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  • richardmitnick 7:48 am on April 16, 2019 Permalink | Reply
    Tags: , , , , Dame Susan Jocelyn Bell Burnell (1943 – ), , Pulsars   

    From NANOGrav via COSMOS: “Now let’s find a pair of black holes” 

    From NANOGrav

    via

    Cosmos Magazine bloc

    COSMOS Magazine

    16 April 2019
    Richard A Lovett

    Last week, scientists studying black holes reported that they’d managed to turn the entire Earth into a giant virtual telescope that allowed them to make an image of a supermassive black hole 55 million light years away.

    Now, another group of black hole researchers is reporting on a way to turn our entire galaxy into an even more gargantuan black hole detector – this time looking for pairs of such supermassive black holes, orbiting each other in distant galaxies.

    The project, called NANOGrav, was described at a meeting of the American Physical Society in Denver, Colorado. It is attempting to spot supermassive black hole pairs via the effect of gravitational waves created by them on a class of astronomical objects known as millisecond pulsars.

    1
    In this radio image, two supermassive black hole engines are seen as red dots, their large-scale jet structures clearly visible. NANOGRAV.

    Gravitational waves are ripples in the fabric of space-time, created by movements of massive objects, including black holes. These waves cause space to expand, contract, or vibrate, thereby distorting the medium in which we all live.

    Pulsars are the collapsed remnants of dead stars, which emit radio beams that sweep across the heavens like the blink-blink-blink of cosmic lighthouses.

    Women in STEM – Dame Susan Jocelyn Bell Burnell

    Dame Susan Jocelyn Bell Burnell, discovered pulsars with radio astronomy. Jocelyn Bell at the Mullard Radio Astronomy Observatory, Cambridge University, taken for the Daily Herald newspaper in 1968. Denied the Nobel.

    Dame Susan Jocelyn Bell Burnell at work on first plusar chart 1967 pictured working at the Four Acre Array in 1967. Image courtesy of Mullard Radio Astronomy Observatory.

    Dame Susan Jocelyn Bell Burnell 2009

    Dame Susan Jocelyn Bell Burnell (1943 – ), still working from http://www. famousirishscientists.weebly.com

    Millisecond pulsars blink so fast that they emit numerous pulses per second.

    “They’re like really stable clocks, scattered all over the Milky Way,” says Joseph Simon, an astrophysicist at NASA’s Jet Propulsion Laboratory, in Pasadena, California.

    “Pulsars are some of the most accurate clocks we have in the universe,” says Brad Tucker, an astrophysicist and cosmologist at Australian National University, who is not a member of the NANOGrav team. “Observations of them are even used to calibrate GPS satellites.”

    Black holes have no direct effect on pulsars, but when galaxies merge, astrophysicists believe, the supermassive black holes at their centres go into orbit around each other for a long time before they too eventually merge.

    As these pairs circle each other, they should emit gravitational waves that oscillate in tandem with their orbital cycle. The goal of NANOGrav is to detect these waves via their effect on the otherwise-precise timing of pulsar signals coming through them.

    “As a gravitational wave passes by the Earth, it will stretch and squeeze space-time,” Simon says. “So, the pulse from that pulsar will have to travel a slightly longer distance or a slightly shorter distance. It will get here a bit sooner or slightly after what we expect.”

    Not that it’s a huge effect. “The change we are searching for is less than a microsecond,” Simon says – a formidable challenge to detect, given that our planet also spins and orbits the Sun, both of which create far greater differences in the arrival time of any given pulsar signal at any given radio telescope than the tiny effect the NANOGrav project is looking for.

    Nor is it a rapid effect. The “nano” in the project’s name doesn’t refer to nanoseconds. Rather, it refers to nanohertz: events that complete only 1 billionth of a cycle per second.

    In other words, a full cycle takes about 30 years.

    To detect this, the NANOGrav team has been monitoring 48 pulsars since late 2006. That means they’ve accumulated 12½ years of data, but that’s not yet a large enough fraction of a nanohertz cycle to be able to spot it.

    It is, however, getting close.

    “We are expecting that within the next three to four years, we will be able to detect this, depending on how strong it actually is,” Simon says.

    The goal, he adds, is very different from that of the LIGO project (and its European counterpart, Virgo), which have successfully used multi-kilometer-long laser detectors to spot the much more rapid gravitational-wave oscillations created by the mergers of much smaller (stellar mass) black holes and neutron stars.

    It’s also a world apart from a project at Louisiana State University, Baton Rouge, which has built a “table-top” version of LIGO that incorporates extremely tiny mirrors, about the diameter of a human hair, in an effort to ratchet up the sensitivity of the next round of advanced detectors used in LIGO and Virgo themselves.

    But gravitational wave researchers of all types are impressed by NANOGrav’s vision.

    “The work that NANOGrav does is fantastic,” says Thomas Corbitt, leader of the Louisiana State University team. “It’s amazing to see that the same physics governs these vastly different black holes.”

    “This is yet another clever way to probe extreme environments in space,” adds Tucker. “These are the sorts of ideas that get me excited – using a precise observation for something completely different – much like how the Kepler Space Telescope, which was designed to find planets, has told us a lot about exploding stars and black holes.”

    Learning more about supermassive black holes, he continues, is important in and of itself. “We think nearly every large galaxy has them,” he says. “[They] are the ultimate laboratory for testing extreme physics—not only of gravity but time itself.”

    “The great thing,” adds David McClelland, director of Australian National University’s Centre for Gravitational Physics, is that LIGO and Virgo have already proved that gravitational waves exist, “and can be detected directly.” It’s only a matter of time, he says, until other projects, such as NANOGrav also detect them.

    See the full article here .

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    NANOGrav stands for North American Nanohertz Observatory for Gravitational Waves. As the name implies, NANOGrav members are drawn from across the United States and Canada and our goal is to study the Universe using gravitational waves. Gravitational waves are ripples in the fabric of space and time that cause objects to shrink and stretch by very, very small amounts. NANOGrav uses the Galaxy itself to detect gravitational waves with the help of objects called pulsars — exotic, dead stars that send out pulses of radio waves with extraordinary regularity. This is known as a Pulsar Timing Array, or PTA. NANOGrav scientists make use of some of the world’s best telescopes and most advanced technology, drawing on physics, computer science, signal processing, and electrical engineering. Our short term goal is to detect gravitational waves within the next decade, an event which may be the first direct detection ever. But detection is only the first step towards studying our Universe in a completely new and revolutionary way, and we are sure to make unexpected discoveries in the process.

    NANOGrav cooperates with similar experiments in Australia (the Parkes Pulsar Timing Array) and Europe (the European Pulsar Timing Array). Together, we make up the International Pulsar Timing Array, or IPTA. By sharing our resources and knowledge, we hope to usher in the era of gravitational wave astronomy more quickly and with greater impact.

    NANOGrav was founded in October 2007 and has since grown to over 60 members at over a dozen institutions. NANOGrav members have been awarded over $10M in competitive scientific grants and awards to perform NANOGrav-related research at their institutions.

     
  • richardmitnick 6:45 pm on March 19, 2019 Permalink | Reply
    Tags: "Astronomers Find “Cannonball Pulsar” Speeding Through Space", , , , , , , PSR J0002+6216, Pulsars   

    From National Radio Astronomy Observatory: “Astronomers Find “Cannonball Pulsar” Speeding Through Space” 


    From National Radio Astronomy Observatory

    NRAO Banner

    March 19, 2019

    Dave Finley, Public Information Officer
    (575) 835-7302
    dfinley@nrao.edu

    Object got powerful “kick” from supernova explosion.

