Milan, Italy

The Istituto Nazionale di Astrofisica , or INAF for short, is the most important Italian institution conducting scientific research in astronomy and astrophysics. Researches performed by the scientific staff of the Institute go from the study of the planets and minor bodies of the solar system up to researches of cosmological interest . Wikipedia.


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News Article | November 30, 2016
Site: www.eurekalert.org

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]. 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." "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). [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. 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). 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".


News Article | November 30, 2016
Site: spaceref.com

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. 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." IMAGE: This artist's view shows how the light coming from the surface of a strongly magnetic neutron star (left) becomes linearly polarized as it travels through the vacuum of space close to the star on its way to the observer on Earth (right). The polarization of the observed light in the extremely strong magnetic field suggests that the empty space around the neutron star is subject to a quantum effect known as vacuum birefringence, a prediction of quantum electrodynamics (QED). This effect was predicted in the 1930s but has not been observed before. The magnetic and electric field directions of the light rays are shown by the red and blue lines. Model simulations by Roberto Taverna (University of Padua, Italy) and Denis Gonzalez Caniulef (UCL/MSSL, UK) show how these align along a preferred direction as the light passes through the region around the neutron star. As they become aligned the light becomes polarized, and this polarization can be detected by sensitive instruments on Earth. 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." "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). [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. 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). 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". Please follow SpaceRef on Twitter and Like us on Facebook.


Mereghetti S.,Istituto di Astrofisica Spaziale e Fisica Cosmica
Advances in Space Research | Year: 2011

This paper reviews the multi-wavelength properties of two groups of pulsars, the Anomalous X-ray Pulsars (AXPs) and the Soft Gamma-ray Repeaters (SGRs), that are generally interpreted as isolated neutron stars with strong magnetic fields of 1014-1015 G. Most of these sources have now been observed at different wavelengths, from the radio band to hard X-rays. Several new members of these classes have been discovered in the last few years, due to their transient nature. The distinction between AXPs and SGRs is becoming less evident, as more observations are collected which show similar properties in all these sources. © 2010 COSPAR. Published by Elsevier Ltd. All rights reserved.


Maccone C.,Istituto di Astrofisica Spaziale e Fisica Cosmica
Acta Astronautica | Year: 2014

In a recent paper (Maccone, 2011 [15]) and in a recent book (Maccone, 2012 [17]), this author proposed a new mathematical model capable of merging SETI and Darwinian Evolution into a single mathematical scheme. This model is based on exponentials and lognormal probability distributions, called "b-lognormals" if they start at any positive time b ("birth") larger than zero. Indeed: Darwinian evolution theory may be regarded as a part of SETI theory in that the factor fl in the Drake equation represents the fraction of planets suitable for life on which life actually arose, as it happened on Earth.In 2008 (Maccone, 2008 [9]) this author firstly provided a statistical generalization of the Drake equation where the number N of communicating ET civilizations in the Galaxy was shown to follow the lognormal probability distribution. This fact is a consequence of the Central Limit Theorem (CLT) of Statistics, stating that the product of a number of independent random variables whose probability densities are unknown and independent of each other approached the lognormal distribution if the number of factors is increased at will, i.e. it approaches infinity.Also, in Maccone (2011 [15]), it was shown that the exponential growth of the number of species typical of Darwinian Evolution may be regarded as the geometric locus of the peaks of a one-parameter family of b-lognormal distributions constrained between the time axis and the exponential growth curve. This was a brand-new result. And one more new and far-reaching idea was to define Darwinian Evolution as a particular realization of a stochastic process called Geometric Brownian Motion (GBM) having the above exponential as its own mean value curve.The b-lognormals may be also be interpreted as the lifespan of any living being, let it be a cell, or an animal, a plant, a human, or even the historic lifetime of any civilization. In Maccone, (2012 [17, Chapters 6, 7, 8 and 11]), as well as in the present paper, we give important exact equations yielding the b-lognormal when its birth time, senility-time (descending inflexion point) and death time (where the tangent at senility intercepts the time axis) are known. These also are brand-new results. In particular, the σ=1 b-lognormals are shown to be related to the golden ratio, so famous in the arts and in architecture, and these special b-lognormals we call "golden b-lognormals".Applying this new mathematical apparatus to Human History leads to the discovery of the exponential trend of progress between Ancient Greece and the current USA Empire as the envelope of the b-lognormals of all Western Civilizations over a period of 2500 years.We then invoke Shannon's Information Theory. The entropy of the obtained b-lognormals turns out to be the index of "development level" reached by each historic civilization. As a consequence, we get a numerical estimate of the entropy difference (i.e. the difference in the evolution levels) between any two civilizations. In particular, this was the case when Spaniards first met with Aztecs in 1519, and we find the relevant entropy difference between Spaniards an Aztecs to be 3.84 bits/individual over a period of about 50 centuries of technological difference. In a similar calculation, the entropy difference between the first living organism on Earth (RNA?) and Humans turns out to equal 25.57 bits/individual over a period of 3.5 billion years of Darwinian Evolution.Finally, we extrapolate our exponentials into the future, which is of course arbitrary, but is the best Humans can do before they get in touch with any alien civilization. The results are appalling: the entropy difference between aliens 1 million years more advanced than Humans is of the order of 1000 bits/individual, while 10,000 bits/individual would be requested to any Civilization wishing to colonize the whole Galaxy (Fermi Paradox).In conclusion, we have derived a mathematical model capable of estimating how much more advanced than humans an alien civilization will be when SETI succeeds. © 2013 IAA.


