How many habitable planets are out there?

Thanks to new research using data from the Kepler space telescope, it's estimated that there could be as many as 300 million potentially habitable planets in our galaxy. Some could even be pretty close, with several likely within 30 light-years of our Sun. The findings will be published in The Astronomical Journal, and research was a collaboration of scientists from NASA, the SETI Institute, and other organizations worldwide.

This illustration depicts one possible appearance of the planet Kepler-452b, the first
near-Earth-size world to be found in the habitable zone of a star similar to our Sun
[Credit: NASA Ames/JPL-Caltech]

"This is the first time that all of the pieces have been put together to provide a reliable measurement of the number of potentially habitable planets in the galaxy," said co-author Jeff Coughlin, an exoplanet researcher at the SETI Institute and Director of Kepler's Science Office. "This is a key term of the Drake Equation, used to estimate the number of communicable civilizations—we're one step closer on the long road to finding out if we're alone in the cosmos."

The Drake Equation is a probabilistic argument that details the factors to consider when estimating the potential number of technologically advanced civilizations in the galaxy that could be detected. The Drake Equation is also often considered to be a roadmap for astrobiology and guides much of the research at the SETI Institute.

To develop a reasonable estimate, the researchers looked at exoplanets similar in size to Earth and thus most likely to be rocky planets. They also looked at so-called Sun-like stars, around the same age as our Sun and approximately the same temperature. Another consideration for habitability is whether the planet could have the conditions necessary to support liquid water.

Previous estimates about determining the number of potentially habitable exoplanets there are in our galaxy were heavily based on the planet's distance from its star. This new research also considers how much light hits the planet from its star, which would impact the likelihood that the planet could support liquid water. To do this, the team looked not only at Kepler data, but also at data from the European Space Agency's Gaia mission about how much energy the planet's star emits.

An illustration representing the legacy of NASA's Kepler space telescope. After nine years in deep
space collecting data that revealed our night sky to be filled with billions of hidden planets –
more planets even than stars – NASA’s Kepler space telescope ran out of fuel needed for
further science operations in 2018 [Credit: NASA/Ames Research Center/W. Stenzel]

By taking both Kepler and Gaia data into account, the results better reflect the diversity of stars, solar systems, and exoplanets in our galaxy.

"Knowing how common different kinds of planets are is extremely valuable for the design of upcoming exoplanet-finding missions," said co-author Michelle Kunimoto, who worked on this paper after finishing her doctorate on exoplanet occurrence rates at the University of British Columbia, and recently joined the Transiting Exoplanet Survey Satellite, or TESS, team at the Massachusetts Institute of Technology in Cambridge, Massachusetts. "Surveys aimed at small, potentially habitable planets around Sun-like stars will depend on results like these to maximize their chance of success."

More research will be needed to understand the role a planet's atmosphere has on its capacity to support liquid water. In this analysis, researchers used a conservative estimate of the atmosphere's effect to estimate the occurrence of Sun-like stars with rocky planets that could have liquid water.

The Kepler mission, which officially ceased collecting data in 2018, has identified over 2,800 confirmed exoplanets, with several thousand more candidates waiting to be confirmed. So far, researchers have identified several hundred planets in the habitable zone of their star in Kepler data. It may take a while to find all 300 million!

Source: SETI Institute [October 30, 2020]

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Assessing the habitability of planets around old red dwarfs

A new study using data from NASA's Chandra X-ray Observatory and Hubble Space Telescope gives new insight into an important question: how habitable are planets that orbit the most common type of stars in the Galaxy? The target of the new study, as reported in our press release, is Barnard's Star, which is one of the closest stars to Earth at a distance of just 6 light years. Barnard's Star is a red dwarf, a small star that slowly burns through its fuel supply and can last much longer than medium-sized stars like our Sun. It is about 10 billion years old, making it twice the age of the Sun.

Credit: Chandra X-ray Center

The authors used Barnard's Star as a case study to learn how flares from an old red dwarf might affect any planets orbiting it. This artist's illustration depicts an old red dwarf like Barnard's Star (right) and an orbiting, rocky planet (left).

The research team's Chandra observations of Barnard's Star taken in June 2019 uncovered one X-ray flare (shown in the inset box) and their Hubble observations taken in March 2019 revealed two ultraviolet high-energy flares (shown in an additional graphic). Both observations were about seven hours long and both plots show X-ray or ultraviolet brightness extending down to zero. Based on the length of the flares and of the observations, the authors concluded that Barnard's Star unleashes potentially destructive flares about 25% of the time.

The team then studied what these results mean for rocky planets orbiting in the habitable zone—where liquid water could exist on their surface—around an old red dwarf like Barnard's Star. Any atmosphere formed early in the life of a habitable-zone planet was likely to have been eroded away by high-energy radiation from the star during its volatile youth. Later on, however, planet atmospheres might regenerate as the star becomes less active with age. This regeneration process may occur by gases released by impacts of solid material or gases being released by volcanic processes.

However, the onslaught of powerful flares like those reported here, repeatedly occurring over hundreds of millions of years, may erode any regenerated atmospheres on rocky planets in the habitable zone. The illustration shows the atmosphere of the rocky planet being swept away to the left by energetic radiation from flares produced by the red dwarf. This would reduce the chance of these worlds supporting life. The team is currently studying high-energy radiation from many more red dwarfs to determine whether Barnard's Star is typical.

A paper describing these results was published in The Astronomical Journal.

Source: NASA [October 30, 2020]

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Where were Jupiter and Saturn born?

New work led by Carnegie's Matt Clement reveals the likely original locations of Saturn and Jupiter. These findings refine our understanding of the forces that determined our Solar System's unusual architecture, including the ejection of an additional planet between Saturn and Uranus, ensuring that only small, rocky planets, like Earth, formed inward of Jupiter.

