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Author Topic: Late December Astronomy Bulletin  (Read 52 times)

Offline Clive

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Late December Astronomy Bulletin
« on: December 25, 2022, 14:16 »


ʻOumuamua was the first known interstellar visitor to pass through the Solar System. Since Space Explored first began reporting on ‘Oumuamua, the quarter-mile-long object passed beyond Pluto’s orbit and is now on its way out of the outer Solar System. Researchers at Harvard’s Smithsonian Center for Astrophysics made waves in the mainstream media after publishing a paper claiming that ‘Oumuamua may have had an “artificial origin” — Presenting speculation that the object could have been sent “intentionally to Earth vicinity by an alien civilization.” This theory is based on the object’s “excess acceleration,” or its unexpected boost in speed separate from the Sun’s gravitational influence. This still stumps researchers today. We haven’t learned much about the interstellar object since its discovery in 2017.

One thing is for certain, though; it’s traveling fast, blistering fast. In fact, when ‘Oumuamua was closest to Earth, it was tumbling through the inner Solar System at 87.3 kilometers per second, according to NASA. That is over 3 times faster than the average speed of a main-belt asteroid and 109 times fast than the average speed of a bullet, however, only .017 percent the speed of light. In case you were wondering. Despite this, almost 5 years later, ‘Oumuamua is just now leaving the outer Solar System. It’s currently cruising just past Pluto, covering a distance of over 4,557,662 km every 24 hours. It won’t completely be out in interstellar space for another 2 years. The quick slingshot from ‘Oumuamua around the Sun in 2017 made observing and classifying the object difficult. To this day, we’ve yet to classify ‘Oumuamua officially. This is in part because we honestly have no idea. At first, we thought it was an asteroid—a large chunk of rock from a distant star system. Then we thought it was a comet—a cosmic iceberg flung loose from somewhere in the great unknown. Now scientists and researchers are stumped. Only left to speculate, with little data, what the cosmic visitor was as it gets further and further from view.


National Radio Astronomy Observatory

While the National Science Foundation's Karl G. Jansky Very Large Array (VLA) and the Atacama Large Millimeter/submillimeter Array (ALMA) frequently reveal important new facts about objects far beyond our own Milky Way Galaxy -- at distances of many millions or billions of light-years -- they also are vital tools for unravelling much closer mysteries, right here in our own Solar System. A pair of recent scientific papers illustrate how these telescopes are helping planetary scientists understand the workings of the Solar System's largest planet, Jupiter, and its innermost moon Io. Jupiter's atmosphere is complex and dynamic, and changes rapidly. To study the giant planet's atmosphere at different depths, scientists combined observations made with instruments aboard NASA's Juno spacecraft, in orbit around Jupiter, with observations with the VLA. They collected data about the distribution of the trace gas ammonia at different levels in the atmosphere to help determine the vertical structure of the atmosphere.

These observations needed to be sufficiently detailed to combine Juno's long wavelength observations with the VLA's high-frequency resolution to understand vertical transport in the atmosphere. The spatial resolution of the ground-based VLA observations was comparable to that of the instrument aboard the spacecraft orbiting the planet. These observations produced the highest-resolution radio image yet made of Jupiter. This technique is helping the scientists advance their understanding of Jupiter's deep atmosphere.  Io, whose interior constantly is heated by strong gravitational tidal forces, is the most volcanically-active body in our Solar System. The moon has a tenuous atmosphere primarily composed of Sulphur Dioxide (SO2), which comes from eruptions of its many volcanoes and sublimation of its SO2 surface frost. Scientists have used ALMA to study the trace gases of Sodium Chloride (NaCl -- table salt) and Potassium Chloride (KCl) in the atmosphere. They found that these compounds are largely confined in extent and are at high temperatures, indicating that they, too, are expelled by volcanoes. They also found that they are in different locations from where the SO2 is emitted, which suggests that there may be differences in the subsurface magma or in the eruptive processes between the volcanoes that emit SO2 and those that emit NaCl and KCl.


