Space news topic and space related news

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Astronomers re-create the formation of Jupiter's Galilean moons using new theory
https://astronomy.com/news/2020/05/astronomers-recreate-the-formation-of-jupiters-galilean-moons-using-new-theory

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ALMA Discovers Massive Rotating Disk in Early Universe
https://www.almaobservatory.org/en/press-release/alma-discovers-massive-rotating-disk-in-early-universe/

In our 13.8 billion-year-old Universe, most galaxies like our Milky Way form gradually, reaching their large mass relatively late. But a new discovery made with the Atacama Large Millimeter/submillimeter Array (ALMA) of a massive rotating disk galaxy, seen when the Universe was only ten percent of its current age, challenges the traditional models of galaxy formation. This research appears on 20 May 2020 in the journal Nature.

Galaxy DLA0817g, nicknamed the Wolfe Disk after the late astronomer Arthur M. Wolfe, is the most distant rotating disk galaxy ever observed. The unparalleled power of ALMA made it possible to see this galaxy spinning at 170 miles (272 kilometers) per second, similar to our Milky Way.

"While previous studies hinted at the existence of these early rotating gas-rich disk galaxies, thanks to ALMA we now have unambiguous evidence that they occur as early as 1.5 billion years after the Big Bang," said lead author Marcel Neeleman of the Max Planck Institute for Astronomy in Heidelberg, Germany.

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ALMA Spots Twinkling Heart of Milky Way
https://www.almaobservatory.org/en/press-release/alma-spots-twinkling-heart-of-milky-way/

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) found quasi-periodic flickers in millimeter-waves from the center of the Milky Way, Sagittarius (Sgr) A*. The team interpreted these blinks to be due to the rotation of radio spots circling the supermassive black hole with an orbit radius smaller than that of Mercury. This is an interesting clue to investigate space-time with extreme gravity.

"It has been known that Sgr A* sometimes flares up in millimeter wavelength," tells Yuhei Iwata, the lead author of the paper published in the Astrophysical Journal Letters and a graduate student at Keio University, Japan. "This time, using ALMA, we obtained high-quality data of radio-wave intensity variation of Sgr A* for 10 days, 70 minutes per day. Then we found two trends: quasi-periodic variations with a typical time scale of 30 minutes and hour-long slow variations."

Astronomers presume that a supermassive black hole with a mass of 4 million suns is located at the center of Sgr A*. Flares of Sgr A* have been observed not only in millimeter wavelength, but also in infrared light and X-ray. However, the variations detected with ALMA are much smaller than the ones previously detected, and it is possible that these levels of small variations always occur in Sgr A*.

The black hole itself does not produce any kind of emission. The source of the emission is the scorching gaseous disk around the black hole. The gas around the black hole does not go straight to the gravitational well, but it rotates around the black hole to form an accretion disk.

The team focused on short timescale variations and found that the variation period of 30 minutes is comparable to the orbital period of the innermost edge of the accretion disk with the radius of 0.2 astronomical units (1 astronomical unit corresponds to the distance between the Earth and the Sun: 150 million kilometers). For comparison, Mercury, the solar system's innermost planet, circles around the Sun at a distance of 0.4 astronomical units. Considering the colossal mass at the center of the black hole, its gravity effect is also extreme in the accretion disk.

"This emission could be related with some exotic phenomena occurring at the very vicinity of the supermassive black hole," says Tomoharu Oka, a professor at Keio University.

Their scenario is as follows. Hot spots are sporadically formed in the disk and circle around the black hole, emitting strong millimeter waves. According to Einstein's special relativity theory, the emission is largely amplified when the source is moving toward the observer with a speed comparable to that of light. The rotation speed of the inner edge of the accretion disk is quite large, so this extraordinary effect arises. The astronomers believe that this is the origin of the short-term variation of the millimeter emission from Sgr A*.

The team supposes that the variation might affect the effort to make an image of the supermassive black hole with the Event Horizon Telescope. "In general, the faster the movement is, the more difficult it is to take a photo of the object," says Oka. "Instead, the variation of the emission itself provides compelling insight for the gas motion. We may witness the very moment of gas absorption by the black hole with a long-term monitoring campaign with ALMA." The researchers aim to draw out independent information to understand the mystifying environment around the supermassive black hole.

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Pluto's strange atmosphere just collapsed
https://astronomy.com/news/2020/05/plutos-strange-atmosphere-just-collapsed

The dramatic fall in atmospheric pressure on Pluto is much larger than astronomers expected.

