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  • richardmitnick 1:24 pm on December 21, 2016 Permalink | Reply
    Tags: A Counterpart for Fast Radio Bursts, , , , , Gamma Rays, Neutron Star Merge   

    From astrobites: “A Counterpart for Fast Radio Bursts” 

    Astrobites bloc


    Dec 20, 2016
    Joanna Bridge

    Title: Discovery of a Transient Gamma-Ray Counterpart to FRB 131104
    Authors: J. J. DeLaunay, D. B. Fox, K. Murase, P. Mézáros, A. Keivani, C. Messick, M. A. Mostafa, F. Oikonomou, G. Tešić, and C. F. Turley
    First Author’s Institution: Department of Physics, Pennsylvania State University
    Status: Published in ApJ Letters

    It’s a mysterious case worthy of Sherlock Holmes – seemingly random bursts of radio emission generated from somewhere outside the Milky Way, with no obvious source. These emissions, known as Fast Radio Bursts (FRB), have plagued astronomers over the last several years.

    FRB Fast Radio Bursts from NAOJ Subaru, Mauna Key, Hawaii, USA
    FRB Fast Radio Bursts from NAOJ Subaru, Mauna Key, Hawaii, USA

    They were initially discovered in data archives of the Parkes radio telescope in Australia, popping up as relatively strong radio bursts that lasted only 5 milliseconds.

    CSIRO/Parkes Observatory, located 20 kilometres north of the town of Parkes, New South Wales, Australia
    CSIRO/Parkes Observatory, located 20 kilometres north of the town of Parkes, New South Wales, Australia

    The usual radio bursts we detect are usually repeating, emanating from rapidly spinning neutron stars known as pulsars. This radio signal was all alone.

    Even stranger, the signal was dispersed, which means the higher frequency portion of the burst was detected before the lower frequencies. Dispersion is a result of the lower frequency signal being slowed preferentially compared to the high frequencies by the electron clouds between us and the source. Measuring the delay between low and high frequency gives us the distance the signal has traveled. This dispersion indicated that the burst must have originated from very far away – by at least 1 Gigaparsec. That’s a distance of over 3 billion light years!

    Since the archival discovery of FRBs, these sneaky radio bursts have been caught in the act by Parkes telescope, as well as Arecibo in Puerto Rico and the Green Bank Telescope in West Virginia.

    NAIC/Arecibo Observatory, Puerto Rico, USA
    NAIC/Arecibo Observatory, Puerto Rico, USA

    GBO radio telescope, Green Bank, West Virginia, USA
    GBO radio telescope, Green Bank, West Virginia, USA

    But until now, there have been no detections in any other wavelengths than radio. In today’s paper, we see for the first time a possible counterpart for an FRB detected in very high energy gamma rays using the Swift telescope.

    NASA/SWIFT Telescope
    NASA/SWIFT Telescope

    Swift has onboard the Burst Alert Telescope (BAT) that is usually triggered when a gamma ray burst goes off somewhere in the universe. If a typical gamma ray burst was responsible for FRBs, then the BAT would have been triggered, providing almost instantaneous gamma ray measurements in the same general direction of the the FRB. The authors of today’s paper, however, wondered if perhaps there is a gamma ray counterpart to the FRBs, but is not luminous enough to trigger the BAT on Swift. They therefore went digging in the archival BAT data, looking for times when Swift just fortuitously happened to be looking in the same direction as an FRB when the radio signal was detected.

    Figure 1 The Swift BAT detection of FRB 131104. (a) shows the portion of the field of view of the BAT where the gamma ray counterpart was detected, denoted by the black circle near the top of the image. The x- and y-axes denote the position on the sky in right ascension (RA) and declination (dec), and the color bar shows how well-detected the emission is, in units of signal above the noise. (b) gives the number of photons detected per second as a function of time for gamma rays in the 5-15 keV energy range.

    Sure enough, there were four times when an FRB was detected within the same field of view as the BAT on Swift. Of these four possibilities, a gamma ray counterpart was detected for the FRB 131104 (so named for two digits for the year, month, and date of observation.) This detection is shown in Figure 1. This FRB is located 3.2 Gigaparsecs away, which corresponds to a redshift of z ~ 0.55. The reason that the BAT was not triggered for this gamma ray burst was because it was on the very edge of the detector, illuminating only 2.9% of the telescope’s detector. The authors were very careful to rule out other causes for the gamma rays.

    Of course, there are still unanswered questions about this detection. One mystery is that while the FRB lasted only 5 milliseconds, the emission detected in gamma rays lasted several minutes and released significantly more energy — a billion times more — than was detected in the radio burst. One theory posits that the sources of FRBs are brightly flaring magnetars, which are neutron stars with extremely high magnetic fields.

    Artist’s impression of the magnetar in star cluster Westerlund 1. Credit: ESO/L. Calçada

    However, if magnetars are the culprit, then the gamma ray emission should not be nearly that long nor that energetic. On the other hand, FRBs with gamma ray counterparts could be caused by binary neutron stars spiraling into each other.

    Neutron Star Merge. NASA Goddard Media Studios

    However, models indicate that we should see only about 25 of these events a year, whereas the inferred rate of FRBs is thought to be on the order of thousands per day.

    Suffice it to say, I think this is a mystery that would stump even the great detective Holmes himself (minus the small detail that he wasn’t an astrophysicist.) In some ways, this new gamma ray counterpart discovery is extremely enlightening, giving clues as to where to look next for the source of FRBs. On the other hand, however, this detection has resulted in even more questions about FRB origins. As is often the case in science, more data are needed! In the future, we should be able to fine tune the threshold for triggering the BAT when the next fast radio burst goes off, allowing us to catch it the FRB and its gamma rays in the act.

    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 7:07 am on November 5, 2016 Permalink | Reply
    Tags: Gamma Rays, MAGIC at LAPALMA, QSO B0218+357 is a blazar   

    From MAGIC: “Detour via gravitational lens makes distant galaxy visible” 

    MAGIC Cherenkov gamma ray telescope  on the Canary island of La Palma, Spain
    MAGIC Cherenkov gamma ray telescope on the Canary island of La Palma, Spain


    November 4, 2016
    No writer credit found.

    The MAGIC telescopes on the canary island of La Palma are shown. Credit: Robert Wagner

    Never before have astrophysicists measured light of such high energy from a celestial object so far away. Around 7 billion years ago, a huge explosion occurred at the black hole in the center of a galaxy. This was followed by a burst of high-intensity gamma rays. A number of telescopes, MAGIC included, have succeeded in capturing this light. An added bonus: it was thus possible to reconfirm Einstein’s General Theory of Relativity, as the light rays encountered a less distant galaxy en route to Earth – and were deflected by this so-called gravitational lens.

    The object QSO B0218+357 is a blazar, a specific type of black hole. Researchers now assume that there is a supermassive black hole at the center of every galaxy. Black holes, into which matter is currently plunging are called active black holes. They emit extremely bright jets. If these bursts point towards Earth, the term blazar is used.

    Full moon prevents the first MAGIC observation

    The event now described in “Astronomy & Astrophysics” took place 7 billion years ago, when the universe was not even half its present age. “The blazar was discovered initially on 14 July 2014 by the Large Area Telescope (LAT) of the Fermi satellite,” explains Razmik Mirzoyan, scientist at the Max Planck Institute for Physics and spokesperson for the MAGIC collaboration. “The gamma ray telescopes on Earth immediately fixed their sights on the blazer in order to learn more about this object.”

