ST/ Supermassive blackhole influences star formation

Paradigm

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Paradigm

36 min readAug 5, 2022

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Space biweekly vol.57, 20th July — 5thAugust

TL;DR

Powerful jets of a supermassive black hole change the conditions for star formation in interstellar clouds.
Supermassive black holes with varying light signatures are actually in different stages of the life cycle.
Because it’s bigger, Jupiter ought to have larger, more spectacular rings than Saturn has. But new research shows Jupiter’s massive moons prevent that vision from lighting up the night sky.
Millisecond pulsars spin far more rapidly than expected for a collapsed star. The best chance to study these neutron stars is to find a black widow system where the pulsar has evaporated and eaten much of its companion star. The Keck I telescope was just able to capture spectra of one such companion, allowing astronomers to weigh its pulsar. It’s the heaviest found to date, and perhaps near the upper limit for a neutron star.
In recent years, a large number of exoplanets have been found around single ‘normal’ stars. New research shows that there may be exceptions to this trend. Researchers suggest a new way of detecting dim bodies, including planets, orbiting exotic binary stars known as Cataclysmic Variables (CVs).
Planetary scientists have an answer to a mystery that’s puzzled the Mars research community since NASA’s Curiosity rover discovered a mineral called tridymite in Gale Crater in 2016.
Using data collected over two decades ago, scientists have compiled the first complete map of hydrogen abundances on the Moon’s surface. The map identifies two types of lunar materials containing enhanced hydrogen and corroborates previous ideas about lunar hydrogen and water, including findings that water likely played a role in the Moon’s original magma-ocean formation and solidification.
A team of astronomers has developed a method that will allow them to ‘see’ through the fog of the early Universe and detect light from the first stars and galaxies.
Astronomers have analyzed archive data for powerful cosmic explosions from the deaths of stars and found a new way to measure distances in the distant Universe.
Researchers demonstrated a 3D-printed plasma sensor for satellites that works just as well as the expensive semiconductor sensors that take weeks of intricate fabrication in a cleanroom. These durable, precise sensors could be used on CubeSats, which are commonly utilized for environmental monitoring or weather prediction.
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Space industry in numbers

The global smart space market size is projected to grow from USD 9.4 billion in 2020 to USD 15.3 billion by 2025, at a Compound Annual Growth Rate (CAGR) of 10.2% during the forecast period. The increasing venture capital funding and growing investments in smart space technology to drive market growth.

Analysts at Morgan Stanley and Goldman Sachs have predicted that economic activity in space will become a multi-trillion-dollar market in the coming decades. Morgan Stanley’s Space Team estimates that the roughly USD 350 billion global space industry could surge to over USD 1 trillion by 2040.

Source: Satellite Industry Association, Morgan Stanley Research, Thomson Reuters. *2040 estimates

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Latest research

Insights into the collapse and expansion of molecular clouds in outflows from observable pressure gradients

by Kalliopi M. Dasyra, Georgios F. Paraschos, Thomas G. Bisbas, Francoise Combes, Juan Antonio Fernández-Ontiveros in Nature Astronomy

A European team of astronomers led by Professor Kalliopi Dasyra of the National and Kapodistrian University of Athens, Greece, under participation of Dr. Thomas Bisbas, University of Cologne modelled several emission lines in Atacama Large Millimeter Array (ALMA) and Very Large Telescope (VLT) observations to measure the gas pressure in both jet-impacted clouds and ambient clouds. With these unprecedented measurements they discovered that the jets significantly change the internal and external pressure of molecular clouds in their path. Depending on which of the two pressures changes the most, both compression of clouds and triggering of star formation and dissipation of clouds and delaying of star formation are possible in the same galaxy.

“Our results show that supermassive black holes, even though they are located at the centers of galaxies, could affect star formation in a galaxy-wide manner” said Professor Dasyra, adding that “studying the impact of pressure changes in the stability of clouds was key to the success of this project. Once few stars actually form in a wind, it is usually very hard to detect their signal on top of the signal of all other stars in the galaxy hosting the wind.”

It is believed that supermassive black holes lie at the centers of most galaxies in our Universe. When particles that were infalling onto these black holes are trapped by magnetic fields, they can be ejected outwards and travel far inside galaxies in the form of enormous and powerful jets of plasma. These jets are often perpendicular to galactic disks. In IC 5063 however, a galaxy 156 million light years away, the jets are actually propagating within the disk, interacting with cold and dense molecular gas clouds. From this interaction, compression of jet-impacted clouds is theorized to be possible, leading to gravitational instabilities and eventually star formation due to the gas condensation.

Spatially-resolved SLED fitting results for the mechanical heating model.

For the experiment, the team used the emission of carbon monoxide (CO) and formyl cation (HCO+) provided by ALMA, and the emission of ionized sulfur and ionized nitrogen provided by VLT. They then used advanced and innovative astrochemical algorithms to pinpoint the environmental conditions in the outflow and in the surrounding medium. These environmental conditions contain information about the strength of the far-ultraviolet radiation of stars, the rate at which relativistic charged particles ionize the gas, and the mechanical energy deposited on the gas by the jets. Narrowing down these conditions revealed the densities and gas temperatures descriptive of different parts of this galaxy, which were then used to provide pressures.

“We have performed many thousands of astrochemical simulations to cover a wide range of possibilities that may exist in IC 5063” said co-author Dr. Thomas Bisbas, DFG Fellow of the University of Cologne and former postdoctoral researcher at the National Observatory of Athens. A challenging part of the work was to meticulously identify as many physical constraints as possible to the examined range that each parameter could have. “This way, we could get the optimal combination of physical parameters of clouds at different locations of the galaxy,” said co-author Mr. Georgios Filippos Paraschos, Ph.D. student at the Max Planck Institute for Radio Astronomy in Bonn and former Master’s student at the National and Kapodistrian University of Athens.

