Zitat von Mar 27, 2023NASA’s Webb Measures the Temperature of a Rocky Exoplanet
An international team of researchers has used NASA’s James Webb Space Telescope to measure the temperature of the rocky exoplanet TRAPPIST-1 b. The measurement is based on the planet’s thermal emission: heat energy given off in the form of infrared light detected by Webb’s Mid-Infrared Instrument (MIRI). The result indicates that the planet’s dayside has a temperature of about 500 kelvins (roughly 450 degrees Fahrenheit) and suggests that it has no significant atmosphere.
This is the first detection of any form of light emitted by an exoplanet as small and as cool as the rocky planets in our own solar system. The result marks an important step in determining whether planets orbiting small active stars like TRAPPIST-1 can sustain atmospheres needed to support life. It also bodes well for Webb’s ability to characterize temperate, Earth-sized exoplanets using MIRI.
“These observations really take advantage of Webb’s mid-infrared capability,” said Thomas Greene, an astrophysicist at NASA’s Ames Research Center and lead author on the study published today in the journal Nature. “No previous telescopes have had the sensitivity to measure such dim mid-infrared light.”
TRAPPIST-1 b, the innermost planet, has an orbital distance about one hundredth that of Earth’s and receives about four times the amount of energy that Earth gets from the Sun. Although it is not within the system’s habitable zone, observations of the planet can provide important information about its sibling planets, as well as those of other M-dwarf systems.
“There are ten times as many of these stars in the Milky Way as there are stars like the Sun, and they are twice as likely to have rocky planets as stars like the Sun,” explained Greene. “But they are also very active – they are very bright when they’re young, and they give off flares and X-rays that can wipe out an atmosphere.”
Previous observations of TRAPPIST-1 b with the Hubble and Spitzer space telescopes found no evidence for a puffy atmosphere, but were not able to rule out a dense one.
One way to reduce the uncertainty is to measure the planet’s temperature. “This planet is tidally locked, with one side facing the star at all times and the other in permanent darkness,” said Pierre-Olivier Lagage from CEA, a co-author on the paper. “If it has an atmosphere to circulate and redistribute the heat, the dayside will be cooler than if there is no atmosphere.”
The team used a technique called secondary eclipse photometry, in which MIRI measured the change in brightness from the system as the planet moved behind the star. Although TRAPPIST-1 b is not hot enough to give off its own visible light, it does have an infrared glow. By subtracting the brightness of the star on its own (during the secondary eclipse) from the brightness of the star and planet combined, they were able to successfully calculate how much infrared light is being given off by the planet.
Webb’s detection of a secondary eclipse is itself a major milestone. With the star more than 1,000 times brighter than the planet, the change in brightness is less than 0.1%.
Zitat von May 8, 2023Webb Looks for Fomalhaut’s Asteroid Belt and Finds Much More
Astronomers used NASA’s James Webb Space Telescope to image the warm dust around a nearby young star, Fomalhaut, in order to study the first asteroid belt ever seen outside of our solar system in infrared light. But to their surprise, the dusty structures are much more complex than the asteroid and Kuiper dust belts of our solar system. Overall, there are three nested belts extending out to 14 billion miles (23 billion kilometers) from the star; that’s 150 times the distance of Earth from the Sun. The scale of the outermost belt is roughly twice the scale of our solar system’s Kuiper Belt of small bodies and cold dust beyond Neptune. The inner belts – which had never been seen before – were revealed by Webb for the first time.
The belts encircle the young hot star, which can be seen with the naked eye as the brightest star in the southern constellation Piscis Austrinus. The dusty belts are the debris from collisions of larger bodies, analogous to asteroids and comets, and are frequently described as ‘debris disks.’ “I would describe Fomalhaut as the archetype of debris disks found elsewhere in our galaxy, because it has components similar to those we have in our own planetary system,” said András Gáspár of the University of Arizona in Tucson and lead author of a new paper describing these results. “By looking at the patterns in these rings, we can actually start to make a little sketch of what a planetary system ought to look like – If we could actually take a deep enough picture to see the suspected planets." ... Fomalhaut's dust ring was discovered in 1983 in observations made by NASA's Infrared Astronomical Satellite (IRAS). The existence of the ring has also been inferred from previous and longer-wavelength observations using submillimeter telescopes on Mauna Kea, Hawaii, NASA’s Spitzer Space Telescope, and Caltech's Submillimeter Observatory.
“The belts around Fomalhaut are kind of a mystery novel: Where are the planets?” said George Rieke, another team member and U.S. science lead for Webb’s Mid-Infrared Instrument (MIRI), which made these observations. “I think it's not a very big leap to say there's probably a really interesting planetary system around the star.”
“We definitely didn't expect the more complex structure with the second intermediate belt and then the broader asteroid belt,” added Wolff. “That structure is very exciting because any time an astronomer sees a gap and rings in a disk, they say, ‘There could be an embedded planet shaping the rings!’”
