ST/ Astronomers discover largest group of rogue planets yet

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Paradigm

36 min readDec 29, 2021

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Space biweekly vol.42, 15th December — 29th December

TL;DR

Rogue planets are elusive cosmic objects that have masses comparable to those of the planets in our Solar System but do not orbit a star, instead roaming freely on their own. Not many were known until now, but a team of astronomers, using data from several ESO telescopes, have just discovered at least 70 new rogue planets in our galaxy. This is the largest group of rogue planets ever discovered, an important step towards understanding the origins and features of these mysterious galactic nomads.
Cosmochemists now present the most comprehensive comparison to date of the isotopic composition of Earth, Mars and pristine building material from the inner and outer Solar System.
Astrophysicists suggest that primordial black holes account for all dark matter in the universe.
Scientists have unraveled a fascinating new insight into how the landscape of the dwarf-planet Pluto has formed.
A new study has solved a 90-year-old mystery by proving the mechanism by which dicarbon — the chemical that makes some comets’ heads green — is broken up by sunlight. This explains why the vibrant green color never reaches the comet’s tail.
Astronomers have produced the most comprehensive image of radio emission from the nearest actively feeding supermassive black hole to Earth. The emission is powered by a central black hole in the galaxy Centaurus A, about 12 million light years away.
Meteorites are remnants of the building blocks that formed Earth and the other planets orbiting our Sun. Recent analysis of their isotopic makeup settles a longstanding debate about the geochemical evolution of our Solar System and our home planet.
Unlike our Sun, most stars live with a companion. Sometimes, two come so close that one engulfs the other. When astronomers used the telescope Alma to study 15 unusual stars, they were surprised to find that they all recently underwent this phase. The discovery promises new insight on the sky’s most dramatic phenomena — and on life, death and rebirth among the stars.
Researchers have developed a computer simulation of asteroid collisions that initially sought to replicate model asteroid strikes performed in a laboratory. After verifying the accuracy of the simulation, it could be used to predict the result of future asteroid impacts or to learn more about past impacts by studying their craters. The simulation was built using the space-time conservation element and solution element method to model shock waves and other acoustic problems.
The growing interest in deep-space exploration has sparked the need for powerful long-lived rocket systems to drive spacecraft through the cosmos. Scientists have developed a tiny version of a Hall thruster propulsion system that increases the lifetime of the rocket and produces high power.
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

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Latest research

A rich population of free-floating planets in the Upper Scorpius young stellar association

by Núria Miret-Roig, Hervé Bouy, Sean N. Raymond, Motohide Tamura, Emmanuel Bertin, David Barrado, Javier Olivares, Phillip A. B. Galli, Jean-Charles Cuillandre, Luis Manuel Sarro, Angel Berihuete, Nuria Huélamo in Nature Astronomy

Rogue planets are elusive cosmic objects that have masses comparable to those of the planets in our Solar System but do not orbit a star, instead roaming freely on their own. Not many were known until now, but a team of astronomers, using data from several European Southern Observatory (ESO) telescopes and other facilities, have just discovered at least 70 new rogue planets in our galaxy. This is the largest group of rogue planets ever discovered, an important step towards understanding the origins and features of these mysterious galactic nomads.

“We did not know how many to expect and are excited to have found so many,” says Núria Miret-Roig, an astronomer at the Laboratoire d’Astrophysique de Bordeaux, France and the University of Vienna, Austria, and the first author of the new study.

*Location of discovered rogue planets Image: ESO/N. Risinger (skysurvey.org)*

Rogue planets, lurking far away from any star illuminating them, would normally be impossible to image. However, Miret-Roig and her team took advantage of the fact that, in the few million years after their formation, these planets are still hot enough to glow, making them directly detectable by sensitive cameras on large telescopes. They found at least 70 new rogue planets with masses comparable to Jupiter’s in a star-forming region close to our Sun, in the Upper Scorpius and Ophiuchus constellations.

To spot so many rogue planets, the team used data spanning about 20 years from a number of telescopes on the ground and in space.

“We measured the tiny motions, the colours and luminosities of tens of millions of sources in a large area of the sky,” explains Miret-Roig. “These measurements allowed us to securely identify the faintest objects in this region, the rogue planets.”

Sky distribution of stars (gold triangles), brown dwarfs (blue squares), and FFPs (red dots) discovered in this study and classified assuming an age of 5 Myr. The dashed ellipse indicates the area analysed with the DANCe catalogue. The background images are in the optical (credit: Mario Cogo96) and at 857 GHz (credit: Planck97).

The team used observations from ESO’s Very Large Telescope (VLT), the Visible and Infrared Survey Telescope for Astronomy (VISTA), the VLT Survey Telescope (VST) and the MPG/ESO 2.2-metre telescope located in Chile, along with other facilities. “The vast majority of our data come from ESO observatories, which were absolutely critical for this study. Their wide field of view and unique sensitivity were keys to our success,” explains Hervé Bouy, an astronomer at the Laboratoire d’Astrophysique de Bordeaux, France, and project leader of the new research. “We used tens of thousands of wide-field images from ESO facilities, corresponding to hundreds of hours of observations, and literally tens of terabytes of data.”

The team also used data from the European Space Agency’s Gaia satellite, marking a huge success for the collaboration of ground- and space-based telescopes in the exploration and understanding of our Universe.

The study suggests there could be many more of these elusive, starless planets that we have yet to discover. “There could be several billions of these free-floating giant planets roaming freely in the Milky Way without a host star,” Bouy explains.

