Topic: Mid July Astronomy Bulletin

[Clive]

POSSIBLE SOURCE FOR CHARON’S RED CAP

Southwest Research Institute

Scientists combined data from NASA's New Horizons mission with novel laboratory experiments and exospheric modelling to reveal the likely composition of the red cap on Pluto's moon Charon and how it may have formed. This first-ever description of Charon's dynamic methane atmosphere using new experimental data provides a fascinating glimpse into the origins of this moon's red spot as described in two recent papers. Soon after the 2015 encounter, New Horizons scientists proposed that a reddish "tholin-like" material at Charon's pole could be synthesized by ultraviolet light breaking down methane molecules. These are captured after escaping from Pluto and then frozen onto the moon's polar regions during their long winter nights. Tholins are sticky organic residues formed by chemical reactions powered by light, in this case the Lyman-alpha ultraviolet glow scattered by interplanetary hydrogen molecules. The team realistically replicated Charon surface conditions at SwRI's new Center for Laboratory Astrophysics and Space Science Experiments (CLASSE) to measure the composition and color of hydrocarbons produced on Charon's winter hemisphere as methane freezes beneath the Lyman-alpha glow. The team fed the measurements into a new atmospheric model of Charon to show methane breaking down into residue on Charon's north polar spot. The team input the results from SwRI's ultra-realistic experiments into the atmospheric model to estimate the distribution of complex hydrocarbons emerging from methane decomposition under the influence of ultraviolet light. The model has polar zones primarily generating ethane, a colourless material that does not contribute to a reddish colour. The team think ionizing radiation from the solar wind decomposes the Lyman-alpha-cooked polar frost to synthesize increasingly complex, redder materials responsible for the unique albedo on this enigmatic moon, Ethane is less volatile than methane and stays frozen to Charon's surface long after spring sunrise. Exposure to the solar wind may convert ethane into persistent reddish surface deposits contributing to Charon's red cap.

VIOLENT STAR FORMATION IN TARANTULA NEBULA

ESO

Astronomers have unveiled intricate details of the star-forming region 30 Doradus, also known as the Tarantula Nebula, using new observations from the Atacama Large Millimeter/submillimeter Array (ALMA). In a high-resolution image released by the European Southern Observatory (ESO) and including ALMA data, we see the nebula in a new light, with wispy gas clouds that provide insight into how massive stars shape this region. These fragments may be the remains of once-larger clouds that have been shredded by the enormous energy being released by young and massive stars, a process dubbed feedback. Astronomers originally thought the gas in these areas would be too sparse and too overwhelmed by this turbulent feedback for gravity to pull it together to form new stars. But the new data also reveal much denser filaments where gravity’s role is still significant. The results imply that even in the presence of very strong feedback, gravity can exert a strong influence and lead to a continuation of star formation. Located in the Large Magellanic Cloud, a satellite galaxy of our own Milky Way, the Tarantula Nebula is one of the brightest and most active star-forming regions in our galactic neighbourhood, lying about 170 000 light-years away from Earth. At its heart are some of the most massive stars known, a few with more than 150 times the mass of our Sun, making the region perfect for studying how gas clouds collapse under gravity to form new stars.

What makes 30 Doradus unique is that it is close enough for us to study in detail how stars are forming, and yet its properties are similar to those found in very distant galaxies, when the Universe was young. Thanks to 30 Doradus, we can study how stars used to form 10 billion years ago when most stars were born. While most of the previous studies of the Tarantula Nebula have focused on its centre, astronomers have long known that massive star formation is happening elsewhere too. To better understand this process, the team conducted high-resolution observations covering a large region of the nebula. Using ALMA, they measured the emission of light from carbon monoxide gas. This allowed them to map the large, cold gas clouds in the nebula that collapse to give birth to new stars — and how they change as huge amounts of energy are released by those young stars. The new research contains detailed clues about how gravity behaves in the Tarantula Nebula’s star-forming regions, but the work is far from finished.

