Tagged: CfA Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 5:42 pm on December 2, 2018 Permalink | Reply
    Tags: "How Do Stellar Binaries Form?, , , , CfA,   

    From Harvard-Smithsonian Center for Astrophysics: “How Do Stellar Binaries Form?” 

    Harvard Smithsonian Center for Astrophysics


    From Harvard-Smithsonian Center for Astrophysics

    November 30, 2018

    1
    An ALMA millimeter-wavelength image of protostellar binary stars early in their formation. (The length scale and the size of the telescope’s beam are shown at the bottom.) Astronomers have studied seventeen multiple systems and found evidence supporting the model of multiple stars developing from disk fragmentation. Tobin et al.

    Most stars with the mass of the sun or larger have one or more companion stars, but when and how these multiple stars form is one of the controversial central problems of astronomy. Gravity contracts the natal gas and dust in an interstellar cloud until clumps develop that are dense enough to coalesce into stars, but how are multiple stars fashioned? Because the shrinking cloud has a slight spin, a disk (possibly a preplanetary system) eventually forms. In one model of binary star formation, this disk fragments due to gravitational instabilities, producing a second star. The other model argues that turbulence in the contracting cloud itself fragments the clumps into multiple star systems. In the first case, simulations show that the two stars should be relatively close together, typically less than about 600 astronomical units (one AU is the average distance of the earth from the sun). If the second mechanism is correct, both close and wide binary pairs can form. A distinguishing feature of the turbulent fragmentation process, and one that facilitates an observational test, is that the seeds for multiplicity are produced early in the pre-stellar phases.

    CfA astronomers Sarah Sadavoy and Mike Dunham were members of a team of astronomers that used the VLA and ALMA radio and millimeter-wave facilities to study seventeen protostellar systems of multiple-stars in the nearby Perseus cloud.

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

    NRAO/Karl V Jansky Expanded Very Large Array, on the Plains of San Agustin fifty miles west of Socorro, NM, USA, at an elevation of 6970 ft (2124 m)

    The sensitive observations were able to reveal the environments of the systems and determine the presence of any small-scale rotation or surrounding material. Twelve of the systems were spatially resolved, and eight showed dust emission structures surrounding the pair. The slightly more evolved systems in the set showed no evidence for circumbinary dust; they have probably reached the end point of their early evolution and finished accreting material. In summary, about two-thirds of the systems were consistent with the disk fragmentation theory and one third was inconsistent with it. The results show that the disk fragmentation mechanism is an important one but probably not the whole story, and a larger sample should help constrain the processes even further.

    Science paper:
    The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Perseus Protostars. VI. Characterizing the Formation Mechanism for Close Multiple Systems
    The Astrophysical Journal John J. Tobin, Leslie W. Looney, Zhi-Yun Li, Sarah I. Sadavoy, Michael M. Dunham, Dominique Segura-Cox, Kaitlin Kratter, Claire J. Chandler, Carl Melis, Robert J. Harris, and Laura Perez

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    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.

    Advertisements
     
  • richardmitnick 3:32 pm on November 25, 2018 Permalink | Reply
    Tags: , , , CfA, , Gravitationally Lensed Quasars, Strong gravitational lensing,   

    From Harvard-Smithsonian Center for Astrophysics: “Gravitationally Lensed Quasars” 

    Harvard Smithsonian Center for Astrophysics


    From Harvard-Smithsonian Center for Astrophysics

    November 16, 2018

    The path of light is bent by mass, an effect predicted by Einstein’s theory of gravity, and when a massive galaxy or cluster lies along our line-of-sight to a more distant galaxy its matter will act as a lens to image the light from that object. So-called strong gravitational lensing creates highly distorted, magnified and often multiple images of a single source.

    Gravitational Lensing NASA/ESA

    Weak gravitational lensing NASA/ESA Hubble

    (Strong lensing is distinct from weak lensing which results in modestly deformed shapes of background galaxies.) Quasars are galaxies with massive black holes at their cores around which vast amounts of energy are being radiated, more than from the rest of the entire host galaxy. Their luminosities allow quasars to be seen at cosmological distances and they are therefore likely candidates for strong lensing, with a few hundred gravitationally lensed quasars known so far. They have provided valuable information not only about quasars and lensing but also on cosmology since the distorted light paths of the distant objects have traveled across cosmological distances.

    CfA astronomer David James was a member of a large international team systematically searching for new gravitationally lensed quasars. They used the WISE infrared all-sky survey to search for candidates whose infrared colors suggested they were galaxies with active nuclei (like quasars). They processed images of these candidates with a sophisticated algorithm looking for evidence of their being multiple components, such as would be expected from a lensed system, and then followed up this subset with spectroscopic and ground-based imaging observations using higher spatial resolution than WISE. Of the original set of fifty-four candidates, they found two whose spectra confirmed that they were gravitationally lensed quasars, one with four sub-images and one with two, each of whose light has been traveling towards us for about ten billion years. The images in these two cases also showed traces of the lensing galaxy, an important verification of the lensing effect, although the galaxies were too faint to obtain measurements of their distances. The scientists also identified another seven objects that are likely to be doubled-quasars, but further research is needed to confirm those results.
    Reference(s):

    “The STRong lensing Insights into the Dark Energy Survey (STRIDES) 2016 Follow-up Campaign – II. New quasar lenses from double component fitting,” T. Anguita et al. MNRAS 480, 5017, 2018.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    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 3:01 pm on November 25, 2018 Permalink | Reply
    Tags: , , “Cherenkov” light, , CfA, CFA/VERITAS is an array of four 12 m diameter optical telescopes located at the SAO's Fred Lawrence Whipple Observatory near Tucson Arizona, , It is common for massive stars to form in binary pairs and so it is not surprising that some pulsars have an orbiting companion that has survived its partner's explosive death, Very high energy (VHE) gamma-ray emitting neutron star-massive star binary pairs   

