From Harvard-Smithsonian Center for Astrophysics: “Dust in the Galaxy”

From Harvard-Smithsonian Center for Astrophysics

October 2, 2020

The Horsehead Nebula, seen here in the optical, is shaped by the absorption of dust grains distributed in clouds in the interstellar medium. Astronomers have completed a statistical analysis of dust absorption and emission properties from extensive recent observations across the sky and reached new conclusions that will aid in modeling the dust’s contribution to many other cosmic phenomena including contamination of the cosmic microwave background emission. Credit: NOIRLab National Optical Astronomy Observatories/Travis Rector.

Dust is found scattered throughout space. It is composed of fine particles made of silicates, like sand on Earth, or of carbon, and these are often blended with other elements. Dust strongly absorbs light at ultraviolet and visible wavelengths, and in our galaxy large clouds of dust are sometimes seen as dark shapes in front of bright nebula as the dust dims our view of the light behind it (the famous Horsehead Nebula is an example of such optical extinction effects). Dust particles are produced and ejected during the final stages of a star life, or in stellar winds, and are the most important component of the interstellar medium after gas, playing a crucial role in the formation of new stars, in facilitating interstellar chemistry, and in producing circumstellar disks of material from which planets form.

Astronomers have been working for decades to model the physical properties of dust grains, not only to better understand all of the processes just mentioned, but also because knowing the size distribution and composition of the dust allows them to correct for the effects of interstellar extinction and to determine accurately the properties of stars whose light has been partially obscured, their intrinsic brightness, for example. The strength of the interstellar dust absorption, moreover, depends on the wavelength such that it tends to make transmitted starlight appear red (described by a “reddening curve”) and an ability to recover intrinsic stellar colors is yet another critical goal of dust models. Not least, the radiation that the dust absorbs heats the grains, causing them to re-radiate the energy in the infrared, with this ubiquitous though uneven emission being a major contributor to the foreground contamination encountered in cosmology experiments trying to measure the cosmic microwave background radiation and its subtly varying distribution on the sky.

Over the decades many useful approximations have been made to the dust properties. Most of them try to model dust extinction with just one or in some cases two dust parameters. CfA astronomers Ioana Zelko and Doug Finkbeiner, building on this long enterprise, have just completed a significant new study of interstellar dust grains, their variations in size and composition, and their effects on interstellar extinction. The astronomers combined published studies of the dust extinction towards tens of thousands of stars and the dust infrared emission seen by the Planck all-sky survey with a large statistical analysis of dust grain models. Their goal was to determine the distribution of dust grain sizes and then to model the shape of the extinction curve versus wavelength, the amount of dust compared to the amount of gas, and the relative abundances of key elements (like silicon and carbon).

Several major new conclusions emerged from this study. The common assumption has been that dust’s infrared emission and uv/optical absorption are perfectly correlated, but the scientists find that this relation is not fixed, but instead depends on the shape of the reddening curve which in turn depends in part on the composition. They also find, in agreement with expectations, that a larger grain size usually leads to a larger value of extinction, as does a higher proportion of carbonaceous to silicate material; they also describe the temperature dependence of the slope of the infrared emission. The new statistical analysis offers possible solutions to a number of outstanding puzzles, but several issues remain (for example, the assumed spherical shape of all grains), and in ongoing work the scientists will include a wider range of dust models for comparison.

Science paper:
Implications of Grain Size Distribution and Composition for the Correlation Between Dust Extinction and Emissivity
The Astrophysical Journal

See the full article here .

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The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

From Harvard-Smithsonian Center for Astrophysics: “Could Life Exist Deep Underground on Mars?”

From Harvard-Smithsonian Center for Astrophysics

September 23, 2020

Amy Oliver
Public Affairs
Center for Astrophysics | Harvard & Smithsonian
Fred Lawrence Whipple Observatory
520-879-4406
amy.oliver@cfa.harvard.edu

Recent science missions and results are bringing the search for life closer to home, and scientists at the Center for Astrophysics | Harvard & Smithsonian (CfA) and the Florida Institute of Technology (FIT) may have figured out how to determine whether life is—or was—lurking deep beneath the surface of Mars, the Moon, and other rocky objects in the universe.