Gas properties derived from NIR VLT SINFONI data.

In fact, pressures were not just measured for a few locations in IC 5063. Instead, maps of this and other quantities in the center of this galaxy were created. These maps allowed the authors to visualize how the gas properties transition from one location to another because of the jet passage. The team is currently looking forward to the next big step of this project: using the James Webb Space Telescope for further investigations of the pressure in the outer cloud layers, as probed by the warm H2. “We are truly excited about getting the JWST data,” said Professor Dasyra, “as they will enable us to study the jet-cloud interaction at an exquisite resolution.”

BASS. XXX. Distribution Functions of DR2 Eddington Ratios, Black Hole Masses, and X-Ray Luminosities

by Tonima Tasnim Ananna, Anna K. Weigel, Benny Trakhtenbrot, Michael J. Koss, et al in The Astrophysical Journal Supplement Series

Black holes with varying light signatures but that were thought to be the same objects being viewed from different angles are actually in different stages of the life cycle, according to a study led by Dartmouth researchers.

The research on black holes known as “active galactic nuclei,” or AGNs, says that it definitively shows the need to revise the widely used “unified model of AGN” that characterizes supermassive black holes as all having the same properties. The study provides answers to a nagging space mystery and should allow researchers to create more precise models about the evolution of the universe and how black holes develop.

“These objects have mystified researchers for over a half-century,” said Tonima Tasnim Ananna, a postdoctoral research associate at Dartmouth and lead author of the paper. “Over time, we’ve made many assumptions about the physics of these objects. Now we know that the properties of obscured black holes are significantly different from the properties of AGNs that are not as heavily hidden.”

Venn diagrams of all Swift/BAT 70 month sources below z = 0.3, after removing all beamed sources and Galactic-plane sources (∣b∣ < 5°), as well as making more subtle cuts that exclude a total of 181 sources (see the text for details).

Supermassive black holes are believed to reside at the center of nearly all large galaxies, including the Milky Way. The objects devour galactic gas, dust and stars, and they can become heavier than small galaxies. For decades, researchers have been interested in the light signatures of active galactic nuclei, a type of supermassive black hole that is “accreting,” or in a rapid growth stage.

Beginning in the late 1980s, astronomers realized that light signatures coming from space ranging from radio wavelengths to X-rays could be attributed to AGNs. It was assumed that the objects usually had a doughnut-shaped ring — or “torus” — of gas and dust around them. The different brightness and colors associated with the objects were thought to be the result of the angle from which they were being observed and how much of the torus was obscuring the view. From this, the unified theory of AGNs became the prevalent understanding. The theory guides that if a black hole is being viewed through its torus, it should appear faint. If it is being viewed from below or above the ring, it should appear bright. According to the current study, however, the past research relied too heavily on data from the less obscured objects and skewed research results.

Swift/BAT cumulative number counts (left) and differential number counts (right) from the 70 month survey, with beamed sources, low-flux dual sources, sources close to the Galactic plane, and weak associations removed (672 sources, at z ≤ 0.3; turquoise data points); the same sample with an additional redshift cut applied (z ≥ 0.01, 619 sources; yellow data points); and then with all Table 1 cuts applied (586 sources; red data points).

The new study focuses on how quickly black holes are feeding on space matter, or their accretion rates. The research found that the accretion rate does not depend upon the mass of a black hole, it varies significantly depending on how obscured it is by the gas and dust ring.

“This provides support for the idea that the torus structures around black holes are not all the same,” said Ryan Hickox, professor of physics and astronomy and a co-author of the study. “There is a relationship between the structure and how it is growing.”

The result shows that the amount of dust and gas surrounding an AGN is directly related to how much it is feeding, confirming that there are differences beyond orientation between different populations of AGNs. When a black hole is accreting at a high rate, the energy blows away dust and gas. As a result, it is more likely to be unobscured and appear brighter. Conversely, a less active AGN is surrounded by a denser torus and appears fainter.

“In the past, it was uncertain how the obscured AGN population varied from their more easily observable, unobscured counterparts,” said Ananna. “This new research definitively shows a fundamental difference between the two populations that goes beyond viewing angle.”

The study stems from a decade-long analysis of nearby AGNs detected by Swift-BAT, a high-energy NASA X-ray telescope. The telescope allows researchers to scan the local universe to detect obscured and unobscured AGNs. The research is the result of an international scientific collaboration — the BAT AGN Spectroscopic Survey (BASS) — that has been working over a decade to collect and analyze optical/infrared spectroscopy for AGN observed by Swift BAT.

“We have never had such a large sample of X-ray detected obscured local AGN before,” said Ananna. “This is a big win for high-energy X-ray telescopes.”

The effect of the low redshift cut and obscuration on the BASS XLF. Left panel: the BASS XLF determined without a low-z cut (blue squares; 672 sources), and the corresponding fit (dotted blue line).

The paper builds on previous research from the research team analyzing AGNs. For the study, Ananna developed a computational technique to assess the effect of obscuring matter on observed properties of black holes, and analyzed data collected by the wider research team using this technique. According to the paper, by knowing a black hole’s mass and how fast it is feeding, researchers can determine when most supermassive black holes underwent most of their growth, thus providing valuable information about the evolution of black holes and the universe.

“One of the biggest questions in our field is where do supermassive black holes come from,” said Hickox. “This research provides a critical piece that can help us answer that question and I expect it to become a touchstone reference for this research discipline.”

Future research could include focusing on wavelengths that allow the team to search beyond the local universe. In the nearer term, the team would like to understand what triggers AGNs to go into high accretion mode, and how long it takes rapidly accreting AGNs to transition from heavily obscured to unobscured.

