ST/ Flickering powered by magnetic ‘reconnection’

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Paradigm

35 min readFeb 9, 2022

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Space biweekly vol.45, 26th January — 9th February

TL;DR

Astrophysicists have identified the mechanism that powers black hole flares. By employing computer simulations of unparalleled power and resolution, the researchers found that energy released near a black hole’s event horizon during the reconnection of magnetic field lines powers the flares. The findings hint at exciting new possibilities for observing the region just outside a black hole’s event horizon.
Astronomers have identified two different cases of ‘mini-Neptune’ planets that are losing their puffy atmospheres and likely transforming into super-Earths.
Researchers studying a Martian meteorite have found the first evidence of high-intensity damage caused by asteroid impact, in findings that have implications for understanding when conditions suitable for life may have existed on early Mars.
Astronomers have confirmed the existence of the second Earth Trojan asteroid known to date, the 2020 XL5, after a decade of search.
New space research has revealed a complex ‘tug-of-war’ lights up aurorae in Jupiter’s upper atmosphere. The study describes the delicate current cycle driven by Jupiter’s rapid rotation and the release of sulphur and oxygen from volcanoes on its moon, Io.
Astronomers have found an explanation for the strange occurrence of massive stars located far from their birthplace in the disk of our Milky Way Galaxy.
Because the moon is so important to life on Earth, scientists conjecture that a moon may be a potentially beneficial feature in harboring life on other planets. Most planets have moons, but Earth’s moon is distinct in that it is large compared to the size of Earth; the moon’s radius is larger than a quarter of Earth’s radius, a much larger ratio than most moons to their planets. New research finds that distinction significant.
Astronomers have found a new and original method for measuring the cosmic microwave background’s temperature when the Universe was still in its infancy. They confirm in their new study the early cooling of our Universe shortly after the Big Bang and open up new perspectives on the elusive dark energy.
More than 35 years ago, a Northwestern professor discovered mysterious, gigantic magnetic filaments in the Milky Way galaxy’s turbulent center. Now, armed with more advanced technology, he and his collaborators have uncovered nearly 1,000 of the strange structures.
An international team analyzed the atmosphere of one of the most extreme known planets in great detail. The results from this hot, Jupiter-like planet that was first characterized with the help of the CHEOPS space telescope, may help astronomers understand the complexities of many other exoplanets — including Earth-like planets.
Upcoming industry events. And more!

Space industry in numbers

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

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

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

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Latest research

Black Hole Flares: Ejection of Accreted Magnetic Flux through 3D Plasmoid-mediated Reconnection

by B. Ripperda, M. Liska, K. Chatterjee, G. Musoke, A. A. Philippov, S. B. Markoff, A. Tchekhovskoy, Z. Younsi in The Astrophysical Journal Letters

Black holes aren’t always in the dark. Astronomers have spotted intense light shows shining from just outside the event horizon of supermassive black holes, including the one at our galaxy’s core. However, scientists couldn’t identify the cause of these flares beyond the suspected involvement of magnetic fields.

By employing computer simulations of unparalleled power and resolution, physicists say they’ve solved the mystery: Energy released near a black hole’s event horizon during the reconnection of magnetic field lines powers the flares, the researchers report.

Plasmoid-mediated reconnection, which takes place at sufficiently high resolutions in MHD, is seen in a 3D GRMHD simulation for the first time. Resolving the dynamics of X-points and plasmoids in the current sheet can be the key to understanding the source of black hole nonthermal emission, e.g., high-energy flares. Dimensionless temperature T = p/ρ, plasma-β, and density ρ (from left to right) in the meridional plane before (top row), during (middle row) in the inner 10rg, and after (bottom row) the large magnetic flux eruption in the inner 40rg. During the magnetic flux eruption, the accretion disk is ejected, and the broad accretion inflow is reduced to a thin plasmoid-unstable current sheet, indicated by X-points and magnetic nulls shown by the antiparallel in-plane field lines (in green; see inset in panel (D)) and the high β (inset panel (E)). The hot exhaust of the reconnection layer heats the jet sheath. Reconnection transforms the horizontal field in the current sheet to a vertical field that is ejected in the form of hot coherent flux tubes (panel (G)) at low β and density (panels (H), (I)).

The new simulations show that interactions between the magnetic field and material falling into the black hole’s maw cause the field to compress, flatten, break and reconnect. That process ultimately uses magnetic energy to slingshot hot plasma particles at near light speed into the black hole or out into space. Those particles can then directly radiate away some of their kinetic energy as photons and give nearby photons an energy boost. Those energetic photons make up the mysterious black hole flares.

In this model, the disk of previously infalling material is ejected during flares, clearing the area around the event horizon. This tidying up could provide astronomers an unhindered view of the usually obscured processes happening just outside the event horizon.

“The fundamental process of reconnecting magnetic field lines near the event horizon can tap the magnetic energy of the black hole’s magnetosphere to power rapid and bright flares,” says study co-lead author Bart Ripperda, a joint postdoctoral fellow at the Flatiron Institute’s Center for Computational Astrophysics (CCA) in New York City and Princeton University. “This is really where we’re connecting plasma physics with astrophysics.”

Ripperda co-authored the new study with CCA associate research scientist Alexander Philippov, Harvard University scientists Matthew Liska and Koushik Chatterjee, University of Amsterdam scientists Gibwa Musoke and Sera Markoff, Northwestern University scientist Alexander Tchekhovskoy and University College London scientist Ziri Younsi.

