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Late May Astronomy Bulletin
« on: May 30, 2021, 07:59 »
ALIEN RADIOACTIVE ELEMENT PROMPTS RETHINK

Australian National University

The first-ever discovery of an extraterrestrial radioactive isotope on Earth has scientists rethinking the origins of the elements on our planet. The tiny traces of plutonium-244 were found in ocean crust alongside radioactive iron-60. The two isotopes are evidence of violent cosmic events in the vicinity of Earth millions of years ago. Star explosions, or supernovae create many of the heavy elements in the periodic table, including those vital for human life, such as iron, potassium and iodine. To form even heavier elements, such as gold, uranium and plutonium it was thought that a more violent event may be needed, such as two neutron stars merging. However, a new study suggests a more complex picture. Any plutonium-244 and iron-60 that existed when the Earth formed from interstellar gas and dust over four billion years ago has long since decayed, so current traces of them must have originated from recent cosmic events in space. The dating of the sample confirms two or more supernova explosions occurred near Earth. The data could be the first evidence that supernovae do indeed produce plutonium-244. Or perhaps it was already in the interstellar medium before the supernova went off, and it was pushed across the solar system together with the supernova ejecta. The VEGA accelerator at Australian Nuclear Science and Technology Organisation, (ANSTO) in Sydney was used to identify the tiny traces of the plutonium-244.

HEAVY METAL VAPOURS FOUND IN COMETS

ESO

A new study using data from the European Southern Observatory’s Very Large Telescope (ESO’s VLT) has shown that iron and nickel exist in the atmospheres of comets throughout our Solar System, even those far from the Sun. A separate study who also used ESO data, reported that nickel vapour is also present in the icy interstellar comet 2I/Borisov. This is the first time heavy metals, usually associated with hot environments, have been found in the cold atmospheres of distant comets. Astronomers know that heavy metals exist in comets’ dusty and rocky interiors. But, because solid metals don’t usually “sublimate” (become gaseous) at low temperatures, they did not expect to find them in the atmospheres of cold comets that travel far from the Sun. Nickel and iron vapours have now even been detected in comets observed at more than 480 million kilometres from the Sun, more than three times the Earth-Sun distance. One team found iron and nickel in comets’ atmospheres in approximately equal amounts. Material in our Solar System, for example that found in the Sun and in meteorites, usually contains about ten times more iron than nickel. This new result therefore has implications for astronomers’ understanding of the early Solar System, though the team is still decoding what these are. While the Belgian team has been studying these “fossil” objects with ESO’s VLT for nearly 20 years, they had not spotted the presence of nickel and iron in their atmospheres until now. The team used data from the Ultraviolet and Visual Echelle Spectrograph (UVES) instrument on ESO’s VLT, which uses spectroscopy, to analyse the atmospheres of comets at different distances from the Sun. This technique allows astronomers to reveal the chemical makeup of cosmic objects: each chemical element leaves a unique signature — a set of lines — in the spectrum of the light from the objects. The team had spotted weak, unidentified spectral lines in their UVES data and on closer inspection noticed that they were signalling the presence of neutral atoms of iron and nickel. A reason why the heavy elements were difficult to identify is that they exist in very small amounts: the team estimates that for each 100 kg of water in the comets’ atmospheres there is only 1 g of iron, and about the same amount of nickel.

Another remarkable study shows that heavy metals are also present in the atmosphere of the interstellar comet 2I/Borisov. A team in Poland observed this object, the first alien comet to visit our Solar System, using the X-shooter spectrograph on ESO’s VLT when the comet flew by about a year and a half ago. They found that 2I/Borisov’s cold atmosphere contains gaseous nickel. The finding is surprising because, before the two studies, gases with heavy metal atoms had only been observed in hot environments, such as in the atmospheres of ultra-hot exoplanets or evaporating comets that passed too close to the Sun. 2I/Borisov was observed when it was some 300 million kilometres away from the Sun, or about twice the Earth-Sun distance. Studying interstellar bodies in detail is fundamental to science because they carry invaluable information about the alien planetary systems they originate from. The two studies show that 2I/Borisov and Solar System comets have even more in common than previously thought.

