With the help of the NASA/ESA Hubble Space Telescope, a German-led group of astronomers have observed the intriguing characteristics of an unusual type of object in the asteroid belt between Mars and Jupiter: two asteroids orbiting each other and exhibiting comet-like features, including a bright coma and a long tail. This is the first known binary asteroid also classified as a comet.
This artist's impression shows the binary asteroid 288P, located in the main asteroid belt between the planets Mars and Jupiter. The object is unique as it is a binary asteroid which also behaves like a comet. The comet-like properties are the result of water sublimation, caused by the heat of the Sun. The orbit of the asteroids is marked by a blue ellipse [Credit: ESA/Hubble, L. Calçada]
In September 2016, just before the asteroid 288P made its closest approach to the Sun, it was close enough to Earth to allow astronomers a detailed look at it using the NASA/ESA Hubble Space Telescope.
The images of 288P, which is located in the asteroid belt between Mars and Jupiter, revealed that it was actually not a single object, but two asteroids of almost the same mass and size, orbiting each other at a distance of about 100 kilometres. That discovery was in itself an important find; because they orbit each other, the masses of the objects in such systems can be measured.
This set of images from the ESA/NASA Hubble Space Telescope reveals two asteroids with comet-like features orbiting each other. These include a bright halo of material, called a coma, and a long tail of dust. The asteroid pair, called 288P, was observed in September 2016 just before the asteroid made its closest approach to the Sun. These images reveal ongoing activity in the binary system. The apparent movement of the tail is a projection effect due to the relative alignment between the Sun, Earth, and 288P changing between observations. The tail orientation is also affected by a change in the particle size. Initially, the tail was pointing towards the direction where comparatively large dust particles (about 1 millimetre in size) were emitted in late July. However, from 20 September 2016 onwards, the tail began to point in the opposite direction from the Sun where small particles (about 10 microns in size) are blown away from the nucleus by radiation pressure [Credit: NASA, ESA, and J. Agarwal (Max Planck Institute for Solar System Research)]
But the observations also revealed ongoing activity in the binary system. "We detected strong indications of the sublimation of water ice due to the increased solar heating -- similar to how the tail of a comet is created," explains Jessica Agarwal (Max Planck Institute for Solar System Research, Germany), the team leader and main author of the research paper. This makes 288P the first known binary asteroid that is also classified as a main-belt comet.
Understanding the origin and evolution of main-belt comets -- comets that orbit amongst the numerous asteroids between Mars and Jupiter -- is a crucial element in our understanding of the formation and evolution of the whole Solar System. Among the questions main-belt comets can help to answer is how water came to Earth. Since only a few objects of this type are known, 288P presents itself as an extremely important system for future studies.
This artist’s impression shows the binary main-belt comet 288P. From a distance the comet-like features of the system can
clearly be seen: among them, the bright coma surrounding both components of the system and the long tail of dust and
water pointing away from from the Sun. Only a closer look reveals the two components of the system: two asteroids
circling each other on an eccentric orbit [Credit: ESA/Hubble, L. Calçada, M. Kornmesser]
The various features of 288P -- wide separation of the two components, near-equal component size, high eccentricity and comet-like activity -- also make it unique among the few known wide asteroid binaries in the Solar System. The observed activity of 288P also reveals information about its past, notes Agarwal: "Surface ice cannot survive in the asteroid belt for the age of the Solar System but can be protected for billions of years by a refractory dust mantle, only a few metres thick."
From this, the team concluded that 288P has existed as a binary system for only about 5000 years. Agarwal elaborates on the formation scenario: "The most probable formation scenario of 288P is a breakup due to fast rotation. After that, the two fragments may have been moved further apart by sublimation torques."
This time-lapse video, assembled from a set of ESA/NASA Hubble Space Telescope images, reveals two asteroids with
comet-like features orbiting each other. The asteroid pair, called 288P, was observed in September 2016,
just before the asteroid made its closest approach to the Sun [Credit: NASA, ESA, and J. Agarwal
(Max Planck Institute for Solar System Research)]
The fact that 288P is so different from all other known binary asteroids raises some questions about whether it is not just a coincidence that it presents such unique properties. As finding 288P included a lot of luck, it is likely to remain the only example of its kind for a long time. "We need more theoretical and observational work, as well as more objects similar to 288P, to find an answer to this question," concludes Agarwal.
The research is presented in a paper published in the journal Nature.