Webb also imaged what Gáspár dubs “the great dust cloud,” which may be evidence for a collision occurring in the outer ring between two protoplanetary bodies. This is a different feature from a suspected planet first seen inside the outer ring by Hubble in 2008. Subsequent Hubble observations showed that by 2014 the object had vanished. A plausible interpretation is that this newly discovered feature, like the earlier one, is an expanding cloud of very fine dust particles from two icy bodies that smashed into each other.
Zitat von July 30, 2023Using the joint NASA/European Space Agency/Canadian Space Agency James Webb Space Telescope, a team of scientists has discovered, for the first time, water vapor within a planet-forming disk. The water vapor, which was found within the inner disk of two circumstellar disks around star PDS 70, is allowing scientists to research the ways by which water makes its way into rocky, terrestrial planets.
Star system PDS 70, located 370 light-years away from Earth, has been the subject of recent discoveries in exoplanet and star system research. In 2018, PDS 70b, which is one of two confirmed exoplanets around PDS 70, became the first protoplanet to ever be directly imaged by a telescope. What’s more, in 2021, a team detected the first-ever circumplanetary disk around PDS 70c — PDS 70b’s sibling planet.
PDS 70 has now returned to the spotlight, as a team of scientists using Webb’s Mid-Infrared Instrument (MIRI) has discovered water vapor within a disk of the star system, which is home to two circumstellar disks (an inner and outer disk). The inner disk is made up of gas, dust, and other cosmic material that may be fueling the formation of new exoplanets. The water vapor detected by Perotti et al. was found less than 160 million kilometers from the star — directly within the region of the inner disk where planets are possibly forming, and at a similar distance to Earth’s separation from the Sun (149.6 million kilometers).
Perotti et al.’s detection of water vapor is the first time water has been found within the terrestrial region of a stellar disk wherein one or more protoplanets are thought to be forming. Scientists have long debated the exact process by which water arrived on Earth, and are using star systems with planet-forming regions like PDS 70 to investigate the ways water can make its way into planets, especially those like Earth.
“We’ve seen water in other disks, but not so close in and in a system where planets are currently assembling. We couldn’t make this type of measurement before Webb,” said Perotti.
Interestingly, the detection of water vapor came as a surprise to Perotti et al., as they believed PDS 70 was too old to efficiently create an environment conducive to planet formation.
PDS 70 is a 5.4-million-year-old K-type star that is cooler than our Sun. Its age and type make it relatively old when compared to other stars with planet-forming disks, so the team of scientists was not expecting to see water vapor in its inner disk.
While these planet-forming disks require a significant amount of material to form planets, the amount of material within the disks can decrease over time and as the host star ages. It is currently thought that either the star’s radiation and stellar wind blow material out of the disks, or the material within the disk clumps together into larger objects that could eventually form planets. Previous studies have not found water within these aged planet-forming disks, which then led scientists to believe that the disks could not survive the stellar radiation and that they were too dry for the formation of rocky planets.
Abschweifung. Aber das es um astronomische Belange geht, parke ich das mal an dieser Stelle.
Zitat Cyberattack shutters major NSF-funded telescopes for more than 2 weeks As astronomers lose valuable windows for observations, cybersecurity experts wonder why hackers would target such facilities 18 Aug 20234:05 PM
A mysterious “cyber incident” at a National Science Foundation (NSF) center coordinating international astronomy efforts has knocked out of commission major telescopes in Hawaii and Chile since the beginning of August. Officials have halted all operations at 10 telescopes, and at a few others only in-person observations can be conducted.
With no clear resolution to the shutdown in sight, research teams are uniting to figure out alternatives as critical observation windows spin out of reach. Given remote control of many telescopes is no longer available, some groups may rush graduate students to Chile to relieve exhausted on-site staff who have spent the past 2 weeks directly operating instruments there.
“We’re all in this together,” says Gautham Narayan, an astronomer at the University of Illinois Urbana-Champaign whose team is trying to save its chance to observe new supernovas using one of the affected Chilean telescopes. The astronomy community has a “grim determination to press on, despite the trying circumstances,” he adds.
NOIRLab, the NSF-run coordinating center for ground-based astronomy, first announced the detection of an apparent cyberattack on its Gemini North telescope in Hilo, Hawaii, in a 1 August press release. Whatever happened may have placed the instrument in physical jeopardy. “Quick reactions by the NOIRLab cyber security team and observing teams prevented damage to the observatory,” the center’s release said.
In response to the incident, NOIRLab powered down all operations at the International Gemini Observatory, which runs the Hilo telescope and its twin, Gemini South, on Cerro Tololo mountain in Chile. (The latter was already offline for a planned outage.) Together, the two 8.1-meter telescopes have revealed vast swaths of celestial wonders—from the birth of supernovae to the closest known black hole to Earth.
Normally, NOIRLab’s computer systems let astronomers remotely operate a variety of other optical ground-based telescopes. But on 9 August the center announced it had also disconnected its computer network from the Mid-Scale Observatories (MSO) network on Cerro Tololo and Cerro Pachon in Chile. This action additionally made remote observations impossible at the Víctor M. Blanco 4-meter and SOAR telescopes. NOIRLab has stopped observations at eight other affiliated telescopes in Chile as well.