The equatorial current sheet that forms during the magnetic flux eruption is unresolved at low and standard resolutions (panels (A), (B)) such that magnetic field lines (green lines) diffuse through the current sheet and do not reconnect, due to the high numerical resistivity. At high and extreme resolutions (C,D), the field lines are antiparallel in the current sheet, and they reconnect in well-defined X-points. Smaller current sheets are resolved in the accretion disk at high and extreme resolutions, potentially heating the plasma through reconnection. Panel (E) shows the magnetic flux on the horizon for the four numerical resolutions. The extreme- and high-resolution runs show two and three large flare periods, respectively, indicated by flux decay at a rate ∝ e−t/500 governed by the reconnection rate (dashed black lines). A miniflare is indicated by the small flux drop at t ≈ 6800rg c−1 in the extreme-resolution run. The standard- and low-resolution runs show a faster flux decay ∝ e−t/350 governed by the enhanced reconnection rate due to an increased numerical resistivity. Flares in the extreme-resolution run are accompanied by clear drops in the mass accretion rate (panel (G)), due to the expulsion of the disk over a large azimuthal angle. Panel (F) shows a cut through the equatorial current sheet at x ≈ 1.5rg during the flare state (indicated by the red dashed line in panels (A)–(D)).

A black hole, true to its name, emits no light. So flares must originate from outside the black hole’s event horizon — the boundary where the black hole’s gravitational pull becomes so strong that not even light can escape. Orbiting and infalling material surrounds black holes in the form of an accretion disk, like the one around the behemoth black hole found in the M87 galaxy. This material cascades toward the event horizon near the black hole’s equator. At the north and south poles of some of these black holes, jets of particles shoot out into space at nearly the speed of light.

Identifying where the flares form in a black hole’s anatomy is incredibly difficult because of the physics involved. Black holes bend time and space and are surrounded by powerful magnetic fields, radiation fields and turbulent plasma — matter so hot that electrons detach from their atoms. Even with the help of powerful computers, previous efforts could only simulate black hole systems at resolutions too low to see the mechanism that powers the flares.

Ripperda and his colleagues went all in on boosting the level of detail in their simulations. They used computing time on three supercomputers — the Summit supercomputer at Oak Ridge National Laboratory in Tennessee, the Longhorn supercomputer at the University of Texas at Austin, and the Flatiron Institute’s Popeye supercomputer located at the University of California, San Diego. In total, the project took millions of computing hours. The result of all this computational muscle was by far the highest-resolution simulation of a black hole’s surroundings ever made, with over 1,000 times the resolution of previous efforts.

The increased resolution gave the researchers an unprecedented picture of the mechanisms leading to a black hole flare. The process centers on the black hole’s magnetic field, which has magnetic field lines that spring out from the black hole’s event horizon, forming the jet and connecting to the accretion disk. Previous simulations revealed that material flowing into the black hole’s equator drags magnetic field lines toward the event horizon. The dragged field lines begin stacking up near the event horizon, eventually pushing back and blocking the material flowing in.

Volume rendering of the temperature T = p/ρ shows plasmoids and hot current sheets. Extreme resolution allows the current sheets to become thinner and hotter than typically seen in GRMHD simulations. (Panel (A):) During a large flare, a relativistically hot T > 1 spiral current sheet forms. Accretion occurs over a small azimuthal angle ϕ < 2π in the T < 1 (white) regions. The green field lines, seeded in the current sheet (T > 1), remain in the current sheet and are mostly attached to the black hole. Blue field lines are seeded in the disk, where some disk field lines are accreting onto the black hole in the T < 1 region. (Panel (B):) In the quiescent state, T ≤ 1 everywhere, and both green and blue field lines (with the same seeds as in panel (A)) are in the disk, accreting onto the black hole. The inset © shows a zoom into the inner rg in the flare state with multiple escaping flux loops (green field lines). In the small black box, we highlight an escaping flux tube with vertical field as the result of reconnection (green) and an infalling flux tube (purple).

With its exceptional resolution, the new simulation for the first time captured how the magnetic field at the border between the flowing material and the black hole’s jets intensifies, squeezing and flattening the equatorial field lines. Those field lines are now in alternating lanes pointing toward the black hole or away from it. When two lines pointing in opposite directions meet, they can break, reconnect and tangle. In between connection points, a pocket forms in the magnetic field. Those pockets are filled with hot plasma that either falls into the black hole or is accelerated out into space at tremendous speeds, thanks to energy taken from the magnetic field in the jets.

“Without the high resolution of our simulations, you couldn’t capture the subdynamics and the substructures,” Ripperda says. “In the low-resolution models, reconnection doesn’t occur, so there’s no mechanism that could accelerate particles.”

Plasma particles in the catapulted material immediately radiate some energy away as photons. The plasma particles can further dip into the energy range needed to give nearby photons an energy boost. Those photons, either passersby or the photons initially created by the launched plasma, make up the most energetic flares. The material itself ends up in a hot blob orbiting in the vicinity of the black hole. Such a blob has been spotted near the Milky Way’s supermassive black hole. “Magnetic reconnection powering such a hot spot is a smoking gun for explaining that observation,” Ripperda says.

Lorentz factor Γ (top rows) and temperature T = p/ρ for the extreme-resolution 3D run with density floor (left) and two supplementary 2D runs with density floors (middle) and (right). Reconnection heats up the plasma in the equatorial current sheet. The hot reconnection exhaust heats up the jet sheath up to temperatures proportional to the magnetization in the jet.

The researchers also observed that after the black hole flares for a while, the magnetic field energy wanes, and the system resets. Then, over time, the process begins anew. This cyclical mechanism explains why black holes emit flares on set schedules ranging from every day (for our Milky Way’s supermassive black hole) to every few years (for M87 and other black holes).

Ripperda thinks that observations from the recently launched James Webb Space Telescope combined with those from the Event Horizon Telescope could confirm whether the process seen in the new simulations is happening and if it changes images of a black hole’s shadow. “We’ll have to see,” Ripperda says. For now, he and his colleagues are working to improve their simulations with even more detail.

Escaping Helium from TOI 560.01, a Young Mini-Neptune

by Michael Zhang, Heather A. Knutson, Lile Wang, Fei Dai, Oscar Barragán in The Astronomical Journal

Astronomers have identified two different cases of “mini-Neptune” planets that are losing their puffy atmospheres and likely transforming into super-Earths. Radiation from the planets’ stars is stripping away their atmospheres, driving hot gas to escape like steam from a pot of boiling water.

“Most astronomers suspected that young, small mini-Neptunes must have evaporating atmospheres,” says Michael Zhang, lead author of both studies and a graduate student at Caltech. “But nobody had ever caught one in the process of doing so until now.”

