ST/ Planets of binary stars as possible homes for alien life

Paradigm

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Paradigm

32 min readMay 25, 2022

Space biweekly vol.52, 11th May — 25th May

TL;DR

Nearly half of Sun-size stars are binary. According to new research, planetary systems around binary stars may be very different from those around single stars. This points to new targets in the search for extraterrestrial life forms.
Researchers have learned how a type of aurora on Mars is formed. The physicists report discrete aurora form through the interaction of the solar wind and the crust at Mars’ southern hemisphere.
Seasonal imbalance between the solar energy absorbed and released by the planet Mars could be a cause of the Red Planet’s dust storms, according to new research. Understanding how the system works on Mars could help scientists predict how climate change could affect Earth.
A unique new instrument, coupled with a powerful telescope and a little help from nature, has given researchers the ability to peer into galactic nurseries at the heart of the young universe.
Scientists have used computer modeling to show how a hypothesized type of supernova would evolve on the scale of thousands of years, giving researchers a way to look for examples of supernovae of this model, known as ‘D6.’
A research team has investigated a meteorite from Mars using neutron and X-ray tomography. The technology, which will probably be used when NASA examines samples from the Red Planet in 2030, showed that the meteorite had limited exposure to water, thus making life at that specific time and place unlikely.
When stars like our Sun use up all their fuel, they shrink to form white dwarfs. Sometimes such dead stars flare back to life in a super hot explosion and produce a fireball of X-ray radiation. A research team has now been able to observe such an explosion of X-ray light for the very first time.
In our sun’s neighborhood of the Milky Way Galaxy is a relatively bright star, and in it, astronomers have been able to identify the widest range of elements in a star beyond our solar system yet.
Novel simulation brings extraordinary fast radio bursts into the laboratory in a way once thought impossible.
Researchers assessed the potential impact of a rocket launch on atmospheric pollution by investigating the heat and mass transfer and rapid mixing of the combustion byproducts. The team modeled the exhaust gases and developing plume at several altitudes along a typical trajectory of a standard present-day rocket. They did this as a prototypical example of a two-stage rocket to transport people and payloads into Earth’s orbit and beyond and found the impact on the atmosphere locally and momentarily in the mesosphere can be significant.
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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

Binarity of a protostar affects the evolution of the disk and planets

by Jørgensen, J.K., Kuruwita, R.L., Harsono, D. et al. in Nature

Nearly half of Sun-size stars are binary. According to University of Copenhagen research, planetary systems around binary stars may be very different from those around single stars. This points to new targets in the search for extraterrestrial life forms.

Since the only known planet with life, the Earth, orbits the Sun, planetary systems around stars of similar size are obvious targets for astronomers trying to locate extraterrestrial life. Nearly every second star in that category is a binary star. A new result from research at University of Copenhagen indicate that planetary systems are formed in a very different way around binary stars than around single stars such as the Sun.

Thermal dust continuum emission towards NGC 1333-IRAS2A.

“The result is exciting since the search for extraterrestrial life will be equipped with several new, extremely powerful instruments within the coming years. This enhances the significance of understanding how planets are formed around different types of stars. Such results may pinpoint places which would be especially interesting to probe for the existence of life,” says Professor Jes Kristian Jørgensen, Niels Bohr Institute, University of Copenhagen, heading the project.

The new discovery has been made based on observations made by the ALMA telescopes in Chile of a young binary star about 1,000 lightyears from Earth. The binary star system, NGC 1333-IRAS2A, is surrounded by a disc consisting of gas and dust. The observations can only provide researchers with a snapshot from a point in the evolution of the binary star system. However, the team has complemented the observations with computer simulations reaching both backwards and forwards in time.

“The observations allow us to zoom in on the stars and study how dust and gas move towards the disc. The simulations will tell us which physics are at play, and how the stars have evolved up till the snapshot we observe, and their future evolution,” explains Postdoc Rajika L. Kuruwita, Niels Bohr Institute, second author of the Nature article.

Notably, the movement of gas and dust does not follow a continuous pattern. At some points in time — typically for relatively shorts periods of ten to one hundred years every thousand years — the movement becomes very strong. The binary star becomes ten to one hundred times brighter, until it returns to its regular state.

Presumably, the cyclic pattern can be explained by the duality of the binary star. The two stars encircle each other, and at given intervals their joint gravity will affect the surrounding gas and dust disc in a way which causes huge amounts of material to fall towards the star.

“The falling material will trigger a significant heating. The heat will make the star much brighter than usual,” says Rajika L. Kuruwita, adding:
“These bursts will tear the gas and dust disc apart. While the disc will build up again, the bursts may still influence the structure of the later planetary system.”