    From Harvard-Smithsonian Center for Astrophysics: “Once-In-A-Lifetime Observations by Veritas Astronomers Reveal High Energy Gamma-Rays from a Binary Star System” 

    Harvard Smithsonian Center for Astrophysics


    From Harvard-Smithsonian Center for Astrophysics

    November 13, 2018
    Tyler Jump
    Public Affairs
    Harvard-Smithsonian Center for Astrophysics
    +1 617-495-7462
    tyler.jump@cfa.harvard.edu

    CfA/VERITAS, a major ground-based gamma-ray observatory with an array of four 12m optical reflectors for gamma-ray astronomy in the GeV – TeV energy range. Located at Fred Lawrence Whipple Observatory, Mount Hopkins, Arizona, US in AZ, USA, Altitude 2,606 m (8,550 ft)

    A new discovery reported in The Astrophysical Journal Letters might lay claim to title of the most unusual extreme class of astronomical object: very high energy (VHE) gamma-ray emitting, neutron star-massive star binary pairs. Of the one-hundred billion stars in our galaxy, fewer than ten are in known to be in gamma-ray binary systems, with this discovery being only the second with an identified neutron star. The gamma-ray emission was discovered during an event that will not happen again until 2067.

    A neutron star is the dense remains of a type of supernova, the explosive death of a star that started its life more massive than about eight solar-masses. Containing as much material as the sun but in an object only the diameter of a city, neutron stars are so dense that most of their matter is in the form of neutrons, the uncharged atomic particles found in atomic nuclei. Neutron stars spin rapidly and generate powerful magnetic fields, fast winds and narrow beams that sweep like a lighthouse across the sky as the star rotates. If the Earth happens to lie in the path of one of these beams as it passes, astronomers can detect the radiation as regular pulses at radio and other wavelengths. There are a few thousand of these “pulsars” known, beating at a variety of rates from more than a thousand times a second to less than about once a second.

    It is common for massive stars to form in binary pairs, and so it is not surprising that some pulsars have an orbiting companion that has survived its partner’s explosive death. Both the pulsar and its companion are likely to have disks of material around them. The rapidly spinning pulsar and its wind can in some cases slam into the disk and wind of the companion star as the two periodically approach in their orbital dance. The energetic collision can produce intense shocks that accelerate charged particles to energies high enough to produce very high energy (VHE) gamma ray radiation by accelerating the particles to nearly the speed of light. When light scatters off such energetic particles it too becomes energized and becomes VHE gamma ray photons each one of which can pack a billion times more energy than a photon of optical light. The precise timing of the radio pulses allows astronomers to use the radio signals to deduce some parameters of the stars and their orbit. Although there are plenty of pulsars, until now most of the explanation was speculation, with only one known case of a binary pulsar system exhibiting VHE gamma-ray emission.

    An international team of astronomers began intensively tracking a second, possible VHE gamma-ray pulsar system in 2016. Located about five thousand light-years away in a massive stellar nursery in the direction of the constellation Cygnus, the pulsar was identified as having a massive stellar companion that orbited it every 50 years in an extreme elliptical orbit. At their closest approach the two were expected to come within a mere one astronomical unit of each other (one AU is the average distance of the Earth from the sun), and the scientists had calculated that this would happen on November 13, 2017 – exactly one year ago.

    CfA astronomers Wystan Benbow, Gareth Hughes, and Michael Daniel direct VERITAS operations and enabled the VERITAS collaboration’s participation in the program to monitor the behavior of this bizarre object before, after and during its expected closest approach. VERITAS is an array of four 12 m diameter optical telescopes located at the SAO’s Fred Lawrence Whipple Observatory near Tucson, Arizona. VERITAS detects gamma rays via the extremely brief flashes of blue “Cherenkov” light created when gamma rays are absorbed in the Earth’s atmosphere. The VERITAS Collaboration consists of about 80 scientists from 20 institutions in the United States, Canada, Germany and Ireland. VERITAS scientists were joined by a team using the two 17 m MAGIC Cherenkov telescopes located at El Roque de Los Muchachos on the island of La Palma, Spain.

    As the binary system is embedded in a larger, diffuse region of VHE gamma-ray emission, the international team of astronomers anxiously awaited the event to see whether the VHE gamma-rays emission brightened near the pulsar. According to Alicia López Oramas, a researcher with MAGIC at the Instituto de Astrofísica de Canarias (IAC), and one of the corresponding authors of the study, “such a unique system was expected to emit very-high-energy gamma rays during this approach, and this opportunity could not be missed.” Graduate student Tyler Williamson and his advisor Professor Jamie Holder, both from University of Delaware’s Department of Physics and Astronomy, played leading roles in the VERITAS campaign, together with Ralph Bird, a post-doctoral researcher at the University of California, Los Angeles.

    Initial observations, in 2016, revealed weak gamma-ray emission, consistent with earlier results. “This low-level, steady emission is most likely from a nebula which is being continuously powered by the pulsar,” explains Dr. Bird. Starting in September 2017, the results became much more exciting. “The gamma-ray flux we observed in September was twice the previous value,” says Williamson. But the fireworks were just beginning. “During the closest approach between the star and the pulsar, in November 2017, the flux increased 10 times in just a single night.”

