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  • 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: , , , , , , NANOGrav-North American Nanohertz Observatory for Gravitational Waves, , Pulsars,   

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

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

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    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 .

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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.

     
  • richardmitnick 9:06 pm on February 28, 2018 Permalink | Reply
    Tags: , Pulsars   

    From GBO: “50 years ago, graduate student Jocelyn Bell (now Dr. Bell Burnell) was the first to spot “a bit of scruff” in her radio surveys. 

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

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    Green Bank Observatory

    That “scruff” turned out to be a new kind of star, the Pulsar.

    Named for the regular radio pulses it emitted every 1.3 seconds, this exotic star had such a rapid rotation rate that scientists knew it must be small–about the size of a city! The fastest pulsars, known as millisecond pulsars, spin at a few hundred times per second… that’s faster than your kitchen blender!

    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. Today, astronomers from NANOGrav (North American Nanohertz Observatory forGravitational Waves) are 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.

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    Graduate student Jocelyn Bell. This year marks the semicentennial of the discovery of pulsars, first observed by Jocelyn Bell Burnell, shown here in 1968 at the Mullard Radio Astronomy Observatory in Cambridge, England.

    3
    Astronomers see galaxies merging throughout the universe, some of which should result in binary supermassive black holes. (Image: NASA)

    From social media, no link.

    Please help promote STEM in your local schools.

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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.

     
  • richardmitnick 1:13 pm on December 20, 2017 Permalink | Reply
    Tags: , , , , , Habitable planets could exist around pulsars, , Pulsars, The first exoplanets ever discovered were around the pulsar PSR B1257+12,   

    From U Cambridge: “Habitable planets could exist around pulsars” 

    U Cambridge bloc

    University of Cambridge

    19 Dec 2017
    Sarah Collins
    sarah.collins@admin.cam.ac.uk

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    It is theoretically possible that habitable planets exist around pulsars – spinning neutron stars that emit short, quick pulses of radiation. According to new research, such planets must have an enormous atmosphere that converts the deadly x-rays and high energy particles of the pulsar into heat. The results, from astronomers at the University of Cambridge and Leiden University, are reported in the journal Astronomy & Astrophysics.

    Pulsars are known for their extreme conditions. Each is a fast-spinning neutron star – the collapsed core of a massive star that has gone supernova at the end of its life. Only 10 to 30 kilometres across, a pulsar possesses enormous magnetic fields, accretes matter, and regularly gives out large bursts of X-rays and highly energetic particles.

    Surprisingly, despite this hostile environment, neutron stars are known to host exoplanets. The first exoplanets ever discovered were around the pulsar PSR B1257+12 – but whether these planets were originally in orbit around the precursor massive star and survived the supernova explosion, or formed in the system later remains an open question. Such planets would receive little visible light but would be continually blasted by the energetic radiation and stellar wind from the host. Could such planets ever host life?

    For the first time, astronomers have tried to calculate the ‘habitable’ zones near neutron stars – the range of orbits around a star where a planetary surface could possibly support water in a liquid form. Their calculations show that the habitable zone around a neutron star can be as large as the distance from our Earth to our Sun. An important premise is that the planet must be a super-Earth, with a mass between one and ten times our Earth. A smaller planet will lose its atmosphere within a few thousand years under the onslaught of the pulsar winds. To survive this barrage, a planet’s atmosphere must be a million times thicker than ours – the conditions on a pulsar planet surface might resemble those of the deep ocean floor on Earth.

    The astronomers studied the pulsar PSR B1257+12 about 2300 light-years away as a test case, using the X-ray Chandra space telescope.

    NASA/Chandra Telescope

    Of the three planets in orbit around the pulsar, two are super-Earths with a mass of four to five times our Earth, and orbit close enough to the pulsar to warm up. According to co-author Alessandro Patruno from Leiden University, “The temperature of the planets might be suitable for the presence of liquid water on their surface. Though, we don’t know yet if the two super-Earths have the right, extremely dense atmosphere.”

    In the future, Patruno and his co-author Mihkel Kama from Cambridge’s Institute of Astronomy would like to observe the pulsar in more detail and compare it with other pulsars. The European Southern Observatory’s ALMA Telescope would be able to show dust discs around neutron stars, which are good predictors of planets. The Milky Way contains about one billion neutron stars, of which about 200,000 are pulsars. So far, 3000 pulsars have been studied and only five pulsar planets have been found.