NOIRLab has provided few further details about the matter, even to employees. The center declined to answer Science’s query on whether the incident was a ransomware attack, in which hackers demand money for the return of information or control of a facility. A NOIRLab spokesperson tells Science that the center’s information technology staff is “working around the clock to get the telescopes back into the sky.” ... Welbanks relies on high-resolution images from Gemini South to study the atmospheres of exoplanets; the shutdown has already caused him to miss three of his seven observation windows this year. Many colleagues, he says, are managing similar losses. Welbanks emphasizes the wider astronomy community may be “doomed” if the telescopes don’t resume operations: A unique spectrograph, capable of characterizing the atmospheres of far-away planets, is currently mounted on Gemini South, but scheduled to move to a smaller northern telescope in May 2024. If Gemini South doesn’t start up soon so the device transfer happens as planned, astronomers will—for the foreseeable future—lose their chance at valuable spectral data from the southern half of the sky.
Cybersecurity experts are perplexed as to why Gemini North was the target. “Quite possibly, the attacker doesn’t even know they are attacking an observatory,” says Von Welch, retired lead of the NSF Cybersecurity Center of Excellence.
He and others say the episode is another wake-up call for the astronomy community. In November 2022, the Atacama Large Millimeter Array radio telescope in Chile also went dark for nearly2 months as its staff scrambled to respond to a cyberattack. However, Welch also acknowledges the unique security challenges faced by international research institutions such as NOIRLab. Unlike independent private companies or banks, for example, who can easily isolate their systems, the very nature of astronomical research is open access and collaborative. “A best practice would be to firewall everything off,” Welch says. “But it’s like, well, no, you just broke all the scientific workflows.”
Zitat James Webb Space Telescope instrument experiences glitch — but observatory remains in 'good health'
There's good news and bad news about the James Webb Space Telescope.
The bad news is that one of the 'scope's instruments named the Mid-Infrared Instrument, or MIRI, has experienced a bit of an anomaly. But before you get too worried, the good news is that the James Webb Space Telescope (JWST) is still happy, healthy and heartily able to continue decoding the invisible universe for us.
Basically, in April, the JWST team announced that one of MIRI's four observing modes indicated a reduction in the amount of light registered by the instrument. However, after conducting an investigation into the issue, NASA said this change doesn't pose a risk to MIRI's science capabilities. "There is no risk to the instrument," NASA said in a blog post on Thursday (Aug. 24).
Although, the anomaly might have an impact on the amount of exposure time needed when the instrument switches to the particular mode that's been affected.
The mode at hand, called Medium-Resolution Spectroscopy (MRS), is calibrated to obtain infrared data coming from distant regions of the cosmos associated with wavelengths between 5 and 28.5 microns. That range, according to NASA, is where emission from molecules and dust are typically found, making MRS perfect for finding things like planet-forming disks. But, as NASA explains in the blog post, the reduced signal is specific for MIRI imaging at the longer wavelengths specifically.
One of MIRI's other modes, called Low-Resolution Spectrography that specializes in wavelengths between 5 and 12 microns normally connected to object surfaces (like planets), is operating normally, the team says. A fourth MIRI mode, called Coronagraphic Imaging, is currently under investigation. That mode is programmed to directly detect exoplanets and dust disks around host stars through a mechanism known as coronagraphy, which relies on blocking light from one source to gather data about surrounding sources.
Zitat von August 24, 2023On Apr. 21, 2023, the James Webb Space Telescope team shared that one of the MIRI (Mid-Infrared Instrument) observing modes, called Medium-Resolution Spectroscopy (MRS), showed a reduction in the amount of light registered by MIRI’s detectors. Initial analysis of MIRI’s imaging mode did not show a similar effect. However, as part of the team’s investigation into the issue, additional monitoring observations were taken with MIRI imaging. Combined with earlier data, these new calibrations have revealed a reduced signal for MIRI imaging at the longer wavelengths.
This change does not substantially impact MIRI’s science capabilities but will have an impact on the exposure times needed for MIRI imaging.
Zitat NASA Webb Telescope@NASAWebb The Webb telescope has detected carbon dioxide and methane in the atmosphere of exoplanet K2-18 b, a potentially habitable world over 8 times bigger than Earth. Webb’s data suggests the planet might be covered in ocean, with a hydrogen-rich atmosphere: https://go.nasa.gov/3sGKNLe 4:08 PM · Sep 11, 2023
Webb also hinted at a detection of dimethyl sulphide (DMS) on K2-18 b. On Earth, this molecule is only produced by microbial life. Because the detection needs to be confirmed, the team plans to follow up and look for additional evidence of biological activity on the planet.
While K2-18 b is in the habitable zone (where conditions are right for liquid water to exist), that does not necessarily mean it can support life. For instance, it may have a hostile environment due to its active star. Its ocean may also be too hot to be habitable.
