Researchers Develop New Monte Carlo Code for Solving Radiative Transfer Equations (Astronomy)

Recently, YANG Xiaolin and his collaborators from Yunnan Observatories of the Chinese Academy of Sciences developed a new fast code, Lemon (Linear Integral Equations’ Monte Carlo Solver Based on Neumann Solution), aiming to solve the radiation transfer processes (RTPs) precisely. The scheme of the code is based on linear integral equation and its Neumann series solution. The study was published in The Astrophysical Journal Supplement Series.

RTs are the most primary and omnipresent physical processes in the field of astrophysics, and they play an important role both in theoretical researches and practical observations. To solve RTs, various methods have been proposed, among which the Monte Carlo (MC) method is the most important and widely used numerical method due to its simplicity yet powerful and remarkable performances.

The conventional MC method (or photon tracing scheme), however, has an intrinsic defect that is the large amount of computations usually produce a result with quit low statics and large variance, since a significant portion of the computational cost are totally wasted.

In order to overcome the defect, YANG Xiaolin and his collaborators proposed a new scheme, in which they suggested that the MC method employed to solve the RTs should be built on the integral equation and its Neumann solution rather than photon tracing.

The new scheme has major advantages. It can compel the photons to make contributions to the results at each scattering site, significantly improving the calculation efficiency and accuracy. As a result, the aforementioned defect is overcome or alleviated in some sense. It can treat the RTs with and without polarizations in a unified framework and simplify the computation procedure, if the geometric configuration of the system has an axial or spherical symmetry. Besides, it can be applied directly to solve any linear differential-integral equations with initial or boundary conditions appropriately provided.

Lemon is developed completely on this new scheme and written in FORTRAN 90 language. It is publicly available and can be downloaded from: https://github.com/yangxiaolinyn/Lemon. At present, Lemon can solve the problems of RTs mainly restricted to flat space-time. To increase the computing speed, Lemon implements the simplest parallel computation by adopting the Message Passing Interface (MPI) scheme.

The validation of Lemon has been verified by reproducing the results of several test problems. One can find that Lemon is characterized by fast speed, flexibility in computational methods, high efficiency and accuracy, which guarantees the potential applications of Lemon for the calculations of RTs in the future.


Reference

A New Fast Monte Carlo Code for Solving Radiative Transfer Equations Based on the Neumann Solution


Provided by Chinese Academy of Sciences

Scientists Identify A Rare Magnetic Propeller in a Binary Star System (Planetary Science)

Researchers at the University of Notre Dame have identified the first eclipsing magnetic propeller in a cataclysmic variable star system, according to research forthcoming in the Astrophysical Journal.

The star system, referred to as J0240, is only the second of its kind on record. It was identified in 2020 as an unusual cataclysmic variable — a binary system consisting of a white dwarf star and a mass-donating red star. Normally, the compact white dwarf star collects the donated gas and grows in mass. In J0240, however, the fast-spinning, magnetic white dwarf rejects the donor’s gas and propels it out of the binary system.

“It takes a rapidly spinning dwarf with a strong magnetic field in order to create a propeller,” said Peter Garnavich, professor of astrophysics and cosmology physics and chair of the Department of Physics at Notre Dame, and lead author of the study that presented evidence of the propeller system. “Normally, gas coming off of the donor star will land on the white dwarf. That’s as common as sand on a beach. But in a magnetic propeller, the gas is ejected from the binary in a wide spiral pattern — like a lawn sprinkler watering your yard.”

White dwarfs are the dense remnants of low-mass stars like our sun, which scientists say will evolve into a white dwarf in another five billion years or so. Without a companion star, however, the sun will never be part of a cataclysmic variable system.

The only other cataclysmic variable similar to J0240 is AE Aquarii, a binary star system known since the 1950s and believed to also be a magnetic propeller system. Conversely, J0240 is observed close to the binary orbital plane, meaning that the gas ejected from the system is seen silhouetted against the light of the stars. This is the first direct evidence that a magnetic propeller ejects the red star’s donated gas.

 “What’s unique about the system is that we actually can see blobs of gas as they’re ejected by the propeller,” Garnavich said. “That gas is blocking some of the light from both stars and we can directly see that absorption in our data.”

Garnavich’s team began observations at the Large Binocular Telescope in Safford, Arizona, where the researchers were able to record the occurrence of flares and eclipses that illustrated the rapid spinning of the white dwarf star, and the pull of the magnetic field — which expels incoming gases that would otherwise be added to the star but instead creates a spiral of gas expanding away from the two stars.

 “The more we observed the star, the more exciting it appeared,” said Garnavich. The team gathered observations in September, October and November of 2020. Data gathered in September captured the first half of J0240’s orbit. In October, the team captured the second half.

“The flares we see are mini-explosions that blow off gas at 6 million miles per hour, or 1 percent of the speed of light,” he said.

The flaring disappears when the red companion gets in the way during an eclipse. From the timing of the eclipses, the team was able to pinpoint the location of the flares. “The flaring is coming from very close to the compact companion, likely from the whack the gas receives as it approaches the rapidly spinning magnetic field,” Garnavich said.

Garnavich hopes to learn a lot more from the J0240 binary from further observations. One of the big unknowns is the white dwarf spin period, which the team was unable to detect.  “The energy of the propeller is coming from the spinning white dwarf, so we expect the spin rate to be slowing over time. When it runs down, the propeller will stop and the system will look like a ordinary cataclysmic variable,” said Garnavich.

“The biggest question is exactly how do you get into this state,” he said. “It’s a very short-lived phase where you have a magnetic white dwarf spinning about as fast as it can spin without actually flying apart. Spinning so fast with a strong magnetic field — seems like it can’t be just coincidence.”

