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Early September Astronomy Bulletin
« on: September 05, 2021, 09:38 »
JAMES WEBB TELESCOPE TESTED

NASA/STIC

After successful completion of its final tests, NASA’s James Webb Space Telescope is being prepped for shipment to its launch site. Engineering teams have completed Webb’s long-spanning comprehensive testing regimen at Northrop Grumman’s facilities. Webb’s many tests and checkpoints were designed to ensure that the world’s most complex space science observatory will operate as designed once in space. Now that observatory testing has concluded, shipment operations have begun. This includes all the necessary steps to prepare Webb for a safe journey through the Panama Canal to its launch location in Kourou, French Guiana, on the northeastern coast of South America. Since no more large-scale testing is required, Webb’s clean room technicians have shifted their focus from demonstrating it can survive the harsh conditions of launch and work in orbit, to making sure it will safely arrive at the launch pad. Webb’s contamination control technicians, transport engineers, and logistics task forces are all expertly prepared to handle the unique task of getting Webb to the launch site. Shipping preparations will be completed in September. While shipment operations are underway, teams at the Space Telescope Science Institute (STScI) in Baltimore will continue to check and recheck the complex communications network it will use in space. Recently this network fully demonstrated that it is capable of seamlessly sending commands to the spacecraft.

Once Webb arrives in French Guiana, launch processing teams will configure the observatory for flight. This involves post-shipment checkouts to ensure the observatory hasn’t been damaged during transport, carefully loading the spacecraft’s propellant tanks with hydrazine fuel and nitrogen tetroxide oxidizer it will need to power its rocket thrusters to maintain its orbit, and detaching ‘remove before flight’ red-tag items like protective covers that keep important components safe during assembly, testing, and transport. Then engineering teams will mate the observatory to its launch vehicle, an Ariane 5 rocket provided by ESA (European Space Agency), before it rolls out to the launch pad. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency. After launch, Webb will undergo a six-month commissioning period. Moments after completing a 26-minute ride aboard the Ariane 5 launch vehicle, the spacecraft will separate from the rocket and its solar array will deploy automatically. After that, all subsequent deployments over the next few weeks will be initiated from ground control located at STScI. Webb will take one month to fly to its intended orbital location in space nearly one million miles away from Earth, slowly unfolding as it goes. Sunshield deployments will begin a few days after launch, and each step can be controlled expertly from the ground, giving Webb’s launch full control to circumnavigate any unforeseen issues with deployment. Once the sunshield starts to deploy, the telescope and instruments will enter shade and start to cool over time. Over the ensuing weeks, the mission team will closely monitor the observatory’s cooldown, managing it with heaters to control stresses on instruments and structures. In the meantime, the secondary mirror tripod will unfold, the primary mirror will unfold, Webb’s instruments will slowly power up, and thruster firings will insert the observatory into a prescribed orbit. Once the observatory has cooled down and stabilized at its frigid operating temperature, several months of alignments to its optics and calibrations of its scientific instruments will occur. Scientific operations are expected to com/mence approximately six months after launch.

WILL IT BE SAFE TO FLY TO MARS?

University of California - Los Angeles

Sending human travellers to Mars would require scientists and engineers to overcome a range of technological and safety obstacles. One of them is the grave risk posed by particle radiation from the Sun, distant stars and galaxies. Answering two key questions would go a long way toward overcoming that hurdle: Would particle radiation pose too grave a threat to human life throughout a round trip to the red planet? And, could the very timing of a mission to Mars help shield astronauts and the spacecraft from the radiation? A team of space scientists answers those two questions with a "no" and a "yes." That is, humans should be able to safely travel to and from Mars, provided that the spacecraft has sufficient shielding and the round trip is shorter than approximately four years. And the timing of a human mission to Mars would indeed make a difference: The scientists determined that the best time for a flight to leave Earth would be when solar activity is at its peak, known as the solar maximum. The scientists' calculations demonstrate that it would be possible to shield a Mars-bound spacecraft from energetic particles from the Sun because, during solar maximum, the most dangerous and energetic particles from distant galaxies are deflected by the enhanced solar activity. A trip of that length would be conceivable. The average flight to Mars takes about nine months, so depending on the timing of launch and available fuel, it is plausible that a human mission could reach the planet and return to Earth in less than two years. The study shows that while space radiation imposes strict limitations on how heavy the spacecraft can be and the time of launch, and it presents technological difficulties for human missions to Mars, such a mission is viable.