    1
    Credit: Composite by Jayanne English, University of Manitoba; F. Schinzel et al.; NRAO/AUI/NSF; DRAO/Canadian Galactic Plane Survey; and NASA/IRAS.

    Astronomers using the National Science Foundation’s Karl G. Jansky Very Large Array (VLA) [below] have found a pulsar speeding away from its presumed birthplace at nearly 700 miles per second, with its trail pointing directly back at the center of a shell of debris from the supernova explosion that created it. The discovery is providing important insights into how pulsars — superdense neutron stars left over after a massive star explodes — can get a “kick” of speed from the explosion.

    Women in STEM – Dame Susan Jocelyn Bell Burnell

    Dame Susan Jocelyn Bell Burnell, discovered pulsars with radio astronomy. Jocelyn Bell at the Mullard Radio Astronomy Observatory, Cambridge University, taken for the Daily Herald newspaper in 1968. Denied the Nobel.

    Dame Susan Jocelyn Bell Burnell 2009

    Dame Susan Jocelyn Bell Burnell (1943 – ), still working from http://www. famousirishscientists.weebly.com

    Dame Susan Jocelyn Bell Burnell at work on first plusar chart 1967 pictured working at the Four Acre Array in 1967. Image courtesy of Mullard Radio Astronomy Observatory.

    “This pulsar has completely escaped the remnant of debris from the supernova explosion,” said Frank Schinzel, of the National Radio Astronomy Observatory (NRAO). “It’s very rare for a pulsar to get enough of a kick for us to see this,” he added.

    The pulsar, dubbed PSR J0002+6216, about 6,500 light-years from Earth, was discovered in 2017 by a citizen-science project called Einstein@Home, running on BOINC software from UC Berkeley Space Science Center. That project uses computer time donated by volunteers to analyze data from NASA’s Fermi Gamma-ray Space Telescope. So far, using more than 10,000 years of computing time, the project has discovered a total of 23 pulsars.

    einstein@home

    NASA/Fermi Gamma Ray Space Telescope

    Radio observations with the VLA clearly show the pulsar outside the supernova remnant, with a tail of shocked particles and magnetic energy some 13 light-years long behind it. The tail points back toward the center of the supernova remnant.

    “Measuring the pulsar’s motion and tracing it backwards shows that it was born at the center of the remnant, where the supernova explosion occurred,” said Matthew Kerr, of the Naval Research Laboratory. The pulsar now is 53 light-years from the remnant’s center.

    “The explosion debris in the supernova remnant originally expanded faster than the pulsar’s motion,” said Dale Frail, of NRAO. “However, the debris was slowed by its encounter with the tenuous material in interstellar space, so the pulsar was able to catch up and overtake it,” he added.

    The astronomers said that the pulsar apparently caught up with the shell about 5,000 years after the explosion. The system now is seen about 10,000 years after the explosion.

    The pulsar’s speed of nearly 700 miles per second is unusual, the scientists said, with the average pulsar speed only about 150 miles per second. “This pulsar is moving fast enough that it eventually will escape our Milky Way Galaxy,” Frail said.

    Astronomers have long known that pulsars get a kick when born in supernova explosions, but still are unsure how that happens.

    “Numerous mechanisms for producing the kick have been proposed. What we see in PSR J0002+6216 supports the idea that hydrodynamic instabilities in the supernova explosion are responsible for the high velocity of this pulsar,” Frail said.

    “We have more work to do to fully understand what’s going on with this pulsar, and it’s providing an excellent opportunity to improve our knowledge of supernova explosions and pulsars,” Schinzel said.

    Schinzel, Kerr, and Frail worked with Urvashi Rau and Sanjay Bhatnagar, both of NRAO. The scientists are reporting their results at the High Energy Astrophysics Division meeting of the American Astronomical Society in Monterey, California, and have submitted a paper to the Astrophysical Journal Letters.

    The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

    The Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership managed by NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

    Fermi was developed in collaboration with the U.S. Department of Energy, with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

    Einstein@Home is a World Year of Physics 2005 and an International Year of Astronomy 2009 project. It is supported by the American Physical Society (APS), the US National Science Foundation (NSF), the Max Planck Society (MPG), and a number of international organizations.

    See the full article here .


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

    The NRAO operates a complementary, state-of-the-art suite of radio telescope facilities for use by the scientific community, regardless of institutional or national affiliation: the Very Large Array (VLA), and the Very Long Baseline Array (VLBA)*.

    ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

    Access to ALMA observing time by the North American astronomical community will be through the North American ALMA Science Center (NAASC).

    NRAO VLBA

    NRAO VLBA

    *The Very Long Baseline Array (VLBA) comprises ten radio telescopes spanning 5,351 miles. It’s the world’s largest, sharpest, dedicated telescope array. With an eye this sharp, you could be in Los Angeles and clearly read a street sign in New York City!

    Astronomers use the continent-sized VLBA to zoom in on objects that shine brightly in radio waves, long-wavelength light that’s well below infrared on the spectrum. They observe blazars, quasars, black holes, and stars in every stage of the stellar life cycle. They plot pulsars, exoplanets, and masers, and track asteroids and planets.

    And the future Expanded Very Large Array (EVLA).

     
  • richardmitnick 1:51 pm on January 10, 2019 Permalink | Reply
    Tags: , , , , , , , Pulsars, Radio magnetars, The team looked at the magnetar named PSR J1745-2900 located in the Milky Way's galactic center using the largest of NASA's Deep Space Network radio dishes in Australia   

    From Caltech: “Magnetar Mysteries in our Galaxy and Beyond” 

    Caltech Logo

    From Caltech

    01/09/2019

    Whitney Clavin
    (626) 395-1856
    wclavin@caltech.edu

    1
    Illustration of a magnetar—a rotating neutron star with incredibly powerful magnetic fields.
    Credit: NASA/CXC/M.Weiss

    2
    The 70-meter radio dish (DSS-43) in Canberra, Australia, part of NASA’s Deep Space Network.
    Credit: NASA/DSN

    New research looks at possible links between magnetars and extragalactic radio bursts.

    In a new Caltech-led study, researchers from campus and the Jet Propulsion Laboratory (JPL) have analyzed pulses of radio waves coming from a magnetar—a rotating, dense, dead star with a strong magnetic field—that is located near the supermassive black hole at the heart of the Milky Way galaxy. The new research provides clues that magnetars like this one, lying in close proximity to a black hole, could perhaps be linked to the source of “fast radio bursts,” or FRBs. FRBs are high-energy blasts that originate beyond our galaxy but whose exact nature is unknown.

    “Our observations show that a radio magnetar can emit pulses with many of the same characteristics as those seen in some FRBs,” says Caltech graduate student Aaron Pearlman, who presented the results today at the 233rd meeting of the American Astronomical Society in Seattle. “Other astronomers have also proposed that magnetars near black holes could be behind FRBs, but more research is needed to confirm these suspicions.”

    The research team was led by Walid Majid, a visiting associate at Caltech and principal research scientist at JPL, which is managed by Caltech for NASA, and Tom Prince, the Ira S. Bowen Professor of Physics at Caltech. The team looked at the magnetar named PSR J1745-2900, located in the Milky Way’s galactic center, using the largest of NASA’s Deep Space Network radio dishes in Australia. PSR J1745-2900 was initially spotted by NASA’s Swift X-ray telescope, and later determined to be a magnetar by NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR), in 2013.