Co-authors on the study include Colin Littlefield, also at Notre Dame; Mark Wagner at Ohio State University and the Large Binocular Telescope Observatory; Jan van Roestel and Amruta Jaodand at the California Institute of Technology; Paula Szkody at the University of Washington; and John Thorstensen at Dartmouth College.

A preprint of the study is available here.

Featured image: An illustration of a fast-spinning, magnetic white dwarf rejecting the donor gas in the cataclysmic variable known as J0240. (Credit: Dr. Mark Garlick)


Reference: Confirmation of a Second Propeller: A High-Inclination Twin of AE~Aquarii. arXiv:2102.08377v1 [astro-ph.SR] arxiv.org/abs/2102.08377


Provided by University of Notre Dame

New X-ray Map Reveals Growing Supermassive Black Holes in Next-gen Survey Fields (Cosmology)

The XMM-SERVS survey lays key groundwork for studying the cosmic history and physical properties of active galaxies

One of the largest X-ray surveys using the European Space Agency’s XMM-Newton space observatory has mapped nearly 12,000 X-ray sources across three large, prime regions of the sky. The X-ray sources represent active galactic nuclei and galaxy clusters, and the survey captures the growth of the supermassive black holes at the cores of these galaxies. This X-ray survey complements previous X-ray surveys, allowing the researchers to map active galactic nuclei in a wide range of cosmic environments.

Qingling Ni and W. Niel Brandt from Penn State will present the results of the XMM-Spitzer Extragalactic Representative Volume Survey (XMM-SERVS) at a press briefing being held Monday, June 7, at 4:30 p.m. during the 238th meeting of the American Astronomical Society. A paper describing the survey, by an international team of astronomers, has been submitted to The Astrophysical Journal Supplement.

“X-ray surveys are the best way to find growing supermassive black holes, which are located at the cores of many large galaxies,” said Ni, a graduate student at Penn State and lead author of the paper. “With this massive new survey, we can access population data about growing supermassive black holes to better understand their physical properties and evolution over cosmic history.”

XMM-Newton image of the 3.2-square-degree ELAIS-S1 field
XMM-Newton image of the 3.2-square-degree ELAIS-S1 field, which is about 15 times larger than the apparent size of the full moon (shown to scale at lower right). XMM-SERVS provides a wide, sensitive X-ray view of this region. IMAGE: ESA/XMM-NEWTON/XMM-SERVS COLLABORATION/Q. NI ET AL.

Currently available X-ray surveys are primarily either deep “pencil-beam” surveys covering a very small part of the sky or shallow surveys covering large sky areas. Deep pencil-beam surveys can only sample active galactic nuclei in a limited cosmic volume, and they lack the ability to explore a wide dynamic range of cosmic environments. Shallow, wide-field surveys can sample a wider variety of environments but lack the sensitivity to detect the bulk of cosmic supermassive black hole growth.

The new XMM-SERVS survey helps to fill the gap between deep pencil-beam X-ray surveys and shallow X-ray surveys over large sky areas. The XMM-SERVS survey provides medium-deep X-ray coverage for three widely separated sky fields that have previously been studied at multiple wavelengths. Additionally, these regions have been selected as Deep-Drilling Fields of the Legacy Survey of Space and Time (LSST) to be conducted by the Vera C. Rubin Observatory. The Rubin Observatory is an 8.4-meter giant survey telescope located in north-central Chile, which is presently being constructed at a cost of more than $600 million. It represents one of the largest investments of the worldwide astronomical community in this decade.

The LSST Deep-Drilling Fields are sky regions where substantially more observations will be obtained compared to typical sky regions during the ten-year LSST survey, enabling new scientific discoveries. The XMM-SERVS survey fields are also the sites of multiple other upcoming surveys at radio, submillimeter, infrared, and optical wavelengths. One of the XMM-SERVS survey fields is also among the Deep Fields of the €600-million space mission Euclid that will launch in 2022. Thus, the X-ray coverage provided by XMM-SERVS has enormous legacy value in conjunction with these other rich datasets.

“These sky fields span a wide variety of cosmic environments,” said Ni. “So we are getting a view of supermassive black hole growth that is hopefully unbiased by local cosmic factors. Additionally, over the past decade astronomers have established that there is a strong correlation between black-hole growth and the properties of galaxies, but the limited sample size restricted these studies to proper investigation of only a few galaxy parameters. Our new large sample of growing supermassive black holes will allow us to look at many more galaxy parameters together.”

XMM-Newton image of the 5.3-square-degree XMM-LSS field
XMM-Newton image of the 5.3-square-degree XMM-LSS field, which is about 25 times larger than the apparent size of the full moon (shown to scale at lower right). XMM-LSS was the first XMM-SERVS field to have been observed by XMM-Newton. Chien-Ting Chen, a former postdoctoral researcher at Penn State who is now an astronomer at USRA, led the work for this field (see Chen et al. 2018, Mon. Not. Roy. Ast. Soc.). XMM-SERVS provides a wide, sensitive X-ray view of this region. IMAGE: ESA/XMM-NEWTON/XMM-SERVS COLLABORATION/Q. NI ET AL.

The fields covered by the XMM-SERVS survey are the Wide Chandra Deep Field-South (W-CDF-S), the European Large-Area Infrared Space Observatory S1 Survey (ELAIS-S1), and the XMM-Newton Large-Scale Structure Survey (XMM-LSS). These sky areas, each spanning a few square degrees, are already among the best-studied fields in the sky, and with the coming LSST and other coverage they will be prime next-generation survey fields.