The most-studied galaxy in the universe -- the Milky Way -- might not be as "typical" as previously thought, according to a new study.
A three-colour optical image of a Milky Way sibling [Credit: Sloan Digital Sky Survey]
The Milky Way, which is home to Earth and its solar system, is host to several dozen smaller galaxy satellites. These smaller galaxies orbit around the Milky Way and are useful in understanding the Milky Way itself.
Early results from the Satellites Around Galactic Analogs (SAGA) Survey indicate that the Milky Way's satellites are much more tranquil than other systems of comparable luminosity and environment. Many satellites of those "sibling" galaxies are actively pumping out new stars, but the Milky Way's satellites are mostly inert, the researchers found.
This is significant, according to the researchers, because many models for what we know about the universe rely on galaxies behaving in a fashion similar to the Milky Way.
"We use the Milky Way and its surroundings to study absolutely everything," said Yale astrophysicist Marla Geha, lead author of the paper, which appears in the Astrophysical Journal. "Hundreds of studies come out every year about dark matter, cosmology, star formation, and galaxy formation, using the Milky Way as a guide. But it's possible that the Milky Way is an outlier."
The SAGA Survey began five years ago with a goal of studying the satellite galaxies around 100 Milky Way siblings. Thus far it has studied eight other Milky Way sibling systems, which the researchers say is too small of a sample to come to any definitive conclusions. SAGA expects to have studied 25 Milky Way siblings in the next two years.
Yet the survey already has people talking. At a recent conference where Geha presented some of SAGA's initial findings, another researcher told her, "You've just thrown a monkey wrench into what we know about how small galaxies form."
"Our work puts the Milky Way into a broader context," said SAGA researcher Risa Wechsler, an astrophysicist at the Kavli Institute at Stanford University. "The SAGA Survey will provide a critical new understanding of galaxy formation and of the nature of dark matter."
Wechsler, Geha, and their team said they will continue to improve the efficiency of finding satellites around Milky Way siblings. "I really want to know the answer to whether the Milky Way is unique, or totally normal," Geha said. "By studying our siblings, we learn more about ourselves."
The scorching hot surface of Mercury seems like an unlikely place to find ice, but research over the past three decades has suggested that water is frozen on the first rock from the sun, hidden away on crater floors that are permanently shadowed from the sun's blistering rays. Now, a new study led by Brown University researchers suggests that there could be much more ice on Mercury's surface than previously thought.
Researchers have found new evidence of ice sheets in permanently shadowed craters near the north pole of Mercury. The researcher also suggests that smaller-scale deposits may exist between craters, which would vastly increase the surface ice inventory in Mercury [Credit: Brown University]
The study, published in Geophysical Research Letters, adds three new members to the list of craters near Mercury's north pole that appear to harbor large surface ice deposits. But in addition to those large deposits, the research also shows evidence that smaller-scale deposits scattered around Mercury's north pole, both inside craters and in shadowed terrain between craters. Those deposits may be small, but they could add up to a lot more previously unaccounted-for ice.
"The assumption has been that surface ice on Mercury exists predominantly in large craters, but we show evidence for these smaller-scale deposits as well," said Ariel Deutsch, the study's lead author and a Ph.D. candidate at Brown. "Adding these small-scale deposits to the large deposits within craters adds significantly to the surface ice inventory on Mercury."
The idea that Mercury might have frozen water emerged in the 1990s, when Earth-based radar telescopes detected highly reflective regions inside several craters near Mercury's poles. The planet's axis doesn't have much tilt, so its poles get little direct sunlight, and the floors of some craters get no direct sunlight at all. Without an atmosphere to hold in any heat from surrounding surfaces, temperatures in those eternal shadows have been calculated to be low enough for water ice to be stable. That raised the possibility these "radar-bright" regions could be ice.
That idea got a boost after NASA's MESSENGER probe entered Mercury's orbit in 2011. The spacecraft detected neutron signals from the planet's north pole that were consistent with water ice.
For this new study, Deutsch worked with Gregory Neumann from NASA's Goddard Space Flight Center to take a deep dive into the data returned from MESSENGER. They looked specifically at readings from the spacecraft's laser altimeter. The device is mostly used to map elevation, but it can also be used to track surface reflectance.
Neumann, an instrument specialist for the MESSENGER mission, helped to calibrate the altimeter's reflectance signal, which can vary depending upon whether the measurement is taken from directly overhead or at an oblique angle (known as "off-nadir"). That calibration enabled the researchers to detect high reflectance deposits consistent with surface ice in three large craters for which only off-nadir detections were available.