PSR J0952–0607: The Fastest and Heaviest Known Galactic Neutron Star

by Roger W. Romani, D. Kandel, Alexei V. Filippenko, Thomas G. Brink, WeiKang Zheng in The Astrophysical Journal Letters

Millisecond pulsars spin far more rapidly than expected for a collapsed star. The best chance to study these neutron stars is to find a black widow system where the pulsar has evaporated and eaten much of its companion star. The Keck I telescope was just able to capture spectra of one such companion, allowing astronomers to weigh its pulsar. It’s the heaviest found to date, and perhaps near the upper limit for a neutron star.

A dense, collapsed star spinning 707 times per second — making it one of the fastest spinning neutron stars in the Milky Way galaxy — has shredded and consumed nearly the entire mass of its stellar companion and, in the process, grown into the heaviest neutron star observed to date. Weighing this record-setting neutron star, which tops the charts at 2.35 times the mass of the sun, helps astronomers understand the weird quantum state of matter inside these dense objects, which — if they get much heavier than that — collapse entirely and disappear as a black hole.

“We know roughly how matter behaves at nuclear densities, like in the nucleus of a uranium atom,” said Alex Filippenko, Distinguished Professor of Astronomy at the University of California, Berkeley. “A neutron star is like one giant nucleus, but when you have one-and-a-half solar masses of this stuff, which is about 500,000 Earth masses of nuclei all clinging together, it’s not at all clear how they will behave.”

Roger W. Romani, professor of astrophysics at Stanford University, noted that neutron stars are so dense — 1 cubic inch weighs over 10 billion tons — that their cores are the densest matter in the universe short of black holes, which because they are hidden behind their event horizon are impossible to study. The neutron star, a pulsar designated PSR J0952–0607, is thus the densest object within sight of Earth. The measurement of the neutron star’s mass was possible thanks to the extreme sensitivity of the 10-meter Keck I telescope on Maunakea in Hawai’i, which was just able to record a spectrum of visible light from the hotly glowing companion star, now reduced to the size of a large gaseous planet. The stars are about 3,000 light years from Earth in the direction of the constellation Sextans.

Discovered in 2017, PSR J0952–0607 is referred to as a “black widow” pulsar — an analogy to the tendency of female black widow spiders to consume the much smaller male after mating. Filippenko and Romani have been studying black widow systems for more than a decade, hoping to establish the upper limit on how large neutron stars/pulsars can grow.

“By combining this measurement with those of several other black widows, we show that neutron stars must reach at least this mass, 2.35 plus or minus 0.17 solar masses,” said Romani, who is a professor of physics in Stanford’s School of Humanities and Sciences and member of the Kavli Institute for Particle Astrophysics and Cosmology. “In turn, this provides some of the strongest constraints on the property of matter at several times the density seen in atomic nuclei. Indeed, many otherwise popular models of dense-matter physics are excluded by this result.”

If 2.35 solar masses is close to the upper limit of neutron stars, the researchers say, then the interior is likely to be a soup of neutrons as well as up and down quarks — the constituents of normal protons and neutrons — but not exotic matter, such as “strange” quarks or kaons, which are particles that contain a strange quark. Romani, Filippenko and Stanford graduate student Dinesh Kandel are co-authors of a paper describing the team’s results.

“A high maximum mass for neutron stars suggests that it is a mixture of nuclei and their dissolved up and down quarks all the way to the core,” Romani said. “This excludes many proposed states of matter, especially those with exotic interior composition.”

Corner plot from the MCMC light-curve t to the trimmed” photometry points.

Astronomers generally agree that when a star with a core larger than about 1.4 solar masses collapses at the end of its life, it forms a dense, compact object with an interior under such high pressure that all atoms are smashed together to form a sea of neutrons and their subnuclear constituents, quarks. These neutron stars are born spinning, and though too dim to be seen in visible light, reveal themselves as pulsars, emitting beams of light — radio waves, X-rays or even gamma rays — that flash Earth as they spin, much like the rotating beam of a lighthouse.

“Ordinary” pulsars spin and flash about once per second, on average, a speed that can easily be explained given the normal rotation of a star before it collapses. But some pulsars repeat hundreds or up to 1,000 times per second, which is hard to explain unless matter has fallen onto the neutron star and spun it up. But for some millisecond pulsars, no companion is visible. One possible explanation for isolated millisecond pulsars is that each did once have a companion, but it stripped it down to nothing.

“The evolutionary pathway is absolutely fascinating. Double exclamation point,” Filippenko said. “As the companion star evolves and starts becoming a red giant, material spills over to the neutron star, and that spins up the neutron star. By spinning up, it now becomes incredibly energized, and a wind of particles starts coming out from the neutron star. That wind then hits the donor star and starts stripping material off, and over time, the donor star’s mass decreases to that of a planet, and if even more time passes, it disappears altogether. So, that’s how lone millisecond pulsars could be formed. They weren’t all alone to begin with — they had to be in a binary pair — but they gradually evaporated away their companions, and now they’re solitary.”

The pulsar PSR J0952–0607 and its faint companion star support this origin story for millisecond pulsars.

“These planet-like objects are the dregs of normal stars which have contributed mass and angular momentum, spinning up their pulsar mates to millisecond periods and increasing their mass in the process,” Romani said.
“In a case of cosmic ingratitude, the black widow pulsar, which has devoured a large part of its mate, now heats and evaporates the companion down to planetary masses and perhaps complete annihilation,” said Filippenko.