“This survey represents key foundational work upon which, I suspect, hundreds of studies will be built over the next decade or two,” said Brandt, Verne M. Willaman Professor of Astronomy and Astrophysics and professor of physics at Penn State, and one of the leaders of the study. “XMM-Newton was the best mission to gather these data, and we needed to invest a lot of observation time for this study — with a total combined exposure of nearly 60 days — because it will be so important for active galaxy studies, galaxy cluster studies, and for understanding large-scale structures in the universe. It required a multiyear, multinational effort and it’s incredibly gratifying to get it done. We are most grateful to the European Space Agency and NASA for their long-term support of this work.”

In addition to Ni and Brandt, the research team includes Chien-Ting Chen, USRA; Bin Luo, Nanjing University; Kristina Nyland, NRC fellow; Guang Yang, Texas A&M University; Fan Zou, Donald P. Schneider and John D. Timlin III, Penn State; James Aird, University of Edinburgh; David M. Alexander, Durham University; Franz Erik Bauer, PUC; Mark Lacy, NRAO; Bret D. Lehmer, University of Arkansas; Labani Mallick, IIA; Mara Salvato, MPE; Paolo Tozzi, Cristian Vignali, Andrea Comastri, Roberto Gilli and Maurizio Paolillo, INAF-Florence, Bologna and Naples; Iris Traulsen and Axel Schwope, AIP; Mattia Vaccari, University of Western Cape; Fabio Vito, SNS-Pisa; Yongquan Xue, USTC; Manda Banerji, University of Southampton; Kate Chow, CSIRO; Agnese Del Moro, DLR; James Mullaney, University of Sheffield; Ohad Shemmer, University of North Texas; Mouyuan Sun, Xiamen University; and Jonathan R. Trump, University of Connecticut.

Many of the non-Penn State authors of this work are former members of the Astronomy and Astrophysics Department at Penn State.

Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member states and the United States (NASA).

Featured image: XMM-Newton image of the 4.6-square-degree W-CDF-S field reveals the wide, sensitive view of the X-ray sky provided by XMM-SERVS. The detected sources, most of which are growing supermassive black holes, are color coded according to the energies of the X-rays detected (with red having the lowest energies and blue the highest). The white outline indicates the area of the Chandra Deep Field-South, a well-known ultradeep pencil-beam X-ray survey. The image highlights how XMM-SERVS has now provided sensitive panoramic X-ray imaging around this survey. The XMM-Newton image covers an area about 20 times larger than the apparent size of the full moon, shown to scale at upper left.Image: ESA/XMM-Newton/XMM-SERVS Collaboration/Q. Ni et al.


Provided by Penn State

Organic Molecules Reveal Clues About Dying Stars and Outskirts of Milky Way (Cosmology)

Researchers from the University of Arizona have detected organic molecules in planetary nebulae, the aftermaths of dying stars, and in the far reaches of the Milky Way, which have been deemed too cold and too removed from the galactic center to support such chemistries. They present their findings at the 238th Meeting of the American Astronomical Society, or AAS, held virtually from June 7-9.

A team led by Lucy Ziurys at the University of Arizona reports observations of organic molecules in planetary nebulae in unprecedented detail and spatial resolution. Using the Atacama Large Millimeter Array, or ALMA, Ziurys and her team observed radio emissions from hydrogen cyanide (HCN), formyl ion (HCO+) and carbon monoxide (CO) in five planetary nebulae: M2-48, M1-7, M3-28, K3-45 and K3-58.

The emission from these molecules was found to outline the shapes of planetary nebulae, which previously had only been observed in visible light. In some cases, molecular signatures revealed previously unseen features. The high resolution of one arcsecond, equivalent to a dime viewed from 2.5 miles away, resulted in striking images of the nebulae, clearly showing the complex geometries of the dense, ejected material with bars, lobes and arcs never clearly observed before.

Planetary nebulae are bright objects, produced when stars of a certain type reach the end of their evolution. Most stars in our galaxy, including the sun, are expected to end their lives this way. As the dying star sheds large amounts of its mass into space and becomes a white dwarf, it usually emits strong ultraviolet radiation. This radiation was long thought to break up any molecules hurled into the interstellar medium from the dying star and reduce them to atoms.

Detection of organic molecules in planetary nebulae in recent years have shown that this is not the case, however, and the observations presented here further support the idea that planetary nebula serve as critical sources that seed the interstellar medium with molecules that serve as the raw ingredients in the formation of new stars and planets. Planetary nebulae are thought to provide 90% of the material in the interstellar medium, with supernovae adding the remaining 10%.

“It was thought that molecular clouds which would give rise to new stellar systems would have to start from scratch and form these molecules from atoms,” said Ziurys, a Regent’s Professor of Chemistry and Astronomy at UArizona. “But if the process starts with molecules instead, it could dramatically accelerate chemical evolution in nascent star systems.”

Ziurys and her team believe the shape shifting behavior in the nebulae’s geometry may be driven by certain processes involved in nucleosynthesis, in other words, the forging of new elements inside a star.

“It tells us that in a dying star, which is spherical until its final phase, some very interesting dynamics occurs once it goes through the planetary nebula stage, which changes that spherical shape,” Ziurys said. “These stars just lose their mass, and so there’s really no mechanism for them to all of a sudden become bipolar or even quadrupolar.”

According to the researchers, one possible explanation could be helium flashes, which originate in a hot, convective shell around the core of a dying star and could possibly provide a source of explosive nuclear synthesis away from the star’s center, resulting in the very complex shapes seen in some nebulae.

“This could probably distort the spherical shape because a helium flash can explode through the poles of a star, where it will be directed by magnetic fields, and that will have an effect on the shape of the nebula that will form around it,” she said.

According to Ziurys, many planetary nebulae are something of an enigma, because they evolved from spherical stars but then gave rise to bipolar or even quadrupolar structures.