    In an attempt to explain not only the strength of the gamma rays, but also their gradual variability and then sudden flaring, the team tried to match a recent theoretical model to their observations. The model contains the latest ideas about pulsars, the binary disk and wind environment, the nature of the ionized nebulosity around the object, the spectrum of emission and tries to refine the orbital parameters of the binary. It was unsuccessful and so the scientists conclude that significant revision is needed to the models in order to fit the observations, including better information about the geometry of the encounter. Since information about the structure of disks and winds around pulsars depends on many diverse yet key parameters like magnetic field strength and environmental history, this object – if it can be successfully modeled – offers to be a potential Rosetta Stone about the birth and evolution of compact objects, and so includes all compact objects produced in supernovae, pulsars without companions, and even many black hole binary systems. In the coming years the scientists plan to continue to monitor this and other pulsars to monitor the exotic behavior of these most unusual and extreme cosmic characters. Wystan Benbow from the CfA states that “continued investment in the operation of unique, leading edge facilities like VERITAS is critical and will ensure further opportunities to achieve transformative science.”

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    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 9:46 am on August 29, 2018 Permalink | Reply
    Tags: , , , CfA, , Unraveling the Stellar Content of Young Clusters   

    From Smithsonian Astrophysical Observatory: “Unraveling the Stellar Content of Young Clusters” 

    Smithsonian Astrophysical Observatory
    From Smithsonian Astrophysical Observatory

    August 10, 2018

    1
    A region of clustered star formation. The left frame shows a high spatial resolution infrared image of the cluster; three young stars are seen in the colored circles, with the white circle showing a fiducial size. The right frame is the same cluster seen at longer wavelengths with a different instrument. The three stars are blended together. A new technique determines the most likely contribution each of the stars makes to this and other long-wavelength images, and uses that to infer the stars’ properties. Martinez-Galarza et al 2018

    About twenty-five percent of young stars in our galaxy form in clustered environments, and stars in a cluster are often close enough to each other to affect the way they accrete gas and grow. Astronomers trying to understand the details of star formation, for example the relative abundance of massive stars to low mass ones, must take such complicated clustering effects into account. Measuring the actual demographics of a cluster is not easy either. Young stars are embedded within obscuring clouds of natal material. Infrared radiation can escape, however, and astronomers probe these regions at infrared wavelengths using the shape of the spectral energy distribution (the SED – the relative amounts of flux emitted at different wavelengths) to diagnose the nature of the young star: its mass, age, accretion activity, developing disk, and similar properties. One major complication is that the various telescopes and instruments used to measure an SED have large and different-sized beams that encompass multiple objects in a cluster. As a result, each point in an SED is a confused blend of emission from all the constituent stars, with the longest wavelength datapoints (from the largest beams) covering a spatial region perhaps ten times larger than the shortest wavelength points.

    CfA astronomers Rafael Martinez-Galarz and Howard Smith and their two colleagues have developed a new statistical analysis technique to address the problem of confused SEDs in clustered environments. Using the highest spatial resolution images for each region, the team identifies the distinguishable stars (at least this many are in the cluster) and their emission at those wavelengths. They combine a Bayesian statistical approach with a large grid of modeled young stellar SEDs to determine the most probable continuation of each individual SED into the blended, longer-wavelength bands and thus leads to the determination of the most likely value of each star’s mass, age, and environmental parameters. The resultant summed SED is not unique but is the most likely solution.

    The astronomers apply their method to seventy young, low mass stellar clusters observed by the Spitzer Space Telescope’s Infrared Array Camera, and derive their physical properties.

    NASA/Spitzer Infrared Telescope

    NASA Spitzer Infrared Array Camera

    Their results are in excellent agreement with general expectations for the distribution of stellar masses. They also find several unexpected preliminary results, including a relationship between the total mass of the cluster and the mass of its largest member. The team plans to extend the wavelength ranges included in their SED analysis and to increase the number of clusters analyzed.

    Science paper:
    Unraveling the Spectral Energy Distributions of Clustered YSOs, J. Rafael Martinez-Galarza, Pavlos Protopapas, Howard A. Smith, and Esteban F. E. Morales ApJ (in press) 2018

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    About CfA

    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. The long relationship between the two organizations, which began when the SAO moved its headquarters to Cambridge in 1955, was formalized by the establishment of a joint center in 1973. The CfA’s history of accomplishments in astronomy and astrophysics is reflected in a wide range of awards and prizes received by individual CfA scientists.

    Today, some 300 Smithsonian and Harvard scientists cooperate in broad programs of astrophysical research supported by Federal appropriations and University funds as well as contracts and grants from government agencies. These scientific investigations, touching on almost all major topics in astronomy, are organized into the following divisions, scientific departments and service groups.

     
  • richardmitnick 7:17 am on August 11, 2018 Permalink | Reply
    Tags: , , , CfA, , ,   

    From Center For Astrophysics: “Spitzer Infrared Observations of a Gravitational Wave Source – a Binary Neutron Star Merger” 

    Harvard Smithsonian Center for Astrophysics


    From Center For Astrophysics

    GW170817 is the name given to a gravitational wave signal seen by the LIGO and Virgo detectors on 17 August 2017.

    14
    See https://sciencesprings.wordpress.com/2017/10/20/from-ucsc-neutron-stars-gravitational-waves-and-all-the-gold-in-the-universe/


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

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

    ESA/eLISA the future of gravitational wave research

    1
    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

    Lasting for about 100 seconds, the signal was produced by the merger of two neutron stars. The observation was then confirmed – the first time this has happened for gravitational waves – by observations with light waves: the preceding five detections of merging black holes did not have (and were not expected to have) any detectable electromagnetic signals. The light from the neutron star merger is produced by the radioactive decay of atomic nuclei created in the event. (Neutron star mergers do more than just produce optical light, by the way: they are also responsible for making most of the gold in the universe.) Numerous ground-based optical observations of the merger concluded that the decaying atomic nuclei fall into at least two groups, a rapidly evolving and fast moving one composed of elements less massive than Lanthanide Series elements, and one that is more slowly evolving and dominated by heavier elements.