Mini-Neptunes are a class of exoplanets, which are planets that orbit stars outside our solar system. These worlds, which are smaller, denser versions of the planet Neptune, consist of large rocky cores surrounded by thick blankets of gas.

Percent excess absorption from TOI 560.01 as a function of time and wavelength, for the first (left panel) and second (right panel) nights of observation. The dashed white line indicates the beginning of the white light transit, while the solid white line indicates the end. The red lines show the wavelengths of planetary helium absorption. At 10830 Å is a deep stellar Si i line, which, like other strong lines, we mask as part of our analysis because optimal extraction deals poorly with very strong lines (Zhang et al. 2021b).

In the new studies, a team of astronomers led by Caltech used Keck Observatory’s Near-Infrared Spectrograph (NIRSPEC) to study one of two mini-Neptune planets in the star system called TOI 560, located 103 light-years away; and they used Hubble to look at two mini-Neptunes orbiting HD 63433, located 73 light-years away. Their results show that atmospheric gas is escaping from the innermost mini-Neptune in TOI 560, called TOI 560.01, and from the outermost mini-Neptune in HD 63433, called HD 63433 c. Furthermore, Keck Observatory data surprisingly showed the gas around TOI 560.01 was escaping predominantly toward the star.

“This was unexpected, as most models predict that the gas should flow away from the star,” says Professor of Planetary Science Heather Knutson, Zhang’s advisor and a co-author of the study. “We still have a lot to learn about how these outflows work in practice.”

Since the first exoplanets orbiting Sun-like stars were discovered in the mid-1990s, thousands of others have been found. Many of these orbit close to their stars, and the smaller, rocky ones generally fall into two groups: mini-Neptunes and super-Earths. The super-Earths are as large as 1.6 times the size of Earth (and occasionally as large as 1.75 times the size of Earth), while the mini-Neptunes are between two and four times the size of Earth. Few planets with sizes between these two planet types have been detected.

One possible explanation for this gap is that mini-Neptunes are transforming into super-Earths. The mini-Neptunes are theorized to be cocooned by primordial atmospheres made of hydrogen and helium. The hydrogen and helium are left over from the formation of the central star, which is born out of clouds of gas. If a mini-Neptune is small enough and close enough to its star, stellar X-rays and ultraviolet radiation can strip away its primordial atmosphere over a period of hundreds of millions of years, scientists theorize. This would then leave behind a rocky super-Earth with a substantially smaller radius, which could, in theory, still retain a relatively thin atmosphere similar to that surrounding our own planet.

Comparison of the four terms of the energy conservation equation (Equation (1)). The advection term switches sign, so we plot the absolute value. The oscillations in the Z = 100 plot are numerical artifacts.

“A planet in the gap would have enough atmosphere to puff up its radius, making it intercept more stellar radiation and thereby enabling fast mass loss,” says Zhang. “But the atmosphere is thin enough that it gets lost quickly. This is why a planet wouldn’t stay in the gap for long.”

Other scenarios could explain the gap, according to the astronomers. For instance, the smaller rocky planets might have never gathered gas envelopes in the first place, and mini-Neptunes could be water worlds and not enveloped in hydrogen gas. This latest discovery of two mini-Neptunes with escaping atmospheres represents the first direct evidence to support the theory that mini-Neptunes are indeed turning into super-Earths.

Neutral hydrogen number density (left), triplet helium density (middle), and temperature (right) from the time-averaged (over the last ∼10 kinematic timescales) fiducial (top) and best-fit (bottom) 3D models. The star is toward the left, and orbital motion is upward. These plots show the profiles in the orbital plane. The white lines are the streamlines, while the dashed black lines represent the inner sonic surface.

The astronomers were able to detect the escaping atmospheres by watching the mini-Neptunes cross in front of, or transit, their host stars. The planets cannot be seen directly but when they pass in front of their stars as seen from our point of view on Earth, telescopes can look for absorption of starlight by atoms in the planets’ atmospheres. In the case of the mini-Neptune TOI 560.01, the researchers found signatures of helium. For the star system HD 63433, the team found signatures of hydrogen in the outermost planet they studied, called HD 63433 c, but not the inner planet, HD 63433 b.

“The inner planet may have already lost its atmosphere,” Zhang explains.

The speed of the gases provides the evidence that the atmospheres are escaping. The observed helium around TOI 560.01 is moving as fast as 20 kilometers per second, while the hydrogen around HD 63433 c is moving as fast as 50 kilometers per second. The gravity of these mini-Neptunes is not strong enough to hold on to such fast-moving gas. The extent of the outflows around the planets also indicates escaping atmospheres: the cocoon of gas around TOI 560.01 is at least 3.5 times as large as the radius of the planet, and the cocoon around HD 63433 c is at least 12 times the radius of the planet. As for the strange discovery that the gas lost from TOI 560.01 was flowing toward — instead of away from — its host star, future observations of other mini-Neptunes should reveal if TOI 560.01 is an anomaly or whether an inward-moving atmospheric outflow is more common.

“As exoplanet scientists, we’ve learned to expect the unexpected,” says Knutson. “These exotic worlds are constantly surprising us with new physics that goes beyond what we observe in our solar system.”

Impact and habitability scenarios for early Mars revisited based on a 4.45-Ga shocked zircon in regolith breccia

by Morgan A. Cox, Aaron J. Cavosie, Kenneth J. Orr, Luke Daly, Laure Martin, Anthony Lagain, Gretchen K. Benedix, Phil A. Bland in Science Advances

Curtin University researchers studying a Martian meteorite have found the first evidence of high-intensity damage caused by asteroid impact, in findings that have implications for understanding when conditions suitable for life may have existed on early Mars.

The research examined grains of the mineral zircon in Martian meteorite NWA 7034. The meteorite, colloquially known as ‘Black Beauty’, is a rare sample of the surface of Mars. The original 320-gram rock was found in northern Africa and first reported in 2013.

Combined element map of the rock chip from Martian meteorite NWA 7034 analyzed in this study.