ULTRA-FAINTFOSSIL GALAXY ON OUTSKIRTS OF ANDROMEDA

Association of Universities for Research in Astronomy (AURA)

An unusual ultra-faint dwarf galaxy has been discovered on the outer fringes of the Andromeda Galaxy thanks to an amateur astronomer examining archival data processed by NSF's NOIRLab's Community Science and Data Center. Follow-up by professional astronomers using the International Gemini Observatory, a Program of NSF's NOIRLab, revealed that the dwarf galaxy -- Pegasus V -- contains very few heavier elements and is likely to be a fossil of the first galaxies. The faintest galaxies are considered to be fossils of the very first galaxies that formed, and these galactic relics contain clues about the formation of the earliest stars. While astronomers expect the Universe to be teeming with faint galaxies like Pegasus V, they have not yet discovered nearly as many as their theories predict. If there are truly fewer faint galaxies than predicted this would imply a serious problem with astronomers' understanding of cosmology and dark matter. Discovering examples of these faint galaxies is therefore an important endeavour, but also a difficult one. Part of the challenge is that these faint galaxies are extremely tricky to spot, appearing as just a few sparse stars hidden in vast images of the sky. The strong concentration of old stars that the team found in Pegasus V suggests that the object is likely a fossil of the first galaxies. When compared with the other faint galaxies around Andromeda, Pegasus V seems uniquely old and metal-poor, indicating that its star formation ceased very early indeed. Upcoming astronomical facilities are set to shed more light on faint galaxies. Pegasus V was witness to a time in the history of the Universe known as reionization, and other objects dating back to this time will soon be observed with NASA's James Webb Space Telescope. Astronomers also hope to discover other such faint galaxies in the future using Vera C. Rubin Observatory, a Program of NSF's NOIRLab. Rubin Observatory will conduct an unprecedented, decade-long survey of the optical sky called the Legacy Survey of Space and Time (LSST).

STAR WITH SHORTEST ORBITAL PERIOD AROUND BLACK HOLE

University of Cologne

Researchers have discovered the fastest known star, which travels around a black hole in record time. The star, S4716, orbits Sagittarius A*, the black hole in the centre of our Milky Way, in four years and reaches a speed of around 8000 kilometres per second. S4716 comes as close as 100 AU (astronomical unit) to the black hole -- a small distance by astronomical standards. In the vicinity of the black hole at the centre of our galaxy is a densely packed cluster of stars. This cluster, called S cluster, is home to well over a hundred stars that differ in their brightness and mass. S stars move particularly fast. By means of continuously refining methods of analysis, together with observations covering almost twenty years, the scientist now identified without a doubt a star that travels around the central supermassive black hole in just four years. A total of five telescopes observed the star, with four of these five being combined into one large telescope to allow even more accurate and detailed observations.Moreover, the discovery sheds new light on the origin and evolution of the orbit of fast-moving stars in the heart of the Milky Way. 'The short-period, compact orbit of S4716 is quite puzzling. Stars cannot form so easily near the black hole. S4716 had to move inwards, for example by approaching other stars and objects in the S cluster, which caused its orbit to shrink significantly.

ONSET OF GALAXY ROTATION IN EARLY UNIVERSE :

Waseda University

As telescopes have become more advanced and powerful, astronomers have been able to detect more and more distant galaxies. These are some of the earliest galaxies to form in our Universe that began to recede away from us as the Universe expanded. In fact, the more the distance, the faster a galaxy appears to move away from us. Interestingly, we can estimate how fast a galaxy is moving, and in turn, when it was formed based on how "redshifted" its emission appears. This is similar to a phenomenon called "Doppler effect," where objects moving away from an observer emit the light that appears shifted towards longer wavelengths (hence the term "redshift") to the observer. The Atacama Large Millimeter/submillimeter Array (ALMA) telescope located in the midst of the Atacama Desert in Chile is particularly well-suited for observing such redshifts in galaxy emissions. Recently, a team of researchers has observed redshifted emissions of a distant galaxy, MACS1149-JD1 (hereafter JD1), which has led them to some interesting conclusions. Beyond finding very distant, galaxies, studying their internal motion of gas and stars provides motivation for understanding the process of galaxy formation in the earliest possible Universe. Galaxy formation begins with the accumulation of gas and proceeds with the formation of stars from that gas. With time, star formation progresses from the centre outward, a galactic disk develops, and the galaxy acquires a particular shape. As star formation continues, newer stars form in the rotating disk while older stars remain in the central part. By studying the age of the stellar objects and the motion of the stars and gas in the galaxy, it is possible to determine the stage of evolution the galaxy has reached.