Channel maps of the silicon monoxide emission at low velocities.

The observed stellar system is still too young for planets to have formed. The team hopes to obtain more observational time at ALMA, allowing to investigate the formation of planetary systems. Not only planets but also comets will be in focus:

“Comets are likely to play a key role in creating possibilities for life to evolve. Comets often have a high content of ice with presence of organic molecules. It can well be imagined that the organic molecules are preserved in comets during epochs where a planet is barren, and that later comet impacts will introduce the molecules to the planet’s surface,” says Jes Kristian Jørgensen.

Understanding the role of the bursts is important in this context:

“The heating caused by the bursts will trigger evaporation of dust grains and the ice surrounding them. This may alter the chemical composition of the material from which planets are formed.”

Thus, chemistry is a part of the research scope:

“The wavelengths covered by ALMA allow us to see quite complex organic molecules, so molecules with 9–12 atoms and containing carbon. Such molecules can be building blocks for more complex molecules which are key to life as we know it. For example, amino acids which have been fund in comets.”

ALMA (Atacama Large Millimeter/submillimeter Array) is not a single instrument but 66 telescopes operating in coordination. This allows for a much better resolution than could have been obtained by a single telescope.

Very soon the new James Webb Space Telescope (JWST) will join the search for extraterrestrial life. Near the end of the decade, JWST will be complemented by the ELT (European Large Telescope) and the extremely powerful SKA (Square Kilometer Array) both planned to begin observing in 2027. The ELT will with its 39-meter mirror be the biggest optical telescope in the world and will be poised to observe the atmospheric conditions of exoplanets (planets outside the Solar System, ed.). SKA will consist of thousands of telescopes in South Africa and in Australia working in coordination and will have longer wavelengths than ALMA.

“The SKA will allow for observing large organic molecules directly. The James Webb Space Telescope operates in the infrared which is especially well suited for observing molecules in ice. Finally, we continue to have ALMA which is especially well suited for observing molecules in gas form. Combining the different sources will provide a wealth of exciting results,” Jes Kristian Jørgensen concludes.

Channel maps for sulfur dioxide emission.

The team has had observation time on the ALMA telescopes in Chile to observe the binary star system NGC 1333-IRAS2A in the Perseus molecular cloud. The distance from Earth to the binary star is about 1,000 lightyears which is a quite short distance in an astronomical context. Formed some 10,000 years ago, it is a very young star.

The two stars of the binary system are 200 astronomical units (AUs) apart. An AU equals the distance from Earth to the Sun. In comparison, the furthest planet of the Solar System, Neptune, is 30 AUs from the Sun.

Discrete Aurora at Mars: Dependence on Upstream Solar Wind Conditions

by Z. Girazian, N. M. Schneider, Z. Milby, X. Fang, J. Halekas, T. Weber, S. K. Jain, J.‐C. Gérard, L. Soret, J. Deighan, C. O. Lee in Journal of Geophysical Research: Space Physics

Physicists led by the University of Iowa have learned how a type of aurora on Mars is formed.

In a new study, the physicists studied discrete aurora, a light-in-the-sky display that occurs mostly during the night in the red planet’s southern hemisphere. While scientists have known about discrete aurora on Mars-which also occur on Earth — they did not know how they formed. That’s because Mars does not have a global magnetic field like Earth, which is a main trigger for aurora, also called the northern and southern lights on our planet.

Observational coverage of the IUVS observations used in this study.

Instead, the physicists report, discrete aurora on Mars are governed by the interaction between the solar wind — the constant jet of charged particles from the sun — and magnetic fields generated by the crust at southern latitudes on Mars. It’s the nature of this localized interaction between the solar wind and the crustal magnetic fields that lead to discrete aurora, the scientists find.

“We have the first detailed study looking at how solar wind conditions affect aurora on Mars,” says Zachary Girazian, associate research scientist in the Department of Physics and Astronomy and the study’s corresponding author. “Our main finding is that inside the strong crustal field region, the aurora occurrence rate depends mostly on the orientation of the solar wind magnetic field, while outside the strong crustal field region, the occurrence rate depends mostly on the solar wind dynamic pressure.”

Discrete aurora detection frequencies as a function of solar wind dynamic pressure.

The findings come from more than 200 observations of discrete aurora on Mars by the NASA-led Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. One of the instruments used to make the observations, the Solar Wind Ion Analyzer, is led by Jasper Halekas, associate professor in the Department of Physics and Astronomy and a co-author on the study.

“Now is a very fruitful and exciting time for researching aurora at Mars. The database of discrete aurora observations we have from MAVEN is the first of its kind, allowing us to understand basic features of the aurora for the first time,” Girazian says.

