SAO: Weekly Science Updates 2015

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SAO: Weekly Science Updates 2015

Post by bystander » Sat Jan 17, 2015 3:23 pm

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SAO: Effect of Starlight on the Atmospheres of Mini-Neptunes

Post by bystander » Sat Jan 17, 2015 3:44 pm

The Effect of Starlight on the Atmospheres of Mini-Neptunes
Harvard-Smithsonian Center for Astrophysics
Smithsonian Astrophysical Observatory
Weekly Science Update | 2015 Jan 02
Exoplanet surveys have discovered the first planets with sizes between 2 and 3.5 Earth radii -- slightly smaller than the size of the planet Neptune in our solar system. These planets, dubbed "mini-Neptunes," have been spotted so far around five low mass stars, but since low mass stars are the most common stars in the universe, and since mini-Neptunes are also expected to be abundant around them, astronomers anticipate finding many more mini-Neptunes in the near future.

Since low-mass stars in general are redder than the Sun, and have lower surface temperatures, most of their flux is emitted in the optical and near-IR. Some of them, however, have active atmospheres that emit copiously in the ultraviolet. A star's ultraviolet radiation can have a significant effect on the atmosphere of any orbiting planets by dissociating molecules and thereby altering the atmospheric chemistry. Astronomers have calculated these effects for a few kinds of exoplanets, but the case of mini-Neptunes has never been explored. Since it now looks like they are likely to be abundant, CfA astronomers Lisa Kaltenegger and Sarah Rugheimer and two colleagues have calculated what happens when they are exposed to stellar ultraviolet, and compared their results to the atmosphere in one of the observed objects, the min-Neptune GJ436b, a relatively cool exoplanet with a surface temperature of about 640 kelvin. ...

The effect of Lyman α radiation on mini-Neptune atmospheres around M stars: application to GJ 436b - Yamila Miguel et al
http://asterisk.apod.com/viewtopic.php?t=19154
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SAO: High-Speed Jets from a Possible New Class of Galaxy

Post by bystander » Sat Jan 17, 2015 4:04 pm

High-Speed Jets from a Possible New Class of Galaxy
Harvard-Smithsonian Center for Astrophysics
Smithsonian Astrophysical Observatory
Weekly Science Update | 2015 Jan 09
Seyfert galaxies are similar to spiral galaxies except that they have extraordinarily prominent, bright nuclei, sometimes as luminous as 100 billion Suns. Their huge energies are thought to be generated as matter falls towards a central supermassive black hole and accretes onto a circumnuclear disk around it. Observations distinguish between two types of Seyferts: those whose nuclear emission appears to be slightly obscured, thought to be the result of viewing the galaxy edge-on through an obscuring disk, and those seen face-on.

Bipolar jets of charged particles moving at relativistic speeds are the most powerful manifestation of the energy release by supermassive black holes. In about 15 per cent of objects, the accretion disc is at the base of a bipolar outflow of such a relativistic plasma. The jets can extend well beyond the host galaxy, producing spectacular lobes of plasma most prominently detected at radio wavelengths but detectable across the entire electromagnetic spectrum. In those cases where the galaxy is seen face-on, and the jet axis is closely aligned with our line of sight, relativistic effects make the jet radiation exceptionally intense and dramatic, with extremely high energy X-ray and gamma-ray light. Since strong radio galaxies are typically seen edge-on (or at somewhat larger angles with the full extent of the outflow observed on the sky), only a small fraction of radio galaxies are observed to have high energy gamma rays.

In 2008, the Fermi satellite discovered high energy gamma ray emission coming from a radio-bright, edge-on Seyfert, PMNJ0948+0022, suggesting the presence of a possible new class of supermassive black hole nucleus. Since then four other examples have been found. ...

The most powerful flaring activity from the NLSy1 PMN J0948+0022 - F. D'Ammando et al
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SAO: The Cosmic Seeds of Black Holes

Post by bystander » Sat Jan 17, 2015 4:19 pm

The Cosmic Seeds of Black Holes
Harvard-Smithsonian Center for Astrophysics
Smithsonian Astrophysical Observatory
Weekly Science Update | 2015 Jan 16
Supermassive black holes with millions or billions of solar-masses of material are found at the nuclei of most galaxies. During the embryonic stages of these galaxies they are thought to play an important role, acting as seeds around which material collected. During the later lifetime of galaxies they can power dramatic outflowing jets of material (among other phenomena) as infalling dust and gas accretes onto the disks that typically surround them. These active, later phases of supermassive black holes can result in turning galaxies into an extremely bright objects like quasars, whose luminosities allow them to be seen at cosmic distances. In fact, quasars have recently been detected from eras less than a billion years after the big bang.

But where do all these black holes come from – especially the ones present in the early universe!? The explosive death of massive stars, one nominal route, can take many hundreds of millions of years while the star itself coalesces from ambient gas and then evolves, after which material must be added to the black hole seed to grow it into a supermassive monster. It is not clear that there is enough time in the early universe for this to happen. A second method has been proposed for these cosmic seeds, the direct collapse of primordial gas into seedlings that are much more massive – about ten thousand solar-masses - than are those present in stellar ashes. ...

Formation of massive protostars in atomic cooling haloes - Fernando Becerra et al
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SAO: A Recoiling, Supermassive Black Hole

Post by bystander » Sat Jan 24, 2015 5:55 pm

A Recoiling, Supermassive Black Hole
Harvard-Smithsonian Center for Astrophysics
Smithsonian Astrophysical Observatory
Weekly Science Update | 2015 Jan 23
When galaxies collide, the central supermassive black holes that reside at their cores will end up orbiting one another in a binary pair, at least according to current simulations. Einstein's general theory of relativity predicts that masses in a binary system should radiate gravitational waves, analogous to the way that accelerating electrical charges radiate electromagnetic waves but very much weaker.

As they radiate away their energy in these waves, orbiting black holes will gradually come closer together until eventually they merge in a coalescence event that is expected to emit a strong burst of gravitational waves. Relativity predicts that the gravitational radiation from black hole coalescence will be preferentially emitted in one direction that depends on the spin- and mass-ratios of the two black holes. In order to conserve momentum, therefore, the newly formed single supermassive black hole will recoil. Indeed, recoiling supermassive black holes are predicted to be one of the key observable signatures of such binary mergers. As they speed away from the center of the galaxy, they are expected to carry along with them their local environments (the discs and hot gas regions).

Amazingly, a few of these bizarre, recoiling candidates have apparently been serendipitously spotted (they are so far only candidates because their character is not yet confirmed). One of them is an X-ray source known as CID-42, which the Hubble Space Telescope resolves into two bright components only a few thousand light-years apart (a relatively small distance in galactic terms). ...

