Wednesday, June 07, 2023

SPACE


Parker Solar Probe flies into the fast solar wind and finds its source


NASA probe got close enough to sun's surface to see hidden granular features

Peer-Reviewed Publication

UNIVERSITY OF CALIFORNIA - BERKELEY

Parker Solar Probe explores the sun 

IMAGE: ARTIST’S CONCEPT OF THE PARKER SOLAR PROBE SPACECRAFT APPROACHING THE SUN. LAUNCHED IN 2018, THE PROBE IS INCREASING OUR ABILITY TO FORECAST MAJOR SPACE-WEATHER EVENTS THAT IMPACT LIFE ON EARTH. view more 

CREDIT: NASA




NASA's Parker Solar Probe (PSP) has flown close enough to the sun to detect the fine structure of the solar wind close to where it is generated at the sun's surface, revealing details that are lost as the wind exits the corona as a uniform blast of charged particles.

It's like seeing jets of water emanating from a showerhead through the blast of water hitting you in the face.

In a paper to be published this week in the journal Nature, a team of scientists led by Stuart D. Bale, a professor of physics at the University of California, Berkeley, and James Drake of the University of Maryland-College Park, report that PSP has detected streams of high-energy particles that match the supergranulation flows within coronal holes, which suggests that these are the regions where the so-called "fast" solar wind originates.

Coronal holes are areas where magnetic field lines emerge from the surface without looping back inward, thus forming open field lines that expand outward and fill most of space around the sun. These holes are usually at the poles during the sun's quiet periods, so the fast solar wind they generate doesn't hit Earth. But when the sun becomes active every 11 years as its magnetic field flips, these holes appear all over the surface, generating bursts of solar wind aimed directly at Earth.

Understanding how and where the solar wind originates will help predict solar storms that, while producing beautiful auroras on Earth, can also wreak havoc with satellites and the electrical grid.

“Winds carry lots of information from the sun to Earth, so understanding the mechanism behind the sun’s wind is important for practical reasons on Earth,” Drake said. “That’s going to affect our ability to understand how the sun releases energy and drives geomagnetic storms, which are a threat to our communication networks.”

Based on the team's analysis, the coronal holes are like showerheads, with roughly evenly spaced jets emerging from bright spots where magnetic field lines funnel into and out of the surface of the sun. The scientists argue that when oppositely directed magnetic fields pass one another in these funnels, which can be 18,000 miles across, the fields often break and reconnect, slinging charged particles out of the sun.

"The photosphere is covered by convection cells, like in a boiling pot of water, and the larger scale convection flow is called supergranulation," Bale said. "Where these supergranulation cells meet and go downward, they drag the magnetic field in their path into this downward kind of funnel. The magnetic field becomes very intensified there because it's just jammed. It's kind of a scoop of magnetic field going down into a drain. And the spatial separation of those little drains, those funnels, is what we're seeing now with solar probe data."

Based on the presence of some extremely high-energy particles that PSP has detected — particles traveling 10 to 100 times faster than the solar wind average — the researchers conclude that the wind could only be made by this process, which is called magnetic reconnection. The PSP was launched in 2018 primarily to resolve two conflicting explanations for the origin of the high-energy particles that comprise the solar wind: magnetic reconnection or acceleration by plasma or Alfvén waves.

"The big conclusion is that it's magnetic reconnection within these funnel structures that's providing the energy source of the fast solar wind," Bale said. "It doesn't just come from everywhere in a coronal hole, it's substructured within coronal holes to these supergranulation cells. It comes from these little bundles of magnetic energy that are associated with the convection flows. Our results, we think, are strong evidence that it's reconnection that's doing that."

The funnel structures likely correspond to the bright jetlets that can be seen from Earth within coronal holes, as reported recently by Nour Raouafi, a co-author of the study and the Parker Solar Probe project scientist at the Applied Physics Laboratory at Johns Hopkins University. APL designed, built, manages and operates the spacecraft.