“It’s been a puzzle to astronomers as to how you go from a spherical geometry into these multipolar geometries,” she said. “The molecules we observed trace the polar geometries beautifully, and so we’re hoping that this is going to give us some insight into the shaping of planetary nebulae.”

In a second presentation, Lilia Koelemay, a doctoral student in Ziurys’ research group, will report on the discovery of organic molecules in the outskirts of the Milky Way, more than twice as far from the galactic center than what is known as the Galactic Habitable Zone, or GHZ.

The Milky Way’s GHZ, which includes the solar system, is a region considered to have favorable conditions for the formation of life. It is thought to extend to only up to 10 kiloparsecs, or about 32,600 light-years, from the galactic center.

Using the UArizona ARO 12-Meter Telescope on Kitt Peak near Tucson, Arizona, Koelemay, Ziurys and team searched 20 molecular clouds in the Milky Way’s Cygnus arms for signature emission spectra of methanol, a basic organic molecule. At a mere 20 Kelvin, these clouds are typically extremely cold and far from the galactic center, at a distance of 13 to 23.5 kiloparsecs. The team detected methanol in all 20 clouds.

According to Koelemay, the detection of these organic molecules at the galactic edge may imply that organic chemistry is still prevalent at the outer reaches of the galaxy, and the GHZ may extend much further from the galactic center than the current established boundary.

“Scientists have wondered about the extent of organic chemistry in our galaxy for a long time, and it was always thought that not too far beyond our sun, we’re not going to see a lot of organic molecules,” Koelemay said. “The widely held assumption was that in the outskirts of our galaxy the chemistry necessary to form organics just doesn’t occur.”

That conclusion was partly based on the supposed dearth of organic molecules in the outer reaches of the galaxy, according to the researchers. The notion of the galactic habitable zone is based on the idea that for habitable conditions to exist where life can evolve, a planetary system can’t be too close to the galactic center with its extremely high density of stars and intense radiation, and it can’t be too far out, because there would not be enough elements critical for life, such as oxygen, carbon and nitrogen.

The observations were made possible by a new 2-millimeter wavelength receiver with unprecedented sensitivity. Developed in a collaboration between Ziurys, Gene Lauria, an engineer at Steward Observatory, and the National Radio Astronomy Observatory, the receiver allows for detection of molecular emission lines in a wavelength bandwidth radio astronomers in the US could not access for many years.

“Without this new instrument, these observations would have taken hundreds of hours, which is not feasible,” Ziurys said. “With this new capability, we expect to dramatically open our observation window and detect molecules in other regions of our galaxy previously thought to be devoid of such chemistry.”

Recently, Koelemay has begun to look for other molecules besides methanol, such as methyl cyanide, organic molecules with ring structures and others that contain functional groups known to be crucial building blocks for biomolecules. Discoveries of these molecules in the interstellar medium have attracted much interest, as many researchers deem them promising candidates for the emergence of life. When organic molecules are present in emerging planetary systems, they can condense onto the surfaces of asteroids, which then deliver them to nascent planets, where they could potentially jump-start the evolution of life.

“We’re finding these species way on the outskirts of the galaxy, and the abundance doesn’t even drop off 10 kiloparsecs from the solar system, where the chemistry necessary for building the molecules necessary for life just wasn’t believed to occur,” said Ziurys, Koelemay’s adviser and a co-author on the report. “The fact that they’re there expands the prospects of habitable planets forming far beyond what has been considered the habitable zone is extremely exciting.”

Researchers from the University of Arizona will present findings from radio-astronomical observations of organic molecules at the 238th Meeting of the American Astronomical Society, or AAS, during a press conference titled “Molecules in Strange Places” at the 238th AAS Meeting on Tuesday, June 8, at 12:15 p.m. EDT.


To know more:


Provided by University of Arizona

Cosmic Cartographers Map Nearby Universe Revealing the Diversity of Star-forming Galaxies (Cosmology)

Study reveals that the makeup and life cycle of star-forming clouds is dependent on location

A team of astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) has completed the first census of molecular clouds in the nearby Universe, revealing that contrary to previous scientific opinion, these stellar nurseries do not all look and act the same. In fact, they’re as diverse as the people, homes, neighborhoods, and regions that make up our own world.  

Stars are formed out of clouds of dust and gas called molecular clouds, or stellar nurseries. Each stellar nursery in the Universe can form thousands or even tens of thousands of new stars during its lifetime. Between 2013 and 2019, astronomers on the PHANGS— Physics at High Angular Resolution in Nearby GalaxieS— project conducted the first systematic survey of 100,000 stellar nurseries across 90 galaxies in the nearby Universe to get a better understanding of how they connect back to their parent galaxies.

“We used to think that all stellar nurseries across every galaxy must look more or less the same, but this survey has revealed that this is not the case, and stellar nurseries change from place to place,” said Adam Leroy, Associate Professor of Astronomy at Ohio State University (OSU), and lead author of the paper presenting the PHANGS ALMA survey. “This is the first time that we have ever taken millimeter-wave images of many nearby galaxies that have the same sharpness and quality as optical pictures. And while optical pictures show us light from stars, these ground-breaking new images show us the molecular clouds that form those stars.”

The scientists compared these changes to the way that people, houses, neighborhoods, and cities exhibit like-characteristics but change from region to region and country to country.