STAR WILL COME WITHIN 24 LIGHT DAYS OF SUN

Universe Today

Within the Milky Way, there are an estimated 200 to 400 billion stars, all of which orbit around the centre of our galaxy in a coordinated cosmic dance. As they orbit, stars in the galactic disk (where our Sun is located) periodically shuffle about and get closer to one another. At times, this can have a drastic effect on the star that experience a close encounter, disrupting their systems and causing planets to be ejected. Knowing when stars will make a close encounter with our Solar System, and how it might shake-up objects within it, is therefore a concern to astronomers. Using data collected by the Gaia Observatory, two researchers with the Russian Academy of Sciences (RAS) determined that a handful of stars will be making close passes by our Solar System in the future, one of which will stray pretty close! The study relied on astrometric data from the Gaia mission’s Early Data Release 3 (EDR3), which revealed kinematic characteristics of stars that are expected to pass within 3.26 light-years (1 Parsec) with the Solar System in the future. To start things off simple: our Solar System is composed of eight designated planets and several minor (aka. dwarf) planets orbiting our main sequence G-type yellow dwarf Sun, which is surrounded by outer ring of icy objects known as the Kuiper Belt. Beyond this, at a distance of roughly light-years from the Sun (0.5 parsecs), is a massive cloud of icy debris known as the Oort Cloud, which is where long-period comets originate.

These comets are generally the result of objects making close flybys with the Solar System and knocking objects loose, to the point that they periodically fly through Solar System and around the Sun before heading back out. The outer edge of the Oort Cloud is estimated to be 0.5 parsecs (1.6 light-years) from our Sun, which makes them particularly responsive to perturbations from a number of sources. For astronomers, the process of searching for stars that may have flown by our Solar System in the past (and which may pass us by in the future) began in the 1960s. The research has improved as more sophisticated instruments have become available, leading to more detailed catalogues on nearby celestial objects. In order to know which stars will make a close encounter, you need to know their distance and their three velocities. These consist the two properties of proper motion – right ascension, declination – and radial velocity. Once you have all that, you can conduct astrometry, which is the precise measurement of the positions and movements of stars and other celestial bodies. It was for this very purpose that the ESA’s Hipparcos satellite (1989-1993) and Gaia Observatory (2013-present) were created. Thanks to the precise data they have provided, and the updated catalogues on millions of stars and other celestial objects, astronomers are able to determine which of them are likely to make a close encounter in the future.

In the end, one star, designated 4270814637616488064 in the Gaia EDR3 database, will be making a particularly close encounter a little over a million years from now. Better-known as Gliese 710 (HIP 89825), this variable K-type orange dwarf star is about 60% as massive as our Sun and located some 62 light years from Earth in the Serpens constellation. The showed that Gliese 710 would be making its close flyby 1.32 million years from now and would pass within 0.20 parsecs (0.65 light-years) of our Sun. So, assuming human beings (or their genetic progeny) are still living in the Solar System 2.32 million years from now, they will be treated to some added comet activity. This could pose some hazards, depending on the trajectories of these comets and the extent of human infrastructure in space. Or it could just mean more opportunities for backyard astronomy, or whatever the futuristic equivalent is.

NOVA BECOMES MUCH BRIGHTER

National Astronomical Observatory of Japan

A new star named V1405 Cas Nova which was discovered by an amateur astronomer in Japan has kept growing brighter over two months and it can be spotted with the naked eye now. Nakamura Yuji of the city of Kameyama in Mie Prefecture in central Japan found the star on March18. It is in the direction of Cassiopeia. It had increased its brightness 50-fold to a star magnitude level of five by May 9. Less than 20 new stars are found every year but most of them grow darker after growing brighter for several days. Experts say that it is rare that a new star grows brighter for a few months and becomes bright enough to be seen without a telescope. Astronomers believe that a major explosive phenomenon occurred on the surface of the star. It’s a very rare and interesting phenomenon and researchers hope that many people will be encouraged to look up to the night sky and stars.