    NASA Neil Gehrels Swift Observatory

    NASA NuSTAR X-ray telescope

    “PSR J1745-2900 is an amazing object. It’s a fascinating magnetar, but it also has been used as a probe of the conditions near the Milky Way’s supermassive black hole,” says Fiona Harrison, the Benjamin M. Rosen Professor of Physics at Caltech and the principal investigator of NuSTAR. “It’s interesting that there could be a connection between PSR J1745-2900 and the enigmatic FRBs.”

    Magnetars are a rare subtype of a group of objects called pulsars; pulsars, in turn, belong to a class of rotating dead stars known as neutron stars. Magnetars are thought to be young pulsars that spin more slowly than ordinary pulsars and have much stronger magnetic fields, which suggests that perhaps all pulsars go through a magnetar-like phase in their lifetime.

    Women in STEM – Dame Susan Jocelyn Bell Burnell

    Dame Susan Jocelyn Bell Burnell, discovered pulsars with radio astronomy. Jocelyn Bell at the Mullard Radio Astronomy Observatory, Cambridge University, taken for the Daily Herald newspaper in 1968. Denied the Nobel.

    The magnetar PSR J1745-2900 is the closest-known pulsar to the supermassive black hole at the center of the galaxy, separated by a distance of only 0.3 light-years, and it is the only pulsar known to be gravitationally bound to the black hole and the environment around it.

    In addition to discovering similarities between the galactic-center magnetar and FRBs, the researchers also gleaned new details about the magnetar’s radio pulses. Using one of the Deep Space Network’s largest radio antennas, the scientists were able to analyze individual pulses emitted by the star every time it rotated, a feat that is very rare in radio studies of pulsars. They found that some pulses were stretched, or broadened, by a larger amount than predicted when compared to previous measurements of the magnetar’s average pulse behavior. Moreover, this behavior varied from pulse to pulse.

    “We are seeing these changes in the individual components of each pulse on a very fast time scale. This behavior is very unusual for a magnetar,” says Pearlman. The radio components, he notes, are separated by only 30 milliseconds on average.

    One theory to explain the signal variability involves clumps of plasma moving at high speeds near the magnetar. Other scientists have proposed that such clumps might exist but, in the new study, the researchers propose that the movement of these clumps may be a possible cause of the observed signal variability. Another theory proposes that the variability is intrinsic to the magnetar itself.

    “Understanding this signal variability will help in future studies of both magnetars and pulsars at the center of our galaxy,” says Pearlman.

    In the future, Pearlman and his colleagues hope to use the Deep Space Network radio dish to solve another outstanding pulsar mystery: Why are there so few pulsars near the galactic center? Their goal is to find a non-magnetar pulsar near the galactic-center black hole.

    “Finding a stable pulsar in a close, gravitationally bound orbit with the supermassive black hole at the galactic center could prove to be the Holy Grail for testing theories of gravity,” says Pearlman. “If we find one, we can do all sorts of new, unprecedented tests of Albert Einstein’s general theory of relativity.”

    The new study, titled, “Pulse Morphology of the Galactic Center Magnetar PSR J1745-2900,” appeared in the October 20, 2018, issue of The Astrophysical Journal and was funded by a Research and Technology Development grant through a contract with NASA; JPL and Caltech’s President’s and Director’s Fund; the Department of Defense; and the National Science Foundation. Other authors include Jonathon Kocz of Caltech and Shinji Horiuchi of the CSIRO (Commonwealth Scientific and Industrial Research Organization) Astronomy & Space Science, Canberra Deep Space Communication Complex.

    See the full article here .


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    Please help promote STEM in your local schools.


    Stem Education Coalition

    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”

    Caltech campus


    Caltech campus

     
  • richardmitnick 1:28 pm on December 4, 2018 Permalink | Reply
    Tags: , , , , , , Pulsars   

    From AAS NOVA: “When Is the Next Glitch on Pulsar J0537-6910?” 

    AASNOVA

    From AAS NOVA

    4 December 2018
    Lisa Drummond

    1
    Pulsars emit radiation that sweeps over the Earth like a lighthouse. We observe this radiation as a sequence of pulses. [Bill Saxton/NRAO/AUI/NSF]

    Title: Predicting the Starquakes in PSR J0537-6910
    Authors: John Middleditch, Francis E. Marshall, Q. Daniel Wang, Eric V. Gotthelf, William Zhang
    First Author’s Institution: Los Alamos National Laboratory

    Status: Published in ApJ

    2
    Artist’s illustration of a pulsar, a fast-spinning, magnetised neutron star. [NASA]

    Pulsars (rotating, magnetised neutron stars) emit radiation that sweeps periodically over the Earth (like the beam of a lighthouse sweeping across the ocean). We detect this radiation as a sequence of pulses, with the frequency of the pulse corresponding to the frequency of rotation of the star. Pulsars will typically spin down over their lifetime due to electromagnetic braking, but this is a fairly slow process. Occasionally, in some pulsars, we will detect a sudden increase in the frequency of the pulses. This is called a pulsar glitch. Essentially, the mismatch in the rotation of the fluid inside the star and the solid crust on the outside of the star causes a catastrophic event that we see as an increase in the frequency of the pulses.

    Women in STEM – Dame Susan Jocelyn Bell Burnell

    Dame Susan Jocelyn Bell Burnell, discovered pulsars with radio astronomy. Jocelyn Bell at the Mullard Radio Astronomy Observatory, Cambridge University, taken for the Daily Herald newspaper in 1968. Denied the Nobel.

    Dame Susan Jocelyn Bell Burnell 2009

    Dame Susan Jocelyn Bell Burnell (1943 – ), still working from http://www. famousirishscientists.weebly.com

    The question that the paper we’re exploring today — originally published in 2006 — seeks to answer is: can you predict the next glitch in a pulsar? In general, this is a challenging task, with different pulsars exhibiting different glitching behaviours that need to be captured in your model. However, for one particular pulsar, PSR J0537-6910, this can be accomplished fairly straightforwardly, due to the strong correlation between the size of each glitch and the waiting time until the next glitch. The authors of today’s paper exploit this correlation to develop a method to predict the next starquake on PSR J0537-6910.

    See the full article here .


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    1

    AAS Mission and Vision Statement

    The mission of the American Astronomical Societyis to enhance and share humanity’s scientific understanding of the Universe.

    The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
    The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
    The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
    The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
    The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

    Adopted June 7, 2009

     
  • richardmitnick 1:09 pm on October 12, 2018 Permalink | Reply
    Tags: , , , , Dame Susan Jocelyn Bell Burnell discovered pulsars with radio astronomy at the Mullard Radio Astronomy Observatory Cambridge University-Denied the Nobel., , , Pulsars   

    From NASA Goddard Space Flight Center: “‘Pulsar in a Box’ Reveals Surprising Picture of a Neutron Star’s Surroundings” 

    NASA Goddard Banner
    From NASA Goddard Space Flight Center

    Oct. 10, 2018
    Francis Reddy
    francis.j.reddy@nasa.gov
    NASA’s Goddard Space Flight Center, Greenbelt, Md.

