Tagged: Neutron stars Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 10:08 pm on December 23, 2016 Permalink | Reply
    Tags: AR Scorpii, , Neutron stars,   

    From astrobites: “AR Sco — The First White Dwarf Pulsar” 

    Astrobites bloc

    Astrobites

    Dec 23, 2016
    Matthew Green

    Title: Polarimetric evidence of a white dwarf pulsar in the binary system AR Scorpii
    Authors: D.A.H. Buckley, P.J. Meintjes, S.B. Potter, T.R. Marsh, & B.T Gänsicke
    First Author’s Institution: South African Astronomical Observatory, PO Box 9, Observatory, 7935, Cape Town, South Africa
    Status: Published on arXiv, open access

    In 1967, Jocelyn Bell Burnell and Anthony Hewish saw a signal that they didn’t understand: a regular flash of radio emission coming from the same point on the sky, once every 1.3 seconds. It was named CP 1919, although privately they nicknamed the star LGM-1 (standing for Little Green Men) after the suggestion that the radio pulses were signals from an alien civilisation. While their signal was — spoiler alert — not aliens, it was the discovery of two things: the first known pulsar, and the first known neutron star.

    Until now, every known pulsar has contained a neutron star with a strong magnetic field. The magnetic field accelerates charged particles in its atmosphere and causes them to emit synchrotron radiation in two beams, pointing away from the north and south magnetic poles of the star. If the magnetic pole is not lined up with the rotation poles, these two beams sweep through space like rays of light from a lighthouse, appearing to observers on Earth as regular flashes of radio waves. Neutron stars have long been thought to be the only stars dense and magnetic enough to cause these beams. Today we see that this is no longer true, as we take a look at the first ever known white dwarf pulsar.

    2
    Figure 1: Artist’s impression of AR Sco. Image by Mark Garlick, taken from the discovery’s press release.

    AR Scorpii

    AR Scorpii, or AR Sco, is a binary system containing a white dwarf and a main sequence star. Earlier this year, it was discovered to pulsate incredibly strongly — its brightness can increase or decrease by as much as a factor of four in as little as thirty seconds! Some of these pulsations are shown in Figure 2. These pulsations are seen across the electromagnetic spectrum, from radio all the way up to ultraviolet. There are three time periods we see in the pulsations. Two are the orbital period of the system (3.5 hours) and the rotation period of the white dwarf (2 minutes, which is much faster than a white dwarf normally spins). The third period we see, which is also around 2 minutes long, is a so-called ‘beat’ period that comes from interference between the orbital and rotation periods. The beat period implies some interaction between the white dwarf itself and the main sequence star, such as pulses from the white dwarf reflecting from the other star’s surface. Strangely, this beat period is the most pronounced period in the data. If it is indeed a reflection effect, we see more of the reflected light than we see light from the white dwarf itself, a state of affairs which is hard to explain.

    3
    Figure 2: The pulsations of AR Sco. These data cover approximately 30 minutes, which is 15% of a full orbital cycle. This is Figure 1 from today’s paper.

    Polarisation

    4
    Figure 3: Percentage of photons which were polarised. The spikes in polarisation line up well with the pulsations in the previous figure. This is Figure 3 from today’s paper.

    Today’s paper presents a new set of data on this system. For the first time, the polarisation of radiation from the system has been measured. Polarisation is the amount by which light is aligned; if you think of light as a collection of waves, polarised light would would have the peaks of each set of waves pointed in the same direction, while unpolarised light would have them pointed in random directions.

    The team behind today’s paper measured how polarised the light was from AR Sco, and found interesting results. Between pulses, the light is only around 5% polarised (meaning that around 5% of photons are polarised). During each pulse, however, they saw the polarisation rise to more like 30%. Take a look at Figure 3 to see for yourself. Clearly, the process causing the pulsations must be able to produce polarised light. The most likely candidate is synchrotron radiation, the process that powers pulsars.

    The Nature of AR Sco

    So where does that leave us? The white dwarf in AR Sco must have formed with an unusually strong magnetic field, up to 500 mega-Gauss (this is around 10 times as strong as an MRI machine, or 10,000 times as strong as a fridge magnet). Its rotation was then sped up to the short rotation period we now see. In neutron star pulsars this ‘spin-up’ occurs during the formation of the neutron star: as the star collapses from a puffy giant star core to a dense neutron star, conservation of angular momentum forces it to spin faster. In AR Sco, because the white dwarf is not as dense as a neutron star, the same explanation won’t cover the extremely fast rotation that we see. It is suggested that the spin-up may instead have involved mass transfer between the two stars in AR Sco. However it happened, we were left with a dense, fast-spinning, highly-magnetic object emitting two beams of synchrotron radiation. There are still questions to be answered, but for now it seems likely that AR Sco is the first white dwarf pulsar!

    Merry Christmas!

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    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 8:29 am on November 30, 2016 Permalink | Reply
    Tags: , , ESO FORS2 VLT, , First Signs of Weird Quantum Property of Empty Space?, Neutron stars, RX J1856.5-3754   

    From ESO: “First Signs of Weird Quantum Property of Empty Space?” 

    ESO 50 Large

    European Southern Observatory

    30 November 2016
    Contacts

    Roberto Mignani
    INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica Milano
    Milan, Italy
    Tel: +39 02 23699 347
    Cell: +39 328 9685465
    Email: mignani@iasf-milano.inaf.it

    Vincenzo Testa
    INAF – Osservatorio Astronomico di Roma
    Monteporzio Catone, Italy
    Tel: +39 06 9428 6482
    Email: vincenzo.testa@inaf.it

    Roberto Turolla
    University of Padova
    Padova, Italy
    Tel: +39-049-8277139
    Email: turolla@pd.infn.it

    Richard Hook
    ESO Public Information Officer
    Garching bei München, Germany
    Tel: +49 89 3200 6655
    Cell: +49 151 1537 3591
    Email: rhook@eso.org

    VLT observations of neutron star may confirm 80-year-old prediction about the vacuum


    Access mp4 video here .

    1
    By studying the light emitted from an extraordinarily dense and strongly magnetised neutron star using ESO’s Very Large Telescope, astronomers may have found the first observational indications of a strange quantum effect, first predicted in the 1930s. The polarisation of the observed light suggests that the empty space around the neutron star is subject to a quantum effect known as vacuum birefringence.

    A team led by Roberto Mignani from INAF Milan (Italy) and from the University of Zielona Gora (Poland), used ESO’s Very Large Telescope (VLT) at the Paranal Observatory in Chile to observe the neutron star RX J1856.5-3754, about 400 light-years from Earth [1].

    4
    This wide field image shows the sky around the very faint neutron star RX J1856.5-3754 in the southern constellation of Corona Australis. This part of the sky also contains interesting regions of dark and bright nebulosity surrounding the variable star R Coronae Australis (upper left), as well as the globular star cluster NGC 6723. The neutron star itself is too faint to be seen here, but lies very close to the centre of the image. Credit: ESO/Digitized Sky Survey 2. Acknowledgement: Davide De Martin

    5
    Colour composite photo of the sky field around the lonely neutron star RX J1856.5-3754 and the related cone-shaped nebula. It is based on a series of exposures obtained with the multi-mode FORS2 instrument at VLT KUEYEN through three different optical filters.

