JimsAstronomy: 3792 - JAMES WEBB TELESCOPE

3792 - JAMES WEBB TELESCOPE - - It's been a year since the James Webb space telescope was launched toward the L2 Lagrange point on the far side of the Earth from the sun.

--------------------- 3792 - JAMES WEBB TELESCOPE

- SEEING FARTHER INTO THE PAST THAN EVER BEFORE. To see the precious rare photons from the most distant galaxies in the universe, the bigger the telescope, the better. Space telescopes don't come bigger than JWST, with its 21-foot (6.5 meters) primary mirror.

- The farther a galaxy is from us, the faster it is receding from us because of the expansion of the universe, so the more its light becomes stretched, shifting the light toward redder wavelengths.

- The most distant galaxies, which are also the earliest galaxies we can see, emit light that is shifted all the way into near-infrared wavelengths by the time it reaches Earth. It's this redshift that prompted scientists to design JWST to specialize in near- and mid-infrared light.

- Prior to JWST's launch, the most distant known galaxy was one called GN-z11. It has a redshift of 11.1, which corresponds to seeing the galaxy as it was 13.4 billion years ago, just 400 million years after the Big Bang. That was the absolute limit of what telescopes before JWST could detect.

- Objects of great mass, such as galaxy clusters, warp space with their gravity, creating a magnifying lens-like effect that amplifies light from more distant objects. Astronomers began finding faint, red smudges in the background of these lenses. These smudges have turned out to be the most distant galaxies ever seen.

First was a galaxy at a redshift of 12.5, called GLASS-z12 (GLASS is the name of a specific survey program, the "Grism Lens-Amplified Survey from Space"). We see this galaxy as it existed 13.45 billion years ago, or 350 million years after the Big Bang.

- Galaxies with even greater redshifts soon followed. One, nicknamed Maisie's Galaxy, is seen as it existed just 280 million years after the Big Bang, at a redshift of 14.3, while another, at redshift 16.7, is seen just 250 million years after the Big Bang. There have even been claims for a galaxy at an astounding redshift of 20, which if confirmed would have existed just 200 million years after the Big Bang.

- DISCOVERING WHAT LIT UP THE UNIVERSE. Following the Big Bang, but before stars and galaxies had formed, the universe was dark and shrouded in a fog of neutral hydrogen gas. Ultimately light, particularly ultraviolet radiation, ionized that fog. But where did that light initially come from to end the cosmic dark ages?

- Astronomers believe that light came either from young galaxies filled with stars, or from active supermassive black holes, which are surrounded by accretion disks of brilliantly hot gas and shoot powerful jets into space

- This characteristic suggests that fully-formed galaxies were on the scene quickly, but whether they already contained supermassive black holes remains to be seen.

- JWST MEASURES EXOPLANET ATMOSPHERE. Astronomers have now found more than 5,000 exoplanets and counting, but despite this remarkable haul, we still know next to nothing about many of them.

- When a planet passes in front of its star, some of the star's light filters through the planet's atmosphere, and molecules in the atmosphere can absorb some of that starlight, creating dark lines in the star's spectrum, a barcode-like breakdown of light by wavelength. Knowing what's in a planet's atmosphere, or even whether it has an atmosphere at all, can teach astronomers about how a planet might have formed and evolved, what its conditions are like and what chemical processes are taking place in that atmosphere.

- In August, 2022, astronomers announced that JWST had made the first confirmed detection of carbon dioxide gas in the atmosphere of an exoplanet, in this case WASP-39b, which is 700 light years-away.

- Later, in November, astronomers released a more complete spectrum showing the absorption lines of elements and molecules in WASP-39b's atmosphere, including not only carbon dioxide but also carbon monoxide, potassium, sodium, sulfur dioxide and water vapor.

- The spectrum showed that there was a lot more oxygen in the planet's atmosphere than carbon, as well as an abundance of sulfur. Scientists think that sulfur must have come from numerous collisions that WASP-39b experienced with smaller planetesimals when it was forming, giving us clues to the planet's evolution that could also hint at how the gas giants in our own solar system, Jupiter and Saturn, formed.

- In addition, the existence of sulfur dioxide is the first example of a product of photochemistry on a planet beyond the solar system, since the compound forms when a star's ultraviolet light reacts with molecules in a planetary atmosphere.

- WEBB SEARCHES FOR HINTS OF LIFE AND HABITABILITY. The planets of the TRAPPIST-1 system of seven rocky planets orbiting a red dwarf star located 40.7 light-years away from Earth. Four of these worlds lie in the star's putative habitable zone, where temperatures would permit liquid water to persist on the surface; given the right conditions they could potentially be habitable to varying degrees.

- Models predict that TRAPPIST-1c will have an atmosphere similar to Venus, with lots of carbon dioxide. While TRAPPIST-1c is likely too hot to be habitable, determining whether it has an atmosphere and, if so, whether that atmosphere possesses carbon dioxide will be a big step toward characterizing Earth-size worlds.

- It will also be a big task, requiring 100 hours of observing time with JWST, which is tackling about 10,000 hours of observations during its first year of science.

- JWST is targeting the other worlds in the TRAPPIST-1 system that are more likely to be habitable, as well as similar worlds around other nearby stars. Astronomers will be on the lookout for biosignatures, such as the presence of both methane and oxygen in an atmosphere.

- The discovery of photochemical reactions in WASP-39b's atmosphere is also an important step, since photochemical reactions drive the formation of the carbon-based molecular building blocks of life.

- JWST STUDIES COSMIC CHEMISTRY & GALAXY EVOLUTION. Some stars live for billions upon billions of years, but others exist for just a short time before either exploding in a supernova or expanding to become a red giant that then puffs off its outer layers into deep space. In both situations, the stars disperse large amounts of cosmic dust formed from elements heavier than hydrogen and helium across space.

- It turns out that there is a relationship between a galaxy's mass, its star-formation rate and its chemical abundances. Deviations from this relationship at high redshift might indicate that galaxies evolved differently in the early universe.

- Prior to JWST, astronomers could only reliably measure the abundances of various elements in galaxies up to a redshift of 3.3; in other words, galaxies that existed about 11.5 billion years ago. But how abundant these heavy elements were in galaxies earlier than this is a bit of a mystery.

- Early results from JWST have shown that the relationship between star formation and mass does hold for galaxies at redshifts as high as 8, but that their abundance of heavier elements is three times lower than expected. This discrepancy suggests that stars and galaxies formed more quickly than we realized, before enough generations of stars had the chance to die out and disperse their elements into the cosmos.

- JWST SETS ITS SIGHTS ON THE SOLAR SYSTEM. Brilliant Jupiter, its faint rings and several of its small moons imaged by JWST.

- Astronomers were not sure what to expect when JWST pointed at Jupiter because of how fast it moves and how bright the planet is compared to the faint distant galaxies JWST usually observes. Scientists worried that Jupiter might overload JWST's sensitive detectors or wipe out fainter features with its glare, but the results were better than could be imagined.

- JWST's images showed Jupiter's faint rings and some of its small moons, as well as the planet's atmospheric bands and auroras. By observing in near- and mid-infrared light, with the high resolution that JWST's giant mirror provides, astronomers are able to peer deeper into Jupiter's atmosphere to see what's going on beneath the cloud tops and learn how deeply the clouds extend.

- JWST has also imaged faraway Neptune, Saturn's moon Titan and Mars. While JWST's portrait of the Red Planet shows temperature variations on Mars' surface and absorption by carbon dioxide in its atmosphere. In the future, JWST will observe Mars to track more tenuous gases, such as mysterious seasonal plumes of methane that could originate in either geological or biological activity.

