of dark matter and were able to demonstrate that their size and rotation speed were linked to their brightness in a similar way to observations made by astronomers.

    One of the simulations is pictured, showing the main ingredients that make up a galaxy: the stars (blue), the gas from which the stars are born (red), and the dark matter halo that surrounds the galaxy (light grey).

    Alternative theories

    Until now, theories of dark matter have predicted a much more complex relationship between the size, mass and brightness (or luminosity) of galaxies than is actually observed, which has led to dark matter sceptics proposing alternative theories that are seemingly a better fit with what we see.

    The research led by Dr Aaron Ludlow of the Institute for Computational Cosmology, is published in the academic journal, Physical Review Letters.

    Most cosmologists believe that more than 80 per cent of the total mass of the Universe is made up of dark matter – a mysterious particle that has so far not been detected but explains many of the properties of the Universe such as the microwave background measured by the Planck satellite.

    CMB per ESA/Planck

    ESA/Planck

    Convincing explanations

    Alternative theories include Modified Newtonian Dynamics, or MOND. While this does not explain some observations of the Universe as convincingly as dark matter theory it has, until now, provided a simpler description of the coupling of the brightness and rotation velocity, observed in galaxies of all shapes and sizes.

    The Durham team used powerful supercomputers to model the formation of galaxies of various sizes, compressing billions of years of evolution into a few weeks, in order to demonstrate that the existence of dark matter is consistent with the observed relationship between mass, size and luminosity of galaxies.

    Long-standing problem resolved

    Dr Ludlow said: “This solves a long-standing problem that has troubled the dark matter model for over a decade. The dark matter hypothesis remains the main explanation for the source of the gravity that binds galaxies. Although the particles are difficult to detect, physicists must persevere.”

    Durham University collaborated on the project with Leiden University, Netherlands; Liverpool John Moores University, England and the University of Victoria, Canada. The research was funded by the European Research Council, the Science and Technology Facilities Council, Netherlands Organisation for Scientific Research, COFUND and The Royal Society.

    See the full article here .

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    Durham U campus

    Durham University is distinctive – a residential collegiate university with long traditions and modern values. We seek the highest distinction in research and scholarship and are committed to excellence in all aspects of education and transmission of knowledge. Our research and scholarship affect every continent. We are proud to be an international scholarly community which reflects the ambitions of cultures from around the world. We promote individual participation, providing a rounded education in which students, staff and alumni gain both the academic and the personal skills required to flourish.

     
  • richardmitnick 6:59 am on April 23, 2017 Permalink | Reply
    Tags: , Astrophysics, , , , Singularity   

    From Science Alert: “Physicists Say They’ve Found a Way to Detect Naked Singularities… if They Exist” 

    ScienceAlert

    Science Alert

    21 APR 2017
    FIONA MACDONALD

    1
    u3d/Shutterstock.com

    Black holes are weird: insanely dense objects that are crammed into such a small space they cause space-time to distort and the laws of physics to break down into a singularity.

    Fortunately, the Universe shields us from this weirdness by wrapping black holes in event horizons. But now, physicists say they’ve found a way we could detect something even more extreme – a naked singularity – and most likely bend the laws of physics in the process.

    “A naked singularity, if such a thing exists, would be an abrupt hole in the fabric of reality – one that would not just distort space-time, but would also wreak havoc on the laws of physics wherever it goes and lead to a catastrophic loss of predictability,” explains Avaneesh Pandey for IB Times.

    If that sounds a little too confronting, don’t worry, this whole study is purely theoretical, and is hinged on one very big assumption – that naked singularities actually exist in our Universe, something that scientists have never confirmed.

    But according to Einstein’s theory of general relativity at least, and our best computer models to date, naked singularities are possible.

    So, what are they? A singularity can form when huge stars collapse at the end of their lives into regions so small and dense, physics as we know it fails to explain what could happen there.

    There are two general laws of physics that govern our understanding of reality: quantum mechanics, which explains all the small stuff, such as the behaviour of subatomic particles; and general relativity, which describes the stuff we can see, such as stars and galaxies.

    When applied to singularities, both these schools of thought predict different and incompatible outcomes.