Colour-magnitude diagram of the members of USC and Oph identified in this work: previously known members (gray) and new members (black). The error bars represent the uncertainty in the photometry reported in the Gaia and DANCe catalogues. The BHAC15 isochrones47 (solid lines) and the PARSEC-COLIBRI isochrones48 (dashed lines) at 3 Myr (red) and 10 Myr (blue) as well as the extinction vector are overplotted.

By studying the newly found rogue planets, astronomers may find clues to how these mysterious objects form. Some scientists believe rogue planets can form from the collapse of a gas cloud that is too small to lead to the formation of a star, or that they could have been kicked out from their parent system. But which mechanism is more likely remains unknown.

Further advances in technology will be key to unlocking the mystery of these nomadic planets. The team hopes to continue to study them in greater detail with ESO’s forthcoming Extremely Large Telescope (ELT), currently under construction in the Chilean Atacama Desert and due to start observations later this decade.

“These objects are extremely faint and little can be done to study them with current facilities,” says Bouy. “The ELT will be absolutely crucial to gathering more information about most of the rogue planets we have found.”

Terrestrial planet formation from lost inner solar system material

by Christoph Burkhardt, Fridolin Spitzer, Alessandro Morbidelli, Gerrit Budde, Jan H. Render, Thomas S. Kruijer, Thorsten Kleine in Science Advances

Earth and Mars were formed from material that largely originated in the inner Solar System; only a few percent of the building blocks of these two planets originated beyond Jupiter’s orbit. A group of researchers led by the University of Münster (Germany) report these findings. They present the most comprehensive comparison to date of the isotopic composition of Earth, Mars and pristine building material from the inner and outer Solar System. Some of this material is today still found largely unaltered in meteorites. The results of the study have far-reaching consequences for our understanding of the process that formed the planets Mercury, Venus, Earth, and Mars. The theory postulating that the four rocky planets grew to their present size by accumulating millimeter-sized dust pebbles from the outer Solar System is not tenable.

Approximately 4.6 billion years ago in the early days of our Solar System, a disk of dust and gases orbited the young Sun. Two theories describe how in the course of millions of years the inner rocky planets formed from this original building material. According to the older theory, the dust in the inner Solar System agglomerated to ever larger chunks gradually reaching approximately the size of our Moon. Collisions of these planetary embryos finally produced the inner planets Mercury, Venus, Earth, and Mars. A newer theory, however, prefers a different growth process: millimeter-sized dust “pebbles” migrated from the outer Solar System towards the Sun. On their way, they were accreted onto the planetary embryos of the inner Solar System, and step by step enlarged them to their present size.

Both theories are based on theoretical models and computer simulations aimed at reconstructing the conditions and dynamics in the early Solar System; both describe a possible path of planet formation. But which one is right? Which process actually took place? To answer these questions, in their current study researchers from the University of Münster (Germany), the Observatoire de la Cote d’Azur (France), the California Institute of Technology (USA), the Natural History Museum Berlin (Germany), and the Free University of Berlin (Germany) determined the exact composition of the rocky planets Earth and Mars.

Possible scenarios of terrestrial planet formation. In the classic “Wetherill-type” model of oligarchic growth, the terrestrial planets formed by mutual collisions among Moon- to Mars-sized planetary embryos after the gas disk dissipated and accreted only a small fraction of CC planetesimals, which were scattered inward during Jupiter’s growth and/or putative migration. Alternatively, the terrestrial planets may have formed within the lifetime of the gas disk by efficiently accreting “pebbles” from the outer solar system, which drift sunward through the disk due to gas drag. The two models differ in the amount of outer solar system (CC) material accreted by the terrestrial planets, which may be quantified using nucleosynthetic isotope anomalies.

“We wanted to find out whether the building blocks of Earth and Mars originated in the outer or inner Solar System,” says Dr. Christoph Burkhardt of the University of Münster, the study’s first author. To this end, the isotopes of the rare metals titanium, zirconium and molybdenum found in minute traces in the outer, silicate-rich layers of both planets provide crucial clues. Isotopes are different varieties of the same element, which differ only in the weight of their atomic nucleus.

Scientists assume that in the early Solar System these and other metal isotopes were not evenly distributed. Rather, their abundance depended on the distance from the Sun. They therefore hold valuable information about where in the early Solar System a certain body’s building blocks originated.

Anomalies in ε95Mo and ε94Mo for BSE and BSM.

As a reference for the original isotopic inventory of the outer and inner Solar System, the researchers used two types of meteorites. These chunks of rock generally found their way to Earth from the asteroid belt, the region between the orbits of Mars and Jupiter. They are considered to be largely pristine material from the beginnings of the Solar System. While so-called carbonaceous chondrites, which can contain up to a few percent carbon, originated beyond Jupiter’s orbit and only later relocated to the asteroid belt due to influence of the growing gas giants, their more carbon-depleted cousins, the non-carbonaceous chondrites, are true children of the inner Solar System.

The precise isotopic composition of Earth’s accessible outer rock layers and that of both types of meteorites have been studied for some time; however, there have been no comparably comprehensive analyses of Martian rocks. In their current study, the researchers now examined samples from a total of 17 Martian meteorites, which can be assigned to six typical types of Martian rock. In addition, the scientists for the first time investigated the abundances of three different metal isotopes.

The Martian Meteorite Elephant Moraine (EETA) 79001. The scientists examined these and other Martian meteorites in the study.

The samples of Martian meteorites were first powdered and subjected to complex chemical pretreatment. Using a multicollector plasma mass spectrometer at the Institute of Planetology at the University of Münster, the researchers were then able to detect tiny amounts of titanium, zirconium, and molybdenum isotopes. They then performed computer simulations to calculate the ratio in which building material found today in carbonaceous and non-carbonaceous chondrites must have been incorporated into Earth and Mars in order to reproduce their measured compositions. In doing so, they considered two different phases of accretion to account for the different history of the titanium and zirconium isotopes as well as of the molybdenum isotopes, respectively. Unlike titanium and zirconium, molybdenum accumulates mainly in the metallic planetary core. The tiny amounts still found today in the silicate-rich outer layers can therefore only have been added during the very last phase of the planet’s growth.

