SAO: Weekly Science Updates 2017

Find out the latest thinking about our universe.
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SAO: Weekly Science Updates 2017

Postby bystander » Tue Jan 10, 2017 6:18 pm

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Outflowing Gas in Ultraluminous Galaxies

Postby bystander » Tue Jan 10, 2017 6:27 pm

Outflowing Gas in Ultraluminous Galaxies
Smithsonian Astrophysical Observatory
Weekly Science Update | 2017 Jan 06

Galaxies evolve over billions of years in part through the activity of star formation and their supermassive nuclear black holes, and also by mergers with other galaxies. Some features of galaxies, in particular the strong correlations found between the mass of the central black hole and properties like galaxy velocity structure or luminosity, imply a fundamental connection between the growth of the nuclear black hole and the assembly of stars on a global scale. Feedback of some kind is therefore expected to explain these tight correlations, and astronomers have been working to identify and study it. One prominent suggestion for feedback is the presence of warm outflowing gas, powered by new stars but which would deplete the galaxy of the raw material needed for making new stars, and/or for enhancing the black hole mass.

In the 1990's, the Infrared Space Observatory (ISO) detected evidence for warm gas in luminous galaxies, the molecule OH, and the recent Herschel Space Observatory followed up those detections with velocity-resolved observations of six of the prominent OH far infrared lines. CfA astronomers Eduardo Gonzalez-Alfonso, Matt Ashby, and Howard Smith led a team of scientists reducing and modeling the four strong lines in fourteen ultra-luminous infrared galaxies (ULIRGs). The set of OH lines from ULIRGs is remarkable in that they appear sometimes in absorption, sometimes in emission, and sometimes with a bit of both depending on the particular line and velocity component. Many of these spectral features are characteristic of gas moving in an outflow, and the team has developed a radiative transfer model to deduce the geometry and kinematics of the flowing gas from the complex line shapes.

The scientists report that there are indeed powerful outflows in these ULIRGs, some with more than a thousand solar-masses per year and the power of a hundred billion Suns (a few percent of the total luminous energy of the galaxy). The typical time it would take for this gas to be blown out of the galaxy is only a few hundred million years, and the astronomers conclude that the outflows must occur erratically (not continuously), and are probably tied to the equally random flaring activity of the central black hole, which in turn can be linked to the gas motions induced by galaxy mergers.

Molecular Outflows in Local ULIRGs: Energetics from Multi-Transition OH Analysis - E. González-Alfonso et al
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Re: Outflowing Gas in Ultraluminous Galaxies

Postby geckzilla » Wed Jan 11, 2017 4:23 am

They left all the cosmic rays running through the chip gap... unfortunate...
Just call me "geck" because "zilla" is like a last name.

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A Catalog of Habitable Zone Exoplanets

Postby bystander » Thu Jan 19, 2017 3:44 pm

A Catalog of Habitable Zone Exoplanets
Smithsonian Astrophysical Observatory
Weekly Science Update | 2017 Jan 13

The last two decades have seen an explosion of detections of exoplanets, as the sensitivity to smaller planets has dramatically improved thanks especially to the Kepler mission. These discoveries have found that the frequency of planets increases to smaller sizes: terrestrial planets are more common than gas giants. The significance of a universe rich in terrestrial sized planets naturally leads to the question about the "habitable zone (HZ)" – the region around a star where a suitable planet could sustain the conditions necessary for life. In this zone, the balance between stellar radiation onto the planet and radiative cooling from the planet allows water on the surface to be a liquid. (The definition also includes consideration of the planet’s atmosphere and solid surface.)

In our solar system, the Earth is cozily situated in the middle of the habitable zone which, depending on the model, extends roughly from Venus to Mars. The Kepler mission has as one of its primary goals the determination of the frequency of terrestrial planets in their habitable zones. CfA astronomer Guillermo Torres and his colleagues have now produced a complete catalog of Kepler exoplanet candidates in their habitable zones from the Kepler data releases to date. After reviewing the various criteria for determining the boundaries of the HZ, they report there are 104 candidates within an optimistic (larger) HZ definition, and twenty within a more conservative (smaller) definition of the HZ and which also have radii less than two Earth-radii, making this group in particular potential "Earth-like" candidates. ...