Der Planet befindet sich in einer Entfernung von etwa 30 Millionen km von seinem Zentralstern und umläuft ihn in 33 Tagen; die Gleichgewichtstemperatur (angenommen als reiner Schwarzlichtstrahler) beträgt 284°K; der Planet befindet sich also in der habitablen Zone. K2-18 ist ein roter Zwergstern mit der Hälfte der Sonnenmasse, Oberflächentemperatur 3500 Grad, 130 Lichtjahre entfernt im Sternbild Löwe, Helligkeit 13. Größenklasse, mit einem Alter von rund 2,5 Milliarden Jahren und geringer Aktivität (wobei es die Vermutung gibt, daß hier Sonnenflecken für falschpositive Meßwerte sorgen könnten).
Und jetzt kommts: in der bislang einzig bekannten Biosphäre (Sol III) dient Dimethylsulfat, das ein Stoffwechselprodukt von Kieselalgen/Radiolaren ist, über den Ozeanen als die Hauptquelle von Kondensationskernen und damit die Wolkenbildung - und damit die Temperaturregelung (die andere Quelle ist verwehter Wüstenstaub). Ohne solche Kerne kann der Wasserdampf nicht aufällen und wirkt als das stärkste Treibhausgas; in Wolken kondensiert als stärkster kühlender Faktor.
Zitat A new investigation with NASA’s James Webb Space Telescope into K2-18 b, an exoplanet 8.6 times as massive as Earth, has revealed the presence of carbon-bearing molecules including methane and carbon dioxide. Webb’s discovery adds to recent studies suggesting that K2-18 b could be a Hycean exoplanet, one which has the potential to possess a hydrogen-rich atmosphere and a water ocean-covered surface.
The first insight into the atmospheric properties of this habitable-zone exoplanet came from observations with NASA’s Hubble Space Telescope, which prompted further studies that have since changed our understanding of the system. ... The inference of DMS is less robust and requires further validation. “Upcoming Webb observations should be able to confirm if DMS is indeed present in the atmosphere of K2-18 b at significant levels,” explained Madhusudhan.
While K2-18 b lies in the habitable zone, and is now known to harbor carbon-bearing molecules, this does not necessarily mean that the planet can support life. The planet's large size — with a radius 2.6 times the radius of Earth — means that the planet’s interior likely contains a large mantle of high-pressure ice, like Neptune, but with a thinner hydrogen-rich atmosphere and an ocean surface. Hycean worlds are predicted to have oceans of water. However, it is also possible that the ocean is too hot to be habitable or be liquid.
"Although this kind of planet does not exist in our solar system, sub-Neptunes are the most common type of planet known so far in the galaxy," explained team member Subhajit Sarkar of Cardiff University. “We have obtained the most detailed spectrum of a habitable-zone sub-Neptune to date, and this allowed us to work out the molecules that exist in its atmosphere.”
Characterizing the atmospheres of exoplanets like K2-18 b — meaning identifying their gases and physical conditions — is a very active area in astronomy. However, these planets are outshone — literally — by the glare of their much larger parent stars, which makes exploring exoplanet atmospheres particularly challenging.
The team sidestepped this challenge by analyzing light from K2-18 b's parent star as it passed through the exoplanet's atmosphere. K2-18 b is a transiting exoplanet, meaning that we can detect a drop in brightness as it passes across the face of its host star. This is how the exoplanet was first discovered in 2015 with NASA’s K2 mission. This means that during transits a tiny fraction of starlight will pass through the exoplanet's atmosphere before reaching telescopes like Webb. The starlight's passage through the exoplanet atmosphere leaves traces that astronomers can piece together to determine the gases of the exoplanet's atmosphere.
"This result was only possible because of the extended wavelength range and unprecedented sensitivity of Webb, which enabled robust detection of spectral features with just two transits," said Madhusudhan. "For comparison, one transit observation with Webb provided comparable precision to eight observations with Hubble conducted over a few years and in a relatively narrow wavelength range."
"These results are the product of just two observations of K2-18 b, with many more on the way,” explained team member Savvas Constantinou of the University of Cambridge. “This means our work here is but an early demonstration of what Webb can observe in habitable-zone exoplanets.”
The team’s results were accepted for publication in The Astrophysical Journal Letters.
The team now intends to conduct follow-up research with the telescope's MIRI (Mid-Infrared Instrument) spectrograph that they hope will further validate their findings and provide new insights into the environmental conditions on K2-18 b.
"Les hommes seront toujours fous; et ceux qui croient les guérir sont les plus fous de la bande." - Voltaire
Zitat Christopher K. Mellon@ChrisKMellon The James Webb telescope appears to have detected dimethyl sulfide (DMS) in the atmosphere of a planet ~125 light-years from earth. This is not conclusive proof of alien life, but to the best of our scientific knowledge, DMS is only produced by living organisms. https://nasa.gov/universe/exoplanets/web...ere-of-k2-18-b/ 6:26 PM · Oct 1, 2023
Streiflicht zum Thema "Woke Politik vergiftet alles".
Zitat Michael Shermer@michaelshermer Whatever happened to the demand to rename NASA’s James Webb Space Telescope (to "Harriet Tubman Freedom Telescope") because Webb allegedly said something offensive in the 1950s? (Offense archaeologists have been digging.) He never said it. @jonkay full story confirms my play on Hitch's book subtitle: Identity Politics Poisons Everything https://quillette.com/2024/02/15/interse...mic-inquisitor/ 6:50 PM · Feb 16, 2024
Zitat von Quilette.com, 15 Feb 2024The smoking gun, according to Webb’s critics, was a newly publicized quotation, dating to his tenure as Under Secretary to Dean Acheson at the State Department between 1949 and 1952: “It is generally believed that those who engage in overt acts of perversion”—a homophobic reference to gay men—“lack the emotional stability of normal persons.”