    Ten days after the merger, the continuum emission peaked at infrared wavelengths with a temperature of approximately 1300 kelvin, and continued to cool and dim. The Infrared Array Camera (IRAC) on the Spitzer Space Telescope observed the region around GW170817 for 3.9 hours in three epochs 43, 74 and 264 days after the event (SAO is the home of IRAC PI Fazio and his team). The shape and evolution of the emission reflect the physical processes at work, for example, the fraction of heavy elements in the ejecta or the possible role of carbon dust. Tracking the flux over time enables the astronomers to refine their models and understanding of what happens when neutron stars merge.

    A team of CfA astronomers, Victoria Villar, Philip Cowperthwaite, Edo Berger, Peter Blanchard, Sebastian Gomez, Kate Alexander, Tarraneh Eftekhari, Giovanni Fazio, James Guillochon, Joe Hora, Matthew Nicholl, and Peter Williams and two colleagues participated in an effort to measure and interpret the infrared observations. The source was extremely faint and moreover lies close to a very bright point source. Using a novel algorithm to prepare and subtract the IRAC images to eliminate the constant-brightness objects, the team was able to spot the merger source clearly in the first two epochs, although it was fainter than was predicted by the models by more than about a factor of two. It had dimmed beyond detection by the third epoch. However the rate of dimming and the infrared colors are consistent with models; at these epochs the material had cooled down to about 1200 kelvin. The team suggests several possible reasons for the surprising faintness, including possible transformation of the ejecta into a nebulous phase and notes that the new dataset will help refine the models.

    The scientists conclude by emphasizing that future binary star merger detections (an improved LISA will begin observing again in 2019) will similarly benefit from infrared observations, and that characterization of the infrared will enable more accurate determination of the nuclear decay processes underway. Their current paper, moreover, shows that Spitzer should be able to spot binary mergers as far away as four hundred million light-years, about the distance that the improved LISA should be able to probe.

    Spitzer Space Telescope Infrared Observations of the Binary Neutron Star Merger GW170817
    The Astrophysical Journal Letters

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    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 6:57 am on August 11, 2018 Permalink | Reply
    Tags: , , , CfA, , Ready for Its Day in the Sun: The SWEAP Investigation,   

    From Center For Astrophysics: “Ready for Its Day in the Sun: The SWEAP Investigation” 

    Harvard Smithsonian Center for Astrophysics


    From Center For Astrophysics

    August 3, 2018
    Megan Watzke
    Harvard-Smithsonian Center for Astrophysics
    +1 617-496-7998
    mwatzke@cfa.harvard.edu

    Peter Edmonds
    Harvard-Smithsonian Center for Astrophysics
    +1 617-571-7279
    pedmonds@cfa.harvard.edu

    1

    When NASA’s Parker Solar Probe launches into space from the Kennedy Space Center, it will begin its journey to the Sun, our nearest star. The Parker Solar Probe will travel almost 90 million miles and eventually enter through the Sun’s outer atmosphere to encounter a dangerous environment of intense heat and solar radiation. During this harrowing journey, it will fly closer to the Sun than any other human-made object.

    To revolutionize our understanding of our most important and life-sustaining star, scientists and engineers have built a suite of instruments aboard the Parker Solar Probe to conduct different experiments. Some of these instruments will be protected by a thick carbon-composite heat shield. However, others will be more exposed.

    The Solar Wind Electrons Alphas and Protons (SWEAP) investigation is the set of instruments that will directly measure the hot ionized gas in the solar atmosphere during the solar encounters. A key instrument on SWEAP called the Solar Probe Cup (SPC) was built at the Smithsonian Astrophysical Observatory (SAO) in Cambridge, Mass.

    The SPC is a small metal device that will peer around the protective heat shield of the spacecraft directly at the Sun. It will face some of the most extreme conditions ever encountered by a scientific instrument, and allow a sample of the Sun’s atmosphere to be swept up for the first time.

    The SPC uses high voltages to determine what type of particles can enter, which is a way of measuring the energy of the particle. This is crucial information for probing the wind of hot ionized gas that is constantly produced by the Sun. As the spacecraft flies towards the Sun for an encounter, the wind is directed straight into the cup. Without the SPC, Parker Solar Probe would miss most of what is in between Earth and the Sun. This unique probe of the solar wind is important for scientists to better understand space weather, which is responsible for effects that range from endangering astronauts on space walks to impacting the electronics in communications satellites.

    The Parker Solar Probe spacecraft, about the size of a small car, will travel towards the Sun’s atmosphere at speeds of about 430,000 mph (700,000 km/hr), becoming the fastest human-made object. Eventually, Parker Solar Probe will enter an orbit that approaches to within only 4 million miles from the star’s surface. (For context, the Earth averages a distance of about 93 million miles from the Sun during its elliptical orbit. Or, to put it another way, the spacecraft will travel about 96% of the way from the Earth to the Sun.) Parker Solar Probe, which will be carried into space by a Delta-IV Heavy rocket, is currently scheduled to launch on August 11, 2018.

    The SWEAP Team is led by Justin Kasper currently at the University of Michigan (and currently an SAO Research Associate). On the SWEAP Investigation, SAO partners with team members from University of California, Berkeley Space Sciences Laboratory, the NASA Marshall Space Flight Center, the University of Alabama Huntsville, NASA Goddard Space Flight Center, Los Alamos National Laboratory, and the Massachusetts Institute of Technology. SAO built the SPC (Instrument Scientist: Tony Case), leads the Science Operations Center (Head of Science Operations: Kelly Korreck), and manages the overall SWEAP program.