    An international team of scientists studying what amounts to a computer-simulated “pulsar in a box” are gaining a more detailed understanding of the complex, high-energy environment around spinning neutron stars, also called pulsars.

    1
    ‘Pulsar in a Box’ Reveals Surprises in Neutron Star’s Surroundings | NASA


    Explore a new “pulsar in a box” computer simulation that tracks the fate of electrons (blue) and their antimatter kin, positrons (red), as they interact with powerful magnetic and electric fields around a neutron star. Lighter tracks indicate higher particle energies. Each particle seen in this visualization actually represents trillions of electrons or positrons. Better knowledge of the particle environment around neutron stars will help astronomers understand how they produce precisely timed radio and gamma-ray pulses.
    Credits: NASA’s Goddard Space Flight Center

    The model traces the paths of charged particles in magnetic and electric fields near the neutron star, revealing behaviors that may help explain how pulsars emit gamma-ray and radio pulses with ultraprecise timing.

    “Efforts to understand how pulsars do what they do began as soon as they were discovered in 1967, and we’re still working on it,” said Gabriele Brambilla, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and the University of Milan who led a study of the recent simulation.

    Dame Susan Jocelyn Bell Burnell, discovered pulsars with radio astronomy. Jocelyn Bell at the Mullard Radio Astronomy Observatory, Cambridge University, taken for the Daily Herald newspaper in 1968. Denied the Nobel.

    Dame Susan Jocelyn Bell Burnell 2009

    “Even with the computational power available today, tracking the physics of particles in the extreme environment of a pulsar is a considerable challenge.”

    A pulsar is the crushed core of a massive star that ran out of fuel, collapsed under its own weight and exploded as a supernova. Gravity forces more mass than the Sun’s into a ball no wider than Manhattan Island in New York City while also revving up its rotation and strengthening its magnetic field. Pulsars can spin thousands of times a second and wield the strongest magnetic fields known.

    These characteristics also make pulsars powerful dynamos, with superstrong electric fields that can rip particles out of the surface and accelerate them into space.

    NASA’s Fermi Gamma-ray Space Telescope has detected gamma rays from 216 pulsars.

    NASA/Fermi LAT


    NASA/Fermi Gamma Ray Space Telescope

    Observations show that the high-energy emission occurs farther away from the neutron star than the radio pulses. But exactly where and how these signals are produced remains poorly known.

    Various physical processes ensure that most of the particles around a pulsar are either electrons or their antimatter counterparts, positrons.

    “Just a few hundred yards above a pulsar’s magnetic pole, electrons pulled from the surface may have energies comparable to those reached by the most powerful particle accelerators on Earth,” said Goddard’s Alice Harding. “In 2009, Fermi discovered powerful gamma-ray flares from the Crab Nebula pulsar that indicate the presence of electrons with energies a thousand times greater.”

    X-ray picture of Crab pulsar, taken by Chandra


    Supernova remnant Crab nebula. NASA/ESA Hubble

    Speedy electrons emit gamma rays, the highest-energy form of light, through a process called curvature radiation. A gamma-ray photon can, in turn, interact with the pulsar’s magnetic field in a way that transforms it into a pair of particles, an electron and a positron.

    To trace the behavior and energies of these particles, Brambilla, Harding and their colleagues used a comparatively new type of pulsar model called a “particle in cell” (PIC) simulation. Goddard’s Constantinos Kalapotharakos led the development of the project’s computer code. In the last five years, the PIC method has been applied to similar astrophysical settings by teams at Princeton University in New Jersey and Columbia University in New York.

    “The PIC technique lets us explore the pulsar from first principles. We start with a spinning, magnetized pulsar, inject electrons and positrons at the surface, and track how they interact with the fields and where they go,” Kalapotharakos said. “The process is computationally intensive because the particle motions affect the electric and magnetic fields and the fields affect the particles, and everything is moving near the speed of light.”

    The simulation shows that most of the electrons tend to race outward from the magnetic poles. The positrons, on the other hand, mostly flow out at lower latitudes, forming a relatively thin structure called the current sheet. In fact, the highest-energy positrons here — less than 0.1 percent of the total — are capable of producing gamma rays similar to those Fermi detects, confirming the results of earlier studies.

    Some of these particles likely become boosted to tremendous energies at points within the current sheet where the magnetic field undergoes reconnection, a process that converts stored magnetic energy into heat and particle acceleration.

    One population of medium-energy electrons showed truly odd behavior, scattering every which way — even back toward the pulsar.

    The particles move with the magnetic field, which sweeps back and extends outward as the pulsar spins. Their rotational speed rises with increasing distance, but this can only go on so long because matter can’t travel at the speed of light.

    The distance where the plasma’s rotational velocity would reach light speed is a feature astronomers call the light cylinder, and it marks a region of abrupt change. As the electrons approach it, they suddenly slow down and many scatter wildly. Others can slip past the light cylinder and out into space.

    The simulation ran on the Discover supercomputer at NASA’s Center for Climate Simulation at Goddard and the Pleiades supercomputer at NASA’s Ames Research Center in Silicon Valley, California.

    NASA Discover SGI Supercomputer- NASA’s Center for Climate Simulation Primary Computing Platform

    NASA SGI Intel Advanced Supercomputing Center Pleiades Supercomputer

    The model actually tracks “macroparticles,” each of which represents many trillions of electrons or positrons. A paper describing the findings was published May 9 in The Astrophysical Journal

    “So far, we lack a comprehensive theory to explain all the observations we have from neutron stars. That tells us we don’t yet completely understand the origin, acceleration and other properties of the plasma environment around the pulsar,” Brambilla said. “As PIC simulations grow in complexity, we can expect a clearer picture.”

    NASA’s Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy and with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

    For more about NASA’s Fermi mission, visit:

    https://www.nasa.gov/fermi.

    See the full article here.

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    Please help promote STEM in your local schools.

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    NASA’s Goddard Space Flight Center is home to the nation’s largest organization of combined scientists, engineers and technologists that build spacecraft, instruments and new technology to study the Earth, the sun, our solar system, and the universe.

    Named for American rocketry pioneer Dr. Robert H. Goddard, the center was established in 1959 as NASA’s first space flight complex. Goddard and its several facilities are critical in carrying out NASA’s missions of space exploration and scientific discovery.


    NASA/Goddard Campus

     
  • richardmitnick 9:00 am on July 25, 2018 Permalink | Reply
    Tags: , , , , , , , Pulsars   

    From CSIROscope: Women in STEM-“The pioneer of pulsars pops into Parkes” 

    CSIRO bloc

    From CSIROscope

    25 July 2018
    Andrew Warren,
    Lucy Thackray

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    Dame Jocelyn with the record of her discovery

    In 1967, as a 24-year-old PhD student at Cambridge University, Dame Jocelyn Bell Burnell made one of the most significant scientific discoveries of the 20th Century when she identified and precisely analysed the first pulsar.

    Dame Jocelyn recently visited Australia, and while she was in Parkes to deliver the John Bolton lecture at the local Astrofest event, she had the chance to pop in to see our Parkes radio telescope, which you probably know as ‘The Dish’. This was the first time Dame Jocelyn had visited The Dish, which has detected more than half of the more than 2500 pulsars found since her original discovery, and when the opportunity presented itself she just ‘couldn’t resist.’ And while she was here we had the chance to catch up with her to hear her thoughts on the breakneck speed of modern science, as well as the adversity women face when pursuing a career in science.

