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Early October Astronomy Bulletin
« on: October 03, 2021, 07:46 »
BILLION-YEAR-OLD FOSSIL
Cosmos Up

Paleontologists at Virginia Tech have announced a remarkable discovery of a billion year old green seaweed micro-fossils, the oldest evidence of green seaweeds yet discovered. Scientists said the plant, named Proterocladus antiquus ¬ which measure just two millimetres in length ¬ had a big role: it engaged in photosynthesis, produced oxygen by transforming sunlight’s energy into chemical energy. That means, these seaweeds could be related to the ancestor of the earliest land plants and trees that colonize the land in Earth’s distant past, an ancestor to everything that grows on our planet. Paleontologists found this seaweed microfossil in rock slabs recovered near the city of Dalian in northern China, which was underwater millions of years ago. Surprisingly, the algae imprints reveal that these ancient weeds looked a lot like green seaweeds found in the ocean today, this add supports to the theory stating terrestrial life evolved from marine lifeforms. A group of modern green seaweeds, known as siphonocladaleans, are particularly similar in shape and size to the fossils we found. Before this Finding, the oldest convincing fossil records of green seaweeds were discovered in rock dated at about 800 million years old but the age of the new fossils totally rewrites the story of when and how the Earth’s flora evolved. These new fossils suggest that green seaweeds were important players in the ocean long before their land-plant descendants moved and took control of dry land.

The entire biosphere is largely dependent on plants and algae for food and oxygen, yet land plants did not evolve until about 450 million years ago. Through geological time¬¬millions upon millions of years¬¬they moved out of the water and became adapted to and prospered on dry land, their new natural environment. These fossils are related to the ancestors of all the modern land plants we see today. However, the caveat that not all geobiologists are on the same page — that debate on the origins of green plants remains debated. Some scientists think that green plants started in rivers and lakes, and then conquered the ocean and land later. These seaweeds display multiple branches, upright growths, and specialised cells known as akinetes that are very common in this type of fossil. Taken together, these features strongly suggest that the fossil is a green seaweed with complex multicellularity that is circa 1 billion years old. These likely represent the earliest fossil of green seaweeds. In short, our study tells us that the ubiquitous green plants we see today can be traced back to at least 1 billion years.


EXOTIC MIX IN CHINA’S MOON ROCKS
Europlanet Society

On 16 December 2020 the Chang'e-5 mission, China's first sample return mission to the Moon, successfully delivered to Earth nearly two kilograms of rocky fragments and dust from our celestial companion. Chang’e-5 landed on an area of the Moon not sampled by the NASA Apollo or the Soviet Luna missions nearly 50 years ago, and retrieved fragments of the youngest lunar rocks ever brought back for analysis in laboratories on Earth. Early-stage findings, which use geological mapping to link ‘exotic’ fragments in the collected samples to features near the landing site. The Chang'e-5 landing site is located on the western edge of the nearside of the Moon in the Northern Oceanus Procellarum. This is one of the youngest geological areas of the Moon with an age of roughly two billion years. The materials scraped from the surface comprise a loose soil that results from the fragmentation and powdering of lunar rocks over billions of years due to impacts of various sizes. The study suggests that ninety percent of the materials collected by Chang’e-5 likely derive from the landing site and its immediate surroundings, which are of a type termed ‘mare basalts’. These volcanic rocks are visible to us as the darker grey areas that spilled over much of the nearside of the Moon as ancient eruptions of lava. Yet ten percent of the fragments have distinctly different, ‘exotic’ chemical compositions, and may preserve records of other parts of the lunar surface as well as hints of the types of space rocks that have impacted the Moon’s surface.