A Catalog of Kepler Habitable Zone Exoplanet Candidates - Stephen R. Kane et al
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The Evolution of Massive Galaxy Clusters

Postby bystander » Sat Jan 21, 2017 4:04 pm

The Evolution of Massive Galaxy Clusters
Smithsonian Astrophysical Observatory
Weekly Science Update | 2017 Jan 20

Galaxy clusters have long been recognized as important laboratories for the study of galaxy formation and evolution. The advent of the new generation of millimeter and submillimeter wave survey telescopes, like the South Pole Telescope (SPT), has made it possible to identify faint galaxy clusters over large fractions of the sky using an effect first recognized by Rashid Sunyaev and Yakov Zel’dovich in 1969: When hot electrons in the cluster gas interact with light from the ubiquitous cosmic microwave background they increase its brightness very slightly.

SAO is a partner institution in the South Pole Telescope, which has been conducting a large survey covering about six percent of the whole sky with a sensitivity and angular resolution suitable for spotting galaxy clusters as far away as those from the epoch about four billion years after the big bang. One advantage of studying this sample of clusters is that because they have been identified from their hot gas signatures (rather than from the starlight of their member galaxies), the evolution of the cluster and its ensemble population is easier to disentangle.

CfA astronomer Brian Stalder and a team of colleagues used the SPT survey data to identify twenty-six of the most massive clusters known, each with a mass of over about a million billion solar-masses. They find that the clusters are broadly in agreement with the current thinking about the evolution of massive clusters and the stars in these galaxies. ...

Galaxy Populations in the 26 Most Massive Galaxy Clusters in the South Pole Telescope SPT-SZ Survey - A. Zenteno et al
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Radio Weak Blazars

Postby bystander » Sat Jan 28, 2017 4:35 pm

Radio Weak Blazars
Smithsonian Astrophysical Observatory
Weekly Science Update | 2017 Jan 27

A blazar is a galaxy whose central nucleus is bright at wavelengths from the low energy radio band to high energy gamma rays (each gamma ray photon is over a hundred million times more energetic than the X-rays seen by the Chandra X-ray Observatory). Astronomers think that the blazar nucleus contains a supermassive black hole, similar to a quasar nucleus. The emission results when matter falls onto the vicinity of the black hole and erupts into powerful, narrow jets of radiating charged particles moving close to the speed of light. Two defining characteristics of blazars, strong radio emission and high variability, are results of the accretion and jets.

Although the nuclei of other galaxies also eject jets of particles, the class of blazars is thought to result from our unique viewing angle: staring directly down the throats of these jets. The orientation makes these objects unique probes of exotic physical activity, with the relative intensities of the radiation providing key diagnostics. In most other galaxies, for example, infrared radiation comes from heated dust, but in blazars the infrared colors indicate that it comes from jet emission. Because the jet emission is so bright the underlying galaxy light can be masked, with the result that in the class of BL Lac blazars emission and absorption lines are not detected, making their distances difficult to determine.

CfA astronomers Raffaele D'Abrusco and Howard Smith and their four colleagues report discovering blazars that challenge this general paradigm. They found two BL Lac blazars with no apparent radio emission: "radio weak" BL Lacs. The astronomers discovered them by using the Fermi catalog of very high energy sources to identify a set of possible new blazars, and the WISE infrared sky catalog to reinforce the categorization and to pinpoint the locations of the sources in the sky. After searching radio catalogs for counterparts to the sources, they discovered two that had no detected radio emission. ...