The addition of those craters to Mercury's ice inventory is significant. Deutsch estimates the total area of the three sheets to be about 3,400 square kilometers -- slightly larger than the state of Rhode Island.
But another major aspect of the work is that the researchers also looked at reflectance data for the terrain surrounding those three large craters. That terrain isn't as bright as the ice sheets inside the craters, but it's significantly brighter than the average Mercury surface.
"We suggest that this enhanced reflectance signature is driven by small-scale patches of ice that are spread throughout this terrain," Deutsch said. "Most of these patches are too small to resolve individually with the altimeter instrument, but collectively they contribute to the overall enhanced reflectance."
To seek further evidence that such smaller-scale deposits exist, the researchers looked though the altimeter data in search of patches that were smaller than the big crater-based deposits, but still large enough to resolve with the altimeter. They found four, each with diameters of less than about 5 kilometers.
"These four were just the ones we could resolve with the MESSENGER instruments," Deutsch said. "We think there are probably many, many more of these, ranging in sizes from a kilometer down to a few centimeters."
Knowing that these small-scale deposits exist, and that they're likely the source of the slightly brighter surface outside craters, could dramatically increase the ice inventory on Mercury. Similar small-scale ice deposits are thought to exist on the poles of the Moon. Research models have suggested that accounting for these small-scale deposits roughly doubles the amount of lunar real estate that could harbor ice. The same could be true on Mercury, the researchers say.
How this polar ice may have found its way to Mercury in the first place remains an open question, Deutsch says. The leading hypothesis is that it was delivered by water-rich comet or asteroid impacts. Another idea is that hydrogen may have been implanted in the surface by solar wind, later combining with an oxygen source to form water.
Jim Head, Deutsch's Ph.D. advisor and co-author of the research, said the work adds a new perspective on a critical question in planetary science.
"One of the major things we want to understand is how water and other volatiles are distributed through the inner solar system -- including Earth, the Moon and our planetary neighbors," Head said. "This study opens our eyes to new places to look for evidence of water, and suggests there's a whole lot more of it on Mercury than we thought."
A group-analysis of 30 exoplanets orbiting distant stars suggests that size, not mass, is a key factor in whether a planet's atmosphere can be detected. The largest population-study of exoplanets to date successfully detected atmospheres around 16 'hot Jupiters', and found that water vapour was present in every case.
Artist’s impression of exoplanetary system [Credit: Alexaldo]
The work by a UCL-led team of European researchers has important implications for the comparison and classification of diverse exoplanets. The results will be presented by Angelos Tsiaras at the European Planetary Science Congress (EPSC) 2017 in Riga on Tuesday 19th September.
"More than 3,000 exoplanets have been discovered but, so far, we've studied their atmospheres largely on an individual, case-by-case basis. Here, we've developed tools to assess the significance of atmospheric detections in catalogues of exoplanets," said Angelos Tsiaras, the lead author of the study. "This kind of consistent study is essential for understanding the global population and potential classifications of these foreign worlds."
Artist’s impression of exoplanetary system [Credit: Alexaldo]
The researchers used archive data from the ESA/NASA Hubble Space Telescope's Wide Field Camera 3 (WFC3) to retrieve spectral profiles of 30 exoplanets and analyse them for the characteristic fingerprints of gases that might be present. About half had strongly detectable atmospheres.
Results suggest that while atmospheres are most likely to be detected around planets with a large radius, the planet's mass does not appear to be an important factor. This indicates that a planet's gravitational pull only has a minor effect on its atmospheric evolution.
Artist’s impression of exoplanetary system [Credit: Alexaldo]
Most of the atmospheres detected show evidence for clouds. However, the two hottest planets, where temperatures exceed 1,700 degrees Celsius, appear to have clear skies, at least at high altitudes. Results for these two planets indicate that titanium oxide and vanadium oxide are present in addition to the water vapour features found in all 16 of the atmospheres analysed successfully.
"To understand planets and planet formation we need to look at many planets: at UCL we are implementing statistical tools and models to handle the analysis and interpretation of large sample of planetary atmospheres. 30 planets is just the start," said Ingo Waldmann, a co-author of the study.
