NIGHT SKIES ARE BRIGHTENING
RAS
Scientists have reported that artificial objects in orbit around the Earth are brightening night skies on our planet significantly more than previously understood. The research finds that the number of objects orbiting Earth could elevate the overall brightness of the night sky by more than 10 percent above natural light levels across a large part of the planet. This would exceed a threshold that astronomers set over 40 years ago for considering a location “light polluted”. The work is the first to consider the overall impact of space objects on the night sky rather than the effect of individual satellites and space debris affecting astronomers’ images of the night sky. The team of researchers, based at institutions in Slovakia, Spain and the US, modelled the space objects’ contribution to the overall brightness of the night sky, using the known distributions of the sizes and brightnesses of the objects as inputs to the model. The study includes both functioning satellites as well as assorted debris such as spent rocket stages. While telescopes and sensitive cameras often resolve space objects as discrete points of light, low-resolution detectors of light such as the human eye see only the combined effect of many such objects. The effect is an overall increase in the diffuse brightness of the night sky, potentially obscuring sights such as the glowing clouds of stars in the Milky Way, as seen away from the light pollution of cities.
Astronomers have expressed unease in recent years about the growing number of objects orbiting the planet, particularly large fleets of communications satellites known informally as ‘mega-constellations’. In addition to crowding the night sky with more moving sources of artificial light, the arrival of this technology increases the probability of collisions among satellites or between satellites and other objects, generating further debris. Recent reports sponsored by the US National Science Foundation and the United Nations Office for Outer Space Affairs identified mega-constellations as a threat to the continued utility of astronomy facilities on the ground and in low-Earth orbit. In the UK the Royal Astronomical Society has established several working groups to understand the impact of mega-constellations on optical and radio astronomical facilities used by scientists. The results imply a further brightening of the night sky proportional to the number of new satellites launched and their optical characteristics in orbit. Satellite operators like SpaceX have recently worked to lower the brightness of their spacecraft through design changes. Despite these mitigating efforts though, the collective effect of a sharp increase in the number of orbiting objects stands to change the experience of the night sky for many across the globe. The researchers hope that their work will change the nature of the ongoing dialog between satellite operators and astronomers concerning how best to manage the orbital space around the Earth.
EARTH SAFE FROM ASTEROID APOPHIS FOR OVER 100 YEARS
Spaceweather.com
The near-Earth object was thought to pose a slight risk of impacting Earth in 2068, but now radar observations have ruled that out. After its discovery in 2004, asteroid 99942 Apophis had been identified as one of the most hazardous asteroids that could impact Earth. But that impact assessment changed as astronomers tracked Apophis and its orbit became better determined. Now, the results from a new radar observation campaign combined with precise orbit analysis have helped astronomers conclude that there is no risk of Apophis impacting our planet for at least a century. Estimated to be about 340 metres across, Apophis quickly gained notoriety as an asteroid that could pose a serious threat to Earth when astronomers predicted that it would come uncomfortably close in 2029. Thanks to additional observations of the near-Earth object (NEO), the risk of an impact in 2029 was later ruled out, as was the potential impact risk posed by another close approach in 2036. Until this month, however, a small chance of impact in 2068 still remained.
When Apophis made a distant flyby of Earth around March 5, astronomers took the opportunity to use powerful radar observations to refine the estimate of its orbit around the Sun with extreme precision, enabling them to confidently rule out any impact risk in 2068 and long after. On April 13, 2029, the asteroid Apophis will pass less than 32,000 kilometres from our planet’s surface – closer than the distance of geosynchronous satellites. During that 2029 close approach, Apophis will be visible to observers on the ground in the Eastern Hemisphere without the aid of a telescope or binoculars. It’s also an unprecedented opportunity for astronomers to get a close-up view of a solar system relic that is now just a scientific curiosity and not an immediate hazard to our planet.
