It’s possible that I shall make an ass of myself. But in that case one can always get out of it with a little dialectic. I have, of course, so worded my proposition as to be right either way (K.Marx, Letter to F.Engels on the Indian Mutiny)
Monday, April 29, 2024
SPACE
Gemini south reveals origin of unexpected differences in giant binary stars
Astronomers confirm that differences in the chemical composition of binary stars can be traced back to the earliest stages of their formation
ASSOCIATION OF UNIVERSITIES FOR RESEARCH IN ASTRONOMY (AURA)
IMAGE:
THIS ARTIST’S IMPRESSION ILLUSTRATES A BINARY PAIR OF GIANT STARS. DESPITE BEING BORN FROM THE SAME molecular cloud, ASTRONOMERS OFTEN DETECT DIFFERENCES IN BINARY STARS’ CHEMICAL COMPOSITIONS AND PLANETARY SYSTEMS. ONE STAR IN THIS SYSTEM IS SHOWN TO HOST THREE SMALL, ROCKY PLANETS, WHILE THE OTHER STAR HOSTS TWO GAS GIANTS. USING GEMINI SOUTH’S GHOST, A TEAM OF ASTRONOMERS HAVE CONFIRMED FOR THE FIRST TIME THAT THESE DIFFERENCES CAN BE TRACED BACK TO INHOMOGENEITIES IN THE PRIMORDIAL MOLECULAR CLOUD FROM WHICH THE STARS WERE BORN.
CREDIT: NOIRLAB/NSF/AURA/J. DA SILVA (SPACEENGINE)/M. ZAMANI
It is estimated that up to 85% of stars exist in binary star systems, some even in systems with three or more stars. These stellar pairs are born together out of the same molecular cloud from a shared abundance of chemical building blocks, so astronomers would expect to find that they have nearly identical compositions and planetary systems. However, for many binaries that isn’t the case. While some proposed explanations attribute these dissimilarities to events occurring after the stars evolved, a team of astronomers have confirmed for the first time that they can actually originate from before the stars even began to form.
Led by Carlos Saffe of the Institute of Astronomical, Earth and Space Sciences (ICATE-CONICET) in Argentina, the team used the Gemini South telescope in Chile, one half of the International Gemini Observatory, supported in part by the U.S. National Science Foundation and operated by NSF NOIRLab. With the new, precise Gemini High Resolution Optical SpecTrograph (GHOST) the team studied the different wavelengths of light, or spectra, given off by a pair of giant stars, which revealed significant differences in their chemical make-up. “GHOST’s extremely high-quality spectra offered unprecedented resolution,” said Saffe, “allowing us to measure the stars’ stellar parameters and chemical abundances with the highest possible precision.” These measurements revealed that one star had higher abundances of heavy elements than the other. To disentangle the origin of this discrepancy, the team used a unique approach.
Previous studies have proposed three possible explanations for observed chemical differences between binary stars. Two of them involve processes that would occur well into the stars’ evolution: atomic diffusion, or the settling of chemical elements into gradient layers depending on each star’s temperature and surface gravity; and the engulfment of a small, rocky planet, which would introduce chemical variations in a star’s composition.
The third possible explanation looks back at the beginning of the stars’ formation, suggesting that the differences originate from primordial, or pre-existing, areas of nonuniformity within the molecular cloud. In simpler terms, if the molecular cloud has an uneven distribution of chemical elements, then stars born within that cloud will have different compositions depending on which elements were available at the location where each formed.
So far, studies have concluded that all three explanations are probable; however, these studies focused solely on main-sequence binaries. The ‘main-sequence’ is the stage where a star spends most of its existence, and the majority of stars in the Universe are main-sequence stars, including our Sun. Instead, Saffe and his team observed a binary consisting of two giant stars. These stars possess extremely deep and strongly turbulent external layers, or convective zones. Owing to the properties of these thick convective zones, the team was able to rule out two of the three possible explanations.
The continuous swirling of fluid within the convective zone would make it difficult for material to settle into layers, meaning giant stars are less sensitive to the effects of atomic diffusion — ruling out the first explanation. The thick external layer also means that a planetary engulfment would not change a star’s composition much since the ingested material would rapidly be diluted — ruling out the second explanation. This leaves primordial inhomogeneities within the molecular cloud as the confirmed explanation. “This is the first time astronomers have been able to confirm that differences between binary stars begin at the earliest stages of their formation,” said Saffe.