    One of these telescopes was MAGIC, on the Canary Island of La Palma, specialized in high-energy gamma rays. It can capture photons – light particles – whose energy is 100 billion times higher than the photons emitted by our Sun and a thousand times higher than those measured by Fermi-LAT. The MAGIC scientists were initially out of luck, however: A full moon meant the telescope was not able to operate during the time in question.

    Photons are emitted from a galaxy QSO B0218+357 in the direction of the Earth. Due to the gravitational effect of the intervening galaxy B0218+357G photons form two paths that reach Earth with a delay of about 11 days. Photons were observed by both the Fermi-LAT instrument and the MAGIC telescopes. Credit: Daniel Lopez/IAC; NASA/ESA; NASA E/PO – Sonoma State University, Aurore Simonnet

    Gravitational lens deflects ultra-high-energy photons

    Eleven days later, MAGIC got a second chance, as the gamma rays emitted by QSO B0218+357 did not take the direct route to Earth: One billion years after setting off on their journey, they reached the galaxy B0218+357G. This is where Einstein’s General Theory of Relativity came into play.

    This states that a large mass in the universe, a galaxy, for example, deflects light of an object behind it. In addition, the light is focused as if by a gigantic optical lens – to a distant observer, the object appears to be much brighter, but also distorted. The light beams also need different lengths of time to pass through the lens, depending on the angle of observation.

    This gravitational lens was the reason that MAGIC was able, after all, to measure QSO B0218+357 – and thus the most distant object in the high-energy gamma ray spectrum. “We knew from observations undertaken by the Fermi space telescope and radio telescopes in 2012 that the photons that took the longer route would arrive 11 days later,” says Julian Sitarek (University of ?ódz, Poland), who led this study. “This was the first time we were able to observe that high-energy photons were deflected by a gravitational lens.”

    Doubling the size of the gamma-ray universe

    The fact that gamma rays of such high energy from a distant celestial body reach Earth’s atmosphere is anything but obvious. “Many gamma rays are lost when they interact with photons which originate from galaxies or stars and have a lower energy,” says Mirzoyan. “With the MAGIC observation, the part of the universe that we can observe via gamma rays has doubled.”

    The fact that the light arrived on Earth at the time calculated could rattle a few theories on the structure of the vacuum – further investigations, however, are required to confirm this. “The observation currently points to new possibilities for high-energy gamma ray observatories – and provides a pointer for the next generation of telescopes in the CTA project,” says Mirzoyan, summing up the situation.

    See the full article here .


    MAGIC (Major Atmospheric Gamma Imaging Cherenkov) is a system of two 17 m diameter, F/1.03 Imaging Atmospheric Cherenkov Telescopes (IACT). They are dedicated to the observation of gamma rays from galactic and extragalactic sources in the very high energy range (VHE, 30 GeV to 100 TeV).

    The MAGIC telescopes are currently run by an international collaboration of about 165 astrophysicists from 24 institutions and consortia from 11 countries.

    MAGIC in a Nutshell

    The main goal of the MAGIC project was to build an instrument that could perform measurements in an energy range below 100 GeV, down to about 30 GeV, up to the high-energetic “terra incognita” of the electromagnetic emission spectrum, traditionally considered as the classical domain of satellite-born instruments. MAGIC researchers were anticipating finding new classes of gamma-ray sources such as, for example, pulsars and Gamma Ray Bursts (GRB). Because of the strong absorption of TeV gamma rays by the extragalactic background light, MAGIC was aiming to measure sources at few tens of GeV, where the universe becomes progressively more transparent. At lower energies, one can search for powerful sources residing at large redshifts. The telescopes measure Cherenkov light images of extended air showers from a target source direction. The software analysis allows, with very high efficiency, to select neutral gamma-ray induced electromagnetic showers from the several orders of magnitudes more intense isotropic background due to the charged particle (mostly hadron) induced showers. The MAGIC telescopes are located at a height of 2200 m a.s.l. on the Roque de los Muchachos European Northern Observatory on the Canary Island of La Palma (28°N, 18°W).

  • richardmitnick 8:59 pm on July 5, 2016 Permalink | Reply
    Tags: , Gamma Rays, ,   

    From Symmetry: “Incredible hulking facts about gamma rays” 


    Matthew R. Francis


    From lightning to the death of electrons, the highest-energy form of light is everywhere.

    Gamma rays are the most energetic type of light, packing a punch strong enough to pierce through metal or concrete barriers. More energetic than X-rays, they are born in the chaos of exploding stars, the annihilation of electrons and the decay of radioactive atoms. And today, medical scientists have a fine enough control of them to use them for surgery. Here are seven amazing facts about these powerful photons.

    Doctors conduct brain surgery using “gamma ray knives.”


    Gamma rays can be helpful as well as harmful (and are very unlikely to turn you into the Hulk). To destroy brain cancers and other problems, medical scientists sometimes use a “gamma ray knife.” This consists of many beams of gamma rays focused on the cells that need to be destroyed. Because each beam is relatively small, it does little damage to healthy brain tissue. But where they are focused, the amount of radiation is intense enough to kill the cancer cells. Since brains are delicate, the gamma ray knife is a relatively safe way to do certain kinds of surgery that would be a challenge with ordinary scalpels.

    [My wife had gamma-knife brain surgery. Whn I asked her neursurgeon how they got gamma rays, he replied from cobalt.]


    The name “gamma rays” came from Ernest Rutherford.

    French chemist Paul Villard first identified gamma rays in 1900 from the element radium, which had been isolated by Marie and Pierre Curie just two years before. When scientists first studied how atomic nuclei changed form, they identified three types of radiation based on how far they penetrated into a barrier made of lead. Ernest Rutherford named the radiation for the first three letters of the Greek alphabet. Alpha rays bounce right off, beta rays went a little farther, and gamma rays went the farthest. Today we know alpha rays are the same thing as helium nuclei (two protons and two neutrons), beta rays are either electrons or positrons (their antimatter versions), and gamma rays are a kind of light.


    Nuclear reactions are a major source of gamma rays.

    When an unstable uranium nucleus splits in the process of nuclear fission, it releases a lot of gamma rays in the process. Fission is used in both nuclear reactors and nuclear warheads. To monitor nuclear tests in the 1960s, the United States launched gamma radiation detectors on satellites. They found far more explosions than they expected to see. Astronomers eventually realized these explosions were coming from deep space—not the Soviet Union—and named them gamma-ray bursts, or GRBs. Today we know GRBs come in two types: the explosions of extremely massive stars, which pump out gamma rays as they die, and collisions between highly dense relics of stars called neutron stars and something else, probably another neutron star or a black hole.


    Gamma rays played a key role in the discovery of the Higgs boson.

    Most of the particles in the Standard Model of particle physics are unstable; they decay into other particles almost as soon as they come into existence. The Higgs boson, for example, can decay into many different types of particles, including gamma rays. Even though theory predicts that a Higgs boson will decay into gamma rays just 0.2 percent of the time, this type of decay is relatively easy to identify and it was one of the types that scientists observed when they first discovered the Higgs boson.

