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News Article | February 15, 2017
Site: spaceref.com

Fast radio bursts (FRBs) are brief spurts of radio emission, lasting just one-thousandth of a second, whose origins are mysterious. Fewer than two dozen have been identified in the past decade using giant radio telescopes such as the 1,000-foot dish in Arecibo, Puerto Rico. Of those, only one has been pinpointed to originate from a galaxy about 3 billion light-years away. The other known FRBs seem to also come from distant galaxies, but there is no obvious reason that, every once in a while, an FRB wouldn't occur in our own Milky Way galaxy too. If it did, astronomers suggest that it would be "loud" enough that a global network of cell phones or small radio receivers could "hear" it. "The search for nearby fast radio bursts offers an opportunity for citizen scientists to help astronomers find and study one of the newest species in the galactic zoo," says theorist Avi Loeb of the Harvard-Smithsonian Center for Astrophysics (CfA). Previous FRBs were detected at radio frequencies that match those used by cell phones, Wi-Fi, and similar devices. Consumers could potentially download a free smartphone app that would run in the background, monitoring appropriate frequencies and sending the data to a central processing facility. "An FRB in the Milky Way, essentially in our own back yard, would wash over the entire planet at once. If thousands of cell phones picked up a radio blip at nearly the same time, that would be a good sign that we've found a real event," explains lead author Dan Maoz of Tel Aviv University. Finding a Milky Way FRB might require some patience. Based on the few, more distant ones, that have been spotted so far, Maoz and Loeb estimate that a new one might pop off in the Milky Way once every 30 to 1,500 years. However, given that some FRBs are known to burst repeatedly, perhaps for decades or even centuries, there might be one alive in the Milky Way today. If so, success could become a yearly or even weekly event. A dedicated network of specialized detectors could be even more helpful in the search for a nearby FRB. For as little as $10 each, off-the-shelf devices that plug into the USB port of a laptop or desktop computer can be purchased. If thousands of such detectors were deployed around the world, especially in areas relatively free from Earthly radio interference, then finding a close FRB might just be a matter of time. This work has been accepted for publication in the Monthly Notices of the Royal Astronomical Society and is available online. Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe. Please follow SpaceRef on Twitter and Like us on Facebook.


Kenyon S.J.,Smithsonian Astrophysical Observatory | Bromley B.C.,University of Utah
Astrophysical Journal, Supplement Series | Year: 2010

We describe comprehensive calculations of the formation of icy planets and debris disks at 30-150 AU around 1-3M · stars. Disks composed of large, strong planetesimals produce more massive planets than disks composed of small, weak planetesimals. The maximum radius of icy planets ranges from ∼ 1500km to 11,500km. The formation rate of 1000km objects - "Plutos" - is a useful proxy for the efficiency of icy planet formation. Plutos form more efficiently in massive disks, in disks with small planetesimals, and in disks with a range of planetesimal sizes. Although Plutos form throughout massive disks, Pluto production is usually concentrated in the inner disk. Despite the large number of Plutos produced in many calculations, icy planet formation is inefficient. At the end of the main sequence lifetime of the central star, Plutos contain less than 10% of the initial mass in solid material. This conclusion is independent of the initial mass in the disk or the properties of the planetesimals. Debris disk formation coincides with the formation of planetary systems containing Plutos. As Plutos form, they stir leftover planetesimals to large velocities. A cascade of collisions then grinds the leftovers to dust, forming an observable debris disk. In disks with small (≲1-10km) planetesimals, collisional cascades produce luminous debris disks with maximum luminosity ∼ 10-2 times the stellar luminosity. Disks with larger planetesimals produce debris disks with maximum luminosity 5 × 10-4 (10km) to ∼ 5 × 10-5 (100km) times the stellar luminosity. Following peak luminosity, the evolution of the debris disk emission is roughly a power law, f α t -n with n ≈ 0.6-0.8. Observations of debris disks around A-type and G-type stars strongly favor models with small planetesimals. In these models, our predictions for the time evolution and detection frequency of debris disks agree with published observations. We suggest several critical observations that can test key features of our calculations. © 2010. The American Astronomical Society. All rights reserved.


