Topic: Mid September Astronomy Bulletin

[Clive]

2000 YEARS AGO BETELGEUSE WAS YELLOW
Friedrich-Schiller-Universität Jena

An interdisciplinary utilized observations from antiquity to prove that Betelgeuse—the bright red giant star in the upper left of the constellation Orion—was yellow-orange some 2,000 years ago. As nuclear fusion in the centre of a star progresses, brightness, size, and colour also change. Astrophysicists can derive from such properties important information on the age and mass of a star. Those stars with significantly more mass than our Sun are blue-white or red—the transition from red to yellow and orange is relatively rapid for astronomical time-scales. Astrophysicists have now successfully detected and dated such a colour change in a bright star. The Chinese court astronomer Sima Qian wrote around 100 BC about star colours: white is like Sirius, red like Antares, yellow like Betelgeuse, blue like Bellatrix. From these specifications, one can conclude that Betelgeuse at that time was in colour between the blue-white Sirius and Bellatrix and the red Antares. Independent from the above, the Roman scholar Hyginus described some 100 years later that Betelgeuse was in colour like the yellow-orange Saturn—thus, one can quantify the former colour of Betelgeuse with even more precision. Additional authors from antiquity like Ptolemy bring further indications that Betelgeuse at their time did not belong to the group of bright red stars like Antares and Aldebaran. The Greek name Antares means "like Mars" in colour; it was indeed reported as red and compared to Mars since millennia from cultures around the world. "From a statement by the Danish astronomer Tycho Brahe, one can conclude that, in the 16th century, Betelgeuse was more red than Aldebaran. Today, Betelgeuse is comparable in brightness and colour to Antares.

Astronomer Ralph Neuhäuser from Jena university in Germany has included historical celestial observations in his astrophysical research for the past ten years—this field is called "Terra-Astronomy." He closely collaborates with colleagues from languages, history, and natural philosophy—including his wife Dagmar. "The view back in time delivers strong impulses and important results," Neuhäuser adds. "There are quite a number of astrophysical problems which can hardly be solved without historical observations." What do those historical transmissions tell us about Betelgeuse? "The very fact that it changed in colour within two millennia from yellow-orange to red tells us, together with theoretical calculations, that it has 14 times the mass of our Sun—and the mass is the main parameter defining the evolution of stars," Neuhäuser explains. "Betelgeuse is now 14 million years old and in its late evolutionary phases. In about 1.5 million years, it will finally explode as supernova."


TWO NEW TEMPERATE ROCKY WORLDS
University of Birmingham

An international research team has announced the discovery of two "super-Earth" planets orbiting LP 890-9, a small, cool star located about 100 light-years from Earth. The star, also called TOI-4306 or SPECULOOS-2, is the second-coolest star found to host planets, after the famous TRAPPIST-1. The system's inner planet, called LP 890-9b, is about 30% larger than Earth and completes an orbit around the star in just 2.7 days. This first planet was initially identified as a possible planet candidate by NASA's Transiting Exoplanet Survey Satellite (TESS), a space mission searching for exoplanets orbiting nearby stars. This candidate was confirmed and characterized by the SPECULOOS telescopes (Search for habitable Planets EClipsing ULtra-cOOl Stars), one of which is operated by the University of Birmingham. SPECULOOS researchers then used their telescopes to seek additional transiting planets in the system that would have been missed by TESS. This follow-up is particularly important in the case of very cold stars, such as LP 890-9, which emit most of their light in the near-infrared and for which TESS has a rather limited sensitivity. The telescopes of the SPECULOOS project, installed at ESO's Paranal Observatory in Chile and on the island of Tenerife, are optimised to observe this type of star with high precision, thanks to cameras that are very sensitive in the near-infrared. The observations of LP 890-9 gathered by SPECULOOS proved fruitful as they not only confirmed the first planet, but they were critical for the detection of a second, previously unknown planet. This second planet, LP 890-9c (renamed SPECULOOS-2c by the SPECULOOS researchers), is similar in size to the first (about 40% larger than Earth) but has a longer orbital period of about 8.5 days. This orbital period, later confirmed with the MuSCAT3 instrument in Hawaii, places the planet in the so-called "habitable zone" around its star. The next step will be to study the atmosphere of this planet, for example with the JWST, for which LP 890-9c appears to be the second-most favourable target among the potentially habitable terrestrial planets known so far, surpassed only by the TRAPPIST-1 planets.