Plunging into the sun

By the time the solar wind reaches Earth, 93 million miles from the sun, it has evolved into a homogeneous, turbulent flow of roiling magnetic fields intertwined with charged particles that interact with Earth's own magnetic field and dump electrical energy into the upper atmosphere. This excites atoms, producing colorful auroras at the poles, but has effects that trickle down into Earth's atmosphere. Predicting the most intense winds, called solar storms, and their near-Earth consequences is one mission of NASA's Living With a Star program, which funded PSP.

The probe was designed to determine what this turbulent wind looks like where it's generated near the sun's surface, or photosphere, and how the wind's charged particles — protons, electrons and heavier ions, primarily helium nuclei — are accelerated to escape the sun's gravity.

To do this, PSP had to get closer than 25 to 30 solar radii, that is, closer than about 13 million miles.

"Once you get below that altitude, 25 or 30 solar radii or so, there's a lot less evolution of the solar wind, and it's more structured — you see more of the imprints of what was on the sun," Bale said.

In 2021, PSP's instruments recorded magnetic field switchbacks in the Alfvén waves that seemed to be associated with the regions where the solar wind is generated. By the time the probe reached about 12 solar radii from the surface of the sun — 5.2 million miles — the data were clear that the probe was passing through jets of material, rather than mere turbulence. Bale, Drake and their colleagues traced these jets back to the supergranulation cells in the photosphere, where magnetic fields bunch up and funnel into the sun.

But were the charged particles being accelerated in these funnels by magnetic reconnection, which would slingshot particles outward, or by waves of hot plasma — ionized particles and magnetic field — streaming out of the sun, as if they're surfing a wave?

The fact that PSP detected extremely high-energy particles in these jets — tens to hundreds of kiloelectron volts (keV), versus a few keV for most solar wind particles — told Bale that it has to be magnetic reconnection that accelerates the particles and generates the Alfvén waves, which likely give the particles an extra boost.

"Our interpretation is that these jets of reconnection outflow excite Alfvén waves as they propagate out," Bale said. "That's an observation that's well known from Earth's magnetotail, as well, where you have similar kind of processes. I don't understand how wave damping can produce these hot particles up to hundreds of keV, whereas it comes naturally out of the reconnection process. And we see it in our simulations, too. "

The PSP won't be able to get any closer to the sun than about 8.8 solar radii above the surface — about 4 million miles — without frying its instruments. Bale expects to solidify the team's conclusions with data from that altitude, though the sun is now entering solar maximum, when activity becomes much more chaotic and may obscure the processes the scientists are trying to view.

"There was some consternation at the beginning of the solar probe mission that we're going to launch this thing right into the quietest, most dull part of the solar cycle," Bale said. "But I think without that, we would never have understood this. It would have been just too messy. I think we're lucky that we launched it in the solar minimum."

'Hot Jupiters' may not be orbiting alone


Reports and Proceedings

INDIANA UNIVERSITY

Songhu Wang 

IMAGE: SONGHU WANG. view more 

CREDIT: JAMES BROSHER, INDIANA UNIVERSITY




BLOOMINGTON, Ind. — Research led by an Indiana University astronomer challenges longstanding beliefs about the isolation of "hot Jupiters" and proposes a new mechanism for understanding the exoplanets’ evolution.

While our Jupiter is far away from the sun, hot Jupiters are gas giant planets that closely orbit stars outside our solar system for an orbital period of less than 10 days.  Previous studies suggested they rarely have any nearby companion planets, leading scientists to believe that hot Jupiters formed and evolved through a violent process that expelled other planets from the area as they moved closer to their host stars. The research team’s findings reveal that hot Jupiters do not always orbit alone.

“Our research shows that at least a fraction of hot Jupiters cannot form through a violent process,” said Songhu Wang, assistant professor of astronomy in the College of Arts and Sciences. “This is a significant contribution to advance our understanding of hot Jupiter formation, which can help us learn more about our own solar system.”

