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Author Topic: Late December Astronomy Bulletin  (Read 532 times)

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Late December Astronomy Bulletin
« on: December 27, 2020, 10:36 »
DARK STORM ON NEPTUNE REVERSES DIRECTION
NASA/Goddard Space Flight Center

Astronomers using NASA's Hubble Space Telescope watched a mysterious dark vortex on Neptune abruptly steer away from a likely death on the giant blue planet.  The storm, which is wider than the Atlantic Ocean, was born in the planet's northern hemisphere and discovered by Hubble in 2018. Observations a year later showed that it began drifting southward toward the equator, where such storms are expected to vanish from sight. To the surprise of observers, Hubble spotted the vortex change direction by August 2020, doubling back to the north. Though Hubble has tracked similar dark spots over the past 30 years, this unpredictable atmospheric behaviour is something new to see. Equally as puzzling, the storm was not alone. Hubble spotted another, smaller dark spot in January this year that temporarily appeared near its larger cousin. It might possibly have been a piece of the giant vortex that broke off, drifted away, and then disappeared in subsequent observations.  Astronomers are excited about these observations because this smaller dark fragment is potentially part of the dark spot's disruption process. This is a process that's never been observed. Other dark spots have faded away, and vanished, but astronomers have never seen anything disrupt, even though it's predicted in computer simulations. The large storm, which is 4,600 miles across, is the fourth dark spot Hubble has observed on Neptune since 1993. Two other dark storms were discovered by the Voyager 2 spacecraft in 1989 as it flew by the distant planet, but they had disappeared before Hubble could observe them.

Neptune's dark vortices are high-pressure systems that can form at mid-latitudes and may then migrate toward the equator. They start out remaining stable due to Coriolis forces, which cause northern hemisphere storms to rotate clockwise, due to the planet's rotation. (These storms are unlike hurricanes on Earth, which rotate counterclockwise because they are low-pressure systems.) However, as a storm drifts toward the equator, the Coriolis effect weakens and the storm disintegrates. In computer simulations by several different teams, these storms follow a more-or-less straight path to the equator, until there is no Coriolis effect to hold them together.  Unlike the simulations, the latest giant storm didn't migrate into the equatorial "kill zone." The Hubble observations also revealed that the dark vortex's puzzling path reversal occurred at the same time that a new spot, informally deemed "dark spot jr.," appeared. The newest spot was slightly smaller than its cousin, measuring about 3,900 miles across. It was near the side of the main dark spot that faces the equator -- the location that some simulations show a disruption would occur. However, the timing of the smaller spot's emergence was unusual. The researchers are continuing to analyze more data to determine whether remnants of dark spot jr. persisted through the rest of 2020. It's still a mystery how these storms form, but this latest giant dark vortex is the best studied so far. The storm's dark appearance may be due to an elevated dark cloud layer, and it could be telling astronomers about the storm's vertical structure. Another unusual feature of the dark spot is the absence of bright companion clouds around it, which were present in Hubble images taken when the vortex was discovered in 2018. Apparently, the clouds disappeared when the vortex halted its southward journey. The bright clouds form when the flow of air is perturbed and diverted upward over the vortex, causing gases to likely freeze into methane ice crystals. The lack of clouds could be revealing information on how spots evolve, say researchers.


SUPERHIGHWAY DISCOVERED IN SOLAR SYSTEM
University of California - San Diego

Researchers have discovered a new superhighway network to travel through the Solar System much faster than was previously possible. Such routes can drive comets and asteroids near Jupiter to Neptune's distance in under a decade and to 100 astronomical units in less than a century. They could be used to send spacecraft to the far reaches of our planetary system relatively fast, and to monitor and understand near-Earth objects that might collide with our planet. The researchers observed the dynamical structure of these routes, forming a connected series of arches inside what's known as space manifolds that extend from the asteroid belt to Uranus and beyond. This newly discovered "celestial autobahn" or "celestial highway" acts over several decades, as opposed to the hundreds of thousands or millions of years that usually characterize Solar System dynamics. The most conspicuous arch structures are linked to Jupiter and the strong gravitational forces it exerts. The population of Jupiter-family comets (comets having orbital periods of 20 years) as well as small-size solar system bodies known as Centaurs, are controlled by such manifolds on unprecedented time scales. Some of these bodies will end up colliding with Jupiter or being ejected from the Solar System. The structures were resolved by gathering numerical data about millions of orbits in our Solar System and computing how these orbits fit within already-known space manifolds. The results need to be studied further, both to determine how they could be used by spacecraft, or how such manifolds behave in the vicinity of the Earth, controlling the asteroid and meteorite encounters, as well as the growing population of artificial human-made objects in the Earth-Moon system.