Shown here as an ALMA (orange/red) composite with Hubble Space Telescope (HST) data, NGC4254 was among the nearly 100 galaxies included in the recent PHANGS project census of galaxies in the nearby Universe. The survey found that stellar nurseries within these galaxies vary widely in appearance and behavior, and that these characteristics heavily depend on where the stellar nurseries are located. NGC4254 is an example of a galaxy featuring M type morphology. Credit: ALMA (ESO/NAOJ/NRAO)/PHANGS, S. Dagnello (NRAO)

“To understand how stars form, we need to link the birth of a single star back to its place in the Universe. It’s like linking a person to their home, neighborhood, city, and region. If a galaxy represents a city, then the neighborhood is the spiral arm, the house the star-forming unit, and nearby galaxies are neighboring cities in the region,” said Eva Schinnerer, an astronomer at the Max Planck Institute for Astronomy (MPIA) and principal investigator for the PHANGS collaboration “These observations have taught us that the “neighborhood” has small but pronounced effects on where and how many stars are born.”

To better understand star formation in different types of galaxies, the team observed similarities and differences in the molecular gas properties and star formation processes of galaxy disks, stellar bars, spiral arms, and galaxy centers. They confirmed that the location, or neighborhood, plays a critical role in star formation.

“By mapping different types of galaxies and the diverse range of environments that exist within galaxies, we are tracing the whole range of conditions under which star-forming clouds of gas live in the present-day Universe. This allows us to measure the impact that many different variables have on the way star formation happens,” said Guillermo Blanc, an astronomer at the Carnegie Institution for Science, and a co-author on the paper.

“How stars form, and how their galaxy affects that process, are fundamental aspects of astrophysics,” said Joseph Pesce, National Science Foundation’s program officer for NRAO/ALMA. “The PHANGS project utilizes the exquisite observational power of the ALMA observatory and has provided remarkable insight into the story of star formation in a new and different way.”

NGC4535 is a galaxy in the nearby Universe featuring grand-design spiral plus stellar bar morphology. It was catalogued along with nearly 100 other galaxies during a recent census by the PHANGS project. The census revealed that contrary to commonly accepted scientific theory, not all stellar nurseries look or act the same way. In fact, they’re quite diverse. NGC4535 is shown here as an ALMA (orange/red) composite with Hubble Space Telescope (HST) data.
Credit: ALMA (ESO/NAOJ/NRAO)/PHANGS, S. Dagnello (NRAO)

Annie Hughes, an astronomer at L’Institut de Recherche en Astrophysique et Planétologie (IRAP), added that this is the first time scientists have a snapshot of what star-forming clouds are really like across such a broad range of different galaxies. “We found that the properties of star-forming clouds depend on where they are located: clouds in the dense central regions of galaxies tend to be more massive, denser, and more turbulent than clouds that reside in the quiet outskirts of a galaxy. The lifecycle of clouds also depends on their environment. How fast a cloud forms stars and the process that ultimately destroys the cloud both seem to depend on where the cloud lives.”

This is not the first time that stellar nurseries have been observed in other galaxies using ALMA, but nearly all previous studies focused on individual galaxies or part of one. Over a five-year period, PHANGS assembled a full view of the nearby population of galaxies. “The PHANGS project is a new form of cosmic cartography that allows us to see the diversity of galaxies in a new light, literally. We are finally seeing the diversity of star-forming gas across many galaxies and are able to understand how they are changing over time. It was impossible to make these detailed maps before ALMA,” said Erik Rosolowsky, Associate Professor of Physics at the University of Alberta, and a co-author on the research. “This new atlas contains 90 of the best maps ever made that reveal where the next generation of stars is going to form.”

For the team, the new atlas doesn’t mean the end of the road. While the survey has answered questions about what and where, it has raised others. “This is the first time we have gotten a clear view of the population of stellar nurseries across the whole nearby Universe. In that sense, it’s a big step towards understanding where we come from,” said Leroy. “While we now know that stellar nurseries vary from place to place, we still do not know why or how these variations affect the stars and planets formed. These are questions that we hope to answer in the near future.”

Ten papers detailing the outcomes of the PHANGS survey are presented this week at the 238th meeting of the American Astronomical Society.

Featured image: Using the Atacama Large Millimeter/submillimeter Array (ALMA), scientists completed a census of nearly 100 galaxies in the nearby Universe, showcasing their behaviors and appearances. The scientists compared ALMA data to that of the Hubble Space Telescope, shown in composite here. The survey concluded that contrary to popular scientific opinion, stellar nurseries do not all look and act the same. In fact, as shown here, they are as different as the neighborhoods, cities, regions, and countries that make up our own world.
Credit: ALMA (ESO/NAOJ/NRAO)/PHANGS, S. Dagnello (NRAO)


Resource
PHANGS-ALMA: Arcsecond CO(2-1) Imaging of Nearby Star-Forming Galaxies, Leroy et al. ApJS accepted, preview [https://arxiv.org/abs/2104.07739]


Provided by NRAO

Scientists Lead Ambitious Study To Reach Infinity and Beyond (Astronomy)

To cover the vast distances between Alpha Centauri and our own solar system, we must think outside the box and forge a new way for interstellar space travel.

Scientists from The Australian National University (ANU) have designed a new type of space-craft propulsion system as part of an ambitious international project that aims to explore the worlds surrounding our second nearest star, Alpha Centauri.  

The Breakthrough Starshot project calls for the design of an ultra-lightweight spacecraft, which acts as a light-sail, to travel with unprecedented speed over tens of trillions of kilometres to the star about four lightyears away, reaching the destination within 20 years.  

The sheer scale and size of the interstellar distances between solar systems is difficult for most people to comprehend. Travel from Earth to Alpha Centauri using today’s conventional spacecraft would take more than 100 lifetimes.  

In a recent paper published in the Journal of the Optical Society of America B, the ANU team, with funding support from Breakthrough Initiatives, outlines their design concept for the laser propulsion system to be used to launch the probes from Earth. 