    Puzzling pulsars

    A pulsar is a small star left behind after a normal star has died in a fiery explosion, which spins up to hundreds of times per second and sends out beams of radio waves. We now know those radio waves can be detected as a ‘pulse’ when the beam is pointed in the direction of our telescopes.

    Dame Jocelyn discovered pulsars by spotting a tiny but of ‘scruff’ in the 30 metres of chart recordings made by the telescope each day.

    “It was troubling me because it didn’t fit into any previously known category, so I was a bit puzzled by what it actually was. I started calling it ‘LGM’, which stood for Little Green Men, although I didn’t seriously believe it was little green men,” Dame Jocelyn said.

    It wasn’t until she found the second pulsar that she was able to relax a little and know that the first detection wasn’t an anomaly.

    “It wasn’t till that point I was able to stop and think aaah…this is a new branch of astronomy we’re opening up.”

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    Celebrating her 75th birthday at The Dish with a surprise cake

    A trailblazing pioneer

    Dame Jocelyn’s ambition when starting out was to develop a career in radio astronomy.

    “I’d already felt like a bit of a pioneering woman during my time as an undergraduate, when I was the only women in a class of fifty people doing their honours physics degree,” she said.

    And even though she’d been credited with such an important scientific discovery, she would go on to face adversity many times during her career. Perhaps the most high profile example is when the Nobel Prize in Physics was awarded to her thesis supervisor and another astronomer in 1974 for the work discovering pulsars.

    Reflecting on the incident now, Dame Jocelyn thinks “…it was far more important that there was a Nobel Prize in astrophysics, rather than what it was for, or who it went to, because it created a precedent and opened the door, because until then astrophysics hadn’t been recognised at all.”

    “There were certainly discouragements, and you sometimes had to find workarounds, but it got even harder when I married and had a child, because mothers weren’t meant to work, so I ended up working part-time for about eighteen years,” Dame Jocelyn said.

    “I knew that I needed to work… I was quite lucky that directors were prepared to give me part-time jobs, they weren’t very wonderful jobs, but they were intellectually engaging and enjoyable, and allowed me to work part-time, so that kept me sane and kept me in touch with the field.”

    “The world is getting much better at recognising women, but there’s still not parity. There’s still more room for women, and as it becomes more normal for women to do scientific things more women will come through and play a role, which will be great,” Dame Jocelyn said.

    Inspiring the next generation

    Shivani Bhandari is one of our postdoctoral astronomers who had the opportunity to hear Dame Jocelyn speak while she was in Australia.

    “It was an absolute honour to chair Dame Jocelyn’s colloquium and see her speak enthusiastically about her 50 year old discovery.” Shivani said.

    “Her struggle to pursue research in a male dominated area of study, driven by pure passion for astrophysics, is truly inspiring for female scientists, including myself.”

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    Our Postoctoral astronomer Shivani Bhandari with Dame Jocelyn

    Science at breakneck speed

    Dame Jocelyn also had time to reflect on the breakneck speed of modern research.

    “It’s fantastic seeing the technological change being applied to astronomy. The equipment on the Parkes telescope and others around the world is forever improving, and the pace of discovery just gets faster and faster as the equipment gets better. It leaves you a bit breathless, but it’s very exciting,” she said.

    “It’s been magnificent to see so many developments in the field since the original discovery of pulsars fifty years ago. It’s since become a major field of astronomical research, especially here at Parkes.”

    “It’s a very exciting time to be around, it’s fascinating!”

    Dame Jocelyn’s discovery

    See the full article here .


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    SKA/ASKAP radio telescope at the Murchison Radio-astronomy Observatory (MRO) in Mid West region of Western Australia

    So what can we expect these new radio projects to discover? We have no idea, but history tells us that they are almost certain to deliver some major surprises.

    Making these new discoveries may not be so simple. Gone are the days when astronomers could just notice something odd as they browse their tables and graphs.

    Nowadays, astronomers are more likely to be distilling their answers from carefully-posed queries to databases containing petabytes of data. Human brains are just not up to the job of making unexpected discoveries in these circumstances, and instead we will need to develop “learning machines” to help us discover the unexpected.

    With the right tools and careful insight, who knows what we might find.

    CSIRO campus

    CSIRO, the Commonwealth Scientific and Industrial Research Organisation, is Australia’s national science agency and one of the largest and most diverse research agencies in the world.

     
  • richardmitnick 10:59 am on July 20, 2018 Permalink | Reply
    Tags: Antimatter plasma reveals secrets of deep space signals, , , , Computer model called OSIRIS, , , Pulsars, The exact conditions necessary to produce a plasma containing positrons remain unclear   

    From Horizon The EU Research and Innovation Magazine: “Antimatter plasma reveals secrets of deep space signals” 

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    From Horizon The EU Research and Innovation Magazine

    16 July 2018
    Jude Gonzalez

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    Mysterious radiation emitted from pulsars – like this one shown leaving a long tail of debris as it races through the Milky Way – have puzzled astronomers for decades. Image credit – NASA

    Mysterious radiation emitted from distant corners of the galaxy could finally be explained with efforts to recreate a unique state of matter that blinked into existence in the first moments after the Big Bang.

    For 50 years, astronomers have puzzled over strange radio waves and gamma rays thrown out from the spinning remnants of dead stars called pulsars.

    Researchers believe that these enigmatic, highly-energetic pulses of radiation are produced by bursts of electrons and their antimatter twins, positrons. The universe was briefly filled with these superheated, electrically charged particles in the seconds that followed the Big Bang before all antimatter vanished, taking the positrons with it. But astrophysicists think the conditions needed to forge positrons may still exist in the powerful electric and magnetic fields generated around pulsars.

    ‘These fields are so strong, and they twist and reconnect so violently, that they essentially apply Einstein’s equation of E = mc^2 and create matter and antimatter out of energy,’ said Professor Luis Silva at the Instituto Superior Técnico in Lisbon, Portugal. Together, the electrons and positrons are thought to form a super-heated form of matter known as a plasma around a pulsar.

    But the exact conditions necessary to produce a plasma containing positrons remain unclear. Scientists also still do not understand why the radio waves emitted by the plasma around pulsars have properties similar to light in a laser beam – a wave structure known as coherence.

    To find out, researchers are now turning to powerful computer simulations to model what might be going on. In the past, such simulations have struggled to mimic the staggering number of particles generated around pulsars. But Prof. Silva and his team, together with researchers at the University of California, Los Angeles in the United States, have adapted a computer model called OSIRIS so that it can run on supercomputers, allowing it to follow billions of particles simultaneously.

    The updated model, which forms part of the InPairs project, has identified the astrophysical conditions necessary for pulsars to generate electrons and positrons when magnetic fields are torn apart and reattached to their neighbours in a process known as magnetic reconnection.

    OSIRIS also predicted that the gamma rays released by electrons and positrons as they race across a magnetic field will shine in discontinuous spurts rather than smooth beams.

    The findings have added weight to theories that the enigmatic signals coming from pulsars are produced by the destruction of electrons as they recombine with positrons in the magnetic fields around these dead stars.

    Prof. Silva is now using the data from these simulations to search for similar burst signatures in past astronomical observations. The tell-tale patterns would reveal details on how magnetic fields evolve around pulsars, offering fresh clues about what is going on inside them. It will also help confirm the validity of the OSIRIS model for researchers trying to create antimatter in the laboratory.