Mars’ emitted energy and seasonal energy imbalance

by Ellen Creecy, Liming Li, Xun Jiang, Michael Smith, David Kass, Armin Kleinböhl, Germán Martínez in Proceedings of the National Academy of Sciences

A seasonal imbalance in the amount of solar energy absorbed and released by the planet Mars is a likely cause of the dust storms that have long intrigued observers, a team of researchers reports.

Mars’ extreme imbalance in energy budget (a term referring to the measurement of solar energy a planet takes in from the sun then releases as heat) was documented by University of Houston researchers Liming Li, associate professor of physics; Xun Jiang, professor of atmospheric science; and Ellen Creecy, doctoral student and lead author of an article.

“One of our most interesting findings is that the energy excess — more energy being absorbed than emitted — could be one of the generating mechanisms of Mars’ dust storms. Understanding how this works on Mars might provide clues about the roles Earth’s energy budget takes in the development of severe storms, including hurricanes, on our own planet,” Creecy said.

UH researchers found a link between Mars’ dust storms and its seasonal energy imbalance. Further studies could grant insight into how ancient climate change affected the Red Planet, perhaps even how Earth’s future may be shaped by climate change. At left, Mars in clear conditions; at right, Mars enveloped by a seasonal dust storm. Photo credit: NASA / JPL / MSSS

A thin atmosphere and very elliptical orbit make Mars especially susceptible to wide temperature differences. It absorbs extreme amounts of solar heat when it swings closest to the sun in its perihelion seasons (spring and summer for Mars’ southern hemisphere), which is the same extreme part of the orbit when its dust storms appear. As its orbit takes Mars further away from the sun, less solar energy is absorbed by the planet. This same phenomenon happens on Earth, too, but the researchers found it to be especially extreme on Mars.

On Earth, energy imbalances can be measured according to season and year, and they play a critical role in our global warming and climate change. In a separate project, Creecy and her colleagues are examining if energy imbalance on Mars also exists on longer time scales, and if it does what the implications would be on the planet’s climate change.

“Mars is not a planet that has any kind of real energy storage mechanisms, like we have on Earth. Our large oceans, for example, help to equilibrate the climate system,” Creecy said.

Yet, Mars bears signs that oceans, lakes and rivers were once abundant. So what happened? The facts are unsettled as to why or when the planet dried into a hot, dusty globe with an abundance of iron oxide — rust, actually, whose tawny color inspired observers from centuries ago to call it the Red Planet.

“Mars had oceans and lakes in the past, but it later experienced global warming and climate change. Somehow, Mars lost its oceans and lakes. We know that climate change is happening on Earth now. So what do the lessons of Mars’ experience hold for the future of Earth?,” Li asked.

Creecy and her colleagues reached their conclusions by comparing four years of data (those are Martian years, roughly equivalent to eight Earth years) of Mars’ orbits and temperatures to conditions as documented by NASA missions. For planetary enthusiasts, they note that much of the data can be accessed free from NASA’s Planetary Data Systems website, although some information is available only to researchers. They also collaborated with NASA scientists, including several who have been key members of past missions, including the Mars Global Surveyor and two rovers, Curiosity and Insight, which are still operating on site.

“If we open our eyes to a wide field, Earth is just one planet. With just one point, we never can see a complete picture. We have to look at all points, all planets, to get a complete picture of the evolution of our own Earth. There are many things we can learn from the other planets,” Li said. “By studying the history of Mars we gain a lot. What is climate change? What’s the future phase for our planet? What’s the evolution of Earth? So many things we can learn from other planets.”

Resolving the H i in damped Lyman α systems that power star formation

by Bordoloi, R., O’Meara, J.M., Sharon, K. et al. in Nature

A unique new instrument, coupled with a powerful telescope and a little help from nature, has given researchers the ability to peer into galactic nurseries at the heart of the young universe.

After the big bang some 13.8 billion years ago, the early universe was filled with enormous clouds of neutral diffuse gas, known as Damped Lyman-α systems, or DLAs. These DLAs served as galactic nurseries, as the gasses within slowly condensed to fuel the formation of stars and galaxies. They can still be observed today, but it isn’t easy.

“DLAs are a key to understanding how galaxies form in the universe, but they are typically difficult to observe since the clouds are too diffuse and don’t emit any light themselves,” says Rongmon Bordoloi, assistant professor of physics at North Carolina State University and corresponding author of the research.

Source plane reconstruction of SGAS J152745.1+065219.