Artist’s impression of exoplanetary system [Credit: Alexaldo]
"30 exoplanet atmospheres is a great step forward compared to the handful of planets observed years ago, but not yet big-data. We are working at launching dedicated space missions in the next decade to bring this number up to hundreds or even thousands," commented Giovanna Tinetti, also UCL.
A team of scientists from NASA, Hampton University and the University of Hong Kong propose a new way of understanding the cooling and transfer of heat from terrestrial planetary interiors and how that affects the generation of the volcanic terrains that dominate the rocky planets. Based on the present dynamics of Jupiter's tidally heated moon, Io, the scientists hypothesize that the geological histories of the solar system's terrestrial bodies, specifically Mercury, Venus, Moon and Mars, are consistent with a mode of early planetary evolution involving heat-pipes. They further propose that heat-pipe cooling is a universal process that may explain the common features seen on the surfaces of terrestrial planets.
Io with a volcanic plume at the top [Credit: The University of Hong Kong]
"We believe that the concept of a heat-pipe mode of planet formation is important and will help explain the evolution of all rocky planets," said Dr. Justin Simon, NASA Planetary Scientist, Center for Isotope Cosmochemistry and Geochronology in the Astromaterials Research and Exploration Science Division at NASA's Johnson Space Center in Houston, Texas and one of the coauthors of the paper. "If shown to be correct, it will be discussed along with the theories of plate tectonics, planetary 'magma oceans' and the 'giant impact theory for the origin of the moon.'"
The scientists hypothesize heat-pipe cooling was involved in the evolution of all terrestrial planets including early Earth and represents the transition from the magma ocean to the rigid-lid or plate tectonic modes of planetary evolution. Heat-pipes transport heat from the interior to the surface via mantle melting and magma ascent. The resulting eruptions lead to global volcanic resurfacing by which older volcanic layers are progressively buried and pushed downward to form thick, cold and strong mechanical lithospheres.
The authors review the observations relevant to the formation of the surfaces of each of the terrestrial planets and current models that have been proposed to explain them. They then discuss the major outstanding problems and show how the heat-pipe hypothesis can resolve these in a consistent way across all planets.
"The terrestrial bodies in our solar system look different enough that the classical view is that they all formed differently, at least in terms of making their outer shells. If our analysis holds merit, it points in the direction of a universal model for the early development of terrestrial planets, across our solar system and beyond," said Dr. Alexander Webb, Associate Professor, The University of Hong Kong.
Dr Alex Webb in the field of Isua, Greenland, studying 3.8 billion year old rocks that may have been produced via heat-pipe processes on Earth [Credit: The University of Hong Kong]
The authors note that Mercury was globally resurfaced early in its evolution by volcanic eruptions emplacing smooth plains with few identifiable eruption centers. The authors conclude that the geological observations of the planet point to an episode of heat-pipes operating for somewhat less than the first billion years of Mercury's evolution. The surface of Venus is also dominated by lavas with broad plains made up of numerous flows spanning hundreds of kilometers at low slope with few identifiable source structures. Venus does not display sufficient volcanic flux to currently experience active heat-pipe cooling, but the authors conclude that the thick, stagnant lithospheric lid is a relict of heat-pipe operation that ceased rapidly several hundred million years ago.
Among the most important surface features on Mars are its large volcanos, ancient cratered terrains and the crustal dichotomy between the elevated southern hemisphere and the depressed northern hemisphere. It remains unclear which processes were responsible for the formation of the dichotomy, but the authors conclude that a strong ancient lithosphere created by heat-pipe volcanism would have aided in the preservation of this ancient feature. Similarly, the Moon stands out as having a shape that is dramatically out of hydrostatic equilibrium, but preserving a disequilibrium shape requires a strong, early-formed lithosphere. The authors argue that a strong lithosphere is precisely the expected behavior of a body experiencing heat-pipe cooling.
The team brought together geological, geochemical and geochronological evidence from the terrestrial bodies in our solar system to show that heat-pipes may have provided the primary mechanism of crustal formation and resurfacing. The heat-pipe hypothesis provides a uniform explanation for common features of the known terrestrial planets that have not undergone plate tectonics and should be considered an important aspect of their evolution.
"The development of this theory is a great example of how exploration of our planetary neighbors, in this case [Jupiter's moon] Io, has led to a deeper understanding of Earth as well as rocky planets across the galaxy," said Dr. William Moore, professor of atmospheric and planetary sciences, Hampton University, USA.