Radio-Weak BL Lac Objects in the Fermi Era - F. Massaro et al
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A Massive Galaxy Long Ago and Far Away

Postby bystander » Mon Feb 06, 2017 6:08 pm

A Massive Galaxy Long Ago and Far Away
Smithsonian Astrophysical Observatory
Weekly Science Update | 2017 Feb 03

Galaxies today fall roughly into two categories: elliptically-shaped collections of reddish, old stars that formed predominantly during a period early in the history of the universe, and spiral shaped objects dominated by blue, young stars. The Milky Way is an example of the latter, a spiral galaxy actively making new stars. In order to understand the growth of galaxies over cosmic time and the past star formation history of the universe, astronomers study the population of old stars in distant ellipticals from earlier epochs, stars which in turn formed at an even early time. Star formation produces supernovae which enrich their environments with elements, including the diagnostic element magnesium. Measuring the amount of magnesium (relative to iron) in a galaxy thus helps to fix the strength and duration of prior episodes of star formation.

CfA astronomers Charlie Conroy and Jieun Choi and eight colleagues used the spectrometer on the Keck telescope (along with some secondary datasets) to obtain very sensitive magnesium measurements in one of the most massive and luminous elliptical galaxies known. The galaxy, seen at an epoch only three billion years after the big bang, has a stellar mass of about three hundred billion solar-masses (the Milky Way’s stellar mass is about ten times less) but is currently making stars at a rate only about half that of the Milky Way. However, it's magnesium-to-iron ratio indicates that earlier in its life it was making stars at a phenomenally high rate, perhaps as many as several thousand solar-masses each year, making it one of the most vigorous examples of star-formation known.

The scientists conclude that the bursts of star formation in this galaxy must have been due to mergers with other galaxies. In fact, they estimate that the object probably doubled in sized as a consequence of accreting smaller galaxies. Unfortunately this particular elliptical is so unusual that it cannot be considered a typical progenitor for any local elliptical galaxy. The team argues that additional observations of more, less extreme ellipticals in the early universe are now needed to fill in the rest of the story. The instruments on the James Webb Space Telescope, to be launched next year, should be capable of doing so.

A Massive, Quiescent, Population II Galaxy at a Redshift of 2.1 - Mariska Kriek et al
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The Lifetime of the Solar Nebula

Postby bystander » Fri Mar 03, 2017 5:24 pm

The Lifetime of the Solar Nebula
Smithsonian Astrophysical Observatory
Weekly Science Update | 2017 Feb 10

Very young stars host gaseous nebulae and protoplanetary disks where planetary systems form. The lifetimes of these disks place important constraints on the timescale of the planet formation, including the final sizes and eccentricities of the rocky terrestrial planets, and so it is a key parameter in the models. Observations of nearby young stellar objects suggest the timescales are typically short, under five million years, but such brief times are surprising because they would require very efficient mechanism(s) to transport material and disperse the disk. How they work is uncertain.

The evolution and dispersal of the gaseous nebula are closely connected to the nebula's magnetic fields. The magnetic fields transport angular momentum, driving disk accretion onto the central star. These processes also determine the structure of the solar nebula, as well as level of disk turbulence, and strongly affect many stages of planet formation. Information about the nebula's magnetic fields may be preserved in solid inclusions, the building blocks of planets and asteroids, and retrieved by analyzing certain types of meteorites, thus placing constraints on the lifetime of the solar nebula.

Angrites are among the oldest and most pristine known samples from meteorites, having cooled rapidly after the solar system was formed. They contain ferromagnetic grains that should have acquired a permanent magnetization if a magnetic field was present when they solidified, and so can be used to obtain direct, precisely dated measurements of the nebular field strength in the terrestrial planet–forming region. ...

Lifetime of the Solar Nebula Constrained by Meteorite Paleomagnetism - Huapei Wang et al

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Dating the Milky Way's Disc

Postby bystander » Fri Mar 03, 2017 5:34 pm

Dating the Milky Way's Disc
Smithsonian Astrophysical Observatory
Weekly Science Update | 2017 Feb 17

When a star like our sun gets to be very old, after another seven billion years or so, it will no longer be able to sustain burning its nuclear fuel. With only about half of its mass remaining, it will shrink to a fraction of its radius and become a white dwarf star. White dwarfs are common, the most famous one being the companion to the brightest star in the sky, Sirius. As remnants of some of the oldest stars in the galaxy, white dwarfs offer an independent means of dating the lifetimes of different galactic populations.

