Topic: Late January Astronomy Bulletin

[Clive]

BRIGHT COMET POSSIBLE FOR YEAR’S END
Earth and Sky

The first comet to be found in 2021 – labelled C/2021 A1 (Leonard) – might become the brightest comet of this year. The comet might be visible to the unaided eye by the end of this year. Astronomer Greg Leonard discovered the comet on January 3, 2021 at the Mount Lemmon Observatory in Arizona. Astronomers report that discovery images show a tail for the comet, suggesting we might see a nice tail as Comet Leonard draws closer to the Earth and Sun. The comet is still far away, currently between the orbits of Jupiter and Mars, heading inward. It’ll reach perihelion, its closest approach to the Sun, around January 3, 2022. And so we’ll have a whole year to watch this comet get brighter, and brighter. NASA/JPL estimates that Comet Leonard’s closest approach to Earth will be on December 12, 2021. It’ll pass Earth at the extremely safe distance of 34,907,464 km. Its orbit also suggests that the comet will then pass relatively close (about 2,632,000 miles) to planet Venus on December 18, 2021. Estimates indicate it might reach a visual magnitude of around 5 or even 4 (the lower the brighter), and although at its brightest the comet will be very close to the horizon, we still might get very good views using binoculars during the days before closest approach to Earth, in early December 2021, with visibility to the eye alone still a possibility. Comet C/2021 A1 is traveling so fast that its position in our skies will change daily during early December 2021.


PERSEVERANCE ROVER GETTING CLOSE TO MARS
NASA

The Mars 2020 Perseverance rover, which has started its approach to the Red Planet, will help answer the next logical question in Mars exploration. With only about 40 million kilometres left to go in its 471 million-kilometre journey, NASA's Mars 2020 Perseverance rover is nearing its new planetary home. The spacecraft has begun its approach to the Red Planet and on Feb. 18, 2021, Perseverance will touch down on the Martian surface. The rover will search for signs of ancient life.  While the surface of Mars is a frozen desert today, scientists have learned from previous NASA missions that the Red Planet once hosted running water and warmer environments at the surface that could have supported microbial life.  Thanks to new technologies that enable Perseverance to target its landing site more accurately and to autonomously avoid landing hazards, the spacecraft can safely touch down in a place as intriguing as Jezero Crater, a 45-kilometer-wide basin that has steep cliffs, sand dunes, and boulder fields. More than 3.5 billion years ago, a river there flowed into a body of water about the size of Lake Tahoe, depositing sediments in a fan shape known as a delta. The Perseverance science team believes this ancient river delta and lake deposits could have collected and preserved organic molecules and other potential signs of microbial life. Perseverance is also collecting important data about Mars' geology and climate. Understanding Mars' past climate conditions and reading the geological history embedded in its rocks will give scientists a richer sense of what the planet was like in its distant past. Studying the Red Planet's geology and climate could also give us a sense of why Earth and Mars – despite some early similarities – ended up so different.

The verification of ancient life on Mars carries an enormous burden of proof. Perseverance is the first rover to bring a sample caching system to Mars in order to package promising samples for return to Earth by a future mission. Rather than pulverizing rock the way the drill on NASA's Curiosity rover does, Perseverance's drill will cut intact rock cores that are about the size of a piece of chalk and will place them in sample tubes that it will store until the rover reaches an appropriate drop-off location on Mars. The rover could also potentially deliver the samples to a lander that is part of the planned Mars sample return campaign. Once the samples are here on Earth, we can examine them with instruments too large and complex to send to Mars, providing far more information about them than even the most sophisticated rover could. Among the future-looking technologies on this mission that will benefit human exploration is Terrain-Relative Navigation. As part of the spacecraft's landing system, Terrain-Relative Navigation will enable the descending spacecraft to quickly and autonomously comprehend its location over the Martian surface and modify its trajectory. Perseverance will also have more autonomy on the surface than any other rover, including self-driving smarts that will allow it to cover more ground in a day's operations with fewer instructions from engineers on Earth. This fast-traverse capability will make exploration of the Moon, Mars, and other celestial bodies more efficient for other vehicles. In addition, Perseverance carries a technology experiment called MOXIE (short for Mars Oxygen In-Situ Resource Utilization Experiment) that will produce oxygen from Mars' carbon dioxide atmosphere. It will demonstrate a way that future explorers might produce oxygen for rocket propellant as well as for breathing.

