SAO: Science Updates 2020

Find out the latest thinking about our universe.
User avatar
bystander
Apathetic Retiree
Posts: 19392
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

SAO: Science Updates 2020

Post by bystander » Mon Jan 06, 2020 8:04 pm

Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

User avatar
bystander
Apathetic Retiree
Posts: 19392
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

Early Galaxies

Post by bystander » Mon Jan 06, 2020 8:14 pm

Early Galaxies
SAO Weekly Science Update | 2020 Jan 03
Galaxies that are very luminous in the infrared are generally active in making new stars whose ultraviolet radiation heats the dust. The energy, re-radiated by the dust at infrared wavelengths, is characterized by having a broad spectral shape with a distinct emission peak. As the universe expands, and as the observed spectra of galaxies shift to the red, light at the wavelength of this peak moves into the submillimeter band leaving the levels of observed infrared flux deficient. Star-forming galaxies in the very distant universe are thus fainter in the infrared than in the submillimeter.

Thousands of galaxies have been discovered dating from epochs only a few billion years after the big bang. Most of them are small, low-mass galaxies that are faint and relatively difficult to study. Although more luminous, massive star-forming galaxies should also be present, these large objects are difficult to assemble at early cosmic times and there are not as many of them. One type of such luminous early galaxy is called a dusty-star-forming galaxy. They contain so much obscuring dust that they are invisible at optical wavelengths, and (based on their luminosities) have star-formation rates exceeding a thousand solar-masses per year; for comparison, the Milky Way produces about one star per year.

Dusty star-forming galaxies in the earliest epochs, less than two billion years after the big bang, are particularly rare and hard to find, but they are extremely valuable in helping understand how the first galaxies develop. CfA astronomer Glen Petitpas was a member of a team of astronomers who used the SCUBA-2 camera (Submillimeter Common User Bolometer Array-2) and the far-infrared Herschel SPIRE instrument to discover and characterize a dusty star-forming galaxy. They serendipitously detected the unusual galaxy in a SCUBA-2 survey. When they realized that the object was not detected by Herschel - or by any other optical or infrared survey, suggesting that its infrared peak had moved very far to the red - they concluded that it likely was from an extremely early epoch.

The team then used the Submillimeter Array, with a spatial resolution about ten times finer than SCUBA-2, to confirm the detection and study the source. Since a firm distance measurement requires detecting a spectral line and measuring its redshift, the scientists also tried using other submillimeter facilities suitable for line searches, but without success. Nevertheless, from the flux limits at various wavelengths they were able to make a strong case that this object is a massive, dusty star-forming galaxy, among the first generation of massive galaxies in the universe and dating from between roughly seven hundred million and one billion years after the big bang.

A SCUBA-2 Selected Herschel-SPIRE Dropout and the Nature of this Population ~ J. Greenslade et al
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

User avatar
bystander
Apathetic Retiree
Posts: 19392
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

The Interiors of Stars

Post by bystander » Sat Jan 11, 2020 4:22 pm

The Interiors of Stars
SAO Weekly Science Update | 2020 Jan 10
The interiors of stars are largely mysterious regions because they are so difficult to observe directly. Our lack of understanding about the physical processes there, like rotation and the mixing of hot gas, introduces considerable ambiguity about how stars shine and how they evolve. Stellar oscillations, detected through brightness fluctuations, offer one way to probe these subsurface regions. In the Sun, these vibrations are due to pressure waves generated by turbulence in its upper layers (the layers dominated by convective gas motions). Helioseismology is the name given to the study of these oscillations in the Sun, and astroseismology is the term used for other stars.

Astronomers have long detected strong brightness variations in other stars, for example the class of Cepheid variable stars used to calibrate the cosmic distance scale, but the small, solar-like oscillations driven by convection near the star's surface are much harder to see. Over the past few decades, space telescopes have successfully applied astroseismology to solar-type stars spanning many stages of stellar life. CfA astronomer Dave Latham was a member of a large team of astronomers who used the new TESS (Transiting Exoplanet Survey Satellite) datasets to study the interiors of the class of intermediate mass stars known as δ Sct and γ Dor stars. These stars are more massive than the Sun but not large enough to burn through their hydrogen fuel very rapidly and die as supernovae. Pulsations generally arise principally from one of two processes, those dominated by pressure (where the gas pressure restores perturbations) or by gravity (where buoyancy does). In these intermediate-mass stars both of these processes can be important, with pulsations having typical periods of roughly about six hours. The complexity of the combined processes, among other things, results in these intermediate-mass stars coming in a veritable zoo of variability types, and this variety offers astronomers more ways to test models of stellar interiors.