A globular cluster is a roughly spherical ensemble of stars (as many as several million) that are gravitationally bound together and typically located in the outer regions of galaxies. The white dwarf stars in the Milly Way's globular clusters reveal an age spread of between eleven and thirteen billion years. By contrast, the thick disk of the galaxy is thought to be older than ten billion years but that figure is not very well constrained. White dwarfs in the disc can be used to refine those age estimates and, since they are closer and brighter to us than those in globular clusters, they can provide more detailed information. However, they are not located in well-defined regions like clusters and so they are also harder to spot. ...

New Halo White Dwarf Candidates in the Sloan Digital Sky Survey - Kyra Dame et al
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Constraining the Chemistry of Carbon-Chain Molecules in Space

Postby bystander » Fri Mar 03, 2017 5:43 pm

Constraining the Chemistry of Carbon-Chain Molecules in Space
Smithsonian Astrophysical Observatory
Weekly Science Update | 2017 Feb 24

The interstellar medium of the Milky Way contains 5-10% of the total mass of the galaxy (excluding its dark matter) and consists primarily of hydrogen gas. There are small but important contributions from other gases as well, including carbon-bearing molecules both simple, like carbon monoxide and carbon dioxide, and complex like ethene, benzene, propynal, methanol and other alcohols, and cyanides. There are even some very large molecules like polycyclic aromatic hydrocarbons and buckyballs with fifty or more carbon atoms. Some species like the cyanides have relative abundances similar to what is seen in comets in our Solar System, suggesting that local carbon chemistry is not unique.

Astronomers think complex interstellar molecules are probably produced on dust grains, although some molecules might be produced in the gas phase. About one percent by mass of the interstellar material, these tiny grains are composed predominantly of silicates and provide the gas molecules with surfaces on which to react with other molecules. Carbon chain molecules are particularly interesting because they are thought to be the starting point for a significant fraction of the known complex chemicals in the interstellar medium. It is even suspected that carbon-chain species are a key stage in the formation of polycyclic aromatic hydrocarbons. Carbon-chain molecular chemistry thus provides insight into a large subset of interstellar chemistry. ...

Non-detection of HC11N towards TMC-1: Constraining the Chemistry of Large Carbon-Chain Molecules - Ryan A. Loomis et al
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Gravity Wave Detection with Atomic Clocks

Postby bystander » Fri Mar 03, 2017 5:55 pm

Gravity Wave Detection with Atomic Clocks
Smithsonian Astrophysical Observatory
Weekly Science Update | 2017 Mar 03

The recent detection of gravitation waves (GW) from the merger of two black holes of about thirty solar-masses each with the ground-based LIGO facility has generated renewed enthusiasm for developing even more sensitive measurement techniques. Ground-based GW instruments have widely spaced sensors that can detect sub-microscopic changes in their separation -- better than one part in a billion trillion, They suffer, however, from the noise produced by small ground tremors -- vibrations from natural or man-made sources that ripple through the precisely tuned detectors. The vibrations most difficult to compensate for are those that change relatively slowly, at frequencies around once a second or less, yet astronomers predict that GW sources producing these slow variations should be interesting and abundant, from compact stellar-mass binary stars to gravitational events in the early universe.

The CfA has long been renowned for its laboratory work producing some of the best precision devices in the world. In particular are its timekeeping hydrogen-maser clocks, used by NASA to track its satellites as well as by radio astronomers around the world to make precision measurements of cosmic phenomena using Very Long Baseline Interferometry. The CfA maser group has continued to develop advanced clock technologies over the years, and to turn them into new tools to probe the heavens, including recently the so-called "laser-combs" for ultraprecise measurement of stellar velocity shifts induced by extrasolar planets. ...