    More information on SAO’s role in Parker Solar Probe can be found at:

    “Extreme Spacecrafting: NASA’s Parker Solar Probe”
    Video of Observatory Night talk by Anthony Case and Kelly Korreck on May 17, 2018

    “Parker Solar Probe’s Mission to Solve Stranger Things”
    Post by Kelly Korreck at National Air & Space Museum’s blog

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    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 2:09 pm on July 2, 2018 Permalink | Reply
    Tags: , , , CfA, , Kepler-186f, More Clues That Earth-Like Exoplanets Are Indeed Earth-Like   

    From Harvard-Smithsonian Center for Astrophysics: “More Clues That Earth-Like Exoplanets Are Indeed Earth-Like” 

    Harvard Smithsonian Center for Astrophysics


    June 29, 2018

    Megan Watzke
    Harvard-Smithsonian Center for Astrophysics
    +1 617-496-7998
    mwatzke@cfa.harvard.edu

    Peter Edmonds
    Harvard-Smithsonian Center for Astrophysics
    +1 617-571-7279
    pedmonds@cfa.harvard.edu

    From Harvard-Smithsonian Center for Astrophysics

    1
    This artist’s concept depicts Kepler-186f. NASA Ames/JPL-Caltech/T. Pyle

    A new study provides new clues indicating that an exoplanet 500 light-years away is much like Earth.

    Kepler-186f is the first identified Earth-sized planet outside the Solar System orbiting a star in the habitable zone. This means it’s the proper distance from its host star for liquid water to pool on the surface.

    The Georgia Tech study used simulations to analyze and identify the exoplanet’s spin axis dynamics. Those dynamics determine how much a planet tilts on its axis and how that tilt angle evolves over time. Axial tilt contributes to seasons and climate because it affects how sunlight strikes the planet’s surface.

    The researchers suggest that Kepler-186f’s axial tilt is very stable, much like the Earth, making it likely that it has regular seasons and a stable climate. The Georgia Tech team thinks the same is true for Kepler-62f, a super-Earth-sized planet orbiting around a star about 1,200 light-years away from us.

    How important is axial tilt for climate? Large variability in axial tilt could be a key reason why Mars transformed from a watery landscape billions of years ago to today’s barren desert.

    “Mars is in the habitable zone in our solar system, but its axial tilt has been very unstable — varying from 0 to 60 degrees,” said Georgia Tech Assistant Professor Gongjie Li, who led the study together with graduate student Yutong Shan from the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass. “That instability probably contributed to the decay of the Martian atmosphere and the evaporation of surface water.”

    As a comparison, Earth’s axial tilt oscillates more mildly — between 22.1 and 24.5 degrees, going from one extreme to the other every 10,000 or so years.

    The orientation angle of a planet’s orbit around its host star can be made to oscillate by gravitational interaction with other planets in the same system. If the orbit were to oscillate at the same speed as the precession of the planet’s spin axis (akin to the circular motion exhibited by the rotation axis of a top or gyroscope), the spin axis would also wobble back and forth, sometimes dramatically.

    Mars and Earth interact strongly with each other, as well as with Mercury and Venus. As a result, by themselves, their spin axes would precess with the same rate as the orbital oscillation, which may cause large variations in their axial tilt. Fortunately, the Moon keeps Earth’s variations in check. The Moon increases our planet’s spin axis precession rate and makes it differ from the orbital oscillation rate. Mars, on the other hand, doesn’t have a large enough satellite to stabilize its axial tilt.

    “It appears that both exoplanets are very different from Mars and the Earth because they have a weaker connection with their sibling planets,” said Li, a faculty member in the School of Physics. “We don’t know whether they possess moons, but our calculations show that even without satellites, the spin axes of Kepler-186f and 62f would have remained constant over tens of millions of years.”

    Kepler-186f is less than 10 percent larger in radius than Earth, but its mass, composition, and density remain a mystery. It orbits its host star every 130 days. According to NASA, the brightness of that star at high noon, while standing on 186f, would appear as bright as the sun just before sunset here on Earth. Kepler-186f is located in the constellation Cygnus as part of a five-planet star system.

    Kepler-62f was the most Earth-like exoplanet until scientists noticed 186f in 2014. It’s about 40 percent larger than our planet and is likely a terrestrial or ocean-covered world. It’s in the constellation Lyra and is the outermost planet among five exoplanets orbiting a single star.

    That’s not to say either exoplanet has water, let alone life. But both are relatively good candidates.

    “Our study is among the first to investigate climate stability of exoplanets and adds to the growing understanding of these potentially habitable nearby worlds,” said Li.

    “I don’t think we understand enough about the origin of life to rule out the possibility of its presence on planets with irregular seasons,” added the CfA’s Shan. “Even on Earth, life is remarkably diverse and has shown incredible resilience in extraordinarily hostile environments.

    “But a climatically stable planet might be a more comfortable place to start.”

    A paper describing these results appeared in the May 17, 2018 issue of The Astronomical Journal.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    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 12:35 pm on June 20, 2018 Permalink | Reply
    Tags: , , , CfA, , XMM-Newton Finds Missing Intergalactic Material   

    From Harvard-Smithsonian Center for Astrophysics: “XMM-Newton Finds Missing Intergalactic Material” 

    Harvard Smithsonian Center for Astrophysics


    From Harvard-Smithsonian Center for Astrophysics

    June 20, 2018
    Megan Watzke
    Harvard-Smithsonian Center for Astrophysics
    +1 617-496-7998
    mwatzke@cfa.harvard.edu

    Peter Edmonds
    Harvard-Smithsonian Center for Astrophysics
    +1 617-571-7279
    pedmonds@cfa.harvard.edu

    ESA/XMM Newton

    1
    This figure shows the filamentary structure of the hot gas that represents part of the warm-hot intergalactic medium (WHIM). It is based on a simulation extending over more than 200 million light years. The red and orange regions have the highest densities & the green regions have lower densities. Princeton University/Renyue Cen