The astronomers analyzed TESS data on 117 of these stars using observations taken every two minutes; accurate distances to the stars (and hence accurate luminosities) were obtained from Gaia satellite measurements. The team was able for the first time to test and successfully refine models of pulsation for these stars. They found, for example, that gas mixing in the outer envelope plays an important role. They also spotted many higher-frequency pulsators, thereby identifying promising targets for future studies. Not least, they showed that the TESS mission has unprecedented potential not just for studying exoplanets, but also for improving our understanding of intermediate mass stars.

The First View of δ Scuti and γ Doradus Stars with the TESS Mission ~ V. Antoci et al
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

User avatar
bystander
Apathetic Retiree
Posts: 19392
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

First Results from the Dark Energy Survey

Post by bystander » Fri Jan 17, 2020 5:14 pm

First Results from the Dark Energy Survey
SAO Weekly Science Update | 2020 Jan 17
The Dark Energy Survey (DES) program uses the patterns of cosmic structure as seen in the spatial distribution of hundreds of millions of galaxies to reveal the nature of "dark energy," the source of cosmic acceleration. Since it began in 2013, DES has mapped over ten percent of the sky with a digital camera containing 570 million pixels and five optical filters that provide galaxy colors to estimates redshift distances. CfA astronomers are part of a team of over 400 scientists in seven countries working on DES, and last year it released the first set of data.

Cosmic voids occupy most of the volume of the universe. Unlike clusters of galaxies and other dense structures which are strongly affected by gravitational effects, not to mention processes associated with galaxy formation, these voids are the most underdense regions of the universe and have relatively simple dynamics. This makes them particularly straightforward probes for constraining cosmological parameters.

CfA astronomer David James is a member of the DES Collaboration and one of the co-authors on a new paper analyzing the first data release, with the aim of describing the relationship between the mass and light around cosmic voids. The scientists use statistical modeling to analyze both the 2-D distribution of galaxies and their 3-D distribution, the latter obtained from calculating galaxy distances from their photometrically determined redshifts. They find the two methods agree well with each other, and with models in which the physics of void environments is very simple, and in which the amount of emitted light scales directly with the mass. Voids with diameters between about one hundred and six hundred million light-years fit well enough to enable tests of the mass-light relationship to better than ten percent. With future observations, the improved statistics should enable useful new consistency tests of gravity and General Relativity and dark-matter scenarios.

Dark Energy Survey Year 1 Results: The Relationship
between Mass and Light around Cosmic Voids
~ Y. Fang et al
viewtopic.php?p=273864#p273864
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

User avatar
bystander
Apathetic Retiree
Posts: 19392
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

X-Ray Detection of a Cepheid Binary

Post by bystander » Fri Jan 24, 2020 6:52 pm

X-Ray Detection of a Cepheid Binary
SAO Weekly Science Update | 2020 Jan 24
A Cepheid variable star is one whose particular mass and age (along with some of its other physical parameters) result in brightness oscillations with a precise period proportional to the star's intrinsic luminosity. This extraordinarily useful property of Cepheid variables, discovered and roughly calibrated at Harvard by Henrietta Leavitt starting in 1908, allows them to be used as cosmic distance calibrators. By comparing the intrinsic brightness as determined from the period (which is easily measured) with the measured brightness, the period-luminosity relationship, a precise distance can in principle be obtained. Cepheids in nearby galaxies that are receding from us provide the basis for the famous distance-velocity relationship of galaxies that underpins the expanding model of the universe (the "big bang" model). Cepheids are so important that they have also become benchmarks for testing our understanding of stellar evolution.

Precise, long-term photometry of Cepheids from new satellites like Kepler and CoRoT has alerted astronomers to the complexity of Cepheid behaviors, and in particular to the subset that have multiple intensity periodicities. The pulsation cycle in these stars results in disturbances both in the stellar photosphere and in the hot layer just above it, the chromosphere, producing intensity fluctuations with more than one period.

The Cepheid variable star V473 Lyr, in addition to having the usual, very regular Cepheid variability (in its case, a period of 1.49 days) also has long-term variations whose approximate period is 3.3 years. Its variations, however, do not conform to the patterns found in other Cepheids. CfA astronomers Nancy Evans, Scott Wolk, Sofia Moschou, Jeremy Drake, and Vinay Kashyap and their colleagues used the XMM-Newton X-ray satellite to monitor V473 Lyr. They find that its X-ray brightness seems to be relatively stable over the cycle. They conclude that the long-term X-ray variations are not from the Cepheid itself, but most likely are caused by an orbiting, low-mass companion star, about one solar mass in size at an estimated separation of 30-300 AU (one AU is about the average distance of the Earth from the Sun). They note that X-ray discoveries of binaries like this one will help provide a more complete statistical accounting of Cepheid binary stars. In the case of V473 Lyr, the result also helps confirm that it is sun-like in its origins, being relatively rich in heavy elements like other stars in the galaxy's spiral arms.