Gravitational Wave Detection with Optical Lattice Atomic Clocks - Shimon Kolkowitz et al
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Superluminous Supernovae

Postby bystander » Fri Mar 10, 2017 4:10 pm

Superluminous Supernovae
Smithsonian Astrophysical Observatory
Weekly Science Update | 2017 Mar 10

Supernovae, the explosive deaths of massive stars, are among the most momentous events in the cosmos because they disburse into space all of the chemical elements that were produced inside their progenitor stars, including the elements essential for making planets and life. Their bright emission also enables them to be used as probes of the very distant universe. Not least, supernovae are astrophysical laboratories for the study of very energetic phenomena. One class of supernovae consists of single stars whose mass is at least eight solar masses as they finish their lives.

A typical supernova shines about as brightly as ten billion Suns at its peak. In the last decade, a new type of supernova was discovered that is ten to one hundred times more luminous than a normal massive stellar collapse supernova, and today over a dozen of these superluminous supernovae (SLSN) have been seen. Astronomers are in agreement that these objects come from the collapse of massive stars, but their tremendous luminosities cannot be explained by the usual physical mechanisms invoked. Instead, the debate has centered on whether the excess emission results from an external source, for example the interaction of material ejected from the explosion with a circumstellar shell, or instead by some kind of powerful internal engine such as a highly magnetized, spinning neutron star.

The SLSN "Gaia6apd" was discovered by the European Gaia satellite, and at a distance of about one and one-half billion light-years it is the second-closest SLSN discovered to date. It is also special in another way: it is extraordinarily bright in the ultraviolet, nearly four times brighter than the next nearest known SLSN despite the fact that in the optical both have comparable luminosities. ...

An Ultraviolet Excess in the Superluminous Supernova Gaia16apd Reveals a Powerful Central Engine - M. Nicholl et al
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Textured Dust Storms on Mars

Postby bystander » Wed Mar 22, 2017 4:44 pm

Textured Dust Storms on Mars
Smithsonian Astrophysical Observatory
Weekly Science Update | 2017 Mar 17
Astronomers studying Mars first noted the presence of yellow clouds on its surface in the 1870's. Today these windblown dust storms on Mars are well known, and can span local, regional or even global in scale. Storms can display visible structures, sometimes periodic with wavelike features, or in other cases streaky or plume-like. Storms with structures are called "textured dust storms" and they result from strong winds or other meteorological effects that lift dust into the Martian atmosphere. In addition to obscuring views of the Martian surface, the dust can affect atmospheric heating and other climatic processes. These dust storms, despite having been studied for more than a century, remain rather mysterious. It is not understood, for example, how textured storms are distributed over the surface of the planet, when their frequency peaks, or how much dust is actually swept up.

CfA astronomer Huiqun Wang and two colleagues have been using the Mars Global Surveyor (MGS) images to analyze textured dust storms. Launched in 1999, MGS has provided about four Mars-years of daily global data that are particularly suitable for studying various aspects of clouds and dust storms. The new analysis focuses on the dust storms that occurred between May 1999 and October 2006, including a global dust storm in June 2001. There were 3955 textured dust storms during these periods. The scientists manually mark the position of each textured dust storm in the MGS image, and categorize its texture into one of three new categories they have developed: pebbled textures, characterized by a granular or crinkled appearance suggestive of strong turbulence, puffy textures with a bubbling appearance and cotton-like structures analogous to cumulus clouds indicative of vertical motions, and plume-like textures composed of multiple parallel elongated features suggestive of dust being uplifted and carried downstream by strong winds.

The scientists find that these three texture types have preferred seasons and distinctive locations; puffy storms, for example, tend to appear in the low latitudes and might therefore result from vertical convective winds there. Pebbled storms occur more frequently in the southern mid-latitudes implying that these zones are more turbulent than the northern mid/high-latitudes. The new results suggest links between storm texture type and meteorological conditions that can lead to improved understanding of the Martian climate. ...