Currently, astrophysicists use quasars — supermassive black holes that emit light — as “backlight” to detect the DLA clouds. And while this method does allow researchers to pinpoint DLA locations, the light from the quasars only acts as small skewers through a massive cloud, hampering efforts to measure their total size and mass. But Bordoloi and John O’Meara, chief scientist at the W.M. Keck Observatory in Kamuela, Hawaii, found a way around the problem by using a gravitationally lensed galaxy and integral field spectroscopy to observe two DLAs — and the host galaxies within — that formed around 11 billion years ago, not long after the big bang.

“Gravitationally lensed galaxies refers to galaxies that appear stretched and brightened,” Bordoloi says. “This is because there is a gravitationally massive structure in front of the galaxy that bends the light coming from it as it travels toward us. So we end up looking at an extended version of the object — it’s like using a cosmic telescope that increases magnification and gives us better visualization.
“The advantage to this is twofold: One, the background object is extended across the sky and bright, so it is easy to take spectrum readings on different parts of the object. Two, because lensing extends the object, you can probe very small scales. For example, if the object is one light year across, we can study small bits in very high fidelity.”

Variation in metal absorption line strengths of the two DLA systems.

Spectrum readings allow astrophysicists to “see” elements in deep space that are not visible to the naked eye, such as diffuse gaseous DLAs and the potential galaxies within them. Normally, gathering the readings is a long and painstaking process. But the team solved that issue by performing integral field spectroscopy with the Keck Cosmic Web Imager.

Integral field spectroscopy allowed the researchers to obtain a spectrum at every single pixel on the part of the sky it targeted, making spectroscopy of an extended object on the sky very efficient. This innovation combined with the stretched and brightened gravitationally lensed galaxy allowed the team to map out the diffuse DLA gas in the sky at high fidelity. Through this method the researchers were able to determine not only the size of the two DLAs, but also that they both contained host galaxies.

“I’ve waited most of my career for this combination: a telescope and instrument powerful enough, and nature giving us a bit of lucky alignments to study not one but two DLAs in a rich new way,” O’Meara says. “It’s great to see the science come to fruition.”

The DLAs are huge, by the way. With diameters greater than 17.4 kiloparsecs, they’re more than two thirds the size of the Milky Way galaxy today. For comparison, 13 billion years ago, a typical galaxy would have a diameter of less than 5 kiloparsecs. A parsec is 3.26 light years, and a kiloparsec is 1,000 parsecs, so it would take light about 56,723 years to travel across each DLA.

“But to me, the most amazing thing about the DLAs we observed is that they aren’t unique — they seem to have similarities in structure, host galaxies were detected in both, and their masses indicate that they contain enough fuel for the next generation of star formation,” Bordoloi says. “With this new technology at our disposal, we are going to be able to dig deeper into how stars formed in the early universe.”

The Double Detonation of a Double-degenerate System, from Type Ia Supernova Explosion to its Supernova Remnant

by Gilles Ferrand, Ataru Tanikawa, Donald C. Warren, Shigehiro Nagataki, Samar Safi-Harb, Anne Decourchelle in The Astrophysical Journal

Scientists from the RIKEN Cluster for Pioneering Research have used computer modeling to show how a hypothesized type of supernova would evolve on the scale of thousands of years, giving researchers a way to look for examples of supernovae of this model, known as “D6.”

Supernovae are important for cosmology, as one type, Ia, is used as a “standard candle” that allows distance to be measured, and in fact they were used for the measurements that showed, surprisingly to initial observers, that the expansion of the universe is accelerating. It is generally accepted that type Ia supernovae arise from the explosion of degenerate stars known as white dwarfs — stars that have burned through their hydrogen and shrunk into compact objects — but the mechanism that causes the explosions is not well understood.

Slice of the ejecta of the D6 explosion, annotated with its specific features. This figure was made from the output data at 50 s of the SN simulation published in Tanikawa et al. (2018).

Recently, the discovery of white dwarfs that are moving extremely rapidly has given added credibility to one proposed mechanism for the origin of these supernovae, D6. In this scenario, one of two white dwarfs in a binary system undergoes what is known as a “double detonation,” where a surface layer of helium first explodes, then igniting a larger explosion in the carbon-oxygen core of the star. This leads to the obliteration of the star, and the companion, suddenly freed from the gravitational attraction of the exploding star, is flung out at enormous velocity.

However, very little is known about what shape the remnant of such an event would look like long after the initial explosion. To explore this, the team decided to simulate the long-term evolution, in the form of a supernova remnant, for thousands of years after the explosion. In fact, they were able to observe some features in the progenitor system that would be specific to this scenario, thus offering a way to probe supernova physics, including a “shadow” or dark patch surrounded by a bright ring. They also concluded that the remnants of type Ia explosions are not necessarily symmetric, as is commonly believed.