New work led by Carnegie's Matt Clement reveals the likely original locations of Saturn and Jupiter 
[Credit: NASA/JPL-Caltech/Space Science Institute]

In its youth, our Sun was surrounded by a rotating disk of gas and dust from which the planets were born. The orbits of early formed planets were thought to be initially close-packed and circular, but gravitational interactions between the larger objects perturbed the arrangement and caused the baby giant planets to rapidly reshuffle, creating the configuration we see today.

"We now know that there are thousands of planetary systems in our Milky Way galaxy alone," Clement said. "But it turns out that the arrangement of planets in our own Solar System is highly unusual, so we are using models to reverse engineer and replicate its formative processes. This is a bit like trying to figure out what happened in a car crash after the fact--how fast were the cars going, in what directions, and so on."

Clement and his co-authors--Carnegie's John Chambers, Sean Raymond of the University of Bordeaux, Nathan Kaib of University of Oklahoma, Rogerio Deienno of the Southwest Research Institute, and Andre Izidoro of Rice University--conducted 6,000 simulations of our Solar System's evolution, revealing an unexpected detail about Jupiter and Saturn's original relationship.

Jupiter in its infancy was thought to orbit the Sun three times for every two orbits that Saturn 
completed. But this arrangement is not able to satisfactorily explain the configuration 
of the giant planets that we see today. Matt Clement and his co-authors showed that 
a ratio of two Jupiter orbits to one Saturnian orbit more consistently produced 
results that look like our familiar planetary architecture [Credit: NASA]

Jupiter in its infancy was thought to orbit the Sun three times for every two orbits that Saturn completed. But this arrangement is not able to satisfactorily explain the configuration of the giant planets that we see today. The team's models showed that a ratio of two Jupiter orbits to one Saturnian orbit more consistently produced results that look like our familiar planetary architecture.

"This indicates that while our Solar System is a bit of an oddball, it wasn't always the case," explained Clement, who is presenting the team's work at the American Astronomical Society's Division for Planetary Sciences virtual meeting today. "What's more, now that we've established the effectiveness of this model, we can use it to help us look at the formation of the terrestrial planets, including our own, and to perhaps inform our ability to look for similar systems elsewhere that could have the potential to host life."

The model also showed that the positions of Uranus and Neptune were shaped by the mass of the Kuiper belt--an icy region on the Solar System's edges composed of dwarf planets and planetoids of which Pluto is the largest member--and by an ice giant planet that was kicked out in the Solar System's infancy.

The study is published in the journal Icarus.

Source: Carnegie Institution for Science [October 29, 2020]

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Earth-sized rogue planet discovered in the Milky Way

Our Galaxy may be teeming with rogue planets, gravitationally unbound to any star. An international team of scientists, led by Polish astronomers, has announced the discovery of the smallest Earth-sized free-floating planet found to date.

Artist's impression of a gravitational microlensing event by a free-floating planet
[Credit: Jan Skowron/Astronomical Observatory, University of Warsaw]

Over four thousand extrasolar planets have been discovered to date. Although many of the known exoplanets do not resemble those in our solar system, they have one thing in common - they all orbit a star. However, theories of planet formation and evolution predict the existence of free-floating (rogue) planets, gravitationally unattached to any star. Indeed, a few years ago Polish astronomers from the OGLE team from the Astronomical Observatory of the University of Warsaw provided the first evidence for the existence of such planets in the Milky Way. Writing in Astrophysical Journal Letters, OGLE astronomers announced the discovery of the smallest rogue planet found to date.

Exoplanets can be only rarely directly observed. Usually, astronomers find planets using observations of the light from the planet's host star. For example, if a planet crosses in front of its parent star's disk, then the observed brightness of the star periodically drops by a small amount causing so called transits. Astronomers can also measure the motion of the star caused by the planet.

Free-floating planets emit virtually no radiation and - by definition - they do not orbit any host star, so they cannot be discovered using traditional methods of astrophysical detection. Nevertheless, rogue planets can be spotted using an astronomical phenomenon called gravitational microlensing. Microlensing results from Einstein's theory of general relativity - a massive object (the lens) may bend the light of a bright background object (the source). The lens' gravity acts as a huge magnifying glass which bends and magnifies the light of distant stars.

'If a massive object (a star or a planet) passes between an Earth-based observer and a distant source star, its gravity may deflect and focus light from the source. The observer will measure a short brightening of the source star' - explains dr Przemek Mroz, a postdoctoral scholar at the California Institute of Technology and a lead author of the study. 'Chances of observing microlensing are extremely slim because three objects - source, lens, and observer - must be nearly perfectly aligned. If we observed only one source star, we would have to wait almost a million year to see the source being microlensed' - he adds.

The gravity of a free-floating planet may deflect and focus light from a distant star when passing 

closely in front of it. Due to the distorted image the star temporarily seems much brighter 

[Credit: Jan Skowron/Astronomical Observatory, University of Warsaw]

This is why modern surveys hunting for gravitational microlensing events are monitoring hundreds of millions of stars in the Milky Way center, where the chances of microlensing are highest. The OGLE survey - led by Warsaw University astronomers - carries out one of such experiments. OGLE is one of the largest and longest sky surveys, it started operations over 28 years ago. Currently, OGLE astronomers are using a 1.3-meter Warsaw Telescope located at Las Campanas Observatory, Chile. Each clear night, they point their telescope to the central regions of the Galaxy and observe hundreds of millions of stars, searching for those which change their brightness.

Gravitational microlensing does not depend on the lens' brightness, so it enables the study of faint or dark objects such as planets. Duration of microlensing events depends on the mass of the lensing object - the less massive the lens, the shorter the microlensing event. Most of the observed events, which typically last several days, are caused by stars. Microlensing events attributed to free-floating planets have timescales of barely a few hours. By measuring the duration of a microlensing event (and shape of its light curve) we can estimate the mass of the lensing object.