    2
    Astronomers have used ESA’s XMM-Newton space observatory (lower right) to detect the WHIM. The white box encloses the filamentary structure of the hot gas that represents part of the WHIM. It is based on a cosmological simulation extending over more than 200 million light years. The red and orange regions have the highest densities & the green regions have lower densities. The discovery was made using observations of a distant quasar – a supermassive black hole that is actively devouring matter and shining brightly from X-rays to radio waves (upper left). The team found the signature of oxygen in the WHIM lying between the observatory and the quasar, at two different locations along the line of sight (shown in the spectrum in the lower left with green and magenta arrows). The blue arrows are signatures of nitrogen in our Milky Way galaxy.
    Illustrations and composition: ESA / ATG medialab; data: ESA / XMM-Newton / F. Nicastro et al. 2018; cosmological simulation: Princeton University/Renyue Cen

    3
    The mysterious dark matter and dark energy make up about 25 and 70 percent of our cosmos respectively, and ordinary matter, which makes up everything we see, including galaxies, stars and planets – amounts to only about five percent. However, stars in galaxies across the Universe only make up about seven percent of all ordinary matter and the cold and hot interstellar gas that permeates galaxies and galaxy clusters together accounts for only about 11 percent. Most of the Universe’s ordinary matter, or baryons, lurks in the cosmic web, the filamentary distribution of both dark and ordinary matter that extends throughout the Universe. In the past astronomers were able to locate a good chunk of the cool and warm parts of this intergalactic material (about 43 percent of all baryons in total). Astronomers have now used ESA’s XMM-Newton space observatory to detect the hot component of this intergalactic material along the line of sight to a quasar. The amount of hot intergalactic gas detected in these observations amounts up to 40 percent of all baryons in the Universe, closing the gap in the overall budget of ordinary matter in the cosmos. ESA

    After a nearly twenty-year long game of cosmic hide-and-seek, astronomers using ESA’s XMM-Newton space observatory have finally found evidence of hot, diffuse gas permeating the cosmos, closing a puzzling gap in the overall budget of ‘normal’ matter in the Universe.

    While the mysterious dark matter and dark energy make up about 25 and 70 percent of our cosmos respectively, the ordinary matter that makes up everything we see – from stars and galaxies to planets and people – amounts to only about five percent.

    But even this five percent turns out to be hard to track down.

    The total amount of ordinary matter, which astronomers refer to as baryons, can be estimated from observations of the Cosmic Microwave Background [CMB], which is the most ancient light in the history of the Universe, dating back to only about 380,000 years after the Big Bang.

    CMB per ESA/Planck

    ESA/Planck 2009 to 2013

    Observations of very distant galaxies allow astronomers to follow the evolution of this matter throughout the Universe’s first couple of billions of years. After that, however, more than half of it seemed to have gone missing.

    “The missing baryons represent one of the biggest mysteries in modern astrophysics,” explains Fabrizio Nicastro, lead author of the paper presenting a solution to the mystery, published today in Nature. Nicastro is from the INAF-Osservatorio Astronomico di Roma, Italy, and the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass.

    “We know this matter must be out there, we see it in the early Universe, but then we can no longer get hold of it. Where did it go?”

    Counting the population of stars in galaxies across the Universe, plus the interstellar gas that permeates galaxies – the raw material to create stars – only gets as far as a mere ten percent of all ordinary matter. Adding up the hot, diffuse gas in the haloes that encompass galaxies and the even hotter gas that fills galaxy clusters, which are the largest cosmic structures held together by gravity, raises the inventory to less than twenty percent.

    This is not surprising: stars, galaxies and galaxy clusters form in the densest knots of the cosmic web, the filamentary distribution of both dark and ordinary matter that extends throughout the Universe. While these sites are dense, they are also rare, so not the best spots to look for the majority of cosmic matter.

    Astronomers suspected that the ‘missing’ baryons must be lurking in the ubiquitous filaments of this cosmic web, where matter is, however, less dense and therefore more challenging to observe. Using different techniques over the years, they were able to locate a good chunk of this intergalactic material – mainly its cool and warm components – bringing up the total budget to a respectable 60 percent, but leaving the overall mystery still unsolved.

    Nicastro and many other astronomers around the world have been on the tracks of the remaining baryons for almost two decades, ever since X-ray observatories such as ESA’s XMM-Newton and NASA’s Chandra X-ray Observatory became available to the scientific community.

    Observing in this portion of the electromagnetic spectrum, they can detect hot intergalactic gas, with temperatures around a million degrees or more, that is blocking the X-rays emitted by even more distant sources.

    For this project, Nicastro and his collaborators used XMM-Newton to look at a quasar – a massive galaxy with a supermassive black hole at its center that is actively devouring matter and shining brightly from X-rays to radio waves. They observed this quasar, whose light takes more than four billion years to reach us, for a total of 18 days, split between 2015 and 2017, in the longest X-ray observation ever performed of such a source.

    “After combing through the data, we succeeded at finding the signature of oxygen in the hot intergalactic gas between us and the distant quasar, at two different locations along the line of sight,” says Nicastro.

    “This is happening because there are huge reservoirs of material – including oxygen – lying there, and just in the amount we were expecting, so we finally can close the gap in the baryon budget of the Universe.”

    This extraordinary result is the beginning of a new quest. Observations of different sources across the sky are needed to confirm whether these findings are truly universal, and to further investigate the physical state of this long-sought-for matter.

    Fabrizio and his colleagues are planning to study more quasars with XMM-Newton and Chandra in the coming years. To fully explore the distribution and properties of this so-called warm-hot intergalactic medium, however, more sensitive instruments will be needed, like ESA’s Athena, the Advanced Telescope for High-Energy Astrophysics, scheduled for launch in 2028.