While the search for life typically focuses on water found on the surface and in the atmosphere of objects, Dr. Avi Loeb, Frank B. Baird Jr. Professor of Science at Harvard and CfA astronomer, and Dr. Manasvi Lingam, assistant professor of astrobiology at FIT and CfA astronomer, suggest that the absence of surface water doesn’t preclude the potential for life elsewhere on a rocky object, like deep in the subsurface biosphere.

“We examined whether conditions amenable to life could exist deep underneath the surface of rocky objects like the Moon or Mars at some point in their histories and how scientists might go about searching for traces of past subsurface life on these objects,” said Lingam, the lead author on the research. “We know that these searches will be technically challenging, but not impossible.”

One challenge for researchers was determining the potential for the existence of water where there appears to be none. “Surface water requires an atmosphere to maintain a finite pressure, without which liquid water cannot exist. However, when one moves to deeper regions, the upper layers exert pressure and thus permit the existence of liquid water in principle,” said Lingam. “For instance, Mars does not currently have any longstanding bodies of water on its surface, but it is known to have subsurface lakes.”

The research analyzes the “thickness” of the subsurface region—where water and life might exist in principle—of the nearby rocky objects, and whether the high pressures therein could rule out life altogether. According to Loeb, the answer is probably not. “Both the Moon and Mars lack an atmosphere that would allow liquid water to exist on their surfaces, but the warmer and pressurized regions under the surface could allow the chemistry of life in liquid water.”

The research also arrived at a limit on the amount of biological material that might exist in deep subsurface environments, and the answer, although small, is surprising. “We found that the biological material limit might be a few percent that of Earth’s subsurface biosphere, and a thousand times smaller than Earth’s global biomass,” said Loeb, adding that cryophiles—organisms that thrive in extremely cold environments—could not only potentially survive, but also multiply, on seemingly lifeless rocky bodies. “Extremophilic organisms are capable of growth and reproduction at low subzero temperatures. They are found in places that are permanently cold on Earth, such as the polar regions and the deep sea, and might also exist on the Moon or Mars.”

In terms of searching for life subsurface on the Moon and Mars, the researchers note it won’t be easy, requiring search criteria and machinery not yet in use on either neighboring body. “There are many criteria involved in determining the most optimal locations to hunt for signs of life,” said Lingam. “Some that we have taken into account for subsurface searches include drilling near to the equator where the subsurface biosphere is situated closer to the surface, and seeking geological hotspots with higher temperatures.” Loeb added that in terms of machinery, “We need to be able to drill tens of kilometers under the surface of Mars, and without geological activity exposing these deep layers, we will not be able to explore them.”

The challenges, however, don’t mean that finding life in the subsurface biosphere of a rocky body is impossible, even in the near future. “Drilling might be possible in the context of the Artemis program to establish a sustainable base on the Moon by 2024. One can imagine robots and heavy machinery that will drill deep under the lunar surface in search of life, just as we do in searching for oil on Earth,” said Loeb, adding that if future missions to Mars and the Moon do unearth subsurface life, the same principles could be applied to missions headed much farther away. “Our study extends to all objects out there and indeed implies that the habitable zone is much larger than traditionally thought, since science currently considers only life on the surface of the object.”

The research is published in The Astrophysical Journal Letters.

See the full article here .

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Please help promote STEM in your local schools.

Stem Education Coalition

The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

From Harvard-Smithsonian Center for Astrophysics: “The Evolving Chemistry of Protoplanetary Disks”

From Harvard-Smithsonian Center for Astrophysics

An artist’s conception of a planet-forming, circumstellar disk around a young star. Astronomers used the ALMA facility to study how the chemistry of volatile molecules – including water and carbon monoxide – evolves as young disks similar to this one develop planets, and the effects of these changes on the developing new planets. Credit: Karne L. Teramura, UH/IfA.

ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres.

September 11, 2020

Planets form from the gas and dust in disks that surround young stars. Chemicals in the disk that evaporate easily, called volatiles, include important molecules like water, carbon monoxide, nitrogen, as well as other simple organic molecules. The amount of volatile material that accumulates in a planet as it forms is a key factor in determining the planet’s atmosphere and suitability for life, and depends on the details of the gas and ice reservoirs in the disk at the time of planet formation. Since disk compositions evolve over disk lifetimes, astronomers interested in planet composition are working hard to understand the evolution of disk chemistry. They have already determined that water and carbon monoxide gas are depleted in young systems as compared with their abundances in the normal interstellar medium, sometimes by as much as a factor of one hundred. Current thinking argues that this is because the volatiles have frozen onto the surfaces of dust grains that then accumulate toward the cold midplane of the disk where they remain frozen out. Since each volatile has different properties, however, each one is depleted to a different extent; oxygen is the most depleted element, followed by carbon and then nitrogen. This general framework explains the observations of the few individual sources studied, but astronomers still lack a systematic view of how volatile chemistry evolves with time.