The scientists announced the discovery of the shortest-timescale microlensing event ever found, called OGLE-2016-BLG-1928, which has the timescale of just 42 minutes. 'When we first spotted this event, it was clear that it must have been caused by an extremely tiny object' - says dr Radoslaw Poleski from the Astronomical Observatory of the University of Warsaw, a co-author of the study. Indeed, models of the event indicate that the lens must have been less massive than Earth, it was probably a Mars-mass object. Moreover, the lens is likely a rogue planet. 'If the lens were orbiting a star, we would detect its presence in the light curve of the event' - adds dr Poleski. 'We can rule out the planet having a star within about 8 astronomical units (the astronomical unit is the distance between the Earth and the Sun)'.

OGLE astronomers provided the first evidence for a large population of rogue planets in the Milky Way a few years ago. However, the newly-detected planet is the smallest rogue world ever found. 'Our discovery demonstrates that low-mass free-floating planets can be detected and characterized using ground-based telescopes' - says Prof. Andrzej Udalski, the PI of the OGLE project.

The gravity of a free-floating planet may deflect and focus light from a distant star when passing 

closely in front of it. Due to the distorted image the star temporarily seems much brighter 

[Credit: Jan Skowron/Astronomical Observatory, University of Warsaw]

Astronomers suspect that free-floating planets actually formed in protoplanetary disks around stars (as "ordinary" planets) and they have been ejected from their parent planetary systems after gravitational interactions with other bodies, for example, with other planets in the system. Theories of planet formation predict that the ejected planets should be typically smaller than Earth. Thus studying free-floating planets enables us to understand the turbulent past of young planetary systems, such as our solar system.

The search for free-floating planets is one of the science drivers of the Nancy Grace Roman Space Telescope, which is currently being constructed by NASA. The observatory is scheduled to start operations in the mid-2020s.

Because of the brevity of the event, additional observations collected by the Korea Microlensing Telescope Network (KMTNet) were needed to characterize the event. KMTNet operates a network of three telescopes - in Chile, Australia, and South Africa.

Source: University of Warsaw [October 29, 2020]

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Black hole 'family portrait' is most detailed to date

An international research collaboration including Northwestern University astronomers has produced the most detailed family portrait of black holes to date, offering new clues as to how black holes form. An intense analysis of the most recent gravitational-wave data available led to the rich portrait as well as multiple tests of Einstein's theory of general relativity. (The theory passed each test.)

This illustration generated by a computer model shows multiple black holes found within the heart
of a dense globular star cluster [Credit: Aaron M. Geller, Northwestern University/CIERA]

The team of scientists who make up the LIGO Scientific Collaboration (LSC) and the Virgo Collaboration is now sharing the full details of its discoveries. This includes new gravitational-wave detection candidates which held up to scrutiny -- a whopping total of 39, representing a variety of black holes and neutron stars -- and new discoveries as a result of combining all the observations. The 39 events averaged more than one per week of observing.

The observations could be a key piece in solving the many mysteries of exactly how binary stars interact. A better understanding of how binary stars evolve has consequences across astronomy, from exoplanets to galaxy formation.

Details are reported in a trio of related papers which will be available in pre-print at arxiv.org [paper1, paper2, paper3]. The studies also are being submitted to peer-reviewed journals.

The gravitational-wave signals on which the studies are based were detected during the first half of the third observing run, called O3a, of the National Science Foundation's Laser Interferometry Gravitational-wave Observatory (LIGO), a pair of identical, 4-kilometer-long interferometers in the United States, and Virgo, a 3-kilometer-long detector in Italy. The instruments can detect gravitational-wave signals from many sources, including colliding black holes and colliding neutron stars.

"Gravitational-wave astronomy is revolutionary -- revealing to us the hidden lives of black holes and neutron stars," said Christopher Berry, an LSC member and author of the papers. "In just five years we have gone from not knowing that binary black holes exist to having a catalog of over 40. The third observing run has yielded more discoveries than ever before. Combining them with earlier discoveries paints a beautiful picture of the universe's rich variety of binaries."

Berry is the CIERA Board of Visitors Research Professor in Northwestern's CIERA (Center for Interdisciplinary Exploration and Research in Astrophysics) and a lecturer at the University of Glasgow. Other Northwestern authors include CIERA members Maya Fishbach and Chase Kimball. CIERA is home to a broad group of researchers in theory, simulation and observation who study black holes, neutron stars, white dwarfs and more.

A collection of masses for a wide range of compact objects. The graphic shows black holes (blue),
 neutron stars (orange) and compact objects of uncertain nature (gray) detected through gravitational
 waves. Each compact binary merger corresponds to three compact objects: the two coalescing 
objects and the final merger remnant [Credit: Aaron M. Geller, Northwestern University 
& Frank Elavsky, LIGO-Virgo]

As a member of the collaboration, Northwestern researchers analyzed data from the gravitational-wave detectors to infer the properties of detected black hole and neutron star binaries and to provide an astrophysical interpretation of these discoveries.

The papers are summarized as follows:

- The "catalog paper" details the detections of black holes and neutron stars from the first half of O3a, bringing the total number of detection candidates for that period to 39. This number vastly exceeds detections from the first two observing runs. (The first run had three gravitational-wave detections, and the second had eight.) Previously announced detections from O3a include a mystery object in the mass gap (GW190814) and the first-of-its-kind intermediate mass black hole (GW190521).

- In the "populations paper," the researchers reconstructed the distribution of masses and spins of the black hole population and estimated the merger rate for binary neutron stars. The results will help scientists understand the detailed astrophysical processes which shape how these systems form. This improved understanding of the mass distribution of black holes and knowing that black hole spins can be misaligned suggests there could be multiple ways for binary black holes to form.

- Using the set of detections reported in the catalog paper, the researchers conducted detailed analysis by combining everything together. In what they call the "testing general relativity paper," the authors placed constraints on Einstein's theory of general relativity. The theory passed with flying colors, and they updated their best measurements on potential modifications.