“Using the precision-measurement capabilities provided by the GHOST instrument, Gemini South is now collecting observations of stars at the end of their lives to reveal the environment in which they were born,” says Martin Still, NSF program director for the International Gemini Observatory. “This gives us the ability to explore how the conditions in which stars form can influence their entire existence over millions or billions of years.”
Three consequences of this study are of particular significance. First, these results offer an explanation for why astronomers see binary stars with such different planetary systems. “Different planetary systems could mean very different planets — rocky, Earth-like, ice giants, gas giants — that orbit their host stars at different distances and where the potential to support life might be very different,” said Saffe.
Second, these results pose a crucial challenge to the concept of chemical tagging — using chemical composition to identify stars that came from the same environment or stellar nursery — by showing that stars with different chemical compositions can still have the same origin.
Finally, observed differences previously attributed to planetary impacts on a star’s surface will need to be reviewed, as they might now be seen as having been there from the very beginning of the star’s life.
“By showing for the first time that primordial differences really are present and responsible for differences between twin stars, we show that star and planet formation could be more complex than initially thought,” said Saffe. “The Universe loves diversity!”
More information
This research was presented in a paper accepted in Astronomy & Astrophysics Letters. DOI: 10.1051/0004-6361/202449263
The team is composed of C. Saffe (ICATE-CONICET/UNSJ, Argentina), P. Miquelarena (ICATE-CONICET/UNSJ, Argentina), J. Alacoria (ICATE-CONICET, Argentina), E. Martioli (LNA/MCTI, Brasil), M. Flores (ICATE-CONICET/UNSJ, Argentina), M. Jaque Arancibia (Universidad de La Serena, Chile), R. Angeloni (International Gemini Observatory/NSF NOIRLab, Chile), E. Jofré (OAC/CONICET, Argentina), J. Yana Galarza (Carnegie Institution for Science, CA), E. González (UNSJ, Argentina), and A. Collado (ICATE-CONICET/UNSJ, Argentina).
NSF NOIRLab (U.S. National Science Foundation National Optical-Infrared Astronomy Research Laboratory), the U.S. center for ground-based optical-infrared astronomy, operates the International Gemini Observatory (a facility of NSF, NRC–Canada, ANID–Chile, MCTIC–Brazil, MINCyT–Argentina, and KASI–Republic of Korea), Kitt Peak National Observatory (KPNO), Cerro Tololo Inter-American Observatory (CTIO), the Community Science and Data Center (CSDC), and Vera C. Rubin Observatory (operated in cooperation with the Department of Energy’s SLAC National Accelerator Laboratory). It is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with NSF and is headquartered in Tucson, Arizona. The astronomical community is honored to have the opportunity to conduct astronomical research on I’oligam Du’ag (Kitt Peak) in Arizona, on Maunakea in Hawai‘i, and on Cerro Tololo and Cerro Pachón in Chile. We recognize and acknowledge the very significant cultural role and reverence that these sites have to the Tohono O’odham Nation, to the Native Hawaiian community, and to the local communities in Chile, respectively.
Samples reveal evidence of changes experienced by the surface of asteroid Ryugu, some probably due to micrometeoroid bombardment.
Analyzing samples retrieved from the asteroid Ryugu by the Japanese Space Agency’s Hayabusa2 spacecraft has revealed new insights into the magnetic and physical bombardment environment of interplanetary space. The results of the study, carried out by Professor Yuki Kimura at Hokkaido University and co-workers at 13 other institutions in Japan, are published in the journal Nature Communications.
The investigations used electron waves penetrating the samples to reveal details of their structure and magnetic and electric properties, a technique called electron holography.
Hayabusa2 reached asteroid Ryugu on 27 June 2018, collected samples during two delicate touchdowns, and then returned the jettisoned samples to Earth in December 2020. The spacecraft is now continuing its journey through space, with plans for it to observe two other asteroids in 2029 and 2031.