Finding black widow pulsars in which the companion is small, but not too small to detect, is one of few ways to weigh neutron stars. In the case of this binary system, the companion star — now only 20 times the mass of Jupiter — is distorted by the mass of the neutron star and tidally locked, similar to the way our moon is locked in orbit so that we see only one side. The neutron star-facing side is heated to temperatures of about 6,200 Kelvin, or 10,700 degrees Fahrenheit, a bit hotter than our sun, and just bright enough to see with a large telescope. Filippenko and Romani turned the Keck I telescope on PSR J0952–0607 on six occasions over the last four years, each time observing with the Low Resolution Imaging Spectrometer in 15-minute chunks to catch the faint companion at specific points in its 6.4-hour orbit of the pulsar. By comparing the spectra to that of similar sun-like stars, they were able to measure the orbital velocity of the companion star and calculate the mass of the neutron star.

Filippenko and Romani have examined about a dozen black widow systems so far, though only six had companion stars bright enough to let them calculate a mass. All involved neutron stars less massive than the pulsar PSR J0952–060. They’re hoping to study more black widow pulsars, as well as their cousins: redbacks, named for the Australian equivalent of black widow pulsars, which have companions closer to one-tenth the mass of the sun; and what Romani dubbed tidarrens — where the companion is around one-hundredth of a solar mass — after a relative of the black widow spider. The male of this species, Tidarren sisyphoides, is about 1% of the female’s size.

“We can keep looking for black widows and similar neutron stars that skate even closer to the black hole brink. But if we don’t find any, it tightens the argument that 2.3 solar masses is the true limit, beyond which they become black holes,” Filippenko said.
“This is right at the limit of what the Keck telescope can do, so barring fantastic observing conditions, tightening the measurement of PSR J0952–0607 likely awaits the 30-meter telescope era,” added Romani.

The Dynamical Viability of an Extended Jupiter Ring System

by Stephen R. Kane, Zhexing Li in Planetary Science

Because it’s bigger, Jupiter ought to have larger, more spectacular rings than Saturn has. But new UC Riverside research shows Jupiter’s massive moons prevent that vision from lighting up the night sky.

“It’s long bothered me why Jupiter doesn’t have even more amazing rings that would put Saturn’s to shame,” said UCR astrophysicist Stephen Kane, who led the research. “If Jupiter did have them, they’d appear even brighter to us, because the planet is so much closer than Saturn.” Kane also had questions about whether Jupiter once had fantastic rings and lost them. It is possible for ring structures to be temporary.

To understand the reason Jupiter currently looks the way it does, Kane and his graduate student Zhexing Li ran a dynamic computer simulation accounting for the orbits of Jupiter’s four main moons, as well as the orbit of the planet itself, and information about the time it takes for rings to form. Saturn’s rings are largely made of ice, some of which may have come from comets, which are also largely made of ice. If moons are massive enough, their gravity can toss the ice out of a planet’s orbit, or change the orbit of the ice enough so that it collides with the moons.

“We found that the Galilean moons of Jupiter, one of which is the largest moon in our solar system, would very quickly destroy any large rings that might form,” Kane said. As a result, it is unlikely that Jupiter had large rings at any point in its past. “Massive planets form massive moons, which prevents them from having substantial rings,” Kane said.

All four giant planets in our solar system — Saturn, Neptune, Uranus and also Jupiter — do in fact have rings. However, both Neptune and Jupiter’s rings are so flimsy they’re difficult to view with traditional stargazing instruments. Coincidentally, some of the recent images from the newly commissioned James Webb Space Telescope included pictures of Jupiter, in which the faint rings are visible.

“We didn’t know these ephemeral rings existed until the Voyager spacecraft went past because we couldn’t see them,” Kane said.

Jupiter and some of its moons with faint ring visible. (NASA/ESA/CSA/B. Holler/J. Stansberry/STScI)

Uranus has rings that are aren’t as large but are more substantial than Saturn’s. Going forward, Kane intends to run simulations of the conditions on Uranus to see what the lifetime of that planet’s rings might be. Some astronomers believe Uranus is tipped over on its side as the result of a collision the planet had with another celestial body. Its rings could be the remains of that impact. Beyond their beauty, rings help astronomers understand the history of a planet, because they offer evidence of collisions with moons or comets that may have happened in the past. The shape and size of the rings, as well as the composition of the material, offers an indication about the type of event that formed them.

“For us astronomers, they are the blood spatter on the walls of a crime scene. When we look at the rings of giant planets, it’s evidence something catastrophic happened to put that material there,” Kane said.

Global Hydrogen Abundances on the Lunar Surface

by David J. Lawrence, Patrick N. Peplowski, Jack T. Wilson, Richard C. Elphic in Journal of Geophysical Research: Planets

Using data collected over two decades ago, scientists from the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, have compiled the first complete map of hydrogen abundances on the Moon’s surface. The map identifies two types of lunar materials containing enhanced hydrogen and corroborates previous ideas about lunar hydrogen and water, including findings that water likely played a role in the Moon’s original magma-ocean formation and solidification.

APL’s David Lawrence, Patrick Peplowski and Jack Wilson, along with Rick Elphic from NASA Ames Research Center, used orbital neutron data from the Lunar Prospector mission to build their map. The probe, which was deployed by NASA in 1998, orbited the Moon for a year and a half and sent back the first direct evidence of enhanced hydrogen at the lunar poles, before impacting the lunar surface.

When a star explodes, it releases cosmic rays, or high-energy protons and neutrons that move through space at nearly the speed of light. When those cosmic rays come into contact with the surface of a planet, or a moon, they break apart atoms located on those bodies, sending protons and neutrons flying. Scientists are able to identify an element and determine where and how much of it exists by studying the motion of those protons and neutrons.

Calibrated epithermal neutron model count rates (Cepi,cal) versus measured count rates.