3D view of the D6 SNR at 500 yr. The solid contours are isocontours of the mass density. Green colors in the inner layers correspond to shocked ejecta, while purple colors in the outer layers correspond to shocked ambient matter. In both panels the contours are clipped to one half of the SNR to see its interior. In the bottom panel, a volume rendering of the mass density of the shocked ejecta is included, over the entire surface of the SNR.

According to Gilles Ferrand, the first author of the study, “The D6 supernova explosion has a specific shape. We were not confident that it would be visible in the remnant long after the initial event, but actually we found that there is a specific signature that we can still see thousands of years after the explosion.”

Shigehiro Nagataki, the leader of the Astrophysical Big Bang Laboratory at RIKEN, says, “This is a very important finding, because it could have an impact on the use of Ia supernovae as cosmic yardsticks. They were once believed to originate from a single phenomenon, but if they are diverse, then it might require a reevaluation of how we use them.”

Ferrand continues, “Moving forward, we plan to learn how to more precisely compute the X-ray emission, taking into account the composition and state of the shocked plasma, in order to make direct comparisons with observations. We hope that our paper will give new ideas to observers, of what to look for in supernova remnants.”

The scale of a martian hydrothermal system explored using combined neutron and x-ray tomography

by Josefin Martell, Carl Alwmark, Luke Daly, Stephen Hall, Sanna Alwmark, Robin Woracek, Johan Hektor, Lukas Helfen, Alessandro Tengattini, Martin Lee in Science Advances

A research team led by Lund University in Sweden has investigated a meteorite from Mars using neutron and X-ray tomography. The technology, which will probably be used when NASA examines samples from the Red Planet in 2030, showed that the meteorite had limited exposure to water, thus making life at that specific time and place unlikely.

In a cloud of smoke, NASA’s spacecraft Perseverance parachuted onto the dusty surface of Mars in February 2021. For several years, the vehicle will skid around and take samples to try to answer the question posed by David Bowie in Life on Mars in 1971. It isn’t until around 2030 that Nasa actually intends to send the samples back to Earth, but material from Mars is already being studied — in the form of meteorites. In a new study, an international research team has studied an approximately 1.3 billion-year-old meteorite using advanced scanning.

“Since water is central to the question of whether life ever existed on Mars, we wanted to investigate how much of the meteorite reacted with water when it was still part of the Mars bedrock,” explains Josefin Martell, geology doctoral student at Lund University.

To answer the question of whether there was any major hydrothermal system, which is generally a favorable environment for life to occur, the researchers used neutron and X-ray tomography. X-ray tomography is a common method of examining an object without damaging it. Neutron tomography was used because neutrons are very sensitive to hydrogen.

This means that if a mineral contains hydrogen, it is possible to study it in three dimensions and see where in the meteorite the hydrogen is located. Hydrogen (H) is always of interest when scientists study material from Mars, because water (H2O) is a prerequisite for life as we know it. The results show that a fairly small part of the sample seems to have reacted with water, and that it therefore probably wasn’t a large hydrothermal system that gave rise to the alteration.

Part of the polished section, chosen for EBSD analysis.

“A more probable explanation is that the reaction took place after small accumulations of underground ice melted during a meteorite impact about 630 million years ago. Of course, that doesn’t mean that life couldn’t have existed in other places on Mars, or that there couldn’t have been life at other times,” says Josefin Martell.

The researchers hope that the results of their study will be helpful when NASA brings back the first samples from Mars around 2030, and there are many reasons to believe that the current technology with neutron and X-ray tomography will be useful when this happens.

“It would be fun if we had the opportunity to study these samples at the research facility European Spallation Source, ESS in Lund, which by then will be the world’s most powerful neutron source,” concludes Josefin Martell.

X-ray detection of a nova in the fireball phase

by Ole König, Jörn Wilms, Riccardo Arcodia, Thomas Dauser, et al in Nature

When stars like our Sun use up all their fuel, they shrink to form white dwarfs. Sometimes such dead stars flare back to life in a super hot explosion and produce a fireball of X-ray radiation. A research team led by FAU has now been able to observe such an explosion of X-ray light for the very first time.

“It was to some extent a fortunate coincidence, really,” explains Ole König from the Astronomical Institute at FAU in the Dr. Karl Remeis observatory in Bamberg, who has published an article about this observation, together with Prof. Dr. Jörn Wilms and a research team from the Max Planck Institute for Extraterrestrial Physics, the University of Tübingen, the Universitat Politécnica de Catalunya in Barcelona und the Leibniz Institute for Astrophysics Potsdam. “These X-ray flashes last only a few hours and are almost impossible to predict, but the observational instrument must be pointed directly at the explosion at exactly the right time,” explains the astrophysicist.