The researchers’ results show that the outer rock layers of Earth and Mars have little in common with the carbonaceous chondrites of the outer Solar System. They account for only about four percent of both planets’ original building blocks.

“If early Earth and Mars had mainly accreted dust grains from the outer Solar System, this value should be almost ten times higher,” says Prof. Dr. Thorsten Kleine of the University of Münster, who is also director at the Max Planck Institute for Solar System Research in Göttingen. “We thus cannot confirm this theory of the formation of the inner planets,” he adds.

Results of Monte Carlo simulations for reproducing the isotopic composition of Earth and Mars in multidimensional isotope space.

But the composition of Earth and Mars does not exactly match the material of the non-carbonaceous chondrites either. The computer simulations suggest that another, different kind of building material must also have been in play.

“The isotopic composition of this third type of building material as inferred by our computer simulations implies it must have originated in the innermost region of the Solar System,” explains Christoph Burkhardt. Since bodies from such close proximity to the Sun were almost never scattered into the asteroid belt, this material was almost completely absorbed into the inner planets and thus does not occur in meteorites. “It is, so to speak, ‘lost building material’ to which we no longer have direct access today,” says Thorsten Kleine. The surprising find does not change the consequences of the study for theory of planet formation.

“The fact that Earth and Mars apparently contain mainly material from the inner Solar System fits well with planet formation from the collisions of large bodies in the inner Solar System,” concludes Christoph Burkhardt.

Photodissociation of dicarbon: How nature breaks an unusual multiple bond

by Jasmin Borsovszky, Klaas Nauta, Jun Jiang, Christopher S. Hansen, Laura K. McKemmish, Robert W. Field, John F. Stanton, Scott H. Kable, Timothy W. Schmidt in Proceedings of the National Academy of Sciences

Every so often, the Kuiper Belt and Oort Cloud throw galactic snowballs made up of ice, dust and rocks our way: 4.6-billion-year-old leftovers from the formation of the solar system.

These snowballs — or as we know them, comets — go through a colourful metamorphosis as they cross the sky, with many comets’ heads turning a radiant green colour that gets brighter as they approach the Sun. But strangely, this green shade disappears before it reaches the one or two tails trailing behind the comet.

Astronomers, scientists and chemists have been puzzled by this mystery for almost a century. In the 1930s, physicist Gerhard Herzberg theorised the phenomenon was due to sunlight destroying diatomic carbon (also known as dicarbon or C2), a chemical created from the interaction between sunlight and organic matter on the comet’s head — but as dicarbon isn’t stable, this theory has been hard to test.

A new UNSW Sydney-led study has finally found a way to test this chemical reaction in a laboratory — and in doing so, has proven this 90-year-old theory correct.

“We’ve proven the mechanism by which dicarbon is broken up by sunlight,” says Timothy Schmidt, a chemistry professor at UNSW Science and senior author of the study. “This explains why the green coma — the fuzzy layer of gas and dust surrounding the nucleus — shrinks as a comet gets closer to the Sun, and also why the tail of the comet isn’t green.”

The key player at the centre of the mystery, dicarbon, is both highly reactive and responsible for giving many comets their green colour. It’s made up of two carbon atoms stuck together and can only be found in extremely energetic or low oxygen environments like stars, comets and the interstellar medium.

Dicarbon is too reactive to store in a bottle, so the researchers needed to make it themselves. Photo: NASA Goddard.

Dicarbon doesn’t exist on comets until they get close to the Sun. As the Sun starts to warm the comet up, the organic matter living on the icy nucleus evaporates and moves to the coma. Sunlight then breaks up these larger organic molecules, creating dicarbon.

The UNSW-led team have now shown that as the comet gets even closer to the Sun, the extreme UV radiation breaks apart the dicarbon molecules it recently created in a process called ‘photodissociation’. This process destroys the dicarbon before it can move far from the nucleus, causing the green coma to get brighter and shrink — and making sure the green tinge never makes it into the tail. This is the first time this chemical interaction has been studied here on Earth.

(A) Velocity-mapped image of the 3P2 state of carbon produced by photolyzing C2 at 49,864.2 cm−1. The two halves of the image are the “raw” image on the left and a 3D slice reconstructed by the rBasex method on the right (34). (B) Averaged photofragment excitation action (PhoFEx) spectrum of the (12−0) band (*Bottom*) overlayed with the corresponding C2 resonant 2-photon ionization (R2PI) spectrum (*Top*) and a simulation illustrating the band structure (*Middle*). These plots demonstrate conclusively that the nascent C(3P) is generated by dissociation ofe3Πg(v = 12) C2. © The three speed distributions in meters per second resulting from the photodissociation of C2 at 49,864.2cm−1.

“I find incredible that someone in the 1930s thought this is probably what’s happening, down to the level of detail of the mechanism of how it was happening, and then 90 years later, we find out it is what’s happening,” says Ms Jasmin Borsovszky, lead author of the study and former UNSW Science Honours student. “Herzberg was an incredible physicist and went on to win a Nobel Prize for Chemistry in the 1970s. It’s pretty exciting to be able to prove one of the things that he theorised.”

Prof. Schmidt, who has been studying dicarbon for 15 years, says the findings help us better understand both dicarbon and comets.