New insights from deep VLA data on the potentially recoiling black hole CID-42 in the COSMOS field - Mladen Novak et al
http://asterisk.apod.com/viewtopic.php?t=28804
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SAO: An Infrared Atlas of Interacting Galaxies

Post by bystander » Tue Feb 03, 2015 6:44 pm

An Infrared Atlas of Interacting Galaxies
Harvard-Smithsonian Center for Astrophysics
Smithsonian Astrophysical Observatory
Weekly Science Update | 2015 Jan 30
[img3="Spitzer View of the Spiral Galaxy M51 ("Whirlpool Galaxy")
The two interacting galaxies M51A and M51B as seen in the infrared by the Spitzer Space Telescope. Emission from warm dust appears in red, and stellar emission in blue. A new Spitzer study of 103 nearby interacting galaxies in many different stages of merging systematically examines their star formation activity.
Credit: NASA/JPL-Caltech/R. Kennicutt (Univ. of Arizona)"]http://www.spitzer.caltech.edu/uploaded ... a2_Med.jpg[/img3]
Most galaxies, including our own Milky Way, have been influenced by an interaction with another galaxy at some time in their past. Interactions between galaxies can trigger an increase in star-formation activity as well an increased level of activity around the nuclear black hole. These general behaviors have been reproduced in simulations of merging galaxies, lending confidence to our understanding of the physical mechanisms at work. But not all interactions lead to such enhancements, and the reasons are not well understood; meanwhile the strength of the triggering mechanism(s) and many other details remain puzzling.

Numerous studies have been conducted to observe the evolution of galaxies undergoing interactions. Merging galaxies have typically been identified either through their disturbed morphology (such as tidal tails and bridges), their infrared brightness (triggered star formation increases the infrared luminosity), or simply because they are close together. The first two methods presuppose the effects, and so tend to have selection biases especially since some distortions may be hard to see (for example, if the galaxies are far away or in the very early stages of merger) while infrared luminosity might in principle be caused by some other phenomena.

CfA astronomers ... have taken the third route, and used the Spitzer Space Telescope to compile and analyze a set of four-color infrared images of 103 nearby galaxies in forty-eight merging systems of all kinds based solely on their separations (with a distance and optical brightness limit imposed), ranging from early to late stages of merging, from low to high mass, and from relatively dim to very bright (galaxies with active nuclei were excluded from this set). The result is an unbiased and statistically meaningful sample that does not neglect mergers just because they are faint or lack visible signs of disturbance.

The scientists use optical data to classify the systems into approximate evolutionary sequences, with the infrared data tracing faintly emitting dust features and providing a measure of the star formation activity underway. They report that, when compared with non-interacting field galaxies, the star formation rate does indeed increase in merging spirals, but that the efficiency of star formation does not appear to increase much as the merger progresses, at least in this limited sample. They also report that systems exhibiting clear morphological distortions do make stars more efficiently than do non-disturbed systems. The new atlas of interacting galaxies that the team has produced, when supplemented with multiwavelength datasets and new simulations, will enable future unbiased studies of colliding galaxies.

The Spitzer Interacting Galaxies Survey: A mid-infrared atlas of star-formation - N. J. Brassington et al
  • Astrophysical Journal (in press 2015)
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SAO: The Ages of Sun-Like Stars

Post by bystander » Mon Feb 09, 2015 7:00 pm

The Ages of Sun-Like Stars
Harvard-Smithsonian Center for Astrophysics
Smithsonian Astrophysical Observatory
Weekly Science Update | 2015 Feb 06
The mass of a star is perhaps its most significant feature. It determines how brightly it shines (a star ten times more massive than the Sun will, during its normal lifetime, shine about forty million times brighter than a star ten times less massive than the Sun), how long it will live (tens of millions of years versus tens of billions of years, respectively, for these two cases), and how it will eventually die (as a supernova or as slowly cooling clump of ashes). The next most significant property of a star is its age, which fixes its current character, the age of its planetary system, and the evolutionary state of its environment, and moreover which can be used to refine details in the theory of how stars evolve.

Unfortunately the ages of the most common stars -- the modest-mass, cool stars like the Sun and smaller -- are difficult to obtain. Traditional dating methods use stellar properties that either change very little as the stars ages or else are hard to determine. Rotation provides an important alternative. Stars rotate (the Sun rotates once approximately every 26 days), and astronomers know that the rotation rate of a cool star decreases with time. Rotation can provide a reliable determinant of stellar age if it can be properly calibrated, in particular across a range of stellar masses. Stars in clusters make perfect reference objects because they all apparently have a similar age. Such age calibrations have indeed, been done, but so far only for stars in clusters less than about one billion years old, not older. This is in part because young stars lose their spin very rapidly as they age, primarily via magnetically powered winds that carry away angular momentum, and after about 600 million years there is a well-defined mass-rotation relationship. The Hyades cluster of stars is about this age, and it has been used to fix the rotation parameters for this young age group. At the older end of the calibration sequence the Sun, at 4.6 billion years, has a well known rotation period. What has been missing is accurate rotation information for the ages in between. ...

A spin-down clock for cool stars from observations of a 2.5-billion-year-old cluster - Soren Meibom et al
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SAO: Embryos of Stars

Post by bystander » Fri Feb 13, 2015 5:27 pm

Embryos of Stars
Harvard-Smithsonian Center for Astrophysics
Smithsonian Astrophysical Observatory
Weekly Science Update | 2015 Feb 13
Stars like the Sun begin their lives as cold, dense cores of dust and gas that gradually collapse under the influence of gravity until nuclear fusion is ignited. Exactly how the critical collapse process occurs in these embryos, however, is poorly understood, with several competing ideas having been advanced. Material might just freely fall to the center, although in more likely scenarios the infall is inhibited by pressure from warm gas, turbulent motions, magnetic fields, or even perhaps by some combination of them. It might be possible to distinguish between these alternative collapse hypotheses by examining how the core's density varies with radius, but it turns out that (at least for spherical clouds) the predicted density distributions all look about the same. The predicted distributions of velocity for the infalling gas, however, are quite different.

The dust in these cores makes them completely opaque in the optical, and so studying their behaviors requires techniques at other wavelengths. One of the most exciting developments in astronomy over the past decade has been the development of far-infrared and millimeter wavelength tools for the tasks of identifying pre-stellar cores as such, and determining their properties. ...

The Dynamics of Collapsing Cores and Star Formation - Eric Keto, Paola Caselli, Jonathan Rawlings
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SAO: Quadruplets in a Stellar Womb

Post by bystander » Mon Feb 23, 2015 4:17 pm

Quadruplets in a Stellar Womb
Harvard-Smithsonian Center for Astrophysics
Smithsonian Astrophysical Observatory
Weekly Science Update | 2015 Feb 20
More than half of all stars are in multiple systems: binary stars, or even triplets or quadruplets, that orbit one another. No one is quite sure how or why they form, but the effects can be significant, for example influencing the character of their planets. Our Sun is uncommon in having no companion star, perhaps suggesting that its configuration of planets is equally uncommon.

There are two principal ideas about how multiple stars form: fragmentation in the early stages of birth, or the gravitational capture of a nearby star later on. Computer simulations of star formation find that both are reasonable possibilities, and so astronomers have been trying to make observations to refine the models and the conclusions. Writing in this week’s journal Nature, Alyssa Goodman and her collaborators report finding a nearby stellar nursery where quadruplets are being born. The region is in the star forming molecular cloud in the direction of the constellation of Perseus, about 825 light-years away. Scientists have known for decades about a protostar in this area, a dense core of material that is developing into a small star about one-tenth of a solar-mass in size.

Using radio wavelength observations of dense molecular gas, ammonia in particular, the team discovered that around this protostar are several filamentary gas structures in which they detected three other condensations. The other three embryos are two to three times more massive than the main protostar, and models suggest they will become stars soon - in roughly forty thousand years. ...

The formation of a quadruple star system with wide separation - Jaime E. Pineda et al
http://asterisk.apod.com/viewtopic.php?t=34440
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SAO: Where Do Stars Form in Merging Galaxies?

Post by bystander » Thu Mar 05, 2015 4:26 pm

Where Do Stars Form in Merging Galaxies?
Harvard-Smithsonian Center for Astrophysics
Smithsonian Astrophysical Observatory
Weekly Science Update | 2015 Feb 27
Collisions between galaxies, and even less dramatic gravitational encounters between them, are recognized as triggering star formation. Observations of luminous galaxies, powered by starbursts, are consistent with this conclusion. Numerical simulations also support this picture, with gravity funneling copious amounts of gas into the central regions of galaxies, fueling powerful bursts of star formation there. But starbursts are not ubiquitous in interacting galaxies. Triggering therefore depends on many factors, including the specific merger geometry (how they come together), the properties of the progenitor galaxies (how much gas is available for new stars), and time-scale (maybe the starburst has yet to happen, or has finished?)

CfA astronomer Lars Hernquist and six colleagues computed seventy-five simulated galaxy collisions under a wide range of conditions in order to investigate the question of where the induced star formation is located. Observational tests of this property are difficult to make because many of the most interesting cases are far enough away that individual regions can’t easily be distinguished for study. For the same reason, it is often hard to tell in which of the two merging galaxies (or both?) the starburst take place.

The results of these simulations were clear: the interactions enhanced the star formation activity in the centers of galaxies, and in particular in roughly the central ten thousand light-years. (By way of comparison, our Sun is about twenty-five thousand light-years away from the Milky Way’s center.) The scientists discovered several other important effects about the star formation as well: it was actually suppressed in the outer regions of the galaxies (depending on the merger geometry); at later merger stages it often formed a ring around the central zone, and its strength was critically dependent on whether the rotations of the galaxies were in the same direction (star formation enhanced) or opposite (star formation suppressed). The new generation of telescopes under construction should have the capability of improving the observations, and this theoretical work will help guide the new research.

Mapping galaxy encounters in numerical simulations: The spatial extent of induced star formation - Jorge Moreno et al
http://asterisk.apod.com/viewtopic.php?t=29811
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SAO: Nanodust Particles in the Interplanetary Medium

Post by bystander » Mon Mar 09, 2015 2:58 pm

Nanodust Particles in the Interplanetary Medium
Harvard-Smithsonian Center for Astrophysics
Smithsonian Astrophysical Observatory
Weekly Science Update | 2015 Mar 06
Dust particles smaller than about a wavelength of light are abundant in our solar system, created by collisions between asteroids and from the evaporation of comets. As they scatter sunlight, these particles produce the zodiacal light, the glow in the night sky that stretches along the zodiac. The zodiacal light is most easily seen after sunset or before sunrise, though it is faint enough that even moonlight can mask it. Nanodust particles are about ten times smaller than normal dust -- too small to efficiently scatter sunlight. They can be sensed by spacecraft, however, because when they impact the spacecraft they generate puffs of ionized gas and electrical pulses that instruments can detect. The Solar TErrestrial RElations Observatory (STEREO) spacecraft has been detecting nanodust pulses since its launch in 2007, and previous studies of these events have confirmed the general picture that these tiny particles are an important constituent of the solar system.

The corona of the Sun, the hot (over a million kelvin), gaseous outer region of its atmosphere, is threaded by intense magnetic fields. The fields loop and twist, stirred by the motions of the hot gas in the underlying atmosphere. When these loops snap, they eject energetic charged particles into the solar wind in events called coronal mass ejections. Nanodust particles carry a slight electric charge, and because of that, the solar wind should be able to redistribute them as it blows toward Earth through interplanetary space. CfA astronomer Gaetan Le Chat and his colleagues have analyzed seven years of data on nanodust obtained from the STEREO spacecraft and found that coronal mass ejections do indeed appear to accelerate and concentrate nanodust particles, leading to increased rates of impact on the spacecraft during periods of solar activity. The scientists also noted longer-term, regular variations in the rate of nanodust impacts, and propose from the periodic behavior that the gravitational influences of Mercury and Venus are responsible, perhaps by perturbing the tails of comets that have passed through the inner solar system, leading to a higher production of nanodust.

Effect of the Interplanetary Medium on Nanodust Observations by the Solar Terrestrial Relations Observatory - G. Le Chat et al
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SAO: Cosmic Bumps on Cosmic Ripples

Post by bystander » Mon Mar 16, 2015 5:06 pm

Cosmic Bumps on Cosmic Ripples
Harvard-Smithsonian Center for Astrophysics
Smithsonian Astrophysical Observatory
Weekly Science Update | 2015 Mar 13
[img3="Abell 1689, one of the most massive galaxy clusters known. The hot gas in this and other galaxy clusters distort the shape of the cosmic microwave background radiation (the "SZ Effect"), and sensitive new results on these distortions from the South Pole Telescope confirm and refine previous conclusions while identifying some puzzling discrepancies.
Credit: NASA, N. Benitez (JHU), T. Broadhurst (Racah Institute of Physics/The Hebrew University), H. Ford (JHU), M. Clampin (STScI), G. Hartig (STScI), G. Illingworth (UCO/Lick Observatory), the ACS Science Team and ESA
"]https://www.cfa.harvard.edu/sites/www.c ... 201511.jpg[/img3]
In 1969, the astrophysicists Rashid Sunyaev and Yakov Zel'dovich realized that the then recently discovered cosmic microwave background radiation (CMBR) would be distorted by hot cosmic gas. Hot electrons in the intergalactic medium preferentially scatter the light in one direction, causing a change in the brightness of the CMBR towards clusters of galaxies where electrons should be abundant. They showed that the effect would reveal the large-scale structure of the universe, the nature of the CMBR, cosmological parameters like the Hubble constant, and physical conditions in galaxy clusters.

The effect, now known as the Sunyaev-Zel'dovich effect (SZE), was first spotted in 1978 after much searching. Both space- and ground-based instruments, including the Planck satellite, the South Pole Telescope (SPT), and others have released new catalogs of galaxy clusters selected using the SZE. CfA astronomers Matt Ashby, Matt Bayliss, Richard Foley, Christine Jones, Steve Murray, Brian Stalder, Tony Stark, and Alexey Vikhlinin were part of a large team that used the SPT to examine the SZE signatures of forty-six X-ray selected groups and clusters of galaxies. The X-ray observations are some of the most sensitive ever used to search for clusters; the most distant of the galaxy clusters detected to date from a cosmic epoch six billion years after the big bang.

The team reports generally very good agreement between the cosmological parameters they measure and those reported by other means, in particular the latest results from the Planck satellite study of the CMBR. However the agreement is not perfect: the team reports an unexpectedly weak SZE signal for less massive galaxy clusters. Although they did identify and measure several potential sources of contamination, the discrepancy is not easily explained away. They suggest one possibility: dust within the clusters is reducing the SZE signal. For now, the reason remains unknown; this mystery will be addressed in subsequent, deeper, more sensitive SZE observations planned for the SPT.

Analysis of Sunyaev-Zel'dovich Effect Mass-Observable Relations using South Pole Telescope
Observations of an X-ray Selected Sample of Low Mass Galaxy Clusters and Groups
- J. Liu et al
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SAO: Measuring Galaxy Evolution with Globular Clusters

Post by bystander » Sun Mar 22, 2015 5:07 pm

Measuring Galaxy Evolution with Globular Clusters
Harvard-Smithsonian Center for Astrophysics
Smithsonian Astrophysical Observatory
Weekly Science Update | 2015 Mar 20
Globular clusters are gravitationally bound ensembles of stars, as many as a million stars in some cases, grouped in roughly spherical clusters with diameters as small as only tens of light-years. Globular clusters are typically located in the outer regions (the halos) of galaxies; the Milky Way galaxy has about two hundred globular clusters orbiting it. Astronomers are interested in globular clusters in part because they are home to many of the oldest known stars, but also because of their locations in the halos. Collisions between galaxies are commonplace, and globular clusters may provide fossil evidence of these encounters because they are strongly affected by such interactions. During a collision, a galaxy can grow by absorbing or merging with its neighbor, and some models predict that clusters form during these interactions. Moreover, it is possible that in a merger large numbers of globular clusters originally belonging to a smaller galaxy may be captured by the larger galaxy. In any case, the distribution of globular clusters around a galaxy holds clues to their origins and the history of its host galaxy.

The Virgo Cluster of galaxies, containing between one and two thousand galaxies, is located about fifty-four thousand light-years away in the direction of the constellation of Virgo. The ten brightest galaxies of the Virgo Cluster alone contain 7053 detected globular clusters. CfA astronomers Raffaele D'Abrusco, Pepi Fabbiano, and Andreas Zezas carefully examined this set of globular clusters looking for information about the history of these galaxies. In a new paper, they report discovering distinctive structures among the globular cluster systems, meaning that the globular clusters around these galaxies are not distributed symmetrically. Their configurations often take shapes ranging from roughly linear to circular, with some more complex shapes as well. The scientists found 229 such structures in this subsample, forty-two of them classified as being medium or large and stretching over as much as seventy-five light-years. The elongated structures tend to be aligned with an axis of the host galaxy, as would be expected if a merger were responsible.

The scientists argue that these structures are indeed the remnants of galaxies that were accreted in the past, and among other things they estimate limits on the masses of these parent galaxies. Computer simulations provide some rough level of agreement. The authors note that with more detailed computations, these structures offer a powerful new tool to advance the study of galaxy evolution.

Spatial Structures In the Globular Cluster Distribution of the Ten Brightest Virgo Galaxies - R. D'Abrusco, G. Fabbiano, A. Zezas
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Re: SAO: Measuring Galaxy Evolution with Globular Clusters

Post by neufer » Sun Mar 22, 2015 5:22 pm

bystander wrote:
Measuring Galaxy Evolution with Globular Clusters
Harvard-Smithsonian Center for Astrophysics
Smithsonian Astrophysical Observatory
Weekly Science Update | 2015 Mar 20
The Virgo Cluster of galaxies, containing between one and two thousand galaxies, is located about fifty-four thousand light-years away in the direction of the constellation of Virgo. The ten brightest galaxies of the Virgo Cluster alone contain 7053 detected globular clusters.
The Virgo Cluster (VC) is a cluster of galaxies whose center is 53.8 ± 0.3 Mly (16.5 ± 0.1 Mpc) away in the constellation Virgo.
Art Neuendorffer

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SAO: An Efficient Star Making Galaxy

Post by bystander » Sat Mar 28, 2015 4:18 am

An Efficient Star Making Galaxy
Harvard-Smithsonian Center for Astrophysics
Smithsonian Astrophysical Observatory
Weekly Science Update | 2015 Mar 27
New stars regularly appear in the night sky as the gas and dust in giant interstellar clouds gradually coalesce under the influence of gravity. The process of making stars, however, is inefficient, and (at least in present-day galaxies) there are copious amounts of material that don't make it into stars. For the Milky Way, the efficiency overall (as measured by the mass in stars compared to the total mass of the galaxy) is about 5%; in clouds with turbulent gas motions this value can be even lower. The low efficiency is a critical parameter in galaxy evolution, and is one reason why stars are still forming nearly fourteen billion years after the Big Bang. Another consequence is seen in the production of star clusters. A low efficiency that produces stars gradually does not easily produce star clusters, because the new stars can drift away from the diffuse cloud. The existence of ancient massive bound star clusters (globular clusters) in the Milky Way, therefore, suggests that when they formed early in galactic history, star formation efficiencies were higher.

A local dwarf galaxy, NGC 5253, has a young star cluster that provides an example of highly efficient star formation. CfA astronomer Jun-Hui Zhao and his colleagues used the Submillimeter Array (SMA) to study the molecular gas (carbon monoxide, CO) at the center of this galaxy in a source called "Cloud D". Usually astronomers use the intensity of the CO radiation to estimate the total gas mass, but this can be a misleading measure since it requires knowing the relative amount of CO to the total material. The team instead used the motions of the gas to infer the total mass present; they used the amount of ultraviolet light to determine the number of stars. The scientists report that their technique is a much more reliable way of measuring the star formation rate.