    And we’ve never really had to deal with that conundrum, because all the singularities we know of are inside black holes, wrapped in an event horizon from which not even light can escape – or at the very birth of our Universe, shrouded by radiation we can’t see past. Out of sight, out of mind, right?

    But naked singularities are theoretical singularities that are exposed to the rest of the Universe for some reason.

    Below you can see an illustration of a black hole wrapped in its event horizon (dotted line) on the left, and a naked singularity on the right. The arrows indicate light, which would be able to escape a naked singularity, but not a black hole.

    2
    Sudip Bhattacharyya/Pankaj Joshi

    Assuming they do exist, the big question then is how would we be able to distinguish a naked singularity from a regular black hole, and this is where the new study comes in.

    Researchers from the Tata Institute of Fundamental Research in India have come up with a two-step plan based on the fact that singularities, as far as we know, are rotating objects, just like black holes.

    According to Einstein’s theory of general relativity, the fabric of space-time in the vicinity of any rotating objects gets ‘twisted’ due to this rotation. And this effect causes a gyroscopic spin and makes the orbits of particles around the rotating objects ‘precess’, or change their rotational axis.

    You can watch the hypnotic precession of a gyroscope below to see what we mean – its axis is no longer straight:

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    LucasVB/WikimediaCommons

    Based on this, the researchers say that we could figure out the nature of a rotating objects by measuring the rate at which a gyroscope precesses – its precession frequency – at two fixed points close to the object.

    According to the new paper, there are two possibilities:

    1. The precession frequency of the gyroscope changes wildly between the two points, which suggests the rotating object in question is a regular black hole.
    2. The precession frequency changes in a regular, well-behaved manner, indicating a naked singularity.

    Obviously getting a gyroscope close enough to a black hole to perform these experiments isn’t exactly easy.

    But that’s okay, because the team has also come up with a way to observe the same effect from here on Earth – measuring the precession frequencies of matter falling into either black holes or naked singularities using X-ray wavelengths.

    “This is because the orbital plane precession frequency increases as the matter approaches a rotating black hole, but this frequency can decrease and even become zero for a rotating naked singularity,” the team’s press release explains.

    Again, we have to make it clear that all of this is wildly speculative at this time – we have never found any candidate naked singularities, and we’re only just beginning to truly understand regular black holes.

    It’s also worth noting that last week, another team of researchers suggested that even if naked singluarities exist, strange quantum effects could keep them hidden from us.

    So there’s definitely no consensus right now on whether we’ll ever get the chance to study naked singularities.

    And that’s not a terrible thing for now, because are we really ready to observe what goes on at the edge of our Universe?

    Maybe, in our lifetime, we’ll find out.

    The research has been published in Physical Review D.

    See the full article here .

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  • richardmitnick 1:23 pm on April 22, 2017 Permalink | Reply
    Tags: , , Astrophysics, ,   

    From AGU: “New study ranks hazardous asteroid effects from least to most destructive” 

    AGU bloc

    American Geophysical Union

    19 April 2017
    Media Contacts

    Nanci Bompey
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    Phone: +1 202 777 7524
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    Phone: +1 202 777 7444
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    The trace left in the sky by the meteor that broke up over Chelyabinsk, Russia, in 2013. A new study explored seven effects associated with asteroid impacts — heat, pressure shock waves, flying debris, tsunamis, wind blasts, seismic shaking and cratering — and estimated their lethality for varying sizes.
    Credit: Alex Alishevskikh

    Violent winds, shock waves from impacts pose greatest threat to humans.

    If an asteroid struck Earth, which of its effects—scorching heat, flying debris, towering tsunamis—would claim the most lives? A new study has the answer: violent winds and shock waves are the most dangerous effects produced by Earth-impacting asteroids.

    The study explored seven effects associated with asteroid impacts—heat, pressure shock waves, flying debris, tsunamis, wind blasts, seismic shaking and cratering—and estimated their lethality for varying sizes. The researchers then ranked the effects from most to least deadly, or how many lives were lost to each effect.