“Imagine you’re playing a game of pool and the cue ball represents neutrons and the billiard balls represent hydrogen,” explained Lawrence. “When you hit a billiard ball with your cue ball, the cue ball stops moving and the billiard ball is pushed into motion, because both objects have the same mass. Similarly, when a neutron comes in contact with hydrogen, it dies and stops moving, and the hydrogen is sent into motion. So when we see a fewer number of neutrons moving about, it’s an indication hydrogen is present.”

The team calibrated the data to quantify the amount of hydrogen by the corresponding decrease of neutrons measured by the Neutron Spectrometer, one of five instruments mounted on Lunar Prospector to complete gravitational and compositional maps of the Moon.

“We were able to combine data from lunar soil samples from the Apollo missions with what we’ve measured from space and finally put together a full picture of lunar hydrogen for the first time,” continued Lawrence.

Global epithermal neutron data versus global Σa values taken from Peplowski et al.

The team’s map confirms enhanced hydrogen in two types of lunar materials. The first, at the Aristarchus Plateau, is home to the Moon’s largest pyroclastic deposit. These deposits are fragments of rock erupted from volcanoes, corroborating prior observations that hydrogen and/or water played a role in lunar magmatic events. The second is KREEP-type rocks. KREEP is an acronym for lunar lava rock that stands for potassium (K), rare earth elements (REE) and phosphorus (P).

“When the Moon originally formed, it’s largely accepted that it was molten debris from a huge impact with Earth,” Lawrence said. “As it cooled, minerals formed out of the melt, and KREEP is thought to be the last type of material to crystallize and harden.”

Lawrence, who was part of the original team that studied initial data from the Lunar Prospector mission in 1998, said building on existing efforts to complete a full map of Earth’s nearest neighbor took time.

“Finalizing the analysis took a number of years,” said Lawrence. “As we were sorting through everything, we began making corrections to data that we discovered was not hydrogen. We went back and fine-tuned previous analyses, and in large part, we were able to do that because of discoveries from other missions. We are continuously building off of previous knowledge and stepping into new territory.”

This new map not only completes the inventory of hydrogen on the Moon but could also lead to quantification of how much hydrogen and water was present in the Moon when it was born. In 2013, APL researchers also confirmed the presence of water ice at the poles on the planet Mercury using data from the neutron spectrometer on the APL-built MESSENGER spacecraft. These discoveries are important not only for understanding the solar system but also in planning future human exploration of the solar system.

Testing the third-body hypothesis in the cataclysmic variables LU Camelopardalis, QZ Serpentis, V1007 Herculis and BK Lyncis

by Carlos E Chavez, Nikolaos Georgakarakos, Andres Aviles, Hector Aceves, Gagik Tovmassian, Sergey Zharikov, J E Perez–Leon, Francisco Tamayo in Monthly Notices of the Royal Astronomical Society

In recent years, a large number of exoplanets have been found around single ‘normal’ stars. New research shows that there may be exceptions to this trend. Researchers from The Autonomous University of Nuevo León (UANL), The National Autonomous University of Mexico (UNAM), and New York University Abu Dhabi suggest a new way of detecting dim bodies, including planets, orbiting exotic binary stars known as Cataclysmic Variables (CVs).

CVs are binary star systems in which the two stars are in extremely close proximity to each other; so close that the less massive object transfers mass to the more massive. CVs are typically formed of a small, cool type of star known as a red dwarf star, and a hot, dense star — a white dwarf. Red dwarf stars have a mass between 0.07 and 0.30 solar masses and a radius of around 20% of the Sun’s, while white dwarf stars have a typical mass of around 0.75 Solar masses and a very small radius similar to that of planet Earth.

In the CV system, the transfer of matter from the small star forms an accretion disk around the compact, more massive star. The brightness of a CV system mainly comes from this disk, and overpowers the light coming from the two stars. A third dim body orbiting a CV can influence the mass transfer rate between the two stars, and hence the brightness of the entire system. The method described in the new work is based on the change of brightness in the accretion disk due to perturbations of the third body that orbits around the inner two stars.

Results for the V1007 Her system. Integrations yield for the third body a mass of M3 = 148 MJ and P2 = 1.08 d.

In their research, team leader Dr Carlos Chavez and his collaborators have estimated the mass and distance of a third body orbiting four different CVs using the changes in the brightness of each system. According to calculations carried out by the team, such brightness variations have very long periods in comparison to the orbital periods in the triple system. Two out of the four CVs appear to have bodies resembling planets in orbit around them.

Dr Chavez comments on the new findings, “Our work has proven that a third body can perturb a cataclysmic variable in such a way that can induce changes in brightness in the system. These perturbations can explain both the very long periods that have been observed — between 42 and 265 days- and the amplitude of those changes in brightness.” He adds, “Of the four systems we studied, our observations suggest that two of the four have objects of planetary mass in orbit around them.”

The scientists believe that this is a promising new technique for finding planets in orbit around binary star systems, adding to the thousands already found in the last three decades.

Tridymite in a lacustrine mudstone in Gale Crater, Mars: Evidence for an explosive silicic eruption during the Hesperian

by V. Payré, K.L. Siebach, M.T. Thorpe, P. Antoshechkina, E.B. Rampe in Earth and Planetary Science Letters

Planetary scientists from Rice University, NASA’s Johnson Space Center and the California Institute of Technology have an answer to a mystery that’s puzzled the Mars research community since NASA’s Curiosity rover discovered a mineral called tridymite in Gale Crater in 2016.

Tridymite is a high-temperature, low-pressure form of quartz that is extremely rare on Earth, and it wasn’t immediately clear how a concentrated chunk of it ended up in the crater. GaleCrater was chosen as Curiosity’s landing site due to the likelihood that it once held liquid water, and Curiosity found evidence that confirmed Gale Crater was a lake as recently as 1 billion years ago.