    See the full article here .

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    U Cambridge Campus

    The University of Cambridge (abbreviated as Cantab in post-nominal letters) is a collegiate public research university in Cambridge, England. Founded in 1209, Cambridge is the second-oldest university in the English-speaking world and the world’s fourth-oldest surviving university. It grew out of an association of scholars who left the University of Oxford after a dispute with townsfolk. The two ancient universities share many common features and are often jointly referred to as “Oxbridge”.

    Cambridge is formed from a variety of institutions which include 31 constituent colleges and over 100 academic departments organised into six schools. The university occupies buildings throughout the town, many of which are of historical importance. The colleges are self-governing institutions founded as integral parts of the university. In the year ended 31 July 2014, the university had a total income of £1.51 billion, of which £371 million was from research grants and contracts. The central university and colleges have a combined endowment of around £4.9 billion, the largest of any university outside the United States. Cambridge is a member of many associations and forms part of the “golden triangle” of leading English universities and Cambridge University Health Partners, an academic health science centre. The university is closely linked with the development of the high-tech business cluster known as “Silicon Fen”.

     
  • richardmitnick 10:07 pm on November 27, 2017 Permalink | Reply
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    From CSIRO: Women in STEM – “Fifty years ago Jocelyn Bell discovered pulsars and changed our view of the universe” Dame Jocelyn Bell Burnell 

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    CSIROscope

    28 November 2017
    George Hobbs
    Dick Manchester
    Simon Johnston

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    Dame Jocelyn Bell Burnell. BBC.

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    CSIRO Parkes radio telescope has discovered around half of all known pulsars. Wayne England, Author provided.

    A pulsar is a small, spinning star – a giant ball of neutrons, left behind after a normal star has died in a fiery explosion.

    With a diameter of only 30 km, the star spins up to hundreds of times a second, while sending out a beam of radio waves (and sometimes other radiation, such as X-rays). When the beam is pointed in our direction and into our telescopes, we see a pulse.

    2017 marks 50 years since pulsars were discovered. In that time, we have found more than 2,600 pulsars (mostly in the Milky Way), and used them to hunt for low-frequency gravitational waves, to determine the structure of our galaxy and to test the general theory of relativity.

    The Discovery

    In mid-1967, when thousands of people were enjoying the summer of love, a young PhD student at the University of Cambridge in the UK was helping to build a telescope.

    It was a poles-and-wires affair – what astronomers call a “dipole array”. It covered a bit less than two hectares, the area of 57 tennis courts.

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    Jocelyn Bell Burnell, who discovered the first pulsar. CC BY-SA

    By July it was built. The student, Jocelyn Bell (now Dame Jocelyn Bell Burnell), became responsible for running it and analysing the data it churned out. The data came in the form of pen-on-paper chart records, more than 30 metres of them each day. Bell analysed them by eye.

    What she found – a little bit of “scruff” on the chart records – has gone down in history.

    Like most discoveries, it took place over time. But there was a turning point. On November 28, 1967, Bell and her supervisor, Antony Hewish, were able to capture a “fast recording” – that is, a detailed one – of one of the strange signals.

    In this she could see for the first time that the “scruff” was actually a train of pulses spaced by one-and-a-third seconds. Bell and Hewish had discovered pulsars.

    But this wasn’t immediately obvious to them. Following Bell’s observation they worked for two months to eliminate mundane explanations for the signals.

    Bell also found another three sources of pulses, which helped to scotch some rather more exotic explanations, such as the idea that the signals came from “little green men” in extraterrestrial civilisations. The discovery paper appeared in Nature on February 24, 1968.

    Later, Bell missed out when Hewish and his colleague Sir Martin Ryle were awarded the 1974 Nobel Prize in Physics.[More discrimination.]

    A pulsar on ‘the pineapple’

    CSIRO’s Parkes radio telescope in Australia made its first observation of a pulsar in 1968, later made famous by appearing (along with the Parkes telescope) on the first Australian $50 note.

    Fifty years later, Parkes has found more than half of the known pulsars. The University of Sydney’s Molonglo Telescope also played a central role, and they both remain active in finding and timing pulsars today.

    U Sidney Molonglo Observatory Synthesis Telescope (MOST), Hoskinstown, Australia

    Internationally, one of the most exciting new instruments on the scene is China’s Five-hundred-metre Aperture Spherical Telescope, or FAST.

    FAST radio telescope, now operating, located in the Dawodang depression in Pingtang county Guizhou Province, South China

    FAST has recently found several new pulsars, confirmed by the Parkes telescope and a team of CSIRO astronomers working with their Chinese colleagues.

    Why look for pulsars?

    We want to understand what pulsars are, how they work, and how they fit into the general population of stars. The extreme cases of pulsars – those that are super fast, super slow, or extremely massive – help to limit the possible models for how pulsars work, telling us more about the structure of matter at ultra-high densities. To find these extreme cases, we need to find lots of pulsars.

    Pulsars often orbit companion stars in binary systems, and the nature of these companions helps us understand the formation history of the pulsars themselves. We’ve made good progress with the “what” and “how” of pulsars but there are still unanswered questions.

    As well as understanding pulsars themselves, we also use them as a clock. For example, pulsar timing is being pursued as a way to detect the background rumble of low-frequency gravitational waves throughout the universe.

    Pulsars have also been used to measure the structure of our Galaxy, by looking at the way their signals are altered as they travel through denser regions of material in space.

    Pulsars are also one of the finest tools we have for testing Einstein’s theory of general relativity.

    This theory has survived 100 years of the most sophisticated tests astronomers have been able throw at it. But it doesn’t play nicely with our other most successful theory of how the universe works, quantum mechanics, so it must have a tiny flaw somewhere. Pulsars help us to try and understand this problem.

    What keeps pulsar astronomers up at night (literally!) is the hope of finding a pulsar in orbit around a black hole. This is the most extreme system we can imagine for testing general relativity.

    Finally, pulsars have some more down-to-earth applications. We’re using them as a teaching tool in our PULSE@Parkes program, in which students control the Parkes telescope over the Internet and use it to observe pulsars. This program has reached over 1,700 students, in Australia, Japan, China, The Netherlands, United Kingdom and South Africa.Pulsars also offer promise as a navigation system for guiding craft travelling through deep space. In 2016 China launched a satellite, XPNAV-1, carrying a navigation system that uses periodic X-ray signals from certain pulsars.Pulsars have changed our our understanding of the universe, and their true importance is still unfolding

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    XPNAV-1 was sent skyward atop a Long March 11 solid-fuelled rocket from the Jiuquan Satellite Launch Center (Image Source: Weibo)

    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 1:17 pm on October 27, 2017 Permalink | Reply
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    From astrobites: “Observing a Strange Pulsar in X-ray and Radio” 

    Astrobites bloc

    astrobites

    27 October 2017
    Joshua Kerrigan

    Title: Simultaneous Chandra and VLA Observations of the Transitional Millisecond Pulsar PSR J1023+0038: Anti-correlated X-ray and Radio Variability
    Authors: Slavko Bogdanov, Adam T. Deller, James C. A. Miller-Jones, et al.
    First Author’s Institution: Columbia University

    Status: Submitted to ApJ, open access

    What’s more interesting than a rapidly spinning neutron star that emits electromagnetic radiation parallel to its magnetic poles? One that doesn’t exactly behave as expected, of course. One such weirdly acting pulsar, PSR J1023+0038, is a transitional millisecond pulsar (tMSP) — which is fancy speak for a pulsar with a millisecond rotational period that switches between radio and X-ray emission on a several-year timescale. The fact that this pulsar emits in both X-ray and radio on these longer timescales isn’t what piques the interest of astronomers, however, in the case of the study in this astrobite.

    Weird Pulsar Behavior

    Pulsars can typically fall into one of the following categories: radio pulsars are powered by exchanging rotational energy from the spinning neutron star into emitting radiation. This means that their rotation slows and their pulse length increases. Meanwhile, X-ray pulsars are accretion powered, meaning they turn heated infalling matter into X-ray emission. What distinguishes PSR J1023+0038 from the background of pulsars that switch between accretion-powered X-ray and rotation-powered radio pulsars is that it has a simultaneous anti-correlated X-ray and radio emission. The authors looked at about 5 hours of overlapping and concurrent observations from the Chandra X-ray Observatory and the Very Large Array (VLA) to try and understand this weird relationship between the X-ray and radio emissions.

    NASA/Chandra Telescope

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

    This is very clearly shown in Fig. 1 where we can see a tiny sample of time of overlapping X-ray and radio flux measurements. The anti-correlation is quite strong, meaning that when the X-ray emissions are weakest, the radio emission is strongest.

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    Figure 1: Radio emissions (black) and x-ray emissions (blue) recorded by the VLA and Chandra respectively over time. This shows that when radio emissions drop off, X-ray emissions pick up.

    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 5:13 pm on August 1, 2017 Permalink | Reply
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    From Goddard: “NASA Continues to Study Pulsars, 50 Years After Their Chance Discovery” 

    NASA Goddard Banner
    NASA Goddard Space Flight Center

    Aug. 1, 2017
    Clare Skelly
    clare.a.skelly@nasa.gov
    NASA’s Goddard Space Flight Center in Greenbelt, Md.

    A little bit of “scruff” in scientific data 50 years ago led to the discovery of pulsars – rapidly spinning dense stellar corpses that appear to pulse at Earth.

    Astronomer Jocelyn Bell made the chance discovery using a vast radio telescope in Cambridge, England. Although it was built to measure the random brightness flickers of a different category of celestial objects called quasars, the 4.5-acre telescope produced unexpected markings on Bell’s paper data recorder every 1.33730 seconds.

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    The 4.5 Acre Array. Reproduced with permission from 40 Years of Pulsars—Millisecond Pulsars, Magnetars, and More, edited by C. G. Bassa, Z. Wang, A. Gumming, and V. M. Kaspi. Copyright 2008, AIP Publishing LLC

    “The pulses were so regular, so much like a ticking clock, that Bell and her supervisor Anthony Hewish couldn’t believe it was a natural phenomenon,” said Zaven Arzoumanian of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Once they found a second, third and fourth they started to think differently.”

    The unusual stellar objects had been previously predicted but never observed. Today, scientists know of over 2,000 pulsars. These rotating “lighthouse” neutron stars begin their lives as stars between about seven and 20 times the mass of our sun. Some are found to spin hundreds of times per second, faster than the blades of a household blender, and they possess enormously strong magnetic fields.

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    Most known neutron stars are observed as pulsars, emitting narrow, sweeping beams of radiation. They squeeze up to two solar masses into a city-size volume, crushing matter to the highest possible stable densities. To explore these exotic states of matter, NICER measures X-ray emissions across the surfaces of neutron stars as they spin, ultimately confronting the predictions of nuclear physics theory.
    Credits: NASA’s Goddard Space Flight Center

    Technology advances in the past half-century allowed scientists to study these compact stellar objects from space using different wavelengths of light, especially those much more energetic than the radio waves received by the Cambridge telescope. Several current NASA missions continue to study these natural beacons.

    The Neutron star Interior Composition Explorer, or NICER, is the first NASA mission dedicated to studying pulsars.

    NASA NICER

    In a nod to the anniversary of Bell’s discovery, NICER observed the famous first pulsar, known today as PSR B1919+21.

    NICER launched to the International Space Station in early June and started science operations last month. Its X-ray observations – the part of the electromagnetic spectrum in which these stars radiate both from their million-degree solid surfaces and from their strong magnetic fields – will reveal how nature’s fundamental forces behave within the cores of these objects, an environment that doesn’t exist and can’t be reproduced anywhere else. “What’s inside a pulsar?” is one of many long-standing astrophysics questions about these ultra-dense, fast-spinning, powerfully magnetic objects.

    The “stuff” of pulsars is a collection of particles familiar to scientists from over a century of laboratory studies on Earth – neutrons, protons, electrons, and perhaps even their own constituents, called quarks. However, under such extreme conditions of pressure and density, their behavior and interactions aren’t well understood. New, precise measurements, especially of the sizes and masses of pulsars are needed to pin down theories.

    “Many nuclear-physics models have been developed to explain how the make-up of neutron stars, based on available data and the constraints they provide,” said Goddard’s Keith Gendreau, the principal investigator for NICER. “NICER’s sensitivity, X-ray energy resolution and time resolution will improve these by more precisely measuring their radii, to an order of magnitude improvement over the state of the art today.”

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    NICER is currently installed on the International Space Station. This turntable animation of the payload calls out the locations of NICER’s star tracker camera, electronics, space station attachment mechanism, 56 sunshields, pointing actuators and stow/deploy actuator.
    Credits: NASA’s Goddard Space Flight Center

    The mission will also pave the way for future space exploration by helping to develop a Global Positioning System-like capability for the galaxy. The embedded Station Explorer for X-ray Timing and Navigation Technology, or SEXTANT, demonstration will use NICER’s X-ray observations of pulsar signals to determine NICER’s exact position in orbit.

    “You can time the pulsations of pulsars distributed in many directions around a spacecraft to figure out where the vehicle is and navigate it anywhere,” said Arzoumanian, who is also the NICER science lead. “That’s exactly how the GPS system on Earth works, with precise clocks flown on satellites in orbit.”

    Scientists have tested this method using computer and lab simulations. SEXTANT will demonstrate pulsar-based navigation for the first time in space.

    NICER-SEXTANT is the first astrophysics mission dedicated to studying pulsars, 50 years after their discovery. “I think it is going to yield many more scientific discoveries than we can anticipate now,” said Gendreau.

    NICER-SEXTANT is a two-in-one mission. NICER is an Astrophysics Mission of Opportunity within NASA’s Explorer program, which provides frequent flight opportunities for world-class scientific investigations from space utilizing innovative, streamlined, and efficient management approaches within the heliophysics and astrophysics science areas. NASA’s Space Technology Mission Directorate supports the SEXTANT component of the mission, demonstrating pulsar-based spacecraft navigation.

    More about NICER: https://www.nasa.gov/nicer/

    Read about five famous pulsars from the past 50 years: https://nasa.tumblr.com/post/163637443034/five-famous-pulsars-from-the-past-50-years ­­­­

    See the full article here.

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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 8:32 pm on May 2, 2017 Permalink | Reply
    Tags: , , , , , , Mystery glow of Milky Way likely not dark matter, Pulsars,   

    From Symmetry: “Mystery glow of Milky Way likely not dark matter” 


    Symmetry

    05/02/17
    Manuel Gnida

    1
    NASA/CXC/University of Massachusetts/D. Wang et al.; Greg Stewart, SLAC National Accelerator Laboratory

    According to the Fermi LAT collaboration, the galaxy’s excessive gamma-ray glow likely comes from pulsars, the remains of collapsed ancient stars.

    NASA/Fermi LAT

    A mysterious gamma-ray glow at the center of the Milky Way is most likely caused by pulsars, the incredibly dense, rapidly spinning cores of collapsed ancient stars that were up to 30 times more massive than the sun.

    That’s the conclusion of a new analysis by an international team of astrophysicists on the Fermi LAT collaboration. The findings cast doubt on previous interpretations of the signal as a potential sign of dark matter, a form of matter that accounts for 85 percent of all matter in the universe but that so far has evaded detection.

    “Our study shows that we don’t need dark matter to understand the gamma-ray emissions of our galaxy,” says Mattia Di Mauro from the Kavli Institute for Particle Astrophysics and Cosmology, a joint institute of Stanford University and the US Department of Energy’s SLAC National Accelerator Laboratory. “Instead, we have identified a population of pulsars in the region around the galactic center, which sheds new light on the formation history of the Milky Way.”

    Di Mauro led the analysis, which looked at the glow with the Large Area Telescope on NASA’s Fermi Gamma-ray Space Telescope, which has been orbiting Earth since 2008. The LAT, a sensitive “eye” for gamma rays, the most energetic form of light, was conceived of and assembled at SLAC, which also hosts its operations center.

    The collaboration’s findings, submitted to The Astrophysical Journal for publication, are available as a preprint.

    A mysterious glow

    Dark matter is one of the biggest mysteries of modern physics. Researchers know that dark matter exists because it bends light from distant galaxies and affects how galaxies rotate. But they don’t know what the substance is made of. Most scientists believe it’s composed of yet-to-be-discovered particles that almost never interact with regular matter other than through gravity, making it very hard to detect them.

    One way scientific instruments might catch a glimpse of dark matter particles is when the particles either decay or collide and destroy each other. “Widely studied theories predict that these processes would produce gamma rays,” says Seth Digel, head of KIPAC’s Fermi group. “We search for this radiation with the LAT in regions of the universe that are rich in dark matter, such as the center of our galaxy.”

    Previous studies have indeed shown that there are more gamma rays coming from the galactic center than expected, fueling some scientific papers and media reports that suggest the signal might hint at long-sought dark matter particles. However, gamma rays are produced in a number of other cosmic processes, which must be ruled out before any conclusion about dark matter can be drawn. This is particularly challenging because the galactic center is extremely complex, and astrophysicists don’t know all the details of what’s going on in that region.

    Most of the Milky Way’s gamma rays originate in gas between the stars that is lit up by cosmic rays, charged particles produced in powerful star explosions called supernovae. This creates a diffuse gamma-ray glow that extends throughout the galaxy. Gamma rays are also produced by supernova remnants, pulsars—collapsed stars that emit “beams” of gamma rays like cosmic lighthouses—and more exotic objects that appear as points of light.

    “Two recent studies by teams in the US and the Netherlands have shown that the gamma-ray excess at the galactic center is speckled, not smooth as we would expect for a dark matter signal,” says KIPAC’s Eric Charles, who contributed to the new analysis. “Those results suggest the speckles may be due to point sources that we can’t see as individual sources with the LAT because the density of gamma-ray sources is very high and the diffuse glow is brightest at the galactic center.”

    Remains of ancient stars

    The new study takes the earlier analyses to the next level, demonstrating that the speckled gamma-ray signal is consistent with pulsars.

    “Considering that about 70 percent of all point sources in the Milky Way are pulsars, they were the most likely candidates,” Di Mauro says. “But we used one of their physical properties to come to our conclusion. Pulsars have very distinct spectra—that is, their emissions vary in a specific way with the energy of the gamma rays they emit. Using the shape of these spectra, we were able to model the glow of the galactic center correctly with a population of about 1,000 pulsars and without introducing processes that involve dark matter particles.”

    The team is now planning follow-up studies with radio telescopes to determine whether the identified sources are emitting their light as a series of brief light pulses—the trademark that gives pulsars their name.

    Discoveries in the halo of stars around the center of the galaxy, the oldest part of the Milky Way, also reveal details about the evolution of our galactic home, just as ancient remains teach archaeologists about human history.

    “Isolated pulsars have a typical lifetime of 10 million years, which is much shorter than the age of the oldest stars near the galactic center,” Charles says. “The fact that we can still see gamma rays from the identified pulsar population today suggests that the pulsars are in binary systems with companion stars, from which they leach energy. This extends the life of the pulsars tremendously.”

    Dark matter remains elusive

    The new results add to other data that are challenging the interpretation of the gamma-ray excess as a dark matter signal.

    “If the signal were due to dark matter, we would expect to see it also at the centers of other galaxies,” Digel says. “The signal should be particularly clear in dwarf galaxies orbiting the Milky Way. These galaxies have very few stars, typically don’t have pulsars and are held together because they have a lot of dark matter. However, we don’t see any significant gamma-ray emissions from them.”

    The researchers believe that a recently discovered strong gamma-ray glow at the center of the Andromeda galaxy, the major galaxy closest to the Milky Way, may also be caused by pulsars rather than dark matter.

    But the last word may not have been spoken. Although the Fermi-LAT team studied a large area of 40 degrees by 40 degrees around the Milky Way’s galactic center (the diameter of the full moon is about half a degree), the extremely high density of sources in the innermost four degrees makes it very difficult to see individual ones and rule out a smooth, dark matter-like gamma-ray distribution, leaving limited room for dark matter signals to hide.

    This work was funded by NASA and the DOE Office of Science, as well as agencies and institutes in France, Italy, Japan and Sweden.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 7:33 am on February 22, 2017 Permalink | Reply
    Tags: , , , , , furthest pulsar in the Universe, Pulsars, The brightest   

    From ESA: “The brightest, furthest pulsar in the Universe” 

    ESA Space For Europe Banner

    European Space Agency

    21 February 2017
    Markus Bauer








    ESA Science and Robotic Exploration Communication Officer









    Tel: +31 71 565 6799









    Mob: +31 61 594 3 954









    Email: markus.bauer@esa.int

    Gian Luca Israel
    INAF, Osservatorio Astronomico di Roma, Italy
    Email: gianluca@oa-roma.inaf.it

    Norbert Schartel
    XMM-Newton project scientist
    Email: Norbert.Schartel@esa.int

    1
    NGC 5907 X-1: record-breaking pulsar

    ESA’s XMM-Newton has found a pulsar – the spinning remains of a once-massive star – that is a thousand times brighter than previously thought possible.

    ESA/XMM Newton
    ESA/XMM Newton

    The pulsar is also the most distant of its kind ever detected, with its light travelling 50 million light-years before being detected by XMM-Newton.

    Pulsars are spinning, magnetised neutron stars that sweep regular pulses of radiation in two symmetrical beams across the cosmos. If suitably aligned with Earth these beams are like a lighthouse beacon appearing to flash on and off as it rotates. They were once massive stars that exploded as a powerful supernova at the end of their natural life, before becoming small and extraordinarily dense stellar corpses.

    This X-ray source is the most luminous of its type detected to date: it is 10 times brighter than the previous record holder. In one second it emits the same amount of energy released by our Sun in 3.5 years.

    XMM-Newton observed the object several times in the last 13 years, with the discovery a result of a systematic search for pulsars in the data archive – its 1.13 s periodic pulses giving it away.

    The signal was also identified in NASA’s Nustar archive data, providing additional information.

    NASA NuSTAR
    NASA/NuSTAR

    “Before, it was believed that only black holes at least 10 times more massive than our Sun feeding off their stellar companions could achieve such extraordinary luminosities, but the rapid and regular pulsations of this source are the fingerprints of neutron stars and clearly distinguish them from black holes,” says Gian Luca Israel, from INAF-Osservatorio Astronomica di Roma, Italy, lead author of the paper describing the result published in Science this week.

    The archival data also revealed that the pulsar’s spin rate has changed over time, from 1.43 s per rotation in 2003 to 1.13 s in 2014. The same relative acceleration in Earth’s rotation would shorten a day by five hours in the same time span

    “Only a neutron star is compact enough to keep itself together while rotating so fast,” adds Gian Luca.

    Although it is not unusual for the rotation rate of a neutron star to change, the high rate of change in this case is likely linked to the object rapidly consuming mass from a companion.

    “This object is really challenging our current understanding of the ‘accretion’ process for high-luminosity stars,” says Gian Luca. “It is 1000 times more luminous than the maximum thought possible for an accreting neutron star, so something else is needed in our models in order to account for the enormous amount of energy released by the object.”

    The scientists think there must be a strong, complex magnetic field close to its surface, such that accretion onto the neutron star surface is still possible while still generating the high luminosity.

    “The discovery of this very unusual object, by far the most extreme ever discovered in terms of distance, luminosity and rate of increase of its rotation frequency, sets a new record for XMM-Newton, and is changing our ideas of how such objects really ‘work’,” says Norbert Schartel, ESA’s XMM-Newton project scientist.

    An accreting pulsar with extreme properties drives an ultraluminous X-ray source in NGC 5907 by G.L. Israel is published in Science.

    See the full article here .

    Please help promote STEM in your local schools.

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    The European Space Agency (ESA), established in 1975, is an intergovernmental organization dedicated to the exploration of space, currently with 19 member states. Headquartered in Paris, ESA has a staff of more than 2,000. ESA’s space flight program includes human spaceflight, mainly through the participation in the International Space Station program, the launch and operations of unmanned exploration missions to other planets and the Moon, Earth observation, science, telecommunication as well as maintaining a major spaceport, the Guiana Space Centre at Kourou, French Guiana, and designing launch vehicles. ESA science missions are based at ESTEC in Noordwijk, Netherlands, Earth Observation missions at ESRIN in Frascati, Italy, ESA Mission Control (ESOC) is in Darmstadt, Germany, the European Astronaut Centre (EAC) that trains astronauts for future missions is situated in Cologne, Germany, and the European Space Astronomy Centre is located in Villanueva de la Cañada, Spain.

    ESA50 Logo large

     
  • richardmitnick 12:36 pm on January 19, 2017 Permalink | Reply
    Tags: , , , , Geminga and B0355+54, , Pulsars   

    From Chandra: “Geminga and B0355+54: Chandra Images Show That Geometry Solves a Pulsar Puzzle” 

    NASA Chandra Banner

    NASA Chandra Telescope

    NASA Chandra
    [I know a guy, JLT, who just might love to see these images.]
    January 18, 2017

    1
    Credit X-ray: NASA/CXC/PSU/B.Posselt et al; Infrared: NASA/JPL-Caltech; Illustration: Nahks TrEhnl
    Release Date January 18, 2017

    X-ray images from Chandra have shown distinctly different shapes for the structures around two pulsars.

    Pulsars are rapidly rotating, highly magnetized, neutron stars born in supernova explosions triggered by the collapse of massive stars.

    In certain cases, pulsars generate extensive clouds of high-energy particles called pulsar wind nebulas.

    By studying the shape and orientation of these structures, astronomers may be able to explain the presence or absence of radio and gamma-ray pulses from these systems.

    NASA’s Chandra X-ray Observatory has taken deep exposures of two nearby energetic pulsars flying through the Milky Way galaxy. The shape of their X-ray emission suggests there is a geometrical explanation for puzzling differences in behavior shown by some pulsars.

    Pulsars – rapidly rotating, highly magnetized, neutron stars born in supernova explosions triggered by the collapse of massive stars- were discovered 50 years ago via their pulsed, highly regular, radio emission. Pulsars produce a lighthouse-like beam of radiation that astronomers detect as pulses as the pulsar’s rotation sweeps the beam across the sky.

    Since their discovery, thousands of pulsars have been discovered, many of which produce beams of radio waves and gamma rays. Some pulsars show only radio pulses and others show only gamma-ray pulses. Chandra observations have revealed steady X-ray emission from extensive clouds of high-energy particles, called pulsar wind nebulas, associated with both types of pulsars. New Chandra data on pulsar wind nebulas may explain the presence or absence of radio and gamma-ray pulses.

    This four-panel graphic shows the two pulsars observed by Chandra. Geminga is in the upper left and B0355+54 is in the upper right. In both of these images, Chandra’s X-rays, colored blue and purple, are combined with infrared data from NASA’s Spitzer Space Telescope that shows stars in the field of view.

    NASA/Spitzer Telescope
    NASA/Spitzer Telescope

    Below each data image, an artist’s illustration depicts more details of what astronomers think the structure of each pulsar wind nebula looks like.

    For Geminga, a deep Chandra observation totaling nearly eight days over several years was analyzed to show sweeping, arced trails spanning half a light year and a narrow structure directly behind the pulsar. A five-day Chandra observation of the second pulsar, B0355+54, showed a cap of emission followed by a narrow double trail extending almost five light years.

    The underlying pulsars are quite similar, both rotating about five times per second and both aged about half a million years. However, Geminga shows gamma-ray pulses with no bright radio emission, while B0355+54 is one of the brightest radio pulsars known yet not seen in gamma rays.

    A likely interpretation of the Chandra images is that the long narrow trails to the side of Geminga and the double tail of B0355+54 represent narrow jets emanating from the pulsar’s spin poles. Both pulsars also contain a torus, a disk-shaped region of emission spreading from the pulsar’s spin equator. These donut-shaped structures and jets are crushed and swept back as the pulsars fly through the Galaxy at supersonic speeds.

    In the case of Geminga, the view of the torus is close to edge-on, while the jets point out to the sides. B0355+54 has a similar structure, but with the torus viewed nearly face-on and the jets pointing nearly directly towards and away from Earth. In B0355+54, the swept-back jets appear to lie almost on top of each other, giving a doubled tail.

    Both pulsars have magnetic poles quite close to their spin poles, as is the case for the Earth’s magnetic field. These magnetic poles are the site of pulsar radio emission so astronomers expect the radio beams to point in a similar direction as the jets. By contrast the gamma-ray emission is mainly produced along the spin equator and so aligns with the torus.

    For Geminga, astronomers view the bright gamma-ray pulses along the edge of the torus, but the radio beams near the jets point off to the sides and remain unseen. For B0355+54, a jet points almost along our line of sight towards the pulsar. This means astronomers see the bright radio pulses, while the torus and its associated gamma-ray emission are directed in a perpendicular direction to our line of sight, missing the Earth.

    These two deep Chandra images have, therefore, exposed the spin orientation of these pulsars, helping to explain the presence, and absence, of the radio and gamma-ray pulses.

    The Chandra observations of Geminga and B0355+54 are part of a large campaign, led by Roger Romani of Stanford University, to study six pulsars that have been seen to emit gamma-rays. The survey sample covers a range of ages, spin-down properties and expected inclinations, making it a powerful test of pulsar emission models.

    A paper on Geminga led by Bettina Posselt of Penn State University was accepted for publication in The Astrophysical Journal and is available online. A paper on B0355+54 led by Noel Klingler of the George Washington University was published in the December 20th, 2016 issue of The Astrophysical Journal and is available online.

    See the full article here .

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

     
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