Kenyon S.J.,Smithsonian Astrophysical Observatory | Bromley B.C.,University of Utah
Astronomical Journal | Year: 2014

Motivated by the New Horizons mission, we consider how Pluto's small satellites - currently Styx, Nix, Kerberos, and Hydra - grow in debris from the giant impact that forms the Pluto-Charon binary. After the impact, Pluto and Charon accrete some of the debris and eject the rest from the binary orbit. During the ejection, high-velocity collisions among debris particles produce a collisional cascade, leading to the ejection of some debris from the system and enabling the remaining debris particles to find stable orbits around the binary. Our numerical simulations of coagulation and migration show that collisional evolution within a ring or a disk of debris leads to a few small satellites orbiting Pluto-Charon. These simulations are the first to demonstrate migration-induced mergers within a particle disk. The final satellite masses correlate with the initial disk mass. More massive disks tend to produce fewer satellites. For the current properties of the satellites, our results strongly favor initial debris masses of 3-10 × 1019g and current satellite albedos A 0.4-1.We also predict an ensemble of smaller satellites,R ≲1-3 km, and very small particles, R 1-100 cm and optical depth τ ≲ 10-10. These objects should have semimajor axes outside the current orbit of Hydra. © 2014.The American Astronomical Society.All rights reserved.


Bromley B.C.,University of Utah | Kenyon S.J.,Smithsonian Astrophysical Observatory
Astrophysical Journal | Year: 2011

Planetary migration poses a serious challenge to theories of planet formation. In gaseous and planetesimal disks, migration can remove planets as quickly as they form. To explore migration in a planetesimal disk, we combine analytic and numerical approaches. After deriving general analytic migration rates for isolated planets, we use N-body simulations to confirm these results for fast and slow migration modes. Migration rates scale as m -1 (for massive planets) and (1 + (e H/3)3)-1, where m is the mass of a planet and e H is the eccentricity of the background planetesimals in Hill units. When multiple planets stir the disk, our simulations yield the new result that large-scale migration ceases. Thus, growing planets do not migrate through planetesimal disks. To extend these results to migration in gaseous disks, we compare physical interactions and rates. Although migration through a gaseous disk is an important issue for the formation of gas giants, we conclude that migration has little impact on the formation of terrestrial planets. © 2011. The American Astronomical Society. All rights reserved..


Bromley B.C.,University of Utah | Kenyon S.J.,Smithsonian Astrophysical Observatory
Astrophysical Journal | Year: 2011

We describe an updated version of our hybrid N-body-coagulation code for planet formation. In addition to the features of our 2006-2008 code, our treatment now includes algorithms for the one-dimensional evolution of the viscous disk, the accretion of small particles in planetary atmospheres, gas accretion onto massive cores, and theresponse of N-bodies to the gravitational potential of the gaseous disk and the swarm of planetesimals. To validate the N-body portion of the algorithm, we use a battery of tests in planetary dynamics. As a first application of the complete code, we consider the evolution of Pluto-mass planetesimals in a swarm of 0.1-1 cm pebbles. In a typical evolution time of 1-3 Myr, our calculations transform 0.01-0.1 M ⊙ disks of gas and dust into planetary systems containing super-Earths, Saturns, and Jupiters. Low-mass planets form more often than massive planets; disks with smaller α form more massive planets than disks with larger α. For Jupiter-mass planets, masses of solid cores are 10-100 M ⊕. © 2011. The American Astronomical Society. All rights reserved.


Schwartz D.A.,Smithsonian Astrophysical Observatory
Review of Scientific Instruments | Year: 2014

The Chandra X-ray Observatory is an orbiting x-ray telescope facility. It is one of the National Aeronautics and Space Administration's four "Great Observatories" that collectively have carried out astronomical observations covering the infrared through gamma-ray portion of the electromagnetic spectrum. Chandra is used by astronomers world-wide to acquire imaging and spectroscopic data over a nominal 0.1-10 keV (124-1.24 Å) range. We describe the three major parts of the observatory: the telescope, the spacecraft systems, and the science instruments. This article will emphasize features of the design and development driven by some of the experimental considerations unique to x-ray astronomy. We will update the on-orbit performance and present examples of the scientific highlights. © 2014 AIP Publishing LLC.