Conducting a series of observations over a period of two months, the astronomers successfully measured small differences in the "redshift" from position to position inside the galaxy and found that JD1 satisfied the criterion for a galaxy dominated by rotation. Next, they modelled the galaxy as a rotating disk and found that it reproduced the observations very well. The calculated rotational speed was about 50 kilometres per second, which was compared to the rotational speed of the Milky Way disk of 220 kilometres per second. The team also measured the diameter of JD1 at only 3,000 light-years, much smaller than that of the Milky Way at 100,000 light-years across. The significance of their result is that JD1 is by far the most distant and, therefore, earliest source yet found that has a rotating disk of gas and stars. Together with similar measurements of nearer systems in the research literature, this has allowed the team to delineate the gradual development of rotating galaxies over more than 95% of our cosmic history. Furthermore, the mass estimated from the rotational speed of the galaxy was in line with the stellar mass previously estimated from the galaxy's spectral signature, and came predominantly from that of "mature" stars that formed about 300 million years ago. This shows that the stellar population in JD1 formed at an even earlier epoch of the cosmic age. The rotation speed of JD1 is much slower than those found in galaxies in later epochs and our Galaxy and it is likely that JD1 is at an initial stage of developing a rotational motion.

AN OCEAN OF GALAXIES AWAITS

California Institute of Technology

Sometime around 400 million years after the birth of our Universe, the first stars began to form. The Universe's so-called dark ages came to an end and a new light-filled era began. More and more galaxies began to take shape and served as factories for churning out new stars, a process that reached a peak about 4 billion years after the Big Bang. Luckily for astronomers, this bygone era can be observed. Distant light takes time to reach us, and our telescopes can pick up light emitted by galaxies and stars billions of years ago (our Universe is 13.8 billion years old). But the details of this chapter in our Universe's history are murky since most of the stars being formed are faint and hidden by dust. A new Caltech project, called COMAP (CO Mapping Array Project), will offer us a new glimpse into this epoch of galaxy assembly, helping to answer questions about what really caused the Universe's rapid increase in the production of stars. The current phase of the project uses a 10.4-meter "Leighton" radio dish at OVRO to study the most common kinds of star-forming galaxies spread across space and time, including those that are too difficult to view in other ways because they are too faint or hidden by dust. The radio observations trace the raw material from which stars are made: cold hydrogen gas. This gas is not easy to pinpoint directly, so instead COMAP measures bright radio signals from carbon monoxide (CO) gas, which is always present along with the hydrogen. COMAP's radio camera is the most powerful ever built to detect these radio signals. The first science results from the project have just been published in seven papers in The Astrophysical Journal. Based on observations taken one year into a planned five-year survey, COMAP set upper limits on how much cold gas must be present in galaxies at the epoch being studied, including the ones that are normally too faint and dusty to see. While the project has not yet made a direct detection of the CO signal, these early results demonstrate that it is on track to do so by the end of the initial five-year survey and ultimately will paint the most comprehensive picture t of the Universe's history of star formation. COMAP works by capturing blurry radio images of clusters of galaxies over cosmic time rather than sharp images of individual galaxies. This blurriness enables the astronomers to efficiently catch all the radio light coming from a larger pool of galaxies, even the faintest and dustiest ones that have never been seen.