Lead author Morgan Cox, a PhD candidate from Curtin’s Space Science and Technology Centre (SSTC) in the School of Earth and Planetary Sciences, described the meteorite as a collection of broken rock fragments and minerals, mostly basalt, that solidified and became a rock over time. A zircon found inside the meteorite preserves evidence of damage that only occurs during large meteorite impacts.

“This grain is truly a one-off gift from the Red Planet. High-pressure shock deformation has not previously been found in any minerals from Black Beauty. This discovery of shock damage in a 4.45 billion-year-old Martian zircon provides new evidence of dynamic processes that affected the surface of early Mars,” Ms Cox said.
“The type of shock damage in the Martian zircon involves ‘twinning’, and has been reported from all of the biggest impact sites on Earth, including the one in Mexico that killed off the dinosaurs, as well as the Moon, but not previously from Mars.”

Schematic timeline showing the impact history and evolution of habitability on Earth and Mars.

Co-author Dr Aaron Cavosie, also from Curtin’s SSTC, said the occurrence of zircon grains in the Black Beauty meteorite provided physical evidence of large impacts on early Mars, and had implications for the habitability of the young planet.

“Prior studies of zircon in Martian meteorites proposed that conditions suitable for life may have existed by 4.2 billion years ago based on the absence of definitive shock damage” Dr Cavosie said.
“Mars remained subject to impact bombardment after this time, on the scale known to cause mass extinctions on Earth. The zircon we describe provides evidence of such impacts, and highlights the possibility that the habitability window may have occurred later than previously thought, perhaps coinciding with evidence for liquid water on Mars by 3.9 to 3.7 billion years ago.”

Relation of Jupiter’s Dawnside Main Emission Intensity to Magnetospheric Currents During the Juno Mission

by J. D. Nichols, S. W. H. Cowley in Journal of Geophysical Research: Space Physics

New Leicester space research has revealed, for the first time, a complex ‘tug-of-war’ lights up aurorae in Jupiter’s upper atmosphere, using a combination of data from NASA’s Juno probe and the Hubble Space Telescope.

The study describes the delicate current cycle driven by Jupiter’s rapid rotation and the release of sulphur and oxygen from volcanoes on its moon, Io. Researchers from the University of Leicester’s School of Physics and Astronomy used data from Juno’s Magnetic Field Investigation (MAG), which measures Jupiter’s magnetic field from orbit around the gas giant, and observations from the Space Telescope Imaging Spectrograph carried by the Hubble Space Telescope.

Schematic showing a cut through a meridian plane of Jupiter’s inner and middle magnetosphere. The solid lines show the magnetic field lines, while the dashed lines show the magnetosphere-ionosphere coupling currents.

Their research provides the strongest evidence yet that Jupiter’s powerful aurorae are associated with an electric current system that acts as part of a tug-of-war with material in the magnetosphere, the region dominated by the planet’s enormous magnetic field.

Dr Jonathan Nichols is a Reader in Planetary Auroras at the University of Leicester and corresponding author for the study. He said:

“We’ve had theories linking these electric currents and Jupiter’s powerful auroras for over two decades now, and it was so exciting to be able to finally test them by looking for this relationship in the data. And when we plotted one against the other I nearly fell off my chair when I saw just how clear the connection is.
“It’s thrilling to discover this relation because it not only helps us understand how Jupiter’s magnetic field works, but also those of planets orbiting other stars, for which we have previously used the same theories, and now with renewed confidence.”

Despite its huge size — with a diameter more than 11 times that of Earth — Jupiter rotates once approximately every nine-and-a-half hours. Io is a similar size and mass to Earth’s moon, but orbits Jupiter at an average distance of 422,000 km; roughly 10% further away. With over 400 active volcanoes, Io is the most geologically active object in the Solar System.

Scientists had long suspected a relationship between Jupiter’s aurorae and the material ejected from Io at a rate of many hundreds of kilograms per second, but the data captured by Juno proved ambiguous.

Dr Scott Bolton, of NASA’s Jet Propulsion Laboratory (JPL), is Principal Investigator (PI) for the Juno mission. He said:

“These exciting results on how Jupiter’s aurorae work are a testament to the power of combining Earth-based observations from Hubble with Juno measurements. The HST images provide the broad overview, while Juno investigates close up. Together they make a great team!”

A gallery of representative northern hemisphere auroral images used in this study (a–h). The images are shown using a Lambert Equal Area Azimuthal projection, with a logarithmic color scale as shown on the right, and oriented such that System III 180° is toward the bottom. A 10° × 45° graticule is overlaid in gray.

Much of the material released from Io is propelled away from Jupiter by the planet’s rapidly rotating magnetic field, and as it moves outward its rotation rate tends to slow down. This results in an electromagnetic tug-of-war, in which Jupiter attempts to keep this material spinning at its rotation speed via a system of electric currents flowing through the planet’s upper atmosphere and magnetosphere. The component of the electric current flowing out of the planet’s atmosphere, carried by electrons fired downward along magnetic field lines into the upper atmosphere, was thought to drive Jupiter’s main auroral emission.

However, prior to Juno’s arrival this idea had never been tested, as no spacecraft with relevant instruments had previously orbited close enough to Jupiter. And when Juno arrived in 2016, the expected signature of such an electric current system was not reported — and, while such signatures have since been found — one of the great surprises of Juno’s mission has been to show that the nature of the electrons above Jupiter’s polar regions is much more complex than was initially expected.

Plots of the currents associated with the RBC partial ring current model versus radial distance and LT (panels a–d) and radial distance (panel e).

The researchers compared the brightness of Jupiter’s main auroral emission with simultaneous measurements of the electric current flowing away from the Solar System’s largest planet in the magnetosphere over an early part of Juno’s mission. These aurorae were observed with instruments on board the Hubble Space Telescope, in Earth orbit. By comparing the dawn-side measurements of current with the brightness of Jupiter’s aurorae, the team demonstrated the relationship between the auroral intensity and magnetospheric current strength.