“Dicarbon comes from the breakup of larger organic molecules frozen into the nucleus of the comet — the sort of molecules that are the ingredients of life,” he says. “By understanding its lifetime and destruction, we can better understand how much organic material is evaporating off comets. Discoveries like these might one day help us solve other space mysteries.”

To solve this puzzle, the team needed to recreate the same galactic chemical process in a controlled environment on Earth. They pulled this off with the help of a vacuum chamber, a lot of lasers, and one powerful cosmic reaction.

“First we had to make this molecule which is too reactive to store in a bottle,” says Prof. Schmidt. “It’s not something we could buy from the shops. “We did this by taking a larger molecule, known as perchloroethylene or C2Cl4, and blasting off its chlorine atoms (Cl) with a high-powered UV laser.”

The newly-made dicarbon molecules were sent travelling through a gas beam in a vacuum chamber, which was around two metres long. The team then pointed another two UV lasers towards the dicarbon: one to flood it with radiation, the other to make its atoms detectable. The radiation hit ripped the dicarbon apart, sending its carbon atoms flying onto a speed detector.

By analysing the speed of these quickly-moving atoms, the team could measure the strength of the carbon bond to about one in 20,000 — which is like measuring 200 metres to the nearest centimetre.

Ms Borsovszky says due to the complexity of the experiment it took nine months before they were able to make their first observation.

“We were about to give up,” she says. “It took so long to make sure everything was precisely lined up in space and time.
“The three lasers were all invisible, so there was a lot of stabbing in the dark — quite literally.” Prof. Schmidt says this is the first time anyone has ever observed this chemical reaction. “It’s extremely satisfying to have solved a conundrum that dates back to the 1930s.”

The three speed distributions in meters per second resulting from the photodissociation of C2 at 49,864.2 cm−1.

There are around 3700 known comets in the solar system, although it’s suspected there could be billions more. On average, a comet’s nucleus is a whopping 10 kilometres wide — but its coma is often 1000 times bigger. Bright comets can put on spectacular shows for those lucky enough to see them. But in the past, comets might have done more than that for Earth — in fact, one of the theories about the origin of life is that comets once delivered the building blocks of life right to our doorstep.

“This exciting research shows us just how complex processes in interstellar space are,” says Professor Martin van Kranendonk, a UNSW astrobiologist and geologist who was not involved in the study. “Early Earth would have experienced a jumble of different carbon-bearing molecules being delivered to its surface, allowing for even more complex reactions to occur in the leadup to life.”

Now that the case of the missing green tail in comets is solved, Prof. Schmidt, who specialises in space chemistry, wants to continue solving other space mysteries. Next, he hopes to investigate diffuse interstellar bands: patterns of dark lines between stars that don’t match any atom or molecule we know of.

“Diffuse interstellar bands are a pretty big unsolved mystery,” he says. “We don’t know why the light that’s arriving on Earth often has nibbles taken out. “This is just one more mystery in a huge inventory of bizarre things in space that we’re yet to discover.”

Multi-scale feedback and feeding in the closest radio galaxy Centaurus A

by B. McKinley, S. J. Tingay, M. Gaspari, R. P. Kraft, C. Matherne, A. R. Offringa, M. McDonald, M. S. Calzadilla, S. Veilleux, S. S. Shabala, S. D. J. Gwyn, J. Bland-Hawthorn, D. Crnojević, B. M. Gaensler, M. Johnston-Hollitt in Nature Astronomy

Astronomers have produced the most comprehensive image of radio emission from the nearest actively feeding supermassive black hole to Earth.

The emission is powered by a central black hole in the galaxy Centaurus A, about 12 million light years away. As the black hole feeds on in-falling gas, it ejects material at near light-speed, causing ‘radio bubbles’ to grow over hundreds of millions of years. When viewed from Earth, the eruption from Centaurus A now extends eight degrees across the sky — the length of 16 full Moons laid side by side. It was captured using the Murchison Widefield Array (MWA) telescope in outback Western Australia.

Lead author Dr Benjamin McKinley, from the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR), said the image reveals spectacular new details of the radio emission from the galaxy.

**Centaurus A with modified intensity and color scale.**

“These radio waves come from material being sucked into the supermassive black hole in the middle of the galaxy,” he said. “It forms a disc around the black hole, and as the matter gets ripped apart going close to the black hole, powerful jets form on either side of the disc, ejecting most of the material back out into space, to distances of probably more than a million light years.
“Previous radio observations could not handle the extreme brightness of the jets and details of the larger area surrounding the galaxy were distorted, but our new image overcomes these limitations.”

Centaurus A is the closest radio galaxy to our own Milky Way.

“We can learn a lot from Centaurus A in particular, just because it is so close and we can see it in such detail,” Dr McKinley said. “Not just at radio wavelengths, but at all other wavelengths of light as well.
“In this research we’ve been able to combine the radio observations with optical and x-ray data, to help us better understand the physics of these supermassive black holes.”

Astrophysicist Dr Massimo Gaspari, from Italy’s National Institute for Astrophysics, said the study corroborated a novel theory known as ‘Chaotic Cold Accretion’ (CCA), which is emerging in different fields.

“In this model, clouds of cold gas condense in the galactic halo and rain down onto the central regions, feeding the supermassive black hole,” he said. “Triggered by this rain, the black hole vigorously reacts by launching energy back via radio jets that inflate the spectacular lobes we see in the MWA image. This study is one of the first to probe in such detail the multiphase CCA ‘weather’ over the full range of scales,” Dr Gaspari concluded.

**Centaurus A in Hα emission with radio and X-ray contours.**

Dr McKinley said the galaxy appears brighter in the centre where it is more active and there is a lot of energy.