    ESO FORS2 VLT
    ESO FORS2 VLT

    The trail of an asteroid is seen in the field with intermittent blue, green and red colours. RX J1856.5-3754 is exactly in the centre of the image. Credit: ESO

    Despite being amongst the closest neutron stars, its extreme dimness meant the astronomers could only observe the star with visible light using the FORS2 instrument on the VLT, at the limits of current telescope technology.

    Neutron stars are the very dense remnant cores of massive stars — at least 10 times more massive than our Sun — that have exploded as supernovae at the ends of their lives. They also have extreme magnetic fields, billions of times stronger than that of the Sun, that permeate their outer surface and surroundings.

    These fields are so strong that they even affect the properties of the empty space around the star. Normally a vacuum is thought of as completely empty, and light can travel through it without being changed. But in quantum electrodynamics (QED), the quantum theory describing the interaction between photons and charged particles such as electrons, space is full of virtual particles that appear and vanish all the time. Very strong magnetic fields can modify this space so that it affects the polarisation of light passing through it.

    Mignani explains: “According to QED, a highly magnetised vacuum behaves as a prism for the propagation of light, an effect known as vacuum birefringence.”

    Among the many predictions of QED, however, vacuum birefringence so far lacked a direct experimental demonstration. Attempts to detect it in the laboratory have not yet succeeded in the 80 years since it was predicted in a paper by Werner Heisenberg (of uncertainty principle fame) and Hans Heinrich Euler.

    “This effect can be detected only in the presence of enormously strong magnetic fields, such as those around neutron stars. This shows, once more, that neutron stars are invaluable laboratories in which to study the fundamental laws of nature.” says Roberto Turolla (University of Padua, Italy).

    After careful analysis of the VLT data, Mignani and his team detected linear polarisation — at a significant degree of around 16% — that they say is likely due to the boosting effect of vacuum birefringence occurring in the area of empty space surrounding RX J1856.5-3754 [2].

    Vincenzo Testa (INAF, Rome, Italy) comments: “This is the faintest object for which polarisation has ever been measured. It required one of the largest and most efficient telescopes in the world, the VLT, and accurate data analysis techniques to enhance the signal from such a faint star.”

    “The high linear polarisation that we measured with the VLT can’t be easily explained by our models unless the vacuum birefringence effects predicted by QED are included,” adds Mignani.

    “This VLT study is the very first observational support for predictions of these kinds of QED effects arising in extremely strong magnetic fields,” remarks Silvia Zane (UCL/MSSL, UK).

    Mignani is excited about further improvements to this area of study that could come about with more advanced telescopes: “Polarisation measurements with the next generation of telescopes, such as ESO’s European Extremely Large Telescope, could play a crucial role in testing QED predictions of vacuum birefringence effects around many more neutron stars.”

    ESO/E-ELT,to be on top of Cerro Armazones in the Atacama Desert of northern Chile
    ESO/E-ELT,to be on top of Cerro Armazones in the Atacama Desert of northern Chile

    “This measurement, made for the first time now in visible light, also paves the way to similar measurements to be carried out at X-ray wavelengths,” adds Kinwah Wu (UCL/MSSL, UK).

    Notes

    [1] This object is part of the group of neutron stars known as the Magnificent Seven. They are known as isolated neutron stars (INS), which have no stellar companions, do not emit radio waves (like pulsars), and are not surrounded by progenitor supernova material.

    [2] There are other processes that can polarise starlight as it travels through space. The team carefully reviewed other possibilities — for example polarisation created by scattering off dust grains — but consider it unlikely that they produced the polarisation signal observed.

    More information

    This research was presented in the paper entitled Evidence for vacuum birefringence from the first optical polarimetry measurement of the isolated neutron star RX J1856.5−3754, by R. Mignani et al., to appear in Monthly Notices of the Royal Astronomical Society.

    The team is composed of R.P. Mignani (INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica Milano, Milano, Italy; Janusz Gil Institute of Astronomy, University of Zielona Góra, Zielona Góra, Poland), V. Testa (INAF – Osservatorio Astronomico di Roma, Monteporzio, Italy), D. González Caniulef (Mullard Space Science Laboratory, University College London, UK), R. Taverna (Dipartimento di Fisica e Astronomia, Università di Padova, Padova, Italy), R. Turolla (Dipartimento di Fisica e Astronomia, Università di Padova, Padova, Italy; Mullard Space Science Laboratory, University College London, UK), S. Zane (Mullard Space Science Laboratory, University College London, UK) and K. Wu (Mullard Space Science Laboratory, University College London, UK).

    See the full article here .

    Please help promote STEM in your local schools.
    STEM Icon

    Stem Education Coalition
    Visit ESO in Social Media-

    Facebook

    Twitter

    YouTube

    ESO Bloc Icon

    ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

    ESO LaSilla
    LaSilla

    ESO VLT
    VLT

    ESO Vista Telescope
    VISTA

    ESO NTT
    NTT

    ESO VLT Survey telescope
    VLT Survey Telescope

    ALMA Array
    ALMA

    ESO E-ELT
    E-ELT

    ESO APEX
    Atacama Pathfinder Experiment (APEX) Telescope

     
  • richardmitnick 9:48 am on November 6, 2016 Permalink | Reply
    Tags: , , , , Neutron stars, ,   

    From CfA: “Pulsar Wind Nebulae” 

    Harvard Smithsonian Center for Astrophysics


    Center For Astrophysics

    November 4, 2016

    Neutron stars are the detritus of supernova explosions, with masses between one and several suns and diameters only tens of kilometers across. A pulsar is a spinning neutron star with a strong magnetic field; charged particles in the field radiate in a lighthouse-like beam that can sweep past the Earth with extreme regularity every few seconds or less. A pulsar also has a wind, and charged particles, sometimes accelerated to near the speed of light, form a nebula around the pulsar: a pulsar wind nebula. The particles’ high energies make them strong X-ray emitters, and the nebulae can be seen and studied with X-ray observatories. The most famous example of a pulsar wind nebula is the beautiful and dramatic Crab Nebula.

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

    When a pulsar moves through the interstellar medium, the nebula can develop a bow-shaped shock. Most of the wind particles are confined to a direction opposite to that of the pulsar’s motion and form a tail of nebulosity. Recent X-ray and radio observations of fast-moving pulsars confirm the existence of the bright, extended tails as well as compact nebulosity near the pulsars. The length of an X-ray tail can significantly exceed the size of the compact nebula, extending several light-years or more behind the pulsar.

    CfA astronomer Patrick Slane was a member of a team that used the Chandra X-ray Observatory to study the nebula around the pulsar PSR B0355+54, located about 3400 light-years away.