X-ray Observations of the Peculiar Cepheid V473 Lyr Identify A Low-Mass Companion ~ Nancy Remage Evans et al
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

User avatar
bystander
Apathetic Retiree
Posts: 19392
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

Driving Massive Galaxy Outflows with Supermassive Blackholes

Post by bystander » Fri Jan 31, 2020 6:11 pm

Driving Massive Galaxy Outflows with Supermassive Blackholes
SAO Weekly Science Update | 2020 Jan 31
Active galactic nuclei (AGN) are supermassive black holes at the centers of galaxies that are accreting material onto their hot circumnuclear disks, releasing the energy in bursts of radiation or as particle jets moving at close to the speed of light. These energetic outbursts in turn drive outflows of ionized, neutral, and molecular gas that can extend over thousands of light-years and move at speeds of hundreds of kilometers per second. The gas flows can be launched directly from the hot accretion disc, though radiation pressure on the dust that is mixed in with the gas, by hot thermal winds, or other mechanisms that generate hot bubbles of gas. By driving the gas out of the galaxy, an active nucleus restricts the fuel available for further star formation and slows down the galaxy’s growth. The mechanism is also self-limiting, since it ultimately suppresses gas accreting onto the black hole. Astronomers tracking the rate of star formation across cosmic time believe this process, called quenching, is responsible for the dramatic decline in star formation since the peak of star-formation activity about ten billion years ago.

CfA astronomer Paul Nulsen and his colleagues used new and archival data from the ALMA millimeter facility to study molecular gas outflows in twelve massive galaxies at the centers of galaxy clusters. The hot gas surrounding the galaxies in these massive clusters should cool, fall back onto the galaxies, and produce more new stars, continuing the feedback cycle. The high spatial resolution of the ALMA images, taken in the emission line of carbon monoxide gas, enabled the scientist to investigate the processes in detail, in particular the filamentary structures that characterize most of the gas in these central cluster galaxies. They find that giant molecular filaments and clouds apparently form as the hot bubbles of escaping gas begin to cool, and that these outflows will eventually stall and recirculate in the galaxy. They also identify a trend between the mass of the molecular gas directly around the central AGN and the power of the jet.

Driving Massive Molecular Gas Flows in Central Cluster Galaxies with AGN Feedback ~ H.R. Russell et al
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

User avatar
bystander
Apathetic Retiree
Posts: 19392
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

The Cosmic Confusion of the Microwave Background

Post by bystander » Wed Feb 12, 2020 5:42 pm

The Cosmic Confusion of the Microwave Background
SAO Weekly Science Update | 2020 Feb 07
Roughly 380,000 years after the big bang, about 13.7 billion years ago, matter (mostly hydrogen) cooled enough for neutral atoms to form, and light was able to traverse space freely. That light, the cosmic microwave background radiation (CMBR), comes to us from every direction in the sky, uniform except for faint ripples and bumps at brightness levels of only a few part in one hundred thousand, the seeds of 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-thirty-three 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. CfA astronomers and their colleagues, working at the South Pole, have been working to find evidence for such curling, the "B-mode polarization."

Traces of this tiny effect are not only difficult to measure, they may be obscured by unrelated phenomena that can confuse or even mask it. CfA astronomer Tony Stark is a member of the large South Pole Telescope (SPT) consortium, a collaboration that has been studying galaxies and galaxy clusters in the distant universe at microwave wavelengths. Individual cosmic sources are in general dominated either by active supermassive black hole nuclei and emit radiation from the charged particle jets ejected from the regions around them, or by star formation whose radiation comes from warm dust. The emission is also probably polarized and could complicate the positive identification of CMBR B-mode radiation signals. The SPT team used a new analysis method to study the combined polarization strength of all the millimeter emission sources they find in a 500 square degree field in the sky, about four thousand objects. They conclude - good news for CMBR researchers - that the extragalactic foreground effects should be smaller than any expected B-mode signals, at least over a wide range of spatial scales.