    NASA Fermi Gamma-ray Space Telescope  Gamma-ray Burst Monitor (GBM)
    NASA Fermi Gamma-ray Space Telescope Gamma-ray Burst Monitor

    To study gamma rays, astronomers build telescopes in space.

    Gamma rays heading toward the Earth from space interact with enough atoms in the atmosphere that almost none of them reach the surface of the planet. That’s good for our health, but not so great for those who want to study GRBs and other sources of gamma rays. To see gamma rays before they reach the atmosphere, astronomers have to build telescopes in space. This is challenging for a number of reasons. For example, you can’t use a normal lens or mirror to focus gamma rays, because the rays punch right through them. Instead an observatory like the Fermi Gamma-ray Space Telescope detects the signal from gamma rays when they hit a detector and convert into pairs of electrons and positrons.

    Some gamma rays come from thunderstorms.

    In the 1990s, observatories in space detected bursts of gamma rays coming from Earth that eventually were traced to thunderclouds. When static electricity builds up inside clouds, the immediate result is lightning. That static electricity also acts like a giant particle accelerator, creating pairs of electrons and positrons, which then annihilate into gamma rays. These bursts happen high enough in the air that only airplanes are exposed—and they’re one reason for flights to steer well away from storms.

    Gamma rays (indirectly) give life to Earth.

    Hydrogen nuclei are always fusing together in the core of the sun. When this happens, one byproduct is gamma rays. The energy of the gamma rays keeps the sun’s core hot. Some of those gamma rays also escape into the sun’s outer layers, where they collide with electrons and protons and lose energy. As they lose energy, they change into ultraviolet, infrared and visible light. The infrared light keeps Earth warm, and the visible light sustains Earth’s plants.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 11:36 am on June 4, 2016 Permalink | Reply
    Tags: , , Gamma Rays   

    From Astro Watch: “At the Cradle of Oxygen: Brand-new Detector to Reveal the Interiors of Stars” 

    Astro Watch bloc

    Astro Watch

    June 4, 2016
    No writer credit found

    No image caption. No image credit

    The most intense source of gamma radiation constructed to date will soon become operational at the ELI Nuclear Physics research facility. It will be possible to study reactions that reveal the details of many processes occurring within stars, in particular those leading to the formation of oxygen. An important part of the equipment will rely on a particle detector built by physicists at the University of Warsaw, Poland. A prototype has recently concluded the first round of testing.

    Oxygen is essential for life: we are immersed in it yet none of it actually originates from our own planet. All oxygen was ultimately formed through thermonuclear reactions deep inside stars. Laboratory studies of the astrophysical processes leading to the formation of oxygen are extremely important. A big step forward in these studies will be possible when work commences in 2018 at the Extreme Light Infrastructure – Nuclear Physics (ELI-NP) facility near Bucharest, using a state-of-the-art source of intense gamma radiation. High energy protons will be intercepted using a specially-designed particle detector acting as a target. A demonstrator version of the detector, constructed at the Faculty of Physics, University of Warsaw (FUW), has recently completed the first round of tests in Romania.

    In terms of mass, the most abundant elements in the Universe are hydrogen (74%) and helium (24%). The percentage by mass of other, heavier elements is significantly lower: oxygen comprises just 0.85% and carbon 0.39% (in contrast, oxygen comprises 65% of the human body and carbon 18% by mass). In nature, conditions supporting the formation of oxygen are present only within evolutionarily-advanced stars which have converted almost all their hydrogen into helium. Helium becomes then their main fuel. At this stage, three helium nuclei start combining into a carbon nucleus. By adding another helium nucleus, this in turn forms an oxygen nucleus and emits one or more gamma photons.

    “Oxygen can be described as the ‘ash’ from the thermonuclear ‘combustion’ of carbon. But what mechanism explains why carbon and oxygen are always formed in stars at more or less the same proportion of 6 to 10?” asks Dr. Chiara Mazzocchi (FUW). She goes on to explain: “Stars evolve in stages. During the first stage, they convert hydrogen into helium, then helium into carbon, oxygen and nitrogen, with heavier elements formed in subsequent stages. Oxygen is formed from carbon during the helium-burning phase. The thing is that, in theory, oxygen could be produced at a faster rate. If the star were to run out of helium and shift to the next stage of its evolution, the proportions between carbon and oxygen would be different.”

    The experiments planned for ELI-NP will not actually recreate thermonuclear reactions converting carbon into oxygen and photons gamma. In fact, researchers are hoping to observe the reverse reaction: collisions between high-energy photons with oxygen nuclei to produce carbon and helium nuclei. Registering the products of this decay should make it possible to study the characteristics of the reaction and fine-tune existing theoretical models of thermonuclear synthesis.

    “We are preparing an eTPC detector for the experiments at ELI-NP. It is an electronic-readout time-projection chamber, which is an updated version of an earlier detector built at the Faculty’s Institute of Experimental Physics. The latter was successfully used by our researchers for the world’s first observations of a rare nuclear process: two-proton decay,” says Dr. Mikolaj Cwiok (FUW).

    The main element of the eTPC detector is a chamber filled with gas comprising many oxygen nuclei (e.g. carbon dioxide). The gas acts as a target. The gamma radiation beam passes through the gas, with some of the photons colliding with oxygen nuclei to produce carbon and helium nuclei. The nuclei formed through the reaction, which are charged particles, ionize the gas. In order to increase their range, the gas is kept at a reduced pressure, around 1/10 of the atmospheric one. The released electrons are directed using an electric field towards the Gas Electron Multiplier (GEM) amplification structures followed by readout electrodes. The paths of the particles are registered electronically using strip electrodes. Processing the data using specialized FPGA processors makes it possible to reconstruct the 3D paths of the particles.

    The active region of the detector will be 35x20x20 cm3, and at nominal intensity of the photon beam it should register up to 70 collisions of gamma photons with oxygen nuclei per day. Tests at ELI-NP used a demonstrator:a smaller but fully functional version of the final detector, named mini-eTPC. The device was tested with a beam of alpha particles (helium nuclei).

    “We are extremely pleased with the results of the tests conducted thus far. The demonstrator worked as we expected and successfully registered the tracks of charged particles. We are certain to use it in future research as a fully operational measuring device. In 2018, ELI-NP will be equipped with a larger detector which we are currently building at our laboratories,” adds Dr. Mazzocchi.

    The project is carried out in collaboration with researchers from ELI-NP/IFIN-HH (Magurele, Romania) and the University of Connecticut in the US. The Warsaw team, led by Prof. Wojciech Dominik, brings together physicists and engineers from the Division of Particles and Fundamental Interactions and the Nuclear Physics Division and students from the University of Warsaw: Jan Stefan Bihalowicz, Jerzy Manczak, Katarzyna Mikszuta and Piotr Podlaski.

    Extreme Light Infrastructure (ELI) is a research project valued at 850 million euro, conducted as part of the European Strategy Forum on Research Infrastructures roadmap. The ELI scientific consortium will encompass three centers in the Czech Republic, Romania and Hungary, focusing on research into the interactions between light and matter under the conditions of the most powerful photon beams and at a wide range of wavelengths and timescales measured in attoseconds (a billionth of a billionth of a second). The Romanian ELI – Nuclear Physics center, in Magurele near Bucharest, conducts research into two sources of radiation: high-intensity radiation lasers (of the order of a 1023 watts per square centimeter), and high-intensity sources of monochromatic gamma radiation. The gamma beam will be formed by scattering laser light off the electrons accelerated by a linear accelerator to speeds nearing the speed of light.