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    The OSIRIS computer model predicts how powerful magnetic fields around pulsars evolve, helping scientists understand where matter and antimatter can be created out of the vacuum of space. Image credit – Fabio Cruz

    Blasting lasers

    Insights gained from the simulations are already being used to help design experiments that will use high-powered lasers to mimic the huge amounts of energy released by pulsars. The Extreme Light Infrastructure will blast targets no wider than a human hair with petawatts of laser power. Under this project, lasers are under construction at three facilities around Europe – in Măgurele in Romania, Szeged in Hungary, and Prague in the Czech Republic. If successful, the experiments could create billions of electron-positrons pairs.

    ‘OSIRIS is helping researchers optimise laser properties to create matter and antimatter like pulsars do,’ said Prof. Silva. ‘The model offers a road map for future experiments.’

    But there are some who are attempting to wield matter-antimatter plasmas in even more controlled ways so they can study them.

    Professor Thomas Sunn Pedersen, an applied physicist at the Max Planck Institute for Plasma Physics in Garching, Germany, is using charged metal plates to confine positrons alongside electrons as a first step towards creating a matter-antimatter plasma on a table top.

    Although Prof. Sunn Pedersen works with the most intense beam of low-energy positrons in the world, concentrating enough particles to ignite a matter-antimatter plasma remains challenging. Researchers use electro-magnetic ‘cages’ generated under vacuum to confine antimatter, but these require openings for the particles to be injected inside. These same openings allow particles to leak back out, however, making it difficult to build up enough particles for a plasma to form.

    Prof. Sunn Pedersen has invented an electro-magnetic field with a ‘trap door’ that can let positrons in before closing behind them. Last year, the new design was able to boost the time the antimatter particles remained confined in the field by a factor of 20, holding them in place for over a second.

    ‘No one has ever achieved that in a fully magnetic trap,’ said Prof. Sunn Pedersen. ‘We have proven that the idea works.’

    But holding these elusive antimatter particles in place is only one milestone towards creating a matter-antimatter plasma in the laboratory. As part of the PAIRPLASMA project, Prof. Sunn Pedersen is now increasing the quality of the vacuum and generating the field with a levitating ring to confine positrons for over a minute. Studying the properties of plasmas ignited under these conditions will offer valuable insights to neighbouring fields.

    In June, for example, Prof. Sunn Pedersen used a variation of this magnetic trap to set a new world record in nuclear fusion reactions ignited in conventional-matter plasmas.

    ‘Collective phenomena like turbulence currently complicate control over big fusion plasmas,’ said Prof. Sunn Pedersen. ‘A lot of that is driven by the fact that the ions are much heavier than the electrons in them.’

    He hopes that by producing electron-positron plasmas like those created by the Big Bang, it may be possible to sidestep this complication because electrons and positrons have the exact same mass. If they can be controlled, such plasmas could help to validate complex models and recreate the conditions around pulsars so they can be studied up close in the laboratory for the first time.

    If successful it may finally give astronomers the answers they have puzzled over for so long.

    See the full article here .


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  • richardmitnick 12:49 pm on July 8, 2018 Permalink | Reply
    Tags: , , , , , Pulsars   

    From H.E.S.S.: “A joint X-ray and gamma-ray study of the Vela X pulsar wind nebula” 

    H.E.S.S. Cherenkov Telescope Array
    HESS Cherenkov Telescope Array, located on the Cranz family farm, Göllschau, in Namibia, near the Gamsberg
    From H.E.S.S.

    July 2018

    Pulsars are extreme stars left behind after the explosions of certain supernovae. They have masses slightly larger than the Sun, but concentrated in a very compact volume with a radius of approximately 10 km. Moreover, they spin very rapidly, with a rotation period that ranges from 1 ms to a few seconds, and they have giant magnetic fields, billions to millions of billions of times more intense than the Earth. Pulsars are identified by measuring short pulses of radiation, from radio to gamma rays, produced by beams of particles accelerated by the giant electromagnetic fields rotating along with the pulsar itself.

    There is, however, another observational manifestation of pulsars, that is, extended nebulae surrounding them that we can see in radio emission, X-rays, and gamma rays. We think that these nebulae are powered by winds of energetic particles and electromagnetic fields left behind by the pulsar, with some mechanism, not fully understood yet, that contributes to further accelerate the particles. It has long been suspected that this may happen close to the place where the pressure of the wind equals the pressure of the material around the pulsar, and the wind is abruptly terminated with the generation of a shock.

    The Vela constellation shelters a well-known pulsar, which also has an associated pulsar wind nebula, called Vela X.

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    http://www.stargazing.net/david/constel/constel/vela.html

    3
    The Vela Pulsar, a neutron star corpse left from a titanic stellar supernova explosion, shoots through space powered by a jet emitted from one of the neutron star’s rotational poles. Now a counter jet in front of the neutron star has been imaged by the Chandra X-ray observatory. The Chandra image above shows the Vela Pulsar as a bright white spot in the middle of the picture, surrounded by hot gas shown in yellow and orange. The counter jet can be seen wiggling from the hot gas in the upper right. Chandra has been studying this jet so long that it’s been able to create a movie of the jet’s motion. The jet moves through space like a firehose, wiggling to the left and right and up and down, but staying collimated: the “hose” around the stream is, in this case, composed of a tightly bound magnetic field. NASA/CXC/PSU/G.Pavlov et al. Public domain.

    The pulsar is at only about 900 light years from Earth, therefore many telescopes are able to make out a lot of details in the structures of the nebula. It extends over more than 30 light years, far beyond the wind termination shock. The complex structures are thought to be produced by the evolution of the supernova remnant and pulsar wind nebula inside an inhomogeneous medium. H.E.S.S. has detected bright very high-energy gamma-ray emission from Vela X [1,2]. The bulk of the emission coincides with an elongated structure, dubbed the cocoon, very bright in X-rays, seemingly emanating from the wind termination.

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    Fig. 1: Map of the Vela X region in X-rays (left, data from the ROSAT telescope) and in very high-energy gamma rays (right, data from H.E.S.S.). The star shows the position of the Vela pulsar. The green boxes show the regions observed by Suzaku. The blue regions are those for which we derived the X-ray and gamma-ray spectra. Note that in the upper region we avoid the immediate surroundings of the pulsar (red circle), where there is bright X-ray emission coming from the star itself and the region of the wind termination.

    ROSAT X-ray satellite built by DLR , with instruments built by West Germany, the United Kingdom and the United States

    X-rays and very high energy gamma rays are highly complementary probes to unveil the physical processes at play in pulsar wind nebulae, because they are produced by the same relativistic electrons. On one hand, X-rays are produced by electrons moving through magnetic fields in a process known as synchrotron radiation. On the other hand, gamma rays are produced by the same electrons impinging on low energy photons, mostly the cosmic microwave background radiation, in a process known as inverse-Compton scattering.

    In principle, by combining all of this information, we can determine the properties of the electrons and of the magnetic fields. In practice, however, often the limited angular resolution of gamma-ray telescopes prevents us from doing so, because in gamma rays we measure emission from particles accumulated over the whole life of the pulsar and sample regions with varying magnetic fields, whilst X-ray emission is dominated by the regions with stronger magnetic fields near the star. For Vela X we can overcome this problem because it is very close to us, thus it has a large apparent size and we can discern the details of its structures (Fig. 1).