Pluto's atmosphere is hard to observe from Earth. It can only be studied when Pluto passes in front of a distant star, allowing astronomers to see the effect the atmosphere has on starlight. When this happened in 2016, it confirmed that Pluto's atmosphere was growing, a trend that astronomers had observed since 1988, when they noticed it for the first time.

Now, all that has changed — Pluto's atmosphere appears to have collapsed. The most recent occultation in July last year was observed by Ko Arimatsu at Kyoto University in Japan and colleagues. They say the atmospheric pressure seems to have dropped by over 20 percent since 2016.

First, some background. Astronomers have long known that Pluto's atmosphere expands as it approaches the sun and contracts as it recedes. When the sun heats its icy surface, it sublimates, releasing nitrogen, methane and carbon dioxide into the atmosphere. When it moves away, the atmosphere is thought to freeze and fall out of the sky in what must be one of the most spectacular ice storms in the solar system.

Pluto reached its point of closest approach to the sun in 1989, and has since been moving away. But its atmosphere has continued to increase to a level that is about 1/100,000 of Earth's.

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Wandering stars pass through our solar system surprisingly often
https://astronomy.com/news/2020/05/wandering-stars-brush-past-our-solar-system-surprisingly-often

Our sun has had close encounters with other stars in the past, and it's due for a dangerously close one in the not-so-distant future.

Every 50,000 years or so, a nomadic star passes near our solar system. Most brush by without incident. But, every once in a while, one comes so close that it gains a prominent place in Earth's night sky, as well as knocks distant comets loose from their orbits.

The most famous of these stellar interlopers is called Scholz's Star. This small binary star system was discovered in 2013. Its orbital path indicated that, about 70,000 years ago, it passed through the Oort Cloud, the extended sphere of icy bodies that surrounds the fringes of our solar system. Some astronomers even think Scholz's Star could have sent some of these objects tumbling into the inner solar system when it passed.

However, Scholz's Star is relatively small and rapidly moving, which should have minimized its effect on the solar system. But in recent years, scientists have been finding that these kinds of encounters happen far more often than once expected. Scholz's Star wasn't the first flyby, and it won't be the last. In fact, we're on track for a much more dramatic close encounter in the not-too-distant future.

"[Scholz's Star] probably didn't have a huge impact, but there should be many more stars that have passed through that are more massive," astronomer Eric Mamajek of NASA's Jet Propulsion Laboratory, whose 2015 paper in Astrophysical Journal Letters put Scholz's Star on the map, tell Astronomy.

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ESO Telescope Sees Signs of Planet Birth
https://www.eso.org/public/news/eso2008/

Observations made with the European Southern Observatory's Very Large Telescope (ESO's VLT) have revealed the telltale signs of a planetary system being born. Around the young star AB Aurigae lies a dense disc of dust and gas in which astronomers have spotted a prominent spiral structure with a 'twist' that marks the site where a planet may be forming. The observed feature could be the first direct evidence of a baby planet coming into existence.

The new images feature a stunning spiral of dust and gas around AB Aurigae, located 520 light-years away from Earth in the constellation of Auriga (The Charioteer). Spirals of this type signal the presence of baby planets, which 'kick' the gas, creating "disturbances in the disc in the form of a wave, somewhat like the wake of a boat on a lake," explains Emmanuel Di Folco of the Astrophysics Laboratory of Bordeaux (LAB), France, who also participated in the study. As the planet rotates around the central star, this wave gets shaped into a spiral arm. The very bright yellow 'twist' region close to the centre of the new AB Aurigae image, which lies at about the same distance from the star as Neptune from the Sun, is one of these disturbance sites where the team believe a planet is being made.

Observations of the AB Aurigae system made a few years ago with the Atacama Large Millimeter/submillimeter Array (ALMA), in which ESO is a partner, provided the first hints of ongoing planet formation around the star. In the ALMA images, scientists spotted two spiral arms of gas close to the star, lying within the disc's inner region. Then, in 2019 and early 2020, Boccaletti and a team of astronomers from France, Taiwan, the US and Belgium set out to capture a clearer picture by turning the SPHERE instrument on ESO's VLT in Chile toward the star. The SPHERE images are the deepest images of the AB Aurigae system obtained to date.