One advantage of collecting samples directly from an asteroid is that it allows researchers to examine long-term effects of its exposure to the environment of space. The ‘solar wind’ of high energy particles from the sun and bombardment by micrometeoroids cause changes known as space-weathering. It is impossible to study these changes precisely using most of the meteorite samples that land naturally on Earth, partly due to their origin from the internal parts of an asteroid, and also due to the effects of their fiery descent through the atmosphere.
“The signatures of space weathering we have detected directly will give us a better understanding of some of the phenomena occurring in the Solar System,” says Kimura. He explains that the strength of the magnetic field in the early solar system decreased as planets formed, and measuring the remnant magnetization on asteroids can reveal information about the magnetic field in the very early stages of the solar system.
Kimura adds, “In future work, our results could also help to reveal the relative ages of surfaces on airless bodies and assist in the accurate interpretation of remote sensing data obtained from these bodies.”
One particularly interesting finding was that small mineral grains called framboids, composed of magnetite, a form of iron oxide, had completely lost their normal magnetic properties. The researchers suggest this was due to collision with high velocity micrometeoroids between 2 and 20 micrometers in diameter. The framboids were surrounded by thousands of metallic iron nanoparticles. Future studies of these nanoparticles will hopefully reveal insights into the magnetic field that the asteroid has experienced over long periods of time.
“Although our study is primarily for fundamental scientific interest and understanding, it could also help estimate the degree of degradation likely to be caused by space dust impacting robotic or manned spacecraft at high velocity,” Kimura concludes.
Magnetite (round particles) particles cut from a Ryugu sample
Magnetite (round particles) particles cut from a Ryugu sample. (A) Bright field transmission electron microscopy image. (B) Magnetic flux distribution image obtained by electron holography. The concentric circular stripes seen inside the particles correspond to magnetic lines of force. They are called vortex magnetic domain structures and are more stable than ordinary hard disks, which can record magnetic fields for more than 4.6 billion years. (Yuki Kimura, et al. Nature Communications. April 29, 2024)
Iron nanoparticles distributed around pseudo-magnetite
Iron nanoparticles distributed around pseudo-magnetite. (A) Dark-field image taken with a scanning transmission electron microscope. (B) Corresponding iron distribution image. White arrows indicate iron nanoparticles. (C) Magnetic flux distribution image of the central region of A and B. No magnetic field lines can be seen in the pseudo-magnetite, whereas concentric vortex-like magnetic domain structures can be seen inside the iron particles as shown by black arrows. (Yuki Kimura, et al. Nature Communications. April 29, 2024)
CREDIT
Yuki Kimura, et al. Nature Communications. April 29, 2024
Nonmagnetic framboid and associated iron nanoparticles with a space-weathered feature from asteroid Ryugu
ARTICLE PUBLICATION DATE
29-Apr-2024
China Set To Launch High-Stakes Mission To Moon’s ‘Hidden’ Side
China will send a robotic spacecraft in coming days on a round trip to the moon’s far side in the first of three technically demanding missions that will pave the way for an inaugural Chinese crewed landing and a base on the lunar south pole.
This week, China is expected to launch Chang’e-6 using the backup spacecraft from the 2020 mission, and collect soil and rocks from the side of the moon that permanently faces away from Earth.
With no direct line of sight with the Earth, Chang’e-6 must rely on a recently deployed relay satellite orbiting the moon during its 53-day mission, including a never-before attempted ascent from the moon’s “hidden” side on its return journey home.
The same relay satellite will support the uncrewed Chang’e-7 and 8 missions in 2026 and 2028, respectively, when China starts to explore the south pole for water and build a rudimentary outpost with Russia. China aims to put its astronauts on the moon by 2030.
On Chang’e-6, China will carry payloads from France, Italy, Sweden and Pakistan, and on Chang’e-7, payloads from Russia, Switzerland and Thailand.
Chang’e 6 will attempt to land on the northeastern side of the vast South Pole-Aitkin Basin, the oldest known impact crater in the solar system.
After touchdown at Malapert A, a site near the south pole that was believed to be relatively flat, the spacecraft tilted sharply to one side amid a host of technical problems, reflecting the high-risk nature of lunar landings.
The south pole has been described by scientists as the “golden belt” for lunar exploration.