    Overall, wind blasts and shock waves were likely to claim the most casualties, according to the study. In experimental scenarios, these two effects accounted for more than 60 percent of lives lost. Shock waves arise from a spike in atmospheric pressure and can rupture internal organs, while wind blasts carry enough power to hurl human bodies and flatten forests.

    “This is the first study that looks at all seven impact effects generated by hazardous asteroids and estimates which are, in terms of human loss, most severe,” said Clemens Rumpf, a senior research assistant at the University of Southampton in the United Kingdom, and lead author of the new study published in Geophysical Research Letters, a journal of the American Geophysical Union.

    Rumpf said his findings, which he plans to present at the 2017 International Academy of Astronautics Planetary Defense Conference in Tokyo, Japan, could help hazard mitigation groups better prepare for asteroid threats because it details which impact effects are most dominant, which are less severe and where resources should be allocated.

    Though studies like his are necessary to reduce harm, deadly asteroid impacts are still rare, Rumpf said. Earth is struck by an asteroid 60 meters (more than 190 feet) wide approximately once every 1500 years, whereas an asteroid 400 meters (more than 1,300 feet) across is likely to strike the planet every 100,000 years, according to Rumpf.

    “The likelihood of an asteroid impact is really low,” said Rumpf. “But the consequences can be unimaginable.”

    Modeling asteroid effects

    Rumpf and his colleagues used models to pepper the globe with 50,000 artificial asteroids ranging from 15 to 400 meters (49 to 1312 feet) across—the diameter range of asteroids that most frequently strike the Earth. The researchers then estimated how many lives would be lost to each of the seven effects.

    Land-based impacts were, on average, an order of magnitude more dangerous than asteroids that landed in oceans.

    Large, ocean-impacting asteroids could generate enough power to trigger a tsunami, but the wave’s energy would likely dissipate as it traveled and eventually break when it met a continental shelf. Even if a tsunami were to reach coastal communities, far fewer people would die than if the same asteroid struck land, Rumpf said. Overall, tsunamis accounted for 20 percent of lives lost, according to the study.

    The heat generated by an asteroid accounted for nearly 30 percent of lives lost, according to the study. Affected populations could likely avoid harm by hiding in basements and other underground structures, Rumpf said.

    Seismic shaking was of least concern, as it accounted for only 0.17 percent of casualties, according to the study. Cratering and airborne debris were similarly less concerning, both garnering fewer than 1 percent of deaths.

    Only asteroids that spanned at least 18 meters (nearly 60 feet) in diameter were lethal. Many asteroids on the lower end of this spectrum disintegrate in Earth’s atmosphere before reaching the planet’s surface, but they strike more frequently than larger asteroids and generate enough heat and explosive energy to deal damage. For example, the meteor involved in the 2013 impact in Chelyabinsk, Russia, was 17 to 20 meters (roughly 55 to 65 feet) across and caused more than 1,000 injuries, inflicting burns and temporary blindness on people nearby.

    Understanding risk

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    This chart shows reported fireball events for which geographic location data are provided. Each event’s calculated total impact energy is indicated by its relative size and by a color.
    Credit: NASA

    “This report is a reasonable step forward in trying to understand and come to grips with the hazards posed by asteroids and comet impactors,” said geophysicist Jay Melosh, a distinguished professor in the Department of Earth, Atmospheric and Planetary Sciences at Purdue University in Lafayette, Indiana.

    Melosh, who wasn’t involved in the study, added that the findings “lead one to appreciate the role of air blasts in asteroid impacts as we saw in Chelyabinsk.” The majority of the injuries in the Chelyabinsk impact were caused by broken glass sent flying into the faces of unknowing locals peering through their windows after the meteor’s bright flash, he noted.

    The study’s findings could help mitigate loss of human life, according to Rumpf. Small towns facing the impact of an asteroid 30 meters across (about 98 feet) may fare best by evacuating. However, an asteroid 200 meters wide (more than 650 feet) headed for a densely-populated city poses a greater risk and could warrant a more involved response, he said.

    “If only 10 people are affected, then maybe it’s better to evacuate the area,” Rumpf said. “But if 1,000,000 people are affected, it may be worthwhile to mount a deflection mission and push the asteroid out of the way.”