Images of the AB Aurigae system showing the disc around it. The image on the right, a zoomed-in version of the central part of the image on the left, shows the inner region of the disc. This inner region includes the 'twist' (in very bright yellow) that scientists believe marks the spot where a planet is forming. This twist lies at about the same distance from the AB Aurigae star as Neptune from the Sun.

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SpaceX's Crew Dragon launch: What to know about the historic mission
https://astronomy.com/news/2020/05/spacexs-crew-dragon-launch-what-to-know-about-the-historic-mission

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JUPITER HAS TRAPPED A COMET IN A BIZARRE ORBIT
Astronomers have discovered a comet trapped in a weird orbit near Jupiter
https://skyandtelescope.org/astronomy-news/jupiter-has-trapped-a-comet-in-a-bizarre-orbit/

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Finally!

SpaceX and Nasa launch Crew Dragon spacecraft
https://www.telegraph.co.uk/technology/2020/05/30/spacex-nasa-launch-crew-dragon-spacecraft-live-updates/

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Hot stars are plagued by giant magnetic spots, ESO data shows
https://www.eso.org/public/news/eso2009/

Astronomers using European Southern Observatory (ESO) telescopes have discovered giant spots on the surface of extremely hot stars hidden in stellar clusters. Not only are these stars plagued by magnetic spots, some also experience superflare events, explosions of energy several million times more energetic than similar eruptions on the Sun. The findings, published today in Nature Astronomy, help astronomers better understand these puzzling stars and open doors to resolving other elusive mysteries of stellar astronomy.

The team, led by Yazan Momany from the INAF Astronomical Observatory of Padua in Italy, looked at a particular type of star known as extreme horizontal branch stars — objects with about half the mass of the Sun but four to five times hotter. "These hot and small stars are special because we know they will bypass one of the final phases in the life of a typical star and will die prematurely," says Momany, who was previously a staff astronomer at ESO's Paranal Observatory in Chile. "In our Galaxy, these peculiar hot objects are generally associated with the presence of a close companion star."

Surprisingly, however, the vast majority of these extreme horizontal branch stars, when observed in tightly packed stellar groups called globular clusters, do not appear to have companions. The team's long-term monitoring of these stars, made with ESO telescopes, also revealed that there was something more to these mysterious objects. When looking at three different globular clusters, Momany and his colleagues found that many of the extreme horizontal branch stars within them showed regular changes in their brightness over the course of just a few days to several weeks.

"After eliminating all other scenarios, there was only one remaining possibility to explain their observed brightness variations," concludes Simone Zaggia, a study co-author from the INAF Astronomical Observatory of Padua in Italy and a former ESO Fellow: "these stars must be plagued by spots!"

Spots on extreme horizontal branch stars appear to be quite different from the dark sunspots on our own Sun, but both are caused by magnetic fields. The spots on these hot, extreme stars are brighter and hotter than the surrounding stellar surface, unlike on the Sun where we see spots as dark stains on the solar surface that are cooler than their surroundings. The spots on extreme horizontal branch stars are also significantly larger than sunspots, covering up to a quarter of the star's surface. These spots are incredibly persistent, lasting for decades, while individual sunspots are temporary, lasting only a few days to months. As the hot stars rotate, the spots on the surface come and go, causing the visible changes in brightness.

Beyond the variations in brightness due to spots, the team also discovered a couple of extreme horizontal branch stars that showed superflares — sudden explosions of energy and another signpost of the presence of a magnetic field. "They are similar to the flares we see on our own Sun, but ten million times more energetic," says study co-author Henri Boffin, an astronomer at ESO's headquarters in Germany. "Such behaviour was certainly not expected and highlights the importance of magnetic fields in explaining the properties of these stars."

After six decades of trying to understand extreme horizontal branch stars, astronomers now have a more complete picture of them. Moreover, this finding could help explain the origin of strong magnetic fields in many white dwarfs, objects that represent the final stage in the life of Sun-like stars and show similarities to extreme horizontal branch stars. "The bigger picture though," says team member, David Jones, a former ESO Fellow now at the Instituto de Astrofísica de Canarias, Spain, "is that changes in brightness of all hot stars — from young Sun-like stars to old extreme horizontal branch stars and long-dead white dwarfs — could all be connected. These objects can thus be understood as collectively suffering from magnetic spots on their surfaces."