The researchers recommend a mission not longer than four years because a longer journey would expose astronauts to a dangerously high amount of radiation during the round trip -- even assuming they went when it was relatively safer than at other times. They also report that the main danger to such a flight would be particles from outside of our solar system. Researchers combined geophysical models of particle radiation for a solar cycle with models for how radiation would affect both human passengers -- including its varying effects on different bodily organs -- and a spacecraft. The modelling determined that having a spacecraft's shell built out of a relatively thick material could help protect astronauts from radiation, but that if the shielding is too thick, it could actually increase the amount of secondary radiation to which they are exposed. The two main types of hazardous radiation in space are solar energetic particles and galactic cosmic rays; the intensity of each depends on solar activity. Galactic cosmic ray activity is lowest within the six to 12 months after the peak of solar activity, while solar energetic particles' intensity is greatest during solar maximum.

INTERSTELLAR COMETS MAY NOT BE RARE

Harvard-Smithsonian Center for Astrophysics

In 2019, astronomers discovered a comet from another star system. Named Borisov, the icy snowball travelled 110,000 miles per hour and marked the first and only interstellar comet ever detected by humans. But what if these interstellar visitors -- comets, meteors, asteroids and other debris from beyond our solar system -- are more common than we think? In a new study, astronomers present new calculations showing that in the Oort Cloud -- a shell of debris in the farthest reaches of our solar system -- interstellar objects outnumber objects belonging to our solar system. The calculations, made using conclusions drawn from Borisov, include significant uncertainties, But even after taking these into consideration, interstellar visitors prevail over objects that are native to the solar system. But if there are so many interstellar visitors, why have we only ever seen one? We just don't have the technology to see them yet. Consider that the Oort Cloud spans a region some 200 billion to 10 trillion miles away from our Sun -- and unlike stars, objects in the Oort Cloud don't produce their own light. Those two factors make debris in the outer solar system incredibly hard to see. These results suggest that the abundances of interstellar and Oort cloud objects are comparable closer to the Sun than Saturn. This can be tested with current and future solar system surveys. When looking at the asteroid data in that region, the question is: are there asteroids that really are interstellar that we just didn't recognize before? Astronomers explain that there are some asteroids that get detected but aren't observed or followed up on year after year. We think they are asteroids, then we lose them without doing a detailed look.

Interstellar objects in the planetary region of the solar system would be rare, but the results clearly show they are more common than solar system material in the dark reaches of the Oort cloud. Observations with next-generation technology may help confirm the team's results. The launch of the Vera C. Rubin Observatory, slated for 2022, will "blow previous searches for interstellar objects out of the water and hopefully help detect many more visitors like Borisov. The Transneptunian Automated Occultation Survey (TAOS II), which is specifically designed to detect comets in the far reaches of our solar system, may also be able to detect one of these passersby. TAOS II may come online as early as this year. The abundance of interstellar objects in the Oort Cloud suggests that much more debris is left over from the formation of planetary systems than previously thought. The findings show that interstellar objects can place interesting constraints on planetary system formation processes, since their implied abundance requires a significant mass of material to be ejected in the form of planetesimals. Together with observational studies of protoplanetary disks and computational approaches to planet formation, the study of interstellar objects could help us unlock the secrets of how our planetary system -- and others -- formed.