    Credit: fuw.edu.pl
    Dr. Chiara Mazzocchi
    Institute of Experimental Physics, Faculty of Physics, University of Warsaw
    tel. +48 22 5532666
    email: chiara.mazzocchi@fuw.edu.pl

    See the full article here .

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  • richardmitnick 11:40 am on May 9, 2016 Permalink | Reply
    Tags: , , Gamma Rays,   

    From New Scientist: “Water telescope’s first sky map shows flickering black holes” 


    New Scientist

    18 April 2016 [just appeared on social media]

    Lisa Grossman

    HAWC High Altitude Cherenkov Experiment, HAWC Collaboration
    HAWC High Altitude Cherenkov Gamma-Ray Collaboration, HAWC Observatory, Sierra Negra volcano near Puebla, Mexico

    Twinkle, twinkle, little black hole. The High Altitude Water Cherenkov observatory has released its first map of the sky, including the first measurements of how often black holes flicker on and off. It has also caught pulsars, supernova remnants, and other bizarre cosmic beasts.

    “This is our deepest look at two-thirds of the sky, as well as the highest energy photons we’ve ever seen from any source,” says Brenda Dingus of Los Alamos National Laboratory, who presented the map at the American Physical Society meeting in Salt Lake City, Utah on 18 April. “We’re at the high energy frontier.”

    HAWC has been operating from the top of a mountain in central Mexico for about a year, and has caught some of the highest-energy photons ever observed. It is sensitive to gamma rays between 0.1 and 100 teraelectronvolts (TeV) in energy – more than 7 times higher energy than the particles produced in the Large Hadron Collider. The most energetic photon they’ve picked up so far is 60 TeV.

    HAWC’s map of the gamma ray sky. HAWC Collaboration

    But this is no normal telescope. “HAWC doesn’t look or work like any other observatory,” Dingus says. The detector is made up of 300 water tanks filled with 200,000 litres of purified water each (see main image, above). When high-energy particles go through the water, they emit a blue light called Cherenkov radiation. Physicists can use that light to reconstruct where the particles came from.

    HAWC doesn’t observe the extremely high-energy photons directly. They are blocked by our atmosphere – luckily for us, as they can damage living tissue. Instead the detector catches the spray of secondary particles that gamma rays produce when they strike the atmosphere, called air showers.

    “20,000 air shower particles per second hit our detector,” Dingus says. “In fact they’re hitting us right now.”

    In the first year of data, HAWC picked up 40 distinct sources of gamma rays, 10 of which had not been seen in gamma rays before. The team is now working to figure out if they were associated with any other known objects that have been seen in other wavelengths like visible or infrared light.

    One, for instance, was associated with a known supernova remnant from an energetic pulsar, says Michelle Hui of NASA’s Marshall Spaceflight Center in Huntsville, Alabama. When massive stars die as supernovas, they slough off material in a cloud called a supernova remnant. The shock wave from the explosion then sweeps through the cloud and accelerates particles in it to extremely high energies, where they radiate gamma rays.

    Another source is a known pulsar 26,000 light years away. A nearby third is still being identified, and might be related to the supernova remnant.

    Three new sources of gamma rays spotted by HAWC. HAWC Collaboration

    Flickering black holes

    HAWC can also pick up gamma rays from galaxies outside the Milky Way, the sources of which are much more mysterious. We think they are caused by the black holes at galactic centres, but the details of how the photons gain so much energy are murky.

    Because it is watching 24 hours a day, the detector can pick up changes in gamma ray brightness more reliably than ever before. Just 10 days ago, HAWC spotted a flare in a galaxy called Markarian 501.

    “On April 5 we didn’t see it, on April 6 it got very bright, and by April 8 it had nearly disappeared again,” said Robert Lauer of the University of New Mexico. The team put out an announcement on the Astronomer’s Telegram network to alert other observatories to follow up in different wavelengths, although it has not had any responses yet.

    Previous telescopes that could catch such energetic photons could only look at one part of the sky at once, so they couldn’t measure the frequency of these flares. Over the next five years, HAWC will be able to make the first measurements of how often they happen. This level of flaring seems to happen about 5 to 10 times per year, Lauer says, but it seems to vary from galaxy to galaxy.

    HAWC will also be able to see such a flare from the black hole at the centre of our own galaxy.

    “We know these things happen, so we expect them to happen here,” Hui says. “We just don’t know how often.”

    See the full article here .

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  • richardmitnick 7:27 pm on April 18, 2016 Permalink | Reply
    Tags: , , Gamma Rays,   

    From phys.org: “HAWC Gamma-ray Observatory reveals new look at the very-high-energy sky” 


    April 18, 2016

    View of two-thirds of the entire sky with very-high-energy gamma rays observed by HAWC. Many sources are clearly visible in our own Milky Way galaxy, as well as two other galaxies: Markarian 421 and Markarian 501. Some well-known constellations are shown as a reference. The center of the Milky Way is located toward Sagittarius. Credit: HAWC Collaboration

    The United States and Mexico constructed the High Altitude Water Cherenkov (HAWC) Gamma-ray Observatory to observe some of the most energetic phenomena in the known universe—the aftermath when massive stars die, glowing clouds of electrons around rapidly spinning neutron stars, and supermassive black holes devouring matter and spitting out powerful jets of particles. These violent explosions produce high-energy gamma rays and cosmic rays, which can travel large distances—making it possible to see objects and events far outside our own galaxy.

    HAWC High Altitude Cherenkov Experiment
    HAWC High Altitude Cherenkov Experiment

    Today, scientists operating HAWC released a new survey of the sky made from the highest energy gamma rays ever observed. The new sky map, which uses data collected since the observatory began running at full capacity last March, offers a deeper understanding of high-energy processes taking place in our galaxy and beyond.

    “HAWC gives us a new way to see the high-energy sky,” said Jordan Goodman, professor of physics at the University of Maryland, and U.S. lead investigator and spokesperson for the HAWC collaboration. “This new data from HAWC shows the galaxy in unprecedented detail, revealing new high-energy sources and previously unseen details about existing sources.”

    HAWC researchers presented the new observation data and sky map April 18, 2016, at the American Physical Society meeting. They also participated in a press conference at the meeting.

    The new sky map shows many new gamma ray sources within our own Milky Way galaxy. Because HAWC observes 24 hours per day and year-round with a wide field-of-view and large area, the observatory boasts a higher energy reach especially for extended objects. In addition, HAWC can uniquely monitor for gamma ray flares by sources in our galaxy and other active galaxies, such as Markarian 421 and Markarian 501.

    HAWC observations show that a previously known gamma ray source in the Milky Way galaxy, TeV J1930+188, which is probably due to a pulsar wind nebula, is far more complicated than originally thought. Where researchers previously identified a single gamma ray source, HAWC identified several hot spots. Credit: HAWC Collaboration

    One of HAWC’s new observations provides a better understanding of the high-energy nature of the Cygnus region—a northern constellation lying on the plane of the Milky Way. A multitude of neutron stars and supernova remnants call this star nursery home. HAWC scientists observed previously unknown objects in the Cygnus region and identified objects discovered earlier with sharper resolution.