CfA astronomers Karin Oberg, Sean Andrews, Jane Huang, Chunhua Qi, and David Wilner were members of a team that used the ALMA facility to study volatiles in five young disk candidates. They combined the results with data from an early study of fourteen more evolved disks and modeled them to develop an evolutionary view of volatile chemistry over the disks’ lifetimes. They conclude that carbon monoxide depletes quickly — in the first 0.5 – 1 million years of a disk’s lifetime. They also find that youngest objects, those still deeply embedded in their envelope of natal material, have distinct chemical signatures probably because molecules in the disk are shielded from the ultraviolet radiation that can disrupt the chemical bonds. The scientists also consider whether evaporation of the ice mantles could add ingredients back into the gas but conclude that too many uncertainties still remain to reach a definitive answer and they argue for the need for a larger sample of young disks. The new study is a significant advance in understanding the evolution of the chemistry of young, planet-forming disks.

Science paper:
An Evolutionary Study of Volatile Chemistry in Protoplanetary Disks
The Astrophysical Journal

See the full article here .

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Please help promote STEM in your local schools.

Stem Education Coalition

The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

From Harvard Gazette: “Far-out findings from the cosmos”

Harvard University

From Harvard Gazette

September 4, 2020
Juan Siliezar

Artist’s conception of a potential solar companion, which theorists believe was developed in the sun’s birth cluster and later lost.
Illustration by M. Weiss.

Harvard astronomers research twin suns, a sneezing star, and ‘Oumuamua.

It was a busy summer for scientists at the Center for Astrophysics | Harvard & Smithsonian.

Researchers put forth a theory that indirectly nods to a famous Star Wars scene, resolved one mystery about the solar system’s first known interstellar visitor, and showed that a star can sort of “sneeze.” We caught up with them and asked about these far-out findings.

A long time ago but not so far, far away

It was an unforgettable scene in the first Star Wars movie: Young Luke, eager for adventure, storms out his house after fighting with his uncle about having to spend another year stuck at home. Outside he gazes up at the fiery twin suns of the planet Tatooine as they slide toward the horizon, John Williams’ The Force Theme rising in the background.

While a new study from a pair of Harvard astronomers may not have the same visual power, it does reveal that a similar view of binary suns may have existed in our very own solar system roughly 4 billion years ago.

In The Astrophysical Journal Letters, Avi Loeb, Frank B. Baird Jr. Professor of Science at Harvard, and Amir Siraj ’21, an astrophysics concentrator, theorize that the solar system originally had two suns instead of one, and if true that could have far-reaching implications for the origins of a dense cloud that surrounds the system and a possible ninth planet.

First, a little info on the sun’s long-lost twin: Loeb and Siraj think it had the same mass as its companion and was formed alongside it when the solar system began, but was situated 1,000 times farther from the Earth than our own sun. As to its fate, the two researchers believe it drifted away well before the Earth formed.

“The binary companion was [most likely] freed by the gravitational influence of a passing star in the sun’s dense birth environment,” Siraj said. “It could now be anywhere in the Milky Way galaxy.”

Siraj and Loeb aren’t the first to theorize a two-star start to the solar system. In fact, most stars are born with companions. But Siraj and Loeb’s theory could help explain the formation of the Oort cloud — the sprawling sphere of debris that sits at the edge of the system and surrounds it.

Many astronomers believe the Oort cloud formed with leftover chunks of rock and ice from our solar system and neighboring ones.

Oort Cloud, The layout of the solar system, including the Oort Cloud, on a logarithmic scale. Credit: NASA, Universe Today.

Siraj and Loeb say their two-sun theory could account for why the cloud is as dense as it is, since binary systems are far better at pulling in and capturing these types of objects than single-star systems.