“Then it’s fainter as you go out because the energy’s been lost and things have settled down,” he said. “But there are interesting features where charged particles have re-accelerated and are interacting with strong magnetic fields.”

MWA director Professor Steven Tingay said the research was possible because of the telescope’s extremely wide field-of-view, superb radio-quiet location, and excellent sensitivity.

“The MWA is a precursor for the Square Kilometre Array (SKA) — a global initiative to build the world’s largest radio telescopes in Western Australia and South Africa,” he said. “The wide field of view and, as a consequence, the extraordinary amount of data we can collect, means that the discovery potential of every MWA observation is very high. This provides a fantastic step toward the even bigger SKA.”

Exploring the high-redshift PBH-ΛCDM Universe: early black hole seeding, the first stars and cosmic radiation backgrounds

by Nico Cappelluti, Günther Hasinger, Priyamvada Natarajan in The Astrophysical Journal

Proposing an alternative model for how the universe came to be, a team of astrophysicists suggests that all black holes — from those as tiny as a pin head to those covering billions of miles — were created instantly after the Big Bang and account for all dark matter.

That’s the implication of a study by astrophysicists at the University of Miami, Yale University, and the European Space Agency that suggests that black holes have existed since the beginning of the universe and that these primordial black holes could be as-of-yet unexplained dark matter. If proven true with data collected from this month’s launch of the James Webb Space Telescope, the discovery may transform scientific understanding of the origins and nature of two cosmic mysteries: dark matter and black holes.

“Our study predicts how the early universe would look if, instead of unknown particles, dark matter was made by black holes formed during the Big Bang — as Stephen Hawking suggested in the 1970s,” said Nico Cappelluti, an assistant professor of physics at the University of Miami and first author of the study.

“This would have several important implications,” continued Cappelluti, who this year expanded the research he began at Yale as the Yale Center for Astronomy and Astrophysics Prize Postdoctoral Fellow. “First, we would not need ‘new physics’ to explain dark matter. Moreover, this would help us to answer one of the most compelling questions of modern astrophysics: How could supermassive black holes in the early universe have grown so big so fast? Given the mechanisms we observe today in the modern universe, they would not have had enough time to form. This would also solve the long-standing mystery of why the mass of a galaxy is always proportional to the mass of the super massive black hole in its center.”

The Star Formation Rate Density (SFRD) for our model realizations.

Dark matter, which has never been directly observed, is thought to be most of the matter in the universe and act as the scaffolding upon which galaxies form and develop. On the other hand, black holes, which can be found at the centers of most galaxies, have been observed. A point in space where matter is so tightly compacted, they create intense gravity.

Co-authored by Priyamvada Natarajan, professor of astronomy and physics at Yale, and Günther Hasinger, director of science at the European Space Agency (ESA), the new study suggests that so-called primordial black holes of all sizes account for all black matter in the universe.

“Black holes of different sizes are still a mystery,” Hasinger explained. “We don’t understand how supermassive black holes could have grown so huge in the relatively short time available since the universe existed.”

Their model tweaks the theory first proposed by Hawking and fellow physicist Bernard Carr, who argued that in the first fraction of a second after the Big Bang, tiny fluctuations in the density of the universe may have created an undulating landscape with “lumpy” regions that had extra mass. These lumpy areas would collapse into black holes.

That theory did not gain scientific traction, but Cappelluti, Natarajan, and Hasinger suggest it could be valid with some slight modifications. Their model shows that the first stars and galaxies would have formed around black holes in the early universe. They also propose that primordial black holes would have had the ability to grow into supermassive black holes by feasting on gas and stars in their vicinity, or by merging with other black holes.

“Primordial black holes, if they do exist, could well be the seeds from which all the supermassive black holes form, including the one at the center of the Milky Way,” Natarajan said. “What I find personally super exciting about this idea is how it elegantly unifies the two really challenging problems that I work on — that of probing the nature of dark matter and the formation and growth of black holes — and resolves them in one fell swoop.”

A schematic of our model of the early Universe in the PBH-CDM Cosmology at z10{15.

Primordial black holes also may resolve another cosmological puzzle: the excess of infrared radiation, synced with X-ray radiation, that has been detected from distant, dim sources scattered around the universe. The study authors said growing primordial black holes would present “exactly” the same radiation signature. And, best of all, the existence of primordial black holes may be proven — or disproven — in the near future, courtesy of the Webb telescope scheduled to launch from French Guiana before the end of the year and the ESA-led Laser Interferometer Space Antenna (LISA) mission planned for the 2030s.

Developed by NASA, ESA, and the Canadian Space Agency to succeed the Hubble Space Telescope, the Webb can look back more than 13 billion years. If dark matter is comprised of primordial black holes, more stars and galaxies would have formed around them in the early universe, which is precisely what the cosmic time machine will be able to see.

“If the first stars and galaxies already formed in the so-called ‘dark ages,’ Webb should be able to see evidence of them,” Hasinger said.

Observational identification of a sample of likely recent common-envelope events

by Theo Khouri, Wouter H. T. Vlemmings, Daniel Tafoya, Andrés F. Pérez-Sánchez, Carmen Sánchez Contreras, José F. Gómez, Hiroshi Imai, Raghvendra Sahai in Nature Astronomy

Unlike our Sun, most stars live with a companion. Sometimes, two come so close that one engulfs the other — with far-reaching consequences. When a team of astronomers led by Chalmers University of Technology, Sweden, used the telescope Alma to study 15 unusual stars, they were surprised to find that they all recently underwent this phase. The discovery promises new insight on the sky’s most dramatic phenomena — and on life, death and rebirth among the stars.