Stan Cowley is Emeritus Professor of Solar-Planetary Physics at the University of Leicester and co-author for the study, and has studied Jupiter’s powerful aurorae for 25 years. Professor Cowley added:

“Having more than five years of in-orbit data from the Juno spacecraft, together with auroral imaging data from the HST, we now have the material to hand to look in detail at the overall physics of Jupiter’s outer plasma environment, and more is to come from Juno’s extended mission, now in progress. We hope our present paper will be followed by many more exploring this treasure trove for new scientific understanding.”

The Transformative Journey of HD 93521

by Douglas R. Gies, Katherine Shepard, Peter Wysocki, Robert Klement in The Astronomical Journal

Astronomers from Georgia State University have found an explanation for the strange occurrence of massive stars located far from their birthplace in the disk of our Milky Way Galaxy.

Stars more massive than the Sun have very hot cores that drive nuclear energy generation at very high rates. They are among the brightest objects in our galaxy. But because they burn through their hydrogen fuel so quickly, their lifetimes are relatively short, perhaps 10 million years compared to 10 billion years for the Sun. Their short lifetime means that there is little time for them to stray too far from their birthplace. Most massive stars are found in the flat disk part of our galaxy, where gas clouds are dense enough to promote star birth and where astronomers find young clusters of massive stars.

A rotation model image of HD 93521 based upon the parameters listed in Table 2. The model star has a polar radius of 6.1R⊙ and and an equatorial radius of 7.4R⊙, and the inclination of the spin axis to the line of sight is i = 90°.

So, when a massive star is found far away from the galaxy’s disk, how did it get there?

“Astronomers are finding massive stars far away from their place of origin, so far, in fact, that it takes longer than the star’s lifetime to get there,” said Georgia State astronomer Douglas Gies. “How this could happen is a topic of active debate among scientists.”

This is the problem presented by the massive star known as HD93521 that lies about 3,600 light years above the galaxy’s disk. A new study by Gies and other astronomers from Georgia State reveals a profound discrepancy: The flight time to reach this location far exceeds the predicted age of this massive star.

The astronomers used a new distance estimate from the European Space Agency’s Gaia spacecraft together with an investigation of the star’s spectrum to determine the star’s mass and age as well as its motion through space. They find that HD93521 has a mass about 17 times larger than the Sun’s, and this leads to a predicted age of about 5 million years. On the other hand, the motion of the star indicates that its journey from the disk has taken much longer, about 39 million years.

The Georgia State astronomers explain this strange difference between the star’s lifetime and travel time by suggesting that HD93521 left the disk as two lower-mass and longer-lived stars, rather than the single massive star we see today. The clue to the mystery is that HD93521 is one of the fastest rotating stars in the galaxy. Stars can spin up through stellar mergers where two close orbiting stars can grow over time and collide to form one star.

“HD93521 probably began life as a close pair of medium-mass stars that were fated to engulf each other and create the single, fast-spinning star we see today,” Gies said.

Such intermediate mass stars live long enough to match the long flight time of HD93521. HD93521 is not the only case of a massive star found so far away from its birthplace. Georgia State graduate student Peter Wysocki is investigating an example of a distant massive binary pair that is probably representative of the stage just before a merger. This star is known as IT Librae, and it has an orientation that creates mutual eclipses as the two stars pass in front of each other. An investigation of the variations in the light output and motions detected in the spectra leads to estimates of the stellar masses.

Wysocki finds a similar conundrum from the mass results — the predicted age is much less than IT Librae’s travel time from the disk. But the study also reveals that the lower-mass star in the pair has already begun to transfer much of its mass to the higher-mass star, initiating the process that may eventually lead to a merger. This means that the higher-mass star is actually older than it appears, having begun life as a lower-mass star.

These distant massive stars provide striking evidence that close pairs of stars can merge to make even larger stars, Gies said, and they are key clues about how rapidly rotating massive stars are able to create black holes with large spins.

Statistical Properties of the Population of the Galactic Center Filaments: the Spectral Index and Equipartition Magnetic Field

by F. Yusef-Zadeh, R. G. Arendt, M. Wardle, I. Heywood, W. Cotton, F. Camilo in The Astrophysical Journal Letters

An unprecedented new telescope image of the Milky Way galaxy’s turbulent center has revealed nearly 1,000 mysterious strands, inexplicably dangling in space.

Stretching up to 150 light years long, the one-dimensional strands (or filaments) are found in pairs and clusters, often stacked equally spaced, side by side like strings on a harp. Using observations at radio wavelengths, Northwestern University’s Farhad Yusef-Zadeh discovered the highly organized, magnetic filaments in the early 1980s. The mystifying filaments, he found, comprise cosmic ray electrons gyrating the magnetic field at close to the speed of light. But their origin has remained an unsolved mystery ever since.

Now, the new image has exposed 10 times more filaments than previously discovered, enabling Yusef-Zadeh and his team to conduct statistical studies across a broad population of filaments for the first time. This information potentially could help them finally unravel the long-standing mystery.

Top (2a): a mosaic image of the Galactic center at 20 cm with a 4'’ resolution taken with MeerKAT (Heywood et al. 2022). Prominent sources are labeled. The names of the filaments are taken from (LaRosa et al. 2001; Yusef-Zadeh et al. 2004; Law et al. 2008). The rms noise in this image ∼80 mJy beam−1. This data product is publicly available in Heywood et al. (2022). Bottom (2b): a filtered version of (a) with rms sensitivity of 1.8–2.3 μJy and a resolution of 6 4. The units of the filtered image do not account for the changed beam size. The subtraction built into the filtering reduces the apparent intensities by a factor of ∼0.13.

“We have studied individual filaments for a long time with a myopic view,” said Yusef-Zadeh, the paper’s lead author. “Now, we finally see the big picture — a panoramic view filled with an abundance of filaments. Just examining a few filaments makes it difficult to draw any real conclusion about what they are and where they came from. This is a watershed in furthering our understanding of these structures.”

Yusef-Zadeh is a professor of physics and astronomy at Northwestern’s Weinberg College of Arts and Sciences and a member of the Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA).