Such a system could also help explain the existence of a potential ninth planet that astronomers believe is out there — an undisputed one this time (no offense, Pluto). Their model supports the theory that this ninth planet was captured into the system, meaning it didn’t form here.

An artist’s rendering of ‘Oumuamua, a visitor from outside the solar system. Credit: The international Gemini Observatory/NOIRLab/NSF/AURA artwork by J. Pollard.

The ‘Oumuamua debate continues

The mystery surrounding our solar system’s first known interstellar visitor deepened after astronomers ruled out a major explanation in a new paper in The Astrophysical Journal Letters.

The study rebuts a theory published earlier this year that suggests the object, dubbed ‘Oumuamua from the Hawaiian for scout, was a cosmic iceberg made of frozen hydrogen. Co-authored by Loeb, the paper concluded this is likely not the case because, if it was, the object wouldn’t have been able to make the journey intact. The scientists argue it would quickly melt or break apart when it passed close to a star. ‘Oumuamua didn’t even flinch when it passed the sun.

The astronomers also looked at what it would take to form a hydrogen iceberg the size of ‘Oumuamua, and where it could have originated. They focused on one of the closest giant molecular clouds to Earth (only 17,000 light-years away). They found the environment there too inhospitable for iceberg formation — and so far away that it would be highly unlikely that it could have survived the journey, even if it somehow managed to form.

The debate around ‘Oumuamua started in 2017, when it was first discovered by observers at the Haleakalā Observatory on the island of Maui in Hawaii. Among other theories, it has been hypothesized to be an interstellar asteroid, a comet, and even an alien artifact — Loeb himself suggested this in 2018 and has put out a body of work on the topic. He has a book on ‘Oumuamua, Extraterrestrial, due out early next year.

All of this is to say that the truth on ‘Oumuamua is still out there, but perhaps it won’t be a mystery for long.

“If ‘Oumuamua is a member of a population of similar objects on random trajectories, then the [new] Vera Rubin Observatory, which is scheduled to [be operational] next year, should detect roughly one ‘Oumuamua-like object per month,” Loeb said.

Vera C. Rubin Observatory Telescope currently under construction on the El Peñón peak at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes, altitude 2,715 m (8,907 ft).

“We will all wait with anticipation to see what it will find.”

Gesundheit … to a star?

In the first two panels a bright, hot blob of plasma is ejected from the emergence of a huge convection cell on Betelgeuse’s surface. In panel three, gas rapidly expands outward, cooling to form an enormous cloud of obscuring dust grains. The final panel reveals the huge dust cloud blocking the light (as seen from Earth) from a quarter of the star’s surface. Credit: NASA, ESA, and E. Wheatley (STScI).

This is the explanation a team of international astronomers led by Andrea Dupree, the CfA’s associate director, published in a paper in The Astrophysical Journal.

Looking at recent observation data, researchers believe the dimming periods were most likely caused by the ejection and cooling of dense, hot gases. Between October and November 2019, data and images gathered by the Hubble Space Telescope showed intense, heated material moving out of the star’s extended atmosphere at 200,000 miles per hour. They believe this mass formed a soot-like dust cloud when it cooled that blocked the southern part of the star, accounting for its dimming in January and February.

While researchers think they can account partially for the anomaly, they have other questions. They can’t, for example, determine how the outburst started or why, nor do they know why the star is losing mass at an exceedingly high rate.

What they do know is that Betelgeuse dims every 420 days. But new observations between late June and early August of this year show it’s off schedule. The star is dimming roughly 300 days earlier than expected. Yet another new mystery.

Researchers also believe Betelgeuse is nearing the end of its life and eventually will go supernova. In fact, it might have happened already, and we just haven’t seen it yet.

“Betelgeuse is so far away, it takes about 750 years for the light to reach us on Earth,” Dupree said. “So, the light from Betelgeuse [we saw] left the star at about 1270 A.D. here on Earth.”

See the full article here .

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Harvard University is the oldest institution of higher education in the United States, established in 1636 by vote of the Great and General Court of the Massachusetts Bay Colony. It was named after the College’s first benefactor, the young minister John Harvard of Charlestown, who upon his death in 1638 left his library and half his estate to the institution. A statue of John Harvard stands today in front of University Hall in Harvard Yard, and is perhaps the University’s best known landmark.