Using the gigantic telescope Alma in Chile, a team of scientists led by Chalmers University of Technology studied 15 unusual stars in our galaxy, the Milky Way, the closest 5000 light years from Earth. Their measurements show that all the stars are double, and all have recently experienced a rare phase that is poorly understood, but is believed to lead to many other astronomical phenomena.

By directing the antennas of Alma towards each star and measuring light from different molecules close to each star, the researchers hoped to find clues to their backstories. Nicknamed “water fountains,” these stars were known to astronomers because of intense light from water molecules — produced by unusually dense and fast-moving gas.

Located 5000 m above sea level in Chile, the Alma telescope is sensitive to light with wavelengths around one millimetre, invisible to human eyes, but ideal for looking through the Milky Way’s layers of dusty interstellar clouds towards dust-enshrouded stars.

“We were extra curious about these stars because they seem to be blowing out quantities of dust and gas into space, some in the form of jets with speeds up to 1.8 million kilometres per hour. We thought we might find out clues to how the jets were being created, but instead we found much more than that,” says Theo Khouri, first author of the new study.

**Images of the integrated intensity of the 12 C 16 O, J=2–1 line towards the water fountain sources.**

The scientists used the telescope to measure signatures of carbon monoxide molecules, CO, in the light from the stars, and compared signals from different atoms (isotopes) of carbon and oxygen. Unlike its sister molecule carbon dioxide, CO2, carbon monoxide is relatively easy to discover in space, and is a favourite tool for astronomers.

“Thanks to Alma’s exquisite sensitivity, we were able to detect the very faint signals from several different molecules in the gas ejected by these stars. When we looked closely at the data, we saw details that we really weren’t expecting to see,” says Theo Khouri.

The observations confirmed that the stars were all blowing off their outer layers. But the proportions of the different oxygen atoms in the molecules indicated that the stars were in another respect not as extreme as they had seemed, explains team member Wouter Vlemmings, astronomer at Chalmers University of Technology.

“We realised that these stars started their lives with the same mass as the Sun, or only a few times more. Now our measurements showed that they have ejected up to 50% of their total mass, just in the last few hundred years. Something really dramatic must have happened to them,” he says.

**Moment-zero map of the 13 C 16 O, J=3–2 line towards IRAS 15445−5449 and IRAS 18043−2116.**

Why were such small stars come losing so much mass so quickly? The evidence all pointed to one explanation, the scientists concluded. These were all double stars, and they had all just been through a phase in which the two stars shared the same atmosphere — one star entirely embraced by the other.

“In this phase, the two stars orbit together in a sort of cocoon. This phase, which we call a “common envelope” phase, is really brief, and only lasts a few hundred years. In astronomical terms, it’s over in the blink of an eye,” says team member Daniel Tafoya of Chalmers University of Technology.

Most stars in binary systems simply orbit around a common centre of mass. These stars, however, share the same atmosphere. It can be a life-changing experience for a star, and may even lead to the stars merging completely.

Scientists believe that this sort of intimate episode can lead to some of the sky’s most spectacular phenomena. Understanding how it happens could help answer some of astronomers’ biggest questions about how stars live and die, Theo Khouri explains.

“What happens to cause a supernova explosion? How do black holes get close enough to collide? What’s makes the beautiful and symmetric objects we call planetary nebulae? Astronomers have suspected for many years that common envelopes are part of the answers to questions like these. Now we have a new way of studying this momentous but mysterious phase,” he says.

Understanding the common envelope phase will also help scientists study what will happen in the very distant future, when the Sun too will become a bigger, cooler star — a red giant — and engulf the innermost planets.

“Our research will help us understand how that might happen, but it gives me another, more hopeful perspective. When these stars embrace, they send dust and gas out into space that can become the ingredients for coming generations of stars and planets, and with them the potential for new life,” says Daniel Tafoya.

Since the 15 stars seem to be evolving on a human timescale, the team plan to keep monitoring them with Alma and with other radio telescopes. With the future telescopes of the SKA Observatory, they hope to study how the stars form their jets and change their surroundings. They also hope to find more — if there are any.

“Actually, we think the known “water fountains” could be almost the only systems of their kind in the whole of our galaxy. If that’s true, then these stars really are the key to understanding the strangest, most wonderful and most important process that two stars can experience in their lives together,” concludes Theo Khouri.

Numerical modeling of laboratory-scale asteroid impact based on elastoplastic flow model and CESE method

by Duoxing Yang in AIP Advances

An asteroid impact can be enough to ruin anyone’s day, but several small factors can make the difference between an out-of-this-world story and total annihilation. A researcher from the National Institute of Natural Hazards in China developed a computer simulation of asteroid collisions to better understand these factors.

The computer simulation initially sought to replicate model asteroid strikes performed in a laboratory. After verifying the accuracy of the simulation, Duoxing Yang believes it could be used to predict the result of future asteroid impacts or to learn more about past impacts by studying their craters.

Schematics of the multi-material interface tracing and the free and contact boundary treatment, which are implemented through the use of the hybrid particle level-set function.

“From these models, we learn generally a destructive impact process, and its crater formation,” said Yang. “And from crater morphologies, we could learn impact environment temperatures and its velocity.”

Yang’s simulation was built using the space-time conservation element and solution element method, designed by NASA and used by many universities and government agencies, to model shock waves and other acoustic problems. The goal was to simulate a small rocky asteroid striking a larger metal asteroid at several thousand meters per second. Using his simulation, Yang was able to calculate the effects this would have on the metal asteroid, such as the size and shape of the crater.

The simulation results were compared against mock asteroid impacts created experimentally in a laboratory. The simulation held up against these experimental tests, which means the next step in the research is to use the simulation to generate more data that can’t be produced in the laboratory.

Impact crater morphology from the AVGR experiment [shot ID180408].