    In a region of the Milky Way where researchers previously identified a single gamma ray source named TeV J1930+188, HAWC identified several hot spots, indicating that the region is more complicated than previously thought.

    “Studying these objects at the highest energies can reveal the mechanism by which they produce gamma rays and possibly help us unravel the hundred-year-old mystery of the origin of high-energy cosmic rays that bombard Earth from space,” said Goodman.

    HAWC—located 13,500 feet above sea level on the slopes of Mexico’s Volcán Sierra Negra—contains 300 detector tanks, each holding 50,000 gallons of ultrapure water with four light sensors anchored to the floor. When gamma rays or cosmic rays reach Earth’s atmosphere they set off a cascade of charged particles, and when these particles reach the water in HAWC’s detectors, they produce a cone-shaped flash of light known as Cherenkov radiation. The effect is much like a sonic boom produced by a supersonic jet, because the particles are traveling slightly faster than the speed of light in water when they enter the detectors.

    The light sensors record each flash of Cherenkov radiation inside the detector tanks. By comparing nanosecond differences in arrival times at each light sensor, scientists can reconstruct the angle of travel for each particle cascade. The intensity of the light indicates the primary particle’s energy, and the pattern of detector hits can distinguish between gamma rays and cosmic rays. With 300 detectors spread over an area equivalent to more than three football fields, HAWC “sees” these events in relatively high resolution.

    “Unlike traditional telescopes, with HAWC we have now an instrument that surveys two-thirds of the sky at the highest energies, day and night,” said Andrés Sandoval, Mexico spokesperson for HAWC.

    HAWC exhibits 15-times greater sensitivity than its predecessor—an observatory known as Milagro that operated near Los Alamos, New Mexico, and ceased taking data in 2008. In eight years of operation, Milagro found new sources of high-energy gamma rays, detected diffuse gamma rays from the Milky Way galaxy and discovered that the cosmic rays hitting earth had an unexpected non-uniformity.

    “HAWC will collect more data in the next few years, allowing us to reach even higher energies,” said Goodman. “Combining HAWC observations with data from other instruments will allow us to extend the reach of our understanding of the most violent processes in the universe.”

    See the full article here .

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  • richardmitnick 6:29 pm on April 18, 2016 Permalink | Reply
    Tags: , , Gamma Rays, ,   

    From NASA Fermi: “NASA’s Fermi Telescope Poised to Pin Down Gravitational Wave Sources” 

    NASA Fermi Banner

    NASA/Fermi Telescope
    NASA Fermi

    April 18, 2016
    Francis Reddy
    NASA’s Goddard Space Flight Center, Greenbelt, Maryland

    On Sept. 14, waves of energy traveling for more than a billion years gently rattled space-time in the vicinity of Earth. The disturbance, produced by a pair of merging black holes, was captured by the Laser Interferometer Gravitational-Wave Observatory (LIGO) facilities in Hanford, Washington, and Livingston, Louisiana.

    Black holes merging Swinburne Astronomy Productions
    Black holes merging Swinburne Astronomy Productions

    Cornell SXS team. Two merging black holes simulation
    Cornell SXS team. Two merging black holes simulation

    MIT/Caltech Advanced aLIGO Hanford Washington USA installation
    MIT/Caltech Advanced aLIGO Hanford Washington USA installation

    This event marked the first-ever detection of gravitational waves and opens a new scientific window on how the universe works.

    Less than half a second later, the Gamma-ray Burst Monitor (GBM) on NASA’s Fermi Gamma-ray Space Telescope picked up a brief, weak burst of high-energy light consistent with the same part of the sky. Analysis of this burst suggests just a 0.2-percent chance of simply being random coincidence. Gamma-rays arising from a black hole merger would be a landmark finding because black holes are expected to merge “cleanly,” without producing any sort of light.

    Access mp4 video here . This visualization shows gravitational waves emitted by two black holes (black spheres) of nearly equal mass as they spiral together and merge. Yellow structures near the black holes illustrate the strong curvature of space-time in the region. Orange ripples represent distortions of space-time caused by the rapidly orbiting masses. These distortions spread out and weaken, ultimately becoming gravitational waves (purple). The merger timescale depends on the masses of the black holes. For a system containing black holes with about 30 times the sun’s mass, similar to the one detected by LIGO in 2015, the orbital period at the start of the movie is just 65 milliseconds, with the black holes moving at about 15 percent the speed of light. Space-time distortions radiate away orbital energy and cause the binary to contract quickly. As the two black holes near each other, they merge into a single black hole that settles into its “ringdown” phase, where the final gravitational waves are emitted. For the 2015 LIGO detection, these events played out in little more than a quarter of a second. This simulation was performed on the Pleiades supercomputer at NASA’s Ames Research Center. Credits: NASA/J. Bernard Kelly (Goddard), Chris Henze (Ames) and Tim Sandstrom (CSC Government Solutions LLC)

    “This is a tantalizing discovery with a low chance of being a false alarm, but before we can start rewriting the textbooks we’ll need to see more bursts associated with gravitational waves from black hole mergers,” said Valerie Connaughton, a GBM team member at the National Space, Science and Technology Center in Huntsville, Alabama, and lead author of a paper on the burst now under review by The Astrophysical Journal.

    Detecting light from a gravitational wave source will enable a much deeper understanding of the event. Fermi’s GBM sees the entire sky not blocked by Earth and is sensitive to X-rays and gamma rays with energies between 8,000 and 40 million electron volts (eV). For comparison, the energy of visible light ranges between about 2 and 3 eV.

    NASA Fermi Gamma-ray Space Telescope  Gamma-ray Burst Monitor (GBM)
    NASA Fermi Gamma-ray Space Telescope Gamma-ray Burst Monitor (GBM)

    With its wide energy range and large field of view, the GBM is the premier instrument for detecting light from short gamma-ray bursts (GRBs), which last less than two seconds. They are widely thought to occur when orbiting compact objects, like neutron stars and black holes, spiral inward and crash together. These same systems also are suspected to be prime producers of gravitational waves.

    “With just one joint event, gamma rays and gravitational waves together will tell us exactly what causes a short GRB,” said Lindy Blackburn, a postdoctoral fellow at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and a member of the LIGO Scientific Collaboration. “There is an incredible synergy between the two observations, with gamma rays revealing details about the source’s energetics and local environment and gravitational waves providing a unique probe of the dynamics leading up to the event.” He will be discussing the burst and how Fermi and LIGO are working together in an invited talk at the American Physical Society meeting in Salt Lake City on Tuesday.

    Currently, gravitational wave observatories possess relatively blurry vision. This will improve in time as more facilities begin operation, but for the September event, dubbed GW150914 after the date, LIGO scientists could only trace the source to an arc of sky spanning an area of about 600 square degrees, comparable to the angular area on Earth occupied by the United States.

    “That’s a pretty big haystack to search when your needle is a short GRB, which can be fast and faint, but that’s what our instrument is designed to do,” said Eric Burns, a GBM team member at the University of Alabama in Huntsville. “A GBM detection allows us to whittle down the LIGO area and substantially shrinks the haystack.”