Harvard University has 12 degree-granting Schools in addition to the Radcliffe Institute for Advanced Study. The University has grown from nine students with a single master to an enrollment of more than 20,000 degree candidates including undergraduate, graduate, and professional students. There are more than 360,000 living alumni in the U.S. and over 190 other countries.

From Harvard-Smithsonian Center for Astrophysics: “Finding the Optical Counterparts of High-Energy Blazars”

From Harvard-Smithsonian Center for Astrophysics

July 10, 2020

An artist’s by now iconic conception of a blazar, the most common type of source detected by NASA’s Fermi gamma-ray spacecraft. Associating a bright gamma-ray source with a blazer is difficult, however, because the Fermi beam is large and encompasses many possible sources. Astronomers have developed a new statistical algorithm that finds most likely associations based on comparisons with objects’ infrared and radio emission. Credit: M. Weiss/CfA

NASA/Fermi LAT

NASA/Fermi Gamma Ray Space Telescope

A blazar is a galaxy whose central nucleus is bright across the spectrum, from low energy radio wavelengths to the high energy gamma rays like those observed by the Fermi Gamma Ray Space Telescope. Astronomers think that a blazar nucleus contains a supermassive black hole that powers jets of charged particles as matter falls into its vicinity. Although the nuclei of other galaxies also eject jets of particles, the class of blazars is thought to result from our unique viewing angle: staring almost directly down the throats of the jets. Two defining characteristics of blazars,strong radio emission and high variability, are result of the accretion and jets.

As Fermi surveys the sky it spots many powerful gamma-ray sources, but its field-of-view is very large, as much as twice the angular size of the moon, and it cannot use spatial location to identify any individual galaxy as responsible for the emission; indirect arguments are made from similarities of brightness, variability, and other inferences. Astronomers think that many of these sources should be blazars, and the most recent catalog of about 5100 sources has about 3000 blazars, but one quarter of the sources still lack any clear counterpart.

CfA astronomer Raffaele D’Abrusco was a member of a team that developed a new statistical method to associate Fermi gamma-ray sources with optical, infrared or radio counterparts. The Likelihood Ratio (LR) method, often used to identify counterparts of high energy sources, has typically relied on angular separation in a geometrical approach to calculate associating probabilities of the counterparts. The new version of this method builds instead on fluxes and colors from infrared and radio sky surveys. Infrared surveys have been instrumental in the discovery (made by the same team of researchers) that gamma-ray detected blazars have unique infrared colors that clearly distinguish them from other extragalactic sources. The new procedure takes advantage of these strong correlations between infrared colors and gamma-ray spectral properties of known blazars.

When applied to the approximately one thousand unassociated Fermi sources with possible infrared counterparts, the method identified 743 new associations with a better than 99% certainty, significantly increasing the number of gamma-ray blazars with likely low energy counterparts. The association will allow the final confirmation of the nature of these candidate blazars through optical spectra. The increase in the number of confirmed gamma-ray blazars is used in investigations of the engines that create the relativistic jets in blazars, helping to constrain the demographics of this elusive class of active galactic nuclei.

Science paper:
On the Physical Association of Fermi-LAT Blazars with Their Low-energy Counterparts
Raniere de Menezes, Raffaele D’Abrusco, Francesco Massaro, Dario Gasparrini, and Rodrigo Nemmen
The Astrophysical Journal Supplement Series 248

See the full article here .

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Please help promote STEM in your local schools.

Stem Education Coalition

The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

From Harvard-Smithsonian Center for Astrophysics: “Where Might Very Unequal Mass Black Hole Binaries Come From?”

From Harvard-Smithsonian Center for Astrophysics

A schematic showing two pathways (each one requiring two prior black hole binary merging events) to assemble a roughly 30 solar-mass black like the one detected in a recent black hole binary gravitational wave merger event. Astronomers trying to explain where the massive spinning black hole in the pair was formed conclude that in dense stellar clusters a three-step process is the most likely path. Rodriguez et al., 2020.

The direct detection of gravitational waves from at least eleven sources during the past five years has offered spectacular confirmation of Einstein’s model of gravity and spacetime, while the modeling of these events has provided information on star formation, gamma-ray bursts,neutron stars, the age of the universe, and even verification of ideas about how very heavy elements are produced. The majority of these gravitational wave events arose from the merger of two black holes of comparable masses in an orbiting pair. Near-equal mass pairs are strongly preferred in models of binary black hole formation, whether they result from the evolution of isolated binary stars or from the dynamical pairing of two black holes. This year, however, the LIGO and Virgo gravitational wave observatories reported the first detection of a very unequal mass pair of black holes, GW190412, whose estimated masses are about 30 and 8 solar-masses. The question, then, is how were they formed?