Comparison of the observed eROSITA slew lightcurve of the X-ray flash and the (averaged) simulation of a constant source with the best-fit black-body parameters.

The instrument in this case is the eROSITA X-ray telescope, which is currently located one and a half million kilometers from Earth and has been surveying the sky for soft X-rays since 2019. On July 7, 2020 it measured strong X-ray radiation in an area of the sky that had been completely inconspicuous four hours previously. When the X-ray telescope surveyed the same position in the sky four hours later, the radiation had disappeared. It follows that the X-ray flash that had previously completely overexposed the center of the detector must have lasted less than eight hours.

X-ray explosions such as this were predicted by theoretical research more than 30 years ago, but have never been observed directly until now. These fireballs of X-rays occur on the surface of stars that were originally comparable in size to the Sun before using up most of their fuel made of hydrogen and later helium deep inside their cores. These stellar corpses shrink until “white dwarfs” remain, which are similar to Earth in size but contain a mass that can be similar to that of our Sun. “One way to picture these proportions is to think of the Sun being the same size as an apple, which means Earth would be the same size as a pin head orbiting around the apple at a distance of 10 meters,” explains Jörn Wilms.

On the other hand, if you were to shrink an apple to the size of a pin head, this tiny particle would retain the comparatively large weight of the apple. “A teaspoon of matter from the inside of a white dwarf easily has the same mass as a large truck,” Jörn Wilms continues. Since these burnt out stars are mainly made up of oxygen and carbon, we can compare them to gigantic diamonds that are the same size as Earth floating around in space. These objects in the form of precious gems are so hot they glow white. However, the radiation is so weak that it is difficult to detect from Earth.

Unless the white dwarf is accompanied by a star that is still burning, that is, and when the enormous gravitational pull of the white dwarf draws hydrogen from the shell of the accompanying star. “In time, this hydrogen can collect to form a layer only a few meters thick on the surface of the white dwarf,” explains FAU astrophysicist Jörn Wilms. In this layer, the huge gravitational pull generates enormous pressure that is so great that it causes the star to reignite. In a chain reaction, it soon comes to a huge explosion during which the layer of hydrogen is blown off. The X-ray radiation of an explosion like this is what hit the detectors of eROSITA on July 7, 2020 producing an overexposed image.

“Using the model calculations we originally drew up while supporting the development of the X-ray instrument, we were able to analyze the overexposed image in more detail during a complex process to gain a behind the scenes view of an explosion of a white dwarf, or nova,” explains Jörn Wilms. According to the results, the white dwarf has around the mass of our Sun and is therefore relatively large. The explosion generated a fireball with a temperature of around 327,000 degrees, making it around sixty times hotter than the Sun.

Since these novae run out of fuel quite quickly, they cool rapidly and the X-ray radiation becomes weaker until it eventually becomes visible light, which reached Earth half a day after the eROSITA detection and was observed by optical telescopes. “A seemingly bright star then appeared, which was actually the visible light from the explosion, and so bright that it could be seen on the night sky by the bare eye,” explains Ole König. Seemingly “new stars” such as this one have been observed in the past and were named “nova stella,” or “new star” on account of their unexpected appearance. Since these novae are only visible after the X-ray flash, it is very difficult to predict such outbreaks and it is mainly down to chance when they hit the X-ray detectors. “We were really lucky,” says Ole König.

The R-Process Alliance: A Nearly Complete R-Process Abundance Template Derived from Ultraviolet Spectroscopy of the R-Process-Enhanced Metal-Poor Star HD 222925

by Ian U. Roederer, James E. Lawler, Elizabeth A. Den Hartog, Vinicius M. Placco, et al. in Astrophysical Journal Supplement Series

In our sun’s neighborhood of the Milky Way Galaxy is a relatively bright star, and in it, astronomers have been able to identify the widest range of elements in a star beyond our solar system yet.

The study, led by University of Michigan astronomer Ian Roederer, has identified 65 elements in the star, HD 222925. Forty-two of the elements identified are heavy elements that are listed along the bottom of the periodic table of elements. Identifying these elements in a single star will help astronomers understand what’s called the “rapid neutron capture process,” or one of the major ways by which heavy elements in the universe were created.

“To the best of my knowledge, that’s a record for any object beyond our solar system. And what makes this star so unique is that it has a very high relative proportion of the elements listed along the bottom two-thirds of the periodic table. We even detected gold,” Roederer said. “These elements were made by the rapid neutron capture process. That’s really the thing we’re trying to study: the physics in understanding how, where and when those elements were made.”