- One of the Hubble Space Telescope's most iconic images was that of the Pillars of Creation, columns of molecular gas many light-years long found in the Eagle Nebula. Those columns are cosmic nurseries where stars are born. JWST has revisited the Pillars of Creation, and the resulting images in near- and mid-infrared light are just as special as the original.

- JWST's infrared vision is able to penetrate through the dust in the Pillars to gain a better view of the star formation going on inside, showing knots of molecular gas on the verge of collapsing into nascent stars. When those stars are just a few hundred thousand years old, they begin to shoot out jets that erode the edges of the Pillars.

- JWST CHANGED HOW SPACE TELESCOPES ARE BUILT. JWST's massive, golden primary mirror, formed by unfolding 18 hexagonal segment, was brand-new engineering to permit a telescope of such great size to be launched into space.

- JWST was launched on December 25, 2021, the $10 billion infrared observatory was designed to learn how galaxies form and grow, to peer far back into the universe to the era of the first galaxies, to watch stars be born inside their nebulous embryos in unprecedented detail, and to probe the atmospheres of exoplanets and characterize some of the closest rocky worlds.

- However, the complexity of the James Webb Space Telescope (Webb or JWST), including its fold-out, segmented 21-foot (6.5 meters) mirror and its delicate sun-shield the size of a tennis court.

- The James Webb Space Telescope launched atop an Ariane 5 rocket from French Guiana on Dec. 25, 2021.

The main reason that JWST is performing so well is because of its superlative optics, which are able to achieve their maximum potential resolution for the majority of infrared wavelengths that the telescope observes in. This success means that JWST's images have a clarity to them that were unobtainable by the likes of the Hubble Space Telescope and NASA's retired Spitzer Space Telescope, or larger telescopes on the ground such as those at the Keck Observatory in Hawaii, whose vision is blurred by Earth's atmosphere.

But with JWST, individual stars so close together they were once indistinguishable can now be resolved; the structures of very distant galaxies are now discernible; and even something close by such as the rings of Neptune pop with the most detail seen in decades.

The James Webb Space Telescope's stunning view of Neptune, with its rings clearly visible.

The James Webb Space Telescope's stunning view of Neptune, with its rings clearly visible. (Image credit: NASA/ESA/CSA/STScI)

"When the JWST's images of Neptune first came out, both Heidi [Hammel, an interdisciplinary scientist on JWST and an expert on the outer planets of the solar system] and myself looked at them, and then at each other, and asked, 'are we really looking at Neptune'?" Naomi Rowe-Gurney, an astronomer at NASA Goddard Space Flight Center in Maryland, told Space.com.

Although the Keck Observatory has imaged Neptune's rings, our most impressive view before JWST came from Voyager 2's flyby in 1989. "Heidi had not seen the rings [this well] since Voyager 2, and I had never seen the rings like this because Voyager was before I was born!" Rowe-Gurney said.

Normally, faint details or features around a bright object, such as the dark and tenuous rings around blue Neptune, are difficult to see against the glare of the bright object. To counteract this, an instrument is required to have the characteristic of "high dynamic range" to take in both the faint and the bright at the same time.

"We didn't realize that JWST would have this amazing dynamic range and be able to resolve really faint things like the rings of Neptune and the small moons and rings of Jupiter," Rowe-Gurney said.

Alien atmospheres

It's not only the planets of our solar system that JWST is scrutinizing. A key aim of the telescope is to detect the composition of exoplanets' atmospheres using a technique called transmission spectroscopy. As a planet transits its star, the star's light shines through the planet's atmosphere, but atoms and molecules within that atmosphere can block some of the light at characteristic wavelengths, which gives away the composition of the atmosphere.