The claim took NASA’s own historians by surprise. While it’s common knowledge that homophobic attitudes and policies were scandalously prevalent in early Cold War-era Washington, this was the first time that Webb had been accused of personally demonizing gay men.
The claim was reported in 2015 by media pundit Dan Savage; as well as by Matthew Francis, a physicist and freelance journalist. Francis told readers that he’d learned about the Webb quotation from the Twitter feed of a University of New Hampshire (UNH) particle physicist named Chanda Prescod-Weinstein. In a widely circulated Forbes column, The Problem With Naming Observatories For Bigots, Francis wrote, “it’s easy for white male physicists like me to ignore the less savory aspects of our scientific heroes, but it’s long past time we stopped.”
Even as late as Fall 2022, months after the James Webb Space Telescope had begun operation, Britain’s Royal Astronomical Society was still instructing its editorial contributors to excise Webb’s name from any references. Instead, authors were to use the acronym JWST.
Activists demanded that NASA come up with a new name. Prescod-Weinstein herself, appearing as the first listed writer in a co-authored Scientific American article, suggested that NASA honour anti-slavery activist Harriet Tubman, on the astronomical basis that “Tubman almost certainly used the North Star, just as it is documented that others did, to navigate her way to freedom.” ... But it was not to be. In early 2021, the case against Webb began falling apart, in large part thanks to a historical investigation conducted by the aforementioned Hakeem Oluseyi, 56, now a visiting professor at George Mason and Princeton Universities.
After becoming interested in Webb’s back story in 2015, Oluseyi raised the subject with NASA’s leadership during his subsequent stint as Space Sciences education manager for the agency’s Science Mission Directorate. As Oluseyi discovered, the case against Webb was based on misinformation that had been added to his Wikipedia entry in 2003 and 2011.
The homophobic quotation in question is real, he learned, but Webb never said it. Whoever first mistakenly associated these words with Webb had apparently confused Webb’s position with that of another State Department official named John Emil Peurifoy, a bona fide bigot who’d helped stir up Washington’s infamous Lavender Scare with lurid tales of a “homosexual underground.”
In late 2022, an independently produced 89-page report from NASA’s chief historian, Brian Odom, backed up Oluseyi’s conclusions, finding that there was “no available evidence” linking Webb to a single action “related to the firing of individuals for their sexual orientation.”
Die Astronomie verkörpert das von Francis Bacon stammende Paradoxon "Antiquitas saeculi, juventus mundi" (*) wohl am treffendsten. Unter anderem zählen die Astronomen die Generationen der Sterne in umgekehrter Reihenfolge: Sterne wie die Sonne, mit einem Alter zwischen 4 und 6 Milliarden Jahren zählen zur Population I, während die allerersten Sterne, die nach dem Urknall entstanden sind, solche der Population III darstellen. Das besondere an diesen ersten Sternen ist, daß sie keine schwereren Elemente als Helium enthalten können, weil beim Big Bang nur Wasserstoff, Deuterium und eben Helium entstanden ist - alle anderen Elemente sind erst in den späten Brennphasen schwerer Sterne durch Nukleosynthese entstanden - es handelt sich bei jedem Atom von ihnen buchstäblich um die Asche erloschener Sterne. Eins der damit verbundenen Paradoxa besteht darin, daß in den Gaswolken, die zur Bildung dieser ersten Generation kollabiert sind, deshalb auch keine Metalle (wie die Astronomen alle Elemente jenseits des Heliums nennen - sehr zum Verdruß der Kollegen aus der Chemikerzunft) enthalten sein konnten - und somit kein Staub. Dieser Staub ist aber entscheidend bei der Kühlung einer solchen Gaswolke, die sich beim Kollabieren naturgemäß aufheizt und dann schnell ein thermisches Gleichgewicht erreicht, an dem der resultierende Gasdruck die Massenanziehung ausgleicht & somit die Kontraktion zum Stillstand kommt. Faustregel: das Gas darf sich auf nicht mehr als 2 Grad Kelvin aufheizen. Damit das nicht der Fall ist, muß die sog. Jeanssche Masse - die Mindestmasse, bei der es zur Sternbildung kommt - exorbitant hoch gewesen sein. Mit dem Resultat, daß diese erste Generation an Sternen selbst eine gewaltige Masse und eine sehr kurze Lebenszeit hatte, bevor sie als Supernova explodiert sind & das interstellare Medium mit Metallen anreicherten. Bislang waren nur einige wenige unsichere Kandidaten als mögliche Signatur in den Spektralanalysen vermerkt worden. (* salopp formuliert: "das Altertum ist die Jugend der Welt" in The Advancement of Learning, 1605)
Zitat von Keith Cooper, published about 6 hours agoEvidence for the first generation of stars to exist in the universe has come to light, thanks to observations made by the James Webb Space Telescope (JWST). The proof is located in one of the most distant galaxies known.