HOW AND WHEN MILKY WAY CAME TOGETHER

Ohio State University

New research provides the best evidence to date into the timing of how our early Milky Way came together, including the merger with a key satellite galaxy. Using relatively new methods in astronomy, the researchers were able to identify the most precise ages currently possible for a sample of about a hundred red giant stars in the galaxy. With this and other data, the researchers were able to show what was happening when the Milky Way merged with an orbiting satellite galaxy, known as Gaia-Enceladus, about 10 billion years ago. Evidence suggests that when the merger occurred, the Milky Way had already formed a large population of its own stars, Many of those "homemade" stars ended up in the thick disc in the middle of the galaxy, while most that were captured from Gaia-Enceladus are in the outer halo of the galaxy. The merging event with Gaia-Enceladus is thought to be one of the most important in the Milky Way's history, shaping how we observe it today. By calculating the age of the stars, the researchers were able to determine, for the first time, that the stars captured from Gaia-Enceladus have similar or slightly younger ages compared to the majority of stars that were born inside the Milky Way. A violent merger between two galaxies can't help but shake things up. Results showed that the merger changed the orbits of the stars already in the galaxy, making them more eccentric.

Astronomers compared the stars' movements to a dance, where the stars from the former Gaia-Enceladus move differently than those born within the Milky Way. The stars even "dress" differently, with stars from outside showing different chemical compositions from those born inside the Milky Way. The researchers used several different approaches and data sources to conduct their study. One way the researchers were able to get such precise ages of the stars was through the use of asteroseismology, a relatively new field that probes the internal structure of stars. Asteroseismologists study oscillations in stars, which are sound waves that ripple through their interiors. That allows us to get very precise ages for the stars, which are important in determining the chronology of when events happened in the early Milky Way. The study also used a spectroscopic survey, called APOGEE, which provides the chemical composition of stars -- another aid in determining their ages. Astronomers now intend to apply this approach to larger samples of stars, and to include even more subtle features of the frequency spectra. This will eventually lead to a much sharper view of the Milky Way's assembly history and evolution, creating a timeline of how our galaxy developed.

DOES THE MILKY WAY MOVE LIKE A SPINNING TOP?

Instituto de Astrofísica de Canarias (IAC)

An investigation questions one of the most interesting findings about the dynamics of the Milky Way in recent years: that the precession, or the wobble in the axis of rotation of the disc warp is incorrect. The Milky Way is a spiral galaxy, which means that it is composed, among other components, of a disc of stars, gas and dust, in which the spiral arms are contained. At first, it was thought that the disc was completely flat, but for some decades now it is known that the outermost part of the disc is distorted into what is called a "warp": in one direction it is twisted upwards, and in the opposite direction downwards. The stars, the gas, and the dust are all warped, and so are not in the same plane as the extended inner part of the disc, and an axis perpendicular to the planes of the warp defines their rotation. In 2020, an investigation announced the detection of the precession of the warp of the Milky Way disc, which means that the deformation in this outer region is not static, but that just like a spinning top the orientation of its axis is itself rotating with time. Furthermore, these researchers found that it was quicker than the theories predicted, a cycle every 600-700 million years, some three times the time it takes the Sun to travel once round the centre of the Galaxy. Precession is not a phenomenon which occurs only in galaxies, it also happens to our planet. As well as its annual revolution around the Sun, and its rotation period of 24 hours, the axis of the Earth precesses, which implies that the celestial pole is not always close to the present pole star, but that (as an example) 14,000 years ago it was close to the star Vega.