"So far, LIGO and Virgo's third observing run has yielded many surprises," said Fishbach, a NASA Einstein Postdoctoral Fellow and LSC member. "After the second observing run, I thought we'd seen the whole spectrum of binary black holes, but the landscape of black holes is much richer and more varied than I imagined. I'm excited to see what future observations will teach us."

This illustration shows the merger of two black holes and the gravitational waves that ripple 
outward as the black holes spiral toward each other [Credit: LIGO/T. Pyle]

Fishbach coordinated writing of the populations paper which outlines what the collaboration has learned about the properties of the family of merging black holes and neutron stars.

Berry helped coordinate analysis as part of a global team to infer the properties of the detections, and he served as an LSC Editorial Board reviewer for the catalog and testing general relativity papers.

Graduate student Chase Kimball, an LSC member, contributed calculations of the rates of mergers to the populations paper. Kimball is co-advised by Berry and Vicky Kalogera, the principal investigator of Northwestern's LSC group, director of CIERA and the Daniel I. Linzer Distinguished University Professor of Physics and Astronomy in the Weinberg College of Arts and Sciences.

The LIGO and Virgo detectors finished their latest observing run this past March. The data analyzed in these three papers were collected from April 1, 2019, to Oct. 1, 2019. Researchers are in the process of analyzing data from the second half of the observing run, O3b.

The detectors are scheduled to resume observing next year after work is done to increase their detection range.

"Merging black hole and neutron star binaries are a unique laboratory," Berry said. "We can use them to study both gravity -- so far Einstein's general relativity has passed every test --and the astrophysics of how massive stars live their lives. LIGO and Virgo have transformed our ability to observe these binaries, and, as our detectors improve, the rate of discovery is only going to accelerate."

Source: Northwestern University [October 28, 2020]

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Astronomers discover activity on distant planetary object

Centaurs are minor planets believed to have originated in the Kuiper Belt in the outer solar system. They sometimes have comet-like features such as tails and comae--clouds of dust particles and gas--even though they orbit in a region between Jupiter and Neptune where it is too cold for water to readily sublimate, or transition, directly from a solid to a gas.

This new image of C/2014 OG392 (PANSTARRS) and its extensive coma combines many digital
images into a single 7,700 second exposure. The dashed lines are star trails caused by the
 long exposure. Images captured October 14, 2020 using the Large Monolithic Imager
on the 4.3 m Lowell Discovery Telescope [Credit: Northern Arizona University]

Only 18 active Centaurs have been discovered since 1927, and much about them is still poorly understood. Discovering activity on Centaurs is also observationally challenging because they are faint, telescope time-intensive and because they are rare.

A team of astronomers, led by doctoral student and Presidential Fellow Colin Chandler in Northern Arizona University's Astronomy and Planetary Science PhD program, earlier this year announced their discovery of activity emanating from Centaur 2014 OG392, a planetary object first found in 2014. They published their findings in a paper in The Astrophysical Journal Letters. Chandler is the lead author, working with four NAU co-authors, graduate student Jay Kueny, associate professor Chad Trujillo, professor David Trilling and PhD student William Oldroyd.

The team's research involved developing a database search algorithm to locate archival images of the Centaur as well as a follow-up observational campaign.

"Our paper reports the discovery of activity emanating from Centaur 2014 OG392, based on archival images we uncovered," Chandler said, "plus our own new observational evidence acquired with the Dark Energy Camera at the Inter-American Observatory in Cerro Tololo, Chile, the Walter Baade Telescope at the Las Campanas Observatory in Chile and the Large Monolithic Imager at Lowell Observatory's Discovery Channel Telescope in Happy Jack, Ariz."

"We detected a coma as far as 400,000 km from 2014 OG392," he said, "and our analysis of sublimation processes and dynamical lifetime suggest carbon dioxide and/or ammonia are the most likely candidates for causing activity on this and other active Centaurs."

"We developed a novel technique," Chandler said, "that combines observational measurements, for example, color and dust mass, with modeling efforts to estimate such characteristics as the object's volatile sublimation and orbital dynamics."

As a result of the team's discovery, the Centaur has recently been reclassified as a comet, and will be known as "C/2014 OG392 (PANSTARRS)."

"I'm very excited that the Minor Planet Center awarded a new comet designation befitting the activity we discovered on this unusual object," he said.

Source: Northern Arizona University [October 28, 2020]

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Solved: the mystery of how dark matter in galaxies is distributed

The gravitational force in the Universe under which it has evolved from a state almost uniform at the Big Bang until now, when matter is concentrated in galaxies, stars and planets, is provided by what is termed 'dark matter'. But in spite of the essential role that this extra material plays, we know almost nothing about its nature, behaviour and composition, which is one of the basic problems of modern physics. In a recent article in Astronomy & Astrophysics Letters, scientists at the Instituto de Astrofisica de Canarias (IAC)/University of La Laguna (ULL) and of the National University of the North-West of the Province of Buenos Aires (Junin, Argentina) have shown that the dark matter in galaxies follows a 'maximum entropy' distribution, which sheds light on its nature.

Dark matter in two galaxies simulated on a computer. The only difference between them is the nature
of dark matter. Without collisions in the top photo and with collisions in the bottom photo. The
work suggests that dark matter in real galaxies looks more like the image on the right,
less clumpy and more diffuse than the one on the left. The circle marks the
 end of the galaxy [Credit: Brinckmann et al. 2018]

Dark matter makes up 85% of the matter of the Universe, but its existence shows up only on astronomical scales. That is to say, due to its weak interaction, the net effect can only be noticed when it is present in huge quantities. As it cools down only with difficulty, the structures it forms are generally much bigger than planets and stars. As the presence of dark matter shows up only on large scales the discovery of its nature probably has to be made by astrophysical studies.

Maximum Entropy

To say that the distribution of dark matter is organized according to maximum entropy (which is equivalent to 'maximum disorder' or 'thermodynamic equilibrium') means that it is found in its most probable state. To reach this 'maximum disorder' the dark matter must have had to collide within itself, just as gas molecules do, so as to reach equilibrium in which its density, pressure, and temperature are related. However, we do not know how the dark matter has reached this type of equilibrium.