“The discovery of tridymite in a mudstone in Gale Crater is one of the most surprising observations that the Curiosity rover has made in 10 years of exploring Mars,” said Rice’s Kirsten Siebach, co-author of a study. “Tridymite is usually associated with quartz-forming, explosive, evolved volcanic systems on Earth, but we found it in the bottom of an ancient lake on Mars, where most of the volcanoes are very primitive.”

(a) Curiosity traverse with the Bradbury Landing and Maria’s Pass waypoints indicated. The red star shows the location of the Buckskin mudstone sample, and the Bradbury and Murray formation are indicated for reference. An inset of Maria’s Pass is showed on the bottom right. Credit: NASA/JPL-Caltech/Univ. of Arizona. (b-c) Images from the Mars Hand Lens Imager onboard the Curiosity rover of (b) Lamoose, a local float block adjacent to Buckskin within the Murray formation showing laminations, and (c) Buckskin.

Siebach, an assistant professor in Rice’s Department of Earth, Environmental and Planetary Sciences, is a mission specialist on NASA’s Curiosity team. To suss out the answer to the mystery, she partnered with two postdoctoral researchers in her Rice research group, Valerie Payré and Michael Thorpe, NASA’s Elizabeth Rampe and Caltech’s Paula Antoshechkina. Payré, the study’s lead author, is now at Northern Arizona University and preparing to join the faculty of the University of Iowa in the fall.

Siebach and colleagues began by reevaluating data from every reported find of tridymite on Earth. They also reviewed volcanic materials from models of Mars volcanism and reexamined sedimentary evidence from the Gale Crater lake. They then came up with a new scenario that matched all the evidence: Martian magma sat for longer than usual in a chamber below a volcano, undergoing a process of partial cooling called fractional crystallization that concentrated silicon. In a massive eruption, the volcano spewed ash containing the extra silicon in the form of tridymite into the Gale Crater lake and surrounding rivers. Water helped break down the ash through natural processes of chemical weathering, and water also helped sort the minerals produced by weathering.

(a) Stratigraphic column of sedimentary units in Gale crater, Mars. Credit: Sedimentology and Stratigraphy working group of the MSL Science Team. (b) SiO2, TiO2, and Al2O3 concentrations (in wt. %) versus elevation (in m) of sedimentary rocks analyzed by APXS. Buckskin (BK) compositions are in red, and Telegraph Peak (TP) and Oudam (OU) are in orange. Lamoose composition is also indicated for reference. (c) Proportions of mineral phases as measured by CheMin within Telegraph Peak, Buckskin, and Oudam (from the bottom to the top).

The scenario would have concentrated tridymite, producing minerals consistent with the 2016 find. It would also explain other geochemical evidence Curiosity found in the sample, including opaline silicates and reduced concentrations of aluminum oxide.

“It’s actually a straightforward evolution of other volcanic rocks we found in the crater,” Siebach said. “We argue that because we only saw this mineral once, and it was highly concentrated in a single layer, the volcano probably erupted at the same time the lake was there. Although the specific sample we analyzed was not exclusively volcanic ash, it was ash that had been weathered and sorted by water.”

If a volcanic eruption like the one in the scenario did occur when Gale Crater contained a lake, it would mean explosive volcanism occurred more than 3 billion years ago, while Mars was transitioning from a wetter and perhaps warmer world to the dry and barren planet it is today.

“There’s ample evidence of basaltic volcanic eruptions on Mars, but this is a more evolved chemistry,” she said. “This work suggests that Mars may have a more complex and intriguing volcanic history than we would have imagined before Curiosity.”

The Optical Two- and Three-dimensional Fundamental Plane Correlations for Nearly 180 Gamma-Ray Burst Afterglows with Swift/UVOT, RATIR, and the Subaru Telescope

by M. G. Dainotti, S. Young, L. Li, D. Levine, K. K. Kalinowski, D. A. Kann, B. Tran, L. Zambrano-Tapia, A. Zambrano-Tapia, et al in The Astrophysical Journal Supplement Series

An international team of 23 researchers led by Maria Dainotti, Assistant Professor at the National Astronomical Observatory of Japan (NAOJ), has analyzed archive data for powerful cosmic explosions from the deaths of stars and found a new way to measure distances in the distant Universe.

With no landmarks in space, it is very difficult to get a sense of depth. One technique astronomers use is to look for “standard candles,” objects or events where the underlying physics dictate that the absolute brightness (what you would see if you were right next to it) is always the same. By comparing this calculated absolute brightness to the apparent brightness (what is actually observed from Earth), it is possible to determine the distance to the standard candle, and by extension other objects in the same area. The lack of standard candles bright enough to be seen more than 11 billion light-years away has hindered research on the distance Universe. Gamma-Ray bursts (GRBs), bursts of radiation produced by the deaths of massive stars, are bright enough, but their brightness depends on the characteristics of the explosion.

The top left panel shows an LC with multiple bands and the upper right panel shows an LC including the Subaru data with the W07 function superimposed. The second row of panels show examples of LCs that present a peak of the prompt emission, indicated by an empty black circle and the end of the plateau emission with a filled black circle with the W07 function superimposed with a dark red curve. The third and fourth rows of panels show the same, but with the simple and smoothly BPL, respectively.

Embracing the challenge of attempting to use these bright events as standard candles, the team analyzed archive data for the visible light observations of 500 GRBs taken by world-leading telescopes such as the Subaru Telescope (owned and operated by NAOJ), RATIR, and satellites such as the Neil Gehrels Swift Observatory. Studying the light curve’s pattern of how the GRB brightens and dims over time, the team identified a class of 179 GRBs which have common features and have likely been caused by similar phenomena. From the characteristics of the light curves, the team was able to calculate a unique brightness and distance for each GRB which can be used as a cosmological tool.

These findings will provide new insights into the mechanics behind this class of GRBs, and provide a new standard candle for observing the distant Universe. Lead author Dainotti had previously found a similar pattern in X-ray observations of GRBs, but visible light observations have been revealed to be more accurate in determining cosmological parameters.

The REACH radiometer for detecting the 21-cm hydrogen signal from redshift z ≈ 7.5–28

by E. de Lera Acedo, D. I. L. de Villiers, N. Razavi-Ghods, W. Handley, et al in Nature Astronomy

A team of astronomers has developed a method that will allow them to ‘see’ through the fog of the early Universe and detect light from the first stars and galaxies.

The researchers, led by the University of Cambridge, have developed a methodology that will allow them to observe and study the first stars through the clouds of hydrogen that filled the Universe about 378,000 years after the Big Bang. Observing the birth of the first stars and galaxies has been a goal of astronomers for decades, as it will help explain how the Universe evolved from the emptiness after the Big Bang to the complex realm of celestial objects we observe today, 13.8 billion years later.

The Square Kilometre Array (SKA) — a next-generation telescope due to be completed by the end of the decade — will likely be able to make images of the earliest light in the Universe, but for current telescopes the challenge is to detect the cosmological signal of the stars through the thick hydrogen clouds. The signal that astronomers aim to detect is expected to be approximately one hundred thousand times weaker than other radio signals coming also from the sky — for example, radio signals originating in our own galaxy. Using a radio telescope itself introduces distortions to the signal received, which can completely obscure the cosmological signal of interest. This is considered an extreme observational challenge in modern radio cosmology. Such instrument-related distortions are commonly blamed as the major bottleneck in this type of observation.

Now the Cambridge-led team has developed a methodology to see through the primordial clouds and other sky noise signals, avoiding the detrimental effect of the distortions introduced by the radio telescope. Their methodology, part of the REACH (Radio Experiment for the Analysis of Cosmic Hydrogen) experiment, will allow astronomers to observe the earliest stars through their interaction with the hydrogen clouds, in the same way we would infer a landscape by looking at shadows in the fog. Their method will improve the quality and reliability of observations from radio telescopes looking at this unexplored key time in the development of the Universe. The first observations from REACH are expected later this year.

“At the time when the first stars formed, the Universe was mostly empty and composed mostly of hydrogen and helium,” said Dr Eloy de Lera Acedo from Cambridge’s Cavendish Laboratory, the paper’s lead author.
He added: “Because of gravity, the elements eventually came together and the conditions were right for nuclear fusion, which is what formed the first stars. But they were surrounded by clouds of so-called neutral hydrogen, which absorb light really well, so it’s hard to detect or observe the light behind the clouds directly.”

In 2018, another research group (running the ‘Experiment to Detect the Global Epoch of Reioniozation Signature’ — or EDGES) published a result that hinted at a possible detection of this earliest light, but astronomers have been unable to repeat the result — leading them to believe that the original result may have been due to interference from the telescope being used.

“The original result would require new physics to explain it, due to the temperature of the hydrogen gas, which should be much cooler than our current understanding of the Universe would allow. Alternatively, an unexplained higher temperature of the background radiation — typically assumed to be the well-known Cosmic Microwave Background — could be the cause” said de Lera Acedo.
He added: “If we can confirm that the signal found in that earlier experiment really was from the first stars, the implications would be huge.”

In order to study this period in the Universe’s development, often referred to as the Cosmic Dawn, astronomers study the 21-centimetre line — an electromagnetic radiation signature from hydrogen in the early Universe. They look for a radio signal that measures the contrast between the radiation from the hydrogen and the radiation behind the hydrogen fog. The methodology developed by de Lera Acedo and his colleagues uses Bayesian statistics to detect a cosmological signal in the presence of interference from the telescope and general noise from the sky, so that the signals can be separated. To do this, state-of-the-art techniques and technologies from different fields have been required. The researchers used simulations to mimic a real observation using multiple antennas, which improves the reliability of the data — earlier observations have relied on a single antenna.

“Our method jointly analyses data from multiple antennas and across a wider frequency band than equivalent current instruments. This approach will give us the necessary information for our Bayesian data analysis,” said de Lera Acedo.
He added: “In essence, we forgot about traditional design strategies and instead focused on designing a telescope suited to the way we plan to analyse the data — something like an inverse design. This could help us measure things from the Cosmic Dawn and into the epoch of reionisation, when hydrogen in the Universe was reionised.”

The telescope’s construction is currently being finalised at the Karoo radio reserve in South Africa, a location chosen for its excellent conditions for radio observations of the sky. It is far away from human-made radio frequency interference, for example television and FM radio signals.

The REACH team of over 30 researchers is multidisciplinary and distributed worldwide, with experts in fields such as theoretical and observational cosmology, antenna design, radio frequency instrumentation, numerical modelling, digital processing, big data and Bayesian statistics. REACH is co-led by the University of Stellenbosch in South Africa. Professor de Villiers, co-lead of the project at the University of Stellenbosch in South Africa said: “Although the antenna technology used for this instrument is rather simple, the harsh and remote deployment environment, and the strict tolerances required in the manufacturing, make this a very challenging project to work on.” He added: “We are extremely excited to see how well the system will perform, and have full confidence we’ll make that elusive detection.”

The Big Bang and very early times of the Universe are well understood epochs, thanks to studies of the Cosmic Microwave Background (CMB) radiation. Even better understood is the late and widespread evolution of stars and other celestial objects. But the time of formation of the first light in the Cosmos is a fundamental missing piece in the puzzle of the history of the Universe.