The first exoplanet result released from JWST was the transmission spectrum of WASP-39b, which is a "hot Jupiter" exoplanet orbiting a sun-like star located 700 light-years away. JWST detected carbon dioxide in WASP-39b's atmosphere, the first time the gas has ever been detected on an exoplanet. Other gases present included carbon monoxide, potassium, sodium, water vapor and sulfur dioxide, the last of which can only be created through photochemistry when atmospheric gases react with the ultraviolet light from the planet's star — another exoplanet first.

The James Webb Space Telescope's analysis of the atmospheric composition of WASP-39b.

The James Webb Space Telescope's analysis of the atmospheric composition of WASP-39b. (Image credit: NASA/ESA/CSA/J. Olmsted (STScI))

"I keep being amazed by what we're able to do with the exoplanet data, like the carbon dioxide and the photochemistry that was found in the atmosphere of WASP-39b," Mullally said. "That was really cool, and I don't remember people talking about [detecting photochemistry] ahead of time. I'm really looking forward to seeing what we can do with the terrestrial exoplanets orbiting the cool M-dwarfs and seeing what their atmospheres are made of."

In particular, the TRAPPIST-1 planetary system of seven worlds orbiting an M-dwarf 40 light-years away is a key target of the JWST. Preliminary results, which failed to detect thick blankets of hydrogen surrounding some of the TRAPPIST-1 worlds, were released during a conference held at STScI in December, but we'll have to be patient for more comprehensive results from these planets, of which up to four could reside in their star's habitable zone.

WASP-39b was an easy first target because its star is bright and the planet's signal is strong. M-dwarfs like TRAPPIST-1 are much fainter, despite being closer.

"We have to wait until we can get enough transits of these guys to build up the signal-to-noise, because you can't do it with just one or two transits," Mullally said. "I think we're going to have to wait until at least the end of the cycle 1 observations [summer 2023] before anybody is going to be in a position to say if they've found anything really spectacular."

Star formation near and far

Another aspect of JWST's mission is to not only observe exoplanets, but to better understand how they, and their stars, form. Star formation in particular is a crucial process to understand it because it connects so many things in the universe both near and far.

Longmore is leading a study to use JWST to observe frantic star formation in a region at the center of our own Milky Way galaxy, called the central molecular zone, some 26,000 light-years from us. The center of our galaxy hosts the highest concentration of stars, and at our distance they all appear packed in — indistinguishable to the likes of the Hubble Space Telescope — while copious amounts of dust shroud most of them from view in optical light. Look with a large-aperture infrared telescope like JWST, however, and those two concerns are shoved aside.

"These are the JWST's two capabilities that are going to blow my field apart," Longmore said. The telescope's superb optics are able to resolve individual baby stars in the center of the galaxy, and infrared light will pass right through the dust to reach the observatory.

"Ordinarily, with Hubble, it's like trying to point your telescope at a brick wall and see through it," he added, "But the JWST is looking through a window in that wall and can count individual stars."

The star-forming Pillars of Creation, imaged in mid-infrared by the JWST in what will surely become an iconic picture.

The star-forming Pillars of Creation, imaged in mid-infrared by the JWST in what will surely become an iconic picture. (Image credit: NASA/ESA/CSA/STScI/J. DePasquale (STScI)/A. Pagan (STScI))

It's taking longer to gather all the data from the center of the galaxy, but that's because it's such a complex environment, with bright, diffuse emission everywhere, and all that has to be disentangled from the relevant signal of star formation via determined and careful data processing.

"On all the projects I'm on, people are still fighting with calibration and things, but hopefully in the next six months that will change," Longmore said. He added an amusing story of how one of his team's observations had been blighted by a mysterious circle on the image. After deeper investigation, it turned out that this wasn't some mysterious new phenomenon, but that JWST had previously been looking at bright Jupiter, and the giant planet's after-image had not yet been properly flushed out of the instrument's electronic sensors!

Longmore and his colleagues are targeting the central molecular zone because it is the region in our galaxy that most resembles star-forming conditions in the early universe, when the star-formation rate was high and dense clusters of stars formed. In the Central Molecular Zone, the astronomers intend to measure a property called the initial mass function (IMF), which describes the range of stellar masses in a star-forming nebula.