To construct the image with unprecedented clarity and detail, astronomers spent three years surveying the sky and analyzing data at the South African Radio Astronomy Observatory (SARAO). Using 200 hours of time on SARAO’s MeerKAT telescope, researchers pieced together a mosaic of 20 separate observations of different sections of the sky toward the center of the Milky Way galaxy, 25,000 light years from Earth.

“I’ve spent a lot of time looking at this image in the process of working on it, and I never get tired of it,” Heywood said. “When I show this image to people who might be new to radio astronomy, or otherwise unfamiliar with it, I always try to emphasize that radio imaging hasn’t always been this way, and what a leap forward MeerKAT really is in terms of its capabilities. It’s been a true privilege to work over the years with colleagues from SARAO who built this fantastic telescope.”

To view the filaments at a finer scale, Yusef-Zadeh’s team used a technique to remove the background from the main image in order to isolate the filaments from the surrounding structures. The resulting picture astounded him.

“It’s like modern art,” he said. “These images are so beautiful and rich, and the mystery of it all makes it even more interesting.”

Top (a): an image of the distribution of the equipartition magnetic field assuming all the features are nonthermal emission and have a spectral index α = −0.5, as calculated from Equation (1). Bottom (b): equipartition magnetic field calculated from Equation (2), employing the measured spectral indices. In this image, features with α > −0.4 have been masked.

While many mysteries surrounding the filaments remain, Yusef-Zadeh has been able to piece together more of the puzzle. In their latest paper, he and his collaborators specifically explored the filaments’ magnetic fields and the role of cosmic rays in illuminating the magnetic fields.

The variation in radiation emitting from the filaments is very different from that of the newly uncovered supernova remnant, suggesting that the phenomena have different origins. It is more likely, the researchers found, that the filaments are related to past activity of the Milky Way’s central supermassive black hole rather than coordinated bursts of supernovae. The filaments also could be related to enormous, radio-emitting bubbles, which Yusef-Zadeh and collaborators discovered in 2019. And, while Yusef-Zadeh already knew the filaments are magnetized, now he can say magnetic fields are amplified along the filaments, a primary characteristic all the filaments share.

“This is the first time we have been able to study statistical characteristics of the filaments,” he said. “By studying the statistics, we can learn more about the properties of these unusual sources.
“If you were from another planet, for example, and you encountered one very tall person on Earth, you might assume all people are tall. But if you do statistics across a population of people, you can find the average height. That’s exactly what we’re doing. We can find the strength of magnetic fields, their lengths, their orientations and the spectrum of radiation.”

Among the remaining mysteries, Yusef-Zadeh is particularly puzzled by how structured the filaments appear. Filaments within clusters are separated from one another at perfectly equal distances — about the distance from Earth to the sun.

“They almost resemble the regular spacing in solar loops,” he said. “We still don’t know why they come in clusters or understand how they separate, and we don’t know how these regular spacings happen. Every time we answer one question, multiple other questions arise.”

Yusef-Zadeh and his team also still don’t know whether the filaments move or change over time or what is causing the electrons to accelerate at such incredible speeds.

“How do you accelerate electrons at close to the speed of light?” he asked. “One idea is there are some sources at the end of these filaments that are accelerating these particles.”

Yusef-Zadeh and his team are currently identifying and cataloging each filament. The angle, curve, magnetic field, spectrum and intensity of each filament will be published in a future study. Understanding these properties will give the astrophysics community more clues into the filaments’ elusive nature.

Microwave background temperature at a redshift of 6.34 from H2O absorption

by Riechers, D.A., Weiss, A., Walter, F. et al. in Nature

An international group of astrophysicists has discovered a new method to estimate the cosmic microwave background temperature of the young Universe only 880 million years after the Big Bang. It is the first time that the temperature of the cosmic microwave background radiation — a relic of the energy released by the Big Bang — has been measured at such an early epoch of the Universe. The prevailing cosmological model assumes that the Universe has cooled off since the Big Bang — and still continues to do so. The model also describes how the cooling process should proceed, but so far it has only been directly confirmed for relatively recent cosmic times. The discovery not only sets a very early milestone in the development of the cosmic background temperature, but could also have implications for the enigmatic dark energy.

The scientists used the NOEMA (Northern Extended Millimeter Array) observatory in the French Alps, the most powerful radio telescope in the Northern Hemisphere, to observe HFLS3, a massive starburst galaxy at a distance corresponding to an age of only 880 million years after the Big Bang. They discovered a screen of cold water gas that casts a shadow on the cosmic microwave background radiation. The shadow appears because the colder water absorbs the warmer microwave radiation on its path towards Earth, and its darkness reveals the temperature difference. As the temperature of the water can be determined from other observed properties of the starburst, the difference indicates the temperature of the Big Bang’s relic radiation, which at that time was about seven times higher than in the Universe today.

**Broad-band, 3-mm spectroscopy of the starburst galaxy HFLS3 at a redshift of 6.34 with NOEMA.**

‘Besides proof of cooling, this discovery also shows us that the Universe in its infancy had some quite specific physical characteristics that no longer exist today,’ said lead author Professor Dr Dominik Riechers from the University of Cologne’s Institute of Astrophysics. ‘Quite early, about 1.5 billion years after the Big Bang, the cosmic microwave background was already too cold for this effect to be observable. We have therefore a unique observing window that opens up to a very young Universe only,’ he continued. In other words, if a galaxy with otherwise identical properties as HFLS3 were to exist today, the water shadow would not be observable because the required contrast in temperatures would no longer exist.

‘This important milestone not only confirms the expected cooling trend for a much earlier epoch than has previously been possible to measure, but could also have direct implications for the nature of the elusive dark energy,’ said co-author Dr Axel Weiss from the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn. Dark energy is thought to be responsible for the accelerated expansion of the Universe over the past few billion years, but its properties remain poorly understood because it cannot be directly observed with the currently available facilities and instruments. However, its properties influence the evolution of cosmic expansion, and hence the cooling rate of the Universe over cosmic time. Based on this experiment, the properties of dark energy remain — for now — consistent with those of Einstein’s ‘cosmological constant’. ‘That is to say, an expanding Universe in which the density of dark energy does not change,’ explained Weiss.