Two other instruments will help engineers design systems for future human explorers to land and survive on Mars: The MEDLI2 (Mars Entry, Descent, and Landing Instrumentation 2) package is a next-generation version of what flew on the Mars Science Laboratory mission that delivered the Curiosity rover, while the MEDA (Mars Environmental Dynamics Analyzer) instrument suite provides information about weather, climate, and surface ultraviolet radiation and dust. Perseverance is also giving a ride to the Ingenuity Mars Helicopter. A technology experiment separate from the rover's science mission, Ingenuity will attempt the first powered, controlled aircraft flight at another world. If the helicopter is successful in its 30-Martian-day (31-Earth-day) demonstration window, the data could help future explorations of the Red Planet – including those by astronauts – by adding a new aerial dimension. The Mars 2020 Perseverance mission carries more cameras than any interplanetary mission in history, with 19 cameras on the rover itself and four on other parts of the spacecraft involved in entry, descent, and landing. As with previous Mars missions, the Mars 2020 Perseverance mission plans to make raw and processed images available on the mission's website. If all goes well, the public will be able to experience in high-definition what it's like to land on Mars – and hear the sounds of landing for the first time with an off-the-shelf microphone affixed to the side of the rover. Another microphone on SuperCam will help scientists understand the property of rocks the instrument is examining and can also listen to the wind. If you are among the 10.9 million people who signed up to send your name to Mars, your name is stenciled on one of three silicon chips embedded on a plate on the rover that carries the words "Explore as one" in Morse code.


WINDS FOUND ON CLOSEST BROWN DWARF
University of Arizona

Researchers have found bands and stripes on the brown dwarf closest to Earth, hinting at the processes churning the brown dwarf's atmosphere from within. Brown dwarfs are mysterious celestial objects that are not quite stars and not quite planets.  They are about the size of Jupiter but typically dozens of times more massive. Still, they are less massive than the smallest stars, so their cores do not have enough pressure to fuse atoms the way stars do. They are hot when they form and gradually
cool, glowing faintly and dimming slowly throughout their lives, making them hard to find. No telescope can clearly see the atmospheres of these objects. The team wondered if brown dwarfs look like Jupiter, with its regular belts and bands shaped by large, parallel, longitudinal jets, or will they be dominated by an ever-changing pattern of gigantic storms known as vortices like those found on Jupiter's poles. The team found that brown dwarfs look strikingly similar to Jupiter. The patterns in the atmospheres reveal high-speed winds running parallel to the brown dwarfs' equators. These winds are mixing the atmospheres, redistributing heat that emerges from the brown dwarfs' hot interiors. Also, like Jupiter, vortices dominate the polar regions. The team used NASA's Transiting Exoplanet Survey Satellite, or TESS, space telescope to study the two brown dwarfs closest to Earth. At only 6 1/2 light-years away, the brown dwarfs are called Luhman 16 A and B. While both are about the same size as Jupiter, they are both more dense and therefore contain more mass. Luhman 16 A is about 34 times more massive than Jupiter, and Luhman 16 B -- which was the main subject of the study -- is about 28 times more massive than Jupiter and about 800 C hotter. Since the space telescope provides extremely precise measurements and it is not interrupted by daylight, the team collected more rotations than ever before, providing the most detailed view of a brown dwarf's atmospheric circulation. The researchers' results show that there is a lot of similarity between the atmospheric circulation of solar system planets and brown dwarfs. As a result, brown dwarfs can serve as more massive analogues of giant planets existing outside of our solar system in future studies.