Lead author Dr Chathura Bandutunga said the light to power the sail will come from the Earth’s surface – a giant laser array with millions of lasers acting in concert to illuminate the sail and push it onto its interstellar journey. 

“To cover the vast distances between Alpha Centauri and our own solar system, we must think outside the box and forge a new way for interstellar space travel,” Dr Bandutunga, from the Applied Metrology Laboratories at the ANU Centre for Gravitational Astrophysics, said.   

“Once on its way, the sail will fly through the vacuum of space for 20 years before reaching its destination. During its flyby of Alpha Centauri, it will record images and scientific measurements which it will broadcast back to Earth.” 

The ANU team has expertise in different areas of optics spanning astronomy, gravitational wave instrumentation, fiber-optic sensors and optical phased arrays. 

The founding scientist who pioneered the ANU node of this project, Dr Robert Ward, said an important part of this grand vision is the development of the laser array – in particular, designing a system to have all the lasers act as one.   

“The Breakthrough Starshot program estimates the total required optical power to be about 100 GW – about 100 times the capacity of the world’s largest battery today,” Dr Ward, from the ANU Research School of Physics, said.  

“To achieve this, we estimate the number of lasers required to be approximately 100 million.  

Researcher and fellow author, Dr Paul Sibley, said one of the main challenges we tackled is how to make measurements of each laser’s drift.  

“We use a random digital signal to scramble the measurements from each laser and unscramble each one separately in digital signal processing,” he said. 

“This allows us to pick out only the measurements we need from a vast jumble of information. We can then break the problem into small arrays and link them together in sections.” 

To orchestrate the show, the ANU design calls for a Beacon satellite – a guide laser placed in Earth orbit which acts as the conductor, bringing the entire laser array together.  

Professor Michael Ireland from the ANU Research School of Astronomy and Astrophysics said the design of the laser “engine” requires compensation for the atmosphere.  

“Unless corrected, the atmosphere distorts the outgoing laser beam, causing it to divert from its intended destination,” he said.  

“Our proposal uses a laser guide star. This is a small satellite with a laser which illuminates the array from Earth orbit. As the laser guide star passes through the atmosphere on the way back to Earth, it measures the changes due to the atmosphere. 

“We have developed the algorithm which allows us to use this information to pre-correct the outgoing light from the array.” 

Dr Bandutunga said just like the eventual light-sail, this research is at the beginning of a long journey. 

“While we are confident with our design, the proof is in the pudding,” he said.  

“The next step is to start testing some of the basic building blocks in a controlled laboratory setting. This includes the concepts for combining small arrays to make larger arrays and the atmospheric correction algorithms.  

“The work done at ANU was to see if this idea would conceivably work. The goal was to find out-of-the-box solutions, to simulate them and determine if they were physically possible.  

“While this proposal was put forward by the ANU team, there is more work happening internationally to come up with unique and clever solutions to other parts of the problem. 

“It’ll be exciting to bring these solutions together to bring the project to life.” 

BACKGROUND: 

Breakthrough Starshot is one of the Breakthrough Initiatives, a suite of scientific and technological programs founded by Yuri Milner, investigating life in the Universe. Other Initiatives include Breakthrough Listen, the largest ever astronomical search for signs of intelligent life beyond Earth, and Breakthrough Watch, a global astronomical program aiming to identify and characterise planets around nearby stars. 

Featured image: Starshot light-sail © Breakthrough Initiatives


Provided by Australian National University

Ten Candles for the Vst (Astronomy)

The Vst (Vlt Survey Telescope) telescope, built by the National Institute of Astrophysics in the Chilean Atacama Desert for the Eso observatory in Cerro Paranal, celebrates ten years of operation and scientific achievements. And paraphrasing Enzo Ferrari, who was an expert in Italian achievements, for this all-Italian telescope in the best site in the world, the best result is what is yet to come.

Ten years and it seems like yesterday. Today we celebrate an important birthday in the history of the Vst telescope , which the National Institute of Astrophysics has designed and implemented at the Eso Observatory of Cerro Paranal , the best in the world for scientific productivity , where it operates alongside the giants of the Very Large Telescope . On June 8, 2011 , OmegaCam’s first recorded VST image was officially released , its wide-field camera of nearly 300 million pixels capable of shooting wide-angle images of 1 degree side. Behind the scenes, the spectacular work of a team with great technical and human qualities.

On the night of the first light, before starting work, an understandable tension hung in the air. When the dust was set on fire, dozens of people crowded behind the control stations, waiting for a few long seconds, in an unreal silence, for the first reading of the detector to end and the first image to be composed on the monitor. It was a success: the first images revealed a system already functioning splendidly with an angular resolution of 0.5 seconds of arc, at the limit imposed by the atmospheric turbulence of that night. Well hidden for good luck, champagne, glasses and even a reproduction of the football world cup jumped out at the right moment, very suited to the celebratory spirit of the moment.

The ESO Cerro Paranal Observatory with VST on the right. Credits: G. Hüdepohl (atacamaphoto.com) / Eso

Since then, time has flown by, leaving behind the first hundreds of articles produced with telescope data by astronomers from Italy and around the world. And at ten you are young and you continue to grow. In fact, over the years the Vst has constantly improved both for scientific production and in reliability: in recent years it has been the telescope with the most science time among the ESO telescopes, notoriously the best in these statistics. Blowing out the candles, let’s turn a confident look to the future: for this all-Italian telescope in the best site in the world, paraphrasing Enzo Ferrari who was an expert in Italian creations, the best result is what is yet to come.