Heat-pipes should also occur on rocky exoplanets orbiting other stars. A planet twice the mass of Earth should take more than twice as long to cool, because the surface area does not grow as fast as the mass. For large exoplanets, the lifetime of the heat-pipe mode may exceed the lifetime of Sun-like parent stars and thus any subsequent plate-tectonic phase may never be observed. This study forces us to rethink our expectations of what types of surfaces and atmospheres to expect as we expand our exploration of other solar systems.
During almost four years of observing the cosmos, the Herschel Space Observatory traced out the presence of water. With its unprecedented sensitivity and spectral resolution at key wavelengths, Herschel revealed this crucial molecule in star-forming molecular clouds, detected it for the first time in the seeds of future stars and planets, and identified the delivery of water from interplanetary debris to planets in our Solar System.
This mosaic combines several observations of the Taurus Molecular Cloud performed by ESA's Herschel Space Observatory. Located about 450 light-years from us, in the constellation Taurus, the Bull, this vast complex of interstellar clouds is where a myriad of stars are being born, and is the closest large region of star formation [Credit: ESA/Herschel/NASA/JPL-Caltech, CC BY-SA 3.0 IGO; Acknowledgement: R. Hurt (JPL-Caltech)]
Water is essential to life as we know it on Earth. It covers over 70% of our planet's surface and is present in trace amounts in the atmosphere. While it may seem abundant, especially if we're looking at the blue-hued stretch of a lake, sea or ocean, water is only a minor component of the total mass of Earth.
In fact, it is not at all clear whether the water that is currently present on our blue planet was there around the time of its formation, 4.6 billion years ago, or it is was delivered by later impacts of smaller celestial objects.
According to one of the leading theories to explain how the Solar System came into being, Earth and the inner planets were extremely hot and dry for the first several hundred million years after their formation. In this scenario, water was delivered to these planets only later by violent impacts of small bodies such as meteorites, asteroids, and/or comets – the remaining debris of the protoplanetary disc out of which the planets and their moons took shape.
There are various avenues to investigate the origin of this crucial molecule on our planet, either following the clues in our cosmic neighbourhood – the Solar System – or looking into the stellar nurseries where analogues of our Sun and planets are being born.
ESA's Herschel Space Observatory, an extraordinary mission that was launched in 2009 and that observed the sky at far-infrared and sub-millimetre wavelengths for almost four years, took a comprehensive approach, tracing water from stars and planets in the forming across our Milky Way galaxy to planets and minor Solar System bodies in our own neck of the woods.
Water in the Universe
Water was first detected in star-forming molecular clouds in the late 1960s. At the time, it was the sixth interstellar molecule to be identified, compared to the nearly 200 that are known to date.
Artist's impression of the TW Hydrae protoplanetary disc [Credit: ESA/NASA/JPL-Caltech]
Ever since its discovery, astronomers suspected that water would be present in a variety of cosmic environments. After all, it is made up of the two most abundant reactive elements that exist – hydrogen, which dates back to the Big Bang, and oxygen, produced in the furnaces of stars throughout the history of the Universe.
In fact, water has been observed in celestial objects as diverse as planets, moons, stars, star-forming clouds, and even beyond our Milky Way, in the stellar cradles of other galaxies. However, due to the water vapour present in the Earth's atmosphere, studying this molecule with astronomical observations is anything but trivial.
Over the decades, astronomers have used a wide range of facilities to study water in the cosmos, from ground-based observatories in the dry climate of mountain-tops and airborne telescopes to experiments on stratospheric balloons and space observatories and even on the Space Shuttle. Far from the moist environment of our planet, a space telescope is of course the ideal tool to investigate cosmic water.
The first satellite dedicated to this topic, ESA's Infrared Space Observatory (ISO), was launched in 1995 and operated until 1998, shortly followed by NASA's Submillimeter Wave Astronomy Satellite (SWAS) and Spitzer Space Telescope, and by the Swedish-led, international Odin satellite.
Stepping into this long-established tradition, Herschel pushed the quest of cosmic water to new heights with a phenomenal piece of hardware, the Heterodyne Instrument for the Far Infrared (HIFI) – one of the three instruments on board.
Herschel: water [Credit: ESA/Herschel/NASA/JPL-Caltech; Acknowledgement: T. Pyle & R. Hurt (JPL-Caltech)]
To reveal the presence of a molecule in a cosmic source, astronomers look for a set of very distinctive fingerprints, or lines, in the source's spectrum, which are caused by rotation or vibration transitions in the structure of the molecule.