To arrive at this result, the astronomers used several instruments on ESO's Very Large Telescope (VLT), including VIMOS, FLAMES and FORS2, as well as OmegaCAM attached to the VLT Survey Telescope at Paranal Observatory. They also employed ULTRACAM on the New Technology Telescope at ESO's La Silla Observatory, also in Chile. The breakthrough came as the team observed the stars in the near-ultraviolet part of the spectrum, allowing them to reveal the hotter, extreme stars standing out bright amongst the cooler stars in globular clusters.

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INTENSE FLASH FROM MILKY WAY'S BLACK HOLE ILLUMINATED GAS FAR OUTSIDE OF OUR GALAXY
https://hubblesite.org/contents/news-releases/2020/news-2020-33

CATACLYSMIC BLAST FELT 200,000 LIGHT-YEARS AWAY
About 3.5 million years ago, our distant hominid ancestors might have noticed a mysterious glowing spot along the arc of the star-studded Milky Way. Today we know that this would have been evidence for a tremendous explosion around a black hole that rocked the center of our galaxy. Scientists using Hubble now see the aftermath of that enormous flash of light that beamed out of our galaxy's center way back then. It illuminated a huge, ribbon-like tail of gas orbiting the Milky Way. Called the Magellanic Stream, this long trail lies far outside of our galaxy, at an average distance of 200,000 light-years. Like an aircraft contrail, It extends from neighboring dwarf galaxies called the Large and Small Magellanic Clouds. Researchers made careful ultraviolet measurements of distant quasars behind the Magellanic Stream. As the ultraviolet light from the quasars passed through the stream, Hubble recorded the telltale fingerprints of how the flash altered the gas.

About 3.5 million years ago, the supermassive black hole at the center of our Milky Way galaxy unleashed an enormous burst of energy. Our primitive ancestors, already afoot on the African plains, likely would have witnessed this flare as a ghostly glow high overhead in the constellation Sagittarius. It might have persisted for 1 million years.

Now, eons later, astronomers are using NASA's Hubble Space Telescope's unique capabilities to uncover even more clues about this cataclysmic explosion. Looking to the far outskirts of our galaxy, they found that the black hole's floodlight reached so far into space it illuminated a vast train of gas trailing the Milky Way's two prominent satellite galaxies: the Large Magellanic Cloud (LMC), and its companion, the Small Magellanic Cloud (SMC).

The black hole outburst was probably caused by a large hydrogen cloud up to 100,000 times the Sun's mass falling onto the disk of material swirling near the central black hole. The resulting outburst sent cones of blistering ultraviolet radiation above and below the plane of the galaxy and deep into space.

The radiation cone that blasted out of the Milky Way's south pole lit up a massive ribbon-like gas structure called the Magellanic Stream. The flash lit up a portion of the stream, ionizing its hydrogen (enough to make 100 million Suns) by stripping atoms of their electrons.

"The flash was so powerful that it lit up the stream like a Christmas tree—it was a cataclysmic event!" said principal investigator Andrew Fox of the Space Telescope Science Institute (STScI) in Baltimore, Maryland. "This shows us that different regions of the galaxy are linked—what happens in the galactic center makes a difference to what happens out in the Magellanic Stream. We're learning about how the black hole impacts the galaxy and its environment."

Fox's team used Hubble's ultraviolet capabilities to probe the stream by using background quasars—the bright cores of distant, active galaxies—as light sources. Hubble's Cosmic Origins Spectrograph can see the fingerprints of ionized atoms in the ultraviolet light from the quasars. The astronomers studied sightlines to 21 quasars far behind the Magellanic Stream and 10 behind another feature called the Leading Arm, a tattered and shredded gaseous "arm" that precedes the LMC and SMC in their orbit around the Milky Way.

"When the light from the quasar passes through the gas we're interested in, some of the light at specific wavelengths gets absorbed by the atoms in the cloud," said STScI's Elaine Frazer, who analyzed the sightlines and discovered new trends in the data. "When we look at the quasar light spectrum at specific wavelengths, we see evidence of light absorption that we wouldn't see if the light hadn't passed through the cloud. From this, we can draw conclusions about the gas itself."

The team found evidence that the ions had been created in the Magellanic Stream by an energetic flash. The burst was so powerful that it lit up the stream, even though this structure is about 200,000 light-years from the galactic center.

Unlike the Magellanic Stream, the Leading Arm did not show evidence of being lit up by the flare. That makes sense, because the Leading Arm is not sitting right below the south galactic pole, so it was not showered with the burst's radiation.

The same event that caused the radiation flare also "burped" hot plasma that is now towering about 30,000 light-years above and below the plane of our galaxy. These invisible bubbles, weighing the equivalent of millions of Suns, are called the Fermi Bubbles. Their energetic gamma-ray glow was discovered in 2010 by NASA's Fermi Gamma-ray Space Telescope. In 2015, Fox used Hubble's ultraviolet spectroscopy to measure the expansion velocity and composition of the ballooning lobes.

Now his team managed to stretch Hubble's reach beyond the bubbles. "We always thought that the Fermi Bubbles and the Magellanic Stream were separate and unrelated to each other and doing their own things in different parts of the galaxy's halo," said Fox. "Now we see that the same powerful flash from our galaxy's central black hole has played a major role in both."

This research was possible only because of Hubble's unique ultraviolet capability. Because of the filtering effects of Earth's atmosphere, ultraviolet light cannot be studied from the ground. "It's a very rich region of the electromagnetic spectrum—there's a lot of features that can be measured in the ultraviolet," explained Fox. "If you work in the optical and infrared, you can't see them. That's why we have to go to space to do this. For this type of work, Hubble is the only game in town."

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HUBBLE MAKES SURPRISING FIND IN THE EARLY UNIVERSE
https://hubblesite.org/contents/news-releases/2020/news-2020-34

DEEP SPACE QUEST DOESN'T FIND THE FIRST STARS, PUSHING BACK THE TIMELINE OF THE UNIVERSE'S EVOLUTION.
In Greek mythology the first deities born from the universe's origin in "the Chaos," created a race of Titans. The powerful Titans were eventually superseded by the gods of Olympus. In modern cosmology, the stellar equivalent of the legendary Titans are so-called Population III stars, that would have been the very first stars born after the big bang. These hypothetical stars are as elusive as the Titans. Unlike the stars of today—like our Sun (that contains heavier elements, such as oxygen, nitrogen, carbon and iron)—the Population III stars would have been solely made out of the few primordial elements first forged in the seething crucible of the big bang. Much more massive and brighter than our Sun, they would have defiantly blazed as lords over the inky void of the newborn universe.

A team of European researchers, led by Rachana Bhatawdekar of the European Space Agency, set out to find the elusive first-generation stars by probing from about 500 million to 1 billion years after the big bang. In their quest they used observations from Hubble, NASA's Spitzer Space Telescope, and the ground-based Very Large Telescope of the European Southern Observatory. They used the gravitational lensing power of a massive foreground galaxy cluster (that acts as a giant magnifying lens in space) to find brightened images of far more distant background galaxies 10 to 100 times fainter than any previously observed. Unfortunately, the team found no evidence of these first-generation Population III stars in this cosmic time interval they explored. These results are nevertheless important because they show that galaxies must have formed even earlier after the big bang than previously thought.

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Eltur tìtxen si...

Ancient Mars may have once had rings, then moons, then rings ...
https://astronomy.com/news/2020/06/ancient-mars-may-have-once-had-rings-then-moons-then-rings

Like a phoenix rising from its ashes, scientists believe one of Mars' current moons, Phobos, may have been born from a ring of dust left by former versions of itself.

For a long time after their discovery in 1877, scientists assumed Mars' two puny moons — Deimos and Phobos — were captured asteroids. This belief persisted until evidence revealed both moons formed at the same time as the Red Planet itself, and that the smaller one, Deimos, has a mysteriously tilted orbit. However, it wasn't until 2017 that researchers put forth a new idea that could explain why Deimos' orbit is slanted by 2 degrees.

"The fact that Deimos' orbit is not exactly in plane with Mars' equator was considered unimportant," said SETI Institute research scientist and lead author Matija Ćuk in a press release. "But once we had a big new idea and we looked at it with new eyes, Deimos' orbital tilt revealed a big secret."

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The history and future of telescopes on the Moon
https://astronomy.com/news/2020/06/the-history-and-future-of-telescopes-on-the-moon

For generations, astronomers have dreamed of building telescopes on the lunar farside. And that dream may soon be a reality.

