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Author Topic: Mid November Astronomy Bulletin  (Read 152 times)

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Mid November Astronomy Bulletin
« on: November 14, 2020, 17:36 »
PHOTOGENIC COMET APPROACHES EARTH
Spaceweather.com

Comet ATLAS (C/2020 M3) is approaching Earth. At closest approach on Nov. 14th it will be 0.358 AU (54 million km) away--not quite close enough to make it a naked-eye object. Glowing like an 8th magnitude star, this remarkably beautiful comet is an easy target for backyard telescopes. The comet's green atmosphere is huge.  Astrophotographers will need a wide field to capture the entire comet. It gets its verdant hue from diatomic carbon (C2), a compound which glows green in the near vacuum of space. The fact that the comet is passing through Orion makes it easy to find. On Nov. 11th, draw a line through the stars of Orion's Belt. On Nov. 15th (within hours of closest approach to Earth), the comet will pass a fraction of a degree from the bright star Bellatrix, the hunter's left shoulder. Deep exposures may show Bellatrix shining through the outskirts of ATLAS's atmosphere.


SLIGHT ORBIT CHANGE FOR APOPHIS
University of Hawaii at Manoa

Astronomers have revealed critical new findings linked to a large asteroid expected to pass extremely close to Earth. Scientists have announced the detection of Yarkovsky acceleration on the near-Earth asteroid Apophis. This acceleration arises from an extremely weak force on an object due to non-uniform thermal radiation.  This force is particularly important for the asteroid Apophis, as it affects the probability of an Earth impact in 2068. All asteroids need to reradiate as heat the energy they absorb from sunlight in order to maintain thermal equilibrium, a process that slightly changes the orbit of the asteroid. Prior to the detection of Yarkovsky acceleration on Apophis, astronomers had concluded that a potential impact with Earth in 2068 was impossible. The detection of this effect acting on Apophis means that the 2068 impact scenario is still a possibility. Apophis is noteworthy because of its extremely close approach to the Earth on Friday, April 13, 2029, when the 300 metre-sized asteroid will become visible to the unaided eye as it passes within the belt of communications satellites orbiting the Earth.

Astronomers who have been accurately tracking the motion of Apophis in the sky since its discovery in 2004have known for some time that an impact with Earth is not possible during the 2029 close approach. The new observations obtained with the Subaru telescope earlier this year were good enough to reveal the Yarkovsky acceleration of Apophis, and they show that the asteroid is drifting away from a purely gravitational orbit by about 170 metres per year, which is enough to keep the 2068 impact scenario in play. The orbit calculations were performed by the Jet Propulsion Laboratory Further observations to refine the amplitude of the Yarkovksy effect and how it affects Apophis' orbit are underway. Astronomers will know well before 2068 if there is any chance of an impact.


BENNU RECENTLY MIGRATED TO NEIGHBOURHOOD
University of Arizona

By studying impact marks on the surface of asteroid Bennu -- the target of NASA's  OSIRIS-REx mission -- a team of has uncovered the asteroid's past and revealed that despite forming hundreds of millions of years ago, Bennu wandered into Earth's neighbourhood only very recently. The study provides a new benchmark for understanding the evolution of asteroids, offers insights into a poorly understood population of space debris hazardous to spacecraft, and enhances scientists' understanding of the solar system. The researchers used images and laser-based measurements taken during a two-year surveying phase in which the van-sized OSIRIS-REx spacecraft orbited Bennu and broke the record as the smallest spacecraft to orbit a small body. Although Earth is being pelted with more than 100 tons of space debris each day, it is virtually impossible to find a rock face pitted by
impacts from small objects at high velocities. Courtesy of our atmosphere, we get to enjoy any object smaller than a few metres as a shooting star rather than having to fear being struck by what essentially amounts to a bullet from outer space.  Planetary bodies lacking such a protective layer, however, bear the full brunt of a perpetual cosmic barrage, and they have the scars to show for it. High-resolution images taken by the OSIRIS-REx spacecraft during its two-year survey campaign allowed researchers to study even tiny craters, with diameters ranging from a centimetre to a metre on Bennu's boulders. On average, the team found boulders of 1 metre or larger to be scarred by anywhere from one to 60 pits -- impacted by space debris ranging in size from a few millimetres to tens of centimetres. The same holds true for a boulder on an asteroid or other airless body’. If a boulder gets hit by something larger than an object that would leave a certain size crater, it would just disappear. In other words, the size distribution of boulders that have persisted on Bennu serve as silent witnesses to its geologic past.