Rossetti M.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Molendi S.,Istituto di Astrofisica Spaziale e Fisica Cosmica
Astronomy and Astrophysics | Year: 2010

Context: X ray clusters are conventionally divided into two classes: "cool core" (CC) and "non-cool core" (NCC) objects, on the basis of the observational properties of their central regions. Recent results have shown that the cluster population is bimodal. Aims: We want to understand whether the observed distribution of clusters is due to a primordial division into two distinct classes or rather to differences in the way these systems evolve across cosmic time. Methods: We systematically search the ICM of NCC clusters in a subsample of the B55 flux limited sample of clusters for regions which have some characteristics typical of cool cores, namely low entropy gas and high metal abundance. Results: We find that most NCC clusters in our sample host regions reminiscent of CC, i.e. characterized by relative low entropy gas (albeit not as low as in CC systems) and a metal abundance excess. We have dubbed these structures "cool core remnants", since we interpret them as the remains of a cool core after a heating event (AGN giant outbursts in a few cases and more commonly mergers). We infer that most NCC clusters have undergone a cool core phase during their life. The fact that most cool core remnants are found in dynamically active objects provides strong support to scenarios where cluster core properties are not fixed "ab initio" but evolve across cosmic time. © 2010 ESO.


Caraveo P.A.,Istituto di Astrofisica Spaziale e Fisica Cosmica
Annual Review of Astronomy and Astrophysics | Year: 2014

Isolated neutron stars (INSs) were the first sources identified in the field of high-energy gamma-ray astronomy. In the 1970s, only two sources had been identified, the Crab and Vela pulsars. However, although few in number, these objects were crucial in establishing the very concept of a gamma-ray source. Moreover, they opened up significant discovery space in both the theoretical and phenomenological fronts. The need to explain the copious gamma-ray emission of these pulsars led to breakthrough developments in understanding the structure and physics of neutron star (NS) magnetospheres. In parallel, the 20-year-long chase to understand the nature of Geminga unveiled the existence of a radio-quiet, gamma-ray-emitting INS, adding a new dimension to the INS family. We are living through an extraordinary time of discovery. The current generation of gamma-ray detectors has vastly increased the population of known gamma-ray-emitting NSs. The 100 mark was crossed in 2011, and we are now over 150. The gamma-ray-emitting NS population exhibits roughly equal numbers of radio-loud and radio-quiet young INSs, plus an astonishing, and unexpected, group of isolated and binary millisecond pulsars (MSPs). The number of MSPs is growing so rapidly that they are on their way to becoming the most numerous members of the family of gamma-ray-emitting NSs. Even as these findings have set the stage for a revolution in our understanding of gamma-ray-emitting NSs, long-term monitoring of the gamma-ray sky has revealed evidence of flux variability in the Crab Nebula as well as in the pulsed emission from PSR J2021+4026, challenging a four-decades-old, constant-emission paradigm. Now we know that both pulsars and their nebulae can, indeed, display variable emission. Copyright © 2014 by Annual Reviews.