"Unlike the molecules in the air, for example, because gravitational action is weak, dark matter particles ought hardly to collide with one another, so that the mechanism by which they reach equilibrium is a mystery", says Jorge Sanchez Almeida, an IAC researcher who is the first author of the article. "However if they did collide with one another this would give them a very special nature, which would partly solve the mystery of their origin", he adds.

The maximum entropy of dark matter has been detected in dwarf galaxies, which have a higher ratio of dark matter to total matter than have more massive galaxies, so it is easier to see the effect in them. However, the researchers expect that it is general behaviour in all types of galaxies.

The study implies that the distribution of matter in thermodynamic equilibrium has a much lower central density that astronomers have assumed for many practical applications, such as in the correct interpretation of gravitational lenses, or when designing experiments to detect dark matter by its self-annihilation.

This central density is basic for the correct interpretation of the curvature of the light by gravitational lenses: if it is less dense the effect of the lens is less. To use a gravitational lens to measure the mass of a galaxy one needs a model, if this model is changed, the measurement changes.

The central density also is very important for the experiments which try to detect dark matter using its self-annihilation. Two dark matter particles could interact and disappear in a process which is highly improbable, but which would be characteristic of their nature. For two particles to interact they must collide. The probability of this collision depends on the density of the dark matter; the higher the concentration of dark matter, the higher is the probability that the particles will collide.

"For that reason, if the density changes so will the expected rate of production of the self-annihilations, and given that the experiments are designed on the prediction of a given rate, if this rate were very low the experiment is unlikely to yield a positive result", says Sanchez Almeida.

Finally, thermodynamic equilibrium for dark matter could also explain the brightness profile of the galaxies. This brightness falls with distance from the centre of a galaxy in a specific way, whose physical origin is unknown, but for which the researchers are working to show that it is the result of an equilibrium with maximum entropy.

Simulation Versus Observation

The density of dark matter in the centres of galaxies has been a mystery for decades. There is a strong discrepancy between the predictions of the simulations (a high density) and that which is observed (a low value). Astronomers have put forward many types of mechanisms to resolve this major disagreement.

In this article, the researchers have shown, using basic physical principles, that the observations can be reproduced on the assumption that the dark matter is in equilibrium, i.e., that it has maximum entropy. The consequences of this result could be very important because they indicate that the dark matter has interchanged energy with itself and/or with the remaining "normal" (baryonic) matter.

"The fact that equilibrium has been reached in such a short time, compared with the age of the Universe, could be the result of a type of interaction between dark matter and normal matter in addition to gravity", suggests Ignacio Trujillo, an IAC researcher and a co-author of this article. "The exact nature of this mechanism needs to be explored, but the consequences could be fascinating to understand just what is this component which dominates the total amount of matter in the Universe".

Source: Instituto de Astrofisica de Canarias [October 28, 2020]

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Star-studded image shows the glittering central parts of the Milky Way

For the first time, over 250 million stars in our galaxy's bulge have been surveyed in near-ultraviolet, optical, and near-infrared light, opening the door for astronomers to reexamine key questions about the Milky Way's formation and history. Using ultraviolet data, and with 450,000 individual images, the team was able to measure the chemical composition of tens of thousands of stars spanning a large area of the bulge. The vast dataset can be explored in spectacular detail in this image.

This photo looking toward the center of the Milky Way galaxy covers 0.5 by 0.25 degrees on the sky
(an area about twice as wide as the full Moon) and contains over 180,000 stars. The image captures
 a portion of our galaxy about 220 by 110 light-years across. It was taken with the Dark Energy
Camera on the Victor M. Blanco 4-meter Telescope at the Cerro-Tololo Inter-American Observatory
 in Chile, a Program of NSF's NOIRLab. By studying the brightnesses of these stars at different
wavelengths of light, astronomers were able to determine how many heavy elements they contain,
which is related to their formation history. The team concluded that the majority of stars in our
 galaxy’s central bulge were formed in a single burst of star formation some 10 billion
years ago [Credit: CTIO/NOIRLab/NSF/AURA/STScI, W. Clarkson
(UM-Dearborn), C. Johnson (STScI), and M. Rich (UCLA)]

The mysteries of the Milky Way are revealed in spectacular detail, thanks to the efforts of a team of astronomers who have observed 250 million stars in the bulge at the heart of the Milky Way using the Dark Energy Camera (DECam). DECam, primarily funded by the U.S. Department of Energy, is mounted on the Victor M.Blanco 4-meter Telescope at the Cerro Tololo Inter-American Observatory (CTIO) in Chile, a program of NSF's NOIRLab. By detecting the ultraviolet light from stars in the bulge known as Red Clump stars, they were able to analyze the chemical composition of over 70,000 stars over an area of sky 1,000 times as large as the full Moon (an area larger than 20 x 10 degrees stretching over the constellations Sagittarius and Scorpius).

The data are hosted and served to the community by NOIRLab's Community Science and Data Center (CSDC), also a program of NSF's NOIRLab, which handled the more than 7,000 DECam exposures, comprising more than 3.5 trillion pixels. A color-composite showing a main part of these data is shown in this image, and can be explored in all its whopping 50,000 x 25,000 pixels in this zoomable version.

The newly published study has shown that the stars near the very center of the Milky Way have a very similar composition, which suggests that they formed at around the same time. Normally composition is measured with a spectrograph, targeting a relatively small number of stars at a time (although the revolutionary DESI instrument at Kitt Peak National Observatory, a program of NSF's NOIRLab, will soon be able to do thousands). However, the Blanco DECam Bulge Survey took a different approach and instead precisely measured the stars' brightness differences from ultraviolet to infrared wavelengths. These differences in brightness at different wavelengths are called photometric colors by astronomers, and can reveal the composition of stars when the dataset is calibrated with stars measured spectroscopically.