The galaxy, designated GN-z11, was discovered by the Hubble Space Telescope in 2015 and, prior to the launch of the James Webb Space Telescope, it was considered the most faraway galaxy known. With a redshift of 10.6, it makes more sense to talk about how long ago it existed, rather than how far away it is. That's because we see GN-z11 as it was just 430 million years after the Big Bang due to the time it took for its light to travel to our corner of the cosmos. For comparison, the universe today is 13.8 billion years old.
As such, GN-z11 was a prime target for the JWST to study. Now, two new papers describe profound discoveries about GN-z11 that reveal vital details about how galaxies that existed in the early universe were able to grow.
GN-z11 is the most luminous galaxy known at this particular redshift, and indeed this has become a common theme for high redshift galaxies now almost regularly being found in the early universe by the JWST. Many of them appear much brighter than what our models of galaxy formation predict they should be. Those predictions are based on the standard model of cosmology.
Now, the JWST's new observations seem to have shed light on what is going on.
An astronomy team, led by Roberto Maiolino of the University of Cambridge, has probed GN-z11 with the JWST's two near-infrared instruments, the Near-Infrared Camera (NIRCam) and the Near-Infrared Spectrometer (NIRSpec). The researchers discovered evidence for the first generation of stars, called Population III stars, as well as for a supermassive black hole gobbling up huge amounts of matter and growing at a vastly accelerated rate.
Scientists can calculate the age of a star based on its abundance of heavy elements, which would have been formed by previous generations of stars that lived and died, spewing those heavy elements into space where they ultimately get recycled in star-forming regions to form new stellar bodies. The youngest stars that have formed during the past five or six billion years are referred to as Population I stars, and have the highest abundance of heavy elements. Our sun is a Population I star. Older stars contain fewer heavy elements because there had been fewer generations of stars before them. We call these Population II stars, and they live in the oldest regions of our Milky Way galaxy.
Population III stars, however, have been purely hypothetical up until now.
These would have been the first stars to form, and because no other stars came before them, they would have contained no heavy elements and be made from only the pristine hydrogen and helium forged during the Big Bang. These first stars are also thought to have been extremely luminous, with masses equal to at least several hundred suns.
Although astronomers still haven't seen Population III stars directly, Maiolino's team detected indirect evidence for them in GN-z11. NIRSpec observed a clump of ionized helium near the edge of GN-z11.
"The fact that we don't see anything else beyond helium suggests that this clump must be fairly pristine," said Maiolino in a statement. "This is something that was expected by theory and simulations in the vicinity of particularly massive galaxies from these epochs — that there should be pockets of pristine gas surviving in the halo, and these may collapse and form Population III stars."
This helium gas is being ionized by something that's producing huge amounts of ultraviolet light, with that something inferred as the Population III stars. Potentially, the helium witnessed is leftover material from those stars' formation. The amount of ultraviolet light required to ionize all that gas requires about 600,000 solar masses of stars in total, shining with a combined luminosity 20 trillion times brighter than our sun. These figures suggest distant galaxies such as GN-z11 would've been more adept at forming massive stars than galaxies in the modern universe.
Meanwhile, according to a second set of results, Maiolino's team also found evidence for a two-million-solar-mass black hole at the heart of GN-z11.
"We found extremely dense gas that is common in the vicinity of supermassive black holes accreting gas," said Maiolino in the same statement. "These were the first clear signatures that GN-z11 is hosting a black hole that is gobbling matter."
The study on the ionized helium clump and Population III stars has been accepted for publication in the journal Astronomy & Astrophysics, and a preprint can be found here. Meanwhile, the study on NIRCam observations of the black hole were published on 17 January in the journal Nature.
"JWST-JADES. Possible Population III signatures at z=10.6 in the halo of GN-z11," Roberto Maiolino et al.
Zitat von AbstractFinding the first generation of stars formed out of pristine gas in the early Universe, known as Population III (PopIII) stars, is one of the most important goals of modern astrophysics. Recent models suggest that PopIII stars may form in pockets of pristine gas in the halo of more evolved galaxies. Here we present NIRSpec-IFU and NIRSpec-MSA observations of the region around GN-z11, an exceptionally luminous galaxy at z=10.6, which reveal a >5σ detection of a feature consistent with being HeIIλ1640 emission at the redshift of GN-z11. The very high equivalent width of the putative HeII emission in this clump (170 A), and the lack of metal lines, can be explained in terms of photoionisation by PopIII stars, while photoionisation by PopII stars is inconsistent with the data. It would also indicate that the putative PopIII stars likely have a top-heavy initial mass function (IMF), with an upper cutoff reaching at least 500 M⊙. The PopIII bolometric luminosity inferred from the HeII line would be ∼2×1010 L⊙, which (with a top-heavy IMF) would imply a total stellar mass formed in the burst of ∼6×105 M⊙. We find that photoionisation by the Active Galactic Nucleus (AGN) in GN-z11 cannot account for the HeII luminosity observed in the clump, but can potentially be responsible for additional HeII emission observed closer to GN-z11. We also consider the possibility of in-situ photoionisation by an accreting Direct Collapse Black Hole (DCBH) hosted by the HeII clump; we find that this scenario is less favoured, but it remains a possible alternative interpretation. We also report the detection of a Lyα halo stemming out of GN-z11 and extending out to ∼2 kpc, as well as resolved, funnel-shaped CIII] emission, likely tracing the ionisation cone of the AGN.