Polar ice could sustain long-term research bases without relying on expensive resources transported from Earth. India’s Chandrayaan-1 launched in 2008 confirmed the existence of ice inside polar craters.
Chang’e-6’s sample return could also shed more light on the early evolution of the moon and the inner solar system.
Chang’e-6, after a successful landing, will collect about 2 kilogrammes (4.4 pounds) of samples with a mechanical scoop and a drill.
The Chang'e 6 lunar probe and the Long March-5 Y8 carrier rocket combination sit atop the launch pad at the Wenchang Space Launch Site in Hainan province, China April 27, 2024. cnsphoto via REUTERS
China will send a robotic spacecraft in coming days on a round trip to the moon's far side in the first of three technically demanding missions that will pave the way for an inaugural Chinese crewed landing and a base on the lunar south pole.
Since the first Chang'e mission in 2007, named after the mythical Chinese moon goddess, China has made leaps forward in its lunar exploration, narrowing the technological chasm with the United States and Russia.
In 2020, China brought back samples from the moon's near side in the first sample retrieval in more than four decades, confirming for the first time it could safely return an uncrewed spacecraft to Earth from the lunar surface.
This week, China is expected to launch Chang'e-6 using the backup spacecraft from the 2020 mission, and collect soil and rocks from the side of the moon that permanently faces away from Earth.
With no direct line of sight with the Earth, Chang'e-6 must rely on a recently deployed relay satellite orbiting the moon during its 53-day mission, including a never-before attempted ascent from the moon's "hidden" side on its return journey home.
The same relay satellite will support the uncrewed Chang'e-7 and 8 missions in 2026 and 2028, respectively, when China starts to explore the south pole for water and build a rudimentary outpost with Russia. China aims to put its astronauts on the moon by 2030.
Beijing's polar plans have worried NASA, whose administrator, Bill Nelson, has repeatedly warned that China would claim any water resources as its own. Beijing says it remains committed to cooperation with all nations on building a "shared" future.
On Chang'e-6, China will carry payloads from France, Italy, Sweden and Pakistan, and on Chang'e-7, payloads from Russia, Switzerland and Thailand.
NASA is banned by U.S. law from any collaboration, direct or indirect, with China.
Under the separate NASA-led Artemis programme, U.S. astronauts will land near the south pole in 2026, the first humans on the moon since 1972.
"International cooperation is key (to lunar exploration)," Clive Neal, professor of planetary geology at the University of Notre Dame, told Reuters. "It's just that China and the U.S. aren't cooperating right now. I hope that will happen."
SOUTH POLE AMBITIONS
Chang'e 6 will attempt to land on the northeastern side of the vast South Pole-Aitkin Basin, the oldest known impact crater in the solar system.
The southernmost landing ever was carried out in February by IM-1, a joint mission between NASA and the Texas-based private firm Intuitive Machines.
After touchdown at Malapert A, a site near the south pole that was believed to be relatively flat, the spacecraft tilted sharply to one side amid a host of technical problems, reflecting the high-risk nature of lunar landings.
The south pole has been described by scientists as the "golden belt" for lunar exploration.
Polar ice could sustain long-term research bases without relying on expensive resources transported from Earth. India's Chandrayaan-1 launched in 2008 confirmed the existence of ice inside polar craters.
Chang'e-6's sample return could also shed more light on the early evolution of the moon and the inner solar system.
The lack of volcanic activity on the moon's far side means there are more craters not covered by ancient lava flows, preserving materials from the moon's early formation.
So far, all lunar samples taken by the United States and the former Soviet Union in the 1970s and China in 2020 were from the moon's near side, where volcanism had been far more active.
Chang'e-6, after a successful landing, will collect about 2 kilogrammes (4.4 pounds) of samples with a mechanical scoop and a drill.
"If successful, China's Chang'e-6 mission would be a milestone-making event," Leonard David, author of "Moon Rush: The New Space Race", told Reuters. "The robotic reach to the Moon's far side, and bringing specimens back to Earth, helps fill in the blanks about the still-murky origin of our Moon."
UC Irvine astronomers’ simulations support dark matter theory
The tests addressed the elusive matter’s existence despite it never having been observed
UNIVERSITY OF CALIFORNIA - IRVINE
Irvine, Calif., April 29, 2024— Computer simulations by astronomers support the idea that dark matter – matter that no one has yet directly detected but which many physicists think must be there to explain several aspects of the observable universe – exists, according to the researchers, who include those at the University of California, Irvine.