MAPPING THE SUN’S NEIGHBOURS
Association of Universities for Research in Astronomy (AURA)

Mapping out our own small pocket of the Universe is a time-honoured quest within astronomy, and citizen scientists have added to this long-running effort by cataloguing the locations of more than 500 cool brown dwarfs in the vicinity of the Sun. An international team of astronomers -- assisted by the legions of volunteers in the Backyard Worlds: Planet 9 collaboration -- have announced an unprecedented census of 525 cool brown dwarfs within 65 light-years of the Sun, including 38 new
discoveries. By determining the distances to all the objects in the census, astronomers have been able to build a 3D map of the distribution of cool brown dwarfs in the Sun's local neighbourhood. This breakthrough relied on novel datasets published by the DESI Legacy Imaging Surveys, which blend huge quantities of astronomical data from a variety of sources to create the best three-dimensional map of the Sun's local neighbourhood to date. Brown dwarfs are sometimes referred to as "failed stars." They are thought to form the way stars do, but they do not become massive enough to trigger nuclear fusion in their cores. Their faintness and relatively small sizes make them difficult to identify without careful analysis of data from sensitive telescopes -- meaning that many have gone undiscovered until now. However, by finding and studying brown dwarfs, astronomers can learn more
about star formation and also about planets around other stars.

One of the most intriguing results of this study is that it provides more evidence that the Sun's immediate neighbourhood (within roughly 7 light-years) is rather unusual. While most stars in the Milky Way are red dwarfs, earlier results revealed that the Sun's closest neighbours are much more diverse, with different types of objects, from Sun-like stars to Jupiter-like brown dwarfs, appearing in roughly equal numbers. The new results add to this disparity by turning up no more extremely cold brown
dwarfs like our close-by neighbour WISE 0855, the coldest known brown dwarf, even though the team expected to find at least several more within 65 light-years of the Sun, given the new study's sensitivity. This result hints at the possibility that yet more cold brown dwarfs have so far eluded detection. The four nearest star systems to the Sun include one G-dwarf star, one K dwarf, two M dwarfs, one L dwarf, one T dwarf, and one Y dwarf.


1700 YEAR-OLD SUPERNOVA
Space Telescope Science Institute

Astronomers are winding back the clock on the expanding remains of a nearby, exploded star. By using NASA's Hubble Space Telescope, they retraced the speedy shrapnel from the blast to calculate a more accurate estimate of the location and time of the stellar detonation. The victim is a star that exploded long ago in the Small Magellanic Cloud, a satellite galaxy to our Milky Way. The doomed star left behind an expanding, gaseous corpse, a supernova remnant named 1E 0102.2-7219, which NASA's Einstein Observatory first discovered in X-rays. Like detectives, researchers sifted through archival images taken by Hubble, analyzing visible-light observations made 10 years apart. The research team measured the velocities of 45 tadpole-shaped, oxygen-rich clumps of ejecta flung by the supernova blast. Ionized oxygen is an excellent tracer because it glows brightest in visible light. To calculate an accurate explosion age, the astronomers picked the 22 fastest moving ejecta clumps, or knots. The researchers determined that these targets were the least likely to have been slowed down by passage through interstellar material. They then traced the knots' motion backward until the ejecta coalesced at one point, identifying the explosion site. Once that was known, they could calculate how long it took the speedy knots to travel from the explosion centre to their current location. According to their estimate, light from the blast arrived at Earth 1,700 years ago, during the decline of the Roman Empire. However, the supernova would only have been visible to inhabitants of Earth's southern hemisphere. Unfortunately, there are no known records of this titanic event.

The researchers' results differ from previous observations of the supernova's blast site and age. Earlier studies, for example, arrived at explosion ages of 2,000 and 1,000 years ago. However, current researchers say their analysis is more robust because their study compares data taken with the same camera, the ACS, making the comparison much more robust. The astronomers also took advantage of the sharp ACS images in selecting which ejecta clumps to analyze. In prior studies, researchers averaged the speed of all of the gaseous debris to calculate an explosion age. However, the ACS data revealed regions where the ejecta slowed down because it was slamming into denser material shed by the star before it exploded as a supernova. Researchers didn't include those knots in the sample. They needed the ejecta that best reflected their original velocities from the explosion, using them to determine an accurate age estimate of the supernova blast.  Hubble also clocked the speed of a suspected neutron star -- the crushed core of the doomed star -- that was ejected from the blast. Based on their estimates, the neutron star must be moving at more than 2 million miles per hour from the centre of the explosion to have arrived at its current position. The suspected neutron star was
identified in observations with the European Southern Observatory's Very Large Telescope in Chile, in combination with data from NASA's Chandra X-ray Observatory.


BURST OF LIGHT LIKELY ERUPTION IN NEARBY GALAXY
NASA/Goddard Space Flight Center

On April 15, 2020, a brief burst of high-energy light swept through the solar system, triggering instruments on several NASA and European spacecraft. Now, multiple international science teams conclude that the blast came from a supermagnetized stellar remnant known as a magnetar located in a neighbouring galaxy. This finding confirms long-held suspicions that some gamma-ray bursts (GRBs) -- cosmic eruptions detected in the sky almost daily -- are in fact powerful flares from magnetars relatively close to home. GRBs, the most powerful explosions in the cosmos, can be detected across billions of light-years. Those lasting less than about two seconds, called short GRBs, occur when a pair of orbiting neutron stars --both the crushed remnants of exploded stars -- spiral into each other and merge. Astronomers confirmed this scenario for at least some short GRBs in 2017, when a burst followed the arrival of gravitational waves -- ripples in space-time -- produced when neutron stars merged 130 million light-years away. Magnetars are neutron stars with the strongest-known magnetic fields, with up to a thousand times the intensity of typical neutron stars and up to 10 trillion times the strength of a refrigerator magnet. Modest disturbances to the magnetic field can cause magnetars to erupt with sporadic X-ray bursts for weeks or longer. Rarely, magnetars produce enormous eruptions called giant flares that produce gamma rays, the highest-energy form of light. Most of the 29 magnetars now catalogued in our Milky Way galaxy exhibit occasional X-ray activity, but only two have produced giant flares. The most recent event, detected on Dec. 27, 2004, produced measurable changes in Earth's upper atmosphere despite erupting from a magnetar located about 28,000 light-years away.

Shortly before 4:42 a.m. EDT on April 15, 2020, a brief, powerful burst of X-rays and gamma rays swept past Mars, triggering the Russian High Energy Neutron Detector aboard NASA's Mars Odyssey spacecraft, which has been orbiting the Red Planet since 2001. About 6.6 minutes later, the burst triggered the Russian Konus instrument aboard NASA's Wind satellite, which orbits a point between Earth and the Sun located about 1.5 million kilometres away. After another 4.5 seconds, the radiation passed Earth, triggering instruments on NASA's Fermi Gamma-ray Space Telescope, as well as on the European Space Agency's INTEGRAL satellite and Atmosphere-Space Interactions Monitor (ASIM) aboard the International Space Station. The eruption occurred beyond the field of view of the Burst Alert Telescope (BAT) on NASA's Neil Gehrels Swift Observatory, so its onboard computer did not alert astronomers on the ground. However, thanks to a new capability called the Gamma-ray Urgent Archiver for Novel Opportunities (GUANO), the Swift team can beam back BAT data when other satellites trigger on a burst. Analysis of this data provided additional insight into the event. The pulse of radiation lasted just 140 milliseconds -- as fast as the blink of an eye or a finger snap. The IPN placed the April 15 burst, called GRB 200415A, squarely in the central region of NGC 253, a bright spiral galaxy located about 11.4 million light-years away in the constellation Sculptor. This is the most precise sky position yet determined for a magnetar located beyond the Large Magellanic Cloud, a satellite of our galaxy and host to a giant flare in 1979, the first ever detected. Giant flares from magnetars in the Milky Way and its satellites evolve in a distinct way, with a rapid rise to peak brightness followed by a more gradual tail of fluctuating emission. These variations result from the magnetar's rotation, which repeatedly brings the flare location in and out of view from Earth, much like a lighthouse. Observing this fluctuating tail is conclusive evidence of a giant flare. Seen from millions of light-years away, though, this emission is too dim to detect with today's instruments. Because these signatures are missing, giant flares in our galactic neighbourhood may be masquerading as much more distant and powerful merger-type GRBs. A detailed analysis of data from Fermi's Gamma-ray Burst Monitor (GBM) and Swift's BAT provides strong evidence that the April 15 event was unlike any burst associated with mergers. In particular, this was the first giant flare known to occur since Fermi's 2008 launch, and the GBM's ability to resolve changes at microsecond timescales proved critical.  The observations reveal multiple pulses, with the first one appearing in just 77 microseconds -- about 13 times the speed of a camera flash and nearly 100 times faster than the rise of the fastest GRBs produced by mergers. The GBM also detected rapid variations in energy over the course of the flare that have never been observed before. Giant flares are poorly understood, but astronomers think they result from a sudden rearrangement of the magnetic field. One possibility is that the field high above the surface of the magnetar may become too twisted, suddenly releasing energy as it settles into a more stable configuration. Alternatively, a mechanical failure of the magnetar's crust -- a starquake -- may trigger the sudden reconfiguration.


DISTANT GALAXY LOSES ABILITY TO FORM STARS
ESO

Galaxies begin to “die” when they stop forming stars, but until now astronomers had never clearly glimpsed the start of this process in a far-away galaxy. Using the Atacama Large Millimeter/submillimeter Array (ALMA), astronomers have seen a galaxy ejecting nearly half of its star-forming gas. This ejection is happening at a startling rate, equivalent to 10 000 Suns-worth of gas a year — the galaxy is rapidly losing its fuel to make new stars. The team believes that this spectacular event was triggered by a collision with another galaxy, which could lead astronomers to rethink how galaxies stop bringing new stars to life. This is the first time astronomers have observed a typical massive star-forming galaxy in the distant Universe about to ‘die’ because of a massive cold gas ejection. The galaxy, ID2299, is distant enough that its light takes some 9 billion years to reach us; we see it when the Universe was just 4.5 billion years old. The gas ejection is removing an astonishing 46% of the total cold gas from ID2299. Because the galaxy is also forming stars very rapidly, hundreds of times faster than our Milky Way, the remaining gas will be quickly consumed, shutting down ID2299 in just a few tens of million years. The event responsible for the spectacular gas loss, the team believes, is a collision between two galaxies, which eventually merged to form ID2299. The elusive clue that pointed the scientists towards this scenario was the association of the ejected gas with a “tidal tail”. Tidal tails are elongated streams of stars and gas extending into interstellar space that result when two galaxies merge, and they are usually too faint to see in distant galaxies. However, the team managed to observe the relatively bright feature just as it was launching into space, and were able to identify it as a tidal tail. Most astronomers believe that winds caused by star formation and the activity of black holes at the centres of massive galaxies are responsible for launching star-forming material into space, thus ending galaxies’ ability to make new stars. However, the new study suggests that galactic mergers can also be responsible for ejecting star-forming fuel into space.