Wang presented the results of the research at the June 2023 meeting of the American Astronomical Society in Albuquerque, New Mexico.

Researchers analyzed the full, four-year data set for hot and warm Jupiters from NASA’s Kepler Mission. Warm Jupiters have a longer orbital period that ranges from 10 to 300 days. Researchers used transit timing variations to determine that at least 12% of hot Jupiters and 70% of warm Jupiters have a nearby planetary companion orbiting their host stars.

Wang and his collaborators combined their results with existing observational constraints to propose a new framework for explaining the evolution of hot and warm Jupiters and why some have companion planets. They determined that the makeup of hot and warm Jupiter systems depends on the occurrence of gas giants in the system, which impacts how much the planets interact and migrate.  

The findings provide a launching point into future research about exoplanets and our solar system’s planets.   

“The ultimate goal for astronomers is to set our solar system into the bigger picture — 'Are we unique?’” Wang said. “This helps us to understand why we don’t have a hot Jupiter in our solar system.”

Additional collaborators are Dong-Hong Wu, lecturer in the Department of Physics at Anhui Normal University, and Malena Rice, 51 Pegasi b Fellow at the Massachusetts Institute of Technology and incoming professor at Yale University.

Wang has long been interested in the configurations and demographics of exoplanets. He uses observational research to try to understand their dynamics and origins, helping astronomers better understand how our solar system fits into a larger cosmic context.

Gravitational waves innovation could help unlock cosmic secrets


Peer-Reviewed Publication

UNIVERSITY OF THE WEST OF SCOTLAND

Supermassive black hole 

IMAGE: SUPERMASSIVE BLACK HOLE view more 

CREDIT: ISTOCK



New frontiers in the study of the universe – and gravitational waves – have been opened up following a breakthrough by University of the West of Scotland (UWS) researchers.

The groundbreaking development in thin film technology promises to enhance the sensitivity of current and future gravitational wave detectors. Developed by academics at UWS’s Institute of Thin Films, Sensors and Imaging (ITFSI), the innovation could enhance the understanding of the nature of the universe.

Gravitational waves, first predicted by Albert Einstein's theory of general relativity, are ripples in the fabric of spacetime caused by the most energetic events in the cosmos, such as black hole mergers and neutron star collisions. Detecting and studying these waves provides invaluable insights into the fundamental nature of the universe.

Dr Carlos Garcia Nuñez, Senior Lecturer at School of Computing, Engineering and Physical Sciences (CEPS), said: “At the Institute of Thin Films, Sensors and Imaging, we are working hard to push the limits of thin film materials, exploring new techniques to deposit them, controlling their properties in order to match the requirements of current and future sensing technology for the detection of gravitational waves.”

“The development of high reflecting mirrors with low thermal noise opens a wide range of applications, which covers from the detection of gravitational waves from cosmological events to the development of quantum computers.”

The technique used in this work - originally developed and patented by Professor Des Gibson, Director of UWS’s Institute of Thin Films, Sensors and Imaging – could enable the production of thin films that achieve low levels of “thermal noise”. The reduction of this kind of noise in mirror coatings is essential to increase the sensitivity of current gravitational wave detectors - allowing the detection of a wider range of cosmological events - and could be deployed to enhance other high-precision devices, such as atomic clocks or quantum computers.

Professor Gibson said: "We are thrilled to unveil this cutting-edge thin film technology for gravitational wave detection. This breakthrough represents a significant step forward in our ability to explore the universe and unlock its secrets through the study of gravitational waves. We believe this advancement will accelerate scientific progress in this field and open up new avenues for discovery."

“UWS's thin film technology has already undergone extensive testing and validation in collaboration with renowned scientists and research institutions. The results have been met with great enthusiasm, fuelling anticipation for its future impact on the field of gravitational wave astronomy. The coating deposition technology is being commercialised by UWS spinout company, Albasense Ltd.”