INTERSTELLAR COMET IS MOST PRISTINE
ESO
New observations with the Very Large Telescope (ESO’s VLT) indicate that the rogue comet 2I/Borisov, which is only the second and most recently detected interstellar visitor to our Solar System, is one of the most pristine ever observed. Astronomers suspect that the comet most likely never passed close to a star, making it an undisturbed relic of the cloud of gas and dust it formed from. 2I/Borisov was discovered in August 2019 and was confirmed to have come from beyond the Solar System a few weeks later. Astronomers used the FORS2 instrument on ESO's VLT, located in northern Chile, to study 2I/Borisov in detail using a technique called polarimetry. Since this technique is regularly used to study comets and other small bodies of our Solar System, this allowed the team to compare the interstellar visitor with our local comets. The team found that 2I/Borisov has polarimetric properties distinct from those of Solar System comets, with the exception of Hale–Bopp. Comet Hale–Bopp received much public interest in the late 1990s as a result of being easily visible to the naked eye, and also because it was one of the most pristine comets astronomers had ever seen. Prior to its most recent passage, Hale–Bopp is thought to have passed by our Sun only once and had therefore barely been affected by solar wind and radiation. This means it was pristine, having a composition very similar to that of the cloud of gas and dust it — and the rest of the Solar System — formed from some 4.5 billion years ago. By analysing the polarisation together with the colour of the comet to gather clues on its composition, the team concluded that 2I/Borisov is in fact even more pristine than Hale–Bopp. This means it carries untarnished signatures of the cloud of gas and dust it formed from.
Even without a space mission, astronomers can use Earth’s many telescopes to gain insight into the different properties of rogue comets like 2I/Borisov. Astronomers used data from the Atacama Large Millimeter/submillimeter Array (ALMA), in which ESO is a partner, as well as from ESO’s VLT, to study 2I/Borisov’s dust grains to gather clues about the comet’s birth and conditions in its home system. They discovered that 2I/Borisov’s coma — an envelope of dust surrounding the main body of the comet — contains compact pebbles, grains about one millimetre in size or larger. In addition, they found that the relative amounts of carbon monoxide and water in the comet changed drastically as it neared the Sun. The team says this indicates that the comet is made up of materials that formed in different places in its planetary system. The observations suggest that matter in 2I/Borisov’s planetary home was mixed from near its star to further out, perhaps because of the existence of giant planets, whose strong gravity stirs material in the system. Astronomers believe that a similar process occurred early in the life of our Solar System. While 2I/Borisov was the first rogue comet to pass by the Sun, it was not the first interstellar visitor. The first interstellar object to have been observed passing by our Solar System was ʻOumuamua, another object studied with ESO’s VLT back in 2017. Originally classified as a comet, ʻOumuamua was later reclassified as an asteroid as it lacked a coma.
MARS’S WATER IS STILL TRAPPED THERE
California Institute of Technology
Billions of years ago, the Red Planet was far more blue; according to evidence still found on the surface, abundant water flowed across Mars and forming pools, lakes, and deep oceans. The question, then, is where did all that water go? The answer: nowhere. According to new research, a significant portion of Mars's water -- between 30 and 99 percent -- is trapped within minerals in the planet's crust. The research challenges the current theory that the Red Planet's water escaped into space. The team found that around four billion years ago, Mars was home to enough water to have covered the whole planet in an ocean about 100 to 1,500 metres deep; a volume roughly equivalent to half of Earth's Atlantic Ocean. But, by a billion years later, the planet was as dry as it is today. Previously, scientists seeking to explain what happened to the flowing water on Mars had suggested that it escaped into space, victim of Mars's low gravity. Though some water did indeed leave Mars this way, it now appears that such an escape cannot account for most of the water loss.