Drake J.J.,Smithsonian Astrophysical Observatory
Astrophysical Journal | Year: 2011

An analysis using modern atomic data of fluxes culled from the literature for O VIII and Ne IX lines observed in solar active regions by the P78 and Solar Maximum Mission satellites confirms that the coronal Ne/O abundance ratio varies by a factor of two or more, and finds an increase in Ne/O with increasing active region plasma temperature. The latter is reminiscent of evidence for increasing Ne/O with stellar activity in low-activity coronae that reaches a "neon saturation" in moderately active stars at approximately twice the historically accepted solar value of about 0.15 by number. We argue that neon saturation represents the underlying stellar photospheric compositions, and that low-activity coronae, including that of the Sun, are generally depleted in neon. The implication would be that the solar Ne/O abundance ratio should be revised upward by a factor of about two to n(Ne)/n(O) ∼ 0.3. Diverse observations of neon in the local cosmos provide some support for such a revision. Neon would still be of some relevance for reconciling helioseismology with solar models computed using recently advocated chemical mixtures with lower metal content. © 2011 The American Astronomical Society. All rights reserved.


Kim D.-W.,Smithsonian Astrophysical Observatory | Fabbiano G.,Smithsonian Astrophysical Observatory
Astrophysical Journal | Year: 2010

We have compared the combined X-ray luminosity function (XLF) of low-mass X-ray binaries (LMXBs) detected in Chandra observations of young, post-merger elliptical galaxies with that of typical old elliptical galaxies.We find that the XLF of the "young" sample does not present the prominent high-luminosity break at LX > 5 × 1038 erg s -1 found in the old elliptical galaxy XLF. The "young" and "old" XLFs differ with a 3s statistical significance (with a probability less than 0.2% that they derive from the same underlying parent distribution). Young elliptical galaxies host a larger fraction of luminous LMXBs (LX > 5 × 1038 erg s-1) than old elliptical galaxies and the XLF of the young galaxy sample is intermediate between that of typical old elliptical galaxies and that of star-forming galaxies. This observational evidence may be related to the last major/minor mergers and the associated star formation. © 2010. The American Astronomical Society. All rights reserved.


Kim D.-W.,Smithsonian Astrophysical Observatory | Fabbiano G.,Smithsonian Astrophysical Observatory
Astrophysical Journal | Year: 2013

We have revisited the X-ray scaling relations of early-type galaxies (ETG) by investigating, for the first time, the L X,Gas-M Total relation in a sample of 14 ETGs. In contrast to the large scatter (a factor of 102-103) in the L X,Total-L B relation, we found a tight correlation between these physically motivated quantities with an rms deviation of a factor of three in L X,Gas = 1038-1043 erg s-1 or M Total = a few × 1010 to a few × 1012 M⊙. More striking, this relation becomes even tighter with an rms deviation of a factor of 1.3 among the gas-rich galaxies (with L X,Gas > 10 40 erg s-1). In a simple power-law form, the new relation is (L X,Gas/1040 erg s-1) = (M Total/3.2 × 1011 M⊙)3. This relation is also consistent with the steep relation between the gas luminosity and temperature, L X,Gas ∼ T Gas 4.5, identified by Boroson et al., if the gas is virialized. Our results indicate that the total mass of an ETG is the primary factor in regulating the amount of hot gas. Among the gas-poor galaxies (with L X,Gas < a few × 1039 erg s-1), the scatter in the L X,Gas-MTotal (and L X,Gas-T Gas) relation increases, suggesting⊙ that secondary factors (e.g., rotation, flattening, star formation history, cold gas, environment, etc.) may become important. © 2013. The American Astronomical Society. All rights reserved.


Bookbindera J.,Smithsonian Astrophysical Observatory
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

The International X-ray Observatory (IXO) project is the result of a merger between the NASA Con-X and ESA/JAXA XEUS mission concepts. A facility-class mission, IXO will address the leading astrophysical questions in the "hot universe" through its breakthrough optics with 20 times more collecting area at 1 keV than any previous X-ray observatory, its 3 m2 collecting area with 5 arcsec angular resolution will be achieved using a 20m focal length deployable optical bench. To reduce risk, two independent optics technologies are currently under development in the U.S. and in Europe. Focal plane instruments will deliver a 100-fold increase in effective area for high-resolution spectroscopy, deep spectral imaging over a wide field of view, unprecedented polarimetric sensitivity, microsecond spectroscopic timing, and high count rate capability. IXO covers the 0.1-40 keV energy range, complementing the capabilities of the next generation observatories, such as ALMA, LSST, JWST, and 30-m ground-based telescopes. These capabilities will enable studies of a broad range of scientific questions such as what happens close to a black hole, how supermassive black holes grow, how large scale structure forms, and what are the connections between these processes? This paper presents an overview of the IXO mission science drivers, its optics and instrumental capabilities, the status of its technology development programs, and the mission implementation approach. © 2010 SPIE.

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