WEBB DETECTS CO2 IN EXOPLANET ATMOSPHERE
NASA, ESA, CSA, STScI

The James Webb Space Telescope has captured the first clear evidence for carbon dioxide in the atmosphere of a planet outside the solar system. This observation of a gas giant planet orbiting a Sun-like star 700 light-years away provides important insights into the composition and formation of the planet. The finding offers evidence that in the future Webb may be able to detect and measure carbon dioxide in the thinner atmospheres of smaller, rocky planets. WASP-39 b is a hot gas giant with a mass roughly one-quarter that of Jupiter (about the same as Saturn) and a diameter 1.3 times greater than Jupiter’s. Its extreme puffiness is related in part to its high temperature (about 900 degrees Celsius. Unlike the cooler, more compact gas giants in our solar system, WASP-39 b orbits very close to its star – only about one-eighth the distance between the Sun and Mercury – completing one circuit in just over four Earth days. The planet’s discovery, reported in 2011, was made based on ground-based detections of the subtle, periodic dimming of light from its host star as the planet transits, or passes in front of the star. Previous observations from Hubble and Spitzer space telescopes, revealed the presence of water vapour, sodium, and potassium in the planet’s atmosphere. Webb’s infrared sensitivity has now confirmed the presence of carbon dioxide on this planet as well.

Transiting planets like WASP-39 b, whose orbits we observe edge-on rather than from above, can provide researchers with ideal opportunities to probe planetary atmospheres. During a transit, some of the starlight is eclipsed by the planet completely (causing the overall dimming) and some is transmitted through the planet’s atmosphere. Because different gases absorb different combinations of colours, researchers can analyze small differences in brightness of the transmitted light across a spectrum of wavelengths to determine exactly what an atmosphere is made of. With its combination of inflated atmosphere and frequent transits, WASP-39 b is an ideal target for transmission spectroscopy. The research team used Webb’s Near-Infrared Spectrograph (NIRSpec) for its observations of WASP-39 b. In the resulting spectrum of the exoplanet’s atmosphere, a small hill between 4.1 and 4.6 microns presents the first clear, detailed evidence for carbon dioxide ever detected in a planet outside the solar system. No observatory has ever measured such subtle differences in brightness of so many individual colours across the 3- to 5.5-micron range in an exoplanet transmission spectrum before. Access to this part of the spectrum is crucial for measuring abundances of gases like water and methane, as well as carbon dioxide, which are thought to exist in many different types of exoplanets. Understanding the composition of a planet’s atmosphere is important because it tells us something about the origin of the planet and how it evolved. Carbon dioxide molecules are sensitive tracers of the story of planet formation. In the coming decade, JWST will make this measurement for a variety of planets, providing insight into the details of how planets form and the uniqueness of our own solar system.


BRIGHT GALAXIES MORE COMMON THAN EXPECTED IN EARLY UNIVERSE
Science

The James Webb Space Telescope has only been watching the sky for a few weeks, and it has already delivered a startling finding: tens, hundreds, maybe even 1000 times more bright galaxies in the early Universe than astronomers anticipated. Galaxy formation models may now need a revision, as current ones hold that gas clouds should be far slower to coalesce into stars and galaxies than is suggested by Webb’s galaxy-rich images of the early Universe, less than 500 million years after the big bang. Webb began observing in late June from its vantage point 1.5 million kilometres from Earth. Much of its time so far has been devoted to projects meant to show off its capabilities, such as the Cosmic Evolution Early Release Science (CEERS) Survey. Webb is designed to delve deeper into cosmic history than its predecessor, the Hubble Space Telescope. Its 6.5-meter mirror—with six times the area of Hubble’s—can catch more light from distant sources, and unlike Hubble it operates at infrared wavelengths, making Webb more sensitive to those faraway sources, whose light is stretched to longer, redder wavelengths by cosmic expansion. Within days after Webb began observations, it spotted a candidate galaxy that appears to have been shining brightly when the Universe was just 230 million years old, 1.7% of its current age, which would make it the most distant ever seen. Surveys since then have shown that object is just one of a stunning profusion of early galaxies, each small by today’s standards, but more luminous than astronomers had expected.