The team studied the quantity of water on Mars over time in all its forms (vapour, liquid, and ice) and the chemical composition of the planet's current atmosphere and crust through the analysis of meteorites as well as using data provided by Mars rovers and orbiters, looking in particular at the ratio of deuterium to hydrogen (D/H). Water is made up of hydrogen and oxygen: H2O. Not all hydrogen atoms are created equal, however. There are two stable isotopes of hydrogen. The vast majority of hydrogen atoms have just one proton within the atomic nucleus, while a tiny fraction (about 0.02 percent) exist as deuterium, or so-called "heavy" hydrogen, which has a proton and a neutron in the nucleus. The lighter-weight hydrogen (also known as protium) has an easier time escaping the planet's gravity into space than its heavier counterpart. Because of this, the escape of a planet's water via the upper atmosphere would leave a telltale signature on the ratio of deuterium to hydrogen in the planet's atmosphere: there would be an outsized portion of deuterium left behind. However, the loss of water solely through the atmosphere cannot explain both the observed deuterium to hydrogen signal in the Martian atmosphere and large amounts of water in the past. Instead, the study proposes that a combination of two mechanisms -- the trapping of water in minerals in the planet's crust and the loss of water to the atmosphere -- can explain the observed deuterium-to-hydrogen signal within the Martian atmosphere. When water interacts with rock, chemical weathering forms clays and other hydrous minerals that contain water as part of their mineral structure. This process occurs on Earth as well as on Mars. Because Earth is tectonically active, old crust continually melts into the mantle and forms new crust at plate boundaries, recycling water and other molecules back into the atmosphere through volcanism. Mars, however, is mostly tectonically inactive, and so the "drying" of the surface, once it occurs, is permanent.
WORLDS WITH UNDERGROUND OCEANS
Southwest Research Institute
One of the most profound discoveries in planetary science over the past 25 years is that worlds with oceans beneath layers of rock and ice are common in our solar system. Such worlds include the icy satellites of the giant planets, like Europa, Titan and Enceladus, and distant planets like Pluto. Scientists conclude that the prevalence of interior water ocean worlds (IWOWs) in our solar system suggests they may be prevalent in other star systems as well, vastly expanding the conditions for planetary habitability and biological survival over time. It has been known for many years that worlds like Earth, with oceans that lie on their surface, must reside within a narrow range of distances from their stars to maintain the temperatures that preserve those oceans. However, IWOWs are found over a much wider range of distances from their stars. This greatly expands the number of habitable worlds likely to exist across the galaxy. Worlds like Earth, with oceans on their exterior, are also subject to many kinds of threats to life, ranging from asteroid and comet impacts, to stellar flares with dangerous radiation, to nearby supernova explosions and more. IWOWs are impervious to such threats because their oceans are protected by a roof of ice and rock, typically several to many tens of kilometres thick, that overlie their oceans. The same layer of rock and ice that protects the oceans on IWOWs also conceals life from being detected by virtually all astronomical techniques. If such worlds are the predominant abodes of life in the galaxy and if intelligent life arises in them -- both big "ifs, -- then IWOWs may also help crack the so-called Fermi Paradox. Posed by Nobel Laureate Enrico Fermi in the early 1960s, the Fermi Paradox questions why we don't see obvious evidence of life if it's prevalent across the Universe.
RESERVOIR OF COMPLEX MOLECULES
Harvard-Smithsonian Center for Astrophysics
Scientists have discovered a vast, previously unknown reservoir of new aromatic material in a cold, dark molecular cloud by detecting individual polycyclic aromatic hydrocarbon molecules in the interstellar medium for the first time, and in doing so are beginning to answer a three-decades-old scientific mystery: how and where are these molecules formed in space? Aromatic molecules, and PAHs -- shorthand for polycyclic aromatic hydrocarbons -- are well known to scientists. Aromatic molecules exist in the chemical makeup of human beings and other animals, and are found in food and medicines. As well, PAHs are pollutants formed from the burning of many fossil fuels and are even amongst the carcinogens formed when vegetables and meat are charred at high temperatures. Polycyclic aromatic hydrocarbons are thought to contain as much as 25-percent of the carbon in the Universe. Now, for the first time, we have a direct window into their chemistry that will let us study in detail how this massive reservoir of carbon reacts and evolves through the process of forming stars and planets. Scientists have suspected the presence of PAHs in space since the 1980s but the new research, detailed in nine papers published over the past seven months, provides the first definitive proof of their existence in molecular clouds. To search out the elusive molecules, the team focused the 100m behemoth radio astronomy GBT on the Taurus Molecular Cloud, or TMC-1 -- a large, pre-stellar cloud of dust and gas located roughly 450 light-years from Earth that will someday collapse in on itself to form stars -- and what they found was astonishing: not only were the accepted scientific models incorrect, but there was a lot more going on in TMC-1 than the team could have imagined.