Applying the technique to boulders ranging in size from pebbles to parking garages, the researchers were able to make inferences about the sizes and type of impactors to which the boulders were exposed, and for how long. The authors conclude that the largest craters on Bennu's boulders were created while Bennu resided in the asteroid belt, where impact speeds are lower than in the near-Earth environment, but are more frequent and often near the limit of what the boulders could withstand.  Smaller craters, on the other hand, were acquired more recently, during Bennu's time in near-Earth space, where impact speeds are higher but potentially disruptive impactors are much less common. Based on these calculations, the authors determine that Bennu is a relative newcomer to Earth's neighbourhood. Although it is thought to have formed in the main asteroid belt more than 100 million years ago, it is estimated that it was kicked out of the asteroid belt and migrated to its current territory only 1.75 million years ago. Extending the results to other near-Earth objects, or NEOs, the researchers also suggest that these objects likely come from parent bodies that fall in the category of asteroids, which are mostly rocky with little or no ice, rather than comets, which have more ice than rock.


PHILAE LANDER REVEALS PRIMITIVE ICE
Nature

On 12 November 2014, the Philae lander descended towards comet 67P/Churyumov –Gerasimenko, bounced twice off the surface, then arrived under an overhanging cliff in the Abydos region. The landing process provided insights into the properties of a cometary nucleus. Scientists now report an investigation of the previously undiscovered site of the second touchdown, where Philae spent almost two minutes of its cross-comet journey, producing four distinct surface contacts on two adjoining
cometary boulders. It exposed primitive water ice—that is, water ice from the time of the comet’s formation 4.5 billion years ago—in their interiors while travelling through a crevice between the boulders. Multi-instrument observations made 19 months later found that this water ice, mixed with ubiquitous dark organic-rich material, has a local dust/ice mass ratio matching values previously observed in freshly exposed water ice from outbursts and water ice in shadow. At the end of the crevice, Philae made a 0.25-metre-deep impression in the boulder ice, providing in situ measurements confirming that primitive ice has a very low compressive strength (less than 12 pascals, softer than freshly fallen light snow) and allowing a key estimation to be made of the porosity (75 ± 7 per cent) of the boulders’ icy interiors.


ACTIVITY ON DISTANT PLANETARY OBJECT
Northern Arizona University

Centaurs are minor planets believed to have originated in the Kuiper Belt in the outer solar system. They sometimes have comet-like features such as tails and comae -- clouds of dust particles and gas -- even though they orbit in a region between Jupiter and Neptune where it is too cold for water to readily sublimate, or transition, directly from a solid to a gas. Only 18 active Centaurs have been discovered since 1927, and much about them is still poorly understood. Discovering activity on Centaurs is also observationally challenging because they are faint, telescope time-intensive and because they are rare. A team of astronomers earlier this year announced their discovery of activity emanating from Centaur 2014 OG392, a planetary object first found in 2014. The team's research involved developing a database search algorithm to locate archival images of the Centaur as well as a follow-up observational campaign. The team detected a coma as far as 400,000 km from 2014 OG392 and analysis of sublimation processes and dynamical lifetime suggest carbon dioxide and/or ammonia are the most likely candidates for causing activity on this and other active Centaurs. Researchers developed a novel technique that combines observational measurements, for example, colour and dust mass, with modelling efforts to estimate such characteristics as the object's volatile sublimation and orbital dynamics. As a result of the team's discovery, the Centaur has recently been reclassified as a comet, and will be known as "C/2014 OG392 (PANSTARRS).


SUPERSONIC WINDS, ROCKY RAINS ON LAVA PLANET
McGill University

Among the most extreme planets discovered beyond the edges of our solar system are lava planets: fiery hot worlds that circle so close to their host star that some regions are likely oceans of molten lava. According to scientists the atmosphere and weather cycle of at least one such exoplanet is even stranger, featuring the evaporation and precipitation of rocks, supersonic winds that rage over 5000 km/hr, and a magma ocean 100 km deep. In a study the scientists use computer simulations to predict the conditions on K2-141b, an Earth-size exoplanet with a surface, ocean, and atmosphere all made up of the same ingredients: rocks. The extreme weather forecasted by their analysis could permanently change the surface and atmosphere of K2-141b over time. In analyzing the illumination pattern of the exoplanet, the team discovered that about two-thirds of K2-141b faces perpetual daylight -- rather than the illuminated hemisphere we are used to on Earth. K2-141b belongs to a subset of rocky planets that orbit very close to their star. This proximity keeps the exoplanet gravitationally locked in place, meaning the same side always faces the star. The night side experiences frigid temperatures of below -200 C. The day side of the exoplanet, at an estimated 3000 C, is hot enough to not only melt rocks but vaporize them as well, ultimately creating a thin atmosphere in some areas. The finding likely means that the atmosphere extends a little beyond the shore of the magma ocean, making it easier to spot with space telescopes.