    Access mp4 video here. Fermi’s GBM saw a fading X-ray flash at nearly the same moment LIGO detected gravitational waves from a black hole merger in 2015. This movie shows how scientists can narrow down the location of the LIGO source on the assumption that the burst is connected to it. In this case, the LIGO search area is reduced by two-thirds. Greater improvements are possible in future detections. Credits: NASA’s Goddard Space Flight Center

    Less than half a second after LIGO detected gravitational waves, the GBM picked up a faint pulse of high-energy X-rays lasting only about a second. The burst effectively occurred beneath Fermi and at a high angle to the GBM detectors, a situation that limited their ability to establish a precise position. Fortunately, Earth blocked a large swath of the burst’s likely location as seen by Fermi at the time, allowing scientists to further narrow down the burst’s position.

    The GBM team calculates less than a 0.2-percent chance random fluctuations would have occurred in such close proximity to the merger. Assuming the events are connected, the GBM localization and Fermi’s view of Earth combine to reduce the LIGO search area by about two-thirds, to 200 square degrees. With a burst better placed for the GBM’s detectors, or one bright enough to be seen by Fermi’s Large Area Telescope, even greater improvements are possible.

    The LIGO event was produced by the merger of two relatively large black holes, each about 30 times the mass of the sun. Binary systems with black holes this big were not expected to be common, and many questions remain about the nature and origin of the system.

    Black hole mergers were not expected to emit significant X-ray or gamma-ray signals because orbiting gas is needed to generate light. Theorists expected any gas around binary black holes would have been swept up long before their final plunge. For this reason, some astronomers view the GBM burst as most likely a coincidence and unrelated to GW150914. Others have developed alternative scenarios where merging black holes could create observable gamma-ray emission. It will take further detections to clarify what really happens when black holes collide.

    Albert Einstein predicted the existence of gravitational waves in his general theory of relativity a century ago, and scientists have been attempting to detect them for 50 years. Einstein pictured these waves as ripples in the fabric of space-time produced by massive, accelerating bodies, such as black holes orbiting each other. Scientists are interested in observing and characterizing these waves to learn more about the sources producing them and about gravity itself.

    For more information about NASA’s Fermi Gamma-ray Space Telescope, please visit:


    See the full article here .

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    The Fermi Gamma-ray Space Telescope , formerly referred to as the Gamma-ray Large Area Space Telescope (GLAST), is a space observatory being used to perform gamma-ray astronomy observations from low Earth orbit. Its main instrument is the Large Area Telescope (LAT), with which astronomers mostly intend to perform an all-sky survey studying astrophysical and cosmological phenomena such as active galactic nuclei, pulsars, other high-energy sources and dark matter. Another instrument aboard Fermi, the Gamma-ray Burst Monitor (GBM; formerly GLAST Burst Monitor), is being used to study gamma-ray bursts. The mission is a joint venture of NASA, the United States Department of Energy, and government agencies in France, Germany, Italy, Japan, and Sweden.

  • richardmitnick 4:37 pm on April 18, 2016 Permalink | Reply
    Tags: , , , Gamma Rays,   

    From AAS NOVA: “Found: A Galaxy’s Missing Gamma Rays” 


    American Astronomical Society

    Recent observations have detected high-energy gamma-ray emission for the first time from the massive, star-forming galaxy Arp 220 (shown here in optical wavelengths, as imaged by Hubble). [NASA/ESA/C. Wilson (McMaster University)]

    NASA/ESA Hubble Telescope
    NASA/ESA Hubble Telescope

    Recent reanalysis of data from the Fermi Gamma-ray Space Telescope has resulted in the first detection of high-energy gamma rays emitted from a nearby galaxy.

    NASA/Fermi Telescope
    NASA/Fermi Telescope

    This discovery reveals more about how supernovae interact with their environments.

    Colliding Supernova Remnant

    Supernova remnant Crab nebula. NASA/ESA Hubble
    Supernova remnant Crab nebula. NASA/ESA Hubble

    After a stellar explosion, the supernova’s ejecta expand, eventually encountering the ambient interstellar medium. According to models, this generates a strong shock, and a fraction of the kinetic energy of the ejecta is transferred into cosmic rays — high-energy radiation composed primarily of protons and atomic nuclei. Much is still unknown about this process, however. One open question is: what fraction of the supernova’s explosion power goes into accelerating these cosmic rays?

    In theory, one way to answer this is by looking for gamma rays.

    Gamma rays from the Fermi Gamma-ray Space Telescope, could be produced by proposed dark matter interactions
    Gamma rays from the Fermi Gamma-ray Space Telescope, could be produced by proposed dark matter interactions

    In a starburst galaxy, the collision of the supernova-accelerated cosmic rays with the dense interstellar medium is predicted to produce high-energy gamma rays. That radiation should then escape the galaxy and be visible to us.

    Pass 8 to the Rescue

    Observational tests of this model, however, have been stumped by Arp 220. This nearby ultraluminous infrared galaxy is the product of a galaxy merger ~700 million years ago that fueled a frenzy of starbirth. Due to its dusty interior and extreme levels of star formation, Arp 220 has long been predicted to emit the gamma rays produced by supernova-accelerated cosmic rays. But though we’ve looked, gamma-ray emission has never been detected from this galaxy … until now.

    In a recent study*, a team of scientists led by Fang-Kun Peng (Nanjing University) reprocessed 7.5 years of Fermi observations using the new Pass 8 analysis software. The resulting increase in resolution revealed the first detection of GeV emission from Arp 220!

    Gamma-ray luminosity vs. total infrared luminosity for LAT-detected star-forming galaxies and Seyferts. Arp 220’s luminosities are consistent with the scaling relation. [Peng et al. 2016]

    Acceleration Efficiency

    Peng and collaborators argue that this emission is due solely to cosmic-ray interactions with interstellar gas. This picture is supported by the lack of variability in the emission, and the fact that Arp 220’s gamma-ray luminosity is consistent with the scaling relation between gamma-ray and infrared luminosity for star-forming galaxies. The authors also argue that, due to Arp 220’s high gas density, all cosmic rays will interact with the gas before escaping.

    Under these two assumptions, Peng and collaborators use the gamma-ray luminosity and the known supernova rate in Arp 220 to estimate how efficiently cosmic rays are accelerated by supernova remnants in the galaxy. They determine that 4.2 ± 2.6% of the supernova remnant’s kinetic energy is used to accelerate cosmic rays above 1 GeV.

    This is the first time such a rate has been measured directly from gamma-ray emission, but it’s consistent with estimates of 3-10% efficiency in the Milky Way. Future analysis of other ultraluminous infrared galaxies like Arp 220 with Fermi (and Pass 8!) will hopefully reveal more about these recent-merger, starburst environments.

    Fang-Kun Peng et al 2016* ApJ 821 L20. doi:10.3847/2041-8205/821/2/L20

    Science paper:

    See the full article here .

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  • richardmitnick 8:39 am on April 14, 2016 Permalink | Reply
    Tags: , Dark Energy/Dark Matter, Gamma Rays,   

    From NOVA: “Dark Matter’s Invisible Hand” 



    13 Apr 2016
    Charles Q. Choi

    Dark matter is currently one of the greatest mysteries in the universe.