The astronomers, writing in the latest issue of Nature, find that when they apply their method to the hot, dense and dusty Cloud D, they find a star-formation efficiency exceeding 50%. They note that their SMA images show a streamer of molecular gas falling into the galaxy toward this cloud, and they argue that this infalling material (about two million solar masses of gas) could compress the cloud and thereby induce the dramatic star formation efficiency seen. The new paper also suggests that a similar kind of infall and compression mechanism might have enabled comparably higher star formation rates at earlier times in cosmic history.

Highly efficient star formation in NGC 5253 possibly from stream-fed accretion - J. L. Turner et al
http://asterisk.apod.com/viewtopic.php?t=30260
http://asterisk.apod.com/viewtopic.php?t=25572

Nearby "Dwarf" Galaxy is Home to Luminous Star Cluster
American Friends of Tel Aviv University | 2015 Jun 09
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SAO: Distance Measurement of a Microlensing Event

Post by bystander » Fri Apr 03, 2015 2:59 pm

Distance Measurement of a Microlensing Event
Harvard-Smithsonian Center for Astrophysics
Smithsonian Astrophysical Observatory
Weekly Science Update | 2015 Apr 03
[img3="A plot of light intensity versus time for a microlensing event. It shows the changing intensity of light of a very distant background star when it was obstructed by a small, unseen star about ten thousand light-years away. Astronomers watched this event happen from two widely separated locations, the Spitzer Space Telescope and the "OGLE" ground-based observatory. (Credit: Spitzer/IRAC; Yee et al.)"]http://cdn.phys.org/newman/csz/news/800 ... cemeas.jpg[/img3]
The distance to celestial objects is key to calculating their intrinsic properties like mass and luminosity. Distance, unfortunately, is also one of the most difficult parameters to measure. The most direct method is called parallax: When a celestial body is viewed from different, widely separated vantage points, its angular position with respect to background stars appears different. Parallax is traditionally used to triangulate the distances to nearby stars by measuring their apparent angles six months apart, at the two opposite sides of the Earth's orbit around the Sun.

Astronomers would like to know the distribution of dark (i.e., unseen) objects in the galaxy, for example free-floating planets or small, dim stars, in order to complete an accurate census of the galaxy. The principle method of detecting these dark objects is through microlensing: the short flash of light produced when the object's gravitational field, acting like a lens (hence the name), changes the intensity of visible light from a more distant, background star when the unseen body happens to pass in front of it. About thirty years ago, scientists predicted that if it ever became possible to observe a microlensing flash from two well-separated vantage points, a parallax measurement would pin down the distance of the dark object. ...

CfA astronomer Jennifer Yee led a team of colleagues in a program of parallax microlensing measurements using both Spitzer and ground-based telescopes. When the team got a warning of an imminent flash from ground-based monitors that watch for brightening effects, they quickly arranged to obtain coordinated observations. The flash they measured not only appeared at slightly different times from the two locations, but also had different brightening profiles. The results enabled the scientists to obtain the mass of the dark object, 0.23(+-0.07) solar-masses, as well as its distance, 10,200 (+- 1300) light-years. Although Spitzer has previously been used to study microlensing events, this is the first space-based microlens parallax measurement of an isolated star, and demonstrates that this method of probing this dark component of the galaxy is likely to become a very productive one.

First Space-based Microlens Parallax Measurement of an Isolated Star: Spitzer Observations of OGLE-2014-BLG-0939 - J. C. Yee et al
Hmm, this article seems to have disappeared from SAO. I've changed the link to PhysOrg.
It's back ...
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SAO: Merging Stars

Post by bystander » Fri Apr 10, 2015 8:13 pm

Merging Stars
Harvard-Smithsonian Center for Astrophysics
Smithsonian Astrophysical Observatory
Weekly Science Update | 2015 Apr 10
[img3="The remains of Nova Vul 1670, the "new star" that was seen in the year 1670. Observations of the molecular gas and its composition in the nebula find strong evidence that the nova was the result of the merger of two stars.
The image shows visible light (blue), dust seen at submillimeter wavelengths (green), and molecular emission at submillimeter wavelengths (red).
(Credit: APEX, SMA, T. Kaminski (ESO, MPIfR))
"]https://www.cfa.harvard.edu/sites/www.c ... 1514_0.jpg[/img3]
Astronomers have known for decades that the merger of two normal stars is a frequent and astronomically important phenomenon. In globular clusters, for example, with as many as several million stars gravitationally bound together, collisions often occur between stars, producing stars that are more massive, hotter, and bluer than usual. In star forming clusters, mergers of small stars have been proposed as a way to form massive young stars, and computer simulations lend some support to this idea. Not least, some kinds of novae -- stars that suddenly brighten and were once thought to be “new” stars -- are the result of stellar mergers or near-mergers.

The variable star CK Vulpeculae (Nova Vul 1670) had a bright outburst in 1670-1672 and then dimmed. No counterpart was seen until 1982 when a nebula was found at its location, presumably a remnant of the outburst of 1670. The star itself remains undetected, presumably hidden behind a heavy dust layer ejected in that outburst. The nebula itself has been of interest to astronomers for decades because it is rich in molecular gas. CfA astronomer Nimesh Patel and his colleagues studied Nova Vul 1670 and its chemical composition using two millimeter telescopes capable of measuring its molecular constituents in detail, the Submillimeter Array (SMA) and the Atacama Pathfinder Experiment (APEX).

The scientists report in the latest issue of Nature that Nova Vul 1670 is not only rich in molecular species, its gas has dramatically unusual isotopic abundances (that is, the atoms present, carbon, oxygen and nitrogen in particular, have extra neutrons in their nuclei). Element synthesis in stars is well understood, and produces specific isotopic ratios; in the solar system, for example, the ratio of carbon with an atomic number of 12 to carbon 13 is 89, but in Nova Vul 1670 it is ten times less. Similarly low ratios were found for nitrogen and oxygen isotopes.

The astronomers conclude that the atoms in Nova Vul 1670 were not produced in a normal stellar furnace, nor for that matter even in a furnace operating under very different conditions. Neither could they identify any kind of explosive event that would produce these ratios. The team argues that the most likely scenario is the violent merger in 1670 of two stars; the event ejected inner parts of the stars into the nebula, exposing the ashes from earlier stages of nuclear burning, and mixing them with more processed material. People watching the nova in 1670 were no doubt amazed at the appearance of a "new star". Imagine what their reaction would have been to find out it was actually the merger of two stars.