Previous studies revealed only that there were PAH molecules out there, but not which specific ones. Much to their surprise, the team didn't discover just one new molecule hiding out in TMC-1. Detailed in multiple papers, the team observed 1-cyanonaphthalene, 1-cyano-cyclopentadiene, HC11N, 2-cyanonaphthalene, vinylcyanoacetylene, 2-cyano-cyclopentadiene, benzonitrile, trans-(E)-cyanovinylacetylene, HC4NC, and propargylcyanide, among others. The discovery of new molecules in TMC-1 also has implications for astrochemistry, and while the team doesn't yet have all of the answers, the ramifications here, too, will last for decades. "We've gone from one-dimensional carbon chemistry, which is very easy to detect, to real organic chemistry in space in the sense that the newly discovered molecules are ones that a chemist knows and recognizes, and can produce on Earth. Before the launch of GOTHAM in 2018, scientists had catalogued roughly 200 individual molecules in the Milky Way's interstellar medium. These new discoveries have prompted the team to wonder, and rightly so, what's out there. This new aromatic chemistry that scientists are finding isn't isolated to TMC-1. A companion survey to GOTHAM, known as ARKHAM -- A Rigorous K/Ka-Band Survey Hunting for Aromatic Molecules -- recently found benzonitrile in multiple additional objects. Incredibly, benzonitrile was found in every single one of the first four objects observed by ARKHAM. This is important because while GOTHAM is pushing the limit of what chemistry we thought is possible in space, these discoveries imply that the things we learn in TMC-1 about aromatic molecules could be applied broadly to dark clouds anywhere. These dark clouds are the initial birthplaces of stars and planets. So, these previously invisible aromatic molecules will also need to be thought about at each later step along the way to the creation of stars, planets, and solar systems like our own.
STARS MISSING FROM HYADES CLUSTER
Astronomy & Astrophysics.
An invisible cosmic behemoth might be tearing apart the closest star cluster to the Sun, leaving one side of the cluster eerily dark and devoid of stars, according to a new study. The culprit may be a dark matter substructure, a relic that contains the mass of 10 million Suns and is made of a mysterious non-luminous substance. The possible presence of this “Galactic lump” was detected in a new map that charts out the enormous extent of the Hyades star cluster, located only 153 light years from Earth. Scientists came across the unnerving lump while examining the Hyades cluster using data collected by ESA’s Gaia satellite. While Gaia has been able to resolve features of the Hyades cluster in unprecedented detail, the bright central region of this stellar group, which spans about 20 light years, is visible even to the naked eye. The cluster dates back some 700 million years and has changed significantly, as stars become unbound due to both interior cluster dynamics as well as gravitational forces from the larger Milky Way galaxy. These outside forces that tug at the cluster have, over the eons, sculpted two structures known as “tidal tails” that sweep out in front and behind the central hub of stars. These tails have long been observed in large stellar populations, but Hyades is the first “open” star cluster—a much smaller and younger version of these groups—that scientists have been able to pinpoint tails on. That breakthrough was published by a different team in 2019, and also relies on Gaia’s advanced surveying power. Now, according to the new study, it looks like something is ripping apart one of those tails. Something we can’t see. Something big. Scientists noticed this presence using the most recent Gaia data-dump in December 2020, which enabled the team to identify far-flung stars that originated within the Hyades. The researchers first produced a simulation of the cluster that predicted the current positions and velocities of stars that might have drifted out of it over time.