CYBORG FINDS 40,000 RING GALAXIES

RAS

Human and machine intelligence worked together to find 40,000 ring galaxies. Galaxies live a chaotic life. Collisions with other galaxies and bursts of energy from supermassive black holes disrupt the colours and orbits of billions of stars, leaving tell-tale markers that volunteers search for on the Galaxy Zoo website. But understanding exactly which cosmic events lead to which markers requires millions of measured images - more than humans could ever search. To help, researchers used a decade of Galaxy Zoo volunteer measurements (totalling over 96 million clicks) to create an automatic assistant - a new AI algorithm. The algorithm, affectionately named “Zoobot”, can not only accurately predict what volunteers would say but understands where it might be mistaken.

The discovery of 40,000 rare ring-shaped galaxies is six times more than previously known. Rings take billions of years to form and are destroyed in galaxy-galaxy collisions, and so this giant new sample will help reveal how isolated galaxies evolve. The dataset will also tell scientists how galaxies age more generally. Zoobot is designed to be retrained again and again for new science goals. Just like a musician can learn a new instrument faster than their first instrument, Zoobot can learn to answer new shape questions easily because it has already learned to answer more than 50 different questions. Galaxy Zoo turns 15 years old this week, and we are still innovating. The work Dr Walmsley is leading will make it possible for a new generation of discoveries to be made from upcoming large galaxy surveys.”


SHEDDING NEW LIGHT ON DARK MATTER

New York University

A team of physicists has developed a method for predicting the composition of dark matter -- invisible matter detected only by its gravitational pull on ordinary matter and whose discovery has been long sought by scientists. Its work centres on predicting "cosmological signatures" for models of dark matter with a mass between that of the electron and the proton. Previous methods had predicted similar signatures for simpler models of dark matter. This research establishes new ways to find these signatures in more complex models, which experiments continue to search for, the paper's authors note.  In the research, scientists focused on big bang nucleosynthesis (BBN) -- a process by which light forms of matter, such as helium, hydrogen, and lithium, are created. The presence of invisible dark matter affects how each of these elements will form. Also vital to these phenomena is the cosmic microwave background (CMB) -- electromagnetic radiation, generated by combining electrons and protons, that remained after the universe's formation. The team sought a means to spot the presence of a specific category of dark matter -- that with a mass between that of the electron and the proton -- by creating models that took into account both BBN and CMB. In its research, the team made predictions of cosmological signatures linked to the presence of certain forms of dark matter. These signatures are the result of dark matter changing the temperatures of different particles or altering how fast the Universe expands. Their results showed that dark matter that is too light will lead to different amounts of light elements than what astrophysical observations see.

LAUNCH DELAY FOR PSYCHE ASTEROID MISSION

NASA

NASA has announced that the Psyche asteroid mission, the agency’s first mission designed to study a metal-rich asteroid, will not make its planned 2022 launch attempt. Due to the late delivery of the spacecraft’s flight software and testing equipment, NASA does not have sufficient time to complete the testing needed ahead of its remaining launch period this year, which ends on Oct. 11. The mission team needs more time to ensure that the software will function properly in flight. NASA selected Psyche in 2017 as part of the agency’s Discovery Program, a line of low-cost, competitive missions led by a single principal investigator. The agency is forming an independent assessment team to review the path forward for the project and for the Discovery Program. The mission’s 2022 launch period, which ran from Aug. 1 through Oct. 11, would have allowed the spacecraft to arrive at the asteroid Psyche in 2026. There are possible launch periods in both 2023 and 2024, but the relative orbital positions of Psyche and Earth mean the spacecraft would not arrive at the asteroid until 2029 and 2030, respectively. The exact dates of these potential launch periods are yet to be determined. Two ride-along projects were scheduled to launch on the same SpaceX Falcon Heavy rocket as Psyche, including NASA’s Janus mission to study twin binary asteroid systems, and the Deep Space Optical Communications technology demonstration to test high-data-rate laser communications that is integrated with the Psyche spacecraft. NASA is assessing options for both projects.