This data is being created in preparation for NASA’s Psyche mission, which aims to be the first spacecraft to explore an asteroid made entirely of metal. Unlike more familiar rocky asteroids, which are made of roughly the same materials as the Earth’s crust, metal asteroids are made of materials found in the Earth’s inner core. NASA believes studying such an asteroid can reveal more about the conditions found in the center of our own planet.

Yang believes computer simulation models can generalize his results to all metal asteroid impacts and, in the process, answer several existing questions about asteroid interactions.

“What kind of geochemistry components will be generated after impacts?” said Yang. “What kinds of impacts result in good or bad consequences to local climate? Can we change trajectory of asteroids heading to us?”

Imprint of chondrule formation on the K and Rb isotopic compositions of carbonaceous meteorites

by Nicole X. Nie, Xin-Yang Chen, Timo Hopp, Justin Y. Hu, Zhe J. Zhang, Fang-Zhen Teng, Anat Shahar, Nicolas Dauphas in Science Advances

Meteorites are remnants of the building blocks that formed Earth and the other planets orbiting our Sun. Recent analysis of their isotopic makeup led by Carnegie’s Nicole Nie settles a longstanding debate about the geochemical evolution of our Solar System and our home planet.

In their youth, stars are surrounded by a rotating disk of gas and dust. Over time, these materials aggregate to form larger bodies, including planets. Some of these objects are broken up due to collisions in space, the remnants of which sometimes hurtle through Earth’s atmosphere as meteorites.

By studying a meteorite’s chemistry and mineralogy, researchers like Nie and Carnegie’s Anat Shahar can reveal details about the conditions these materials were exposed to during the Solar System’s tumultuous early years. Of particular interest is why so-called moderately volatile elements are more depleted on Earth and in meteoritic samples than the average Solar System, represented by the Sun’s composition. They are named because their relatively low boiling points mean they evaporate easily.

Correlations between the isotopic compositions of Rb, K, Te, and Zn in bulk CCs.

It’s long been theorized that periods of heating and cooling resulted in the evaporation of volatiles from meteorites. Nie and her team showed that an entirely different phenomenon is the culprit in the case of the missing volatiles.

Solving the mystery involved studying a particularly primitive class of meteorites called carbonaceous chondrites that contain crystalline droplets, called chondrules, which were part of the original disk of materials surrounding the young Sun. Because of their ancient origins, these beads are an excellent laboratory for uncovering the Solar System’s geochemical history.

“Understanding the conditions under which these volatile elements are stripped from the chondrules can help us work backward to learn the conditions they were exposed to in the Solar System’s youth and all the years since,” Nie explained.

She and her co-authors set out to probe the isotopic variability of potassium and rubidium, two moderately volatile elements. The research team included Shahar and colleagues from The University of Chicago, where Nie was a graduate student prior to joining Carnegie — Timo Hopp, Justin Y. Hu, Zhe J. Zhang, and Nicolas Dauphas — as well as Xin-Yang Chen and Fang-Zhen Teng from University of Washington Seattle.

Each element contains a unique number of protons, but its isotopes have varying numbers of neutrons. This means that each isotope has a slightly different mass than the others. As a result, chemical reactions discriminate between the isotopes, which, in turn, affects the proportion of that isotope in the reaction’s end products.

“This means that the different kinds of chemical processing that the chondrules experienced will be evident in their isotopic composition, which is something we can probe using precision instruments,” Nie added.

The model results of condensation during chondrule cooling.

Their work enabled the researchers to settle the debate about how and when in their lifespans the chondrules lost their volatiles. The isotopic record unveiled by Nie and her team indicates that the volatiles were stripped as a result of massive shockwaves passing through the material circling the young Sun that likely drove melting of the dust to form the chondrules. These types of events can be generated by gravitational instability or by larger baby planets moving through the nebular gas.

“Our findings offer new information about our Solar System’s youth and the events that shaped the geochemistry of the planets, including our own,” Nie concluded.
“The revelation that shockwaves modified the material from which the planets were born has major implications for Earth science as well,” added Carnegie Earth and Planets Laboratory Director Richard Carlson. “Once a planet gets as big as ours, its gravity is sufficient that losing most volatile elements becomes very difficult. Knowing that moderately volatile elements were stripped from the planetary building blocks themselves answers fundamental questions about Earth’s geochemical evolution.”

Mitigation of breathing oscillations and focusing of the plume in a segmented electrode wall-less Hall thruster

by J. Simmonds, Y. Raitses in Applied Physics Letters

The growing interest in deep-space exploration has sparked the need for powerful long-lived rocket systems to drive spacecraft through the cosmos. Scientists at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) have now developed a tiny modified version of a plasma-based propulsion system called a Hall thruster that both increases the lifetime of the rocket and produces high power.

The miniaturized system powered by plasma — the state of matter composed of free-floating electrons and atomic nuclei, or ions — measures little more than an inch in diameter and eliminates the walls around the plasma propellent to create innovative thruster configurations. Among these innovations are the cylindrical Hall thruster, first proposed and studied at PPPL, and a fully wall-less Hall thruster. Both configurations reduce channel erosion caused by plasma-wall interactions that limit the thruster lifetime — a key problem for conventional annular, or ring-shaped, Hall thrusters and especially for miniaturized low-power thrusters for applications on small satellites.

Graduate student Jacob Simmonds, center, with advisors Masaaki Yamada, left, and Yevgeny Raitses with figure of wall-less Hall thruster behind them. (Yamada and Raitses photos by Elle Starkman/Office of Communications; Simmonds photo by Tyler Boothe. Collage by Kiran Sudarsanan.)