NASA/Goddard Space Flight Center

Astronomers say that the solar system is enveloped in a faint eerie glow of light. One possible explanation is that a shell of dust envelops our solar system all the way out to Pluto, and is reflecting sunlight. Seeing airborne dust caught in sunbeams is no surprise when cleaning the house. But this must have a more exotic origin. Because the glow is so smoothy distributed, the likely source is innumerable comets -- free-flying dusty snowballs of ice. They fall in toward the Sun from all different directions, spewing out an exhaust of dust as the ices sublimate due to heat from the Sun. If real, this would be a newly discovered architectural element of the solar system. It has remained invisible until very imaginative and curious astronomers, and the power of Hubble, came along. Aside from a tapestry of glittering stars, and the glow of the waxing and waning Moon, the nighttime sky looks inky black to the casual observer. But how dark is dark? To find out, astronomers decided to sort through 200,000 images from NASA's Hubble Space Telescope and made tens of thousands of measurements on these images to look for any residual background glow in the sky, in an ambitious project called SKYSURF. This would be any leftover light after subtracting the glow from planets, stars, galaxies, and from dust in the plane of our solar system (called zodiacal light). When researchers completed this inventory, they found an exceedingly tiny excess of light, equivalent to the steady glow of 10 fireflies spread across the entire sky. That's like turning out all the lights in a shuttered room and still finding an eerie glow coming from the walls, ceiling, and floor. The researchers say that one possible explanation for this residual glow is that our inner solar system contains a tenuous sphere of dust from comets that are falling into the solar system from all directions, and that the glow is sunlight reflecting off this dust. If real, this dust shell could be a new addition to the known architecture of the solar system.

This idea is bolstered by the fact that in 2021 another team of astronomers used data from NASA's New Horizons spacecraft to also measure the sky background. New Horizons flew by Pluto in 2015, and a small Kuiper belt object in 2018, and is now heading into interstellar space. The New Horizons measurements were done at a distance of 4 billion to 5 billion miles from the Sun. This is well outside the realm of the planets and asteroids where there is no contamination from interplanetary dust. New Horizons detected something a bit fainter that is apparently from a more distant source than Hubble detected. The source of the background light seen by New Horizons also remains unexplained. There are numerous theories ranging from the decay of dark matter to a huge unseen population of remote galaxies. If the analysis is correct there's another dust component between us and the distance where New Horizons made measurements. That means this is some kind of extra light coming from inside our solar system. Because the measurement of residual light is higher than New Horizons we think it is a local phenomenon that is not from far outside the solar system. It may be a new element to the contents of the solar system that has been hypothesized but not quantitatively measured until now. More than 95% of the photons in the images from Hubble's archive come from distances less than 3 billion miles from Earth. Since Hubble's very early days, most Hubble users have discarded these sky-photons, as they are interested in the faint discrete objects in Hubble's images such as stars and galaxies.



A team led by of researchers at the University of Montreal has found evidence that two exoplanets orbiting a red dwarf star are “water worlds,” where water makes up a large fraction of the entire planet. These worlds, located in a planetary system 218 light-years away in the constellation Lyra, are unlike any planets found in our solar system. Astronomers observed exoplanets Kepler-138c and Kepler-138d with NASA’s Hubble and the retired Spitzer space telescopes and discovered that the planets could be composed largely of water. These two planets and a smaller planetary companion closer to the star, Kepler-138b, had been discovered previously by NASA’s Kepler Space Telescope. The new study found evidence for a fourth planet, too. Water wasn’t directly detected at Kepler-138c and d, but by comparing the sizes and masses of the planets to models, astronomers conclude that a significant fraction of their volume – up to half of it – should be made of materials that are lighter than rock but heavier than hydrogen or helium (which constitute the bulk of gas giant planets like Jupiter). The most common of these candidate materials is water.

With volumes more than three times that of Earth and masses twice as big, planets c and d have much lower densities than Earth. This is surprising because most of the planets just slightly bigger than Earth that have been studied in detail so far all seemed to be rocky worlds like ours. The closest comparison, say researchers, would be some of the icy moons in the outer solar system that are also largely composed of water surrounding a rocky core. Researchers caution the planets may not have oceans like those on Earth directly at the planet’s surface. “The temperature in Kepler-138d’s atmosphere is likely above the boiling point of water, and we expect a thick, dense atmosphere made of steam on this planet. Only, under that steam atmosphere there could potentially be liquid water at high pressure, or even water in another phase that occurs at high pressures, called a supercritical fluid. In 2014, data from NASA’s Kepler Space Telescope allowed astronomers to announce the detection of three planets orbiting Kepler-138. This was based on a measurable dip in starlight as the planet momentarily passed in from of their star. The two possible water worlds, Kepler-138c and d, are not located in the habitable zone, the area around a star where temperatures would allow liquid water on the surface of a rocky planet. But in the Hubble and Spitzer data, researchers additionally found evidence for a new planet in the system, Kepler-138e, in the habitable zone. This newly found planet is small and farther from its star than the three others, taking 38 days to complete an orbit. The nature of this additional planet, however, remains an open question because it does not seem to transit its host star. Observing the exoplanet’s transit would have allowed astronomers to determine its size.