    We study three compact regions in the Vela X cocoon covering distances of 1 light year to 15 light years from the wind termination (Fig. 1). For the three regions, we determine how bright the very high-energy gamma-ray emission is for different gamma-ray energies, using 100 hours of observations performed by H.E.S.S., and how bright the X-ray emission for different X-ray energies is, using data from the Suzaku space telescope. Then we calculate the synchrotron and inverse-Compton emission of a population of electrons in a magnetic field and compare it to the measurements from H.E.S.S. and Suzaku.

    JAXA/Suzaku satellite

    We find a very good agreement between this model and our data. Furthermore, this procedure enables us to infer the characteristics of the electrons and magnetic field. Within the uncertainties, the properties of the electrons and the strengths of the magnetic field look the same in the three regions. We can compare these results with two alternative scenarios for the origin of the relativistic particles in the cocoon.

    In a first scenario the electrons accelerated at or near the wind termination are quickly transported across the cocoon by the asymmetric shock wave resulting from the interaction of the supernova remnant with the interstellar medium. In this case, the properties of the particles in all three regions reflect simply the outcome of the acceleration process. The peak in the gamma-ray emission (Fig. 2) therefore reveals the maximum of the acceleration efficiency, beyond which the number of particles starts declining. From this we can determine the acceleration efficiency, which turns out to be 100 times smaller than in the Crab Nebula, the most famous pulsar wind nebula and the best studied.

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    Fig. 2: Brightness of X-ray emission (blue) and gamma-ray emission (green) at different energies (upper panel). The shaded band shows a range of possible models that reproduce the data. The black like shows the model closer to the data, with the difference between the two shown in the bottom panel.

    In a second scenario the electrons slowly move from the termination shock through the cocoon along the magnetic field lines, zig-zagging whenever they hit small fluctuations of the magnetic field in a process known as diffusion. In this case the electrons get to spend a lot more time in the high-magnetic-field region close to the termination shock where they loose energy by producing synchrotron emission. Since the higher-energy electrons tend to loose more energy in this process, this may explain the decline in the gamma-ray emission at the highest energies. The gamma-ray energy at which we find the maximum is consistent with this hypothesis based on the observations of synchrotron emission near the pulsar in X-rays.

    A question that remains open is: is the strength of the magnetic field always the same or does it vary? The results show that on average it does not change over the 15 light years spanned by the cocoon. On the other hand, there may be variations around the average value everywhere. If this was the case, we would expect a boost of the synchrotron emission at the highest energies [3]. When we search for this effect using H.E.S.S. and Suzaku data, we cannot find a final answer. This pushes us to extend the observations to even higher energies in both X-ray and gamma rays, which we can do with existing or forthcoming telescopes such as NuStar and CTA.

    NASA NuSTAR X-ray telescope

    Cherenkov Telescope Array, http://www.isdc.unige.ch/cta/ at Cerro Paranal, located in the Atacama Desert of northern Chile on Cerro Paranal at 2,635 m (8,645 ft) altitude, 120 km (70 mi) south of Antofagasta; and at at the Instituto de Astrofisica de Canarias (IAC), Roque de los Muchachos Observatory in La Palma, Spain searches for cosmic rays

    References:

    Sorry, no links provided

    [1] H.E.S.S. collaboration, F. A. Aharonian et al., “First detection of a VHE gamma-ray spectral maximum from a cosmic source: HESS discovery of the Vela X nebula”, Astrophys. Journal 448 (2006) L43
    [2] H.E.S.S. collaboration, A. Abramowski et al., “Probing the extent of the non-thermal emission from the Vela X region at TeV energies with H.E.S.S.”, A&A 548 (2012) A38
    [3] S. R. Kelner, F. A. Aharonian, and D. Khangulyan, “On the Jitter Radiation”, Astrophys. Journal 774 (2013) 61

    See the full article here .


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    The High Energy Stereoscopic System

    H.E.S.S. is a system of Imaging Atmospheric Cherenkov Telescopes that investigates cosmic gamma rays in the energy range from 10s of GeV to 10s of TeV. The name H.E.S.S. stands for High Energy Stereoscopic System, and is also intended to pay homage to Victor Hess , who received the Nobel Prize in Physics in 1936 for his discovery of cosmic radiation. The instrument allows scientists to explore gamma-ray sources with intensities at a level of a few thousandths of the flux of the Crab nebula (the brightest steady source of gamma rays in the sky). H.E.S.S. is located in Namibia, near the Gamsberg mountain, an area well known for its excellent optical quality. The first of the four telescopes of Phase I of the H.E.S.S. project went into operation in Summer 2002; all four were operational in December 2003, and were officially inaugurated on September 28, 2004. A much larger fifth telescope – H.E.S.S. II – is operational since July 2012, extending the energy coverage towards lower energies and further improving sensitivity.

    crab
    Crab nebula

     
  • richardmitnick 9:12 am on March 9, 2018 Permalink | Reply
    Tags: , , , , , Pulsars, , Susan Jocelyn Bell Burnell   

    From ScienceNews: “50 years ago, pulsars burst onto the scene” 


    ScienceNews

    March 8, 2018
    Emily Conover

    Excerpt from the March 16, 1968 issue of Science News

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    LIKE CLOCKWORK Scientists reported the first discovery of a pulsar 50 years ago. The rapidly rotating neutron stars emit beams of radiation (illustrated), which sweep past Earth at regular intervals. NASA’s Goddard Space Flight Center.

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    The strangest signals reaching Earth

    The search for neutron stars has intensified because of a relatively small area, low in the northern midnight sky, from which the strangest radio signals yet received on Earth are being detected. If the signals come from a star, the source broadcasting the radio waves is very likely the first neutron star ever detected. — Science News, March 16, 1968

    Susan Jocelyn Bell


    Update

    That first known neutron star’s odd pulsating signature earned it the name “pulsar.” The finding garnered a Nobel Prize just six years after its 1968 announcement — although one of the pulsar’s discoverers, astrophysicist Dame Jocelyn Bell Burnell, was famously excluded.

    Dame Susan Jocelyn Bell Burnell 2009

    Since then, astronomers have found thousands of these blinking collapsed stars, which have confirmed Einstein’s theory of gravity and have been proposed as a kind of GPS for spacecraft.

    See the full article here .

    Science News is edited for an educated readership of professionals, scientists and other science enthusiasts. Written by a staff of experienced science journalists, it treats science as news, reporting accurately and placing findings in perspective. Science News and its writers have won many awards for their work; here’s a list of many of them.

    Published since 1922, the biweekly print publication reaches about 90,000 dedicated subscribers and is available via the Science News app on Android, Apple and Kindle Fire devices. Updated continuously online, the Science News website attracted over 12 million unique online viewers in 2016.

    Science News is published by the Society for Science & the Public, a nonprofit 501(c) (3) organization dedicated to the public engagement in scientific research and education.

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  • richardmitnick 9:43 pm on March 1, 2018 Permalink | Reply
    Tags: , , , , , , , , Pulsars,   

    From GBO: “Pulsar Watchers Close In On Galaxy Merger History” 

    gbo-logo

    Green Bank Radio Telescope, West Virginia, USA
    Green Bank Radio Telescope, West Virginia, USA

    gbo-sign

    Green Bank Observatory

    2018-02-28
    Paul Vosteen

    1
    Astronomers see galaxies merging throughout the universe, some of which should result in binary supermassive black holes. Credit: NASA

    Fifty years after pulsar discovery published, massive new data set moves closer to finding very-low-frequency gravitational waves, researchers say.

