Topic: Early July Astronomy Bulletin

[Clive]

PERSEVERANCE STUDIES WILD WINDS OF JEZERO CRATER
NASA

During its first couple hundred days in Jezero Crater, NASA’s Perseverance Mars rover saw some of the most intense dust activity ever witnessed by a mission sent to the Red Planet’s surface. Not only did the rover detect hundreds of dust-bearing whirlwinds called dust devils, Perseverance captured the first video ever recorded of wind gusts lifting a massive Martian dust cloud. The new findings enable scientists to better understand dust processes on Mars and contribute to a body of knowledge that could one day help them predict the dust storms that Mars is famous for – and that pose a threat to future robotic and human explorers. The study authors found that at least four whirlwinds pass Perseverance on a typical Martian day and that more than one per hour passes by during a peak hourlong period just after noon. The rover’s cameras also documented three occasions in which wind gusts lifted large dust clouds, something the scientists call “gust-lifting events.” The biggest of these created a massive cloud covering 4 square kilometres. A key objective for Perseverance’s mission on Mars is astrobiology, including the search for signs of ancient microbial life. The rover will characterize the planet’s geology and past climate, pave the way for human exploration of the Red Planet, and be the first mission to collect and cache Martian rock and regolith (broken rock and dust).


HOW AURORA ON MARS IS FORMED
University of Iowa

Physicists have studied discrete aurora, a light-in-the-sky display that occurs mostly during the night in the southern hemisphere of Mars . While scientists have known about discrete aurora on Mars-which also occur on Earth -- they did not know how they formed. That's because Mars does not have a global magnetic field like Earth, which is a main trigger for aurora, also called the northern and southern lights on our planet. Instead, the physicists report, discrete aurora on Mars are governed by the interaction between the solar wind -- the constant jet of charged particles from the Sun -- and magnetic fields generated by the crust at southern latitudes on Mars. It's the nature of this localized interaction between the solar wind and the crustal magnetic fields that lead to discrete aurora, the scientists find. The findings come from more than 200 observations of discrete aurora on Mars by the NASA-led Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft.


FIRST ANALYSIS OF ROCKS FROM ASTEROID RYUGU
University of Chicago


In 2018, Hayabusa2 landed atop a moving asteroid named Ryugu and collected particles from above and below its surface. After spending a year and a half orbiting the asteroid, it returned to Earth with a sealed capsule containing about five grams of dust and rock. Scientists around the world have been eagerly anticipating the unique sample -- one that could help redefine our understanding of how planets evolve and how our solar system formed. Scientists are particularly excited because these particles would never have reached Earth without the protective barrier of a spacecraft. The rock is similar to a class of meteorites known as "Ivuna-type carbonaceous chondrites. These rocks have a similar chemical composition to what we measure from the Sun and are thought to date back to the very beginnings of the solar system approximately four-and-a-half billion years ago -- before the formation of the Sun, the Moon and Earth. Back then, all that existed was a gigantic, rotating cloud of gas. Scientists think that most of that gas was pulled into the centre and formed the star we know as the Sun. As the remnants of that gas expanded into a disk and cooled, it transformed into rocks, which still float around the solar system today; it appears Ryugu may be one of them. Scientists said the fragments show signs of having been soaked in water at some point. Using radioisotope dating, they estimated that Ryugu was altered by water circulation only about five million years after the solar system formed. These findings are particularly interesting to researchers because they hint at similar formation conditions between comets and some asteroids such as Ryugu. The scientists noted that a percentage of the find will be set aside so that we can analyze them in the future with more advanced technology -- much as we did with lunar samples from Apollo. This mission is the first of several international missions that will bring back samples from another asteroid named Bennu, as well as unexplored areas on our moon, Mars, and Mars' moon Phobos. This should all be taking place in the next 10 to 20 years.