Featured image: The first image officially released by VST on June 8, 2011: the star-forming region Messier 17, also known as the Omega Nebula or the Swan Nebula. Credits: ESO / INAF-VST / OmegaCAM. Acknowledgment: OmegaCen / Astro-WISE / Kapteyn Institute


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Provided by INAF

Tracking RNA Through Space and Time (Medicine)

A research team at the MDC has succeeded in tracking genes through space and time within a one-cell zebrafish embryo – even before cell division occurs. They have now described a method in the journal “Nature Communications” that may one day allow scientists to measure cell response to drugs, for example, in organoids.

The “miracle of life” is most obvious at the very beginning: When the fertilized egg cell divides by means of furrows into blastomeres, envelops itself in an amniotic sac, and unfolds to form germ layers. When the blastomeres begin to differentiate into different cells – and when they eventually develop into a complete organism.

“We wanted to find out whether the later differences between the various cells are already partly hard-wired into the fertilized egg cell,” says Dr. Jan Philipp Junker, who heads the Quantitative Developmental Biology Lab at the Berlin Institute for Systems Biology (BIMSB) of the Max Delbrück Center for Molecular Medicine in the Helmholtz Association (MDC). Junker and his team are investigating how cells make decisions and what dictates whether they become nerve, muscle, or skin cells. This involves creating cell lineage trees that allow them to determine the lineage and cell type of thousands of individual cells from an organism. Using these lineage trees, they can understand how and by what mechanisms cells come together to form a functioning organism or how they respond to perturbations.

Blueprints for different cell types already exist in the one-cell embryo

“The program for subsequent cell differentiation is hard-wired into the fertilized egg cell.”, Karoline Holler, Lead author of the study.

Yet this search for clues by means of cell lineage trees begins at a later stage – namely, when cell division and differentiation is already under way. What’s more, the observations cover long time periods. In their current study, which has just been published in the journal “Nature Communications”, Junker and his team focus on a very short time period: the first hours after fertilization, from the one-cell stage to the process of gastrulation – the formation of the germ layers – of the embryo. The scientists wanted to know whether the one-cell embryo already contains parts of the blueprint for the multitude of different cell types that later develop from it. To do this, they studied zebrafish and clawed frog embryos. Researchers had previously succeeded in finding individual genes whose RNA is localized at specific sites within one-cell zebrafish embryos. The Berlin scientists have now shown that there are many more such genes. “We have discovered ten times more genes whose RNA is spatially localized in the fertilized egg cell than previously known,” explains Karoline Holler, lead author of the study. “Many of these RNA molecules are later transported into the primordial germ cells. This means that the program for subsequent cell differentiation is hard-wired into the fertilized egg cell.”

New approaches in transcriptomics

One-cell zebrafish embryo
One-cell zebrafish embryo: The MDC research lab found numerous localized genes at this early stage of development. Much of their genetic information flows into the precursor cells of the later germ cells© AG Junker, MDC

State-of-the-art methods of single-cell transcriptomics provide a good understanding of cell differentiation. Scientists order individual cells according to the similarity of their transcriptome – the complete collection of RNA molecules present in a cell – and can use the patterns that emerge to decipher how the cells became what they are. However, they cannot use this method to reconstruct the earliest stages of embryonic development, because here the spatial arrangement of RNA

molecules is crucial. His team instead used a specialized technique called tomo-seq, which Junker developed at the Hubrecht Institute in the Netherlands in 2014. It enables scientists to spatially track RNA molecules within the cell. This is achieved by cutting embryos of the model organisms into thin slices. It is then possible read the RNA profiles on the cut surfaces and convert them into spatial expression patterns. Holler refined the tomo-seq technique to now measure the spatial distribution of the transcriptome within the fertilized egg cell.

zebrafish
The zebrafish is used as model organism in the laboratory of Jan-Philipp Junker.© Pablo Castagnola/MDC

The scientists used another new technique to study which localized genes later contribute to which cells. “We labeled the RNA molecules so as to be able to track them over different developmental stages. This allows us to observe the RNA not only in space but also over time,” explains Junker. In this way, the scientists can distinguish the RNA transferred to the embryo by the mother from the RNA produced by the embryo itself. This RNA labeling method, called scSLAM-seq, was fine-tuned at BIMSB in the labs of Professor Markus Landthaler and Professor Nikolaus Rajewsky, enabling it to be applied in living zebrafish. “Labeling RNA molecules allows us to measure with high precision how gene expression changes in individual cells, for example, after an experimental intervention,” explains Junker.

How do drugs affect cell differentiation?

RNA labeling opens up completely new avenues for studying such things as the mechanism of action of drug therapies. “We can use it in organoids to investigate how different cell types respond to substances,” explains the physicist. The method, Junker says, is not suitable for long-term processes of change. “But we can see which genes change within five to six hours after treatment, providing a pathway to understanding how we might influence cell differentiation.”

“We can see which genes change within five to six hours after treatment, providing a pathway to understanding how we might influence cell differentiation.”, Jan Philipp Junker, Head of the Quantitative Developmental Biology lab.

Spatial analysis also has medical relevance: Looking further into the future, it could be useful for studying those diseases that result from mislocalized RNA, such as cancer or neurodegenerative diseases. In such diseases a large number of molecules are transported through the cell. “If we understand these transport processes, then we may be able to identify risk factors for these diseases,” explains Holler. But, for now, that is a long way off. “There is still much work to be done before the one-cell zebrafish embryo can be used as a model system for studying human neurodegenerative diseases,” stresses Junker.

The scientists next want to uncover the mechanisms involved in RNA localization: How does the detected RNA differ from other transcripts in the cell? Junker’s team plans to work with Professor Irmtraud Meyer’s lab at BIMSB to characterize the sequence features of the localized RNA. With the help of algorithms, they hope to predict whether the localized genes share a two- or three-dimensional fold. They are also working on further developing their method so that it can be used in other systems than the one-cell zebrafish embryo.