Remarkably, the rock vapour atmosphere created by the extreme heat undergoes precipitation. Just like the water cycle on Earth, where water evaporates, rises into the atmosphere, condenses, and falls back as rain, so too does the sodium, silicon monoxide, and silicon dioxide on K2-141b. On Earth, rain flows back into oceans, where it will once more evaporate and the water cycle is repeated. On K2-141b, the mineral vapour formed by evaporated rock is swept to the frigid night side by supersonic winds and rocks "rain" back down into a magma ocean. The resulting currents flow back to the hot day side of the exoplanet, where rock evaporates once more. Still, the cycle on K2-141b is not as stable as the one on Earth, say the scientists. The return flow of the magma ocean to the day side is slow, and as a result they predict that the mineral composition will change over time -- eventually changing the very surface and atmosphere of K2-141b. All rocky planets, including Earth, started off as molten worlds but then rapidly cooled and solidified. Lava planets give us a rare glimpse at this stage of planetary evolution. The next step will be to test if these predictions are correct, say the scientists. The team now has data from the Spitzer Space Telescope that should give them a first glimpse at the day-side and night-side temperatures of the exoplanet. With the James Webb Space Telescope launching in 2021, they will also be able to verify whether the atmosphere behaves as predicted.


SHORT, INTENSE RADIO BURST IN MILKY WAY
McGill University

New data from a Canadian-led team of astronomers strongly suggest that magnetars -- a type of neutron star believed to have an extremely powerful magnetic field -- could be the source of some fast radio bursts (FRBs). Though much research has been done to explain the mysterious phenomenon, their source has thus far remained elusive and the subject of some debate. On 28 April 2020, a
team of approximately 50 students, postdocs and professors from the Canadian Hydrogen Intensity Mapping Experiment (CHIME) Fast Radio Burst Collaboration detected an unusually intense radio burst emanating from a nearby magnetar located in the Milky Way. They show that the intensity of the radio burst was three thousand times greater than that of any magnetar measured thus far, lending weight to the theory that magnetars are at the origin of at least some FRBs. They calculated that such an intense burst coming from another galaxy would indistinguishable from some fast radio bursts, so this really gives weight to the theory suggesting that magnetars could be behind at least some FRBs. FRBs were first discovered over a decade ago. Originally thought to be singular events, astronomers have since discovered that some of these high-intensity blasts of radio emissions -- more intense than the energy generated by the Sun over millions to billions of years -- in fact repeat. One theory hypothesized FRBs to be extragalactic magnetars -- young extremely magnetic neutron stars that occasionally flare to release enormous amounts of energy. So far, all of the FRBs that telescopes like CHIME have picked up were in other galaxies, which makes them quite hard to study in great detail. Moreover, the magnetar theory was not supported by observations of magnetars in our own galaxy as they were found to be far less intense than the energy released by extragalactic FRBs until now. However, given the large gaps in energetics and activity between the brightest and most active FRB sources and what is observed for magnetars, perhaps younger, more energetic and active magnetars are needed to explain all FRB observations. Smoking-gun proof of a magnetar origin for some FRBs would come from the simultaneous detection of an extragalactic radio burst and an X-ray burst. However, this will likely only be possible for nearby FRBs. Fortunately, CHIME/FRB is discovering these in good numbers.


FARTHEST BLACK HOLE BELONGING TO RARE FAMILY OF GALAXIES
Instituto de Astrofísica de Canarias (IAC)