Cylindrical Hall thrusters were invented by PPPL physicists Yevgeny Raitses and Nat Fisch in 1999 and have been studied with students on the Laboratory’s Hall Thruster Experiment (HTX) since then. The PPPL devices have also been studied in countries including Korea, Japan, China, Singapore, and the European Union, with Korea and Singapore considering plans to fly them.

While wall-less Hall thrusters can minimize channel erosion, they face the problem of extensive widening, or divergence, of the plasma thrust plume, which degrades the system’s performance. To reduce this problem, PPPL has installed a key innovation on its new wall-less system in the form of a segmented electrode, a concentrically joined carrier of current. This innovation not only reduces the divergence and helps to intensify the rocket thrust, Raitses said, but also, suppresses the hiccups of small-size Hall thruster plasmas that interrupt the smooth delivery of power.

The new findings cap a series of papers that Jacob Simmonds, a graduate student in the Princeton University Department of Mechanical and Aerospace Engineering, has published with Raitses, his doctoral co-adviser; PPPL physicist Masaaki Yamada serves as the other co-advisor.

“In the last two years we have published three papers on new physics of plasma thrusters that led to the dynamic thruster described in this one,” said Raitses, who leads PPPL research on low-temperature plasma physics and the HTX. “It describes a novel effect that promises new developments in this field.”

Application of segmented electrodes to Hall thrusters is not new. Raitses and Fisch had previously used such electrodes to control the plasma flow in conventional annular Hall thrusters. But the effect that Simmonds measured and described is much stronger and has greater impact on the overall thruster operation and performance.

The new device helps overcome the problem for wall-less Hall thrusters that allows the plasma propellant to shoot from the rocket at wide angles, contributing little to the rocket’s thrust.

“In short, wall-less Hall thrusters while promising have an unfocused plume because of the lack of channel walls,” Simmonds said. “So we needed to figure out a way to focus the plume to increase the thrust and efficiency and make it a better overall thruster for spacecraft.”

The segmented electrode diverts some electric current away from the thruster’s high-voltage standard electrode to shape the plasma and narrow and improve the focus of the plume. The electrode creates this effect by changing the directions of the forces within the plasma, particularly those on the ionized xenon plasma that the system accelerates to propel the rocket. Ionization turned the xenon gas the process used into free-standing electrons and atomic nuclei, or ions.

These developments increased the density of the thrust by shaping more of it in a reduced volume, a key goal for Hall thrusters. An added benefit of the segmented electrode has been the reduction of plasma instabilities called breathing mode oscillations, “where the amount of plasma increases and decreases periodically as the ionization rate changes with time” Simmonds said. Surprisingly, he added, the segmented electrode caused these oscillations to go away. “Segmented electrodes are very useful for Hall thrusters for these reasons,” he said.

The new high-thrust-density rocket can be especially beneficial for tiny cubic satellites, or CubeSats. Masaaki Yamada, Simmonds’ co-doctoral adviser who heads the Magnetic Reconnection Experiment (MRX) that studies the process behind solar flares, Northern lights and other space phenomena, proposed the use of a wall-less segmented electrode system to power a CubeSat. Simmonds and his team of undergraduate students working under the guidance of Prof. Daniel Marlow, the Evans Crawford 1911 Professor of Physics at Princeton, took up that proposal to develop a CubeSat and such a rocket — a project that was halted near completion by the COVID-19 pandemic and that could be resumed in the future.

Sublimation-driven convection in Sputnik Planitia on Pluto

by Adrien Morison, Stéphane Labrosse, Gaël Choblet in Nature

Scientists have unravelled a fascinating new insight into how the landscape of the dwarf-planet Pluto has formed.

A team of international researchers, including Dr Adrien Morison from the University of Exeter, has shown how vast ice forms have been shaped in one of the planet’s largest craters, Sputnik Planita.

**Surface topography as a function of the driving buoyancy source.**

Perhaps the most striking feature on Pluto’s surface, Sputnik Planitia is an impact crater, consisting of a bright plain, slightly larger than France, and filled with nitrogen ice.

For the new study, researchers have used sophisticated modelling techniques to show that these ice forms, polygonal in shape, are formed by the sublimation of ice — a phenomenon where the solid ice is able to turn into gas without going through a liquid state.

The research team show this sublimation of the nitrogen ice powers convection in the ice layer of Sputnik Planitia by cooling down its surface. Dr Morison, a Research Fellow from Exeter’s Physics and Astronomy department said:

“When the space probe New Horizon performed the only, to date, fly-by of Pluto in 2015, the collected data was enough to drastically change our understanding of this remote world. “In particular, it showed that Pluto is still geologically active despite being far away from the Sun and having limited internal energy sources. This included at Sputnik Planitia, where the surface conditions allow the gaseous nitrogen in its atmosphere to coexist with solid nitrogen.
“We know that the surface of the ice exhibits remarkable polygonal features — formed by thermal convection in the nitrogen ice, constantly organizing and renewing the surface of the ice. However, there remained questions behind just how this process could occur.”

**Evolution of the layer with an imposed bottom heat flux *qbot* = 0.26 mW m−2.**

In the new study, the research team conducted a series of numerical simulations that showed the cooling from sublimation is able to power convection in a way that is consistent with numerous data coming from New Horizons — including the size of polygons, amplitude of topography and surface velocities.

It is also consistent with the timescale at which climate models predict sublimation of Sputnik Planitia, beginning around 1–2 million years ago. It showed that the dynamics of this nitrogen ice layer echo those found on Earth’s oceans, being driven by the climate.

Such climate-powered dynamics of a solid layer could also occur at the surface of other planetary bodies, such as Triton (one of Neptune’s moons), or Eris and Makemake (from Kuiper’s Belt).