Nuclear ashes and outflow in the eruptive star Nova Vul 1670 - Tomasz Kamiński et al
http://asterisk.apod.com/viewtopic.php?t=34574
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SAO: Cosmologically Complicating Dust

Post by bystander » Tue Apr 21, 2015 6:33 am

Cosmologically Complicating Dust
Harvard-Smithsonian Center for Astrophysics
Smithsonian Astrophysical Observatory
Weekly Science Update | 2015 Apr 17
The universe was created 13.7 billion years ago in a blaze of light: the big bang. Roughly 380,000 years later, after matter (mostly hydrogen) had cooled enough for neutral atoms to form, light was able to traverse space freely. That light, the cosmic microwave background radiation (CMBR), comes to us from every direction in the sky uniformly ... or so it first seemed. In the last decades, astronomers discovered that the radiation actually has very faint ripples and bumps in it at a level of brightness of only a part in one hundred thousand – the seeds for future structures, like galaxies.

Astronomers have conjectured that these ripples also contain traces of an initial burst of expansion -- the so-called inflation – which swelled the new universe by thirty-three orders of magnitude in a mere ten-to-the-power-minus-33 seconds. Clues about the inflation should be faintly present in the way the cosmic ripples are curled, an effect that is expected to be perhaps one hundred times fainter than the ripples themselves. One year ago, CfA astronomers working at the South Pole amazed the world by reporting evidence for such curling, the "B-mode polarization," and cautiously calculated that the measured strength supported the simplest models of inflation. ...

A Joint Analysis of BICEP2/Keck Array and Planck Data - BICEP2/Keck, Planck Collaborations
http://asterisk.apod.com/viewtopic.php?t=33147
http://asterisk.apod.com/viewtopic.php?t=33140
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SAO: Birth of a Radio Phoenix

Post by bystander » Mon Apr 27, 2015 5:06 pm

Birth of a Radio Phoenix
Harvard-Smithsonian Center for Astrophysics
Smithsonian Astrophysical Observatory
Weekly Science Update | 2015 Apr 24
Abell 1033 is a cluster of over 350 galaxies located about 1.7 billion light-years away. Collisions between galaxies in clusters are common events, and each merger heats and shocks the nearby gas. The rapidly moving, ionized gas then radiates intensely at radio wavelengths. There are three types of radio sources found in these clusters. The first, called radio relics, are found in the outskirts of galaxies and have radiation signatures characteristic of shocked material over large scales. The second type, called radio haloes, are centrally located in the cluster and are probably the result of large turbulent motions set up during collisions.

A radio phoenix is the third type of cluster radio source, and is much less well studied. After the initial effects of a collision have died down and the gas has cooled, the radio emission subsides. But a subsequent merger nearby can produce a strong shock wave, and if that passes through the fossil material it can compress and re-energize it to emit in the radio again.

CfA astronomers Georgiana Ogrean and Reinout van Weeren, with five colleagues, used data from the Chandra X-ray Observatory, the Westerbork Synthesis Radio Telescope, the Very Large Array ad the optical Sloan Digital Sky Survey to study the Abell 1033 cluster and its family of galaxies. They discovered two subclusters in the source that seem to have recently collided; they were spotted from their X-ray emission. Close to this region, and to a galactic nucleus, the team spotted a radio source with the emission and charged particle characteristics of a radio phoenix. The scientists conclude that shocks from the recent merger have propagated into old gas, reinvigorating this fossil remnant to new life.

Abell 1033: Birth of a Radio Phoenix - F. de Gasperin et al
Abell 1033: Birth of a Radio Phoenix
Technology.org | 2015 Jan 05
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SAO: An Improved Model for Star Formation

Post by bystander » Fri May 08, 2015 12:52 pm

An Improved Model for Star Formation
Harvard-Smithsonian Center for Astrophysics
Smithsonian Astrophysical Observatory
Weekly Science Update | 2015 May 01
[img3="A three-color composite of the star-forming complex M 17 as seen in near-infrared wavelengths. A new technique for modeling star formation tracks the evolution of the gas and dust temperatures and also the radiation as it propagates through the material in the cloud, enabling scientists to probe more accurately cloud cores and their turbulence. (Credit: ESO: ISAAC/VLT ANTU)"]http://cdn.eso.org/images/screen/eso0416a.jpg[/img3]
Star formation, once thought to consist essentially of just the simple coalescence of material by gravity, actually occurs in a complex series of stages. As the gas and dust in giant molecular clouds come together into stars, circumstellar disks develop (possibly pre-planetary in nature), and later on dramatic outflowing jets appear. Key to initiating the process is the behavior of the gas. Although it has a finite temperature and hence a finite outward pressure, the pressure must be insufficient to support the gas against gravitational collapse. The subsequent cloud evolution also depends on the detailed density structure of the gas with a variety of different outcomes being possible, for example, fragmentation into smaller clouds. A key relationship is that between the temperature and density within the medium, and, as a result, the way the cloud radiates as the initial cooling dominance of molecular gas is overtaken by cooling from its dust grains.

In the latest issue of Monthly Notices of the Royal Astronomical Society, CfA astronomer Eric Keto and his colleague present a new method for modelling the thermal evolution of star-forming molecular clouds. Their technique combines modeling both the temperature characteristics of the gas and dust and the propagation of radiation as it is produced by, and passes through, the medium. The method enables the prediction of the molecular cloud's evolution and also the growth of protostars. Unlike most previously published star formation calculations, the new model tracks the temperatures of the gas, dust, and radiation separately. The results are in good agreement with the accepted literature, providing confidence about the model's performance, but push the range of investigations as they probe the structures in the cloud cores and their turbulent behavior.

The scientists plan to apply their new model to more realistic computer simulations of star formation, particularly for molecular clouds with unusual conditions (for example very low densities or low abundances of complex elements). They note, however, that their model is far from complete; it relies on generic estimates rather than exact calculations for some processes, for example, the evolution of the chemistry in the cloud as the gas warms up. Future research, building on this important first step, will be able to incorporate these effects more accurately, and should lead to an even more complete understanding of the star formation process.

Combining radiative transfer and diffuse interstellar medium physics to model star formation - Matthew R. Bate, Eric R. Keto
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SAO: The Cosmic Evolution of Galaxies

Post by bystander » Fri May 08, 2015 1:19 pm

The Cosmic Evolution of Galaxies
Harvard-Smithsonian Center for Astrophysics
Smithsonian Astrophysical Observatory
Weekly Science Update | 2015 May 08
[attachment=0]illustris_box_dmdens_gasvel.jpg[/attachment]

Our knowledge of the big bang has increased dramatically in the past decade, as satellites and ground-based studies of the cosmic microwave background have refined parameters associated with the very early universe, achieving amazing precisions (though not necessarily accuracies) of a few percent. Unfortunately, our knowledge of what happened after that - from those first few hundred thousand years until today, 13.7 billion years later - is very much a work-in-progress. We know that galaxies and their stars formed out of the cooling, filamentary network of matter from that early era. They re-ionized the hydrogen gas, and then continued to evolve, and collide with one another as the universe steadily expanded. Distant galaxies are faint and hard to detect, however, and although observations have made excellent progress in piecing together the story line, astronomers have turned to theory and computer simulations to try to complete the picture.