Scientists looked at the potential sources of beads of rapidly cooled glassy material. They have traced these glassy droplets to now extinct volcanic vents known as ‘Rima Mairan’ and ‘Rima Sharp’ located roughly 230 and 160 kilometres southeast and northeast of the Chang’e-5 landing site. These fragments could give insights into past episodes of energetic, fountain-like volcanic activity on the Moon. The team has also looked at the potential sources of impact-related fragments. The young geological age of the rocks at the landing site narrows the search, as only craters with ages less than 2 billion years can be responsible, and these are relatively rare on the side of the Moon that faces Earth. The team has modelled the potential contributions from specific craters to the south and southeast (Aristarchus, Kepler, and Copernicus), northwest (Harding), and northeast (Harpalus). Qian’s findings show that Harpalus is a significant contributor of many exotic fragments among Chang’e-5’s sample haul, and these pieces of rock could offer a way to address persisting uncertainty about this crater’s age. Some fragments may have been thrown into Chang’e-5 landing area from nearly 1,300 kilometres away.


LIFE SUPPORT COOKED UP FROM LUNAR ROCKS
Europlanet Society

Engineers have successfully shown how water and oxygen can be extracted by cooking up lunar soil, in order to support future Moon bases. A laboratory demonstrator, developed by the European scientists uses a two-step process, well known in industrial chemistry for terrestrial applications, that has been customised to work with a mineral mixture that mimics the lunar soil. Around 50% of lunar soil in all regions of the Moon is made up of silicon- or iron-oxides, and these in turn are around 26% oxygen. This means that a system that efficiently extracts oxygen from the soil could operate at any landing site or installation on the Moon. In the experimental set-up, the soil simulant is vaporised in the presence of hydrogen and methane, then “washed” with hydrogen gas. Heated by a furnace to temperatures of around 1000 degrees Celsius, the minerals turn directly from a solid to a gas, missing out a molten phase, which reduces the complexity of the technology needed. Gases produced and residual methane are sent to a catalytic converter and a condenser that separates out water. Oxygen can then be extracted through electrolysis. By-products of methane and hydrogen are recycled in the system.

Experiments show that the rig is scalable and can operate in an almost completely self-sustained closed loop, without the need for human intervention and without getting clogged up. To accurately understand the process and prepare the technology needed for a flight test, experiments have been carried out to optimise the temperature of the furnace, the length and frequency of the washing phases, the ratio of the mixtures of gases, and the mass of the soil simulant batches. Results show that yield is maximised by processing the soil simulant in small batches, at the highest temperatures possible and using long washing phases. The solid by-product is rich in silica and metals that can undergo further processing for other resources useful for in-situ exploration of the Moon.


MUSHBALLS ABSORB MISSING AMMONIA AT URANUS AND NEPTUNE
RAS

Mushballs – giant, slushy hailstones made from a mixture of ammonia and water – may be responsible for an atmospheric anomaly at Neptune and Uranus that has been puzzling scientists. A study shows that mushballs could be highly effective at carrying ammonia deep into the ice giants’ atmospheres, hiding the gas from detection beneath opaque clouds.
Recently, remote observations at infrared and radio wavelengths have shown that Uranus and Neptune lack ammonia in their atmosphere compared to the other giant planets in our Solar System. This is surprising because they are otherwise very rich in other compounds, such as methane, found in the primordial cloud from which the planets formed. Either the planets formed under special conditions, from material that was also poor in ammonia, or some ongoing process must be responsible. The Juno observations at Jupiter have shown that ammonia-water hailstones can form rapidly during storms because of ammonia’s ability to liquefy water ice crystals, even at very low temperatures of around -90 degrees Celsius. Models indicate that these mushballs in Jupiter may grow to weights of up to a kilogram or more, slightly higher than the largest hailstones on Earth. As they plunge downwards, they transport ammonia very efficiently to the deep atmosphere, where it ends up locked away beneath the cloud base. To determine exactly how deep down the mushballs are carrying ammonia and water may have to wait until an orbiter with instruments can probe the atmospheres of the ice giants close up.