Some researchers caution that the abundance, based on images of a small patch of sky, may be an illusion. Researchers wonder whether Webb just got “extra lucky” and stared into a huge clump of galaxies, denser than the rest of the early Universe. That question will be resolved when CEERS broadens its scope later this year and results come in from other wide-ranging surveys. It is also possible that astronomers are misidentifying galaxies from slightly more recent times as very early ones. Spectra are the gold standard for gauging a galaxy’s age because they allow the reddening of its light to be measured precisely. But gathering spectra from many galaxies takes time. Instead, Webb surveys so far have estimated galaxy ages from the colour they appear in images—a relatively crude method. Webb’s near-infrared camera filters their light into a few wide wavelength bins, giving astronomers a rough measurement of colour; redder equals more distant. But dust surrounding a galaxy can fool observers, as it can absorb starlight and re-emit it at longer wavelengths, making the galaxy look redder. Webb’s early science teams have already identified a few such masquerading galaxies, as they report in several recent preprints. But if the profusion of early galaxies is real, astronomers may have to fundamentally rethink galaxy formation or the reigning cosmology.


UNIVERSE’S MOST MASSIVE KNOWN STAR
Association of Universities for Research in Astronomy (AURA)


By harnessing the capabilities of the 8.1-meter Gemini South telescope in Chile, astronomers have obtained the sharpest image ever of the star R136a1, the most massive known star in the Universe. Their research challenges our understanding of the most massive stars and suggests that they may not be as massive as previously thought. Astronomers have yet to fully understand how the most massive stars -- those more than 100 times the mass of the Sun -- are formed. One particularly challenging piece of this puzzle is obtaining observations of these giants, which typically dwell in the densely populated hearts of dust-shrouded star clusters. Giant stars also live fast and die young, burning through their fuel reserves in only a few million years. In comparison, our Sun is less than halfway through its 10 billion year lifespan. The combination of densely packed stars, relatively short lifetimes, and vast astronomical distances makes distinguishing individual massive stars in clusters a daunting technical challenge. By pushing the capabilities of the Zorro instrument on the Gemini South telescope of the International Gemini Observatory, operated by NSF's NOIRLab, astronomers have obtained the sharpest-ever image of R136a1 -- the most massive known star. This colossal star is a member of the R136 star cluster, which lies about 160,000 light-years from Earth in the centre of the Tarantula Nebula in the Large Magellanic Cloud, a dwarf companion galaxy of the Milky Way. Previous observations suggested that R136a1 had a mass somewhere between 250 to 320 times the mass of the Sun. The new Zorro observations, however, indicate that this giant star may be only 170 to 230 times the mass of the Sun. Even with this lower estimate, R136a1 still qualifies as the most massive known star. Astronomers are able to estimate a star's mass by comparing its observed brightness and temperature with theoretical predictions. The sharper Zorro image allowed NSF's NOIRLab to more accurately separate the brightness of R136a1 from its nearby stellar companions, which led to a lower estimate of its brightness and therefore its mass.

This result also has implications for the origin of elements heavier than helium in the Universe. These elements are created during the cataclysmicly explosive death of stars more than 150 times the mass of the Sun in events that astronomers refer to as pair-instability supernovae. If R136a1 is less massive than previously thought, the same could be true of other massive stars and consequently pair instability supernovae may be rarer than expected. The star cluster hosting R136a1 has previously been observed by astronomers using the NASA/ESA Hubble Space Telescope and a variety of ground-based telescopes, but none of these telescopes could obtain images sharp enough to pick out all the individual stellar members of the nearby cluster. Gemini South's Zorro instrument was able to surpass the resolution of previous observations by using a technique known as speckle imaging, which enables ground-based telescopes to overcome much of the blurring effect of Earth's atmosphere [1]. By taking many thousands of short-exposure images of a bright object and carefully processing the data, it is possible to cancel out almost all this blurring [2]. This approach, as well as the use of adaptive optics, can dramatically increase the resolution of ground-based telescopes, as shown by the team's sharp new Zorro observations of R136a1 [3]. Zorro and its twin instrument `Alopeke are identical imagers mounted on the Gemini South and Gemini North telescopes, respectively. Their names are the Hawaiian and Spanish words for "fox" and represent the telescopes' respective locations on Maunakea in Hawai'i and on Cerro Pachón in Chile.


ALMOST PERFECT EINSTEIN RING IN DISTANT SPACE
SPACE

The first James Webb Space Telescope has done it again, this time capturing an almost perfect Einstein ring whose light has travelled roughly 12 billion light-years to reach us. An Einstein ring occurs when a distant galaxy has been magnified and wrapped into an almost-perfect ring by a massive galaxy in front of it. The galaxy in question is called SPT-S J041839-4751.8. The presence of Einstein rings allows us to study these otherwise almost impossible to see galaxies. This process is known as gravitational lensing, and it's an effect predicted by Einstein – hence the name. The effect only happens when the distant galaxy, the closer magnifying galaxy, and the observer (in this case the Webb space telescope) line up.

DATA GLITCH SOLVED ON VOYAGER 1
NASA

Engineers have repaired an issue affecting data from NASA’s Voyager 1 spacecraft. Earlier this year, the probe’s attitude articulation and control system (AACS), which keeps Voyager 1’s antenna pointed at Earth, began sending garbled information about its health and activities to mission controllers, despite operating normally. The rest of the probe also appeared healthy as it continued to gather and return science data. The team has since located the source of the garbled information: The AACS had started sending the telemetry data through an onboard computer known to have stopped working years ago, and the computer corrupted the information. Voyager’s project manager, said that when they suspected this was the issue, they opted to try a low-risk solution: commanding the AACS to resume sending the data to the right computer. Engineers don’t yet know why the AACS started routing telemetry data to the incorrect computer, but it likely received a faulty command generated by another onboard computer. If that’s the case, it would indicate there is an issue somewhere else on the spacecraft. The team will continue to search for that underlying issue, but they don’t think it is a threat to the long-term health of Voyager 1. Voyager 1 and Voyager 2 have been exploring our solar system for 45 years. Both probes are now in interstellar space, the region outside the heliopause, or the bubble of energetic particles and magnetic fields from the Sun.



FRANK DRAKE

The astronomer Frank Drake has passed away peacefully at 92 in his California home, near the site of his final academic position at the University of California, Santa Cruz. Drake made a number of contributions to radio astronomy, including serving as director of the Arecibo radio telescope facility. But Drake is probably best known for an equation that bears his name and his subsequent involvement in SETI efforts. His equation was the first significant attempt to estimate the probability of intelligent extraterrestrial life. Drake did his PhD in radio astronomy, and his academic career continued with astronomy as a focus. That eventually brought him to the Arecibo observatory. Drake was involved in the observatory's conversion from a military research site to a civilian, science-focused facility, and he later became its director. But Drake always had a side hustle: the attempt to find other intelligent life in the Universe. His most prominent contribution in this area was the formulation of what's now known as the Drake equation. It's purportedly a calculation—plug in the probabilities of a handful of things like the frequency of exoplanets around stars and the probability of life forming spontaneously, and out would pop the overall number of intelligent civilizations in our galaxy. More realistically, however, the Drake equation is an effective way to organize our thinking about the question. For example, understanding the probability of life emerging spontaneously from chemicals is a hard problem, but it's a problem we can tackle because we understand a lot of chemistry. The probability of life being intelligent is essentially an impossible one to estimate given how poorly we understand the foundations of conscious thought. Similarly, the equation can help direct technology development. Once exoplanets were discovered, it was clear that existing technology could be repurposed to provide an estimate of the frequency of planets around stars in our galaxy. Once we had a good estimate, work shifted to focusing on the habitability of those planets. Drake first presented his equation in 1961, and he maintained an interest in the question of extraterrestrial life throughout his career. While at Arecibo, he was involved in a project that beamed a message from that facility to a cluster of stars. He also helped craft two messages sent with our first hardware that was expected to leave the Solar System: a plaque on Pioneer 10 and 11 and gold records placed on the Voyager probes. He was also involved with the SETI institute and served on its board of trustees.