Now, a new study has taken into account the variation of the amplitude of the warp with the ages of the stars. The study concludes that, using the warp of the old stars whose velocities have been measured, it is possible that the precession can disappear, or at least become slower than what is presently believed. To arrive at this result the researchers have used data from the Gaia Mission of the European Space Agency (ESA), analysing the positions and velocities of hundreds of millions of stars in the outer disc. In previous studies it had not been noticed that the stars which are a few tens of millions of years old, such as the Cepheids, have a much larger warp than that of the stars visible with the Gaia mission, which are thousands of millions of years old. "This does not necessarily mean that the warp does not precess at all, it could do so, but much more slowly, and we are probably unable to measure this motion until we obtain better data.



36 DWARF GALAXIES HAD SIMULTANEOUS 'BABY BOOM'

Rutgers University

Three dozen dwarf galaxies far from each other had a simultaneous "baby boom" of new stars, an unexpected discovery that challenges current theories on how galaxies grow and may enhance our understanding of the Universe. Galaxies more than 1 million light-years apart should have completely independent lives in terms of when they give birth to new stars. But galaxies separated by up to 13 million light-years slowed down and then simultaneously accelerated their birth rate of stars. It appears that these galaxies are responding to a large-scale change in their environment in the same way a good economy can spur a baby boom. Regardless of whether these galaxies were next-door neighbours or not, they stopped and then started forming new stars at the same time, as if they'd all influenced each other through some extra-galactic social network. The simultaneous decrease in the stellar birth rate in the 36 dwarf galaxies began 6 billion years ago, and the increase began 3 billion years ago. Understanding how galaxies evolve requires untangling the many processes that affect them over their lifetimes (billions of years). Star formation is one of the most fundamental processes. The stellar birth rate can increase when galaxies collide or interact, and galaxies can stop making new stars if the gas (mostly hydrogen) that makes stars is lost.

Star formation histories can paint a rich record of environmental conditions as a galaxy "grew up." Dwarf galaxies are the most common but least massive type of galaxies in the Universe, and they are especially sensitive to the effects of their surrounding environment. The 36 dwarf galaxies included a diverse array of environments at distances as far as 13 million light-years from the Milky Way. The environmental change the galaxies apparently responded to must be something that distributes fuel for galaxies very far apart. That could mean encountering a huge cloud of gas, for example, or a phenomenon in the Universe we don't yet know about. The scientists used two methods to compare star formation histories. One uses light from individual stars within galaxies; the other uses the light of a whole galaxy, including a broad range of colours. The full impact of the discovery is not yet known as it remains to be seen how much our current models of galaxy growth need to be modified to understand this surprise. If the result cannot be explained within our current understanding of cosmology, that would be a huge implication

HUBBLE TRACKS DOWN FAST RADIO BURSTS

NASA/Goddard Space Flight Center

Astronomers using the Hubble Space Telescope have traced the locations of five brief, powerful radio blasts to the spiral arms of five distant galaxies. Called fast radio bursts (FRBs), these extraordinary events generate as much energy in a thousandth of a second as the Sun does in a year. Because these transient radio pulses disappear in much less than the blink of an eye, researchers have had a hard time tracking down where they come from, much less determining what kind of object or objects is causing them. Therefore, most of the time, astronomers don't know exactly where to look. Locating where these blasts are coming from, and in particular, what galaxies they originate from, is important in determining what kinds of astronomical events trigger such intense flashes of energy. The new Hubble survey of eight FRBs helps researchers narrow the list of possible FRB sources. The first FRB was discovered in archived data recorded by the Parkes radio observatory on July 24, 2001. Since then astronomers have uncovered up to 1,000 FRBs, but they have only been able to associate roughly 15 of them to particular galaxies. In the Hubble study, astronomers not only pinned all of them to host galaxies, but they also identified the kinds of locations they originated from. Hubble observed one of the FRB locations in 2017 and the other seven in 2019 and 2020. The galaxies in the Hubble study existed billions of years ago. Astronomers, therefore, are seeing the galaxies as they appeared when the universe was about half its current age. Many of them are as massive as our Milky Way. The observations were made in ultraviolet and near-infrared light with Hubble's Wide Field Camera 3. Ultraviolet light traces the glow of young stars strung along a spiral galaxy's winding arms. The researchers used the near-infrared images to calculate the galaxies' mass and find where older populations of stars reside. The images display a diversity of spiral-arm structure, from tightly wound to more diffuse, revealing how the stars are distributed along these prominent features. A galaxy's spiral arms trace the distribution of young, massive stars. However, the Hubble images reveal that the FRBs found near the spiral arms do not come from the very brightest regions, which blaze with the light from hefty stars. The images help support a picture that the FRBs likely do not originate from the youngest, most massive stars.