    ESA/Athena spacecraft depiction

    “The discovery of the missing baryons with XMM-Newton is the exciting first step to fully characterize the circumstances and structures in which these baryons are found,” says co-author Jelle Kaastra from the Netherlands Institute for Space Research.

    “For the next steps, we will need the much higher sensitivity of Athena, which has the study of the warm-hot intergalactic medium as one of its main goals, to improve our understanding of how structures grow in the history of the Universe.”

    “It makes us very proud that XMM-Newton was able to discover the weak signal of this long elusive material, hidden in a million-degree hot fog that extends through intergalactic space for hundreds of thousands of light years,” says Norbert Schartel, XMM-Newton project scientist at ESA.

    “Now that we know these baryons are no longer missing, we can’t wait to study them in greater detail.”

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    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 3:17 pm on May 30, 2018 Permalink | Reply
    Tags: , , , CfA, , Parker Solar Probe's Faraday cup,   

    From Harvard-Smithsonian Center for Astrophysics and U Michigan : “Key Parker Solar Probe Sensor Bests Sun Simulator—Last Launch Hurdle” 

    U Michigan bloc

    University of Michigan

    Harvard Smithsonian Center for Astrophysics


    From Harvard-Smithsonian Center for Astrophysics

    April 30, 2018
    Megan Watzke
    Harvard-Smithsonian Center for Astrophysics
    +1 617-496-7998
    mwatzke@cfa.harvard.edu

    Peter Edmonds
    Harvard-Smithsonian Center for Astrophysics
    +1 617-571-7279
    pedmonds@cfa.harvard.edu

    1
    Researchers use a quartet of IMAX projectors to create the light and heat the Parker Solar Probe cup will experience during its trips through the sun’s atmosphere. The cup sits inside a vacuum chambers set up in a lab at the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts. Image credit: Levi Hutmacher, Michigan Engineering

    2
    Artist’s concept of the Parker Solar Probe spacecraft approaching the sun. In order to unlock the mysteries of the corona, but also to protect a society that is increasingly dependent on technology from the threats of space weather, we will send Parker Solar Probe to touch the sun. Image credit: NASA

    3
    Justin Kasper, (left), a University of Michigan associate professor of climate and space sciences engineering, awaits test results with Anthony Case, an astrophysicist at the Harvard Smithsonian Institute for Astrophysics. Image creidt: Levi Hutmacher, Michigan Engineering

    You don’t get to swim in the sun’s atmosphere unless you can prove you belong there. And the Parker Solar Probe’s Faraday cup, a key sensor aboard the $1.5 billion NASA mission launching this summer, earned its stripes last week by enduring testing in a homemade contraption designed to simulate the sun.

    The cup will scoop up and examine the solar wind as the probe passes closer to the sun than any previous manmade object. Justin Kasper, University of Michigan associate professor of climate and space sciences and engineering, is principal investigator for Parker’s Solar Wind Electrons Alphas and Protons (SWEAP) investigation.

    In order to confirm the cup will survive the extreme heat and light of the sun’s corona, researchers previously tortured a model of the Faraday cup at temperatures exceeding 3,000 degrees Fahrenheit, courtesy of the Oak Ridge National Laboratory’s Plasma Arc Lamp. The cup, built from refractory metals and sapphire crystal insulators, exceeded expectations.

    But the final test took place last week, in a homemade contraption Kasper and his research team call the Solar Environment Simulator. While being blasted with roughly 10 kilowatts of light on its surface—enough to heat a sheet of metal to 1,800 degrees Fahrenheit in seconds—the Faraday cup model ran through its paces, successfully scanning a simulated stream of solar wind.

    “Watching the instrument track the signal from the ion beam as if it was plasma flowing from the sun was a thrilling preview of what we will see with Parker Solar Probe,” Kasper said.

    Roilings in the sun’s atmosphere can violently fling clouds of plasma into space, known as coronal mass ejections, sometimes directly at Earth. Without precautionary measures, such clouds can set up geomagnetic oscillations around Earth that can trip up satellite electronics, interfere with GPS and radio communications and—at their worst—can create surges of current through power grids that can overload and disrupt the system for extended periods of time, up to months.

    By understanding what makes up the solar corona and what drives the constant outpouring of solar material from the sun, scientists on Earth will be better equipped to interpret the solar activity we see from afar and create a better early-warning system. That’s where Parker Solar Probe, slated for launch on July 31, 2018, comes in, with its complement of experiments that includes the Faraday cup.

    To test the cup model, researchers had to create something new. Their simulator sits in a first-floor lab at the Smithsonian Astrophysical Observatory in Cambridge, Mass., and embodies the adage that necessity is the mother of invention.

    It has the look of a makeshift operating room, with a metal frame holding up thick blue tarps around three sides creating a 16×8 workspace.

    Inside the area, recreating the sun’s heat and light fell to a quartet of modified older model IMAX projectors that Kasper’s team purchased on eBay for a few thousand dollars apiece. These are not the digital machines you find in today’s Cineplexes, but an earlier generation that utilized bulbs.

    “It turns out a movie theater bulb on an IMAX projector runs at about the same 5,700 degrees Kelvin—the same effective temperature as the surface of the sun,” Kasper said. “And it gives off nearly the same spectrum of light as the surface.”

    Space offers essentially no atmosphere, meaning a proper testing environment for the Faraday cup would have as little air as possible. So researchers placed the cup in a metal vacuum chamber for testing.

    Resembling an iron lung, the seven-foot-long silver chamber has a hatch at one end that swings outward and has a small round window in it. The night before testing, the team began pumping the atmosphere out of the vacuum chamber.