Fractional Polarisation of Extragalactic Sources in the 500 deg2 SPTpol Survey ~ N. Gupta et al
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

User avatar
bystander
Apathetic Retiree
Posts: 19392
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

A Submillimeter Survey of Protostars

Post by bystander » Wed Feb 19, 2020 3:46 pm

A Submillimeter Survey of Protostars
SAO Weekly Science Update | 2020 Feb 14
The formation of stars involves the complex interactions of many phenomena, including gravitational collapse, magnetic fields, turbulence, stellar feedback, and cloud rotation. The balance between these effects varies significantly between sources, and astronomers have adopted a statistical approach to understand the typical, early-stage star formation sequence. The earliest stage is called the protostellar stage. For low-mass stars (those with masses about that of the sun) this stage is usually separated into two subclasses as the star grows by accreting material from a massive envelope whose size can extend between five hundred and ten thousand astronomical units (AU) in a process that can last roughly half a million years. There are considerable uncertainties, however: some gas is ejected back into the medium in strong outflows, for example.

The lack of a large, systematic survey of such sources has made it hard for astronomers to sort out the multiple processes at play. CfA astronomers Ian Stephens, Tyler Bourke, Mike Dunham, Phil Myers, Sarah Sadavoy, Katherine Lee, Mark Gurwell, and Alyssa Goodman led a team using the Submillimeter Array to compile and publish the largest public, high resolution submillimeter spectral line survey of young protostars. The team observed seventy-four young objects in the Perseus molecular cloud located about one thousand light-years away. The program, called MASSES (Mass Assembly of Stellar Systems and Their Evolution with the SMA), observed the protostars with both high and low spatial resolution, sampling scales from about three hundred AU to more than nine thousand AU in as many as forty molecular lines (although not every source had all lines).

This region had been studied before and was known to have many bipolar protostellar outflows, but the new high-resolution images reveal a wealth of outflow properties, mostly as seen in carbon monoxide gas. The study examined six of these objects that are so young they are not yet hot enough to dissociate their primary constituent gas, molecular hydrogen. These protostars are known as "first cores" and the MASSES program detected outflows in four of them, identifying one as being the most promising example of its type because of its compact nature and slow outflow velocity. This new study, the largest and most complete public survey of its kind, offers astronomers a new database for studying low-mass star formation in its earliest stages.

Mass Assembly of Stellar Systems and Their Evolution with
the SMA (MASSES)—Full Data Release
~ Ian W. Stephens et al
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

User avatar
bystander
Apathetic Retiree
Posts: 19392
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

The Radcliffe Wave

Post by bystander » Tue Feb 25, 2020 8:59 pm

The Radcliffe Wave
SAO Weekly Science Update | 2020 Feb 21
The Gould Belt is an expanding ring of young stars, gas and dust situated about a thousand light-years from the Sun - which is to say, in our solar neighborhood. It stretches over a few thousand light-years and is thought to subsume many famous nearby nebulae like the one in Orion. The physical relationships between its many gas clouds, if any, have been unknown because the uncertainties in their distances are comparable to or even larger than their dimensions.

CfA astronomers Catherine Zucker, Alyssa Goodman, Josh Speagle, and Doug Finkbeiner and their colleagues used new astrometric surveys like the Gaia mission, coupled with detailed analyses of stellar brightenesses, colors, and distances to construct three-dimensional maps of the Milky Way around the Gold Belt to higher accuracies than ever before. The new distance information reveals for the first time the three-dimensional structure of the clouds in the solar neighborhood, including the presumptive Gould Belt clouds and others like the North American Nebula that had not been previously associated with the Gould Belt. They discovered that the clouds are not quasi-randomly distributed in a ring, as had been thought, but rather form a dramatic, elongated structure stretching about nine thousand light-years in length. The formation includes the majority of nearby star-forming regions, has an aspect ratio of about twenty-to-one, and contains about three million solar masses of gas. Most remarkably, this structure appears to be undulating, with a three-dimensional shape well described by a damped sinusoidal wave on the plane of the Milky Way with an average period of about seven thousand light-years and a maximum amplitude of about five hundred light-years.

The astronomers have named the structure the Radcliffe Wave in honor of both the early-20th-century female astronomers from Radcliffe College and the interdisciplinary spirit of the current Radcliffe Institute, which contributed to the discovery. The origin of the Radcliffe Wave is unclear but the scientists speculate that it could be the outcome of a large-scale galactic process, perhaps a shock front in the galaxy's nearby spiral arm. Why it should be such a well-defined wave, however, is even harder to explain; possibly it implies some sort of collision. The Radcliffe Wave provides a new framework for understanding molecular cloud formation and evolution. The team concludes by calling for a revision in the architecture of the gas in the solar neighborhood and a re-interpretation of other local structural phenomena.

A Galactic-Scale Gas Wave in the Solar Neighbourhood ~ João Alves et al
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor