ST/ Astronomers uncover a one-in-ten-billion binary star system: Kilonova progenitor system

Paradigm

Published in

Paradigm

32 min readFeb 9, 2023

Space biweekly vol.70, 26th January — 9th February

TL;DR

Astronomers using data from the SMARTS 1.5-meter Telescope at the Cerro Tololo Inter-American Observatory (CTIO), have made the first confirmed detection of a star system that will one day form a kilonova — the ultra-powerful, gold-producing explosion created by merging neutron stars. These systems are so phenomenally rare that only about 10 such systems are thought to exist in the entire Milky Way.
Astronomers have directly measured the mass of a single, isolated white dwarf — the surviving core of a burned-out, Sun-like star. Researchers found that the white dwarf is 56 percent the mass of our Sun. This agrees with earlier theoretical predictions of the white dwarf’s mass and corroborates current theories of how white dwarfs evolve as the end product of a typical star’s evolution. The unique observation yields insights into theories of the structure and composition of white dwarfs.
Researchers have completed the first real-world study of Martian dust dynamics based on Ingenuity’s historic first flights on the Red Planet, paving the way for future extraterrestrial rotorcraft missions. The work could support NASA’s Mars Sample Return Program, which will retrieve samples collected by Perseverance, or the Dragonfly mission that will set course for Titan, Saturn’s largest moon, in 2027.
When a scientist discovered surprising evidence that Saturn’s smallest, innermost moon could generate the right amount of heat to support a liquid internal ocean, colleagues began studying Mimas’ surface to understand how its interior may have evolved. Numerical simulations of the moon’s Herschel impact basin, the most striking feature on its heavily cratered surface, determined that the basin’s structure and the lack of tectonics on Mimas are compatible with a thinning ice shell and geologically young ocean.
In October 2020, a highly magnetic neutron star called SGR 1935+2154 abruptly began spinning more slowly. Astrophysicist now show the magnetar’s rotational slowdown could have been caused by a volcano-like rupture near its magnetic pole.
By analyzing meteorites, researchers have uncovered the likely far-flung origin of Earth’s volatile chemicals, some of which form the building blocks of life.
Scientists have discovered the first gamma-ray eclipses from a special type of binary star system using data from NASA’s Fermi Gamma-ray Space Telescope. These so-called spider systems each contain a pulsar — the superdense, rapidly rotating remains of a star that exploded in a supernova — that slowly erodes its companion.
Astronomers used observations from the James Webb Space Telescope (JWST) to achieve the darkest ever view of a dense interstellar cloud. These observations have revealed the composition of a virtual treasure chest of ices from the early universe, providing new insights into the chemical processes of one of the coldest, darkest places in the universe as well as the origins of the molecules that make up planetary atmospheres.
Earth’s potassium arrived by meteoritic delivery service finds new research led by Earth and planetary scientists. Their work shows that some primitive meteorites contain a different mix of potassium isotopes than those found in other, more-chemically processed meteorites. These results can help elucidate the processes that shaped our Solar System and determined the composition of its planets.
Space weather can interfere with spaceflight and the operation of satellites, but the phenomenon is very difficult to study on Earth because of the difference in gravity. Researchers effectively reproduced the type of gravity that exists on or near stars and other planets inside of a glass sphere measuring 3 centimeters in diameter, or about 1.2 inches. The achievement could help scientists overcome the limiting role of gravity in experiments that are intended to model conditions in stars and other planets.
Upcoming industry events. And more!

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

Space industry news

Latest research

A high-mass X-ray binary descended from an ultra-stripped supernova

by Noel D. Richardson, Clarissa M. Pavao, Jan J. Eldridge, Herbert Pablo, André-Nicolas Chené, Peter Wysocki, Douglas R. Gies, George Younes, Jeremy Hare in Nature

Astronomers using the SMARTS 1.5-meter Telescope at Cerro Tololo Inter-American Observatory in Chile, a Program of NSF’s NOIRLab, have uncovered the first example of a phenomenally rare type of binary star system, one that has all the right conditions to eventually trigger a kilonova — the ultra-powerful, gold-producing explosion created by colliding neutron stars. Such an arrangement is so vanishingly rare that only about 10 such systems are thought to exist in the entire Milky Way Galaxy.

This unusual system, known as CPD-29 2176, is located about 11,400 light-years from Earth. It was first identified by NASA’s Neil Gehrels Swift Observatory. Later observations with the SMARTS 1.5-meter Telescope allowed astronomers to deduce the orbital characteristics and types of stars that make up this system — a neutron star created by an ultra-stripped supernova and a closely orbiting massive star that is in the process of becoming an ultra-stripped supernova itself.

An ultra-stripped supernova is the end-of-life explosion of a massive star that has had much of its outer atmosphere stripped away by a companion star. This class of supernova lacks the explosive force of a traditional supernova, which would otherwise “kick” a nearby companion star out of the system.

A typical spectrum of CPD −29 2176 around the He II λ 4686 absorption line.

“The current neutron star would have to form without ejecting its companion from the system. An ultra-stripped supernova is the best explanation for why these companion stars are in such a tight orbit,” said Noel D. Richardson at Embry-Riddle Aeronautical University and lead author of the paper. “To one day create a kilonova, the other star would also need to explode as an ultra-stripped supernova so the two neutron stars could eventually collide and merge.”

As well as representing the discovery of an incredibly rare cosmic oddity, finding and studying kilonova progenitor systems such as this can help astronomers unravel the mystery of how kilonovae form, shedding light on the origin of the heaviest elements in the Universe.

“For quite some time, astronomers speculated about the exact conditions that could eventually lead to a kilonova,” said NOIRLab astronomer and co-author André-Nicolas Chené. “These new results demonstrate that, in at least some cases, two sibling neutron stars can merge when one of them was created without a classical supernova explosion.”

The Fourier spectrum of the radial velocities shown in Extended Data Table

Producing such an unusual system, however, is a long and unlikely process. “We know that the Milky Way contains at least 100 billion stars and likely hundreds of billions more. This remarkable binary system is essentially a one-in-ten-billion system,” said Chené. “Prior to our study, the estimate was that only one or two such systems should exist in a spiral galaxy like the Milky Way.”

Though this system has all the right stuff to eventually form a kilonova, it will be up to future astronomers to study that event. It will take at least one million years for the massive star to end its life as a titanic supernova explosion and leave behind a second neutron star. This new stellar remnant and the pre-existing neutron star will then need to gradually draw together in a cosmic ballet, slowly losing their orbital energy as gravitational radiation.

When they eventually merge, the resulting kilonova explosion will produce much more powerful gravitational waves and leave behind in its wake a large amount of heavy elements, including silver and gold.

“This system reveals that some neutron stars are formed with only a small supernova kick,” concluded Richardson. “As we understand the growing population of systems like CPD-29 2176 we will gain insight into how calm some stellar deaths may be and if these stars can die without traditional supernovae.”

First semi-empirical test of the white dwarf mass–radius relationship using a single white dwarf via astrometric microlensing

by Peter McGill, Jay Anderson, Stefano Casertano, et al in Monthly Notices of the Royal Astronomical Society

Astronomers using NASA’s Hubble Space Telescope have for the first time directly measured the mass of a single, isolated white dwarf — the surviving core of a burned-out, Sun-like star.

Researchers found that the white dwarf is 56 percent the mass of our Sun. This agrees with earlier theoretical predictions of the white dwarf’s mass and corroborates current theories of how white dwarfs evolve as the end product of a typical star’s evolution. The unique observation yields insights into theories of the structure and composition of white dwarfs.

Until now, previous white dwarf mass measurements have been gleaned from observing white dwarfs in binary star systems. By watching the motion of two co-orbiting stars, straightforward Newtonian physics can be used to measure their masses. However, these measurements can be uncertain if the white dwarf’s companion star is in a long-period orbit of hundreds or thousands of years. Orbital motion can be measured by telescopes only over a brief slice of the dwarf’s orbital motion.

MMRs for 26 white dwarfs in eclipsing binary systems from Parsons et al.

For this companion-less white dwarf, researchers had to employ a trick of nature, called gravitational microlensing. The light from a background star was slightly deflected by the gravitational warping of space by the foreground dwarf star. As the white dwarf passed in front of the background star, microlensing caused the star to appear temporarily offset from its actual position on the sky. The lead author is Peter McGill, formerly of the University of Cambridge (now based at the University of California, Santa Cruz).

McGill used Hubble to precisely measure how light from a distant star bent around the white dwarf, known as LAWD 37, causing the background star to temporarily change its apparent position in the sky. Kailash Sahu of the Space Telescope Science Institute in Baltimore, Maryland, the principal Hubble investigator on this latest observation, first used microlensing in 2017 to measure the mass of another white dwarf, Stein 2051 B. But that dwarf is in a widely separated binary system. “Our latest observation provides a new benchmark because LAWD 37 is all by itself,” Sahu said.

The collapsed remains of a star that burned out 1 billion years ago, LAWD 37 has been extensively studied because it is only 15 light-years away in the constellation Musca. “Because this white dwarf is relatively close to us, we’ve got lots of data on it — we’ve got information about its spectrum of light, but the missing piece of the puzzle has been a measurement of its mass,” said McGill.

The team zeroed in on the white dwarf thanks to ESA’s Gaia space observatory, which makes extraordinarily precise measurements of nearly 2 billion star positions. Multiple Gaia observations can be used to track a star’s motion. Based on this data, astronomers were able to predict that LAWD 37 would briefly pass in front of a background star in November 2019. Once this was known, Hubble was used to precisely measure over several years how the background star’s apparent position in the sky was temporarily deflected during the white dwarf’s passage.

“These events are rare, and the effects are tiny,” said McGill. “For instance, the size of our measured offset is like measuring the length of a car on the Moon as seen from Earth.”

Since the light from the background star was so faint, the main challenge for astronomers was extracting its image from the glare of the white dwarf, which is 400 times brighter than the background star. Only Hubble can make these kinds of high-contrast observations in visible light.

“The precision of LAWD 37’s mass measurement allows us to test the mass-radius relationship for white dwarfs,” said McGill. “This means testing the theory of degenerate matter (a gas so super-compressed under gravity it behaves more like solid matter) under the extreme conditions inside this dead star,” he added.

*HST* F814W-band image cutouts (co-added stacks by epoch) for each epoch of data during the LAWD 37 event. North is directly upwards in each epoch.

The researchers say their results open the door for future event predictions with Gaia data. In addition to Hubble, these alignments can now be detected with NASA’s James Webb Space Telescope. Because Webb works at infrared wavelengths, the blue glow of a foreground white dwarf looks dimmer in infrared light, and the background star looks brighter. Based on Gaia’s predictive powers, Sahu is observing another white dwarf, LAWD 66, with NASA’s James Webb Space Telescope. The first observation was done in 2022. More observations will be taken as the deflection peaks in 2024 and then subsides.

“Gaia has really changed the game — it’s exciting to be able to use Gaia data to predict when events will happen, and then observe them happening,” said McGill. “We want to continue measuring the gravitational microlensing effect and obtain mass measurements for many more types of stars.”

In his 1915 theory of general relativity, Einstein predicted that when a massive compact object passes in front of a background star, the light from the star would bend around the foreground object due to the warping of space by its gravitational field.

Exactly a century before this latest Hubble observation, in 1919, two British-organized expeditions to the southern hemisphere first detected this lensing effect during a solar eclipse on May 19th. It was hailed as the first experimental proof of general relativity — that gravity warps space. However, Einstein was pessimistic that the effect could ever be detected for stars outside our solar system because of the precision involved. “Our measurement is 625 times smaller than the effect measured at the 1919 solar eclipse,” said McGill.

Lifting and Transport of Martian Dust by the Ingenuity Helicopter Rotor Downwash as Observed by High‐Speed Imaging From the Perseverance Rover

by M. T. Lemmon, R. D. Lorenz, J. Rabinovitch, C. E. Newman, N. R. Williams, R. Sullivan, M. P. Golombek, J. F. Bell, J. N. Maki, A. Vicente‐Retortillo in Journal of Geophysical Research: Planets

Mars is a dusty planet. From tiny dust devils to vast storms that shroud the planet, dust is a constant challenge for research missions. That was especially true for Ingenuity, the rotorcraft that since February 2021 has been exploring Mars alongside NASA’s Perseverance rover. Now, researchers at Stevens Institute of Technology, the Space Science Institute, and the Jet Propulsion Laboratory have completed the first real-world study of Martian dust dynamics based on Ingenuity’s historic first flights on the Red Planet, paving the way for future extraterrestrial rotorcraft missions.

The work could support NASA’s Mars Sample Return Program, which will retrieve samples collected by Perseverance, or the Dragonfly mission that will set course for Titan, Saturn’s largest moon, in 2027.

“There’s a reason that helicopter pilots on Earth prefer to land on helipads,” said Jason Rabinovitch, a co-author and assistant professor at Stevens. “When a helicopter lands in the desert, its downdraft can stir up enough dust to cause a zero-visibility ‘brownout’ — and Mars is effectively one big desert.”

*Ingenuity* on Mars. This sol-47 Mastcam-Z image includes the first three landing sites.

Rabinovitch has been working on the Ingenuity program since 2014, joining the Jet Propulsion Laboratory soon after the concept was first pitched to NASA and creating the first theoretical models of helicopter dust lifting in the dusty Martian environments. At Stevens, Rabinovitch continues to work with JPL and investigates plume-surface interactions during powered descent of a spacecraft. He also models supersonic parachute inflation and geophysical phenomena, such as plumes on Enceladus.

Studying dust dynamics on another planet isn’t easy, explained Rabinovitch. “Space is a data-poor environment. It’s hard to send videos and images back to Earth, so we have to work with what we can get.”

To overcome that challenge, Rabinovitch and colleagues at JPL used advanced image-processing techniques to extract information from six helicopter flights, all low-resolution videos captured by Perseverance. By identifying tiny variations between video frames, and the light intensity of individual pixels, the researchers were able to calculate both the size and the total mass of dust clouds kicked up as Ingenuity took off, hovered, maneuvered, and landed.

The results were within striking distance of Rabinovitch’s engineering models — itself a remarkable achievement, given the limited information available to the team way back in 2014, when Rabinovitch and his colleagues were writing back-of-the-envelope calculations intended to support the original design of Ingenuity. The research shows that, as predicted, dust is a significant consideration for extra-terrestrial rotorcraft, with Ingenuity estimated to have kicked up about a thousandth of its own mass (four pounds) in dust each time it flew. That’s many times more dust than would be generated by an equivalent helicopter on Earth, though Rabinovitch cautions that it’s tricky to draw direct comparisons.

“It was exciting to see the Mastcam-Z video from Perseverance, which was taken for engineering reasons, ended up showing Ingenuity lifting so much dust from the surface that it opened a new line of research,” said Mark Lemmon, senior research scientist at the Space Science Institute Mars Science Laboratory and first author of the study.

“When you think about dust on Mars, you have to consider not just the lower gravity, but also the effects of air pressure, temperature, air density — there’s a lot we don’t yet fully understand,” Rabinovich said. Still, he added, that’s what makes studying Ingenuity’s dust clouds so exciting.

A better understanding of brownouts could help NASA extend future robotic missions by keeping solar panels operational for longer or make it easier to land delicate equipment safely on the dusty Martian surface. It could also offer new insights into the role of wind and wind-carried dust in weather patterns and erosion, both on Earth and in extreme environments around the Solar System.

Tracking the Evolution of an Ocean Within Mimas Using the Herschel Impact Basin

by C. A. Denton, A. R. Rhoden in Geophysical Research Letters

When a Southwest Research Institute scientist discovered surprising evidence that Saturn’s smallest, innermost moon could generate the right amount of heat to support a liquid internal ocean, colleagues began studying Mimas’ surface to understand how its interior may have evolved. Numerical simulations of the moon’s Herschel impact basin, the most striking feature on its heavily cratered surface, determined that the basin’s structure and the lack of tectonics on Mimas are compatible with a thinning ice shell and geologically young ocean.

“In the waning days of NASA’s Cassini mission to Saturn, the spacecraft identified a curious libration, or oscillation, in Mimas’ rotation, which often points to a geologically active body able to support an internal ocean,” said SwRI’s Dr. Alyssa Rhoden, a specialist in the geophysics of icy satellites, particularly those containing oceans, and the evolution of giant planet satellite systems. She is the second author of a new paper on the subject. “Mimas seemed like an unlikely candidate, with its icy, heavily cratered surface marked by one giant impact crater that makes the small moon look much like the Death Star from Star Wars. If Mimas has an ocean, it represents a new class of small, ‘stealth’ ocean worlds with surfaces that do not betray the ocean’s existence.”

Mimas’ heavily cratered surface (left, PIA12570) suggests a cold history, but its librations rule out a homogeneous interior.

Rhoden worked with Purdue graduate student Adeene Denton to better understand how a heavily cratered moon like Mimas could possess an internal ocean. Denton modeled the formation of the Hershel impact basin using iSALE-2D simulation software. The models showed that Mimas’ ice shell had to be at least 34 miles (55 km) thick at the time of the Herschel-forming impact. In contrast, observations of Mimas and models of its internal heating limit the present-day ice shell thickness to less than 19 miles (30 km) thick, if it currently harbors an ocean. These results imply that a present-day ocean within Mimas must have been warming and expanding since the basin formed. It is also possible that Mimas was entirely frozen both at the time of the Herschel impact and at present. However, Denton found that including an interior ocean in impact models helped produce the shape of the basin.

“We found that Herschel could not have formed in an ice shell at the present-day thickness without obliterating the ice shell at the impact site,” said Denton, who is now a post-doctoral researcher at the University of Arizona. “If Mimas has an ocean today, the ice shell has been thinning since the formation of Herschel, which could also explain the lack of fractures on Mimas. If Mimas is an emerging ocean world, that places important constraints on the formation, evolution and habitability of all of the mid-sized moons of Saturn.”
“Although our results support a present-day ocean within Mimas, it is challenging to reconcile the moon’s orbital and geologic characteristics with our current understanding of its thermal-orbital evolution,” Rhoden said. “Evaluating Mimas’ status as an ocean moon would benchmark models of its formation and evolution. This would help us better understand Saturn’s rings and mid-sized moons as well as the prevalence of potentially habitable ocean moons, particularly at Uranus. Mimas is a compelling target for continued investigation.”

Magnetar spin-down glitch clearing the way for FRB-like bursts and a pulsed radio episode

by G. Younes, M. G. Baring, A. K. Harding, T. Enoto, Z. Wadiasingh, et al in Nature Astronomy

On Oct. 5, 2020, the rapidly rotating corpse of a long-dead star about 30,000 light years from Earth changed speeds. In a cosmic instant, its spinning slowed. And a few days later, it abruptly started emitting radio waves.

Thanks to timely measurements from specialized orbiting telescopes, Rice University astrophysicist Matthew Baring and colleagues were able to test a new theory about a possible cause for the rare slowdown, or “anti-glitch,” of SGR 1935+2154, a highly magnetic type of neutron star known as a magnetar.

In a study, Baring and co-authors used X-ray data from the European Space Agency’s X-ray Multi-Mirror Mission (XMM-Newton) and NASA’s Neutron Star Interior Composition Explorer (NICER) to analyze the magnetar’s rotation. They showed the sudden slowdown could have been caused by a volcano-like rupture on the surface of the star that spewed a “wind” of massive particles into space. The research identified how such a wind could alter the star’s magnetic fields, seeding conditions that would be likely to switch on the radio emissions that were subsequently measured by China’s Five-hundred-meter Aperture Spherical Telescope (FAST).

“People have speculated that neutron stars could have the equivalent of volcanoes on their surface,” said Baring, a professor of physics and astronomy. “Our findings suggest that could be the case and that on this occasion, the rupture was most likely at or near the star’s magnetic pole.”

SGR 1935+2154 and other magnetars are a type of neutron star, the compact remains of a dead star that collapsed under intense gravity. About a dozen miles wide and as dense as the nucleus of an atom, magnetars rotate once every few seconds and feature the most intense magnetic fields in the universe.

Magnetars emit intense radiation, including X-rays and occasional radio waves and gamma rays. Astronomers can decipher much about the unusual stars from those emissions. By counting pulses of X-rays, for example, physicists can calculate a magnetar’s rotational period, or the amount of time it takes to make one complete rotation, as the Earth does in one day. The rotational periods of magnetars typically change slowly, taking tens of thousands of years to slow by a single rotation per second. Glitches are abrupt increases in rotational speed that are most often caused by sudden shifts deep within the star, Baring said.

An artist’s impression of a magnetar eruption. (Image courtesy of NASA’s Goddard Space Flight Center)

“In most glitches, the pulsation period gets shorter, meaning the star spins a bit faster than it had been,” he said. “The textbook explanation is that over time, the outer, magnetized layers of the star slow down, but the inner, non-magnetized core does not. This leads to a buildup of stress at the boundary between these two regions, and a glitch signals a sudden transfer of rotational energy from the faster spinning core to the slower spinning crust.”

Abrupt rotational slowdowns of magnetars are very rare. Astronomers have only recorded three of the “anti-glitches,” including the October 2020 event. While glitches can be routinely explained by changes inside the star, anti-glitches likely cannot. Baring’s theory is based on the assumption that they are caused by changes on the surface of the star and in the space around it. In the new paper, he and his co-authors constructed a volcano-driven wind model to explain the measured results from the October 2020 anti-glitch. Baring said the model uses only standard physics, specifically changes in angular momentum and conservation of energy, to account for the rotational slowdown.

“A strong, massive particle wind emanating from the star for a few hours could establish the conditions for the drop in rotational period,” he said. “Our calculations showed such a wind would also have the power to change the geometry of the magnetic field outside the neutron star.”

The rupture could be a volcano-like formation, because “the general properties of the X-ray pulsation likely require the wind to be launched from a localized region on the surface,” he said.

“What makes the October 2020 event unique is that there was a fast radio burst from the magnetar just a few days after the anti-glitch, as well as a switch-on of pulsed, ephemeral radio emission shortly thereafter,” he said. “We’ve seen only a handful of transient pulsed radio magnetars, and this is the first time we’ve seen a radio switch-on of a magnetar almost contemporaneous with an anti-glitch.”

Baring argued this timing coincidence suggests the anti-glitch and radio emissions were caused by the same event, and he’s hopeful that additional studies of the volcanism model will provide more answers.

“The wind interpretation provides a path to understanding why the radio emission switches on,” he said. “It provides new insight we have not had before.”

Nucleosynthetic isotope anomalies of zinc in meteorites constrain the origin of Earth’s volatiles

by Rayssa Martins, Sven Kuthning, Barry J. Coles, Katharina Kreissig, Mark Rehkämper in Science

By analysing meteorites, Imperial researchers have uncovered the likely far-flung origin of Earth’s volatile chemicals, some of which form the building blocks of life.

They found that around half the Earth’s inventory of the volatile element zinc came from asteroids originating in the outer Solar System — the part beyond the asteroid belt that includes the planets Jupiter, Saturn, and Uranus. This material is also expected to have supplied other important volatiles such as water.

Volatiles are elements or compounds that change from solid or liquid state into vapour at relatively low temperatures. They include the six most common elements found in living organisms, as well as water. As such, the addition of this material will have been important for the emergence of life on Earth.

Prior to this, researchers thought that most of Earth’s volatiles came from asteroids that formed closer to the Earth. The findings reveal important clues about how Earth came to harbour the special conditions needed to sustain life.

Mass independent Zn isotope compositions measured using internal normalization to 64Zn/67Zn.

Senior author Professor Mark Rehka?mper, of Imperial College London’s Department of Earth Science and Engineering, said: “Our data show that about half of Earth’s zinc inventory was delivered by material from the outer Solar System, beyond the orbit of Jupiter. Based on current models of early Solar System development, this was completely unexpected.”

Previous research suggested that the Earth formed almost exclusively from inner Solar System material, which researchers inferred was the predominant source of Earth’s volatile chemicals. In contrast, the new findings suggest the outer Solar System played a bigger role than previously thought.

Professor Rehka?mper added: “This contribution of outer Solar System material played a vital role in establishing the Earth’s inventory of volatile chemicals. It looks as though without the contribution of outer Solar System material, the Earth would have a much lower amount of volatiles than we know it today — making it drier and potentially unable to nourish and sustain life.”

To carry out the study, the researchers examined 18 meteorites of varying origins — eleven from the inner Solar System, known as non-carbonaceous meteorites, and seven from the outer Solar System, known as carbonaceous meteorites.

For each meteorite they measured the relative abundances of the five different forms — or isotopes — of zinc. They then compared each isotopic fingerprint with Earth samples to estimate how much each of these materials contributed to the Earth’s zinc inventory. The results suggest that while the Earth only incorporated about ten per cent of its mass from carbonaceous bodies, this material supplied about half of Earth’s zinc.

The researchers say that material with a high concentration of zinc and other volatile constituents is also likely to be relatively abundant in water, giving clues about the origin of Earth’s water.

First author on the paper Rayssa Martins, PhD candidate at the Department of Earth Science and Engineering, said: “We’ve long known that some carbonaceous material was added to the Earth, but our findings suggest that this material played a key role in establishing our budget of volatile elements, some of which are essential for life to flourish.”

Neutron star mass estimates from gamma-ray eclipses in spider millisecond pulsar binaries

by C. J. Clark, M. Kerr, E. D. Barr, B. Bhattacharyya, et al in Nature Astronomy

Scientists have discovered the first gamma-ray eclipses from a special type of binary star system using data from NASA’s Fermi Gamma-ray Space Telescope. These so-called spider systems each contain a pulsar — the superdense, rapidly rotating remains of a star that exploded in a supernova — that slowly erodes its companion.

An international team of scientists scoured over a decade of Fermi observations to find seven spiders that undergo these eclipses, which occur when the low-mass companion star passes in front of the pulsar from our point of view. The data allowed them to calculate how the systems tilt relative to our line of sight and other information.

“One of the most important goals for studying spiders is to try to measure the masses of the pulsars,” said Colin Clark, an astrophysicist at the Max Planck Institute for Gravitational Physics in Hannover, Germany, who led the work. “Pulsars are basically balls of the densest matter we can measure. The maximum mass they can reach constrains the physics within these extreme environments, which can’t be replicated on Earth.”

Gamma-ray orbital light curves of seven eclipsing spider pulsars.

Spider systems develop because one star in a binary evolves more swiftly than its partner. When the more massive star goes supernova, it leaves behind a pulsar. This stellar remnant emits beams of multiwavelength light, including gamma rays, that sweep in and out of our view, creating pulses so regular they rival the precision of atomic clocks.

Early on, a spider pulsar “feeds” off its companion by siphoning away a stream of gas. As the system evolves, the feeding stops as the pulsar begins to spin more rapidly, generating particle outflows and radiation that superheat the companion’s facing side and erode it.

Scientists divide spider systems into two types named after spider species whose females sometimes eat their smaller mates. Black widows contain companions with less than 5% of the Sun’s mass. Redback systems host bigger companions, both in size and mass, weighing between 10% and 50% of the Sun.

“Before Fermi, we only knew of a handful of pulsars that emitted gamma rays,” said Elizabeth Hays, the Fermi project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “After over a decade of observations, the mission has identified over 300 and collected a long, nearly uninterrupted dataset that allows the community to do trailblazing science.”

Researchers can calculate the masses of spider systems by measuring their orbital motions. Visible light observations can measure how quickly the companion is traveling, while radio measurements reveal the pulsar’s speed. However, these rely on motion towards and away from us. For a nearly face-on system, such changes are slight and potentially confusing. The same signals also could be produced by a smaller, slower-orbiting system that’s seen from the side. Knowing the system’s tilt relative to our line of sight is vital for measuring mass.

Search results for the two candidate redback systems in which eclipses are detected.

The tilt’s angle is normally measured using visible light, but these measurements come with some potential complications. As the companion orbits the pulsar, its superheated side comes in and out of view, creating a fluctuation in visible light that depends on the tilt. However, astronomers are still learning about the superheating process, and models with different heating patterns sometimes predict different pulsar masses.

Gamma rays, however, are only generated by the pulsar and have so much energy that they travel in a straight line, unaffected by debris, unless blocked by the companion. If gamma rays disappear from the data set of a spider system, scientists can infer that the companion eclipsed the pulsar. From there, they can calculate the system’s tilt into our sight line, the stars’ velocities, and the pulsar’s mass.

PSR B1957+20, or B1957 for short, was the first-known black widow, discovered in 1988. Earlier models for this system, built from visible light observations, determined that it was tipped about 65 degrees into our line of sight and the pulsar’s mass was 2.4 times the Sun’s. That would make B1957 the heaviest-known pulsar, straddling the theoretical mass limit between pulsar and black hole.

By looking at the Fermi data, Clark and his team found 15 missing gamma-ray photons. The timing of the gamma-ray pulses from these objects is so dependable that 15 missing photons over a decade is significant enough that the team could determine the system is eclipsing. They then calculated that the binary is inclined 84 degrees and the pulsar weighs only 1.8 times as much as the Sun.

“There’s a quest to find massive pulsars, and these spider systems are thought to be one of the best ways to find them,” said Matthew Kerr, a co-author on the new paper and research physicist at the U.S. Naval Research Laboratory in Washington. “They’ve undergone a very extreme process of mass transfer from the companion star to the pulsar. Once we really get these models fine-tuned, we’ll know for sure whether these spider systems are more massive than the rest of the pulsar population.”

An Ice Age JWST inventory of dense molecular cloud ices

by M. K. McClure, W. R. M. Rocha, K. M. Pontoppidan, et al in Nature Astronomy

An international team including Southwest Research Institute, Leiden University and NASA used observations from the James Webb Space Telescope (JWST) to achieve the darkest ever view of a dense interstellar cloud. These observations have revealed the composition of a virtual treasure chest of ices from the early universe, providing new insights into the chemical processes of one of the coldest, darkest places in the universe as well as the origins of the molecules that make up planetary atmospheres.

“The JWST allowed us to study ices that exist on dust grains within the darkest regions of interstellar molecular clouds,” said SwRI Research Scientist Dr. Danna Qasim, co-author of the study. “The clouds are so dense that these ices have been mostly protected from the harsh radiation of nearby stars, so they are quite pristine. These are the first ices to be formed and also contain biogenic elements, which are important to life.”

NASA’s JWST has a 6.5-meter-wide mirror providing remarkable spatial resolution and sensitivity, optimized for infrared light. As a result, the telescope has been able to image the densest, darkest clouds in the universe for the first time.

“These observations provide new insights into the chemical processes in one of the coldest, darkest places in the universe to better understand the molecular origins of protoplanetary disks, planetary atmospheres, and other Solar System objects,” Qasim said.

Global fit of the combined spectrum for NIR38.

Most interstellar ices contain very small amounts of elements like oxygen and sulfur. Qasim and her co-authors seek to understand the lack of sulfur in interstellar ices.

“The ices we observed only contain 1% of the sulfur we’re expecting. 99% of that sulfur is locked-up somewhere else, and we need to figure out where in order to understand how sulfur will eventually be incorporated into the planets that may host life,” Qasim explained.

In the study, Qasim and colleagues propose that the sulfur may be locked in reactive minerals like iron sulfide, which may react with ices to form the sulfur-bearing ices observed.

“Iron sulfide is a highly reactive mineral that has been detected in the accretion disks of young stars and in samples returned from comets. It’s also the most common sulfide mineral in lunar rocks,” Qasim said. “If sulfur is locked-up in these minerals, that could explain the low amount of sulfur in interstellar ices, which has implications for where sulfur is stored in our Solar System. For example, the atmosphere of Venus has sulfur-containing molecules, in which the sulfur could have partially come from interstellar-inherited minerals.”

Meteorites have inherited nucleosynthetic anomalies of potassium-40 produced in supernovae

by Nicole X. Nie, Da Wang, Zachary A. Torrano, Richard W. Carlson, Conel M. O’D. Alexander, Anat Shahar in Science

Earth’s potassium arrived by meteoritic delivery service finds new research led by Carnegie’s Nicole Nie and Da Wang. Their work shows that some primitive meteorites contain a different mix of potassium isotopes than those found in other, more-chemically processed meteorites. These results can help elucidate the processes that shaped our Solar System and determined the composition of its planets.

“The extreme conditions found in stellar interiors enable stars to manufacture elements using nuclear fusion,” explained Nie, a former Carnegie postdoc now at Caltech. “Each stellar generation seeds the raw material from which subsequent generations are born and we can trace the history of this material across time.”

Some of the material produced in the interiors of stars can be ejected out into space, where it accumulates as a cloud of gas and dust. More than 4.5 billion years ago, one such cloud collapsed in on itself to form our Sun. The remnants of this process formed a rotating disk around the newborn star. Eventually, the planets and other Solar System objects coalesced from these leftovers, including the parent bodies that later broke apart to become asteroids and meteorites.

A meteorite thin section under a microscope. Different colors represent different minerals, because light travels through them in different ways. The round mineral aggregates are chondrules, which are a major component in primitive meteorites. ***Credit:*** *Nicole Xike Nie.*

“By studying variations in the isotopic record preserved within meteorites, we can trace the source materials from which they formed and build a geochemical timeline of our Solar System’s evolution,” added Wang, who is now at Chengdu University of Technology.

Each element contains a unique number of protons, but its isotopes have varying numbers of neutrons. The distribution of different isotopes of the same element throughout the Solar System is a reflection of the makeup of the cloud of material from which the Sun was born. Many stars contributed to this so-called solar molecular cloud, but their contributions were not uniform, which can be determined by studying the isotopic content of meteorites. Wang and Nie — along with Carnegie colleagues Anat Shahar, Zachary Torrano, Richard Carlson, and Conel Alexander — measured the ratios of three potassium isotopes in samples from 32 different meteorites.

Potassium is particularly interesting because it’s what’s called a moderately volatile element, which are named for having relatively low boiling points that cause them to evaporate fairly easily. As a result, it’s challenging to look for patterns that predate the Sun in the isotopic ratios of volatiles — they just don’t stick around in the hot star-forming conditions long enough to maintain an easily readable record.

“However, using very sensitive and suitable instruments, we found patterns in the distribution of our potassium isotopes that were inherited from pre-solar materials and differed between types of meteorites,” Nie said.

They found that some of the most primitive meteorites called carbonaceous chondrites, which formed in the outer Solar System, contained more potassium isotopes that were produced by huge stellar explosions, called supernovae. Whereas other meteorites — those that most frequently crash to Earth, called non-carbonaceous chondrites — contain the same potassium isotope ratios seen on our home planet and elsewhere in the inner Solar System.

“This tells us that, like a poorly mixed cake batter, there wasn’t an even distribution of materials between the outer reaches of the Solar System where the carbonaceous chondrites formed, and the inner Solar System, where we live,” concluded Shahar.

For years, Carnegie Earth and planetary scientists have worked to reveal the origins of Earth’s volatile elements. Some of these elements may have been transported here all the way from the outer Solar System on the backs of carbonaceous chondrites. However, since the pattern of pre-solar potassium isotopes found in non-carbonaceous chondrites matched that seen on Earth, these meteorites are the probable source of our planet’s potassium.

“It is only recently that scientists challenged a once long-held belief that the conditions in the solar nebula that birthed our Sun were hot enough to burn off all volatile elements,” Shahar added. “This research provides fresh evidence that volatiles could survive the Sun’s formation.”

Thermal Convection in a Central Force Field Mediated by Sound

by John P. Koulakis, Yotam Ofek, Seth Pree, Seth Putterman in Physical Review Letters

Solar flares and other types of space weather can wreak havoc with spaceflight and with telecommunications and other types of satellites orbiting the Earth. But, to date, scientists’ ability to research ways to overcome that challenge has been severely limited. That’s because experiments they conduct in laboratories here on Earth are affected by gravity in ways that are so different from conditions in space.

But a new study by UCLA physicists could, at last, help conquer that issue — which could be a big step toward safeguarding humans (and equipment) during space expeditions, and to ensuring the proper functioning of satellites.

The UCLA researchers effectively reproduced the type of gravity that exists on or near stars and other planets inside of a glass sphere measuring 3 centimeters in diameter (about 1.2 inches). To do so, they used sound waves to create a spherical gravitational field and generate plasma convection — a process in which gas cools as it nears the surface of a body and then reheats and rises again as it nears the core — creating a fluid current that in turn generates a magnetic current. The achievement could help scientists overcome the limiting role of gravity in experiments that are intended to model convection that occurs in stars and other planets.

(a) Convection cells driven by the radial “acoustic gravity” of a spherical standing sound wave in a rotating sulfur plasma bulb. Direction of flow indicated by the streamlines has been extracted from high speed video available in the Supplemental Material. Cells are axisymmetric about the rotation axis (vertical line centered in figure). The hexagonal pattern visible in the image is the shadow of the metal mesh which forms the microwave cavity. (b) The acoustic velocity and effective gravity as a function of radius. Note that the acoustic gravity changes sign at the velocity antinode, which occurs at nearly half the bulb radius (dashed white circle).

“People were so interested in trying to model spherical convection with laboratory experiments that they actually put an experiment in the space shuttle because they couldn’t get a strong enough central force field on the ground,” said Seth Putterman, a UCLA physics professor and the study’s senior author. “What we showed is that our system of microwave-generated sound produced gravity so strong that Earth’s gravity wasn’t a factor. We don’t need to go into space to do these experiments anymore.”

UCLA researchers used microwaves to heat sulfur gas to 5,000 degrees Fahrenheit inside the glass sphere. The sound waves inside the ball acted like gravity, constraining movement of the hot, weakly ionized gas, known as plasma, into patterns that resemble the currents of plasma in stars.

“Sound fields act like gravity, at least when it comes to driving convection in gas,” said John Koulakis, a UCLA project scientist and the study’s first author. “With the use of microwave-generated sound in a spherical flask of hot plasma, we achieved a gravity field that is 1,000 times stronger than Earth’s gravity.”

Side view of instability evolution. Panels (a)–(d) and (i)–(l) are frames of high speed video while panels (e)–(h) and (m)–(p) are false color images of the difference in brightness from panel (a). Red (blue) coloring indicates the pixel value is lower (higher) than it was in panel (a).

On Earth’s surface, hot gas rises because gravity holds denser, colder gas closer to the planet’s center. Indeed, the researchers found that hot, bright gas near the outer half of the sphere also moved outward toward the walls of the sphere. The strong, sustained gravity generated turbulence that resembled that seen near the Sun’s surface. In the inner half of the sphere, the acoustic gravity changed direction and pointed outward, which causes hot gas to sink to the center. In the experiment, acoustic gravity naturally held the hottest plasma at the center of the sphere, where it also occurs in stars.

The ability to control and manipulate plasma in ways that mirror solar and planetary convection will help researchers understand and predict how solar weather affects spacecraft and satellite communications systems. Last year, for example, a solar storm knocked out 40 SpaceX satellites. The phenomenon has also been problematic for military technology: the formation of turbulent plasma around hypersonic missiles, for example, can interfere with weapons systems communications.