    By the time the simulation cranked up for testing, the chamber registered roughly one-billionth of the Earth’s atmosphere.

    All four of the IMAX projectors sit atop wheeled tables, and to set up for the test, researchers rolled them into place, with their beams pointed through the vacuum tube window directly at the Faraday cup.

    The final element of the simulator is its ability to generate the kinds of particles the Faraday cup will need to sense and evaluate. To do that, the team attached an ion gun to the vacuum tube hatch, with the “barrel” of the device reaching inside and pointed at the cup.

    “The ion gun takes a pellet of metal and heats it up,” said Anthony Case, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics. “When it gets hot, ions start boiling off this piece of metal. Then you hook it up to a battery, accelerating the ions out of the gun. And we can direct them right toward the Faraday cup’s aperture where they’ll be measured.”

    In this final test, the Faraday cup took the heat and delivered—putting Parker Solar Probe on track for its summer launch.

    Kelly Korreck, a U-M alumna and astrophysicist at the institute, serves as head of science operations on Parker’s SWEAP investigation as well as SWEAP activities for the Smithsonian.

    “As for the test today, it confirmed what I had suspected—when you take an amazing team of scientists and engineers, give them a complex, difficult, interesting project and the motivation of exploring a region of the universe humankind has never been to, before remarkable things happen,” she said.

    See the full CfA article here .
    See the full U Michigan article here .


    five-ways-keep-your-child-safe-school-shootings


    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.

    U MIchigan Campus

    The University of Michigan (U-M, UM, UMich, or U of M), frequently referred to simply as Michigan, is a public research university located in Ann Arbor, Michigan, United States. Originally, founded in 1817 in Detroit as the Catholepistemiad, or University of Michigania, 20 years before the Michigan Territory officially became a state, the University of Michigan is the state’s oldest university. The university moved to Ann Arbor in 1837 onto 40 acres (16 ha) of what is now known as Central Campus. Since its establishment in Ann Arbor, the university campus has expanded to include more than 584 major buildings with a combined area of more than 34 million gross square feet (781 acres or 3.16 km²), and has two satellite campuses located in Flint and Dearborn. The University was one of the founding members of the Association of American Universities.

    Considered one of the foremost research universities in the United States,[7] the university has very high research activity and its comprehensive graduate program offers doctoral degrees in the humanities, social sciences, and STEM fields (Science, Technology, Engineering and Mathematics) as well as professional degrees in business, medicine, law, pharmacy, nursing, social work and dentistry. Michigan’s body of living alumni (as of 2012) comprises more than 500,000. Besides academic life, Michigan’s athletic teams compete in Division I of the NCAA and are collectively known as the Wolverines. They are members of the Big Ten Conference.

     
  • richardmitnick 2:50 pm on May 30, 2018 Permalink | Reply
    Tags: , , , CfA, , X-Ray Binary Stars at the Galactic Center   

    From Harvard-Smithsonian Center for Astrophysics: “X-Ray Binary Stars at the Galactic Center” 

    Harvard Smithsonian Center for Astrophysics


    From Harvard-Smithsonian Center for Astrophysics

    1
    The central few light-years of our Milky Way. This X-ray image by Chandra shows the locations of some of the X-ray emitting point sources, including X-ray binary stars (cyan circles). A new analysis of archival Chandra data reports the first convincing evidence for this predicted, dense cluster of black holes. Chandra X-Ray Observatory/NASA, Hailey et al. 2018

    NASA/Chandra X-ray Telescope

    The center of our Milky Way galaxy is about twenty-five thousand light years from Earth, in the direction of the constellation Sagittarius. At the core of the galaxy is a supermassive black hole with about four million solar-masses of material and around it, within a volume just a few light-years in radius, orbit hundreds of massive stars and probably hundreds of thousands of smaller, harder to detect stars. The whole region is invisible to us in optical light because of the extensive amounts of absorbing, intervening dust. Other wavelengths, however, including the infrared, radio, and energetic X-rays, can penetrate the veiling material and enable us to study this unique environment.

    The supermassive black hole at a galaxy’s center is expected gradually to accumulate many small, stellar-mass black holes around it. In the case of our own galaxy, as many as 20,000 black holes may have settled around the central few light-years. So far, however, no such density cusp has been reported. One of the best ways to look for such black holes is via binary stars in which one member is stellar-mass black hole, because accretion around the black hole would generate detectable X-rays.

    CfA astronomer Jaesub Hong was a member of a six-person team that used the Chandra X-ray Observatory to search for such binaries. They examined the equivalent of several weeks worth of archival Chandra observations obtained over twelve years, in an area corresponding to a volume that stretches to about sixty light-years from the galactic nucleus. In this region, thousands of X-ray point sources are seen, produced by a range of processes including hot gas, stellar atmospheres, binaries with white dwarf star members, neutron stars, and black holes. The innermost region itself, out to about twelve light-years, has hundreds of sources. (For comparison, the nearest star to the Sun is four light-years away.) The X-ray energies of the sources can be used to diagnose their character, but in this dense complex source confusion was a challenge. To minimize the confusion, the team focused on relatively bright sources, about one hundred of them, and also used simulations as a reality check. They found that twelve of the sources in the central dozen light-years had relatively “soft” X-ray spectra consistent with these sources being black-hole binaries. Although some alternative explanations cannot be ruled out (for example, a class of pulsars), the observed X-ray properties of these sources are the first strong evidence for the population of black hole binaries predicted to settle near the galactic center. The results suggest there are a larger number of (still undetected) isolated BHs present, and not least emphasize the complex and fascinating nature of this unique location in our galaxy.

    Science paper:
    A Density Cusp of Quiescent X-Ray Binaries in the Central Parsec of the Galaxy. Nature

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    stem

    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.

     
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
%d bloggers like this: