Topic: Late November Astronomy Bulletin

[Clive]

SMALL ASTEROID DISINTEGRATES OVER CANADA
Spaceweather.com

On November 19th for the 6th time in recent history, an Earth-bound asteroid was discovered before it hit Earth. Astronomer David Rankin was conducting a routine survey at Mt Lemmon, Arizona, on Nov. 19th when he spotted the 1-meter space rock coming in from the asteroid belt. Three hours later it was blazing through the atmosphere above Canada. The discovery triggered warnings of an imminent impact. According to the Minor Planet Center, seven observatories had time to photograph the sub-meter object before it hit on Nov. 19th at 08:27 UTC. This is a testament to astronomers' improving ability to catch incoming dangers from space. After the asteroid entered the atmosphere, ground-based weather radars tracked pieces of the disintegrating space rock as far down as 850 metres above Earth's surface. It was a deep hit, with most of the fall landing in Lake Ontario. The fireball's peak brightness was between magnitude -10 and -20. For some people the fireball was brighter than a full Moon. The Minor Planet Center has posthumously designated this asteroid 2022 WJ1. For the record, previous asteroids detected just before they hit Earth are: 2008 TC3, 2014 AA, 2018 LA, 2019 MO, and 2022 EB5. There have been two this year alone!


MARS ONCE COVERED IN 300-METRE DEEP OCEAN
University of Copenhagen - The Faculty of Health and Medical Sciences

Mars is called the red planet. But once, it was actually blue and covered in water, bringing us closer to finding out if Mars had ever harboured life. Most researchers agree that there has been water on Mars, but just how much water is still debated. Now a study shows that some 4.5 billion years ago, there was enough water for the entire planet to be covered in a 300-metre-deep ocean. At this time, Mars was bombarded with asteroids filled with ice. It happened in the first 100 million years of the planet's evolution. In addition to water, the icy asteroids also brought biologically relevant molecules such as amino acids to the Red Planet. Amino acids are used when DNA and RNA form bases that contain everything a cell needs. The new study indicates that the oceans that covered the entire planet in water were at least 300 metres deep. They may have been up to one kilometre deep. In comparison, there is actually very little water on Earth.

It was by means of a meteorite that is billions of years old that the researchers have been able to look into Mars's past history. The meteorite was once part of Mars's original crust and offers a unique insight into what happened at the time when the solar system was formed. The whole secret is hiding in the way Mars's surface has been created -- and of which the meteorite was once a part -- because it is a surface that does not move. On Earth it is opposite. The tectonic plates are in perpetual motion and recycled in the planet's interior. Plate tectonics on Earth erased all evidence of what happened in the first 500 million years of our planet's history. The plates constantly move and are recycled back and destroyed into the interior of our planet. In contrast, Mars does not have plate tectonics such that planet's surface preserves a record of the earliest history of the planet.


WEBB CATCHES NEW STAR FORMING
NASA/Goddard Space Flight Center

NASA's James Webb Space Telescope has revealed the once-hidden features of the protostar within the dark cloud L1527, providing insight into the beginnings of a new star. These blazing clouds within the Taurus star-forming region are only visible in infrared light, making it an ideal target for Webb's Near-Infrared Camera (NIRCam). The protostar itself is hidden from view within the "neck" of this hourglass shape. An edge-on protoplanetary disk is seen as a dark line across the middle of the neck. Light from the protostar leaks above and below this disk, illuminating cavities within the surrounding gas and dust. Webb also reveals filaments of molecular hydrogen that have been shocked as the protostar ejects material away from it. Shocks and turbulence inhibit the formation of new stars, which would otherwise form all throughout the cloud. As a result, the protostar dominates the space, taking much of the material for itself. Despite the chaos that L1527 causes, it's only about 100,000 years old -- a relatively young body. Given its age and its brightness in far-infrared light as observed by missions like the Infrared Astronomical Satellite, L1527 is considered a class 0 protostar, the earliest stage of star formation. Protostars like these, which are still cocooned in a dark cloud of dust and gas, have a long way to go before they become full-fledged stars. L1527 doesn't generate its own energy through nuclear fusion of hydrogen yet, an essential characteristic of stars. Its shape, while mostly spherical, is also unstable, taking the form of a small, hot, and puffy clump of gas somewhere between 20 and 40% the mass of our Sun. As the protostar continues to gather mass, its core gradually compresses and gets closer to stable nuclear fusion. The scene shown in this image reveals L1527 doing just that. The surrounding molecular cloud is made up of dense dust and gas being drawn to the centre, where the protostar resides. As the material falls in, it spirals around the centre. This creates a dense disk of material, known as an accretion disk, which feeds material to the protostar. As it gains more mass and compresses further, the temperature of its core will rise, eventually reaching the threshold for nuclear fusion to begin.


BIRTHPLACE OF GOLD-RICH STARS
RAS

Researchers have revealed the birthplace of so-called ‘gold-rich’ stars – stars with an abundance of heavy elements beyond iron, including gold and platinum. Hundreds of gold-rich stars have been discovered by state-of-the-art telescopes worldwide. The mystery was when, where, and how these stars were formed in the history of the Milky Way. The team found that most gold-rich stars formed in small progenitor galaxies of the Milky Way over 10 billion years ago, shedding light on the stars’ past for the first time. In order to reach this conclusion, the team tracked the Milky Way's formation from the Big Bang to the present with a numerical simulation. This simulation has the highest time resolution yet achieved - it can precisely resolve the cycle of materials formed by stars in the Milky Way. The simulation was produced over several months using the ATERUI II supercomputer in the Centre for Computational Science at the National Astronomical Observatory of Japan. The simulation made it possible to analyse the formation of gold-rich stars in the Milky Way for the first time.

The standard cosmology it used predicts that the Milky Way grows by the accretion and merging of small progenitor galaxies. The simulation data revealed that some of the progenitor galaxies - that existed over 10 billion years ago - contained large amounts of the heaviest elements. Each event of neutron star merger – a confirmed site of heavy element nucleosynthesis – increased the abundance of the heaviest elements in these small galaxies. The gold-rich stars formed in these galaxies, and their predicted abundances can be compared with the observations of the stars today. The gold-rich stars today tell us the history of the Milky Way - most gold-rich stars are formed in dwarf galaxies over 10 billion years ago. These ancient galaxies are the building blocks of the Milky Way. Our findings mean many of the gold-rich stars we see today are the fossil records of the Milky Way's formation over 10 billion years ago.


TRUE SHAPE OF MILKY WAY GALAXY
Harvard-Smithsonian Center for Astrophysics

A new study has revealed the true shape of the diffuse cloud of stars surrounding the disk of our galaxy. For decades, astronomers have thought that this cloud of stars -- called the stellar halo -- was largely spherical, like a beach ball. Now a new model based on modern observations shows the stellar halo is oblong and tilted, much like a football that has just been kicked. The findings offer insights into a host of astrophysical subject areas. The results, for example, shed light on the history of our galaxy and galactic evolution, while also offering clues in the ongoing hunt for the mysterious substance known as dark matter. The Milky Way's stellar halo is the visible portion of what is more broadly called the galactic halo. This galactic halo is dominated by invisible dark matter, whose presence is only measurable through the gravity that it exerts. Every galaxy has its own halo of dark matter. These halos serve as a sort of scaffold upon which ordinary, visible matter hangs. In turn, that visible matter forms stars and other observable galactic structure. To better understand how galaxies form and interact, as well as the underlying nature of dark matter, stellar haloes are accordingly valuable astrophysical targets. Fathoming the shape of the Milky Way's stellar halo, though, has long challenged astrophysicists for the simple reason that we are embedded within it. The stellar halo extends out several hundred thousand light years above and below the star-filled plane of our galaxy, where our Solar System resides. Unlike with external galaxies, where we just look at them and measure their halos we lack the same sort of aerial, outside perspective of our own galaxy's halo.

Complicating matters further, the stellar halo has proven to be quite diffuse, containing only about one percent of the mass of all the galaxy's stars. Yet over time, astronomers have succeeded in identifying many thousands of stars that populate this halo, which are distinguishable from other Milky Way stars due to their distinctive chemical makeup (gaugeable by studies of their starlight), as well as by their distances and motions across the sky. Through such studies, astronomers have realized that halo stars are not evenly distributed. The goal has since been to study the patterns of over-densities of stars -- spatially appearing as bunches and streams -- to sort out the ultimate origins of the stellar halo. The new study by CfA researchers and colleagues leverages two major datasets gathered in recent years that have plumbed the stellar halo as never before. The first set is from Gaia, a revolutionary spacecraft launched by the European Space Agency in 2013. Gaia has continued compiling the most precise measurements of the positions, motions, and distances of millions of stars in the Milky Way, including some nearby stellar halo stars. The second dataset is from H3 (Hectochelle in the Halo at High Resolution), a ground-based survey conducted at the MMT, located at the Fred Lawrence Whipple Observatory in Arizona, and a collaboration between the CfA and the University of Arizona. H3 has gathered detailed observations of tens of thousands of stellar halo stars too far away for Gaia to assess.

Combining these data in a flexible model that allowed for the stellar halo shape to emerge from all the observations yielded the decidedly non-spherical halo -- and the football shape nicely dovetails with other findings to date. The shape, for example, independently and strongly agrees with a leading theory regarding the formation of the Milky Way's stellar halo. According to this framework, the stellar halo formed when a lone dwarf galaxy collided 7-10 billion years ago with our far-larger galaxy. The departed dwarf galaxy is amusingly known as Gaia-Sausage-Enceladus (GSE), where "Gaia" refers to the aforementioned spacecraft, "Sausage" for a pattern appearing when plotting the Gaia data and "Enceladus" for the Greek mythological giant who was buried under a mountain -- rather like how GSE was buried in the Milky Way. As a consequence of this galactic collisional event, the dwarf galaxy was ripped apart and its constituent stars strewn out into a dispersed halo. Such an origin story accounts for the stellar halo stars' inherent unlikeness to stars born and bred in the Milky Way. The study's results further chronicle just how GSE and the Milky Way interacted all those eons ago. The football shape -- technically called a triaxial ellipsoid -- reflects the observations of two pileups of stars in the stellar halo. The pileups ostensibly formed when GSE went through two orbits of the Milky Way. During these orbits, GSE would have slowed down twice at so-called apocenters, or the furthest points in the dwarf galaxy's orbit of the greater gravitational attractor, the hefty Milky Way; these pauses led to the extra shedding of GSE stars. Meanwhile, the tilt of the stellar halo indicates that GSE encountered the Milky Way at an incident angle and not straight-on. Notably, so much time has passed since the GSE-Milky Way smashup that the stellar halo stars would have been expected to dynamically settle into the classical, long-assumed spherical shape. The fact that they haven't likely speaks to the broader galactic halo, the team says. This dark matter-dominated structure is itself probably askew, and through its gravity, is likewise keeping the stellar halo off-kilter.


DUSTY INNER REGION OF DISTANT GALAXY :
Georgia State University

An international team of scientists has achieved the milestone of directly observing the long-sought, innermost dusty ring around a supermassive black hole, at a right angle to its emerging jet. Such a structure was thought to exist in the nucleus of galaxies but had been difficult to observe directly because intervening material obscured our line of sight. Now the inner disk is detected using the highest spatial resolution in the infrared wavelengths ever done for an extragalactic object. A supermassive black hole is thought to exist at the centre of every large galaxy. As material in the surrounding region gets pulled toward the centre, the gas forms a hot and bright disk-like structure. In some cases, a jet emerges from the vicinity of the black hole in a direction at a right angle to the disk. However, this flat structure, which is essentially the 'engine' of this active supermassive black hole system, has never been directly seen because it's too small to be captured by conventional telescopes. One way to approach this key structure is to directly see an outer 'dusty ring' -- interstellar gas contains dust grains, tiny solid particles made of heavy elements, which can only survive in the outer region where temperature is low enough (< ~1500K -- otherwise metals evaporate). The heated dust emits thermal infrared radiation, and thus would look like an outer ring around the black hole, if the central system indeed has a flat structure. The detection of its structure would be a key step to delineate how the central engine works. Attempts to see this structure from edge-on directions are difficult, because the system is obscured by the same dust acting as an absorber of light. Instead, in the new investigation the team focused on a system with a face-on view, the brightest such object in the nearby Universe. However, the detection needed very high spatial resolution in the infrared wavelengths, and at the same time, a large array of telescopes that is laid out suitably to observe objects at different orientations.

The CHARA Array interferometer at the Mount Wilson Observatory in California is the only facility which meets both of these requirements. The Array consists of 6 telescopes, each of which has a 1-meter diameter mirror, that are combined to achieve the spatial resolution of a much larger telescope. While each individual telescope is relatively small, the array layout is optimized to observe objects in a variety of angles and with large distances between telescopes. This achieves a very high spatial resolution capability. The CHARA Array actually has the sharpest eyes in the world in infrared wavelengths. With the CHARA Array, the team finally detected the dusty ring, at a right angle to the emerging jet in the centre of the galaxy NGC 4151. Over the last nearly 40 years, researchers in the field believed that this dusty ring is a key to understanding different characteristics of accreting supermassive blackhole systems. The properties we observe depend on whether we have an obscured, edge-on view or clear, face-on view of the nucleus of the active galaxy. The detection of this ring-like structure validates this model. Furthermore, the detection probably is not just an indication of a flat structure. Additional studies have been showing that the structure seen at slightly longer infrared wavelengths, corresponding to an even larger outer region, seems elongated along the jet, and not at a right angle to it. This has been interpreted as an indication for a dusty wind being blown out toward the jet direction. The present finding that the inner structure looks flat and perpendicular to the jet, is an important link to the windy structure and its interaction with the rest of the galaxy surrounding the active black hole system.


WEBB OBSERVES UNIVERSE’S EARLY GALAXIES
NASA/Goddard Space Flight Center

A few days after officially starting science operations, NASA's James Webb Space Telescope propelled astronomers into a realm of early galaxies, previously hidden beyond the grasp of all other telescopes until now. These initial findings are from a broader Webb research initiative involving two Early Release Science (ERS) programs: the Grism Lens-Amplified Survey from Space (GLASS), and the Cosmic Evolution Early Release Science Survey (CEERS). With just four days of analysis, researchers found two exceptionally bright galaxies in the GLASS-JWST images. These galaxies existed approximately 450 and 350 million years after the big bang (with a redshift of approximately 10.5 and 12.5, respectively), though future spectroscopic measurements with Webb will help confirm. The previous record holder is galaxy GN-z11, which existed 400 million years after the big bang (redshift 11.1), and was identified in 2016 by Hubble and Keck Observatory in deep-sky programs. While the distances of these early sources still need to be confirmed with spectroscopy, their extreme brightnesses are a real puzzle, challenging our understanding of galaxy formation. The Webb observations nudge astronomers toward a consensus that an unusual number of galaxies in the early Universe were much brighter than expected. This will make it easier for Webb to find even more early galaxies in subsequent deep sky surveys

Astronomers believe they have unearthed something that is incredibly fascinating. These galaxies would have had to have started coming together maybe just 100 million years after the big bang. Nobody expected that the dark ages would have ended so early. The primal Universe would have been just one hundredth its current age. It's a sliver of time in the 13.8 billion-year-old evolving cosmos. These galaxies are very different than the Milky Way or other big galaxies we see around us today. The team emphasized the two bright galaxies found by these teams have a lot of light. One option is that they could have been very massive, with lots of low-mass stars, like later galaxies. Alternatively, they could be much less massive, consisting of far fewer extraordinarily bright stars, known as Population III stars. Long theorized, they would be the first stars ever born, blazing at blistering temperatures and made up only of primordial hydrogen and helium -- before stars could later cook up heavier elements in their nuclear fusion furnaces. No such extremely hot, primordial stars are seen in the local Universe. Indeed, the farthest source is very compact, and its colours seem to indicate that its stellar population is particularly devoid of heavy elements and could even contain some Population III stars. Present Webb distance estimates to these two galaxies are based on measuring their infrared colours. Eventually, follow-up spectroscopy measurements showing how light has been stretched in the expanding Universe will provide independent verification of these cosmic yardstick measurements.


INNERMOST STRUCTURE OF QUASAR JET OBSERVED
National Institutes of Natural Sciences

An international team of scientists has observed the narrowing of a quasar jet for the first time by using a network of radio telescopes across the world. The results suggest that the narrowing of the jet is independent of the activity level of the galaxy which launched it. Nearly every galaxy hosts a supermassive black hole in its centre. In some cases, enormous amounts of energy are released by gas falling towards the black hole, creating a phenomenon known as a quasar. Quasars emit narrow, collimated jets of material at nearly the speed of light. But how and where quasar jets are collimated has been a long-standing mystery. Astronomers captured an image with the highest angular resolution to date that shows the deepest part of the jet in a bright quasar known as 3C 273. The team found that the jet flowing from the quasar narrows down over a very long distance. This narrowing part of the jet continues incredibly far, well beyond the area where the black hole's gravity dominates. The results show that the structure of the jet is similar to jets launched from nearby galaxies with a low luminosity active nucleus. This would indicate that the collimation of the jet is independent of the activity level in the host galaxy, providing an important clue to unravelling the inner workings of jets.


2400 NEW EYES ON THE SKY
National Institutes of Natural Sciences

The Subaru Telescope successfully demonstrated engineering first light with a new instrument that will use about 2400 fiberoptic cables to capture the light from heavenly objects. Full operation is scheduled to start around 2024. The ability to observe thousands of objects simultaneously will provide unprecedented amounts of data to fuel Big Data Astronomy in the coming decade. In addition to cameras, astronomers also use instruments known as spectrographs to study celestial object. A spectrograph breaks the light from an object into its component colours, in other words it creates a precise rainbow. Studying the strengths of the different colours in the rainbow from an object can tell astronomers various details about the object such as its motion, temperature, and chemical composition. This new instrument, called PFS (Prime Focus Spectrograph), breaks visible light rainbows into two components: the red side and the blue side. So it might be more correct to refer to the data sets as half-rainbows. Combined with a third kind of detector which can see the infrared light invisible to humans, that makes one-and-a-half rainbows for an object studied with all three types of detectors. Together with a widefield camera (HSC: Hyper Suprime-Cam), PFS will help launch the Subaru Telescope 2.0 project which will reveal the nature of dark matter and dark energy, structure formation in the Universe, and the physical processes of galaxy formation and evolution.