MIT /Caltech Advanced aLigo

Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

VIRGO Gravitational Wave interferometer, near Pisa, Italy

VIRGO Gravitational Wave interferometer, near Pisa, Italy

Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

CfA astronomer Carl Rodriguez led a team of colleagues in a theoretical investigation of how such an unequal mass binary might form. The most obvious solution is look in a dense star cluster, where low-spin, comparable mass black hole pairs can naturally form, in part because massive black holes and stars tend to sink toward the center of the cluster and can more readily encounter each other. But even there those encounters are unlikely to produce an unequal mass pair. The spin of each black hole adds a further complicating factor. The spin is quantified by a number between zero and one. If each of the black holes in a merger has a low value of spin, as is expected, then their merger will normally produce a more massive black hole whose spin is large, perhaps around 0.7, but the inferred spin of the massive black hole in GW190412 is well determined to be about 0.43, suggesting that it did not arise from such a simple merger.

The astronomers argue that the most likely way to produce this unlikely pair may be through two prior black hole pair mergers in the cluster, a process that can ultimately result in a black hole with the correct inferred spin. First, two black hole binary pairs each merge; each of these pairs has black holes of comparable moderate masses and each produces a more massive black hole. Next, these two new black holes themselves form a binary pair and then merge, producing the roughly 30 solar-mass, moderate spin black hole as seen. Then that blackhole pairs up with a low mass black hole to form the binary whose collapse produced the event seen as GW190412. (Similar multi-step variants are possible as well.) Although such a series of events are rare, the scientists show that known star clusters could provide the right environments for it to occur. The new result and analysis, as in the case of previous gravitational wave discoveries, have expanded our view of cosmic variety while tacking fundamental assumptions. One of those assumptions is that black holes are typically formed from stellar collapse with low spins. Future work will show whether a three-step merger process is needed to explain events like GW190412, or whether assumptions like this one about spin need to be challenged instead.

Science paper:
GW190412 as a Third-generation Black Hole Merger from a Super Star Cluster
Carl L. Rodriguez, Kyle Kremer, Michael Y. Grudić, Zachary Hafen, Sourav Chatterjee, Giacomo Fragione, Astrid Lamberts, Miguel A.S. Martinez, Frederic A. Rasio, Newlin Weatherford , and Claire S. Ye
The Astrophysical Journal Letters

See the full article here .

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Please help promote STEM in your local schools.

Stem Education Coalition

The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

From Harvard-Smithsonian Center for Astrophysics: “Forming the TRAPPIST-1 Exoplanets”

From Harvard-Smithsonian Center for Astrophysics

A size comparison of the planets of the TRAPPIST-1 system, lined up in order of increasing distance from their host star. The planetary surfaces are portrayed with an artist’s impression of their potential surface features, including water, ice, and atmospheres. NASA

ESO Belgian robotic Trappist National Telescope at Cerro La Silla, Chile

ESO Belgian robotic Trappist-South National Telescope at Cerro La Silla, Chile, 600 km north of Santiago de Chile at an altitude of 2400 metres.

TRAPPIST-1 is a system of seven Earth-sized worlds orbiting an ultra-cool dwarf star about forty light-years away. The IRAC camera on Spitzer was used to help discover these seven Earth-sized planets orbiting the star, at least three of them lying in the star’s habitable zone.

IRAC camera on the Spitzer space telescope

NASA/Spitzer Infrared Telescope. No longer in service.

The star, and hence its system of planets, is thought to be about eight billion years old, almost twice as old as our own solar system. For scientists seeking evidence for life elsewhere, the advanced age provides more time for chemistry and evolution to operate than the Earth had. On the other hand, the planets are all close to the star (in fact they are probably tidally locked to the star with one side always facing it), and consequently would have soaked up billions more year’s-worth of high energy radiation from the star’s winds, perhaps adversely affecting any atmospheres they host.