    Dark matter cosmic web and the large-scale structure it forms The Millenium Simulation, V. Springel et al
    Dark matter cosmic web and the large-scale structure it forms The Millenium Simulation, V. Springel et al

    It’s thought to be an invisible substance that makes up roughly five-sixths of all matter in the cosmos, a dark fog suffusing the universe that rarely interacts with ordinary matter. But when it does, according to an unexpected finding by theoretical physicist Lisa Randall, the consequences could be momentous.

    Astronomers first detected dark matter through its gravitational pull, which apparently keeps the Milky Way and other galaxies from ripping themselves apart given the speeds at which they spin.

    Scientists have mostly ruled out all known ordinary materials as candidates for dark matter. The current consensus is that dark matter lies outside the Standard Model of particle physics, currently the best description of how all known subatomic particles behave.

    The Standard Model of elementary particles , with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.
    The Standard Model of elementary particles , with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    Specifically, physicists have suggested that dark matter is composed of new kinds of particles that have very weak interactions—not just with ordinary matter but also with themselves.

    Gamma rays from the Fermi Gamma-ray Space Telescope, could be produced by proposed dark matter interactions
    Gamma rays from the Fermi Gamma-ray Space Telescope, could be produced by proposed dark matter interactions.

    NASA/Fermi Gamma Ray Telescope
    NASA/Fermi Gamma Ray Telescope

    However, Randall and other scientists have suggested that dark matter might interact more strongly with itself than we suspect, experiencing as-yet undetected “dark forces” that would influence dark matter particles alone. Just as electromagnetism can make particles of ordinary matter attract or repel each other and emit and absorb light, so too might “dark electromagnetism” cause similar interactions between dark matter particles and cause them to emit “dark light” that’s invisible to ordinary matter.

    Differentiated Dark Matter

    The evidence for this theory can be seen in potential discrepancies between predictions and observations of the way matter is distributed in the universe on relatively modest scales, such as that of dwarf galaxies, says Randall, a professor at Harvard University.

    Dwarf Galaxies with Messier 101  Allison Merritt  Dragonfly Telephoto Array
    Dwarf Galaxies with Messier 101 Allison Merritt Dragonfly Telephoto Array

    For example, repulsive interactions between dark matter particles might keep these particles apart and reduce their overall density, explaining why current estimates of the density of the innermost portion of galaxies are higher than what is actually seen.

    Most dark matter models suggest that dark matter particles are all of one type—they either all interact with each other or they all do not. However, Randall and her colleagues propose a more complex version that they call “partially-interacting dark matter,” where dark matter has both a non-interacting component and a self-interacting one. A similar example in real particles can be seen with protons, electrons, and neutrons—positively charged protons and negatively charged electrons attract one another, while neutrally charged neutrons are not attracted to either protons or electrons.

    “There’s no reason to think that dark matter is composed of all the same type of particle,” Randall says. “We certainly see a diversity of particles in the one sector of matter we do know about, ordinary matter. Why shouldn’t we think the same of dark matter?”

    In this model, Randall and her colleagues suggest that only a small portion of dark matter—maybe about 5%—experiences interactions reminiscent of those seen in ordinary matter. However, this fraction of dark matter could influence not only the evolution of the Milky Way, but of life on Earth as well, an idea Randall explores in her latest book, Dark Matter and the Dinosaurs: The Astounding Interconnectedness of the Universe.

    Standard dark matter models predict that dwarf galaxies orbiting larger galaxies should be scattered in spherical patterns around their parents. However, astronomical data suggest that many dwarf galaxies orbiting the Milky Way and Andromeda lie roughly in the same plane as each other. Randall and her colleagues suggest that if dark matter particles can interact with each other, they can shed energy, potentially creating a structure that could not only solve this dwarf galaxy mystery, but also have triggered the cosmic disruption that doomed the dinosaurs.

    Dark Disks

    In the partially interacting dark matter scenario, the non-interacting component would still form spherical clouds around galaxies, consistent with what astronomers know of their general structure. However, self-interacting dark matter particles would lose energy and cool as they jostled with each other. Cooling would slow these particles down, and gravity would make them cluster together. If these clouds were relatively immobile, they would simply shrink into smaller balls.

    However, since they likely rotate—just like the rest of the matter in their galaxies—this rotation would make these clouds of self-interacting dark matter collapse into flat disks, in much the same way as spherical clouds of ordinary matter collapsed to form the spiral disks of the Milky Way and many other galaxies. Conservation of angular momentum causes these would-be spheres to flatten out. While cooling would still cause them to collapse vertically, they would not collapse along the same plane as their rotation.

    If dark matter in large galaxies was concentrated in disks, it’s likely that at least some of the orbiting dwarf galaxies would be concentrated in flat planes because of the gravitational pull of dark matter on the dwarf galaxies, Randall and her colleagues say. The researchers suggest these “dark disks” should be embedded in the visible disk of larger galaxies.

    But here’s where dark matter begins to exert its influence. The relationship between the dark disk and the stars in the galaxy is not entirely stable. The Sun, for example, completes a circuit around the Milky Way’s core roughly every 240 million years. During its orbit, it bobs up and down in a wavy motion through the galactic plane about every 32 million years. Coincidentally, some researchers previously suggested that meteor impacts on Earth rise and fall in cycles about 30 million to 35 million years long, leading to regular mass extinctions.

    Earlier researchers proposed a cosmic trigger for this deadly cycle, such as a potential companion star for the Sun dubbed “Nemesis” that would ensnare meteoroids and send them hurling toward Earth. Instead, Randall and her colleagues suggest that the Sun’s regular passage through the Milky Way’s dark disk might have warped the orbits of comets in the outer solar system, flinging them inward. Such disruption may have then led to disastrous cosmic impacts on Earth, including the collision about 67 million years ago that likely caused the Cretaceous-Tertiary extinction event, the most recent and most familiar mass extinction which killed off all dinosaurs (except those which would evolve into birds).

    The main suspect behind this disaster is an impact from an asteroid or comet that left behind a gargantuan crater more than 110 miles wide near the town of Chicxulub in Mexico. The collision, likely caused by a meteor about 6 miles across, would have released as much energy as 100 trillion tons of TNT, more than a billion times more than the atomic bombs that destroyed Hiroshima and Nagasaki, killing off at least 75% of life on Earth.

    In research* detailed in 2014 in the journal Physical Review Letters, Randall and her colleague Matthew Reece analyzed craters that are more than 12.4 miles in diameter and were created in the past 250 million years. When they compared the ages of these craters against the 35-million-year cycle they proposed, they discovered that it was three times more likely that the craters matched the dark matter cycle instead of simply occurring randomly.

    “I want to be clear that I did not set out to explain the extinction of the dinosaurs,” Randall says. “This work was about exploring the story of how our universe came about, to explore one possible connection between many different levels of the universe, from the universe down to the Milky Way, the solar system, Earth, and life on Earth.”

    Geologist Michael Rampino at New York University, who did not participate in this study, finds a potential link between a dark disk and mass extinctions “an interesting idea,” he says. “If true, it ties together events that happened on Earth to large-scale cycles in the rest of the solar system and even the galaxy in general.”

    Dark Life?

    However, not everyone agrees that Randall and her colleagues present a convincing case. “They tie mass extinctions to the cratering record, but there are all kinds of estimates one can make with the cratering record depending on what craters one think makes the cut—do you accept all craters above a certain size or craters out to a certain age?” says astrobiophysicist Adrian Melott at the University of Kansas, who did not take part in this research. “You can get all different kind of answers, from cycles 20 million to 37 million years long.”