OLDER WHITE DWARFS BECOME MORE MAGNETIC
by Isaac Newton Group of Telescopes

At least one out of four white dwarfs (WDs) will end its life as a magnetic star, and therefore magnetic fields are an essential component of WD physics. New insights into the magnetism of degenerate stars from a recent analysis of a volume-limited sample of WDs have provided the best evidence obtained so far of how the frequency of magnetism in WDs correlates with age. This could help to explain the origin and evolution of magnetic fields in WDs. More than 90% of the stars of our Galaxy end their lives as WDs. Although many have a magnetic field, it's still unknown when it appears on the surface, whether it evolves during the cooling phase of the WD and, above all, what are the mechanisms that generate it. Astronomical observations are frequently subject to strong biases. Because WDs are dying stars, they become cooler, and hence fainter and fainter with time. As a consequence, observations tend to favour the study of the brightest WDs, which are hot and young. There is also a more subtle and counterintuitive effect. Because of their degenerate status, more massive WDs are smaller than less massive ones (imagine a series of spheres where the smaller ones are the heavier). Because smaller WDs are also fainter, observations tend to also favour the less massive stars. In summary, observations of targets selected according to their brightness (for instance, observing all WDs brighter than a certain magnitude) tend to concentrate on young and less massive stars, totally neglecting older WDs. Another issue is that most of the observations of WDs are made with spectroscopic techniques which are sensitive only to the strongest magnetic fields, thus failing to identify a substantial fraction of magnetic WDs. The sensitivity of spectropolarimetry to magnetic fields may be more than two orders of magnitude better than spectroscopy. Spectropolarimetry has demonstrated that weak fields, which escape detection via spectroscopic techniques, are actually quite common in WDs. In order to carry out a complete spectropolarimetric survey, astronomers from Armagh Observatory and the University of Western Ontario selected all the WDs from the Gaia catalogue in a volume within 20 parsecs of the Sun.

About two thirds of this sample, or approximately 100 WDs, had not been observed before and hence there were no data available in the literature. Consequently, the team observed them using the ISIS spectrograph and polarimeter on the William Herschel Telescope (WHT), together with similar instruments on other telescopes. They found that magnetic fields are rare at the beginning of the life of a WD, when the star no longer produces energy in its interior, and starts its cooling phase. Therefore a magnetic field does not appear to be a characteristic of a WD since its "birth." Most frequently, it is either generated, or brought to the stellar surface during the WD's cooling phase. They also found that the magnetic fields of WDs do not show obvious signs of Ohmic decay, again an indication that these fields are generated during the cooling phase, or at least continue to emerge at the stellar surface as the WD ages. This picture is totally different from what is observed for instance in magnetic Ap and Bp stars of the upper main sequence, where it is found that not only are magnetic fields present as soon as the star reaches the zero-age main sequence, but also that the field strength quickly decreases with time. Magnetism in WDs therefore seems to be a totally different phenomenon than magnetism of Ap and Bp stars. Not only does magnetic field frequency increase with WD age, but it is known that the frequency is correlated with stellar mass, and that fields appear more frequently after the star's carbon-oxygen core has started to crystallize. A dynamo mechanism can explain the weakest fields among those observed in WDs, and recent work suggests that the same mechanism could be capable of producing fields stronger than originally predicted. For comparison, the strength of the Earth's magnetic field, produced by a dynamo mechanism, is about one Gauss. A dynamo mechanism can explain fields up to 0.1 million Gauss strength, but in WDs fields up to several hundred million Gauss have been observed. Furthermore, a dynamo mechanism needs fast rotation, but this is not generally observed in WDs. Further theoretical and observational investigation is needed to untangle this situation.


CLOUD-SPOTTING ON DISTANT EXOPLANET
Europlanet Society

An international team of astronomers has not only detected clouds on the distant exoplanet WASP-127b, but also measured their altitude with unprecedented precision. WASP-127b, located more than 525 light-years away, is a “hot Saturn” – a giant planet similar in mass to Saturn that orbits very close to its sun. The team observed the planet passing in front of its host star to detect patterns that become embedded in the starlight as it is filtered through the planet’s atmosphere and altered by the chemical constituents. By combining infrared observations from the ESA/NASA Hubble Space Telescope and visible light measurements from the ESPRESSO spectrograph at the European Southern Observatory’s Very Large Telescope in Chile, the researchers were able to probe different regions of the atmosphere. The results brought a few surprises. First, as found before in this type of planet, scientists detected the presence of sodium, but at a much lower altitude than expected . Second, there were strong water vapour signals in the infrared but none at all at visible wavelengths. This implies that water-vapour at lower levels is being screened by clouds that are opaque at visible wavelengths but transparent in the infrared. The combined data from the two instruments enabled the researchers to narrow down the altitude of the clouds to an atmospheric layer with a pressure ranging between 0.3 and 0.5 millibars.

The composition of the clouds is not yet known, except that they are not composed of water droplets like on Earth. Researchers are also puzzled about why the sodium is found in an unexpected place on this planet. Future studies will help us understand not only more about the atmospheric structure, but about WASP-127b, which is proving to be a fascinating place.
With a full orbit around its star occurring in about four days, WASP-127b receives 600 times more irradiation than the Earth and experiences temperatures up to 1100 degrees Celsius. This puffs the planet up to a radius 1.3 times larger than Jupiter, with just a fifth of the mass, making it one of the least dense or “fluffiest” exoplanets ever discovered. The extended nature of fluffy exoplanets makes them easier to observe, and thus WASP-127b is an ideal candidate for researchers working on atmospheric characterisation.


MYSTERY SURROUNDING 900 YEAR OLD SUPERNOVA SOLVED
University of Manchester

A 900-year-old cosmic mystery surrounding the origins of a famous supernova first spotted over China in 1181AD has finally been solved, according to an international team of astronomers. New research says that a faint, fast expanding nebula called Pa30, surrounding one of the hottest stars in the Milky Way, known as Parker's Star, fits the profile, location and age of the historic supernova. There have only been five bright supernovae in the Milky Way in the last millennium (starting in 1006). Of these, the Chinese supernova, which is also known as the 'Chinese Guest Star' of 1181AD has remained a mystery. It was originally seen and documented by Chinese and Japanese astronomers in the 12th century who said it was as bright as the planet Saturn and remained visible for six months. They also recorded an approximate location in the sky of the sighting, but no confirmed remnant of the explosion has even been identified by modern astronomers. The other four supernovae are all now well known to modern day science and include the famous Crab nebula. In the new paper, the astronomers found that the Pa 30 nebula is expanding at an extreme velocity of more than 1,100 km per second (at this speed, travelling from the Earth to the Moon would take only 5 minutes). They use this velocity to derive an age at around 1,000 years, which would coincide with the events of 1181AD. The historical reports place the guest star between two Chinese constellations, Chuanshe and Huagai. Parker's Star fits the position well. That means both the age and location fit with the events of 1181. Pa 30 and Parker's Star have previously been proposed as the result of a merger of two White Dwarfs. Such events are thought to lead to a rare and relatively faint type of supernova, called a 'Type Iax supernova'.

Only around 10% of supernovae are of this type and they are not well understood. The fact that SN1181 was faint but faded very slowly fits this type. It is the only such event where we can study both the remnant nebula and the merged star, and also have a description of the explosion itself. The merging of remnant stars, white dwarfs and neutron stars, give rise to extreme nuclear reactions and form heavy, highly neutron-rich elements such as gold and platinum. Combining all this information such as the age, location, event brightness and historically recorded 185-day duration, indicates that Parker's star and Pa30 are the counterparts of SN 1181. This is the only Type Iax supernova where detailed studies of the remnant star and nebula are possible.