The development of coatings with low thermal noise will not only make future generation of gravitational wave detectors more precise and sensitive to cosmic events, but will also provide new solutions to atomic clocks and quantum mechanics, both highly relevant for the United Nations’ Sustainable Development Goals 7, 9 and 11. 

Not your average space explosion: Very long baseline array finds classical novae are anything but simple

Reports and Proceedings

NATIONAL RADIO ASTRONOMY OBSERVATORY

V1674Her Binary System with Classical Nova 

IMAGE: THIS ARTIST’S CONCEPTION DEPICTS V1674 HERCULIS, A CLASSICAL NOVA HOSTED IN A BINARY STAR SYSTEM THAT IS MADE UP OF A WHITE DWARF AND DWARF COMPANION STAR. SCIENTISTS STUDYING THIS NOVA HAVE DETECTED NON-THERMAL EMISSION, A DEPARTURE FROM THE HISTORICAL BELIEF THAT THESE SYSTEMS PRODUCE ONLY THERMAL EMISSIONS. view more 

CREDIT: B. SAXTON (NRAO/AUI/NSF)



While studying classical novae using the National Radio Astronomy Observatory’s Very Long Baseline Array (VLBA), a graduate researcher uncovered evidence the objects may have been erroneously typecast as simple. The new observations, which detected non-thermal emission from a classical nova with a dwarf companion, were presented today at a press conference during the 242nd proceedings of the American Astronomical Society in Albuquerque, New Mexico. 

V1674 Herculis is a classical nova hosted by a white dwarf and dwarf companion and is currently the fastest classical nova on record. While studying V1674Her with the VLBA, Montana Williams, a graduate student at New Mexico Tech who is leading the investigation into the VLBA properties of this nova, confirmed the unexpected: non-thermal emission coming from it. This data is important because it tells Williams and her collaborators a lot about what’s happening in the system. What the team has found is anything but the simple heat-induced explosions scientists previously expected from classical novae. 

“Classical novae have historically been considered simple explosions, emitting mostly thermal energy,” said Williams. “However, based on recent observations with the Fermi Large Area Telescope, this simple model is not entirely correct. Instead, it seems they’re a bit more complicated. Using the VLBA, we were able to get a very detailed picture of one of the main complications, the non-thermal emission.”

Very long baseline interferometry (VLBI) detections of classical novae with dwarf companions like V1674Her are rare. They’re so rare, in fact, that this same type of detection, with resolved radio synchrotron components, has been reported just one other time to date. That’s partly because of the assumed nature of classical novae. 

“VLBI detections of novae are only recently becoming possible because of improvements to VLBI techniques, most notably the sensitivity of the instruments and the increasing bandwidth or the amount of frequencies we can record at a given time,” said Williams. “Additionally, because of the previous theory of classical novae they weren’t thought to be ideal targets for VLBI studies. We now know this isn’t true because of multi-wavelength observations which indicate a more complex scenario.”

That rarity makes the team’s new observations an important step in understanding the hidden lives of classical novae and what ultimately leads to their explosive behavior. 

“By studying images from the VLBA and comparing them to other observations from the Very Large Array (VLA), Fermi-LAT, NuSTAR, and NASA-Swift, we can determine what might be the cause of the emission and also make adjustments to the previous simple model,” said Williams. “Right now, we’re trying to determine if the non-thermal energy is coming from clumps of gas running into other clumped gas which produces shocks, or something else.” 