These clues helped the researchers rule out some of the possible triggers of types of these brilliant flares, including the explosive deaths of the youngest, most massive stars, which generate gamma-ray bursts and some types of supernovae. Another unlikely source is the merger of neutron stars, the crushed cores of stars that end their lives in supernova explosions. These mergers take billions of years to occur and are usually found far from the spiral arms of older galaxies that are no longer forming stars. The team's Hubble results, however, are consistent with the leading model that FRBs originate from young magnetar outbursts. Magnetars are a type of neutron star with powerful magnetic fields. They're called the strongest magnets in the Universe, possessing a magnetic field that is 10 trillion times more powerful than a refrigerator door magnet. Astronomers last year linked observations of an FRB spotted in our Milky Way galaxy with a region where a known magnetar resides. Owing to their strong magnetic fields, magnetars are quite unpredictable. In this case, the FRBs are thought to come from flares from a young magnetar. Massive stars go through stellar evolution and becomes neutron stars, some of which can be strongly magnetized, leading to flares and magnetic processes on their surfaces, which can emit radio light. Our study fits in with that picture and rules out either very young or very old progenitors for FRBs. The observations also helped the researchers strengthen the association of FRBs with massive, star-forming galaxies. Previous ground-based observations of some possible FRB host galaxies did not as clearly detect underlying structure, such as spiral arms, in many of them. Astronomers, therefore, could not rule out the possibility that FRBs originate from a dwarf galaxy hiding underneath a massive one. In the new Hubble study, careful image processing and analysis of the images allowed researchers to rule out underlying dwarf galaxies. Although the Hubble results are exciting, the researchers say they need more observations to develop a more definitive picture of these enigmatic flashes and better pinpoint their source.

CHARTING EXPANSION OF UNIVERSE WITH SUPERNOVAE

National Institutes of Natural Sciences

An international research team analyzed a database of more than 1000 supernova explosions and found that models for the expansion of the Universe best match the data when a new time dependent variation is introduced. If proven correct with future, higher-quality data from the Subaru Telescope and other observatories, these results could indicate still unknown physics working on the cosmic scale. Edwin Hubble's observations over 90 years ago showing the expansion of the Universe remain a cornerstone of modern astrophysics. But when you get into the details of calculating how fast the Universe was expanding at different times in its history, scientists have difficulty getting theoretical models to match observations. To solve this problem, a team of researchers analysed a catalogue of 1048 supernovae which exploded at different times in the history of the Universe. The team found that the theoretical models can be made to match the observations if one of the constants used in the equations, appropriately called the Hubble constant, is allowed to vary with time. There are several possible explanations for this apparent change in the Hubble constant. A likely but boring possibility is that observational biases exist in the data sample. To help correct for potential biases, astronomers are using Hyper Suprime-Cam on the Subaru Telescope to observe fainter supernovae over a wide area. Data from this instrument will increase the sample of observed supernovae in the early Universe and reduce the uncertainty in the data. But if the current results hold-up under further investigation, if the Hubble constant is in fact changing, that opens the question of what is driving the change. Answering that question could require a new, or at least modified, version of astrophysics.