Waseda University

Spiral galaxies represent one of the most spectacular features in our Universe. Among them, spiral galaxies in the distant Universe contain significant information about their origin and evolution. However, we have had a limited understanding of these galaxies due to them being too distant to study in detail. While these galaxies were already detected among the previous observations using NASA's Hubble Space Telescope and Spitzer Space Telescope, their limited spatial resolution and/or sensitivity did not allow us to study their detailed shapes and properties. Now, NASA's James Webb Space Telescope (JWST) has taken things to the next level. In its very first imaging of the galaxy cluster, SMACS J0723.3-7327, JWST has managed to capture infrared images of a population of red spiral galaxies at an unprecedented resolution, revealing their morphology in detail. Against this backdrop, a team of researchers comprising has revealed surprising insights into these red spiral galaxies. Among the several red spiral galaxies detected, the researchers focused on the two most extremely red galaxies, RS13 and RS14. Using spectral energy distribution (SED) analysis, the researchers measured the distribution of energy over wide wavelength range for these galaxies. The SED analysis revealed that these red spiral galaxies belong to the early Universe from a period known as the "cosmic noon" (8-10 billion years ago), which followed the Big Bang and the "cosmic dawn." Remarkably, these are among the farthest known spiral galaxies till date.

Rare, red spiral galaxies account for only 2% of the galaxies in the local Universe. This discovery of red spiral galaxies in the early Universe, from the JWST observation covering only an insignificant fraction of space, suggests that such spiral galaxies existed in large numbers in the early Universe. The researchers further discovered that one of the red spiral galaxies, RS14, is a "passive" (not forming stars) spiral galaxy, contrary to the intuitive expectation that galaxies in the early Universe would be actively forming stars. This detection of a passive spiral galaxy in the JWST's limited field of view is particularly surprising, since it suggests that such passive spiral galaxies could also exist in large numbers in the early Universe. Overall, the findings of this study significantly enhances our knowledge about red spiral galaxies, and the Universe as a whole. The study showed for the first time that passive spiral galaxies could be abundant in the early Universe. While this paper is a pilot study about spiral galaxies in the early Universe, confirming and expanding upon this study would largely influence our understanding of the formation and evolution of galactic morphologies.


University of Bath

Gamma-ray bursts (GRBs) have been detected by satellites orbiting Earth as luminous flashes of the most energetic gamma-ray radiation lasting milliseconds to hundreds of seconds. These catastrophic blasts occur in distant galaxies, billions of light years from Earth. A sub-type of GRB known as a short-duration GRB starts life when two neutron stars collide. These ultra-dense stars have the mass of our Sun compressed down to half the size of a city like London, and in the final moments of their life, just before triggering a GRB, they generate ripples in space-time -- known to astronomers as gravitational waves. Until now, space scientists have largely agreed that the 'engine' powering such energetic and short-lived bursts must always come from a newly formed black hole (a region of space-time where gravity is so strong that nothing, not even light, can escape from it). However, new research by a team of astrophysicists is challenging this scientific orthodoxy. According to the study's findings, some short-duration GRBs are triggered by the birth of a supramassive star (otherwise known as a neutron star remnant) not a black hole. Much is known about short-duration GRBs. They start life when two neutron stars, which have been spiralling ever closer, constantly accelerating, finally crash. And from the crash site, a jetted explosion releases the gamma-ray radiation that makes a GRB, followed by a longer-lived afterglow. A day later, the radioactive material that was expelled in all directions during the explosion produces what researchers call a kilonova. However, precisely what remains after two neutron stars collide -- the 'product' of the crash -- and consequently the power source that gives a GRB its extraordinary energy, has long been a matter of debate. Scientists may now be closer to resolving this debate, thanks to the findings of the Bath-led study.

Space scientists are split between two theories. The first theory has it that neutron stars merge to briefly form an extremely massive neutron star, only for this star to then collapse into a black hole in a fraction of a second. The second argues that the two neutron stars would result in a less heavy neutron star with a higher life expectancy. So the question that has been needling astrophysicists for decades is this: are short-duration GRBs powered by a black hole or by the birth of a long-lived neutron star? To date, most astrophysicists have supported the black hole theory, agreeing that to produce a GRB, it is necessary for the massive neutron star to collapse almost instantly. Astrophysicists learn about neutron star collisions by measuring the electromagnetic signals of the resultant GRBs. The signal originating from a black hole would be expected to differ from that coming from a neutron star remnant. The electromagnetic signal from the GRB explored for this study (named GRB 180618A) made it clear that a neutron star remnant rather than a black hole must have given rise to this burst. What initially puzzled the researchers was that the optical light from the afterglow that followed GRB 180618A disappeared after just 35 minutes. Further analysis showed that the material responsible for such a brief emission was expanding close to the speed of light due to some source of continuous energy that was pushing it from behind. What was more surprising was that this emission had the imprint of a newborn, rapidly spinning and highly magnetised neutron star, called a millisecond magnetar. The team found that the magnetar after GRB 180618A was reheating the leftover material of the crash as it was slowing down. In GRB 180618A, the magnetar-powered optical emission was one-thousand times brighter than what was expected from a classical kilonova.

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