There are three main theoretical approaches to study the cosmic frequency of galaxy mergers, which differ in how they model galaxies. The first approach does not attempt to model galaxy formation from first principles, and instead "paints" galaxies onto the dark matter environment (they are called "halos") according to constraints set by observations. The second approach models galaxy formation by means of simple mathematical recipes, again using dark matter halos as the backbone of the model. The third method, hydrodynamic simulations, attempts to model everything (dark matter, gas and stars) self-consistently, a task that until recently had been computationally too difficult.

CfA astronomers Vicente Rodriguez-Gomez, Shy Genel, Annalisa Pillepich, Dylan Nelson, and Lars Hernquist and their colleagues have developed a new theoretical framework for calculating the frequency of galaxy mergers in the Illustris Project, a cosmological hydrodynamic simulation which models the formation of galaxies in cosmic volumes about three hundred million light-years in size, huge enough to replicate many known properties of galaxies and clusters both locally and at earlier epochs. The large volume, the self-consistent treatment of normal matter, and the realistic galaxy formation model used, allows the Illustris simulation to provide an unprecedented and precise study of mergers over cosmic time.

The astronomers find clear evidence for steadily decreasing galaxy merger rates (the merger frequency three billion years after the big bang was about fifteen times higher than it is today), and they clarify the nature of mergers, for example, finding the most useful definition for the mass ratio of the merging galaxies and constraining the epoch of mass infall during a collision. They report some sharp differences between their results and those predicted by some other popular theories, as well as some ambiguities in the (still imprecise) observed datasets. Their important research marks the start of a more detailed series of investigations into the cosmic evolution of galaxies.

The Merger Rate of Galaxies in the Illustris Simulation: A Comparison
with Observations and Semi-empirical Models
- Vicente Rodriguez-Gomez et al
  • Monthly Notices of the RAS 449(1) 2643 (2015 May 01) DOI: [url=httphttp://dx.doi.org/10.1093/mnras/stv264]10.1093/mnras/stv264[/url]
    arXiv.org > astro-ph > arXiv:1502.01339 > 04 Feb 2015 (v1), 20 Mar 2015 (v2)
Attachments
A snapshot from the Illustris Project computer simulation of cosmic structure <br />formation. This artificially colored image shows filaments and galaxies in the <br />web of cosmic matter, as seen today over a field-of-view about fifty million <br />light-years across. A new paper examines the changing frequency of galaxy <br />collisions, as computed by in Illustris, as the universe evolves from the big <br />bang to the present day. (Credit: The Illustris Project)
A snapshot from the Illustris Project computer simulation of cosmic structure
formation. This artificially colored image shows filaments and galaxies in the
web of cosmic matter, as seen today over a field-of-view about fifty million
light-years across. A new paper examines the changing frequency of galaxy
collisions, as computed by in Illustris, as the universe evolves from the big
bang to the present day. (Credit: The Illustris Project)
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SAO: The Kinematics of Merging Galaxies

Post by bystander » Sat May 16, 2015 10:27 am

The Kinematics of Merging Galaxies
Harvard-Smithsonian Center for Astrophysics
Smithsonian Astrophysical Observatory
Weekly Science Update | 2015 May 15
[img3="A false-color image of the merging galaxies UGC9618. Astronomers have studied whether it is possible to use internal gas motions to characterize luminous galaxies in the early universe as mergers when they are too distant to see morphological signs of distortions. (Credit: NASA/ESA/Hubble)"]http://www.cfa.harvard.edu/sites/www.cf ... 201521.jpg[/img3][hr][/hr]
The unprecedented sensitivity of space telescopes has powered a revolution over the past decade in our understanding of galaxies in the young universe during its first billion years of existence. These primitive objects are so remote that their light has been traveling towards us for more than ninety percent of the age of the universe, but they could be detected by space observatories because they are intrinsically bright in the infrared. Their luminosity is almost surely the result of huge numbers of newly formed stars whose light warms the dust that then radiates at infrared wavelengths.

Do distant galaxies, the forebears of our current cosmic neighbors, make stars in the same way our galaxy does today? Astronomers are trying to unravel if and how galaxies in the early universe are different from local ones. In the local universe, starbursts and luminous infrared emission is often the result of the merger of two galaxies, and astronomers naturally suspect that the physics of mergers is also implicated in distant, luminous galaxies. The problem is that local mergers are readily identified as such because their morphologies display effects like disrupted structures, tidal arms, or bridges of material connecting the two galaxies. Distant objects are too far away to see these physical structures, however, and even ones that are somewhat closer would have features that are faint and hard to discern.

A collision between galaxies should disorder each galaxy's disk and disrupt the corresponding, systematic rotational motions. CfA astronomers Chao-Ling Hung and Howard Smith and their colleagues studied whether it was practical to use these "kinematic" effects to identify and classify distant mergers. The astronomers took twenty-four local, luminous mergers and artificially degraded their images to simulate their being far away (i.e., in the early universe). They then determined the internal motions via the Doppler effect in the emission lines of atomic hydrogen and nitrogen gas as it is appears across the image. (Recall that the Doppler effect is the apparent shift in the wavelength of a spectral line due to motion.) Their conclusions are that in some select situations (depending on the relative sizes of the merging galaxies and the stage of the merger) the kinematics does clearly reveal the presence of a merger, but for a high proportion of cases kinematics are not sufficient to identify mergers. Other merger indicators, for example as traced by the luminosity of temperature of the dust, are needed.

Kinematic Classifications of Local Interacting Galaxies: Implications for the Merger/Disk Classifications at High-z - Chao-Ling Hung et al

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SAO: A Curious Family of Giants

Post by bystander » Sat May 23, 2015 4:15 pm

A Curious Family of Giants
Harvard-Smithsonian Center for Astrophysics
Smithsonian Astrophysical Observatory
Weekly Science Update | 2015 May 22
[attachment=0]Kepler-432[1].jpg[/attachment]
There are 565 exoplanets currently known that are as massive as Jupiter or bigger, about one third of the total known, confirmed exoplanet population. About one quarter of the massive population orbits very close to its star, with periods of less than ten days (the Earth takes about 365 days to orbit the Sun). Heated by the nearby star’s radiation, these giants are often called hot Jupiters.

Despite the large and diverse population of known giant exoplanets, only two of them orbit older, evolved stars. How and why there are so many giant planets close to their host stars is still a mystery: perhaps over time they migrate in from more distant parts of their planetary system, or instead perhaps they are born there? Evolved stars that host close-in, giant exoplanets provide a valuable wrinkle to the picture, and some clues: these stars, as they age, cool off and swell in diameter, could disrupt or even swallow any nearby planets. Finding examples allows astronomers to refine their models of planet formation and evolution.