**H2O line emission integrated moment 0 and continuum maps of HFLS3.**

Having discovered one such cold water cloud in a starburst galaxy in the early Universe, the team is now setting out to find many more across the sky. Their aim is to map out the cooling of the Big Bang echo within the first 1.5 billion years of cosmic history. ‘This new technique provides important new insights into the evolution of the Universe, which are very difficult to constrain otherwise at such early epochs,’ Riechers said.

‘Our team is already following this up with NOEMA by studying the surroundings of other galaxies,’ said co-author and NOEMA project scientist Dr Roberto Neri. ‘With the expected improvements in precision from studies of larger samples of water clouds, it remains to be seen if our current, basic understanding of the expansion of the Universe holds.’

Large planets may not form fractionally large moons

by Miki Nakajima, Hidenori Genda, Erik Asphaug, Shigeru Ida in Nature Communications

Earth’s moon is vitally important in making Earth the planet we know today: the moon controls the length of the day and ocean tides, which affect the biological cycles of lifeforms on our planet. The moon also contributes to Earth’s climate by stabilizing Earth’s spin axis, offering an ideal environment for life to develop and evolve.

Because the moon is so important to life on Earth, scientists conjecture that a moon may be a potentially beneficial feature in harboring life on other planets. Most planets have moons, but Earth’s moon is distinct in that it is large compared to the size of Earth; the moon’s radius is larger than a quarter of Earth’s radius, a much larger ratio than most moons to their planets.

Miki Nakajima, an assistant professor of earth and environmental sciences at the University of Rochester, finds that distinction significant. And in a new study that she led, she and her colleagues at the Tokyo Institute of Technology and the University of Arizona examine moon formations and conclude that only certain types of planets can form moons that are large in respect to their host planets.

“By understanding moon formations, we have a better constraint on what to look for when searching for Earth-like planets,” Nakajima says. “We expect that exomoons [moons orbiting planets outside our solar system] should be everywhere, but so far we haven’t confirmed any. Our constraints will be helpful for future observations.”

**Snapshots of giant impacts (Runs ID2 and ID20).**

Many scientists have historically believed Earth’s large moon was generated by a collision between proto-Earth — Earth at its early stages of development — and a large, Mars-sized impactor, approximately 4.5 billion years ago. The collision resulted in the formation of a partially vaporized disk around Earth, which eventually formed into the moon.

In order to find out whether other planets can form similarly large moons, Nakajima and her colleagues conducted impact simulations on the computer, with a number of hypothetical Earth-like rocky planets and icy planets of varying masses. They hoped to identify whether the simulated impacts would result in partially vaporized disks, like the disk that formed Earth’s moon. The researchers found that rocky planets larger than six times the mass of Earth (6M) and icy planets larger than one Earth mass (1M) produce fully — rather than partially — vaporized disks, and these fully-vaporized disks are not capable of forming fractionally large moons.

“We found that if the planet is too massive, these impacts produce completely vapor disks because impacts between massive planets are generally more energetic than those between small planets,” Nakajima says.

After an impact that results in a vaporized disk, over time, the disk cools and liquid moonlets — a moon’s building blocks — emerge. In a fully-vaporized disk, the growing moonlets in the disk experience strong gas drag from vapor, falling onto the planet very quickly. In contrast, if the disk is only partially vaporized, moonlets do not feel such strong gas drag.

“As a result, we conclude that a completely vapor disk is not capable of forming fractionally large moons,” Nakajima says. “Planetary masses need to be smaller than those thresholds we identified in order to produce such moons.”

**Schematic view of the mass range in which a fractionally large exomoon can form by an impact.**

The constraints outlined by Nakajima and her colleagues are important for astronomers investigating our universe; researchers have detected thousands of exoplanets and possible exomoons, but have yet to definitively spot a moon orbiting a planet outside our solar system. This research may give them a better idea of where to look.

As Nakajima says: “The exoplanet search has typically been focused on planets larger than six earth masses. We are proposing that instead we should look at smaller planets because they are probably better candidates to host fractionally large moons.”

Orbital stability analysis and photometric characterization of the second Earth Trojan asteroid 2020 XL5

by T. Santana-Ros, M. Micheli, L. Faggioli, R. Cennamo, M. Devogèle, A. Alvarez-Candal, D. Oszkiewicz, O. Ramírez, P.-Y. Liu, P. G. Benavidez, A. Campo Bagatin, E. J. Christensen, R. J. Wainscoat, R. Weryk, L. Fraga, C. Briceño, L. Conversi in Nature Communications

An International team of astronomers led by researcher Toni Santana-Ros, from the University of Alicante and the Institute of Cosmos Sciences of the University of Barcelona (ICCUB), has confirmed the existence of the second Earth Trojan asteroid known to date, the 2020 XL5, after a decade of search.

All celestial objects that roam around our solar system feel the gravitational influence of all the other massive bodies that build it, including the Sun and the planets. If we consider only the Earth-Sun system, Newton’s laws of gravity state that there are five points where all the forces that act upon an object located at that point cancel each other out. These regions are called Lagrangian points, and they are areas of great stability. Earth Trojan asteroids are small bodies that orbit around the L4 or L5 Lagrangian points of the Sun-Earth system.

These results confirm that 2020 XL5 is the second transient Earth Trojan asteroid known to date, and everything indicates it will remain Trojan — that is, it will be located at the Lagrangian point — for four thousand years, thus it is qualified as transient. The researchers have provided an estimation of the object bulk size (around one kilometer in diameter, larger than the Earth Trojan asteroid known to date, the 2010 TK7, which was 0.3 kilometres in diameter), and have made a study of the impulse a rocket needs to reach the asteroid from Earth.