An international team of astronomers has identified one of the rarest known classes of gamma-ray emitting galaxies, called BL Lacertae, within the first 2 billion years of the age of the Universe. Only a small fraction of the galaxies emits gamma rays, which is the most extreme form of light. Astronomers believe that these highly energetic photons originate from the vicinity of a supermassive black hole residing at the centres of these galaxies. When this happens, they are known as active galaxies. The black hole swallows matter from its surroundings and emits jets or, in other words, collimated streams of matter and radiation. Few of these active galaxies (less than 1%) have their jets pointing by chance toward Earth. Scientists call them blazars and are one of the most powerful sources of radiation in the Universe. Blazars come in two flavours: BL Lacertae (BL Lac) and flat-spectrum radio-quasars (FSRQs). Our current understanding about these mysterious astronomical objects is that FSRQs are relatively young active galaxies, rich in dust and gas that surround the central black hole. As time passes, the amount of matter available to feed the black hole is consumed and the FSRQ evolves to become a BL Lac object. "In other words, BL Lacs may represent the elderly and evolved phase of a blazar's life, while FSRQs resemble an adult. Since the speed of light is limited, the farther we look, the earlier in the age of the Universe we investigate. Astronomers believe that the current age of the Universe is around 13.8 billion years.  The most distant FSRQ was identified at a distance when the age of the Universe was merely 1 billion years. For a comparison, the farthest BL Lac that is known was found when the age of the Universe was around 2.5 billion years. Therefore, the hypothesis of the evolution from FSRQ to BL Lacs appears to be valid. Now, the team of international scientists has discovered a new BL Lac object, named 4FGL J1219.0+3653, much farther away than the previous record holder – a BL Lac existing even 800 million years earlier, this is when the Universe was less than 2 billion years old. This finding challenges the current scenario that BL Lacs are actually an evolved phase of FSRQ. This discovery has challenged our knowledge of the cosmic evolution of blazars and active galaxies in general.


EARLY GALAXIES SURPRISINGLY MATURE
National Radio Astronomy Observatory

Massive galaxies were already much more mature in the early Universe than previously expected. This was shown by an international team of astronomers who studied 118 distant galaxies with the Atacama Large Millimeter/submillimeter Array (ALMA). Most galaxies formed when the Universe was still very young. Our own galaxy, for example, likely started forming 13.6 billion years ago, in our 13.8 billion-year-old Universe. When the Universe was only ten percent of its current age (1-1.5 billion years after the Big Bang), most of the galaxies experienced a "growth spurt." During this time, they built up most of their stellar mass and other properties, such as dust, heavy element content, and spiral-disk shapes, that we see in today's galaxies. Therefore, if we want to learn how galaxies like our Milky Way formed, it is important to study this epoch. In a survey called ALPINE (the ALMA Large Program to Investigate C+ at Early Times), an international team of astronomers studied 118 galaxies experiencing such a "growth spurt" in the early Universe. Surprisingly, many of them were much more mature than astronomers had expected.  Galaxies are considered more "mature" than "primordial" when they contain a significant amount of dust and heavy elements. Dust and heavy elements (defined by astronomers as all elements heavier than hydrogen and helium) are considered to be a by-product of dying stars. But galaxies in the early Universe have not had much time to build stars yet, so astronomers don't expect to see much dust or heavy elements there either. However, around 20 percent of the galaxies that assembled during this early epoch are already very dusty and a significant fraction of ultraviolet light from newborn stars is already hidden by this dust.

Many of the galaxies were also considered to be relatively grown-up because they showed a diversity in their structures, including the first signs of rotationally supported disks -- which may later lead to galaxies with a spiral structure as is observed in galaxies such as our Milky Way. Astronomers generally expect that galaxies in the early Universe look like train wrecks because they often collide.
ALMA has spotted very distant galaxies before, such as MAMBO-9 (a very dusty galaxy) and the Wolfe Disk (a galaxy with a rotating disk). But it was hard to say whether these discoveries were unique, or whether there were more galaxies like them out there. ALPINE is the first survey that enabled astronomers to study a significant number of galaxies in the early Universe, and it shows that they might evolve faster than expected. But the scientists don't yet understand how these galaxies grew up so fast, and why some of them already have rotating disks. Observations from ALMA were crucial for this research because the radio telescope can see the star formation that is hidden by dust and trace the motion of gas emitted from star-forming regions. Surveys of galaxies in the early Universe commonly use optical and infrared telescopes. These allow the measurement of unobscured star formation and stellar masses. However, these telescopes have difficulties measuring dust obscured regions, where stars form, or the motions of gas in these galaxies. And sometimes they don't see a galaxy at all. ALMA discovered a few distant galaxies for the first time. Astronomers call these galaxies Hubble-dark as they could not be detected even with the Hubble telescope.