The work addresses a fundamental debate in astrophysics – does invisible dark matter need to exist to explain how the universe works the way it does, or can physicists explain how things work based solely on the matter we can directly observe? Currently, many physicists think something like dark matter must exist to explain the motions of stars and galaxies.
“Our paper shows how we can use real, observed relationships as a basis to test two different models to describe the universe,” said Francisco Mercado, lead author and recent Ph.D. graduate from the UC Irvine Department of Physics & Astronomy who is now a postdoctoral scholar at Pomona College. “We put forth a powerful test to discriminate between the two models.”
The test involved running computer simulations with both types of matter – normal and dark – to explain the presence of intriguing features measured in real galaxies. The team reported their results in Monthly Notices of the Royal Astronomy Society.
The features in galaxies the team found “are expected to appear in a universe with dark matter but would be difficult to explain in a universe without it,” said Mercado. “We show that such features appear in observations of many real galaxies. If we take these data at face value, this reaffirms the position of the dark matter model as the one that best describes the universe we live in.”
These features Mercado noted describe patterns in the motions of stars and gas in galaxies that seem to only be possible in a universe with dark matter.
“Observed galaxies seem to obey a tight relationship between the matter we see and the inferred dark matter we detect, so much so that some have suggested that what we call dark matter is really evidence that our theory of gravity is wrong,” said co-author James Bullock, professor of physics at UCI and dean of the UCI School of Physical Sciences. “What we showed is that not only does dark matter predict the relationship, but for many galaxies it can explain what we see more naturally than modified gravity. I come away even more convinced that dark matter is the right model.”
The features also appear in observations made by proponents of a dark matter-free universe. “The observations we examined – the very observations where we found these features – were conducted by adherents of dark matter-free theories,” said co-author Jorge Moreno, associate professor of physics and astronomy at Pomona College. “Despite their obvious presence, little-to-no analysis was performed on these features by that community. It took folks like us, scientists working with both regular and dark matter, to start the conversation.”
Moreno added that he expects debate within his research community to follow in the wake of the study, but that there may be room for common ground, as the team also found that such features only appear in their simulations when there is both dark matter and normal matter in the universe.
“As stars are born and die, they explode into supernovae, which can shape the centers of galaxies, naturally explaining the existence of these features,” said Moreno. “Simply put, the features we examined in observations require both the existence of dark matter and the incorporation of normal-matter physics.”
Now that the dark matter model of the universe appears to be the leading one, the next step, Mercado explained, is to see if it remains consistent across a dark matter universe.
“It would be interesting to see if we could use this same relationship to even distinguish between different dark matter models,” said Mercado. “Understanding how this relationship changes under distinct dark matter models could help us constrain the properties of dark matter itself.”
Funding came from a National Science Foundation MSP-Ascend Award AST-2316748 to Mercado. Mercado and Bullock were supported by NSF grant AST-1910965 and NASA grant 80NSSC22K0827. Moreno receives funding from the Hirsch Foundation. Collaborators include Michael Boylan-Kolchin (The University of Texas at Austin), Philip F. Hopkins (California Institute of Technology), Andrew Wetzel (University of California, Davis) and Claude-André Faucher-Giguère (Northwestern University) and Jenna Samuel (The University of Texas at Austin).
About the University of California, Irvine: Founded in 1965, UC Irvine is a member of the prestigious Association of American Universities and is ranked among the nation’s top 10 public universities by U.S. News & World Report. The campus has produced five Nobel laureates and is known for its academic achievement, premier research, innovation and anteater mascot. Led by Chancellor Howard Gillman, UC Irvine has more than 36,000 students and offers 224 degree programs. It’s located in one of the world’s safest and most economically vibrant communities and is Orange County’s second-largest employer, contributing $7 billion annually to the local economy and $8 billion statewide. For more on UC Irvine, visit www.uci.edu.
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JOURNAL
Monthly Notices of the Royal Astronomical Society
ARTICLE TITLE
Hooks & Bends in the radial acceleration relation: discriminatory tests for dark matter and MOND
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