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What has the Juno spacecraft taught us about Jupiter?
The workhorse spacecraft has been circling our solar system's largest planet since 2016. Here are four things we've learned so far about the gas giant.

https://astronomy.com/news/2020/06/jupiter-revealed

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Tower Extension Test a Success for NASA's James Webb Space Telescope
https://www.technology.org/2020/06/10/tower-extension-test-a-success-for-nasas-james-webb-space-telescope/

To test the James Webb Space Telescope's readiness for its journey in space, technicians successfully commanded it to deploy and extend a critical part of the observatory known as the Deployable Tower Assembly.

The primary purpose of the deployable tower is to create a large gap between the upper part of the observatory that houses its iconic gold mirrors and scientific instruments, and the lower section known as the spacecraft bus which holds its comparatively warm electronics and propulsion systems. By creating a space between the two, it allows for Webb's active and passive cooling systems to bring its mirrors and sensors down to staggeringly cold temperatures required to perform optimal science.

Webb was designed to look for faint traces of infrared light, which is essentially heat energy. To detect the extremely faint heat signals of astronomical objects that are incredibly far away, the telescope itself has to be very cold and stable.

During the test, the tower was slowly extended 48 inches (1.2 meters) upward over the course of several hours, in the same maneuver it will perform once in space. Simulating the zero-gravity environment Webb will operate in, engineers employed an innovative series of pulleys, counterbalances and a special crane called a gravity-negation system that perfectly offloaded all of the effects of Earth's gravity on the observatory. Now that Webb is fully assembled, the difficulty of testing and properly simulating a zero-gravity environment has increased significantly.

"The Deployable Tower Assembly worked beautifully during the test," said Alphonso Stewart the Webb deployment systems lead for NASA's Goddard Space Flight Center in Greenbelt, Maryland. "It performed exactly as predicted, and from our expectations from previous tests before the full observatory was assembled. This was the first time that this part of Webb was tested in its flight-like configuration to the highest level of fidelity we possibly could. This test provides the opportunity to assess all interfaces and interactions between the instrument and bus sections of the observatory."

In addition to helping the observatory cool down, the Deployable Tower Assembly is also a big part of how Webb is able to pack into a much smaller size to fit inside an Ariane 5 rocket for launch. Webb is the largest space science observatory ever built, but to fit a telescope that big into a rocket, engineers had to design it to fold down into a much smaller configuration. Webb's Deployable Tower Assembly helps Webb to just barely fit inside a 17.8-foot (5.4-meter) payload fairing. Once in space, the tower will extend to give the rest of Webb's deployable parts, such as the sunshield and mirrors, the necessary amount of room needed to unpack and unfold into a fully functional infrared space observatory.

"We need to know that Webb will work the way we expect it to before we send it to space," said Stewart. "This is why we test, and when we do, we test as flight-like as possible. The way we send the commands to the spacecraft, the sequence, the individual sitting at the console, the communication that we use. We replicate all of these things to see if we are missing something, to see if there is something that needs to be changed, and to make sure that all of our planning to date has been correct."

Following augmented personal safety procedures due to COVID-19, the James Webb Space Telescope's Northrop Grumman team in California continued integration and testing work with significantly reduced on-site personnel and shifts. The NASA/Northrop Grumman team recently resumed near-full operations. NASA is evaluating potential impacts on the March 2021 launch date, and will continually assess the schedule and adjust decisions as the situation unfolds.

NASA's James Webb Space Telescope will be the world's premier space science observatory when it launches. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.

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Neutron Stars Could Have a Layer of Exotic Quark Matter Inside Them
https://www.technology.org/2020/06/12/neutron-stars-could-have-a-layer-of-exotic-quark-matter-inside-them/

Neutron stars are strange things. They can form when gravity kills a star, crushing its remains into a dense ball the size of a small city. They are so dense that only quantum forces and the Pauli exclusion principle keeps it from collapsing into a black hole singularity. The interior of a neutron star is so dense that matter behaves in ways we still don't fully understand.

They are called neutron stars because their gravity destroys the structure of atoms. Electrons are squeezed into protons to create neutrons. Much of the star's interior becomes a sea of neutrons as dense as the nuclei of atoms. But we know these stars aren't purely made of neutrons. They have atmospheres only a few centimeters thick. Young neutron stars have a sky of mostly carbon and as dense as diamonds. Like Earth, neutron stars have a rigid crust that floats on a fluid interior. This crust is made of iron nuclei. It actively changes, and can undergo starquakes, much like earthquakes on our world.