Abundances near the Fe peak in the solar system and four metal-poor stars.

The process, also called the “r-process,” begins with the presence of lighter elements such as iron. Then, rapidly — on the order of a second — neutrons are added to the nuclei of the lighter elements. This creates heavier elements such as selenium, silver, tellurium, platinum, gold and thorium, the kind found in HD 222925, and all of which are rarely detected in stars, according to the astronomers.

“You need lots of neutrons that are free and a very high energy set of conditions to liberate them and add them to the nuclei of atoms,” Roederer said. “There aren’t very many environments in which that can happen — two, maybe.”

One of these environments has been confirmed: the merging of neutron stars. Neutron stars are the collapsed cores of supergiant stars, and are the smallest and densest known celestial objects. The collision of neutron star pairs causes gravitational waves and in 2017, astronomers first detected gravitational waves from merging neutron stars. Another way the r-process might occur is after the explosive death of massive stars.

“That’s an important step forward: recognizing where the r-process can occur. But it’s a much bigger step to say, ‘What did that event actually do? What was produced there?” Roederer said. “That’s where our study comes in.”

The elements Roederer and his team identified in HD 222925 were produced in either a massive supernovae or a merger of neutron stars very early in the universe. The material was ejected and thrown back into space, where it later reformed into the star Roederer is studying today. This star can then be used as a proxy for what one of those events would have produced. Any model developed in the future that demonstrates how the r-process or nature produces elements on the bottom two-thirds of the periodic table must have the same signature as HD 222925, Roederer says.

Crucially, the astronomers used an instrument on the Hubble Space Telescope that can collect ultraviolet spectra. This instrument was key in allowing the astronomers to collect light in the ultraviolet part of the light spectrum — light that is faint, coming from a cool star such as HD 222925.

The astronomers also used one of the Magellan telescopes — a consortium of which U-M is a partner — at Las Campanas Observatory in Chile to collect light from HD 222925 in the optical part of the light spectrum. These spectra encode the “chemical fingerprint” of elements within stars, and reading these spectra allows the astronomers not only to identify the elements contained in the star, but also how much of an element the star contains.

Anna Frebel is a co-author of the study and professor of physics at the Massachusetts Institute of Technology. She helped with the overall interpretation of the HD 222925’s element abundance pattern and how it informs our understanding of the origin of the elements in the cosmos.

“We now know the detailed element-by-element output of some r-process event that happened early in the universe,” Frebel said. “Any model that tries to understand what’s going on with the r-process has to be able to reproduce that.”

Collective plasma effects of electron–positron pairs in beam-driven QED cascades

by Kenan Qu, Sebastian Meuren, Nathaniel J. Fisch in Physics of Plasmas

Mysterious fast radio bursts release as much energy in one second as the Sun pours out in a year and are among the most puzzling phenomena in the universe. Now researchers at Princeton University, the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) and the SLAC National Accelerator Laboratory have simulated and proposed a cost-effective experiment to produce and observe the early stages of this process in a way once thought to be impossible with existing technology.

Producing the extraordinary bursts in space are celestial bodies such as neutron, or collapsed, stars called magnetars (magnet + star) enclosed in extreme magnetic fields. These fields are so strong that they turn the vacuum in space into an exotic plasma composed of matter and anti-matter in the form of pairs of negatively charged electrons and positively charged positrons, according to quantum electrodynamic (QED) theory. Emissions from these pairs are believed to be responsible for the powerful fast radio bursts.

The matter-antimatter plasma, called “pair plasma,” stands in contrast to the usual plasma that fuels fusion reactions and makes up 99% of the visible universe. This plasma consists of matter only in the form of electrons and vastly higher-mass atomic nuclei, or ions. The electron-positron plasmas are composed of equal mass but oppositely charged particles that are subject to annihilation and creation. Such plasmas can exhibit quite different collective behavior.

“Our laboratory simulation is a small-scale analog of a magnetar environment,” said physicist Kenan Qu of the Princeton Department of Astrophysical Sciences. “This allows us to analyze QED pair plasmas,” said Qu, first author of a study.
“Rather than simulating a strong magnetic field, we use a strong laser,” Qu said. “It converts energy into pair plasma through what are called QED cascades. The pair plasma then shifts the laser pulse to a higher frequency,” he said. “The exciting result demonstrates the prospects for creating and observing QED pair plasma in laboratories and enabling experiments to verify theories about fast radio bursts.”

Laboratory-produced pair plasmas have previously been created, noted physicist Nat Fisch, a professor of astrophysical sciences at Princeton University and associate director for academic affairs at PPPL who serves as principle investigator for this research. “And we think we know what laws govern their collective behavior,” Fisch said. “But until we actually produce a pair plasma in the laboratory that exhibits collective phenomena that we can probe, we cannot be absolutely sure of that.