TWO GIANT RADIO GALAXIES DISCOVERED
RAS

Two giant radio galaxies have been discovered with South Africa's powerful MeerKAT telescope. These galaxies are thought to be amongst the largest single objects in the Universe. Whereas normal radio galaxies are fairly common, only a few hundred of these have radio jets exceeding 700 kilo-parsecs in size, or around 22 times the size of the Milky Way. These truly enormous systems are dubbed 'giant radio galaxies'. Despite the scarcity of giant radio galaxies, the authors found two of these cosmic beasts in a remarkably small patch of sky which is only about 4 times the area of the full Moon. Based on our current knowledge of the density of giant radio galaxies in the sky, the probability of finding two of them in this region is less than 0.0003 per cent. This means that giant radio galaxies are probably far more common than we thought! These two galaxies are special because they are amongst the largest giants known, and in the top 10 per cent of all giant radio galaxies. They are more than 2 Mega-parsecs across, which is around 6.5 million light years or about 62 times the size of the Milky Way. Yet they are fainter than others of the same size. Why so few radio galaxies have such gigantic sizes remains something of a mystery. It is thought that the giants are the oldest radio galaxies, which have existed for long enough (several hundred million years) for their radio jets to grow outwards to these enormous sizes. If this is true, then many more giant radio galaxies should exist than are currently known.

The giant radio galaxies were spotted in new radio maps of the sky created by the MeerKAT International Gigahertz Tiered Extragalactic Exploration (MIGHTEE) survey. It is one of the large survey projects underway with South Africa's impressive MeerKAT radio telescope, a precursor to the Square Kilometre Array (SKA), which is due to become fully operational in the mid-2020s. In the past, this population of galaxies has been hidden from our 'sight' by the technical limitations of radio telescopes. However, it is now being revealed thanks to the impressive capabilities of the new generation of telescopes. Construction of the highly anticipated trans-continental SKA telescope is due to commence in South Africa and Australia in 2021, and continue until 2027. Science commissioning observations could begin as early as 2023, and it is hoped that the telescope will reveal larger populations of radio galaxies than ever before and revolutionise our understanding of galaxy evolution.


NEW DISTANCE RECORD FOR QUASAR
National Radio Astronomy Observatory

A team of astronomers has discovered the most distant quasar yet found -- a cosmic monster more than 13 billion light-years from Earth powered by a supermassive black hole more than 1.6 billion times more massive than the Sun and more than 1,000 times brighter than our entire Milky Way Galaxy. The quasar, called J0313-1806, is seen as it was when the Universe was only 670 million years old and is providing astronomers with valuable insight on how massive galaxies -- and the supermassive black holes at their cores -- formed in the early Universe. The new discovery beats the previous distance record for a quasar set three years ago. Observations with the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile confirmed the distance measurement to high precision. Quasars occur when the powerful gravity of a supermassive black hole at a galaxy's core draws in surrounding material that forms an orbiting disk of superheated material around the black hole. The process releases tremendous amounts of energy, making the quasar extremely bright, often outshining the rest of the galaxy. The black hole at the core of J0313-1806 is twice as massive as that of the previous record holder and that fact provides astronomers with a valuable clue about such black holes and their effect on their host galaxies. The huge mass of J0313-1806's black hole at such an early time in the Universe's history rules out two theoretical models for how such objects formed, the astronomers said. In the first of these models, individual massive stars explode as supernovae and collapse into black holes that then coalesce into larger black holes. In the second, dense clusters of stars collapse into a massive black hole. In both cases, however, the process takes too long to produce a black hole as massive as the one in J0313-1806 by the age at which we see it. The ALMA observations of J0313-1806 provided tantalizing details about the quasar host galaxy, which is forming new stars at a rate 200 times that of our Milky Way. The quasar's brightness indicates that the black hole is swallowing the equivalent of 25 Suns every year. The energy released by that rapid feeding, the astronomers said, probably is powering a powerful outflow of ionized gas seen moving at about 20 percent of the speed of light. Such outflows are thought to be what ultimately stops star formation in the galaxy.