This image shows a wide-field view of the center of the Milky Way with a pull-out image taken by
the Dark Energy Camera (DECam) at the Cerro-Tololo Inter-American Observatory in Chile. While
the Milky Way photo spans 71 degrees of the sky, the DECam image covers 0.5 by 0.25 degrees
(an area about twice as wide as the full Moon) [Credit: Milky Way photo: Akira Fujii;
Inset photo: CTIO/NOIRLab/NSF/AURA/STScI, W. Clarkson (UM-Dearborn),
C. Johnson (STScI), and M. Rich (UCLA)]

The team used DECam's three square degree field of view to take over 450,000 individual images, before focusing on the subsample of 70,000 stars, which is substantially larger than previous spectroscopic bulge surveys. Future work with the full DECam data set will yield millions of composition measurements, a sample size more than 200 times that of even the largest spectroscopic surveys.

Kathy Vivas, co-author and NOIRLab astronomer said, "This is exactly the strength of the Dark Energy Camera -- to undertake these kinds of studies. While it was originally aimed at the study of the distant Universe to measure its expansion, DECam has proven to be a powerful instrument to study our Milky Way as well."

The survey results are providing key insights into the formation of the bulge and a glimpse of what is to come when the upcoming Vera C. Rubin Observatory begins acquiring its own images of the Milky Way. "Many other spiral galaxies look like the Milky Way and have similar bulges, so if we can understand how the Milky Way formed its bulge then we'll have a good idea of how the other galaxies did too," said Johnson.

These data would also surely have fascinated Victor M. Blanco and his wife Betty Blanco, after whom the Blanco DECam Bulge Survey is named. Almost 50 years ago they used the same telescope to explore, amongst other things, the Milky Way's bulge. Half a century later, our home galaxy has plenty of surprises to offer.

This research was presented in two papers which appeared in the Monthly Notices of the Royal Astronomical Society [paper1, paper2].

Source: Association of Universities for Research in Astronomy (AURA) [October 27, 2020]

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Galaxies in the infant universe were surprisingly mature

Massive galaxies were already much more mature in the early universe than previously expected. This was shown by an international team of astronomers who studied 118 distant galaxies with the Atacama Large Millimeter/submillimeter Array (ALMA).

Artist's illustration of a dusty, rotating distant galaxy [Credit: B. Saxton NRAO/AUI/NSF,
ESO, NASA/STScI; NAOJ/Subaru]

Most galaxies formed when the universe was still very young. Our own galaxy, for example, likely started forming 13.6 billion years ago, in our 13.8 billion-year-old universe. When the universe was only ten percent of its current age (1-1.5 billion years after the Big Bang), most of the galaxies experienced a "growth spurt". During this time, they built up most of their stellar mass and other properties, such as dust, heavy element content, and spiral-disk shapes, that we see in today's galaxies. Therefore, if we want to learn how galaxies like our Milky Way formed, it is important to study this epoch.

In a survey called ALPINE (the ALMA Large Program to Investigate C+ at Early Times), an international team of astronomers studied 118 galaxies experiencing such a "growth spurt" in the early universe. "To our surprise, many of them were much more mature than we had expected," said Andreas Faisst of the Infrared Processing and Analysis Center (IPAC) at the California Institute of Technology (Caltech).

Galaxies are considered more "mature" than "primordial" when they contain a significant amount of dust and heavy elements. "We didn't expect to see so much dust and heavy elements in these distant galaxies," said Faisst. Dust and heavy elements (defined by astronomers as all elements heavier than hydrogen and helium) are considered to be a by-product of dying stars. But galaxies in the early universe have not had much time to build stars yet, so astronomers don't expect to see much dust or heavy elements there either.

These are two of the galaxies in the early universe that ALMA observed in radio waves. The
galaxies are considered more "mature" than "primordial" because they contain large amounts
 of dust (yellow). ALMA also revealed the gas (red), which is used to measure the obscured
star-formation and motions in the galaxies [Credit: B. Saxton NRAO/AUI/NSF,
ALMA (ESO/NAOJ/NRAO), ALPINE team]

"From previous studies, we understood that such young galaxies are dust-poor," said Daniel Schaerer of the University of Geneva in Switzerland. "However, we find around 20 percent of the galaxies that assembled during this early epoch are already very dusty and a significant fraction of the ultraviolet light from newborn stars is already hidden by this dust," he added.

Many of the galaxies were also considered to be relatively grown-up because they showed a diversity in their structures, including the first signs of rotationally supported disks - which may later lead to galaxies with a spiral structure as is observed in galaxies such as our Milky Way. Astronomers generally expect that galaxies in the early universe look like train wrecks because they often collide. "We see many galaxies that are colliding, but we also see a number of them rotating in an orderly fashion with no signs of collisions," said John Silverman of the Kavli Institute for the Physics and Mathematics of the Universe in Japan.

ALMA has spotted very distant galaxies before, such as MAMBO-9 (a very dusty galaxy) and the Wolfe Disk (a galaxy with a rotating disk). But it was hard to say whether these discoveries were unique, or whether there were more galaxies like them out there. ALPINE is the first survey that enabled astronomers to study a significant number of galaxies in the early universe, and it shows that they might evolve faster than expected. But the scientists don't yet understand how these galaxies grew up so fast, and why some of them already have rotating disks.

Artist's illustration of a galaxy in the early universe that is very dusty and shows the first signs of a rotationally 

supported disk. In this image, the red color represents gas, and blue/brown represents dust as seen in radio 

waves with ALMA. Many other galaxies are visible in the background, based on optical data from VLT 

and Subaru [Credit: B. Saxton NRAO/AUI/NSF, ESO, NASA/STScI; NAOJ/Subaru]

Observations from ALMA were crucial for this research because the radio telescope can see the star formation that is hidden by dust and trace the motion of gas emitted from star-forming regions. Surveys of galaxies in the early universe commonly use optical and infrared telescopes. These allow the measurement of the unobscured star formation and stellar masses. However, these telescopes have difficulties measuring dust obscured regions, where stars form, or the motions of gas in these galaxies. And sometimes they don't see a galaxy at all. "With ALMA we discovered a few distant galaxies for the first time. We call these Hubble-dark as they could not be detected even with the Hubble telescope," said Lin Yan of Caltech.