CfA astronomers Dave Latham, David Kipping, Matthew Payne, David Sliski, Lars Buchhave, Gilbert Esquerdo, Michel Calkins, and Perry Berlind and their colleagues have discovered two new giant exoplanets around an evolved star. Kepler-432b is about 5.4 Jupiter-masses in size and orbits every 52.5 days – it is the third known example of a close-in giant around an evolved star; Kepler-434c is 2.4 Jupiter-masses and orbits much farther away, in 406 days. The host star, Kepler-432 has a mass of about 1.35 solar-masses, an age of about 3.5 billion years, and it has just finished its stable lifetime burning hydrogen and begun to swell in size, with a current diameter of 4.16 solar-diameters. ...

Kepler-432: a red giant interacting with one of its two long period giant planets - Samuel N. Quinn et al Kepler-432 b: a massive planet in a highly eccentric orbit transiting a red giant - Simona Ciceri et al Kepler-432 b: a massive warm Jupiter in a 52-day eccentric orbit transiting a giant star - Mauricio Ortiz et al
Attachments
Near infrared image of Kepler-432 showing a faint companion star. <br />(Credit: NIRC2/Keck II/ApJ S. Quinn et al)
Near infrared image of Kepler-432 showing a faint companion star.
(Credit: NIRC2/Keck II/ApJ S. Quinn et al)
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SAO: The Interstellar Medium A Billion Years After the Big B

Post by bystander » Thu Jun 04, 2015 7:06 pm

The Interstellar Medium A Billion Years After the Big Bang
Harvard-Smithsonian Center for Astrophysics
Smithsonian Astrophysical Observatory
Weekly Science Update | 2015 May 29
[img3="A false color, far-infrared image containing a galaxy (the red dot at the center) dating from about 900 million years after the big bang. Its red color is the result the cosmic expansion and its abundance of warm dust. The other galaxies in the image (circled) are much closer. Astronomers have measured the emission from ionized carbon in seventeen similar, young galaxies in their study of star formation and the interstellar medium at this early epoch. (Credit: ESA/NASA/Herschel; Guilberg et al.)"]https://www.cfa.harvard.edu/sites/www.c ... 201522.jpg[/img3][hr][/hr]
The first stars and galaxies began forming a few hundred million years after the big bang, and after a billion years their physical processes dominated the evolution of cosmic structure. More than a thousand candidates for these early galaxies have been spotted so far, despite their being distant and faint. A subset of them was discovered to be extremely bright at submillimeter wavelengths and making stars at fantastic rates, over a thousand per year, the result of their containing unusually large reservoirs of warm dust and gas. Early galaxies are the direct ancestors of today’s systems, and astronomers modeling their birth and evolution expect that they approximately resemble modern galaxies. There are some potential key differences, however, like the amount of warm dust; another is the relative lack of the chemical elements that are taken for granted today but which were made over the next twelve billion years of cooking in stellar furnaces.

CfA astronomer Tony Stark and a team of colleagues have completed a study of carbon in the interstellar medium of these early galaxies. They identified a set of very bright, distant objects in their South Pole submillimeter telescope survey; the sources were also spotted having strong far infrared luminosity in Herschel Space Telescope surveys. Followup observations confirmed twenty dusty, star-forming galaxies from the early era of galaxies, and discovered that they are bright in part because they are being gravitationally lensed by closer clusters of galaxies. (The path of light is bent by the presence of mass, so that matter in a foreground cluster of galaxies can act like a "gravitational lens" to re-image more distant objects lying behind it.)

The team used an emission line from ionized carbon for their research. The line lies at an infrared wavelength that is masked by the atmosphere, but because of the high recession velocities of these distant galaxies, the spectrum is shifted to submillimeter wavelengths which are free of atmospheric effects. The particular carbon line chosen is produced when ultraviolet radiation from new stars ionizes neutral carbon atoms in the interstellar medium. Seventeen of the galaxies had this strong carbon line emission; carbon monoxide was also measured. The scientists report that the carbon line provides a good measure of the rate of star formation in the very early universe (except in sources deficient in carbon), that the UV fields are about 100-1000 times as strong as they are near the Sun, and that the density of the emitting medium is moderate, about ten thousand atoms per cubic centimeter. The team concludes that future observations will study individual regions within these early galaxies and measure other atomic lines to obtain better estimates of element deficiencies.

The nature of the [CII] emission in dusty star-forming galaxies from the SPT survey - Bitten Gullberg et al
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SAO: The Ages of Extragalactic Jets

Post by bystander » Mon Jun 08, 2015 5:11 pm

The Ages of Extragalactic Jets
Harvard-Smithsonian Center for Astrophysics
Smithsonian Astrophysical Observatory
Weekly Science Update | 2015 Jun 05
[c][attachment=0]su201523.jpg[/attachment][/c][hr][/hr]
The longest known highly collimated structures in the universe are the narrow jets that emanate from the vicinity of powerful black holes in certain types of galactic nuclei. These narrow beams, often in pairs propagating in opposite directions, can stretch across millions of light-years. They transport huge amounts of energy from the nuclear black hole regions where they originate into intergalactic space. The jets were discovered at radio wavelengths but they emit at X-ray wavelengths as well because the electrons in the jets move at close to the speed of light. These galaxies are active areas of research both because they are among the most energetic phenomena in the universe and because they are the primary mechanism that injects energy into the clusters of galaxies in which these radio monsters reside.

The development of these jets, their ages, and their ultimate dispositions are only vaguely understood. Astronomers suspect their lives have three phases, starting with the supersonic inflation of lobes of hot gas around the particle jets. It appears that in most sources this first phase is brief. Afterwards, the lobes expand gradually until their internal temperatures and pressures drop down to the values of the ambient gas. In the final phase, the jet ejection mechanisms shut down and the associated lobes become unobservable. There are numerous examples of galaxies at these various stages that provide the basis for these notions. ...

New insights into the evolution of the FR I radio galaxy 3C 270 (NGC 4261)
from VLA and GMRT radio observations
- Konstantinos Kolokythas et al
Attachments
The bright radio galaxy NGC 4261 as seen in visible light (white) and <br />radio (orange), showing a pair of opposed jets emanating from the <br />nucleus. Astronomers have determined that the lobes are about thirty <br />million years old, and were produced from multiple outbursts from <br />around the nuclear black hole. (Credit: WFPC HST, NRAO)
The bright radio galaxy NGC 4261 as seen in visible light (white) and
radio (orange), showing a pair of opposed jets emanating from the
nucleus. Astronomers have determined that the lobes are about thirty
million years old, and were produced from multiple outbursts from
around the nuclear black hole. (Credit: WFPC HST, NRAO)
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