“The problem is that collective behavior in pair plasmas is notoriously hard to observe,” he added. “Thus, a major step for us was to think of this as a joint production-observation problem, recognizing that a great method of observation relaxes the conditions on what must be produced and in turn leads us to a more practicable user facility.”

The unique simulation the paper proposes creates high-density QED pair plasma by colliding the laser with a dense electron beam travelling near the speed of light. This approach is cost-efficient when compared with the commonly proposed method of colliding ultra-strong lasers to produce the QED cascades. The approach also slows the movement of plasma particles, thereby allowing stronger collective effects.

“No lasers are strong enough to achieve this today and building them could cost billions of dollars,” Qu said. “Our approach strongly supports using an electron beam accelerator and a moderately strong laser to achieve QED pair plasma. The implication of our study is that supporting this approach could save a lot of money.”

Currently underway are preparations for testing the simulation with a new round of laser and electron experiments at SLAC. “In a sense what we are doing here is the starting point of the cascade that produces radio bursts,” said Sebastian Meuren, a SLAC researcher and former postdoctoral visiting fellow at Princeton University who coauthored the two papers with Qu and Fisch.

“If we could observe something like a radio burst in the laboratory that would be extremely exciting,” Meuren said. “But the first part is just to observe the scattering of the electron beams and once we do that we’ll improve the laser intensity to get to higher densities to actually see the electron-positron pairs. The idea is that our experiment will evolve over the next two years or so.”

The overall goal of this research is understanding how bodies like magnetars create pair plasma and what new physics associated with fast radio bursts are brought about, Qu said. “These are the central questions we are interested in.”

Atmospheric pollution from rockets

by Ioannis W. Kokkinakis, Dimitris Drikakis in Physics of Fluids

Reusable space technology has led to a rise in space transportation at a lower cost, as popularized by commercial spaceflights of companies like SpaceX and Virgin Galactic. What is poorly understood, however, is rockets’ propulsion emissions creating significant heating and compositional changes in the atmosphere.

Researchers from the University of Nicosia in Cyprus assessed the potential impact of a rocket launch on atmospheric pollution by investigating the heat and mass transfer and rapid mixing of the combustion byproducts for altitudes up to 67 kilometers into the atmosphere.

Illustration of the considered rocket design highlighting the nozzles arrangement considered.

“Improved understanding of rocket emissions requires modeling and simulation of fluid dynamics of rocket exhaust gases into the atmosphere,” said co-author Dimitris Drikakis.

The team modeled the exhaust gases and developing plume at several altitudes along a typical trajectory of a standard present-day rocket. They did this as a prototypical example of a two-stage rocket to transport people and payloads into Earth’s orbit and beyond.

“We show that pollution from rockets should not be underestimated as frequent future rocket launches could have a significant cumulative effect on the Earth’s climate,” said co-author Ioannis Kokkinakis.

The researchers found the production of thermal nitrogen oxides (NOx), components of the combustion exhaust, can remain high up to altitudes with an ambient atmospheric pressure above or even slightly below the nozzles’ exit pressure, i.e., below an altitude of approximately 10 km. At the same time, the emitted mass of carbon dioxide as the rocket climbs 1 kilometer in altitude in the mesosphere is equivalent to that contained in 26 cubic kilometers of atmospheric air at the same altitude.

Three-dimensional view of the rocket exhaust plume obtained at an altitude of 10, 30, 50, and 67 km from left-to-right then top-to-bottom. Temperature varies from 680 K (dark yellow) to 2400 K (bright yellow). At 67 km, the temperature contours down to 350 K (dark orange) are additionally shown.

They found the impact on the atmosphere locally and momentarily in the mesosphere can be significant. While air currents will gradually transport and mix the exhaust CO2 throughout the atmosphere, eventually bringing the CO2 back down to its naturally occurring levels, the time scale over which this happens is not clear. The scientists believe a certain number of rocket launches might still exist above which mesospheric carbon dioxide could accumulate over time, thus increasing the naturally occurring levels and affecting our climate.

Their results suggest that in the worst-case scenario, sufficient NOx could be produced over the time it takes the rocket to reach an altitude of 10 kilometers to pollute over 2 cubic kilometers of atmospheric air with a NOx concentration that, according to the World Health Organization, would be at a level hazardous to human health.

“We hope that commercial flight companies, such as SpaceX, Virgin Galactic, and the New Shepard, and their associated engine manufacturers, will consider these effects in future designs,” said Drikakis.