FIRST LIGHT ON NEXT-GEN ASTRONOMICAL SURVEY
Carnegie Institution for Science

The Sloan Digital Sky Survey's fifth generation collected its very first observations of the cosmos on October 24, 2020. This groundbreaking all-sky survey will bolster our understanding of the formation and evolution of galaxies -- including our own Milky Way -- and the supermassive black holes that lurk at their centers. The newly -launched SDSS-V will continue the path-breaking tradition set by the survey's previous generations, with a focus on the ever-changing night sky and the physical processes primarily by member institutions, along with grants from the Alfred P. Sloan Foundation, the U.S. National Science Foundation, and the Heising-Simons Foundation, SDSS-V will focus on three primary areas of investigation, each exploring different aspects of the cosmos using different spectroscopic tools. Together these three project pillars -- called "Mappers" -- will observe more than six million objects in the sky, and monitor changes in more than a million of those objects over time. The survey's Local Volume Mapper will enhance our understanding of galaxy formation and evolution by probing the interactions between the stars that make up galaxies and the interstellar gas and dust that is dispersed between them. The Milky Way Mapper will reveal the physics of stars in our Milky Way, the diverse architectures of its star and planetary systems, and the chemical enrichment of our galaxy since the early universe. The Black Hole Mapper will measure masses and growth over cosmic time of the supermassive black holes that reside in the hearts of galaxies as well as the smaller black holes left behind when stars die.


SEEING DARK MATTER IN A NEW LIGHT
RAS

A small team of astronomers have found a new way to ‘see’ the elusive dark matter haloes that surround galaxies, with a new technique 10 times more precise than the previous-best method. Scientists currently estimate that up to 85% of the mass in the Universe is effectively invisible. This ‘dark matter’ cannot be observed directly, because it does not interact with light in the same way as the ordinary matter that makes up stars, planets, and life on Earth. So how do we measure what cannot be
seen? The key is to measure the effect of gravity that the dark matter produces.  The new research focuses on an effect called weak gravitational lensing, which is a feature of Einstein’s general theory of relativity. The dark matter will very slightly distort the image of anything behind it. The effect is a bit like reading a newspaper through the base of a wine glass. Weak gravitational lensing is already one of the most successful ways to map the dark matter content of the Universe. Now, the Swinburne team has used the ANU 2.3m Telescope in Australia to map how gravitationally lensed galaxies are rotating. Because we know how stars and gas are supposed to move inside galaxies, we know roughly what that galaxy should look like. By measuring how distorted the real galaxy images are, then we can
figure out how much dark matter it would take to explain what we see. The new research shows how this velocity information enables a much more precise measurement of the lensing effect than is possible using shape alone. With our way of seeing the dark matter, we hope to get a clearer picture of where the dark matter is, and what role it plays in how galaxies form. Future space missions such as NASA’s Nancy Grace Roman Space Telescope and the European Space Agency’s Euclid Space Telescope are designed, in part, to make these kinds of measurements based on the shapes of hundreds of millions of galaxies.


NASA CONTACTS VOYAGER 2
NASA

On Oct. 29, mission operators sent a series of commands to NASA's Voyager 2 spacecraft for the first time since mid-March. The spacecraft has been flying solo while the 70-metre-wide radio antenna used to talk to it has been offline for repairs and upgrades. Voyager 2 returned a signal confirming it had received the "call" and executed the commands without issue. The call to Voyager 2 was a test of new hardware recently installed on Deep Space Station 43, the only dish in the world that can send commands to Voyager 2. Located in Canberra, Australia, it is part of NASA's Deep Space Network (DSN), a collection of radio antennas around the world used primarily to communicate with spacecraft operating beyond the Moon. Since the dish went offline, mission operators have been able to receive health updates and science data from Voyager 2, but they haven't been able to send commands to the far-flung probe, which has travelled billions of miles from Earth since its 1977 launch. Among the upgrades to DSS43, as the dish is known, are two new radio transmitters. One of them, which is used to talk with Voyager 2, hasn't been replaced in over 47 years. Engineers have also upgraded heating and cooling equipment, power supply equipment, and other electronics needed to run the new transmitters. The successful call to Voyager 2 is just one indication that the dish will be back online in February 2021. While mission operators haven't been able to command Voyager 2 since DSS43 went offline, the three 34-metre-wide radio antennas at the Canberra facility can be used together to capture the signals that Voyager 2 sends to Earth. The probe is sending back science data from interstellar space, or the region outside our Sun's heliosphere - the protective bubble of particles and magnetic fields created by the Sun that surrounds the planets and the Kuiper Belt (the collection of small, icy bodies beyond Neptune's orbit). DSS43 began operating in 1972 (five years before the launch of Voyager 2 and Voyager 1) and was only 64 metres wide at the time. It was expanded to 70 metres in 1987 and has received a variety of upgrades and repairs since then. But the engineers overseeing the current work say this is one of the most significant makeovers the dish has received and the longest it's been offline in over 30 years.
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