Nevertheless, the three planets in the habitable zone could have liquid water if they formed with the right composition and/or if water was subsequently deposited on their surfaces. The Kuiper Belt in our solar system is an orbiting disk of comets and small objects that extends roughly from Neptune out to fifty AU from the Sun (one AU being the average Earth-Sun distance). It is thought that comets brought water to the Earth during its youth, and comets in TRAPPIST-1’s Kuiper belt – if there are any – might provide a way to deposit water onto its seven planets. With the right atmospheric conditions, the three planets in the habitable zone might even have liquid water on their surfaces.

CfA astronomer Luca Matra was a member of a team that used the ALMA submillimeter facility to study the TRAPPIST-1 system to look for signs of an exo-Kuiper belt and clues about the formation of its planets.

ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

The scientists searched for radiation emitted by dust grains and carbon monoxide gas, but did not find any. The limits were sensitive enough, however, to reach some important conclusions when combined with conservative estimates of the system’s age and evolution. They conclude that probably the TRAPPIST-1 system was born with a planetary disk smaller than forty AU in radius whose mass was less than about twenty Earth-masses, and moreover that very possibly most of the dust grains in the disk were transported inward and used to form the seven planets. The scientists used their modeling code to examine archival ALMA data on the closeby star Proxima Cen and its exoplanetary system.

Centauris Alpha Beta Proxima 27, February 2012. Skatebiker

It also showed only upper limits to the dust and gas emission, implying that its young disk was less than about one-tenth as massive as the one that formed our solar system. These results leave the question of early water transport undecided in these systems, but have encouraged the scientists to apply their techniques to younger and closer stellar systems in order to increase their detections and refine their models.

Science paper:
MNRAS

See the full article here .

five-ways-keep-your-child-safe-school-shootings
Please help promote STEM in your local schools.

Stem Education Coalition

The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

From Harvard-Smithsonian Center for Astrophysics:”Astronomers Detect First Double Helium-Core White Dwarf Gravitational Wave Source”

From Harvard-Smithsonian Center for Astrophysics

April 3, 2020
Amy Oliver
Public Affairs
Center for Astrophysics | Harvard & Smithsonian
Fred Lawrence Whipple Observatory
520-879-4402
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Scientists at the Center for Astrophysics | Harvard & Smithsonian today announced the detection of J2322+0509, a detached binary white dwarf composed of two helium-core stars with a short orbital period. It is the first gravitational wave source of its kind ever detected.

“Theories predict that there are many double helium-core white dwarf binaries out there,” said Dr. Warren Brown, CfA astronomer and lead author on the study. “This detection provides an anchor for those models, and for doing future experiments so that we can find more of these stars and determine their true numbers.”

The star will be used for verification on the much-anticipated LISA (Laser Interferometer Space Antenna) gravitational wave observatory, planned for launch in 2034, said Dr. Mukremin Kilic, from the University of Oklahoma, and a co-author on the study. “Verification binaries are important because we know that LISA will see them within a few weeks of turning on the telescopes,” said Kilic. “There’s only a handful of LISA sources that we know of today. The discovery of the first prototype of a new class of verification binary puts us well ahead of where anyone could have anticipated.”

Early on, scientists found J2322+0509 a challenge to study, collecting critical information about the class of stars that will shape future scientific results through multiple avenues. Optical light curve studies yielded no result, said Brown. “This binary had no light curve. We couldn’t detect a photometric signal because there isn’t one.” Spectroscopic studies, however, shaped the story of a difficult-to-detect yet scientifically important binary system, and revealed its orbital motion.

“We’re finding that the binaries that might be the hardest to detect may actually be the strongest sources of gravitational waves,” said Brown. “This binary was difficult to detect because it is oriented face-on to us, like a bull’s eye, rather than edge-on. Remarkably, the binary’s gravitational waves are 2.5 times stronger at this orientation than if it were orientated edge-on like an eclipsing binary.”

The pair also held another surprise for researchers. With an orbital period of 1201 seconds, or just over 20 minutes, the pair is confirmed as having the third shortest period of all known detached binaries. “This pair is at the extreme end of stars with short orbital periods,” said Brown. “And the orbit of this pair of objects is decaying. The gravitational waves that are being emitted are causing the pair to lose energy; in six or seven million years they will merge into a single, more-massive white dwarf.”