    See the full post here .

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    The purpose of the American Geophysical Union is to promote discovery in Earth and space science for the benefit of humanity.

    To achieve this mission, AGU identified the following core values and behaviors.

    Core Principles

    As an organization, AGU holds a set of guiding core values:

    The scientific method
    The generation and dissemination of scientific knowledge
    Open exchange of ideas and information
    Diversity of backgrounds, scientific ideas and approaches
    Benefit of science for a sustainable future
    International and interdisciplinary cooperation
    Equality and inclusiveness
    An active role in educating and nurturing the next generation of scientists
    An engaged membership
    Unselfish cooperation in research
    Excellence and integrity in everything we do

    When we are at our best as an organization, we embody these values in our behavior as follows:

    We advance Earth and space science by catalyzing and supporting the efforts of individual scientists within and outside the membership.
    As a learned society, we serve the public good by fostering quality in the Earth and space science and by publishing the results of research.
    We welcome all in academic, government, industry and other venues who share our interests in understanding the Earth, planets and their space environment, or who seek to apply this knowledge to solving problems facing society.
    Our scientific mission transcends national boundaries.
    Individual scientists worldwide are equals in all AGU activities.
    Cooperative activities with partner societies of all sizes worldwide enhance the resources of all, increase the visibility of Earth and space science, and serve individual scientists, students, and the public.
    We are our members.
    Dedicated volunteers represent an essential ingredient of every program.
    AGU staff work flexibly and responsively in partnership with volunteers to achieve our goals and objectives.

     
  • richardmitnick 8:07 pm on April 21, 2017 Permalink | Reply
    Tags: , Astrophysics, , , ,   

    From Chandra: “NGC 4696: The Arrhythmic Beating of a Black Hole Heart” 

    NASA Chandra Banner

    NASA Chandra Telescope

    NASA Chandra

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    Composite

    2
    X-ray

    3
    Optical

    4
    Radio
    Credit: X-ray: NASA/CXC/MPE/J.Sanders et al.; Optical: NASA/STScI; Radio: NSF/NRAO/VLA
    Release Date: April 19, 2017

    A black hole has been “beating” about every 5 to 10 million years, pumping material and energy into its environment.

    This black hole is at the center of a large elliptical galaxy located within the core of the Centaurus Cluster of galaxies.

    Data from Chandra and other telescopes show evidence for repeated bursts, or eruptions, from the black hole.

    These bursts created cavities within the hot, X-ray emitting gas that pervades the cluster.

    At the center of the Centaurus galaxy cluster, there is a large elliptical galaxy called NGC 4696. Deeper still, there is a supermassive black hole buried within the core of this galaxy.

    New data from NASA’s Chandra X-ray Observatory and other telescopes has revealed details about this giant black hole, located some 145 million light years from Earth. Although the black hole itself is undetected, astronomers are learning about the impact it has on the galaxy it inhabits and the larger cluster around it.

    In some ways, this black hole resembles a beating heart that pumps blood outward into the body via the arteries. Likewise, a black hole can inject material and energy into its host galaxy and beyond.

    By examining the details of the X-ray data from Chandra, scientists have found evidence for repeated bursts of energetic particles in jets generated by the supermassive black hole at the center of NGC 4696. These bursts create vast cavities in the hot gas that fills the space between the galaxies in the cluster. The bursts also create shock waves, akin to sonic booms produced by high-speed airplanes, which travel tens of thousands of light years across the cluster.

    This composite image contains X-ray data from Chandra (red) that reveals the hot gas in the cluster, and radio data from the NSF’s Karl G. Jansky Very Large Array (blue) that shows high-energy particles produced by the black hole-powered jets. Visible light data from the Hubble Space Telescope (green) show galaxies in the cluster as well as galaxies and stars outside the cluster.

    NRAO/VLA, on the Plains of San Agustin fifty miles west of Socorro, NM, USA

    NASA/ESA Hubble Telescope Also involved in this project

    .

    5
    Cavity processing scale: This image shows a larger field of view than the main composite image above and is about 122,000 light years across. This image has also been rotated slightly clockwise to the main composite image above.