Compact Retarding Potential Analyzers Enabled by Glass-Ceramic Vat Polymerization for CubeSat and Laboratory Plasma Diagnostics

by Javier Izquierdo-Reyes, Zoey Bigelow, Nicholas K. Lubinsky, Luis Fernando Velásquez-García in Additive Manufacturing

MIT scientists have created the first completely digitally manufactured plasma sensors for orbiting spacecraft. These plasma sensors, also known as retarding potential analyzers (RPAs), are used by satellites to determine the chemical composition and ion energy distribution of the atmosphere.

The 3D-printed and laser-cut hardware performed as well as state-of-the-art semiconductor plasma sensors that are manufactured in a cleanroom, which makes them expensive and requires weeks of intricate fabrication. By contrast, the 3D-printed sensors can be produced for tens of dollars in a matter of days. Due to their low cost and speedy production, the sensors are ideal for CubeSats. These inexpensive, low-power, and lightweight satellites are often used for communication and environmental monitoring in Earth’s upper atmosphere. The researchers developed RPAs using a glass-ceramic material that is more durable than traditional sensor materials like silicon and thin-film coatings. By using the glass-ceramic in a fabrication process that was developed for 3D printing with plastics, there were able to create sensors with complex shapes that can withstand the wide temperature swings a spacecraft would encounter in lower Earth orbit.

“Additive manufacturing can make a big difference in the future of space hardware. Some people think that when you 3D-print something, you have to concede less performance. But we’ve shown that is not always the case. Sometimes there is nothing to trade off,” says Luis Fernando Velásquez-García, a principal scientist in MIT’s Microsystems Technology Laboratories (MTL) and senior author of a paper presenting the plasma sensors. Joining Velásquez-García on the paper are lead author and MTL postdoc Javier Izquierdo-Reyes; graduate student Zoey Bigelow; and postdoc Nicholas K. Lubinsky.

Schematics of the digitally manufactured RPAs developed in this study: exploded view (a), cross-section of assembled RPA (b), and close-up cross-section of electrode stack and electrode housing when assembled (c). Schematics of the constant-aperture (d) and aperture-optimized architectures (e). In (d) and (e) FG = floating grid, FERG = first electron-repelling grid, SERG = second electron-repelling grid, IRG = ion-retarding grid, and CE = collector electrode.

An RPA was first used in a space mission in 1959. The sensors detect the energy in ions, or charged particles, that are floating in plasma, which is a superheated mix of molecules present in the Earth’s upper atmosphere. Aboard an orbiting spacecraft like a CubeSat, the versatile instruments measure energy and conduct chemical analyses that can help scientists predict the weather or monitor climate change. The sensors contain a series of electrically charged meshes dotted with tiny holes. As plasma passes through the holes, electrons and other particles are stripped away until only ions remain. These ions create an electric current that the sensor measures and analyzes. Key to the success of an RPA is the housing structure that aligns the meshes. It must be electrically insulating while also able to withstand sudden, drastic swings in temperature.

The researchers used a printable, glass-ceramic material that displays these properties, known as Vitrolite. Pioneered in the early 20th century, Vitrolite was often used in colorful tiles that became a common sight in art deco buildings. The durable material can also withstand temperatures as high as 800 degrees Celsius without breaking down, whereas polymers used in semiconductor RPAs start to melt at 400 degrees Celsius.

“When you make this sensor in the cleanroom, you don’t have the same degree of freedom to define materials and structures and how they interact together. What made this possible is the latest developments in additive manufacturing,” Velásquez-García says.

Simulation results of the von Mises stress during maximum actuation of a spring on the collector electrode. Very similar results are obtained for the springs used in the other electrodes. The array of evenly distributed holes enables the pogo pins to route electrical signals to other electrodes that are part of the electrode stack.

The 3D printing process for ceramics typically involves ceramic powder that is hit with a laser to fuse it into shapes, but this process often leaves the material coarse and creates weak points due to the high heat from the lasers. Instead, the MIT researchers used vat polymerization, a process introduced decades ago for additive manufacturing with polymers or resins. With vat polymerization, a 3D structure is built one layer at a time by submerging it repeatedly into a vat of liquid material, in this case Vitrolite. Ultraviolet light is used to cure the material after each layer is added, and then the platform is submerged in the vat again. Each layer is only 100 microns thick (roughly the diameter of a human hair), enabling the creation of smooth, pore-free, complex ceramic shapes.

In digital manufacturing, objects described in a design file can be very intricate. This precision allowed the researchers to create laser-cut meshes with unique shapes so the holes lined up perfectly when they were set inside the RPA housing. This enables more ions to pass through, which leads to higher-resolution measurements. Because the sensors were cheap to produce and could be fabricated so quickly, the team prototyped four unique designs. While one design was especially effective at capturing and measuring a wide range of plasmas, like those a satellite would encounter in orbit, another was well-suited for sensing extremely dense and cold plasmas, which are typically only measurable using ultraprecise semiconductor devices. This high precision could enable 3D-printed sensors for applications in fusion energy research or supersonic flight. The rapid prototyping process could even spur more innovation in satellite and spacecraft design, Velásquez-García adds.

“If you want to innovate, you need to be able to fail and afford the risk. Additive manufacturing is a very different way to make space hardware. I can make space hardware and if it fails, it doesn’t matter because I can make a new version very quickly and inexpensively, and really iterate on the design. It is an ideal sandbox for researchers,” he says.

While Velásquez-García is pleased with these sensors, in the future he wants to enhance the fabrication process. Reducing the thickness of layers or pixel size in glass-ceramic vat polymerization could create complex hardware that is even more precise. Moreover, fully additively manufacturing the sensors would make them compatible with in-space manufacturing. He also wants to explore the use of artificial intelligence to optimize sensor design for specific use cases, such as greatly reducing their mass while ensuring they remain structurally sound.