UNRAVELLING THE MYSTERY OF BROWN DWARFS

Université de Genève

Brown dwarfs are astronomical objects with masses between those of planets and stars. The question of where exactly the limits of their mass lie remains a matter of debate, especially since their constitution is very similar to that of low-mass stars. So how do we know whether we are dealing with a brown dwarf or a very low mass star? An international team has identified five objects that have masses near the border separating stars and brown dwarfs that could help scientists understand the nature of these mysterious objects. Like Jupiter and other giant gas planets, stars are mainly made of hydrogen and helium. But unlike gas planets, stars are so massive and their gravitational force so powerful that hydrogen atoms fuse to produce helium, releasing huge amounts of energy and light. Brown dwarfs, on the other hand, are not massive enough to fuse hydrogen and therefore cannot produce the enormous amount of light and heat of stars. Instead, they fuse relatively small stores of a heavier atomic version of hydrogen: deuterium. This process is less efficient and the light from brown dwarfs is much weaker than that from stars. This is why scientists often refer to them as 'failed stars'. However, we still do not know exactly where the mass limits of brown dwarfs lie, limits that allow them to be distinguished from low-mass stars that can burn hydrogen for many billions of years, whereas a brown dwarf will have a short burning stage and then a colder life. These limits vary depending on the chemical composition of the brown dwarf, for example, or the way it formed, as well as its initial radius. So far, astronomers have only accurately characterised about 30 brown dwarfs. Compared to the hundreds of planets that astronomers know in detail, this is very few. All the more so if one considers that their larger size makes brown dwarfs easier to detect than planets.

The team characterized five companions that were originally identified with the Transiting Exoplanet Survey Satellite (TESS) as TESS objects of interest (TOI) -- TOI-148, TOI-587, TOI-681, TOI-746 and TOI-1213. These are called 'companions' because they orbit their respective host stars. They do so with periods of 5 to 27 days, have radii between 0.81 and 1.66 times that of Jupiter and are between 77 and 98 times more massive. This places them on the borderline between brown dwarfs and stars. These five new objects therefore contain valuable information. One of the clues the scientists found to show these objects are brown dwarfs is the relationship between their size and age. Brown dwarfs are supposed to shrink over time as they burn up their deuterium reserves and cool down. Here the team found that the two oldest objects, TOI 148 and 746, have a smaller radius, while the two younger companions have larger radii. Yet these objects are so close to the limit that they could just as easily be very low-mass stars, and astronomers are still unsure whether they are brown dwarfs. Even with these additional objects, they still lack the numbers to draw definitive conclusions about the differences between brown dwarfs and low-mass stars.

NEW CLASS OF HABITABLE PLANETS

University of Cambridge

A new class of exoplanet very different to our own, but which could support life, has been identified by astronomers, which could greatly accelerate the search for life outside our Solar System. In the search for life elsewhere, astronomers have mostly looked for planets of a similar size, mass, temperature and atmospheric composition to Earth. However, astronomers from the University of Cambridge believe there are more promising possibilities out there. The researchers have identified a new class of habitable planets, dubbed 'Hycean' planets -- hot, ocean-covered planets with hydrogen-rich atmospheres -- which are more numerous and observable than Earth-like planets.  The researchers say the results could mean that finding biosignatures of life outside our Solar System within the next two or three years is a real possibility. Many of the prime Hycean candidates identified by the researchers are bigger and hotter than Earth, but still have the characteristics to host large oceans that could support microbial life similar to that found in some of Earth's most extreme aquatic environments. These planets also allow for a far wider habitable zone, or 'Goldilocks zone', compared to Earth-like planets. This means that they could still support life even though they lie outside the range where a planet similar to Earth would need to be in order to be habitable. Thousands of planets outside our Solar System have been discovered since the first exoplanet was identified nearly 30 years ago. The vast majority are planets between the sizes of Earth and Neptune and are often referred to as 'super-Earths' or 'mini-Neptunes': they can be predominantly rocky or ice giants with hydrogen-rich atmospheres, or something in between. Most mini-Neptunes are over 1.6 times the size of Earth: smaller than Neptune but too big to have rocky interiors like Earth. Earlier studies of such planets have found that the pressure and temperature beneath their hydrogen-rich atmospheres would be too high to support life. However, a recent study on the mini-Neptune K2-18b found that in certain conditions these planets could support life. The result led to a detailed investigation into the full range of planetary and stellar properties for which these conditions are possible, which known exoplanets may satisfy those conditions, and whether their biosignatures may be observable.