To learn more about distant galaxies, the astronomers want to point ALMA at individual galaxies for a longer time. "We want to see exactly where the dust is and how the gas moves around. We also want to compare the dusty galaxies to others at the same distance and figure out if there might be something special about their environments," added Paolo Cassata of the University of Padua in Italy, formerly at the Universidad de Valparaiso in Chile.

ALPINE is the first and largest multi-wavelength survey of galaxies in the early universe. For a large sample of galaxies the team collected measurements in the optical (including Subaru, VISTA, Hubble, Keck and VLT), infrared (Spitzer), and radio (ALMA). Multi-wavelength studies are needed to get the full picture of how galaxies are built up. "Such a large and complex survey is only possible thanks to the collaboration between multiple institutes across the globe," said Matthieu Bethermin of the Laboratoire d'Astrophysique de Marseille in France.

The study is published in Astronomy & Astrophysics.

Source: National Radio Astronomy Observatory [October 27, 2020]

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Study shows comets impacted start of life on earth

The Big Bang may have started the universe, but it's likely that littler bangs played a key role in life on Earth, say Albion College Physics Professor Nicolle Zellner and Chemistry Professor Vanessa McCaffrey. They (along with former student Jayden Butler, '17) share their fascinating findings on the interspace dispersal of glycolaldehyde (GLA) in an article recently published by the journal Astrobiology.

An artist’s rendition of the comet exploding in Earth’s atmosphere
[Credit: Terry Bakker]

Their project, funded by NASA and conducted at the Experimental Impact Laboratory at Johnson Space Center, exposed GLA samples to impact pressures between 4.5 and 25 gigapascals—at the low end, forces far greater than the deepest ocean water pressures, or that of a piano dropped from hundreds of miles above the Earth. Albion's team discovered that GLA, a sugar important in the chemistry leading to ribose, can retain its integrity under such intense pressures.

"Experiments that simulate impacts have shown time and time again that biomolecules found on comets, asteroids, and meteorites are not completely destroyed," says Zellner. "The fact that GLA can remain intact under these kinds of pressures provides another piece of the puzzle in our understanding of how biomolecules survived impact delivery to an early Earth."

In addition to the GLA remaining unchanged throughout such intense conditions, McCaffrey noted that several new molecules were seen after impact and that some of these could have important biological implications.

Zellner notes that the Albion work predates recent observations by astronomers, who reported that GLA is present on several comets. These findings support the Albion team's assertion that GLA was likely dispersed throughout the solar system—and onto Earth—via comet impacts.

The project findings, says Zellner, add an important piece to the picture of how life began.

"Everybody assumed GLA was a starting molecule for ribose or amino acids, but little consideration was given as to its source," Zellner says. "We're showing what the source of that molecule could be."

Author: Jake Weber | Source: Albion College [October 27, 2020]

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ALMA shows volcanic impact on Io's atmosphere

New radio images from the Atacama Large Millimeter/submillimeter Array (ALMA) show for the first time the direct effect of volcanic activity on the atmosphere of Jupiter's moon Io.

Composite image showing Jupiter's moon Io in radio (ALMA), and optical light (Voyager 1 and
Galileo). The ALMA images of Io show for the first time plumes of sulfur dioxide (in yellow)
rise up from its volcanoes. Jupiter is visible in the background (Hubble)
[Credit: ALMA (ESO/NAOJ/NRAO), I. de Pater et al.;
NRAO/AUI NSF, S. Dagnello; NASA/ESA]

Io is the most volcanically active moon in our solar system. It hosts more than 400 active volcanoes, spewing out sulfur gases that give Io its yellow-white-orange-red colors when they freeze out on its surface.

Although it is extremely thin—about a billion times thinner than Earth's atmosphere—Io has an atmosphere that can teach us about Io's volcanic activity and provide us a window into the exotic moon's interior and what is happening below its colorful crust.

Previous research has shown that Io's atmosphere is dominated by sulfur dioxide gas, ultimately sourced from volcanic activity. "However, it is not known which process drives the dynamics in Io's atmosphere," said Imke de Pater of the University of California, Berkeley. "Is it volcanic activity, or gas that has sublimated (transitioned from solid to gaseous state) from the icy surface when Io is in sunlight?"

To distinguish between the different processes that give rise to Io's atmosphere, a team of astronomers used ALMA to make snapshots of the moon when it passed in and out of Jupiter's shadow (they call this an "eclipse").

"When Io passes into Jupiter's shadow, and is out of direct sunlight, it is too cold for sulfur dioxide gas, and it condenses onto Io's surface. During that time we can only see volcanically-sourced sulfur dioxide. We can therefore see exactly how much of the atmosphere is impacted by volcanic activity," explained Statia Luszcz-Cook from Columbia University, New York.

This video shows images of Jupiter's moon Io in radio (made with ALMA), and optical light (made with Voyager 1 and Galileo missions). The ALMA images were taken when Io passed into Jupiter's shadow in March 2018 (eclipse), and from Jupiter's shadow into sunlight in September 2018. These radio images for the first time show plumes of sulfur dioxide (in yellow) rise up from the volcanoes on Io [Credit: ALMA (ESO/NAOJ/NRAO), I. de Pater et al.; NRAO/AUI NSF, S. Dagnello; NASA]

Thanks to ALMA's exquisite resolution and sensitivity, the astronomers could, for the first time, clearly see the plumes of sulfur dioxide (SO2) and sulfur monoxide (SO) rise up from the volcanoes. Based on the snapshots, they calculated that active volcanoes directly produce 30-50 percent of Io's atmosphere.