LARGE NUMBER OF BROWN DWARFS DISCOVERED
University of Bern


Brown dwarfs are mysterious astronomical objects that fill the gap between the heaviest planets and the lightest stars, with a mix of stellar and planetary characteristics. Due to this hybrid nature, these puzzling objects are crucial to improve our understanding of both stars and giant planets. Brown dwarfs orbiting a parent star from sufficiently far away are particularly valuable as they can be directly photographed -- unlike those that are too close to their star and are thus hidden by its brightness. This provides scientists with a unique opportunity to study the details of the cold, planet-like atmospheres of brown dwarf companions. However, despite remarkable efforts in the development of new observing technologies and image processing techniques, direct detections of brown dwarf companions to stars have remained rather sparse, with only around 40 systems imaged in almost three decades of searches. Researchers have now directly imaged four new brown dwarfs. Wide-orbit brown dwarf companions are rare to start with, and detecting them directly poses huge technical challenges since the host stars completely blind our telescopes. Most surveys conducted so far have been blindly targeting random stars from young clusters. An alternative approach to increase the number of detections is to only observe stars that show indications of an additional object in their system. For example, the way a star moves under the gravitational tug of a companion can be an indicator of the existence of that companion, whether it is a star, a planet or something in between. The team developed the COPAINS tool which predicts the types of companions that could be responsible for observed anomalies in stellar motions. Applying the COPAINS tool the research team carefully selected 25 nearby stars that seemed promising for the direct detection of hidden, low-mass companions based on data from the Gaia spacecraft of the European Space Agency (ESA). Using then the SPHERE planet-finder at the Very Large Telescope in Chile to observe these stars, they successfully detected ten new companions with orbits ranging from that of Jupiter to beyond that of Pluto, including five low-mass stars, a white dwarf (a dense stellar remnant), and a remarkable four new brown dwarfs. These findings significantly advance the number of known brown dwarfs orbiting stars from large distances, with a major boost in detection rate compared to any previous imaging survey. While for now this approach is mostly limited to signatures from brown dwarf and stellar companions, future phases of the Gaia mission will push these methods to lower masses and allow for the discovery of new giant exoplanets.


EVIDENCE OF GALACTIC METAL SHROUDED IN DUST
University of California - Irvine

A thorough understanding of galaxy evolution depends in part on an accurate measurement of the abundance of metals in the intergalactic medium -- the space between stars -- but dust can impede observations in optical wavelengths. An international team of astronomers uncovered evidence of heavier elements in local galaxies -- found to be deficient in earlier studies -- by analysing infrared data gathered during a multiyear campaign. To determine the abundance of gas-phase metals in the intergalactic medium, the astronomers sought to acquire data on the ratios of proxies, oxygen and nitrogen, because infrared emissions from these elements are less obscured by galactic dust. Observing this process in infrared wavelengths is a challenge for astronomers because water vapour in Earth's atmosphere blocks radiation on this part of the electromagnetic spectrum, making measurements from even the highest-altitude ground telescopes -- like those at the Keck Observatory in Hawaii -- insufficient. Part of the dataset used by the team came from the now-retired Herschel Space Telescope, but Herschel was not equipped with a spectrometer capable of reading a specific emission line that the UCI-led team needed for its study. The researchers' solution was to take to the skies -- reaching more than 45,000 feet above sea level -- in the Stratospheric Observatory for Infrared Astronomy, NASA's Boeing 747 equipped with a 2.5-meter telescope. By analysing infrared emissions, the researchers were able to compare the metallicity of their target ultraluminous infrared galaxies with less dusty galaxies with similar mass and star formation rates. Chartab explained that these new data show that ultraluminous infrared galaxies are in line with the fundamental metallicity relation determined by stellar mass, metal abundance and star formation rate. The new data further show that the underabundance of metals derived from optical emission lines is likely due to "heavy dust obscuration associated with starburst," according to the paper.


SUPERMASSIVE BLACK HOLES INSIDE OF DYING GALAXIES
National Institutes of Natural Sciences

Astronomers used a database combining observations from the best telescopes in the world to detect the signal from the active supermassive black holes of dying galaxies in the early Universe. The appearance of these active supermassive black holes correlates with changes in the host galaxy, suggesting that a black hole could have far reaching effects on the evolution of its host galaxy. The Milky Way includes stars of various ages, including stars still forming. But in some other galaxies, known as elliptical galaxies, all of the stars are old and about the same age. This indicates that early in their histories elliptical galaxies had a period of prolific star formation that suddenly ended. Why this star formation ceased in some galaxies but not others is not well understood. One possibility is that a supermassive black hole disrupts the gas in some galaxies, creating an environment unsuitable for star formation. To test this theory, astronomers look at distant galaxies. Due to the finite speed of light, it takes time for light to travel across the void of space. The light we see from an object 10 billion light-years away had to travel for 10 billion years to reach Earth. Thus the light we see today shows us what the galaxy looked like when the light left that galaxy 10 billion years ago. So looking at distant galaxies is like looking back in time. But the intervening distance also means that distant galaxies look fainter, making study difficult.

To overcome these difficulties an international team used the Cosmic Evolution Survey (COSMOS) to sample galaxies 9.5-12.5 billion light-years away. COSMOS combines data taken by world leading telescopes, including the Atacama Large Millimeter/submillimeter Array (ALMA) and the Subaru Telescope. COSMOS includes radio wave, infrared light, visible light, and x-ray data. The team first used optical and infrared data to identify two groups of galaxies: those with ongoing star formation and those where star formation has stopped. The x-ray and radio wave data signal-to-noise ratio was too weak to identify individual galaxies. So the team combined the data for different galaxies to produce higher signal to noise ratio images of "average" galaxies. In the averaged images, the team confirmed both x-ray and radio emissions for the galaxies without star formation. This is the first time such emissions have been detected for distant galaxies more than 10 billion light-years away. Furthermore, the results show that the x-ray and radio emissions are too strong to be explained by the stars in the galaxy alone, indicating the presence of an active supermassive black hole. This black hole activity signal is weaker for galaxies where star formation is ongoing. These results show that an abrupt end in star formation in the early Universe correlates with increased supermassive black hole activity. More research is needed to determine the details of the relationship.