Literature

Karoline Holler et al (2021): „Spatio-temporal mRNA tracking in the early zebrafish embryo“, Nature Communications, DOI: 10.1038/s41467-021-23834-1


Provided by MDC Berlin

Super Productive 3D Bioprinter Could Help Speed Up Drug Development (Engineering)

A 3D printer that rapidly produces large batches of custom biological tissues could help make drug development faster and less costly. Nanoengineers at the University of California San Diego developed the high-throughput bioprinting technology, which 3D prints with record speed—it can produce a 96-well array of living human tissue samples within 30 minutes. Having the ability to rapidly produce such samples could accelerate high-throughput preclinical drug screening and disease modeling, the researchers said.

The process for a pharmaceutical company to develop a new drug can take up to 15 years and cost up to $2.6 billion. It generally begins with screening tens of thousands of drug candidates in test tubes. Successful candidates then get tested in animals, and any that pass this stage move on to clinical trials. With any luck, one of these candidates will make it into the market as an FDA approved drug.

The high-throughput 3D bioprinting technology developed at UC San Diego could accelerate the first steps of this process. It would enable drug developers to rapidly build up large quantities of human tissues on which they could test and weed out drug candidates much earlier.

“With human tissues, you can get better data—real human data—on how a drug will work,” said Shaochen Chen, a professor of nanoengineering at the UC San Diego Jacobs School of Engineering. “Our technology can create these tissues with high-throughput capability, high reproducibility and high precision. This could really help the pharmaceutical industry quickly identify and focus on the most promising drugs.”

The work was published in the journal Biofabrication.

The researchers note that while their technology might not eliminate animal testing, it could minimize failures encountered during that stage.

“What we are developing here are complex 3D cell culture systems that will more closely mimic actual human tissues, and that can hopefully improve the success rate of drug development,” said Shangting You, a postdoctoral researcher in Chen’s lab and co-first author of the study.

Examples of the geometries that the high-throughput 3D bioprinter can rapidly produce. © UCSD

The technology rivals other 3D bioprinting methods not only in terms of resolution—it prints lifelike structures with intricate, microscopic features, such as human liver cancer tissues containing blood vessel networks—but also speed. Printing one of these tissue samples takes about 10 seconds with Chen’s technology; printing the same sample would take hours with traditional methods. Also, it has the added benefit of automatically printing samples directly in industrial well plates. This means that samples no longer have to be manually transferred one at a time from the printing platform to the well plates for screening.

“When you’re scaling this up to a 96-well plate, you’re talking about a world of difference in time savings—at least 96 hours using a traditional method plus sample transfer time, versus around 30 minutes total with our technology,” said Chen.

Reproducibility is another key feature of this work. The tissues that Chen’s technology produces are highly organized structures, so they can be easily replicated for industrial scale screening. It’s a different approach than growing organoids for drug screening, explained Chen. “With organoids, you’re mixing different types of cells and letting them to self-organize to form a 3D structure that is not well controlled and can vary from one experiment to another. Thus, they are not reproducible for the same property, structure and function. But with our 3D bioprinting approach, we can specify exactly where to print different cell types, the amounts and the micro-architecture.”

How it works

To print their tissue samples, the researchers first design 3D models of biological structures on a computer. These designs can even come from medical scans, so they can be personalized for a patient’s tissues. The computer then slices the model into 2D snapshots and transfers them to millions of microscopic-sized mirrors. Each mirror is digitally controlled to project patterns of violet light—405 nanometers in wavelength, which is safe for cells—in the form of these snapshots. The light patterns are shined onto a solution containing live cell cultures and light-sensitive polymers that solidify upon exposure to light. The structure is rapidly printed one layer at a time in a continuous fashion, creating a 3D solid polymer scaffold encapsulating live cells that will grow and become biological tissue.

The digitally controlled micromirror array is key to the printer’s high speed. Because it projects entire 2D patterns onto the substrate as it prints layer by layer, it produces 3D structures much faster than other printing methods, which scans each layer line by line using either a nozzle or laser.

“An analogy would be comparing the difference between drawing a shape using a pencil versus a stamp,” said Henry Hwang, a nanoengineering Ph.D. student in Chen’s lab who is also co-first author of the study. “With a pencil, you’d have to draw every single line until you complete the shape. But with a stamp, you mark that entire shape all at once. That’s what the digital micromirror device does in our technology. It’s orders of magnitude difference in speed.”

This recent work builds on the 3D bioprinting technology that Chen’s team invented in 2013. It started out as a platform for creating living biological tissues for regenerative medicine. Past projects include 3D printing liver tissuesblood vessel networksheart tissues and spinal cord implants, to name a few. In recent years, Chen’s lab has expanded the use of their technology to print coral-inspired structures that marine scientists can use for studying algae growth and for aiding coral reef restoration projects.

Now, the researchers have automated the technology in order to do high-throughput tissue printing. Allegro 3D, Inc., a UC San Diego spin-off company co-founded by Chen and a nanoengineering Ph.D. alumnus from his lab, Wei Zhu, has licensed the technology and recently launched a commercial product.

Paper: “High throughput direct 3D bioprinting in multiwell plates.” Co-authors include Xuanyi Ma, Leilani Kwe, Grace Victorine, Natalie Lawrence, Xueyi Wan, Haixu Shen and Wei Zhu.

This work was supported in part by the National Institutes of Health (R01EB021857, R21AR074763, R21HD100132, R33HD090662) and the National Science Foundation (1903933, 1937653).

Featured image: The high-throughput 3D bioprinting setup performing prints on a standard 96-well plate. Images adapted from Biofabrication © UCSD


Provided by UCSD