    NASA/Chandra Telescope
    NASA/Chandra Telescope

    The pulsar’s observed movement over the sky (its proper motion) is measured to be about sixty kilometer per second. Earlier observations by Chandra had determined that the pulsar’s nebula had a long tail, extending over at least seven light-years (it might be somewhat longer, but the field of the detector was limited to this size); it also has a bright compact core. The scientists used deep Chandra observations to examine the nebula’s faint emission structures, and found that the shape of the nebula, when compared to the direction of the pulsar’s motion through the medium, suggests that the spin axis of the pulsar is pointed nearly directly towards us. They also estimate many of the basic parameters of the nebula including the strength of its magnetic field, which is lower than expected (or else turbulence is re-accelerating the particles and modifying the field). Other conclusions include properties of the compact core and details of the physical mechanisms powering the X-ray and radio radiation.
    Reference(s):

    Deep Chandra Observations of the Pulsar Wind Nebula Created by PSR B0355+54</emKlingler, Noel; Rangelov, Blagoy; Kargaltsev, Oleg; Pavlov, George G.; Romani, Roger W.; Posselt, Bettina; Slane, Patrick; Temim, Tea; Ng, C.-Y.; Bucciantini, Niccolò; Bykov, Andrei; Swartz, Douglas A.; Buehler, Rolf, ApJ 2016 (in press).

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

     
  • richardmitnick 10:15 am on June 22, 2016 Permalink | Reply
    Tags: , , , , , Neutron stars,   

    From Goddard: “Astronomers Find the First ‘Wind Nebula’ Around a Magnetar” 

    NASA Goddard Banner
    NASA Goddard Space Flight Center

    June 21, 2016
    Francis Reddy
    francis.j.reddy@nasa.gov
    NASA’s Goddard Space Flight Center, Greenbelt, Maryland

    Astronomers have discovered a vast cloud of high-energy particles called a wind nebula around a rare ultra-magnetic neutron star, or magnetar, for the first time. The find offers a unique window into the properties, environment and outburst history of magnetars, which are the strongest magnets in the universe.

    1
    This X-ray image shows extended emission around a source known as Swift J1834.9-0846, a rare ultra-magnetic neutron star called a magnetar. The glow arises from a cloud of fast-moving particles produced by the neutron star and corralled around it. Color indicates X-ray energies, with 2,000-3,000 electron volts (eV) in red, 3,000-4,500 eV in green, and 5,000 to 10,000 eV in blue. The image combines observations by the European Space Agency’s XMM-Newton spacecraft taken on March 16 and Oct. 16, 2014. Credits: ESA/XMM-Newton/Younes et al. 2016

    ESA/XMM Newton
    ESA/XMM Newton

    A neutron star is the crushed core of a massive star that ran out of fuel, collapsed under its own weight, and exploded as a supernova. Each one compresses the equivalent mass of half a million Earths into a ball just 12 miles (20 kilometers) across, or about the length of New York’s Manhattan Island. Neutron stars are most commonly found as pulsars, which produce radio, visible light, X-rays and gamma rays at various locations in their surrounding magnetic fields. When a pulsar spins these regions in our direction, astronomers detect pulses of emission, hence the name.

    2
    This illustration compares the size of a neutron star to Manhattan Island in New York, which is about 13 miles long. A neutron star is the crushed core left behind when a massive star explodes as a supernova and is the densest object astronomers can directly observe. Credits: NASA’s Goddard Space Flight Center

    Typical pulsar magnetic fields can be 100 billion to 10 trillion times stronger than Earth’s. Magnetar fields reach strengths a thousand times stronger still, and scientists don’t know the details of how they are created. Of about 2,600 neutron stars known, to date only 29 are classified as magnetars.

    The newfound nebula surrounds a magnetar known as Swift J1834.9-0846 — J1834.9 for short — which was discovered by NASA’s Swift satellite on Aug. 7, 2011, during a brief X-ray outburst.

    NASA/SWIFT Telescope
    NASA/SWIFT Telescope

    Astronomers suspect the object is associated with the W41 supernova remnant, located about 13,000 light-years away in the constellation Scutum toward the central part of our galaxy.

    “Right now, we don’t know how J1834.9 developed and continues to maintain a wind nebula, which until now was a structure only seen around young pulsars,” said lead researcher George Younes, a postdoctoral researcher at George Washington University in Washington. “If the process here is similar, then about 10 percent of the magnetar’s rotational energy loss is powering the nebula’s glow, which would be the highest efficiency ever measured in such a system.”

    A month after the Swift discovery, a team led by Younes took another look at J1834.9 using the European Space Agency’s (ESA) XMM-Newton X-ray observatory, which revealed an unusual lopsided glow about 15 light-years across centered on the magnetar. New XMM-Newton observations in March and October 2014, coupled with archival data from XMM-Newton and Swift, confirm this extended glow as the first wind nebula ever identified around a magnetar. A paper describing the analysis will be published by The Astrophysical Journal.

    “For me the most interesting question is, why is this the only magnetar with a nebula? Once we know the answer, we might be able to understand what makes a magnetar and what makes an ordinary pulsar,” said co-author Chryssa Kouveliotou, a professor in the Department of Physics at George Washington University’s Columbian College of Arts and Sciences.

    The most famous wind nebula, powered by a pulsar less than a thousand years old, lies at the heart of the Crab Nebula supernova remnant in the constellation Taurus. Young pulsars like this one rotate rapidly, often dozens of times a second. The pulsar’s fast rotation and strong magnetic field work together to accelerate electrons and other particles to very high energies. This creates an outflow astronomers call a pulsar wind that serves as the source of particles making up in a wind nebula.

    Supernova remnant Crab nebula. NASA/ESA Hubble
    The best-known wind nebula is the Crab Nebula, located about 6,500 light-years away in the constellation Taurus. At the center is a rapidly spinning neutron star that accelerates charged particles like electrons to nearly the speed of light. As they whirl around magnetic field lines, the particles emit a bluish glow. This image is a composite of Hubble observations taken in late 1999 and early 2000. The Crab Nebula spans about 11 light-years. Credits: NASA, ESA, J. Hester and A. Loll (Arizona State University)

    “Making a wind nebula requires large particle fluxes, as well as some way to bottle up the outflow so it doesn’t just stream into space,” said co-author Alice Harding, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “We think the expanding shell of the supernova remnant serves as the bottle, confining the outflow for a few thousand years. When the shell has expanded enough, it becomes too weak to hold back the particles, which then leak out and the nebula fades away.” This naturally explains why wind nebulae are not found among older pulsars, even those driving strong outflows.

    A pulsar taps into its rotational energy to produce light and accelerate its pulsar wind. By contrast, a magnetar outburst is powered by energy stored in the super-strong magnetic field. When the field suddenly reconfigures to a lower-energy state, this energy is suddenly released in an outburst of X-rays and gamma rays. So while magnetars may not produce the steady breeze of a typical pulsar wind, during outbursts they are capable of generating brief gales of accelerated particles.

    “The nebula around J1834.9 stores the magnetar’s energetic outflows over its whole active history, starting many thousands of years ago,” said team member Jonathan Granot, an associate professor in the Department of Natural Sciences at the Open University in Ra’anana, Israel. “It represents a unique opportunity to study the magnetar’s historical activity, opening a whole new playground for theorists like me.”