Zitat The formation of the first stars and galaxies marks a fundamental transitional phase in cosmic history, during which the Universe evolved from a relatively simple state into the highly structured system we observe today (Bromm & Larson 2004). Almost all baryonic matter formed after the Big Bang and the “dark ages” is composed of hydrogen and helium. Consequently, the very first stars to form must have condensed out of these elements, primarily as a result of cooling due to the small amounts of H2 that could form at such early epochs (e.g. Kashlinsky & Rees 1983). These stars, called Population III (PopIII), are potentially very massive, up to several 100M⊙, as a consequence of inefficient gas cooling and hence poor fragmentation of pre-stellar cores at these early epochs (e.g. Bromm et al. 1999, Abel et al. 2002,Tan& McKee 2004; Hirano et al. 2014; Susa et al. 2014). Indirect studies of Pop III stars via stellar archaeology confirm these predictions, suggesting that their masses extend up to 1000M⊙with a characteristic mass>1M⊙(Rossi et al. 2021; Pagnini et al.2023). Such massive PopIII stars are expected to be very hot and leading to an energetic photoionising spectrum, capable of doubly ionising helium. Indeed, an expected signature of PopIII stars is prominent HeII nebular lines, with very large equivalent widths (EW(HeIIλ1640)>20 Å), unaccompanied by metal lines (Tumlinson & Shull 2000, Oh et al. 2001, Tumlinson et al.2001, Schaerer 2003, Nakajima & Maiolino 2022). However,other models have also predicted that primordial gas might fragment more efficiently, resulting into the formation of cooler and less massive stars (e.g. Clark et al. 2011; Greif et al. 2011, 2012;Stacy et al. 2016.
While observations have found potential chemical finger-prints of the enrichment produced by the first generation of stars(Beers & Christlieb 2005; Frebel et al. 2007; Cooke et al. 2011;Hartwig et al. 2015, 2018; Salvadori et al. 2023; Saccardi et al.2023; Klessen & Glover 2023), PopIII stars in early galaxies have eluded detection so far, with some claims not confirmed by subsequent studies (Sobral et al. 2015, Bowler et al. 2017,Harikane et al. 2018). However, the unprecedented sensitivity of JWST is pushing the frontier of observations to high redshift and very faint galaxies, discovering very low metallicity systems(Vanzella et al. 2023), indicating that the detection of PopIII stars may be within reach of this observatory (see also e.g. Zackrissonet al. 2011).
Further encouraging expectations about the detectability of PopIII stars have been obtained by recent cosmological simulations. Indeed, two main formation phases of PopIII stars have been proposed: firstly, PopIII stars could have formed in dark matter mini haloes at redshifts z∼10-30 (e.g. Tegmark et al.1997; Bromm et al. 2009; Pallottini et al. 2014; Jeon et al. 2015,Vikaeus et al. 2022; Ventura et al. 2023; Trinca et al. 2023b).Secondly, PopIII stars could still have formed at later times,down to redshifts of about z∼3-6, in pristine/low-metallicity pockets of gas due to the highly inhomogeneous nature of metalenrichment in the Universe, as well as a consequence of reaccretion of pristine gas (e.g. Tornatore et al. 2007a; Johnson2010; Liu & Bromm 2020, Sarmento et al. 2018; Jaacks et al.2019, Katz et al. 2022, Volonteri et al. 2023). In these cases,PopIII stars are expected to be found in the haloes of more massive galaxies, and their hard ionizing spectrum may be ionizing mildly enriched gas, resulting in weak emission of metal lines (Nakajima & Maiolino 2022, Katz et al. 2022, Jaacks et al.2018). ... The main observational findings are the following:
–We detect a spectral feature at 1.902μm in a clump at∼0.5−0.6′′(∼2 kpc) to the NE of GN-z11. This wavelength corresponds to HeIIλ1640 at z=10.600, fully consistent with the redshift of GN-z11. The line is detected both in the MSA-prism (3.7σ) and in the IFU-grating (5.5σ).
–The HeII emission is also detected over a more extended area in the NE quadrant of GN-z11, possibly with a second (fainter) clump. There is also a HeII plume extending towards the West of GN-z11.
–Lyα and CIII] are also clearly extended and well resolved. Lyα has a sharp feature extending towards the SW of GN-z11, where bright CIII] also extends in a funnel-shaped geometry (however, we remind that these extended features towards the West will need to be re-examined with new data). At lower surface brightness Lyα also extends over a larger region of up to∼2 kpc to the NE of GN-z11, and with a peak at about 1.5 kpc from the galaxy.
GN-z11, mit 26. Größenklasse, liegt in Sternbild Ursa Major, mit einer rechten Azension 2h 36m 46s und einer Deklination von +62°15'4". Die gegenwärtige Distanz beträgt 32 Milliarden Lichtjahre. Das mag auf den ersten 👁️ paradox anmuten, das das Universum nur ein Alter von 13,7/13,8 Miliarden Jahren aufweist & kein Lichtstrahl aus weiterer Tiefe auf unsere CCD-Chips gefallen ist. Aber in der Entfernung von 13,4 Mrd Lj befand sich die Galaxie 400 Millionen Jahre nach dem Big Bang & hat sich seitdem mit über 97% der Lichtgeschwindigkeit von uns fortbewegt. Der Kleine Zyniker meint, als junger Spunt habe er sich unter Popstars etwas leicht anderes vorgestellt.
"Les hommes seront toujours fous; et ceux qui croient les guérir sont les plus fous de la bande." - Voltaire
Zitat von Ulrich Elkmann im Beitrag #34Bislang waren nur einige wenige unsichere Kandidaten als mögliche Signatur in den Spektralanalysen vermerkt worden.
Zitat Population II, or metal-poor, stars are those with relatively little of the elements heavier than helium. These objects were formed during an earlier time of the universe. Intermediate population II stars are common in the bulge near the centre of the Milky Way, whereas population II stars found in the galactic halo are older and thus more metal-deficient. Globular clusters also contain high numbers of population II stars
A characteristic of population II stars is that despite their lower overall metallicity, they often have a higher ratio of "alpha elements" (elements produced by the alpha process, like oxygen and neon) relative to iron (Fe) as compared with population I stars; current theory suggests that this is the result of type II supernovas being more important contributors to the interstellar medium at the time of their formation, whereas type Ia supernova metal-enrichment came at a later stage in the universe's development. ... Scientists have targeted these oldest stars in several different surveys, including the HK objective-prism survey of Timothy C. Beers et al.[22] and the Hamburg-ESO survey of Norbert Christlieb et al.,[23] originally started for faint quasars. Thus far, they have uncovered and studied in detail about ten ultra-metal-poor (UMP) stars (such as Sneden's Star, Cayrel's Star, BD +17° 3248) and three of the oldest stars known to date: HE 0107-5240, HE 1327-2326 and HE 1523-0901. Caffau's star was identified as the most metal-poor star yet when it was found in 2012 using Sloan Digital Sky Survey data. However, in February 2014 the discovery of an even lower-metallicity star was announced, SMSS J031300.36-670839.3 located with the aid of SkyMapper astronomical survey data. Less extreme in their metal deficiency, but nearer and brighter and hence longer known, are HD 122563 (a red giant) and HD 140283 (a subgiant).
Population III stars[24] are a hypothetical population of extremely massive, luminous and hot stars with virtually no "metals", except possibly for intermixing ejecta from other nearby, early population III supernovae. The term was first introduced by Neville J. Woolf in 1965.
PS. Das Bacon-Zitat, aus Buch 1,V, lautet vollständig
Zitat The first of these is the extreme affecting of two extremities: the one antiquity, the other novelty; wherein it seemeth the children of time do take after the nature and malice of the father. For as he devoureth his children, so one of them seeketh to devour and suppress the other; while antiquity envieth there should be new additions, and novelty cannot be content to add but it must deface; surely the advice of the prophet is the true direction in this matter, State super vias antiquas, et videte quænam sit via recta et bona et ambulate in ea. Antiquity deserveth that reverence, that men should make a stand thereupon and discover what is the best way; but when the discovery is well taken, then to make progression. And to speak truly, Antiquitas sæculi juventus mundi.
These times are the ancient times, when the world is ancient, and not those which we account ancient ordine retrogrado, by a computation backward from ourselves.
"Ordine retrogrado" - das war's, was ich gesucht hatte.
PPS. Ich stelle gerade baß erstaunt fest, das "The Advancement of Learning," soweit feststellbar, noch nie ins Deutsche übertragen worden ist in den letzten 419 Jahren.
PPPS. Der kleine Fliegenbeinzähler, sehe ich, bekommt heute auch mal wieder Gelegenheit zu etwas Auslauf. In der Ausgabe der "Philosophical Works of Francis Bacon," ediert von John M. Robertson (London: George Routledge and Sons und New York: E.P.Dutton and Co., 1905), in der ich das Zitat nachprüfe, findet es sich auf S. 58 als "ordine retrograde" - aber im Bd. IV des "Oxford Francis Bacon" (Clarendon Press, 2000, hg. von Michael Kiernan), der sich buchstabengenau an den Text der Erstausgaben hält, lese ich auf S. 29: "These are the ancient times when the world is ancient, & not those we count antient Ordine retrogrado, by a computacion backward from our selues." (Pagination des Originals G1r)
PPPPS. Ad fontes. In der editio princeps von 1605 ("London: Printed by Thomas Purfoot and Thomas Creede for Henrie Tomes, and are to be sould at his shop at Graies Inne gate in Holborne, 1605") heißt es auf Seite 24 tatsächlich "retrogrado".
"Les hommes seront toujours fous; et ceux qui croient les guérir sont les plus fous de la bande." - Voltaire
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