The ALMA images also showed a third gas coming out of volcanoes: potassium chloride (KCl). "We see KCl in volcanic regions where we do not see SO2 or SO," said Luszcz-Cook. "This is strong evidence that the magma reservoirs are different under different volcanoes."

 

Io is volcanically active due to a process called tidal heating. Io orbits Jupiter in an orbit that is not quite circular and, like our Moon always faces the same side of Earth, so does the same side of Io always face Jupiter. The gravitational pull of Jupiter's other moons Europa and Ganymede causes tremendous amounts of internal friction and heat, giving rise to volcanoes such as Loki Patera, which spans more than 200 kilometers (124 miles) across. "By studying Io's atmosphere and volcanic activity we learn more about not only the volcanoes themselves, but also the tidal heating process and Io's interior," added Luszcz-Cook.

A big unknown remains the temperature in Io's lower atmosphere. In future research, the astronomers hope to measure this with ALMA. "To measure the temperature of Io's atmosphere, we need to obtain a higher resolution in our observations, which requires that we observe the moon for a longer period of time. We can only do this when Io is in sunlight since it does not spend much time in eclipse," said de Pater. "During such an observation, Io will rotate by tens of degrees. We will need to apply software that helps us make un-smeared images. We have done this previously with radio images of Jupiter made with ALMA and the Very Large Array (VLA)."

The findings are published in the Planetary Science Journal.

Source: National Radio Astronomy Observatory [October 27, 2020]

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'Fireball' meteorite contains pristine extraterrestrial organic compounds

On the night of January 16, 2018, a fireball meteor streaked across the sky over the Midwest and Ontario before landing on a frozen lake in Michigan. Scientists used weather radar to find where the pieces landed and meteorite hunters were able to collect the meteorite quickly, before its chemical makeup got changed by exposure to liquid water. And, as a new paper in Meteoritics & Planetary Science shows, that gave scientists a glimpse of what space rocks are like when they're still in outer space--including a look at pristine organic compounds that could tell us about the origins of life.

The meteorite fragment that fell on Strawberry Lake which contains pristine
extraterrestrial organic compounds [Credit: Field Museum]

"This meteorite is special because it fell onto a frozen lake and was recovered quickly. It was very pristine. We could see the minerals weren't much altered and later found that it contained a rich inventory of extraterrestrial organic compounds," says Philipp Heck, a curator at the Field Museum, associate professor at the University of Chicago, and lead author of the new paper. "These kinds of organic compounds were likely delivered to the early Earth by meteorites and might have contributed to the ingredients of life."

Meteorites, simply put, are space rocks that have fallen to Earth. When things like asteroids collide in outer space, fragments can break off. These pieces of rock, called meteoroids, continue floating through space, and sometimes, their new paths collide with moons or planets. When a meteoroid breaks through the Earth's atmosphere and we can see it as a fireball or shooting star, it's called a meteor. If pieces of that meteor survive the trip through the atmosphere, the bits that actually land on Earth are called meteorites.

When the fireball arrived in Michigan, scientists used NASA's weather radar to track where the pieces went. "Weather radar is meant to detect hail and rain," explains Heck. "These pieces of meteorite fell into that size range, and so weather radar helped show the position and velocity of the meteorite. That meant that we were able to find it very quickly."

Less than two days after it landed, meteorite hunter Robert Ward found the first piece of the meteorite on the frozen surface of Strawberry Lake, near Hamburg, Michigan. Ward worked with Terry Boudreaux to donate the meteorite to the Field Museum, where Heck and Jennika Greer, a graduate student at the Field and the University of Chicago and one of the paper's authors, began to study it.

"When the meteorite arrived at the Field, I spent the entire weekend analyzing it, because I was so excited to find out what kind of meteorite it was and what was in it," says Greer. "With every meteorite that falls, there's a chance that there's something completely new and totally unexpected."

The researchers quickly determined that the meteorite was an H4 chondrite--only 4% of all meteorites falling to Earth these days are of this type. But the real thing that makes the Hamburg meteorite exceptional is because of how quickly it was collected and how well-analyzed it is.

"This meteorite shows a high diversity of organics, in that if somebody was interested in studying organics, this is not normally the type of meteorite that they would ask to look at," says Greer. "But because there was so much excitement surrounding it, everybody wanted to apply their own technique to it, so we have an unusually comprehensive set of data for a single meteorite."

Scientists aren't sure how the organic (carbon-containing) compounds responsible for life on Earth got here; one theory is that they hitched their way here on meteorites. That doesn't mean that the meteorites themselves contain extraterrestrial life; rather, some of the organic compounds that help make up life might have first formed in an asteroid that later fell to Earth. (In short, sorry, we didn't find any aliens.)

"Scientists who study meteorites and space sometimes get asked, do you ever see signs of life? And I always answer, yes, every meteorite is full of life, but terrestrial, Earth life," says Heck. "As soon as the thing lands, it gets covered with microbes and life from Earth. We have meteorites with lichens growing on them. So the fact that this meteorite was collected so quickly after it fell, and that it landed on ice rather than in the dirt, helped keep it cleaner."

The buzz around the meteorite when it landed also helped scientists learn much more about it than many other meteorites of its kind--they used a wide variety of analytical techniques and studied samples from different parts of the meteorite to get a more complete picture of the minerals it contains. "You learn a lot more about a meteorite when you sample different pieces. It's like if you had a supreme pizza, if you only looked at one little section, you might think it was just pepperoni, but there might be mushrooms or peppers somewhere else," says Greer.

"This study is a demonstration of how we can work with specialists around the world to get most out of the small piece of raw, precious piece of rock," says Heck. "When a new meteorite falls onto a frozen lake, maybe even sometime this winter, we'll be ready. And that next fall might be something we have never seen before."

Source: Field Museum [October 27, 2020]

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