RAPID RADIO BURST SHOWS HOT SPACE BETWEEN GALAXIES
Cornell University


A recently discovered, rare and persistent rapid-fire fast radio burst source -- sending out an occasional and informative cosmic ping from more than 3.5 billion light years away -- helps to reveal the secrets of the broiling hot space between the galaxies. Fast Radio Burst 20190520B -- a prolific repeating burst source -- was first observed in June 2019 by the Five-hundred-meter Aperture Spherical radio Telescope (FAST), in Ghizou province, southwest China. Astronomers generally consider this telescope as the spiritual successor to the now-defunct, Cornell University-built Arecibo Observatory in Puerto Rico. After FAST found the burst, scientists then pinpointed the burst's location using the Very Large Array, Socorro, New Mexico. What excites astronomers about the repeating fast radio bursts (FRBs) -- since they only burst once, generally speaking -- is that these quick-fire surges provide a pathway for scientists to comprehend the perplexing, mysterious and million-degree intergalactic medium. Four bursts were detected during the initial 24-second scan in 2019, according to the paper. Between April and September 2020, during follow-up observations, FAST detected 75.

Due to the rapidly repeating bursts, astronomers believe that FRB 20190520B may be quite young. It seems to reside in a complex plasma environment, like that expected in a young supernova remnant. So one possibility is that the highly active source may be a newborn, and if so, it paints an intriguing evolutionary picture of FRB sources, where young burst sources are associated with persistent radio emission. The persistent emission fades away as the burst repetition rate slows down. Astronomers usually assume that FRBs pass through only a modest amount of gas (free electrons) in their host galaxies, which makes counting electrons in the intergalactic medium an easier task. FRB 20190520B shows the opposite: It has encountered far more gas in its host galaxy than scientists expected, calling into question previous assumptions. Ultimately, astronomers want to know how the intergalactic medium is formed. Astronomers want to deconstruct how many free electrons are in the intergalactic medium, because it has been extremely difficult to study.


NUSTAR STUDIES X-RAY UNIVERSE FOR 10 YEARS
NASA

NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) is turning 10. Launched on June 13, 2012, this space telescope detects high-energy X-ray light and studies some of the most energetic objects and processes in the Universe, from black holes devouring hot gas to the radioactive remains of exploded stars. Here are some of the ways NuSTAR has opened our eyes to the X-ray Universe over the last decade. Different colours of visible light have different wavelengths and different energies; similarly, there is a range of X-ray light, or light waves with higher energies than those human eyes can detect. NuSTAR detects X-rays at the higher end of the range. There aren’t many objects in our solar system that emit the X-rays NuSTAR can detect, but the Sun does: Its high-energy X-rays come from microflares, or small bursts of particles and light on its surface. NuSTAR’s observations contribute to insights about the formation of bigger flares, which can cause harm to astronauts and satellites. These studies could also help scientists explain why the Sun’s outer region, the corona, is many times hotter than its surface.

NuSTAR has identified dozens of black holes hidden behind thick clouds of gas and dust. Visible light typically can’t penetrate those clouds, but the high-energy X-ray light observed by NuSTAR can. This gives scientists a better estimate of the total number of black holes in the Universe. In recent years scientists have used NuSTAR data to find out how these giants become surrounded by such thick clouds, how that process influences their development, and how obscuration relates to a black hole’s impact on the surrounding galaxy. NuSTAR is a kind of zombie hunter: It’s deft at finding the undead corpses of stars. Known as neutron stars, these are dense nuggets of material left over after a massive star runs out of fuel and collapses. Though neutron stars are typically only the size of a large city, they are so dense that a teaspoon of one would weigh about a billion tons on Earth. Their density, combined with their powerful magnetic fields, makes these objects extremely energetic: One neutron star located in the galaxy M82 beams with the energy of 10 million Suns. During their lives, stars are mostly spherical, but NuSTAR observations have shown that when they explode as supernovae, they become an asymmetrical mess. The space telescope solved a major mystery in the study of supernovae by mapping the radioactive material left over by two stellar explosions, tracing the shape of the debris and in both cases revealing significant deviations from a spherical shape. Because of NuSTAR’s X-ray vision, astronomers now have clues about what happens in an environment that would be almost impossible to probe directly. The NuSTAR observations suggest that the inner regions of a star are extremely turbulent at the time of detonation.