GAMMA RAYS AND NEUTRINOS FROM DORMANT SUPERMASSIVE BLACK HOLES
Tohoku University


The Universe is filled with energetic particles, such as X rays, gamma rays, and neutrinos. However, most of the high-energy cosmic particles' origins remain unexplained. Now, an international research team has proposed a scenario that explains these; black holes with low activity act as major factories of high-energy cosmic particles. Gamma rays are high-energy photons that are many orders of magnitude more energetic than visible light. Space satellites have detected cosmic gamma rays with energies of megaelectron to gigaelectron volts. Neutrinos are subatomic particles whose mass is nearly zero. They rarely interact with ordinary matter. Researchers at the IceCube Neutrino Observatory have also measured high-energy cosmic neutrinos. Both gamma rays and neutrinos should be created by powerful cosmic-ray accelerators or surrounding environments in the Universe. However, their origins are still unknown. It is widely believed that active supermassive black holes (so-called active galactic nuclei), especially those with powerful jets, are the most promising emitters of high-energy gamma rays and neutrinos. However, recent studies have revealed that they do not explain the observed gamma rays and neutrinos, suggesting that other source classes are necessary. The new model shows that not only active black holes but also non-active, "mellow" ones are important, acting as gamma-ray and neutrino factories.

All galaxies are expected to contain supermassive black holes at their centres. When matter falls into a black hole, a huge amount of gravitational energy is released. This process heats the gas, forming high-temperature plasma. The temperature can reach as high as tens of billions of Celsius degrees for low-accreting black holes because of inefficient cooling, and the plasma can generate gamma rays in the megaelectron volt range. Such mellow black holes are dim as individual objects, but they are numerous in the Universe. The research team found that the resulting gamma rays from low-accreting supermassive black holes may contribute significantly to the observed gamma rays in the megaelectron volt range. In the plasma, protons can be accelerated to energies roughly 10,000 times higher than those achieved by the Large Hadron Collider -- the largest human-made particle accelerator. The sped-up protons produce high-energy neutrinos through interactions with matter and radiation, which can account for the higher-energy part of the cosmic neutrino data. This picture can be applied to active black holes as demonstrated by previous research. The supermassive black holes including both active and non-active galactic nuclei can explain a large fraction of the observed IceCube neutrinos in a wide energy range.


HAVE SCIENTISTS DETECTED DARK ENERGY?
University of Cambridge

Dark energy, the mysterious force that causes the Universe to accelerate, may have been responsible for unexpected results from the XENON1T experiment, deep below Italy's Apennine Mountains. A new study suggests that some unexplained results from the XENON1T experiment in Italy may have been caused by dark energy, and not the dark matter the experiment was designed to detect. Scientist constructed a physical model to help explain the results, which may have originated from dark energy particles produced in a region of the Sun with strong magnetic fields, although future experiments will be required to confirm this explanation. The researchers say their study could be an important step toward the direct detection of dark energy. Everything our eyes can see in the skies and in our everyday world -- from tiny moons to massive galaxies, from ants to blue whales -- makes up less than five percent of the Universe. The rest is dark. About 27% is dark matter -- the invisible force holding galaxies and the cosmic web together -- while 68% is dark energy, which causes the Universe to expand at an accelerated rate. Despite both components being invisible, we know a lot more about dark matter, since its existence was suggested as early as the 1920s, while dark energy wasn't discovered until 1998. Large-scale experiments like XENON1T have been designed to directly detect dark matter, by searching for signs of dark matter 'hitting' ordinary matter, but dark energy is even more elusive. To detect dark energy, scientists generally look for gravitational interactions: the way gravity pulls objects around. And on the largest scales, the gravitational effect of dark energy is repulsive, pulling things away from each other and making the Universe's expansion accelerate.