POSSIBLE RADIO EMISSION FROM EXOPLANET :
Cornell University

By monitoring the cosmos with a radio telescope array, an international team of scientists has detected radio bursts emanating from the constellation Bo÷tes -- that could be the first radio emission collected from a planet beyond our solar system.  The signal is from the Tau Bo÷tes system, which contains a binary star and an exoplanet. The team make the case for an emission by the planet itself. From the strength and polarization of the radio signal and the planet's magnetic field, it is compatible with theoretical predictions. If confirmed through follow-up observations, this radio detection opens up a new window on exoplanets, giving us a novel way to examine alien worlds that are tens of light-years away. Using the Low Frequency Array (LOFAR), a radio telescope in the Netherlands, the team uncovered emission bursts from a star-system hosting a so-called hot Jupiter, a gaseous giant planet that is very close to its own sun. The group also observed other potential exoplanetary radio-emission candidates in the 55 Cancri (in the constellation Cancer) and Upsilon Andromedae systems. Only the Tau Bo÷tes exoplanet system -- about 51 light-years away -- exhibited a significant radio signature, a unique potential window on the planet's magnetic field. Observing an exoplanet's magnetic field helps astronomers decipher a planet's interior and atmospheric properties, as well as the physics of star-planet interactions. Earth's magnetic field protects it from solar wind dangers, keeping the planet habitable. The magnetic field of Earth-like exoplanets may contribute to their possible habitability by shielding their own atmospheres from solar wind and cosmic rays, and protecting the planet from atmospheric loss.

Two years ago, the team examined the radio emission signature of Jupiter and scaled those emissions to mimic the possible signatures from a distant Jupiter-like exoplanet. Those results became the template for searching radio emission from exoplanets 40 to 100 light-years away. After poring over nearly 100-hours of radio observations, the researchers were able to find the expected hot Jupiter signature in Tau Bo÷tes. Astronomers learned from our own Jupiter what this kind of detection looks like. They went searching for it and found it. The signature, though, is weak. There remains some uncertainty that the detected radio signal is from the planet. The need for follow-up observations is critical. The team has already begun a campaign using multiple radio telescopes to follow up on the signal from Tau Bo÷tes.


PAIR OF PLANET-LIKE OBJECTS BORN LIKE STARS
University of Bern

Star-forming processes sometimes create mysterious astronomical objects called brown dwarfs, which are smaller and colder than stars, and can have masses and temperatures down to those of exoplanets in the most extreme cases. Just like stars, brown dwarfs often wander alone through space, but can also be seen in binary systems, where two brown dwarfs orbit one another and travel together in the galaxy.  Researchers have discovered a curious starless binary system of brown dwarfs. The system CFHTWIR-Oph 98 (or Oph 98 for short) consists of the two very low-mass objects Oph 98 A and Oph 98 B. It is located 450 light years away from Earth in the constellation Ophiuchus. The researchers were surprised by the fact that Oph 98 A and B are orbiting each other from a strikingly large distance, about 5 times the distance between Pluto and the Sun, which corresponds to 200 times the distance
between the Earth and the Sun. The pair is a rare example of two objects similar in many aspects to extra-solar giant planets, orbiting around each other with no parent star. The more massive component, Oph 98 A, is a young brown dwarf with a mass of 15 times that of Jupiter, which is almost exactly on the boundary separating brown dwarfs from planets. Its companion, Oph 98 B, is only 8 times heavier than Jupiter. Components of binary systems are tied by an invisible link called gravitational binding energy, and this bond gets stronger when objects are more massive or closer to one another. With extremely low masses and a very large separation, Oph 98 has the weakest binding energy of any binary system known to date.