Because Fermi-LAT and Nu-Star observations had already indicated that there might be non-thermal emission coming from V1674Her, that made the classical nova an ideal candidate for study because Williams and her collaborators are on a mission to either confirm or deny those types of findings. It was also more interesting, or cute, as Williams puts it, because of its hyper-fast evolution, and because, unlike supernovae, the host system isn’t destroyed during that evolution, but rather, remains almost completely intact and unchanged after the explosion. “Many astronomical sources don’t change much over the course of a year or even 100 years. But this nova got 10,000 times brighter in a single day, then faded back to its normal state in just about 100 days,” she said. “Because the host systems of classical novae remain intact they can be recurrent, which means we might see this one erupt, or cutely explode, again and again, giving us more opportunities to understand why and how it does.” 

The National Radio Astronomy Observatory (NRAO) is a major facility of the National Science Foundation (NSF) operated under cooperative agreement by Associated Universities, Inc. 

Researchers discover chemical evidence for pair-instability supernova from a very massive first star

Peer-Reviewed Publication

CHINESE ACADEMY OF SCIENCES HEADQUARTERS

Stellar fossil: imprints of pair instability supernovae from very massive first stars 

IMAGE: STELLAR FOSSIL: IMPRINTS OF PAIR INSTABILITY SUPERNOVAE FROM VERY MASSIVE FIRST STARS. view more 

CREDIT: NAOC


The first stars illuminated the Universe during the Cosmic Dawn and put an end to the cosmic "dark ages" that followed the Big Bang. However, the distribution of their mass is one of the great unsolved mysteries of the cosmos.

Numerical simulations of the formation of the first stars estimate that the mass of the first stars reached up to several hundred solar masses. Among them, the first stars with masses between 140 and 260 solar masses ended up as pair-instability supernovae (PISNe). PISNe are quite different from ordinary supernovae (i.e., Type II and Type Ia supernovae) and would have imprinted a unique chemical signature in the atmosphere of the next-generation stars. However, no such signature has been found.

A new study led by Prof. ZHAO Gang from the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC) has identified a chemically peculiar star (LAMOST J1010+2358) in the Galactic halo as clear evidence of the existence of PISNe from very massive first stars in the early Universe, based on the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) survey and follow-up high-resolution spectra observation by Subaru Telescope. It has been confirmed that this star was formed in the gas cloud dominated by the yields of a PISN with 260 solar masses.

The team also includes the researchers from Yunnan Observatories of CAS, National Astronomical Observatory of Japan and Monash University, Australia.

This study was published online in Nature on June 7th.

The research team has performed follow-up high-resolution spectroscopic observation for J1010+2358 with the Subaru telescope and derived abundances for more than ten elements. The most significant feature of this star is its extremely low sodium and cobalt abundances. Its sodium-to-iron ratio is lower than 1/100 of the solar value. This star also exhibits a very large abundance variance between the odd and even charge number elements, such as sodium/magnesium and cobalt/nickel.

"The peculiar odd-even variance, along with deficiencies of sodium and α-elements in this star, are consistent with the prediction of primordial PISN from first-generation stars with 260 solar masses," said Dr. XING Qianfan, first author of the study.

The discovery of J1010+2358 is direct evidence of the hydrodynamical instability due to electron–positron pair production in the theory of very massive star evolution. The creation of electron–positron pairs reduces thermal pressure inside the core of a very massive star and leads to a partial collapse.

"It provides an essential clue to constraining the initial mass function in the early universe," said Prof. ZHAO Gang, corresponding author of the study. "Before this study, no evidence of supernovae from such massive stars has been found in the metal-poor stars."

Moreover, the iron abundance of LAMOST J1010+2358 ([Fe/H] = -2.42) is much higher than the most metal-poor stars in the Galactic halo, suggesting that the second-generation stars formed in the PISN-dominated gas may be more metal-rich than expected.

"One of the holy grails of searching for metal-poor stars is to find evidence for these early pair-instability supernovae," said Prof. Avi Loeb, former chair of the Astronomy Department at Harvard University.

Prof. Timothy Beers, the provost's chair of astrophysics at Notre Dame University, commented on the results: "This paper presents what is, to my knowledge, the first definitive association of a Galactic halo star with an abundance pattern originating from a PISN."

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