    Astronomers employed special processing to the X-ray data (shown above) to emphasize nine cavities visible in the hot gas. These cavities are labeled A through I in an additional image, and the location of the black hole is labeled with a cross. The cavities that formed most recently are located nearest to the black hole, in particular the ones labeled A and B.

    The researchers estimate that these black hole bursts, or “beats”, have occurred every five to ten million years. Besides the vastly differing time scales, these beats also differ from typical human heartbeats in not occurring at particularly regular intervals.

    A different type of processing of the X-ray data reveals a sequence of curved and approximately equally spaced features in the hot gas. These may be caused by sound waves generated by the black hole’s repeated bursts. In a galaxy cluster, the hot gas that fills the cluster enables sound waves — albeit at frequencies far too low for the human hear to detect — to propagate. (Note that both images showing the labeled cavities and this image are rotated slightly clockwise to the main composite.)

    The features in the Centaurus Cluster are similar to the ripples seen in the Perseus cluster of galaxies. The pitch of the sound in Centaurus is extremely deep, corresponding to a discordant sound about 56 octaves below the notes near middle C. This corresponds to a slightly higher (by about one octave) pitch than the sound in Perseus. Alternative explanations for these curved features include the effects of turbulence or magnetic fields.

    6
    Curved processing scale: This image also shows a larger field of view than the main composite image and is about 550,000 light years across. This image has also been rotated slightly clockwise to the main composite image.

    The black hole bursts also appear to have lifted up gas that has been enriched in elements generated in supernova explosions. The authors of the study of the Centaurus cluster created a map (shown above) showing the density of elements heavier than hydrogen and helium. The brighter colors in the map show regions with the highest density of heavy elements and the darker colors show regions with a lower density of heavy elements. Therefore, regions with the highest density of heavy elements are located to the right of the black hole. A lower density of heavy elements near the black hole is consistent with the idea that enriched gas has been lifted out of the cluster’s center by bursting activity associated with the black hole. The energy produced by the black hole is also able to prevent the huge reservoir of hot gas from cooling. This has prevented large numbers of stars from forming in the gas.

    A paper describing these results was published in the March 21st 2016 issue of the Monthly Notices of the Royal Astronomical Society. The first author is Jeremy Sanders from the Max Planck Institute for Extraterrestrial Physics in Garching, Germany.

    7

    NASA’s Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA’s Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra’s science and flight operations.

    See the full article here .

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    NASA’s Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA’s Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra’s science and flight operations from Cambridge, Mass.

     
  • richardmitnick 12:24 pm on April 21, 2017 Permalink | Reply
    Tags: 2 furious, 2 slow, , , Astrophysics, , , MASSIVE survey, SAMI galaxy survey   

    From astrobites: “2 slow, 2 furious” 

    Astrobites bloc

    Astrobites

    Apr 21, 2017
    Paddy Alton

    Titles:
    1. The MASSIVE survey – VII. The relationship of Angular Momentum, Stellar Mass and Environment of Early-Type Galaxies
    2. The SAMI galaxy survey: mass as the driver of the kinematic morphology – density relation in clusters

    Authors:
    1. Melanie Veale, Chung-Pei Ma, Jenny E. Greene, et al.
    2. Sarah Brough, Jesse van de Sande, Matt S. Owers, et al.

    First Authors’ Institutions:
    1. University of California, Berkeley, USA

    2. University of New South Wales, Australia

    Statuses:
    1. Submitted to Monthly Notices of the Royal Astronomical Society [open access]
    2. Submitted to the Astrophysical Journal [open access]

    Introduction

    Scientific papers are a bit like buses. Sometimes you wait for ages waiting for one to take you where you want to go, then – surprise, surprise – two come along at once. This is, of course, a fundamental physical law, to which even astrophysicists are not immune.

    In today’s article I’m going to break with tradition a little bit and highlight not one, but two papers, released weeks apart and with similar goals. This happens reasonably often, principally because if the science is both exciting and possible, chances are more than one team are looking into it! It’s always interesting to see independent groups take on the same question – and of course, the replicability of results is at the core of the scientific method. So for those reasons, and in the interests of fairness, let’s look at two takes on the origin of fast and slow rotating elliptical galaxies.