    Moreover, other research suggests that the cycle of mass extinctions on Earth is actually roughly 27 million years long, Melott says. “That’s way too short a duration for motion oscillating back and forth through the disk.”

    Randall notes that data from the European Space Agency’s satellite Hipparcos, launched in 1989 to precisely measure the positions and velocities of stars, allowed for the theoretical existence of a dark disk. She adds that ESA’s Gaia mission, launched in 2013 to create a precise 3D map of matter throughout the Milky Way, could reveal or refute the dark disk’s existence.

    ESA/Gaia satellite
    ESA/Gaia satellite

    One intriguing possibility raised by interacting dark matter models is the existence of dark atoms that might have given rise to dark life, neither of which would be easily detected, Randall says. Although she admits that the concept of dark life might be far-fetched, “life is complicated, and we have yet to understand life and what’s necessary for it.”

    *Science paper:
    Dark Matter as a Trigger for Periodic Comet Impacts

    Science team:
    Lisa Randall and Matthew Reece

    Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA

    See the full article here .

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    NOVA is the highest rated science series on television and the most watched documentary series on public television. It is also one of television’s most acclaimed series, having won every major television award, most of them many times over.

  • richardmitnick 12:23 pm on February 18, 2016 Permalink | Reply
    Tags: , , Gamma Rays, , ,   

    From Penn State: “New clues in the hunt for the sources of cosmic neutrinos” 

    Penn State Bloc

    Pennsylvania State University

    cosmic-ray accelerator hidden
    This illustration is an example of a hidden cosmic-ray accelerator. Cosmic rays are accelerated up to extremely high energies in dense environments close to black holes. High-energy gamma rays (marked by the “Y” gamma symbol) are blocked from escaping, while neutrinos (marked by the “V”nu symbol) easily escape and can reach the Earth. Credit: Bill Saxton at NRAO/AUI/NSF, modified by Kohta Murase at Penn State University

    The sources of the high-energy cosmic neutrinos that are detected by the IceCube Neutrino Observatory buried in the Antarctic ice may be hidden from observations of high-energy gamma rays, new research reveals.

    ICECUBE neutrino detector
    IceCube neutrino detector interior
    U Wisconsin/NSF/ICECUBE

    These high-energy cosmic neutrinos, which are likely to come from beyond our Milky Way Galaxy, may originate in incredibly dense and powerful objects in space that prevent the escape of the high-energy gamma rays that accompany the production of neutrinos. A paper describing the research will be published in the early online edition of the journal Physical Review Letters on February 18, 2016.

    “Neutrinos are one of the fundamental particles that make up our universe,” said Kohta Murase, assistant professor of physics and of astronomy and astrophysics at Penn State and the corresponding author of the studies. “High-energy neutrinos are produced along with gamma rays by extremely high-energy radiation known as cosmic rays in objects like star-forming galaxies, galaxy clusters, supermassive black holes, or gamma-ray bursts [GRB’s]. It is important to reveal the origin of these high-energy cosmic neutrinos in order to better understand the underlying physical mechanisms that produce neutrinos and other extremely high-energy astroparticles and to enable the use of neutrinos as new probes of particle physics in the universe.”

    Neutrinos are neutral particles, so they are not affected by electromagnetic forces as they travel through space. Neutrinos detected here on Earth therefore trace a direct path back to their distant astrophysical sources. Additionally, these neutrinos rarely interact with other kinds of matter — many pass directly through the Earth without interacting with other particles — making them incredibly difficult to detect, but ensuring that they escape the incredibly dense environments in which they are produced.

    The high-energy cosmic neutrinos detected by IceCube are believed to originate from cosmic-ray interactions with matter (proton-proton interactions); from cosmic-ray interactions with radiation (proton-photon interactions); or from the decay or destruction of heavy, invisible dark matter. Because these processes generate both high-energy neutrinos and high-energy gamma rays, the scientists compared the IceCube neutrino data to high-energy gamma rays detected by the Fermi Gamma-ray Space Telescope.

    NASA Fermi Telescope
    Fermi Gamma-ray Space Telescope

    “If all of the high-energy gamma rays are allowed to escape from the sources of neutrinos, we had expected to find corresponding data from IceCube and Fermi,” said Murase. In previous papers, including one that was featured as an Editorial Suggestion in Physical Review Letters in 2015, Murase and his colleagues showed the power of such a “multi-messenger” comparison. Now, the researchers suggest that the new neutrino data collected by IceCube has lead to intriguing contradictions with the gamma-ray data collected by Fermi.

    “Using sophisticated calculations and a detailed comparison of the IceCube data with the gamma-ray data from Fermi has led to new and interesting implications for the sources of high-energy cosmic neutrinos,” said Murase. “Surprisingly, with the latest IceCube data, we don’t see matching high-energy gamma-ray data detected by Fermi, which suggests a ‘hidden accelerator’ origin of high-energy cosmic neutrinos that Fermi has not detected.”

    In order to explain the multi-messenger data without any of the intriguing contradictions, the scientists propose that the high-energy gamma rays must be blocked from escaping the sources that created them. The researchers then asked what kinds of astrophysical events could produce high-energy neutrinos but also could suppress the high-energy gamma rays detectable by Fermi. “Interestingly, we found that the suppression of high-energy gamma rays should naturally occur when neutrinos are produced via proton-photon interactions,” said Murase. The low-energy photons that interact with protons to produce neutrinos in these events simultaneously prevent high-energy gamma rays from escaping via a process called ‘two-photon annihilation.’ The new finding implies that the amount of high-energy gamma rays associated with the neutrinos that reach the Earth can easily be below the level detectable by Fermi.

    According to the researchers, the results imply that high-energy cosmic neutrinos can be used as special probes of dense astrophysical environments that cannot be seen in high-energy gamma rays. Candidate sources include supermassive black holes and certain types of gamma-ray bursts. The results also motivate further theoretical and observational studies, such as the use of lower-energy gamma rays or X rays to help scientists understand the origin of high-energy neutrinos and cosmic rays.

    “The next decade will be a golden era for multi-messenger particle astrophysics with high-energy neutrinos detected in IceCube as well as gravitational waves detected with advanced-LIGO,” said Murase.

    Caltech Ligo
    MIT/Caltech Advanced aLIGO

    “Our work demonstrates that multi-messenger approaches are indeed very powerful tools for probing fundamental questions in particle astrophysics. I believe that the future is bright and that we will be able to find sources of neutrinos and cosmic rays, probably with other surprising new discoveries.”

    In addition to Murase, the research team includes Dafne Guetta from the Osservatorio Astronomic di Roma in Italy and ORT Braude College in Israel, and Markus Ahlers from the University of Wisconsin.

    The research was funded by Penn State University, the U.S. Nation Science Foundation (grant numbers OPP-0236449 and PHY-0236449) and by the U.S. Israel Binational Science Foundation.

    See the full article here.

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    We teach students that the real measure of success is what you do to improve the lives of others, and they learn to be hard-working leaders with a global perspective. We conduct research to improve lives. We add millions to the economy through projects in our state and beyond. We help communities by sharing our faculty expertise and research.

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