    ESA’s XMM-Newton satellite was launched on Dec. 10, 1999, from Kourou, French Guiana, and continues to make observations. NASA funded elements of the XMM-Newton instrument package and provides the NASA Guest Observer Facility at Goddard, which supports use of the observatory by U.S. astronomers.

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    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

    NASA/Goddard Campus

    NASA image

     
  • richardmitnick 7:38 am on May 21, 2016 Permalink | Reply
    Tags: , , Gold production, , Neutron stars,   

    From Kavli: “Galactic ‘Gold Mine’ Explains the Origin of Nature’s Heaviest Elements” 

    KavliFoundation

    The Kavli Foundation

    5.21.16
    Adam Hadhazy, Spring 2016

    Neutron star merger depicted Goddard
    Neutron star merger depicted. NASA/Goddard

    A unique galaxy loaded with hard-to-produce, heavy elements sheds light on stellar histories and galactic evolution.

    RESEARCHERS HAVE SOLVED a 60-year-old mystery regarding the origin of the heaviest elements in nature, conveyed in the faint starlight from a distant dwarf galaxy.

    Most of the chemical elements, composing everything from planets to paramecia, are forged by the nuclear furnaces in stars like the Sun. But the cosmic wellspring for a certain set of heavy, often valuable elements like gold, silver, lead and uranium, has long evaded scientists.

    Astronomers studying a galaxy called Reticulum II have just discovered that its stars contain whopping amounts of these metals—collectively known as “r-process” elements (See “What is the R-Process?”).

    Reticulum II galaxy. Dark Energy Survey, DECam, CTIO/Blanco Telescope, Cerro Tololo, Chile
    Reticulum II galaxy. Dark Energy Survey, DECam, CTIO/Blanco Telescope, Cerro Tololo, Chile

    Of the 10 dwarf galaxies that have been similarly studied so far, only Reticulum II bears such strong chemical signatures. The finding suggests some unusual event took place billions of years ago that created ample amounts of heavy elements and then strew them throughout the galaxy’s reservoir of gas and dust. This r-process-enriched material then went on to form Reticulum II’s standout stars.

    Based on the new study*, from a team of researchers at the Kavli Institute at the Massachusetts Institute of Technology, the unusual event in Reticulum II was likely the collision of two, ultra-dense objects called neutron stars. Scientists have hypothesized for decades that these collisions could serve as a primary source for r-process elements, yet the idea had lacked solid observational evidence. Now armed with this information, scientists can further hope to retrace the histories of galaxies based on the contents of their stars, in effect conducting “stellar archeology.”

    The Kavli Foundation recently spoke with three astrophysicists about how this discovery can unlock clues about galactic evolution as well as the abundances of certain elements on Earth we use for everything from jewelry-making to nuclear power generation. The participants were:

    3
    Alexander Ji – is a graduate student in physics at the Massachusetts Institute of Technology (MIT) and a member of the MIT Kavli Institute for Astrophysics and Space Research (MKI). He is lead author of a paper in Nature describing this discovery.

    4
    Anna Frebel – is the Silverman Family Career Development Assistant Professor in the Department of Physics at MIT and also a member of MKI. Frebel is Ji’s advisor and coauthored the Nature paper. Her work delves into the chemical and physical conditions of the early universe as conveyed by the oldest stars.

    5
    Enrico Ramirez-Ruiz – is a Professor of Astronomy and Astrophysics at the University of California, Santa Cruz. His research explores violent events in the universe, including the mergers of neutron stars and their role in generating r-process elements.

    The following is an edited transcript of their roundtable discussion. The participants have been provided the opportunity to amend or edit their remarks.

    THE KAVLI FOUNDATION: What was your reaction to discovering an abundance of heavy elements in the stars in the galaxy called Reticulum II?

    ALEX JI: I had spent some time looking at stars in other galaxies like this, and in every one of those, the content of this type of element – which we call r-process elements – was very low. So we went into this whole project thinking we would get very low detections as well with this galaxy. When we read off the r-process content of that first star in our telescope, it just looked wrong, like it could not have come out of this galaxy! I spent a long time making sure the telescope was pointed at the right star. Then I called Anna—actually, I had to wake her up, it was 3 A.M.—and we started doing instrument checks to make sure we were looking at the right thing. It turns out we were.

    ANNA FREBEL: It was quite funny, because usually when I get a call in the middle of the night from someone at the telescope, it means something really bad has happened! [Laughter] In this case, we were all super-excited because Alex had found something in the data that was really unexpected and also was a smoking gun. We pretty quickly confirmed that at least that first star he was looking at really had all these heavy elements in rather large quantities.

    Then another star showed the same kind of signature. I was like, “Oh my god—we’ve hit the lottery . . . twice!” We would have been happy walking away with just one awesome star, and then it turned into two, then into three, and four, five and so forth. The universe had thrown us a really big bone!

    ENRICO RAMIREZ-RUIZ: I’ve been working on neutron star mergers for a while, so I was extremely excited to see Alex and Anna’s results. Their study is indeed a smoking gun that exotic neutron star mergers were occurring very early in the history of this particular dwarf galaxy, and for that matter likely in many other small galaxies. Neutron star mergers are therefore probably responsible for the bulk of the precious substances we call r-process elements throughout the universe.

    _________________________________________________________________________________________________

    3
    An artist’s conception of a supernova forging heavy elements. Credit: Supernova illustration: Akihiro Ikeshita/Particle CG: Naotsugu Mikami (NAOJ)

    What Is the R-Process?

    The r-process stands for “rapid neutron-capture process.” This phenomenon, first theoretically described by nuclear physicists in 1957, creates elements in nature that are heavier than iron. In the supernova explosions of massive stars and in neutron star collisions, tremendous numbers of freely moving neutrons bind with iron atoms. As more and more neutrons pile up in the atom’s nucleus, the neutrons undergo a radioactive decay, turning into protons. Accordingly, new, heavier elements are formed, because elements are differentiated by the number of protons in their nucleus. As its name implies, this process must occur rapidly in order to build up to very heavy, neutron-rich nuclei that then decay into heavy elements, such as uranium, which has 92 protons compared to iron’s 26. While a theoretical understanding of the r-process is sound, scientists have debated over the astrophysical conditions and sites where the process can actually occur.

    _________________________________________________________________________________________________

    TKF: Why has the provenance of these elements been such a tough nut to crack?

    FREBEL: The question of the cosmic origin of all of the elements has been a longstanding problem. The precursor question was, “Why do stars shine?” Scientists tackled that in the early part of the last century and solved the mystery only around 1950. We found out that stars do nuclear fusion in their cores, generating heat and light, and as part of that process, heavier elements are created. That led to a phase where a lot of people worked on figuring out how all the elements are made.

    Understanding how heavy, r-process elements, are formed is one of hardest problems in nuclear physics. The production of these really heavy elements takes so much energy that it’s nearly impossible to make them experimentally, even with current particle accelerators and apparatuses. The process for making them just doesn’t work on Earth. So we have had to use the stars and the objects in the cosmos as our lab.

    JI: As Anna just mentioned, we have been mostly stuck with astronomy, trying to measure what could have made all of these elements out in the stars. But it’s also very difficult to find stars that give you any information about the r-process.

    RAMIREZ-RUIZ: Right, it is very difficult to see these elements shine when they’re created in the universe because they are very rare. For example, gold is only one part in a billion in the Sun. So even though the necessary physical conditions needed to make these elements were clear to physicists more than 50 years ago, it was a mystery as to what sort of objects and astrophysics would provide these conditions, because we couldn’t see r-process elements being produced in explosion remnants in our own galaxy.

    Two competing theories did emerge, which are that these elements are produced by supernovae and neutron star mergers. These phenomena are very different in terms of how often they should happen and in the amount of these elements they should theoretically produce. Just to give you an example, the explosion of a star with more than eight times the mass of the Sun is thought to produce about a Moon’s mass-worth of gold. A neutron star merger, however, is thought to produce a Jupiter’s mass-worth of gold. That’s over 25,000 times more! So just one neutron star merger can provide the gold we would expect to find in about six million to 10 million stars.

    Alex and Anna’s observations are so unbelievably useful because they really show that the phenomenon which created these elements is something rare, but that produces a lot of these elements, as a neutron star merger should.

    FREBEL: It took 60-something years of work to figure this out, and a variety of astronomers—observers as well as theorists—have all put in their share. That’s exactly what we and Enrico are continuing to do.

    TKF: Enrico, you study the ionized gas called plasma that composes stars. How is the material in neutron stars different than the plasma in run-of-the-mill stars like the Sun, and how does this provide the raw ingredients for making r-process elements?

    RAMIREZ-RUIZ: Neutron stars are only about the size of San Francisco Bay, which I live close by, yet they pack in as much mass as the Sun—about 330,000 times the mass of the Earth. Neutron stars are the densest objects in the universe. A neutron star the size of a Starbucks cup would weigh as much as Mount Everest! We call them neutron stars because they are neutron-rich, and that’s a key aspect for making r-process elements, as I’ll let Alex and Anna explain.

    JI: So the nuclear fusion in stars can only make the elements up to iron. That’s because iron is the most stable nucleus. If you try to fuse two things to make elements heavier than iron, it actually takes more energy than the fusion reaction itself releases. A neutron that gets close enough to this dense iron nucleus can join it thanks to one of the fundamental forces of nature, the strong force, which binds protons and neutrons together.

    You can keep increasing the size of this nucleus by adding more neutrons, but there’s a trade-off. That nucleus will undergo a radioactive decay called a beta decay. Specifically, one of those added neutrons will spontaneously release some energy and turn into a proton. The r-process is what happens when you capture neutrons faster than the beta decays happen, and in that way you can build up to heavier nuclei.

    FREBEL: This process can only happen when you have lots and lots of free neutrons outside of an atomic nucleus, and that’s actually a difficult thing to do, because neutrons only survive for about 15 minutes before they decay into a proton. In other words, almost as soon as you have free neutrons, they just disappear. So it’s really hard to find places where there are even free neutrons to undergo this neutron capture. As far back as the 1930s, neutron stars had been postulated as something that could exist, and it wasn’t until the late 1960s that we knew they were real.

    RAMIREZ-RUIZ: As we learned more about neutron stars, we found out that about two percent of them have companion stars, and a very small fraction have another neutron star orbiting around them. If the neutron stars are close enough, they will merge within several billion years or less because they produce gravitational waves as they spin around each other. These waves simply carry off energy and angular momentum, so the stars get closer and closer, and eventually they touch each other.

    TKF: What happens to these heavy elements once two neutron stars collide?

    RAMIREZ-RUIZ: As these neutron stars come together, the stars eject some material in their tidal tails into space at very close to the speed of light. So the atoms of these elements are moving very fast when they are first formed. By the time the ambient gas and dust in the galaxy is able to slow these elements down, they have probably mixed with about a thousand Sun-masses worth of material, enriching it atom-by-atom.

    FREBEL: Everything gets nicely mixed, like dough. And from that mixed material, the next generation of stars then forms. This stellar generation contains many, little, low-mass stars that have very long life times. It’s these low-mass, long-lived stars that we observed today in Reticulum II for this study.

    TKF: Anna, you published a book last year called “Searching for the Oldest Stars: Ancient Relics from the Early Universe.” How do these results demonstrate what you call “stellar archeology?”

    8

    FREBEL: Finding these elements at Reticulum II thoroughly illustrates the concept of stellar archaeology. The idea is that we can use the composition of individual stars to trace the processes that created the elements in the early universe. Because the elements that we observe in our stars today were made prior to the stars’ birth—the stars inherited these heavy elements like “cosmic genes”—we have this incredible opportunity to look back in time to study the early chemical and physical processes that ushered in stars and galaxy formation soon after the Big Bang.

    Reticulum II is actually a perfect example of what we now call dwarf galaxy archaeology. It’s pretty much the same thing I just described, but now we are able to add other dimensions by not just using individual stars, but the entire dwarf galaxy and all the information that comes with it. We can use galactic environmental conditions and the star formation history to trace what happened very early on in that galaxy that provided the various elements we see today.

    It’s very nice that despite all the progress we have made in this field, there is more to come. I really think these findings have opened a new door for studying galaxy formation with individual stars and to some extent individual elements. We are seriously connecting the really small scales of stars with the really big scales of galaxies. I’m very excited to see what else we find. I don’t think we’ll find another galaxy like Reticulum II anytime soon, but hey, we’re going to keep looking!

    JI: The way I like to think about this is, imagine if you were an actual archaeologist and you wandered around on the surface of the Earth picking up artifacts whenever you found them. You’d find a collection of random artifacts from different periods and places, and you wouldn’t be sure how to associate them. In contrast, looking at galaxies like Reticulum II is like digging into a coherent, subterranean layer and finding a collection of artifacts that are all telling the same story . . .

    FREBEL: Like Pompeii!

    JI: Yeah, like Pompeii!

    TKF: Ah yes, the Roman town, and its residents, who were completely buried under volcanic ash. That was not a very nice outcome . . .

    FREBEL: Not for the people, no.

    RAMIREZ-RUIZ: But the archeological evidence did remain pristine .

    TKF: Bad for Pompeians, but good for archeologists. Shifting gears here, what tools do you need to dig even deeper, if you will, into how elements like gold and silver originate, and otherwise find more cosmic archeological clues?

    JI: There are two types of things that we need. First, we have to find dwarf galaxies and that requires very large sky surveys like the Dark Energy Survey—which discovered Reticulum II—as well as surveys conducted by the Large Synoptic Survey Telescope, which will start operations in the 2020s.

    LSST/Camera, built at SLAC
    LSST Interior
    LSST telescope, currently under construction at Cerro Pachón Chile
    LSST/Camera, built at SLAC; LSST telescope, currently under construction at Cerro Pachón Chile

    The second thing is we have to look at the stars in those galaxies. The problem with galaxies is that they are far away, so we need pretty large telescopes to do that.

    FREBEL: The stars that Alex has been observing are actually really, really faint. We had to work very hard to squeeze out whatever information we could about them. It was only because these stars had such a strong signal of r-process elements that we could see those signals in their light, very little of which we’re actually able to capture with current telescopes.

    So that really shows why we need larger telescopes. Multiple telescope projects are underway and are scheduled to open in the 2020s. They will have mirrors more than twice as big as today’s best ground-based telescopes. These include the Giant Magellan Telescope, the Thirty Meter Telescope and the European Extremely Large Telescope.

    Giant Magellan Telescope,  Las Campanas Observatory, some 115 km (71 mi) north-northeast of La Serena, Chile
    Giant Magellan Telescope, Las Campanas Observatory, some 115 km (71 mi) north-northeast of La Serena, Chile

    TMT-Thirty Meter Telescope, proposed for Mauna Kea, Hawaii, USA
    TMT-Thirty Meter Telescope, proposed for Mauna Kea, Hawaii, USA

    ESO/E-ELT,to be on top of Cerro Armazones in the Atacama Desert of northern Chile
    ESO/E-ELT,to be on top of Cerro Armazones in the Atacama Desert of northern Chile

    They promise more light per unit of time hour, which means we can observe fainter stars, but we can also go back to brighter stars and get insanely high quality data. That is what we need for these r-process stars because there is so much information in their light. I think the next five to 10 years will be very exciting in this regard.

    RAMIREZ-RUIZ: I want to make a plug for the Laser Interferometer Gravitational-Wave Observatory, or LIGO.

    Caltech/MIT Advanced aLigo detector in Livingston, Louisiana
    Caltech/MIT Advanced aLigo detector in Livingston, Louisiana

    The ultimate dream of mine would be to detect the gravitational wave signal of a neutron-neutron star merger.

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib
    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    When we have multiple gravitational wave observatories in operation, such as when LIGO India is built next decade, we will be able to pinpoint the location of these rare events. We can then use our conventional, light-based telescopes to look at the transient light signals from the merged neutron star, which we actually think will be powered by the decay of these precious elements. That would be the ultimate direct evidence that these mergers are indeed producing all of these elements.

    FREBEL: Pinpointing the location of neutron star mergers might become possible for events in the nearby universe. But I don’t think we’ll go back far enough in space, and therefore time, to see a merger like in Reticulum II that went off billions of years ago. I agree with Enrico, though, it would be really great to have a nearby example that shows us, right in front of our eyes, how this really all works.

    RAMIREZ-RUIZ: Anna’s absolutely right. We won’t see the r-process enrichment events that took place at the time when a galaxy like Reticulum II was being formed, but hopefully we’ll see the newly synthesized gold closer to home! [Laughter]

    TKF: Let’s take a moment to consider that most of the gold, silver and platinum in our valuable jewelry, as well as the uranium in our nuclear reactors, was created when mind- bogglingly dense neutron stars crushed into each other at incredible speeds. As you’re doing your research, does this sort of notion ever stop you in your tracks?

    JI: It does stop you in your tracks, right? Definitely one of the things that I think attracts people to astronomy is understanding the origin of everything around us. The other part of it for me is these neutron stars mergers are happening on really small scales, but these events are explosive enough to affect a whole galaxy! Imagining that event, then zooming out to the whole galactic scale, then zooming back down to us on Earth—I think it’s pretty cool to be able to follow the consequences of the production of these elements from beginning to end.

    RAMIREZ-RUIZ: Something to think about is that all the gold originally here on Earth sank into the planet’s center because the early Earth was molten. So all the gold we have today on or near the surface is from asteroid impacts!

    FREBEL: As we’ve been saying, the gold wasn’t made in the asteroids, it was probably made in a neutron star merger. It then mixed into the cloud of gas and dust in which all the asteroids and planets formed. That gold was then transported to us on Earth as a special delivery. [Laughter]

    RAMIREZ-RUIZ: We have some gold atoms in our bodies, too. If we were to “talk” to one of these atoms, it would tell us a story how it was formed in billions of degrees, how it flew through space. Because just one of these neutron star mergers produced so much gold, probably all of the gold atoms that are in the four of us in this roundtable discussion came from the same event. So we’re not only linked by genetics, but by these exotic phenomena that happen in the universe.

    *Science paper:
    R-process enrichment from a single event in an ancient dwarf galaxy

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition
    The Kavli Foundation, based in Oxnard, California, is dedicated to the goals of advancing science for the benefit of humanity and promoting increased public understanding and support for scientists and their work.

    The Foundation’s mission is implemented through an international program of research institutes, professorships, and symposia in the fields of astrophysics, nanoscience, neuroscience, and theoretical physics as well as prizes in the fields of astrophysics, nanoscience, and neuroscience.

     
  • richardmitnick 7:02 pm on January 3, 2016 Permalink | Reply
    Tags: , , , Neutron stars   

    From Nautilus: “The Inside of a Neutron Star Looks Spookily Familiar” 

    Nautilus

    Nautilus

    December 17, 2015
    Matthew R. Francis
    Illustration by Magoz

    Temp 1

    Hot fluids of neutrons that flow without friction, superconductors made of protons, and a solid crust built of exotic atoms—features like these make neutron stars some of the strangest objects we’ve found in the cosmos so far. They pack all the mass of a star into a sphere the size of a city, resulting in states of matter we just don’t have on Earth.

    And yet, despite their extreme weirdness, neutron stars contain a mishmash of vaguely familiar features, as if seen darkly through a funhouse mirror. One of the weirdest is the fact that deep inside a neutron star you can find a whole menu full of (nuclear) pasta.

    The pasta is made of protons and neutrons, held together by the extreme pressures. These oddball nuclei arrange themselves into weird configurations that Matt Caplan of Indiana University and his colleagues call “nuclear pasta.” (1) The pasta layer lies in the inner crust, a transitional zone between a neutron star’s outer crust and core. In the top of this layer, the nuclei form blobs called “gnocchi.” Deeper down, they join together into cylindrical shapes called “spaghetti.” More pressure, and the spaghetti compresses into “lasagna”: flattish sheets of nuclear matter. Then the pasta transitions into “anti-pasta”: The sheets of lasagna form cylindrical hollows where neutrons begin leaking out, which Caplan calls “anti-spaghetti.” And finally, when the pressure is high enough, those hollows break into small bubbles, the “anti-gnocchi” phase.

    And yes, these are all terms used in papers published by Caplan and his team. One paper even makes reference to “nuclear waffles,” which are like lasagna with holes. (2)

    Temp 2
    Exotic pasta: Simulations of the shapes taken by nuclear matter inside stars shows a “pasta phase,” with forms resembling lasagna, spaghetti, and gnocchi.“Physical Review C.”*

    Weirder still is the resemblance of the nuclear pasta to structures formed by certain biological molecules. These molecules are lipid polymers, which are found in fats. Because they are made of a water-loving and water-repelling layer sandwiched together, their interactions with a watery environment make them self-assemble into the spaghetti- and lasagna-like structures known as Endoplasmic reticulum, found in complex (eukaryotic) cells.

    The similarity is striking, even though the systems couldn’t appear more different in most respects. Nuclear pasta is roughly 100 trillion times denser than the interior of a cell—that’s 1^14, or a 1 followed by 14 zeroes. The forces in a neutron star are strong electromagnetism and the nuclear forces; cells are governed by weaker molecular electric forces and the microscopic properties of water. Even the building blocks are different: The raw materials for nuclear pasta are protons and neutrons, while endoplasmic reticulum is made of long chains of molecules strung together.

    Caplan says, “What’s in common is that they want to minimize surface energy.” Think of a soap bubble or a splash of water aboard the International Space Station: They form roughly spherical shapes. That’s because the surface forces draw the molecules together into spheres, which involve the lowest amount of energy on the surface. The forces that create nuclear pasta and endoplasmic reticulum aren’t as symmetrical, thanks to the competing attractive and repulsive interactions between the lasagna layers and the surrounding material. However, the laws of physics are still at work and want to minimize the energy involved. The result is blobs and folded sheets and cavities in the neutron star crust or the watery interior of a cell. The forces and densities couldn’t be more different, yet the shapes that emerge are amazingly similar.

    Another eerie resemblance explains why scientists are so interested in nuclear pasta to begin with. The pasta layer is sandwiched between the neutron star’s hard outer crust and superfluid interior. Below the anti-gnocchi layer, nearly every proton merges with an electron to make neutrons, which marks the boundary where the inner crust ends. Below that is the neutron star core, which is a neutron superfluid: a liquid that flows without any resistance. (Researchers think there’s an inner core as well, but exactly how that works is a matter of some contention.) Sitting between the freely-flowing neutron fluid and the rigid iron outer crust, nuclear pasta is the interface between very different zones.

    This is just like the plastic-like mantle on Earth, which lies between the flowing molten outer core and the solid crust. Earth’s mantle is key to understanding earthquakes, and a neutron star’s pasta layer is essential for describing one of the most dramatic stress releases anywhere in the universe: the starquake.

    “If you have a very large magnitude earthquake, seismologists detect both the initial rupture of the crust and the seismic waves bouncing around inside the Earth,” says Anna Watts, a neutron star astronomer at the University of Amsterdam. Similarly, “starquakes become quite an interesting thing, because they effectively let you peer inside the [neutron] star by looking at the response of the star.” Just as earthquakes led researchers to discover the existence and nature of Earth’s core, starquakes vibrate through the entire neutron star interior. (3) What happens on the crust doesn’t stay there: A shattering of the solid crystal transmits vibrations through the pasta layer into the core, and in turn can feed back into how the crust behaves. But what we observe—indirectly—is the way the crust fractures and reforms. “When you look at a neutron star, what you see is the crust,” says Caplan. “You have to understand the crust, otherwise you don’t understand anything.”

    In fact, it’s when a neutron star is undergoing a starquake that it’s most visible from Earth. Neutron stars are too tiny to see directly, but a few have such intense magnetic fields that they are known as magnetars.

    Temp 4
    Artist’s conception of a magnetar, with magnetic field lines.

    These are likely among the youngest neutron stars, and their strong magnetic fields produce space weather similar to what we see from the sun during solar storms—though cranked up to 11. Magnetic fields don’t like to be packed tightly together, so they “recombine,” snapping together and releasing a huge amount of energy. The result is the fracturing of the magnetar’s crust, a huge starquake, and a burst of gamma rays.

    “The very bright initial flash of gamma rays tends to fry any satellite looking at it immediately,” says Watts—though a telescope doesn’t have to be looking right at a magnetar to see these bursts. Fortunately for satellites, but unfortunately for scientists, gamma ray flares like this are rare: Only three have happened since we’ve had the equipment to see them.

    But that’s what we see from the Earth: the gamma rays and other light from the neutron star. Using the magic combination of observation, theory, and computer simulations, we can trace the burst back to the starquake—and the pasta layer between the fractured crust and fluid core.

    Understanding nuclear pasta could help us understand not only what’s going on during crust-rupturing starquakes, but reveal some of the mysterious dynamics of the neutron star core. The core of a neutron star is a phenomenal dynamo, producing the most intense magnetic fields we know. These magnetic fields must be made by moving electric charges, but the precise nature of the dynamo is unknown. That’s because nearly everything about the neutron star core is inaccessible to experiments on Earth, thanks to the intense pressures involved. Researchers don’t have a clear theoretical picture connecting the pressure of the core substance to its density and temperature either, which would let us describe all sorts of useful things, like the neutron star size. The churning of material deep in the core is essential for comprehending the entire neutron star, and the pasta layer is the connection between that unknown and the observable properties.

    The neutron star is not the first example in nature of a similarity of form across vastly different scales and materials. Unusually persistent waves called solitons are seen in superconducting wires and across oceans, shockwave fronts happen across the light-year expanses of galaxies and in tiny bubbles of water, and vortices characterize everything from tornadoes to magnetic fields. The idea of persistent forms goes back at least to Plato’s Timaeus dialogue, where a demiurge, or divine craftsman, stamps shapes into the material world from eternal and unchanging models. Philosophers and scientists have uncovered a world where the strange echo of the neutron star is not just common, but expected.

    References

    1. Caplan, M.E., Schneider, A.S., Horowitz, C.J., & Berry, D.K. Pasta nucleosynthesis: Molecular dynamics simulations of nuclear statistical equilibrium. Physical Review C 91, 065802 (2015).

    2. Schneider, A.S., Berry, D.K., Briggs, C.M., Caplan, M.E., & Horowitz, C.J. Nuclear “waffles.” Physical Review C 90, 055805 (2014).

    3. Lander, S.K., Andersson, N., Antonopoulou, D., & Watts, A.L. Magnetically driven crustquakes in neutron stars. Monthly Notices of the Royal Astronomical Society 449, 2047-2058 (2015).

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Welcome to Nautilus. We are delighted you joined us. We are here to tell you about science and its endless connections to our lives. Each month we choose a single topic. And each Thursday we publish a new chapter on that topic online. Each issue combines the sciences, culture and philosophy into a single story told by the world’s leading thinkers and writers. We follow the story wherever it leads us. Read our essays, investigative reports, and blogs. Fiction, too. Take in our games, videos, and graphic stories. Stop in for a minute, or an hour. Nautilus lets science spill over its usual borders. We are science, connected.

     
  • richardmitnick 6:59 am on August 4, 2015 Permalink | Reply
    Tags: , , , Neutron stars, ,   

    From NRAO: “Neutron Stars Strike Back at Black Holes in Jet Contest” 

    NRAO Icon
    National Radio Astronomy Observatory

    NRAO Banner

    4 August 2015
    Dave Finley, Public Information Officer
    (575) 835-7302
    dfinley@nrao.edu

    1
    Artist’s impression of material flowing from a companion star onto a neutron star. The material forms an accretion disk around the neutron star and produces a superfast jet of ejected material. The material closest to the neutron star is so hot that it glows in X-rays, while the jet is most prominent at radio wavelengths. A similar mechanism is at work with black holes. CREDIT: Bill Saxton, NRAO/AUI/NSF.

    Some neutron stars may rival black holes in their ability to accelerate powerful jets of material to nearly the speed of light, astronomers using the Karl G. Jansky Very Large Array (VLA) have discovered.

    “It’s surprising, and it tells us that something we hadn’t previously suspected must be going on in some systems that include a neutron star and a more-normal companion star,” said Adam Deller, of ASTRON, the Netherlands Institute for Radio Astronomy.

    Black holes and neutron stars are respectively the densest and second most dense forms of matter known in the Universe. In binary systems where these extreme objects orbit with a more normal companion star, gas can flow from the companion to the compact object, producing spectacular displays when some of the material is blasted out in powerful jets at close to the speed of light

    Previously, black holes were the undisputed kings of forming powerful jets. Even when only nibbling on a small amount of material, the radio emission that traces the jet outflow from the black hole was relatively bright. In comparison, neutron stars seemed to make relatively puny jets — the radio emission from their jets was only bright enough to see when they were gobbling material from their companion at a very high rate. A neutron star sedately consuming material was therefore predicted to form only very weak jets, which would be too faint to observe.

    Recently, however, combined radio and X-ray observations of the neutron star PSR J1023+0038 completely contradicted this picture. PSR J1023+0038, which was discovered by ASTRON astronomer Anne Archibald in 2009, is the prototypical “transitional millisecond pulsar”– a neutron star which spends years at a time in a non-accreting state, only to “transition” occasionally into active accretion. When observed in 2013 and 2014, it was accreting only a trickle of material, and should have been producing only a feeble jet.

    “Unexpectedly, our radio observations with the Very Large Array showed relatively strong emission, indicating a jet that is nearly as strong as we would expect from a black hole system,” Deller said.

    NRAO VLA
    VLA

    Two other such “transitional” systems are now known, and both of these now have been shown to exhibit powerful jets that rival those of their black-hole counterparts. What makes these transitional systems special compared to their other neutron star brethren? For that, Deller and colleagues are planning additional observations of known and suspected transitional systems to refine theoretical models of the accretion process.

    Deller led a team of astronomers who reported their findings in the Astrophysical Journal.

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    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), the Robert C. Byrd Green Bank Telescope (GBT), and the Very Long Baseline Array (VLBA)*.

    ALMA Array

    NRAO ALMA

    NRAO GBT
    NRAO GBT

    NRAO VLA
    NRAO VLA

    The NRAO is building two new major research facilities in partnership with the international community that will soon open new scientific frontiers: the Atacama Large Millimeter/submillimeter Array (ALMA), and the Expanded Very Large Array (EVLA). Access to ALMA observing time by the North American astronomical community will be through the North American ALMA Science Center (NAASC).
    *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.

     
  • richardmitnick 10:08 am on November 28, 2014 Permalink | Reply
    Tags: , , , , Neutron stars,   

    From SPACE.com: “Ripples in Space-Time Could Reveal ‘Strange Stars” 

    space-dot-com logo

    SPACE.com

    November 28, 2014
    Charles Q. Choi

    By looking for ripples in the fabric of space-time, scientists could soon detect “strange stars” — objects made of stuff radically different from the particles that make up ordinary matter, researchers say.

    The protons and neutrons that make up the nuclei of atoms are made of more basic particles known as quarks. There are six types, or “flavors,” of quarks: up, down, top, bottom, charm and strange. Each proton or neutron is made of three quarks: Each proton is composed of two up quarks and one down quark, and each neutron is made of two down quarks and one up quark.

    In theory, matter can be made with other flavors of quarks as well. Since the 1970s, scientists have suggested that particles of “strange matter” known as strangelets — made of equal numbers of up, down and strange quarks — could exist. In principle, strange matter should be heavier and more stable than normal matter, and might even be capable of converting ordinary matter it comes in contact with into strange matter. However, lab experiments have not yet created any strange matter, so its existence remains uncertain.

    One place strange matter could naturally be created is inside neutron stars, the remnants of stars that died in catastrophic explosions known as supernovas. Neutron stars are typically small, with diameters of about 12 miles (19 kilometers) or so, but are so dense that they weigh as much as the sun. A chunk of a neutron star the size of a sugar cube can weigh as much as 100 million tons.

    Under the extraordinary force of this extreme weight, some of the up and down quarks that make up neutron stars could get converted into strange quarks, leading to strange stars made of strange matter, researchers say.

    A strange star that occasionally spurts out strange matter could quickly convert a neutron star orbiting it in a binary system into a strange star as well. Prior research suggests that a neutron star that receives a seed of strange matter from a companion strange star could transition to a strange star in just 1 millisecond to 1 second.

    Now, researchers suggest they could detect strange stars by looking for the stars’ gravitational waves — invisible ripples in space-time first proposed by Albert Einstein as part of his theory of general relativity.

    Gravitational waves are emitted by accelerating masses. Really big gravitational waves are emitted by really big masses, such as pairs of neutron stars merging with one another.

    i
    Scene from a NASA animation showing two neutron stars colliding.
    Credit: NASA’s Goddard Space Flight Center

    Pairs of strange stars should give off gravitational waves that are different from those emitted by pairs of “normal” neutron stars because strange stars should be more compact, researchers said. For instance, a neutron star with a mass one-fifth that of the sun should be more than 18 miles (30 km) in diameter, whereas a strange star of the same mass should be a maximum of 6 miles (10 km) wide.

    The researchers suggest that events involving strange stars could explain two short gamma-ray bursts — giant explosions lasting less than 2 seconds — seen in deep space in 2005 and 2007. The Laser Interferometer Gravitational-Wave Observatory (LIGO) did not detect gravitational waves from either of these events, dubbed GRB 051103 and GRB 070201.

    Neutron star mergers are the leading explanations for short gamma-ray bursts, but LIGO should, in principle, have detected gravitational waves from such mergers. However, if strange stars were involved in both of these events, LIGO would not have been able to detect any gravitational waves they emitted, researchers said. (The more compact a star is within a binary system of two stars, the higher the frequency of the gravitational waves it gives off.)

    Still, future research could detect strange-star events. Using the Advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO), whose first observing run is scheduled for 2015, the researchers expect to detect about 0.13 mergers per year of neutron stars with strange stars, or about one such merger every eight years. Using the Einstein Telescope currently being designed in the European Union, the scientists eventually expect to detect about 700 such events per year, or about two per day.

    There may also be a chance that scientists can re-examine LIGO data from GRB 051103 and GRB 070201 to look for signs of strange-star involvement.

    “The possibility of a re-analysis of LIGO signals for GRB 070201 and GRB 051103, taking into account some possible cases involving strange stars, is really exciting,” lead study author Pedro Moraes, an astrophysicist at Brazil’s National Institute for Space Research, told Space.com.

    Moraes and his colleague Oswaldo Miranda detailed their findings in the Nov. 21 issue of the journal Monthly Notices of the Royal Astronomical Society: Letters.

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

     
c
Compose new post
j
Next post/Next comment
k
Previous post/Previous comment
r
Reply
e
Edit
o
Show/Hide comments
t
Go to top
l
Go to login
h
Show/Hide help
shift + esc
Cancel