About a year ago, the XENON1T experiment reported an unexpected signal, or excess, over the expected background. At the time, the most popular explanation for the excess were axions -- hypothetical, extremely light particles -- produced in the Sun. However, this explanation does not stand up to observations, since the amount of axions that would be required to explain the XENON1T signal would drastically alter the evolution of stars much heavier than the Sun, in conflict with what we observe. We are far from fully understanding what dark energy is, but most physical models for dark energy would lead to the existence of a so-called fifth force. There are four fundamental forces in the Universe, and anything that can't be explained by one of these forces is sometimes referred to as the result of an unknown fifth force. However, we know that Einstein's theory of gravity works extremely well in the local universe. Therefore, any fifth force associated to dark energy is unwanted and must be 'hidden' or 'screened' when it comes to small scales, and can only operate on the largest scales where Einstein's theory of gravity fails to explain the acceleration of the Universe. To hide the fifth force, many models for dark energy are equipped with so-called screening mechanisms, which dynamically hide the fifth force. The team constructed a physical model, which used a type of screening mechanism known as chameleon screening, to show that dark energy particles produced in the Sun's strong magnetic fields could explain the XENON1T excess. The chameleon screening shuts down the production of dark energy particles in very dense objects, avoiding the problems faced by solar axions. It also allows us to decouple what happens in the local very dense Universe from what happens on the largest scales, where the density is extremely low. The researchers used their model to show what would happen in the detector if the dark energy was produced in a particular region of the Sun, called the tachocline, where the magnetic fields are particularly strong. Their calculations suggest that experiments like XENON1T, which are designed to detect dark matter, could also be used to detect dark energy. However, the original excess still needs to be convincingly confirmed. If the excess was the result of dark energy, upcoming upgrades to the XENON1T experiment, as well as experiments pursuing similar goals such as LUX-Zeplin and PandaX-xT, mean that it could be possible to directly detect dark energy within the next decade.


ASTROPHYSICISTS SOLVE 'EMPTY SKY' GAMMA RAY MYSTERY
Australian National University

Star-forming galaxies are responsible for creating gamma-rays that until now had not been associated with a known origin, researchers have confirmed. until now it has been unclear what created gamma-rays -- one of the most energetic forms of light in the Universe -- that appear in patches of seemingly 'empty sky'. The discovery could offer clues to help astronomers solve other mysteries of the Universe, such as what kind of particles make up Dark Matter -- one of the holy grails of astrophysics. There are two obvious sources that produce large amounts of gamma-rays seen in the Universe. One when gas falls into the supermassive black holes which are found at the centres of all galaxies -- called an active galactic nucleus (AGN) -- and the other associated with star formation in the disks of galaxies. The team modelled the gamma-ray emission from all the galaxies in the Universe and compared our results with the predictions for other sources and found that it is star-forming galaxies that produce the majority of this diffuse gamma-ray radiation and not the AGN process. Researchers were able to pinpoint what created these mysterious gamma-rays after obtaining a better understanding of how cosmic rays -- particles that travel at speeds very close to the speed of light -- move through the gas between the stars. Cosmic rays are important because they create large amounts of gamma-ray emission in star-forming galaxies when they collide with the interstellar gas. Data from NASA's Hubble Space Telescope and Fermi Gamma-Ray Space Telescope was a key resource used to uncover the unknown origins of the gamma-rays. Researchers analysed information about many galaxies such as their star-formation rates, total masses, physical size and distances from Earth. The model can also be used to make predictions for radio emission -- the electromagnetic radiation that has a frequency similar to a car radio -- from star-forming


PART OF UNIVERSE’S MISSING MATTER FOUND
CNRS

An international team4successfully used the MUSE instrument to generate a detailed map of the galactic wind driving exchanges between a young galaxy in formation and a nebula (a cloud of gas and interstellar dust). The team chose to observe galaxy Gal1 due to the proximity of a quasar, which served as a "lighthouse" for the scientists by guiding them toward the area of study. They also planned to observe a nebula around this galaxy, although the success of this observation was initially uncertain, as the nebula's luminosity was unknown. The perfect positioning of the galaxy and the quasar, as well as the discovery of gas exchange due to galactic winds, made it possible to draw up a unique map. This enabled the first observation of a nebula in formation that is simultaneously emitting and absorbing magnesium -- some of the Universe's missing baryons -- with the Gal1 galaxy. This type of normal matter nebula is known in the near Universe, but their existence for young galaxies in formation had only been supposed. Scientists thus discovered some of the Universe's missing baryons, thereby confirming that 80-90% of normal matter is located outside of galaxies, an observation that will help expand models for the evolution of galaxies.



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