The Seasonal and Spatial Distribution of Textured Dust Storms
Observed by Mars Global Surveyor Mars Orbiter Camera
- Laura Kulowski et al
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Re: Superluminous Supernovae

Postby Ann » Thu Mar 23, 2017 1:23 am

bystander wrote:Superluminous Supernovae
Smithsonian Astrophysical Observatory
Weekly Science Update | 2017 Mar 10

Supernovae, the explosive deaths of massive stars, are among the most momentous events in the cosmos because they disburse into space all of the chemical elements that were produced inside their progenitor stars, including the elements essential for making planets and life. Their bright emission also enables them to be used as probes of the very distant universe. Not least, supernovae are astrophysical laboratories for the study of very energetic phenomena. One class of supernovae consists of single stars whose mass is at least eight solar masses as they finish their lives.

A typical supernova shines about as brightly as ten billion Suns at its peak. In the last decade, a new type of supernova was discovered that is ten to one hundred times more luminous than a normal massive stellar collapse supernova, and today over a dozen of these superluminous supernovae (SLSN) have been seen. Astronomers are in agreement that these objects come from the collapse of massive stars, but their tremendous luminosities cannot be explained by the usual physical mechanisms invoked. Instead, the debate has centered on whether the excess emission results from an external source, for example the interaction of material ejected from the explosion with a circumstellar shell, or instead by some kind of powerful internal engine such as a highly magnetized, spinning neutron star.

The SLSN "Gaia6apd" was discovered by the European Gaia satellite, and at a distance of about one and one-half billion light-years it is the second-closest SLSN discovered to date. It is also special in another way: it is extraordinarily bright in the ultraviolet, nearly four times brighter than the next nearest known SLSN despite the fact that in the optical both have comparable luminosities. ...



Smithsonian Astrophysical Observatory wrote:
The SLSN "Gaia6apd" was discovered by the European Gaia satellite, and at a distance of about one and one-half billion light-years it is the second-closest SLSN discovered to date. It is also special in another way: it is extraordinarily bright in the ultraviolet, nearly four times brighter than the next nearest known SLSN despite the fact that in the optical both have comparable luminosities.
...
The scientists review all the known data and conclude that the most likely source is an internal central engine like a rapidly spinning neutron star. They also emphasize the key role that UV wavelengths played in diagnosing the mechanisms and urge that future studies of SLSN include UV coverage.


I really, really hope that good-quality UV observations will still be made in the coming age of James Webb Infrared Telescope (and planned manned missions to Mars).

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The Fate of Exomoons

Postby bystander » Fri Mar 24, 2017 3:47 pm

The Fate of Exomoons
Smithsonian Astrophysical Observatory
Weekly Science Update | 2017 Mar 24

When a star like our sun gets to be very old, after another seven billion years or so, it will shrink to a fraction of its radius and become a white dwarf star, no longer able to sustain nuclear burning. Studying the older planetary systems around white dwarfs provides clues to the long-term fate of our Sun and its planetary system. The atmosphere of a white dwarf star is expected to break up any material that accretes onto it into the constituent chemical elements and then to stratify them according to their atomic weights. The result is that the visible, uppermost layers of the atmosphere of a white dwarf should contain only a combination of hydrogen, helium (and some carbon). About one thousand white dwarf stars, however, show evidence in their spectra of pollution by some form of rocky material. This suggests that there is frequent, ongoing accretion onto these white dwarf stars of fragmentary material coming from somewhere - the precise origins are not clear.

CfA astronomers Matt Payne and Matt Holman, with two colleagues, have completed a series of simulations of the late evolution of planetary systems to try to understand where this material might be coming from. It was already known that the moons of planets can be easily knocked out of their orbits during planet-planet interactions in white dwarf systems. The question was whether these freed moons might themselves accrete onto the star to provide the polluting elements, or whether they might act to scatter asteroids towards the star. The difficulty has been the computational limits of simulating a complex evolving system that included the moons around planets. ...

The Fate of Exomoons in White Dwarf Planetary Systems - Matthew J. Payne et al
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