Paizis A.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Sidoli L.,Istituto di Astrofisica Spaziale e Fisica Cosmica
Monthly Notices of the Royal Astronomical Society | Year: 2014

We have analysed in a systematic way about nine years of INTEGRAL data (17-100 keV) focusing on supergiant fast X-ray transients (SFXTs) and three classical high-mass X-ray binaries (HMXBs). Our approach has been twofold: image-based analysis, sampled over a ~ks time frame to investigate the long-term properties of the sources and light-curve-based analysis, sampled over a 100 s time frame to seize the fast variability of each source during its ~ks activity.We find that while the prototypical SFXTs (IGR J17544-2619, XTE J1739-302 and SAX J1818.6-1703) are among the sources with the lowest ~ ks-based duty cycle (<1 per cent activity over nine years of data), when studied at the 100 s level, they are the ones with the highest detection percentage, meaning that, when active, they tend to have many bright short-term flares with respect to the other SFXTs. To investigate in a coherent and self-consistent way all the available results within a physical scenario, we have extracted cumulative luminosity distributions for all the sources of the sample. The characterization of such distributions in hard X-rays, presented for the first time in this work for the SFXTs, shows that a power-law model is a plausible representation for SFXTs, while it can only reproduce the very high luminosity tail of the classical HMXBs, and even then, with a significantly steeper power-law slope with respect to SFXTs. The physical implications of these results within the frame of accretion in wind-fed systems are discussed. © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


Vercellone S.,Istituto di Astrofisica Spaziale e Fisica Cosmica
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2014

The Cherenkov Telescope Array (CTA) is a large collaborative effort aimed at the design and operation of an observatory dedicated to the very high-energy gamma-ray astrophysics in the energy range 30 GeV-100 TeV, which will improve by about one order of magnitude the sensitivity with respect to the current major arrays (H.E.S.S., MAGIC, and VERITAS). In order to achieve such improved performance, for both the northern and southern CTA sites, four units of 23 m diameter Large Size Telescopes (LSTs) will be deployed close to the centre of the array with telescopes separated by about 100 m. A larger number (about 25 units) of 12 m Medium Size Telescopes (MSTs, separated by about 150 m), will cover a larger area. The southern site will also include up to 24 Schwarzschild-Couder dual-mirror medium-size Telescopes (SCTs) with the primary mirror diameter of 9.5 m. Above a few TeV, the Cherenkov light intensity is such that showers can be detected even well outside the light pool by telescopes significantly smaller than the MSTs. To achieve the required sensitivity at high energies, a huge area on the ground needs to be covered by Small Size Telescopes (SSTs) with a field of view of about 10° and an angular resolution of about 0.2°, making the dual-mirror configuration very effective. The SST sub-array will be composed of 50-70 telescopes with a mirror area of about 5-10 m2 and about 300 m spacing, distributed across an area of about 10 km2. In this presentation we will focus on the innovative solution for the optical design of the medium and small size telescopes based on a dual-mirror configuration. This layout will allow us to reduce the dimension and the weight of the camera at the focal plane of the telescope, to adopt Silicon-based photo-multipliers as light detectors thanks to the reduced plate-scale, and to have an optimal imaging resolution on a wide field of view. © 2014 Elsevier B.V.


Mereghetti S.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Pons J.A.,University of Alicante | Melatos A.,University of Melbourne
Space Science Reviews | Year: 2015

Magnetars are neutron stars in which a strong magnetic field is the main energy source. About two dozens of magnetars, plus several candidates, are currently known in our Galaxy and in the Magellanic Clouds. They appear as highly variable X-ray sources and, in some cases, also as radio and/or optical pulsars. Their spin periods (2–12 s) and spin-down rates (∼10−13–10−10 s s−1) indicate external dipole fields of ∼1013−15 G, and there is evidence that even stronger magnetic fields are present inside the star and in non-dipolar magnetospheric components. Here we review the observed properties of the persistent emission from magnetars, discuss the main models proposed to explain the origin of their magnetic field and present recent developments in the study of their evolution and connection with other classes of neutron stars. © 2015, Springer Science+Business Media Dordrecht.


Mereghetti S.,Istituto di Astrofisica Spaziale e Fisica Cosmica
Brazilian Journal of Physics | Year: 2013

The high-energy sources known as anomalous X-ray pulsars (AXPs) and soft γ-ray repeaters (SGRs) are well explained as magnetars: isolated neutron stars powered by their own magnetic energy. After explaining why it is generally believed that the traditional energy sources at work in other neutron stars (accretion, rotation, residual heat) cannot power the emission of AXPs/SGRs, I review the observational properties of the 20 AXPs/SGRs currently known and describe the main features of the magnetar model. In the last part of this review, I discuss the recent discovery of magnetars with low external dipole field and some of the relations between AXPs/SGRs and other classes of isolated neutron stars. © 2013 Sociedade Brasileira de Física.

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