But it is the deep interior where things get strange. Although the interior of a neutron star is extremely hot, the density is so high that the neutron sea becomes superfluid. Its behavior is similar to that of liquid helium when cooled to only a couple degrees above absolute zero. The fluid interior can generate tremendous magnetic fields, turning these stars into magnetars and pulsars.

We can't observe the interior of a neutron star directly, so our understanding of them depends upon our understanding of its equation of state. For neutron stars, this is given by the Tolman–Oppenheimer–Volkoff (TOV) equation. While this equation can work well for regular stars, it poses a challenge for neutron stars because neutrons aren't fundamental particles.

Neutrons are made of three quarks, two down quarks and one up quark. Up and down quarks are only two of the six types of known quarks. In our everyday lives, and even in the hearts of stars, the quarks of a neutron stick tightly together. For all practical purposes, a neutron can be treated like a simple particle. But in the core of a neutron star, things get complicated. Tightly packed neutrons might melt into a fluid of quarks, and when up and down quarks collide at high energies they might produce other quarks such as strange or charm. Or they might not.

To answer this question, a recent study compared the physics of quarks with observed neutron star properties. The study started with a detailed theoretical calculation of the properties quark matter would have. One of these properties involves the speed of sound in quark matter. Since pressure waves from things such as starquakes travel at the speed of sound, it plays a crucial role in the structure of neutron stars.

In turns out that in pure quark matter speed of sound is independent of the temperature and pressure of the material. This is not true of neutron matter. Given some reasonable assumptions about neutron star interiors, pressure waves in the deep interior of a neutron star could free quarks from their neutrons, creating a quark core. The size of this core depends upon the total mass of the neutron star.

The authors note that there is some small possibility that neutron stars don't have quark cores, but there is other evidence to support the idea. Recent gravitational-wave observations of a merging neutron star confirm that its size agrees with the quark model. Astronomers have also recently found several neutrons stars with a mass greater than two solar masses. These large-mass neutron stars are much more likely to have quark cores.

While further studies are needed to confirm this result, it seems clear that the interior of neutron stars have much more structure than was earlier thought.

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NASA's New Horizons Conducts the First Interstellar Parallax Experiment
https://www.technology.org/2020/06/15/nasas-new-horizons-conducts-the-first-interstellar-parallax-experiment/

For the first time, a spacecraft has sent back pictures of the sky from so far away that some stars appear to be in different positions than we'd see from Earth.

More than four billion miles from home and speeding toward interstellar space, NASA's New Horizons has traveled so far that it now has a unique view of the nearest stars. "It's fair to say that New Horizons is looking at an alien sky, unlike what we see from Earth," said Alan Stern, New Horizons principal investigator from Southwest Research Institute (SwRI) in Boulder, Colorado. "And that has allowed us to do something that had never been accomplished before — to see the nearest stars visibly displaced on the sky from the positions we see them on Earth."

On April 22-23, the spacecraft turned its long-range telescopic camera to a pair of the "closest" stars, Proxima Centauri and Wolf 359, showing just how they appear in different places than we see from Earth. Scientists have long used this "parallax effect" – how a star appears to shift against its background when seen from different locations — to measure distances to stars.

An easy way to see parallax is to place one finger at arm's length and watch it jump back and forth when you view it successively with each eye. Similarly, as Earth makes it way around the Sun, the stars shift their positions. But because even the nearest stars are hundreds of thousands of times farther away than the diameter of Earth's orbit, the parallax shifts are tiny, and can only be measured with precise instrumentation.

"No human eye can detect these shifts," Stern said.

But when New Horizons images are paired with pictures of the same stars taken on the same dates by telescopes on Earth, the parallax shift is instantly visible. The combination yields a 3D view of the stars "floating" in front of their background star fields.

"The New Horizons experiment provides the largest parallax baseline ever made — over 4 billion miles — and is the first demonstration of an easily observable stellar parallax," said Tod Lauer, New Horizons science team member from the National Science Foundation's National Optical-Infrared Astronomy Research Laboratory who coordinated the parallax demonstration.

"The New Horizons spacecraft is truly a mission of firsts, and this demonstration of stellar parallax is no different" said Kenneth Hansen, New Horizons program scientist at NASA Headquarters in Washington. "The New Horizons spacecraft continues to speed away from Earth toward interstellar space and is continuing to return exciting new data for planetary science."

[Vawmataw]

Txantsan! Maybe they should try Barnard's star, too.

[Toliman]

Yeah, Barnard's star (+ maybe few other relative close stars) would be good target for this too.