Spectroscopic data for J2322+0509 was collected using the MMT telescope at the Fred Lawrence Whipple Observatory in Amado, Arizona; the Magellan Baade telescope at the Las Campanas Observatory in Chile; and, the Gemini-North telescope on Mauna Kea, Hawaii.

CfA U Arizona Fred Lawrence Whipple Observatory Steward Observatory MMT 6.5-m Telescope at the summit of Mount Hopkins near Tucson, Arizona, USA, Altitude 2,616 m (8,583 ft)

Carnegie 6.5 meter Magellan Baade and Clay Telescopes located at Carnegie’s Las Campanas Observatory, Chile. over 2,500 m (8,200 ft) high

Frederick C Gillett Gemini North Telescope Maunakea, Hawaii, USA, Altitude 4,213 m (13,822 ft)

The results of the study will be published in Astrophysical Journal Letters.

See the full article here .

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Please help promote STEM in your local schools.

Stem Education Coalition

The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

From Harvard-Smithsonian Center for Astrophysics: “First Results from the Dark Energy Survey”

From Harvard-Smithsonian Center for Astrophysics

January 17, 2020

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.

Dark Energy Survey

Dark Energy Camera [DECam], built at FNAL

NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam at an altitude of 7200 feet

Timeline of the Inflationary Universe WMAP

The Dark Energy Survey (DES) is an international, collaborative effort to map hundreds of millions of galaxies, detect thousands of supernovae, and find patterns of cosmic structure that will reveal the nature of the mysterious dark energy that is accelerating the expansion of our Universe. DES began searching the Southern skies on August 31, 2013.

According to Einstein’s theory of General Relativity, gravity should lead to a slowing of the cosmic expansion. Yet, in 1998, two teams of astronomers studying distant supernovae made the remarkable discovery that the expansion of the universe is speeding up. To explain cosmic acceleration, cosmologists are faced with two possibilities: either 70% of the universe exists in an exotic form, now called dark energy, that exhibits a gravitational force opposite to the attractive gravity of ordinary matter, or General Relativity must be replaced by a new theory of gravity on cosmic scales.

DES is designed to probe the origin of the accelerating universe and help uncover the nature of dark energy by measuring the 14-billion-year history of cosmic expansion with high precision. More than 400 scientists from over 25 institutions in the United States, Spain, the United Kingdom, Brazil, Germany, Switzerland, and Australia are working on the project. The collaboration built and is using an extremely sensitive 570-Megapixel digital camera, DECam, mounted on the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory, high in the Chilean Andes, to carry out the project.

Over six years (2013-2019), the DES collaboration used 758 nights of observation to carry out a deep, wide-area survey to record information from 300 million galaxies that are billions of light-years from Earth. The survey imaged 5000 square degrees of the southern sky in five optical filters to obtain detailed information about each galaxy. A fraction of the survey time is used to observe smaller patches of sky roughly once a week to discover and study thousands of supernovae and other astrophysical transients.

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.,
MNRAS

See the full article here .

five-ways-keep-your-child-safe-school-shootings
Please help promote STEM in your local schools.

Stem Education Coalition

The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

From Harvard-Smithsonian Center for Astrophysics: “The Interiors of Stars”

From Harvard-Smithsonian Center for Astrophysics

January 10, 2020

An illustration of vibration modes in the Sun. Astronomers have used the TESS mission to study for the first time stellar oscillations in intermeidate mass stars.

NASA/MIT TESS replaced Kepler in search for exoplanets

Kosovichev et al., Structure and Rotation of the Solar Interior: Initial Results from the MDI Medium-L Program [Springer]

_________________________________________________________

The interiors of stars are largely mysterious regions because they are so difficult to observe. Our lack of understanding about the physical processes there, like rotation and the mixing of hot gas, introduces considerable ambuguity 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 outer layers (the layers dominated by convective gas motions). Helioseismology is the name given to the study of these oscillations in the Sun, and asteroseismology is the term used for the same study in 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.

ESA/GAIA satellite

The team was able for the first time to fully 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 enormous potential not just for studying exoplanets, but also for improving our understanding the interiors of intermediate mass stars.

Science paper:
The First View of δ Scuti and γ Doradus Stars with the TESS Mission,
MNRAS

See the full article here .

five-ways-keep-your-child-safe-school-shootings
Please help promote STEM in your local schools.

Stem Education Coalition

The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.