Astronomers discovered the companion to Oph 98 A using images from the Hubble Space Telescope. Low-mass brown dwarfs are very cold and emit very little light, only through infrared thermal radiation. This heat glow is extremely faint and red, and brown dwarfs are hence only visible in infrared light. Furthermore, the stellar association in which the binary is located, Ophiuchus, is embedded in a dense, dusty cloud which scatters visible light. Infrared observations are the only way to see through this dust. Detecting a system like Oph 98 also requires a camera with a very high resolution, as the angle separating Oph 98 A and B is a thousand times smaller than the size of the moon in the sky. The Hubble Space Telescope is among the few telescopes capable of observing objects as faint as these brown dwarfs, and able to resolve such tight angles. Because brown dwarfs are cold enough, water vapour forms in their atmospheres, creating prominent features in the infrared that are commonly used to identify brown dwarfs. However, these water signatures cannot be easily detected from the surface of the Earth. Located above the atmosphere in the vacuum of space, Hubble allows astronomers to probe the existence of water vapour in astronomical objects. Both objects looked very red and showed clear signs of water molecules. This immediately confirmed that the faint source observed next to Oph 98 A was very likely to also be a cold brown dwarf, rather than a random star that happened to be aligned with the brown dwarf in the sky. The team also found images in which the binary was visible, collected 14 years ago with the Canada-France-Hawaii Telescope (CFHT) in Hawaii. The Oph 98 binary system formed only 3 million years ago making it a newborn on astronomical timescales. The age of the system is much shorter than the typical time needed to build planets. Brown dwarfs like Oph 98 A are formed by the same mechanisms as stars. Despite Oph 98 B being the right size for a planet, the host Oph 98 A is too small to have a sufficiently large reservoir of material to build a planet that big. This tells us that Oph 98 B, like its host, must have formed through the same mechanisms that produce stars and shows that the processes that create binary stars operate on scale-down versions all the way down to these planetary masses.


THE FARTHEST GALAXY IN THE UNIVERSE
University of Tokyo

A team of astronomers used the Keck I telescope to measure the distance to an ancient galaxy. They deduced the target galaxy GN-z11 is not only the oldest galaxy but also the most distant. It's so distant it defines the very boundary of the observable Universe itself. The team hopes this study can shed light on a period of cosmological history when the Universe was only a few hundred million years old. We've all asked ourselves the big questions at times: "How big is the Universe?" or"How and when did galaxies form?" Astronomers take these questions very seriously, and use fantastic tools that push the boundaries of technology to try and answer them. From previous studies, the galaxy GN-z11 seems to be the farthest detectable galaxy from us, at 13.4 billion light years. But measuring and verifying such a distance is not an easy task. The team measured what's known as the redshift of GN-z11; this refers to the way light stretches out, becomes redder, the farther it travels. Certain chemical signatures, called emission lines, imprint distinct patterns in the light from distant objects. By measuring how stretched these tell-tale signatures are, astronomers can deduce how far the light must have travelled, thus giving away the distance from the target galaxy.

The team looked at ultraviolet light specifically, as that is the area of the electromagnetic spectrum it expected to find the redshifted chemical signatures.  The Hubble Space Telescope detected the signature multiple times in the spectrum of GN-z11. However, even the Hubble cannot resolve ultraviolet emission lines to the degree we needed. So astronomers turned to a more up-to-date ground-based spectrograph, an instrument to measure emission lines, called MOSFIRE, which is mounted to the Keck I telescope in Hawaii. The MOSFIRE captured the emission lines from GN-z11 in detail, which allowed the team to make a much better estimation on its distance than was possible from previous data. When working with distances at these scales, astronomers use a value known as the redshift number denoted by z. The team improved the accuracy of the galaxy's z value by a factor of 100. If subsequent observations can confirm this, then the astronomers can confidently say GN-z11 is the farthest galaxy ever detected in the Universe.



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