**Beginning of the non-deterministic regime.**

Although Trojan asteroids have been known to exist for decades in other planets such as Venus, Mars, Jupiter, Uranus and Neptune, it was not until 2011 that the first Earth Trojan asteroid was found. The astronomers have described many observational strategies for the detection of new Earth Trojans. “There have been many previous attempts to find Earth Trojans, including in situ surveys such as the search within the L4 region, carried out by the NASA OSIRIS-Rex spacecraft, or the search within the L5 region, conducted by the JAXA Hayabusa-2 mission,” notes Toni Santana-Ros, author of the publication. He adds that “all the dedicated efforts had so far failed to discover any new member of this population.”

The low success in these searches can be explained by the geometry of an object orbiting the Earth-Sun L4 or L5 as seen from our planet. These objects are usually observable close to the sun. The observation time window between the asteroid rising above the horizon and sunrise is, therefore, very small. Therefore, astronomers point their telescopes very low on the sky where the visibility conditions are at their worst and with the handicap of the imminent sunlight saturating the background light of the images just a few minutes in the observation.

To solve this problem, the team carried out a search of 4-meter telescopes that would be able to observe under such conditions, and they finally obtained the data from the 4.3m Lowel Discovery telescope (Arizona, United States), and the 4.1m SOAR telescope, operated by the National Science Foundation NOIRLab (Cerro Pachón, Chile).

The discovery of the Earth Trojan asteroids is very significant because these can hold a pristine record on the early conditions in the formation of the Solar System, since the primitive trojans might have been co-orbiting the planets during their formation, and they add restrictions to the dynamic evolution of the Solar System. In addition, Earth Trojans are the ideal candidates for potential space missions in the future.

Since the L4 Lagrangian point shares the same orbit as the Earth, it takes a low change in velocity to be reached. This implies that a spacecraft would need a low energy budget to remain in its shared orbit with the Earth, keeping a fixed distance to it. “Earth Trojans could become ideal bases for an advanced exploration of the Solar System; they could even become a source of resources,” concludes Santana-Ros.

The discovery of more trojans will enhance our knowledge of the dynamics of these unknown objects and will provide a better understanding of the mechanics that allow them to be transient.

Titanium oxide and chemical inhomogeneity in the atmosphere of the exoplanet WASP-189 b

by Bibiana Prinoth, H. Jens Hoeijmakers, Daniel Kitzmann, et al. in Nature Astronomy

An international team including researchers from the University of Bern and the University of Geneva as well as the National Centre of Competence in Research (NCCR) PlanetS analyzed the atmosphere of one of the most extreme known planets in great detail. The results from this hot, Jupiter-like planet that was first characterized with the help of the CHEOPS space telescope, may help astronomers understand the complexities of many other exoplanets — including Earth-like planets.

The atmosphere of Earth is not a uniform envelope but consists of distinct layers that each have characteristic properties. The lowest layer that spans from sea level beyond the highest mountain peaks, for example — the troposphere -, contains most of the water vapour and is thus the layer in which most weather phenomena occur. The layer above it — the stratosphere — is the one that contains the famous ozone layer that shields us from the Sun’s harmful ultraviolet radiation.

In a new study, an international team of researchers led by the University of Lund show for the first time that the atmosphere of one of the most extreme known planets may have similarly distinct layers as well — albeit with very different characteristics.

Schematic showing the contributions of the terminators throughout the course of the transit in the example of a toy-planet atmosphere with a hot dayside component, and a cooler nightside component with a clearly reduced scale height (day–night gradient).

WASP-189b is a planet outside our own solar system, located 322 light years from Earth. Extensive observations with the CHEOPS space telescope in 2020 revealed among other things that the planet is 20 times closer to its host star than Earth is to the Sun and has a daytime temperature of 3200 degrees Celsius. More recent investigations with the HARPS spectrograph at the La Silla Observatory in Chile now for the first time allowed the researchers to take a closer look at the atmosphere of this Jupiter-like planet.

“We measured the light coming from the planet’s host star and passing through the planet’s atmosphere. The gases in its atmosphere absorb some of the starlight, similar to Ozone absorbing some of the sunlight in Earth’s atmosphere, and thereby leave their characteristic ‘fingerprint’. With the help of HARPS, we were able to identify the corresponding substances,” lead author of the study and doctoral student at Lund University, Bibiana Prinoth, explains. According to the researchers, the gases that left their fingerprints in the atmosphere of WASP-189b included iron, chromium, vanadium, magnesium and manganese.

**Overview of the detections of TiO, Ti, Ti+, Fe, Fe+, Cr, Mg, V and Mn.**

One particularly interesting substance the team found is a gas containing titanium: titanium oxide. While titanium oxide is very scarce on Earth, it could play an important role in the atmosphere of WASP-189b — similar to that of ozone in Earth’s atmosphere. “Titanium oxide absorbs short wave radiation, such as ultraviolet radiation. Its detection could therefore indicate a layer in the atmosphere of WASP-189b that interacts with the stellar irradiation similarly to how the Ozone layer does on Earth,” study co-author Kevin Heng, a professor of astrophysics at the University of Bern and a member of the NCCR PlanetS, explains.

Indeed, the researchers found hints of such a layer and other layers on the ultra-hot Jupiter-like planet. “In our analysis, we saw that the ‘fingerprints’ of the different gases were slightly altered compared to our expectation. We believe that strong winds and other processes could generate these alterations. And because the fingerprints of different gases were altered in different ways, we think that this indicates that they exist in different layers — similarly to how the fingerprints of water vapour and ozone on Earth would appear differently altered from a distance, because they mostly occur in different atmospheric layers,” Prinoth explains. These results may change how astronomers investigate exoplanets.

“In the past, astronomers often assumed that the atmospheres of exoplanets exist as a uniform layer and try to understand it as such. But our results demonstrate that even the atmospheres of intensely irradiated giant gas planets have complex three-dimensional structures,” study co-author and associate senior lecturer at Lund University Jens Hoeijmakers points out.
“We are convinced that to be able to fully understand these and other types of planets — including ones more similar to Earth, we need to appreciate the three-dimensional nature of their atmospheres. This requires innovations in data analysis techniques, computer modelling and fundamental atmospheric theory,” Kevin Heng concludes.