    For the past twelve years, a group of astronomers have been watching the sky carefully, timing pulses of radio waves being emitted by rapidly spinning stars called pulsars, first discovered 50 years ago. These astronomers are interested in understanding pulsars, but their true goal is much more profound; the detection of a new kind of gravitational waves. With a new, more sophisticated analysis, they are much closer than ever before.

    Gravitational waves are wrinkles in space-time that stretch and squeeze the distances between objects. In 2015, a hundred years after Albert Einstein realized that accelerating massive objects should produce them, these waves were finally detected from black holes with masses roughly 30 times the mass of our sun colliding with each other. However, Einstein’s theory also predicts another kind of wave, one that comes from the mergers of black holes with masses of hundred million times the sun’s.

    Astronomers believe that nearly all galaxies have supermassive black holes at their centers. When two galaxies collide, these black holes will slowly fall toward each other, finally merging long after the initial galaxy collision. In the last stage of this process, as the two black holes spiral closer to each other, strong gravitational waves can be produced.

    While these waves travel at the speed of light, their strength varies quite slowly, on timescales ranging from months to years. This means that gravitational wave observatories on Earth can’t measure them. For that, you need an observatory with detectors light-years apart.

    “We know that galaxy mergers are an important part of galaxy growth and evolution through cosmic time. By detecting gravitational waves from supermassive binary black holes at the cores of merging galaxies, we will be able to probe how galaxies are shaped by those black holes,” said Sarah Burke-Spolaor, assistant professor at West Virginia University.

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    Nature publication of the discovery of pulsar B1919+21. Credit: Reproduced by permission from Springer Nature

    Fifty years ago, the February 24, 1968 edition of the journal Nature provided the solution, with the discovery of a new kind of star. This new star was curious, emitting regular radio pulses once every 1.3 seconds. Graduate student Jocelyn Bell (now Dr. Bell Burnell [now really Dame Susan Jocelyn Bell Burnell, one of the many women denied a deserved Nobel]) was the first to spot the signal, seeing it as “a bit of scruff” in her radio surveys. Zooming in on the scruff, Bell saw the regular pulses from the star.

    After first entertaining the possibility that the pulses could be the result of LGM, or “little green men,” the new star was dubbed a pulsar, with the understanding that the pulses represented the rotation rate of the star. Such a rapid rotation rate meant that the star must be small, about the size of a city. Only a few years later, a pulsar in a binary system was found, and the first mass estimate indicated that this tiny object held about one and a half times the mass of our sun.

    “Before this time, no one thought stars so small could actually exist! It wasn’t until a pulsar was found at the center of a supernova remnant in 1968 that astronomers realized that pulsars were neutron stars born in the explosions of massive stars,” said Maura McLaughlin, professor at West Virginia University.

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    After detecting unexpected signals at the same location in the sky (top left), graduate student Jocelyn Bell (right) [now Dame Susan Jocelyn Bell Burnell] observed individual pulses from the new source (bottom left) in late 1967. Credit: UK National Science & Media Museum

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    2009 Dame Susan Jocelyn Bell Burnell. Wikipedia

    The fastest pulsars, called millisecond pulsars, spin hundreds of times every second (faster than your kitchen blender!), and are the most stable natural clocks known in the universe. Pulsar astronomers around the globe are monitoring these stellar clocks in order to form a new kind of cosmic gravitational wave detector known as a “Pulsar Timing Array.” By carefully measuring when radio pulses arrive from millisecond pulsars, astronomers can track the tiny changes in the distance from the Earth to the pulsars caused by the stretching and squeezing of spacetime due to a gravitational wave.

    In the US and Canada, a group called NANOGrav (North American Nanohertz Observatory for Gravitational Waves) is searching for these gravitational waves using some of the largest telescopes in the world, including the Green Bank Telescope in West Virginia and the Arecibo Observatory in Puerto Rico.

    NAIC/Arecibo Observatory, Puerto Rico, USA, at 497 m (1,631 ft)

    NANOGrav routinely joins forces with groups in Europe and Australia to improve their sky coverage and sensitivity. Collectively known as the International Pulsar Timing Array, the combined observations from these groups constitute the most sensitive data set in the world for searching for low-frequency gravitational waves.

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    International Pulsar Timing Array

    This month, fifty years after the publication of the first pulsar discovery, NANOGrav has submitted a pair of companion papers to The Astrophysical Journal describing eleven years of monthly observations of 45 millisecond pulsars along with the astrophysical implications of their results. For the first time, the data set includes a six-pulsar “high-frequency” sample, with measurements made every week to expand the pulsar timing array’s sensitivity range. NANOGrav is able to set sensitive upper limits that constrain the physical processes at play in galaxy mergers. As their sensitivity improves, NANOGrav is uncovering new sources of background noise that must be accounted for. Most recently, uncertainties in the pull of Jupiter on the sun have been found to affect pulsar timing. As a result, the team is implementing new computational methods to account for this, in effect determining Jupiter’s orbit more precisely than possible except by planetary missions.

    “This is the most sensitive pulsar timing dataset ever created for both gravitational wave analysis and a host of other astrophysical measurements. And with each new release, we will add more pulsars and data, which increase our sensitivity to gravitational waves”, said David Nice, professor at Lafayette College.

    Last year, the journal that announced the discovery of pulsars once again played host to a pulsar first. In November, Nature Astronomy published their first-ever article describing the gravitational wave environment that pulsar timing arrays are working to uncover. By looking at galaxy surveys, the article estimates there are about 100 supermassive black hole binaries that are close enough to affect pulsar timing array measurements. Given their expected future sensitivity, the authors state that pulsar timing arrays should be able to isolate the gravitational waves from a specific individual galaxy within about 10 years.

    “From city-sized pulsars spinning fast in galaxies to large, massive galaxies themselves and their merging central black holes, all in 50 years! That is a large step for humankind, and not one that we could have foreseen. What will the next 50 years bring? Pulsars and gravitational waves will continue to be big news, I’m sure!” said Jocelyn Bell Burnell.

    A century after Einstein first predicted them, gravitational waves were finally detected. Now, 50 years after Jocelyn Bell’s discovery, pulsars have become a new tool for measuring both gravitational waves and the distant black holes that create them. If predictions are correct, the next decade will be an exciting period of discovery for radio astronomers, pulsars, and gravitational waves!

    Links to supporting materials:
    1-page summary of 11-year results: https://nanograv.github.io/11yr_stochastic_analysis/ Submitted to the Astrophysical Journal, Dec 31, 2017

    11-Year Data Release paper: https://arxiv.org/abs/1801.01837 Submitted to The Astrophysical Journal

    Gravitational Wave Search paper: https://arxiv.org/abs/1801.02617 Submitted to The Astrophysical Journal

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

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    Mission Statement

    Green Bank Observatory enables leading edge research at radio wavelengths by offering telescope, facility and advanced instrumentation access to the astronomy community as well as to other basic and applied research communities. With radio astronomy as its foundation, the Green Bank Observatory is a world leader in advancing research, innovation, and education.

    History

    60 years ago, the trailblazers of American radio astronomy declared this facility their home, establishing the first ever National Radio Astronomy Observatory within the United States and the first ever national laboratory dedicated to open access science. Today their legacy is alive and well.

     
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