MOST ANCIENT SPIRAL GALAXY DISCOVERED

National Institutes of Natural Sciences

Analyzing data obtained with the Atacama Large Millimeter/submillimeter Array (ALMA), researchers found a galaxy with a spiral morphology by only 1.4 billion years after the Big Bang. This is the most ancient galaxy of its kind ever observed. The discovery of a galaxy with a spiral structure at such an early stage is an important clue to solving the classic questions of astronomy: "How and when did spiral galaxies form?" The Milky Way Galaxy, where we live, is a spiral galaxy. Spiral galaxies are fundamental objects in the Universe, accounting for as much as 70% of the total number of galaxies. However, other studies have shown that the proportion of spiral galaxies declines rapidly as we look back through the history of the Universe. So, when were the spiral galaxies formed? Researchers noticed a galaxy called BRI 1335-0417 in the ALMA Science Archive. The galaxy existed 12.4 billion years ago and contained a large amount of dust, which obscures the starlight. This makes it difficult to study this galaxy in detail with visible light. On the other hand, ALMA can detect radio emissions from carbon ions in the galaxy, which enables us to investigate what is going on in the galaxy. The researchers found a spiral structure extending 15,000 light-years from the centre of the galaxy. This is one third of the size of the Milky Way Galaxy. The estimated total mass of the stars and interstellar matter in BRI 1335-0417 is roughly equal to that of the Milky Way. Then the question becomes, how was this distinct spiral structure formed in only 1.4 billion years after the Big Bang?

The researchers considered multiple possible causes and suggested that it could be due to an interaction with a small galaxy. BRI 1335-0417 is actively forming stars and the researchers found that the gas in the outer part of the galaxy is gravitationally unstable, which is conducive to star formation. This situation is likely to occur when a large amount of gas is supplied from outside, possibly due to collisions with smaller galaxies. The fate of BRI 1335-0417 is also shrouded in mystery. Galaxies that contain large amounts of dust and actively produce stars in the ancient Universe are thought to be the ancestors of the giant elliptical galaxies in the present Universe. In that case, BRI 1335-0417 changes its shape from a disk galaxy to an elliptical one in the future. Or, contrary to the conventional view, the galaxy may remain a spiral galaxy for a long time. BRI 1335-0417 will play an important role in the study of galaxy shape evolution over the long history of the Universe.



METHOD TO REDUCE STRAY LIGHT ON SPACE TELESCOPES

University of Liege

A team of researchers has developed a method to identify the contributors and origins of stray light on space telescopes. This is a major advance in the field of space engineering that will help in the acquisition of even finer space images and the development of increasingly efficient space instruments. Space telescopes are becoming more and more powerful. Technological developments in recent years have made it possible, for example, to observe objects further and further into the Universe or to measure the composition of the Earth's atmosphere with ever greater precision. However, there is still one factor limiting the performance of these telescopes: stray light. A phenomenon that has been known fora long time, stray light results in light reflections (ghost reflections between lenses, scattering, etc.) that damage the quality of images and often lead to blurred images. Until now, the methods for checking and characterizing this stray light during the development phase of the telescopes have been very limited, making it possible to "just" know whether or not the instrument was sensitive to the phenomenon, forcing engineers to revise all their calculations in positive cases, leading to considerable delays in the commissioning of these advanced tools.

Researchers have developed a revolutionary method for solving this problem by using a femto-second pulsed laser to send light beams to illuminate the telescope. Thanks to this, and using an ultra-fast detector (of the order of 10-9 seconds of resolution, i.e. a thousandth of a millionth of a second), the image is measured and the different stray light effects at different times. In addition to this decomposition, each of the contributors can be measured using their arrival times, which are directly related to the optical path, and thus know the origin of the problem. This method could lead to a small revolution in the field of high-performance space instruments and responds to an urgent problem that has been unresolved until now. In the near future, researchers intend to continue the development of this method, to increase its TRL (Technology Readiness Level) and bring it to an industrial level. An industrial application is already planned for the FLEX (Fluorescence Explorer) project, an Earth observation telescope that is part of ESA's Living Planet Program. The researchers hope to be able to apply it to scientific instruments as well.

 


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