The investigation led the researchers to identify a new class of planets, Hycean planets, with massive planet-wide oceans beneath hydrogen-rich atmospheres. Hycean planets can be up to 2.6 times larger than Earth and have atmospheric temperatures up to nearly 200 degrees Celsius, but their oceanic conditions could be similar to those conducive for microbial life in Earth's oceans. Such planets also include tidally locked 'dark' Hycean worlds that may have habitable conditions only on their permanent night sides, and 'cold' Hycean worlds that receive little radiation from their stars. Planets of this size dominate the known exoplanet population, although they have not been studied in nearly as much detail as super-Earths. Hycean worlds are likely quite common, meaning that the most promising places to look for life elsewhere in the Galaxy may have been hiding in plain sight. However, size alone is not enough to confirm whether a planet is Hycean: other aspects such as mass, temperature and atmospheric properties are required for confirmation. When trying to determine what the conditions are like on a planet many light years away, astronomers first need to determine whether the planet lies in the habitable zone of its star, and then look for molecular signatures to infer the planet's atmospheric and internal structure, which govern the surface conditions, presence of oceans and potential for life. Astronomers also look for certain biosignatures which could indicate the possibility of life. Most often, these are oxygen, ozone, methane and nitrous oxide, which are all present on Earth. There are also a number of other biomarkers, such as methyl chloride and dimethyl sulphide, that are less abundant on Earth but can be promising indicators of life on planets with hydrogen-rich atmospheres where oxygen or ozone may not be as abundant. The team identified a sizeable sample of potential Hycean worlds which are prime candidates for detailed study with next-generation telescopes, such as the James Webb Space Telescope (JWST), which is due to be launched later this year. These planets all orbit red dwarf stars between 35-150 light years away: close by astronomical standards. Planned JWST observations of the most promising candidate, K2-18b, could lead to the detection of one or more biosignature molecules.



ORIGIN OF MILKY WAY’S COSMIC RAYS

Nagoya University

Astronomers have succeeded for the first time in quantifying the proton and electron components of cosmic rays in a supernova remnant. At least 70% of the very-high-energy gamma rays emitted from cosmic rays are due to relativistic protons, according to the novel imaging analysis of radio, X-ray, and gamma-ray radiation. The acceleration site of protons, the main components of cosmic rays, has been a 100-year mystery in modern astrophysics, this is the first time that the amount of cosmic rays being produced in a supernova remnant has been quantitatively shown and is an epoch-making step in the elucidation of the origin of cosmic rays. The origin of cosmic rays, the particles with the highest energy in the Universe, has been a great mystery since their discovery in 1912. Because cosmic rays promote the chemical evolution of interstellar matter, understanding their origin is critical in understanding the evolution of our Galaxy. The cosmic rays are thought to be accelerated by supernova remnants (the after-effects of supernova explosions) in our Galaxy and travelled to the Earth at almost the speed of light. Recent progress in gamma-ray observations has revealed that many supernova remnants emit gamma-rays at teraelectronvolts (TeV) energies. If gamma rays are produced by protons, which are the main component of cosmic rays, then the supernova remnant origin of cosmic rays can be verified. However, gamma rays are also produced by electrons, it is necessary to determine whether the proton or electron origin is dominant, and to measure the ratio of the two contributions. The results of this study provide compelling evidence of gamma rays originating from the proton component, which is the main component of cosmic rays, and clarify that Galactic cosmic rays are produced by supernova remnants.

The originality of this research is that gamma-ray radiation is represented by a linear combination of proton and electron components. Astronomers knew a relation that the intensity of gamma-ray from protons is proportional to the interstellar gas density obtained by radio-line imaging observations. On the other hand, gamma-rays from electrons are also expected to be proportional to X-ray intensity from electrons. Therefore, they expressed the total gamma-ray intensity as the sum of two gamma-ray components, one from the proton origin and the other from the electron origin. This led to a unified understanding of three independent observables. This method was first proposed in this study. As a result, it was shown that gamma rays from protons and electrons account for 70% and 30% of the total gamma-rays, respectively. This is the first time that the two origins have been quantified. The results also demonstrate that gamma rays from protons are dominated in interstellar gas-rich regions, whereas gamma rays from electrons are enhanced in the gas-poor region. This confirms that the two mechanisms work together and supporting the predictions of previous theoretical studies.

HOW YOUNG GALAXIES GROW UP AND MATURE

Lund University

Using a supercomputer simulation, a research team in Sweden has succeeded in following the development of a galaxy over a span of 13.8 billion years. The study shows how, due to interstellar frontal collisions, young and chaotic galaxies over time mature into spiral galaxies such as the Milky Way. Soon after the Big Bang 13.8 billion years ago, the Universe was an unruly place. Galaxies constantly collided. Stars formed at an enormous rate inside gigantic gas clouds. However, after a few billion years of intergalactic chaos, the unruly, embryonic galaxies became more stable and over time matured into well-ordered spiral galaxies. The exact course of these developments has long been a mystery to the world's astronomers. However, in a new study, researchers have been able to provide some clarity on the matter. Astronomers use the Milky Way's stars as a starting point. The stars act as time capsules that divulge secrets about distant epochs and the environment in which they were formed. Their positions, speeds and amounts of various chemical elements can therefore, with the assistance of computer simulations, help us understand how our own galaxy was formed. They have discovered that when two large galaxies collide, a new disc can be created around the old one due to the enormous inflows of star-forming gas. Our simulation shows that the old and new discs slowly merged over a period of several billion years. This is something that not only resulted in a stable spiral galaxy, but also in populations of stars that are similar to those in the Milky Way. The new findings will help astronomers to interpret current and future mappings of the Milky Way. The study points to a new direction for research in which the main focus will be on the interaction between large galaxy collisions and how spiral galaxies' discs are formed. The research team in Lund has already started new super computer simulations in cooperation with the research infrastructure PRACE (Partnership for Advanced Computing in Europe).

NEUTRONS MAY ACTUALLY 'TALK' TO ONE ANOTHER

University of Chicago

Scientists have proposed a new theory that neutrons might communicate under certain circumstances, forming a new sort of ‘unparticle’—which could offer evidence of a new kind of symmetry in physics. Even though neutrons love to partner with protons to make the nucleus of an atom, the particles have always been notorious for their reluctance to bind with each other. But according to a new proposed theory, these particles might communicate under certain circumstances, forming a new sort of 'unparticle'—which could offer evidence of a new kind of symmetry in physics.  Dam Thanh Son, the University Professor of Physics at the University of Chicago, laid out the argument in a study published in Proceedings of the National Academy of Sciences, which he co-authored with Hans-Werner Hammer of the Technical University of Darmstadt in Germany. The new study was inspired by an idea first proposed in 2007 by Harvard University professor Howard Georgi, who suggested that there could be a phenomenon beyond our traditional idea of matter. Son and Hammer wanted to try applying this concept to understand the behaviour of particles in the nuclei of atoms—especially more exotic nuclei, which wink in and out existence during violent events in the Universe, such as when stars explode. To study these exotic atomic nuclei on Earth, scientists smash heavy nuclei into each other in accelerators. What comes out is a new nucleus, and a shower of neutrons. Son and Hammer observed that as the neutrons stream out and away, a few that are going in the same direction may continue to "talk" to one another—even after the others have stopped interacting. This sustained communication between neutrons could constitute a fuzzy "unnucleus," with its own properties distinct from normal nuclei.

It's a bit like the difference between being hit by a stone, and being hit by a stream of water. Both carry energy, but the form is different. In their new study, Son and Hammer laid out how and where to look for evidence of these "unnuclei" in accelerators, and a general explanation for the field of what they playfully called "unnuclear physics." This could be a manifestation, the scientists said, of a type of symmetry called conformal symmetry. Symmetries are fundamental to modern physics; they are common features that remain even as a system changes—the most famous being that the speed of light is constant throughout the Universe. In conformal symmetry, a space distorted, but all angles are kept unchanged. For example, when one draws a 2D map of the entire 3D Earth, it is impossible to preserve all distances and angles at the same time. However, some maps, such as a common version first drawn by Gerardus Mercator, are drawn so that all angles remain correct, but at the cost of greatly distorting the distances near the poles. Because the calculations are so robust even if some details are missing, Son said that if the argument is confirmed, physicists might be able to use these formulas to check other calculations. He and Hammer also noted that this behaviour may occur when atoms are cooled to super-low temperatures, and in exotic particles called tetraquarks, made up of two quarks and two antiquarks.


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