Because Gaia’s goal is to catalogue the movement and distance of every observable star in the Milky Way, the team was then able to compare the simulation to the real data and spot the stars with trajectories and motions that matched a Hyades origin. This approach extended the known range of the two tails to an astonishing breadth of several thousand light years each. But while the simulated map of the tails predicted that they would be relatively symmetrical, the real observations showed that the trailing tail was comparatively unpopulated with stars, an asymmetry that had also been noted by the 2019 study of the cluster. The team is the first to suggest that “a close encounter with a massive Galactic lump can explain the observed asymmetry in the tidal tails of the Hyades,” according to the study. Based on the observations, this lump would have to be incredibly massive and elusively hidden, because there is no sign of a visible gas cloud or star cluster that might be tugging stars off the trailing tail. To that point, the team proposes that the lurking lump may be a dark matter substructure, also known as a sub-halo. These clumps emerge in the early years of galactic formation and drift across galaxies thereafter. As the name suggests, they are made of dark matter, a non-luminous material that is far more abundant in the universe than the regular matter that makes up stars and planets. Scientists only know about dark matter because of its gravitational effects on luminous objects—potentially including, in this case, the Hyades cluster. The missing stars aren’t being gobbled up, as they might be by a black hole. Rather “the orbits of the stars in the Galaxy are being affected/changed by the encounter” which may cause them to disappear from view because of the “disruption of the cluster and the tails. These sub-haloes are like smaller versions of galactic dark matter haloes, which are gargantuan structures that account for about 84 percent of the total mass of galaxies. The Milky Way’s galactic halo, for instance, is estimated to be more than a trillion times more massive than the Sun, far bigger than the 10-million-Sun mass of the entity that might be causing the asymmetry in the Hyades’ trailing tail. Stars that are bundled into star clusters might swap planets, or disrupt the orbits of planets in neighbouring systems, but we also shouldn’t worry about that outcome because the Sun is a lonely star that left its natal cluster long ago. It’s thrilling to imagine that scientists may have stumbled across such a huge and poorly understood dark matter monster, let alone one that is casually plucking stars off of the Hyades cluster. But to get a better idea of what’s really going on in this cluster tail, we’ll have to wait for future Gaia data releases, among other observational advances. This data will not only help to resolve the mystery of the missing stars in the Hyades, but could yield insights into other stellar and galactic enigmas as well.
EIGHT NEW MILLISECOND PULSARS
Phys.org
Pulsars are highly magnetized, rotating neutron stars emitting a beam of electromagnetic radiation. The most rapidly rotating pulsars, with rotation periods below 30 milliseconds, are known as millisecond pulsars (MSPs). Astronomers assume that they are formed in binary systems when the initially more massive component turns into a neutron star that is then spun up due to accretion of matter from the secondary star. A class of extreme binary pulsars with semi-degenerate companion stars is dubbed "spider pulsars." These objects are further categorized as "black widows" if the companion has extremely low mass (less than 0.1 solar masses), while if the secondary star is heavier, they are called "redbacks." Now, a group of astronomers report the detection of eight new MSPs, out of which five are binary systems and three turned out to be faint isolated pulsars. The discovery was made using the 64-dish MeerKAT radio telescope array in South Africa. Five new MSPs, designated 47 Tuc ac, 47 Tuc ad, NGC 6624G, M62G, and Ter 5, were found in binary systems, while the objects NGC 6522D, NGC 6624H and NGC 6752F, are faint isolated MSPs. The spin periods of the newfound pulsars are within the range from 2.74 to 8.48 ms. According to the paper, 47 Tuc ac (spin period of 2.74 ms) and 47 Tuc ad (spin period of 3.74 ms) are eclipsing "spider pulsars" with low-mass companions and regular occultations of their pulsed emission. 47 Tuc ac was found to be a "black widow" with an orbital period of about 0.18 days and a minimum companion mass of 0.0075 solar masses. With an orbital period of approximately 0.32 days and a minimum companion mass of about 0.2 solar masses, 47 Tuc ad turns out to be a "redback." Both MSPs are located in the globular cluster 47 Tuc, some 15,300 light years away from the Earth.
With a spin period at a level of 6.09 ms, NGC 6624G is a binary MSP with a highly eccentric orbit in the cluster NGC 6624. It has an orbital period 1.54 days, pulsar mass of around 2.1 solar masses and its companion is estimated to be about half as massive as the sun. The astronomers assume that the companion star could be either a massive white dwarf or a neutron star. Another MSP found in this cluster, designated NGC 6624H, is isolated and has a spin period of approximately 5.13 ms. M62G is a binary MSP with a circular orbit located in a massive cluster M62, some 22,000 light years away. It has a spin period of about 4.61 ms, orbital period of around 0.77 days and the mass of its companion is estimated to be at least 0.1 solar masses. The remaining binary MSP, designated Ter 5 an (spin period of 4.8 ms), has a slightly eccentric orbit with the longest orbital period (about 9.62 days) out of the newly detected five binary pulsars. The secondary object in this system is assumed to be a white dwarf with a minimum mass of 0.43 solar masses. The object is part of the Ter 5 globular cluster located in the galactic bulge. The isolated pulsars NGC 6522D and NGC 6752F have spin periods 5.53 ms and 8.48 ms, respectively. NGC 6522D resides in the cluster NGC 6522, which is at a distance of about 25,000 light years, close to the centre of our galaxy. When it comes to the slowest spinning object reported in the paper, it is located in a core-collapsed cluster known as NGC 6752, some 13,000 light years away.
ANCIENT LIGHT ILLUMINATES MATTER
Cornell University
Using light from the Big Bang, cosmologists have begun to unveil the material which fuels galaxy formation. Proto galaxies are always full of gas and when they cool, the galaxies start to form. If we were to just do a back-of-the-envelope calculation, gas should turn into stars but it doesn't. Galaxies are inefficient when they manufacture stars - about 10% of the gas -- at most -- in any given galaxy gets turned into stars. The scientists can now check their longtime theoretical work and simulations, by looking at microwave observations with data and applying a 1970s-era mathematical equation. They've looked at data from Atacama Cosmology Telescope (ACT) -- which observes the Big Bang's static-filled cosmic microwave background (CMB) radiation -- and search for the Sunyaev-Zel'dovich effects. That combination of data enables the scientists to map out the material around that indicate the formation of galaxies in various stages. Effectively, the scientists are using the cosmic microwave background -- remnants of the Big Bang -- as a backlit screen that is 14 billion years old to find this material around galaxies. It's like a watermark on a bank note - if you put it in front of a backlight then the watermark appears as a shadow. In this instance, the backlight is the cosmic microwave background. It serves to illuminate the gas from behind, so we can see the shadow as the CMB light travels through that gas.
FIRST IMAGES OF COSMIC WEB REVEAL DWARF GALAXIES
CNRS
Although the filaments of gas in which galaxies are born have long been predicted by cosmological models, we have so far had no real images of such objects. Now for the first time, several filaments of the 'cosmic web' have been directly observed using the MUSE instrument installed on ESO's Very Large Telescope in Chile. The filamentary structure of hydrogen gas in which galaxies form, known as the cosmic web, is one of the major predictions of the model of the Big Bang and of galaxy formation. Until now, all that was known about the web was limited to a few specific regions, particularly in the direction of quasars, whose powerful radiation acts like car headlights, revealing gas clouds along the line of sight. However, these regions are poorly representative of the whole network of filaments where most galaxies, including our own, were born. Direct observation of the faint light emitted by the gas making up the filaments was a holy grail which has now been attained by an international team of astronomers. The team took the bold step of pointing ESO's Very Large Telescope, equipped with the MUSE instrument coupled to the telescope's adaptive optics system, at a single region of the sky for over 140 hours. Together, the two instruments form one of the most powerful systems in the world. The region selected forms part of the Hubble Ultra-Deep Field, which was until now the deepest image of the cosmos ever obtained. However, Hubble has now been surpassed, since 40% of the galaxies discovered by MUSE have no counterpart in the Hubble images. After meticulous planning, it took eight months to carry out this exceptional observing campaign. This was followed by a year of data processing and analysis, which for the first time revealed light from the hydrogen filaments, as well as images of several filaments as they were one to two billion years after the Big Bang, a key period for understanding how galaxies formed from the gas in the cosmic web. However, the biggest surprise for the team was when simulations showed that the light from the gas came from a hitherto invisible population of billions of dwarf galaxies spawning a host of stars. Although these galaxies are too faint to be detected individually with current instruments, their existence will have major consequences for galaxy formation models, with implications that scientists are only just beginning to explore.
Topic: Early April Astronomy Bulletin (Read 1344 times)