Currently, astronomers do not understand what determines why stars form with the masses that they have, only that low-mass stars are much more common than luminous high-mass stars, at least in the local universe. Was this still the case over 13 billion years ago in the first galaxies? Answering that question could help explain both how galaxies formed and what ended the universe's dark ages.

Deep fields and the first galaxies

After she saw President Joe Biden reveal the first deep-field image from the JWST, of the galaxy cluster SMACS 0723, a "gravitational lens" whose massive gravity magnifies objects behind it, Frye and her student, Massimo Pascale at the University of California, Berkeley, raced to analyze the image.

"We didn't sleep for three-and-a-half days, and our paper was one of the first two papers submitted on JWST data," Frye said.

Together, they found 42 new gravitationally lensed images of 14 different high-redshift galaxies, galaxies located so far away that the expanding universe has stretched their light, making them appear redder. Further studies and more deep fields followed, and a host of high-redshift candidates were discovered by Frye's team and others, including some galaxies at record-breaking redshifts of 12, 13 and above; these redshifts mean that we see the galaxies as they existed less than 300 million years after the Big Bang.

These high-redshift galaxies have proven something of a surprise, in that they appear more luminous than models of galaxy formation predicted they should be.

"One possible explanation is that they're producing too many high-mass stars, that they have a top-heavy IMF," Longmore said, noting the importance of measuring the IMF in the central molecular zone to understand stellar masses in young neighborhoods.

Why the IMF would be different over 13.5 billion years ago is not understood, but then again the early universe seems to have been a far more intense place than it is today. "In the present day, galaxies in general are not forming stars so actively, but many galaxies formed stars more actively in the early universe," Frye said.

Frye is a member of the PEARLS (Prime Extragalactic Area for Reionization and Lensing Science) team. PEARLS is a JWST project to image a variety of deep fields, including two apparently sparse regions of sky and a number of galaxy clusters and proto-clusters, to observe the first few billion years of galaxy formation.

The PEARLS field looking toward the North Celestial Pole. Inset are numerous types of galaxy, from interacting galaxies to ruby-red dusty star-forming galaxies.

The PEARLS field looking toward the North Celestial Pole. Inset are numerous types of galaxy, from interacting galaxies to ruby-red dusty star-forming galaxies. (Image credit: NASA/ESA/CSA/Rolf A. Jansen, Jake Summers, Rosalia O'Brien, Rogier Windhorst (ASU)/Aaron Robotham (UWA)/Anton M. Koekemoer (STScI)/Christopher Willmer (University of Arizona)/JWST PEARLS Team)

In December, the PEARLs team released their first dataset, of an extraordinary field of distant galaxies close to the North Ecliptic Pole. This region is directly above the main plane of the Milky Way and so is constantly visible to JWST, and it's also high above interfering features such as zodiacal dust.

Within the image are a whole host of galaxies. Some interact and some show a clear spiral structure; the collection exhibits a whole range of colors, from cobalt blue to ruby red. The latter are of great interest to Frye.

"We can now observe [in the PEARLS image] an abundance of red disk galaxies, which we think might be red spirals," Frye said. "This type of galaxy is very interesting because they are analogs of what the Milky Way might have looked like when it was younger."

The reddening is caused by huge amounts of dust in these galaxies; the dust is the result of rapid formation of massive stars that quickly die in supernova explosions and spill vast amounts of dust into space. Such galaxies are completely hidden from Hubble, but infrared light can pass through the dust and make the galaxies visible to JWST.

"The analogy is a New Year's Eve fireworks display," Frye said. "If you have a lot of fireworks going off then eventually they are obscured by dusty smoke."

JimsAstronomy

Thursday, December 29, 2022

3792 - JAMES WEBB TELESCOPE

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