    Fast and Slow Rotators

    In the last decade the terms ‘fast rotator’ and ‘slow rotator’ entered astrophysical parlance as detailed studies revealed important differences among nearby galaxies. At first sight all elliptical galaxies look much alike, being more-or-less featureless red-ish blobs (see figure). However, a closer look reveals that they exhibit two quite distinct types of kinematic behaviour (the term kinematic in this context refers to the movement of stars within a galaxy, in other words its internal motions). This important detail has been highlighted by Astrobites before.

    The terminology here is not particularly imaginative: the principal difference between fast and slow rotators is, well, that the former rotate faster than the latter. But let us go into a bit more depth. Galaxies are collisionless systems, meaning that the gulf separating stars is sufficiently vast relative to their size that head-on collisions never happen in practice. Instead, all interactions are through gravity; stars whip around their host galaxy, their motions governed by its gravitational potential well. The orbits of the stars can be correlated, so that they are mostly orbiting around the same axis and in the same direction – or messy, with disordered orbits. Moreover, while all closed orbits are ellipses, there’s a big difference between a nearly circular orbit (like the Earth going round the sun) and a highly elongated orbit (like that of a long-period comet). These extremes are sometimes respectively referred to as tangential and radial orbits.

    If the orbits of stars in a galaxy are mostly correlated and tangential, the galaxy ends up as a flattened, more oblate rotating system. By contrast, disordered radial orbits give you blob-like systems without much rotation. In the first case, we might say that the system is ‘rotation supported’ (it doesn’t collapse down to a point under its own gravity because it’s rotating and can’t shed its angular momentum) and in the second that it is ‘pressure supported’ (stars falling in towards the centre are balanced by stars that have already passed through the centre and are now travelling outwards). This gets to the crux of the matter: most elliptical galaxies are rotation-supported fast rotators, but a significant fraction (about 15%) are pressure-supported slow rotators. The stark difference in their kinematics has led to suggestions that despite their apparent similarities, an alternate formation channel is required to create slow rotators.

    Today’s papers

    In order to get to the bottom of this, the two teams conducted similar investigations. Both used data from large surveys of many galaxies, the MASSIVE survey and the SAMI galaxy survey respectively. Both surveys provide detailed spectroscopy of many galaxies – large samples are necessary since the aim is to draw statistical conclusions about the population of slow rotator galaxies as a whole. From this data, the kinematics of each target can be inferred (I explained how that works in some detail in a previous article, but it’s not essential to recap all that here).

    Encouragingly, both studies hold some conclusions in common. As was already believed to be the case, both find that slow rotators are preferentially found among the most massive galaxies. Both teams looked at the effect of galaxy environment (i.e. whether the galaxy is isolated or contained in a cluster with many nearby neighbours). Massive galaxies do tend to be more commonly found in clusters, so given the dependence on mass already established such a trend must exist. What’s important is that when mass is controlled for there is no additional dependence on environment: both teams concur on this point.

    Conclusions

    Galaxies tend to grow via a series of mergers – collisions – between smaller galaxies, a process that takes place faster in dense environments where the chance of encountering another galaxy is much higher. This is the explanation for the point made above, that galaxies in clusters tend to be more massive than their isolated counterparts.

    In the past it has been suggested that slow rotators might form due to a major collision between two similar sized galaxies, a highly disruptive event that would of course tend to leave behind a particularly massive galaxy. This kind of event would be much more common in the centre of a cluster of galaxies. However, neither of the studies presented here find strong evidence for a ‘special’ formation channel like this!

    It’s certainly true that slow rotator galaxies tend to be particularly massive, but they don’t seem to care how they were put together (i.e. by many minor mergers or one big major merger): whether minor or major, galaxy mergers will tend to add mass and (usually) decrease the angular momentum of a galaxy. The more mergers that occur (i.e. the more massive a galaxy gets), the slower it will tend to rotate. In other words, fast rotators that grow large enough will eventually transition to become slow rotators instead.

    See the full article here .

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    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
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