These lines are observed within a stretch of the electromagnetic spectrum, covering infrared to microwave wavelengths, depending on the type of molecule and its temperature. In the case of water, some of the most interesting lines – the ones that correspond to the lowest energetic configuration of water vapour, in other words its ground or 'cold' state – are found in the far-infrared and sub-millimetre ranges, which are inaccessible from the ground.
Specially designed for the hunt for water and other molecules, Herschel's HIFI instrument had an unprecedented spectral resolution that could target about 40 different water lines, each coming from a different transition of the water molecule and thus sensitive to a different temperature.
In particular, unlike its predecessors, Herschel was sensitive to two different transitions of the ground state of water that correspond to the two 'spin' forms of the molecule, called ortho and para, in which the spins of the hydrogen nuclei have different orientations. This key feature allowed astronomers to determine the temperatures under which the water formed by comparing the relative amounts of ortho and para water.
Two of the observatory's Key Programmes – Water in Star-forming regions with Herschel and Water and Related Chemistry in the Solar System – dedicated several hundred hours to the quest for cosmic water.
Exploiting the outstanding data collected by HIFI, along with observations performed with Herschel's two other instruments, the Photodetector Array Camera and Spectrometer (PACS) and the Spectral and Photometric Imaging Receiver (SPIRE), astronomers have been able to greatly expand our understanding of the role of water in the Universe.
Water in the progenitors of stars and planets
While water vapour in star-forming regions had been known for quite a while, Herschel discovered it, for the first time, in a pre-stellar core – a cold lump of dense material that will later turn into a star. The pre-stellar core, called Lynds 1544, is located in the Taurus molecular cloud, a vast region of gas and dust that is incubating the seeds of future stars and planets.
Distribution of water in Jupiter's stratosphere [Credit: Water map: ESA/Herschel/T. Cavalié et al.; Jupiter image: NASA/ESA/Reta Beebe (New Mexico State University)]
With the Herschel data, astronomers could estimate also the amount of water vapour in Lynds 1544 – the equivalent of over 2000 times the water content of Earth's oceans. The water vapour derives from icy dust grains, hinting at a reservoir of over a thousand times more water in the form of ice. If any planets are to emerge around the star taking shape from this core, it is likely that some of the water detected by Herschel will find its way to the planets as well.
En route to becoming stars, pre-stellar cores keep accreting matter from their parent cloud until they separate from it, turning into a protostar, an independent object that is collapsing under its own gravity. Normally, a rotating disc of gas and dust – a protoplanetary disc – takes shape around protostars, providing the material for the formation of future planets. Finally, when nuclear reactions ignite in the core of the protostar, counteracting the collapse, a fully-fledged star is born.
Herschel has spotted water in objects spanning all stages of star formation, including in a large number of low-mass protostars found in many nearby star-forming regions.
For the first time, astronomers using Herschel have detected cold water vapour in a protoplanetary disc. While previous studies had revealed either hot water vapour in the inner part of similar discs, or water ice in their outskirts, Herschel's observations targeting the disc around the nearby young star TW Hydrae were the first to identify cold water vapour, with temperatures lower than 100 K, in such an object.
The cold vapour appears to be located in a thin layer at intermediate depths in the disc, where the evaporation of gas and the freeze-out of ice find a balance. The data indicate a small amount of cold vapour, equivalent to about 0.5 per cent of the water in Earth's oceans, but point to a much larger reservoir of water ice – several thousand Earth oceans – in the disc.
This was the first evidence that large amounts of water ice can be stored in the precursor of a planetary system like our own, thus contributing more evidence to tackling the puzzle of the origin of water on Earth and other planets.
Water in the Solar System
Besides proving that water is an important constituent of stars and planets since their early formation, Herschel also followed its trail all the way to our local neighbourhood, the Solar System.
Deuterium-to-hydrogen ratio in the Solar System [Credit: Data from Altwegg et al. 2014]
To compare water found in different celestial bodies, astronomers analyse the relative abundance of molecules with a slightly different composition. Most notably, they look at the D/H ratio, comparing 'ordinary' water, composed of two hydrogen (H) and one oxygen (O) atoms, and semi-heavy water, where one of the hydrogen atoms appears as deuterium (D), an isotopical form with an extra neutron.
Before Herschel, this measurement had been performed on a handful of comets, all of them thought to originate in the Oort cloud at the outskirts of our Solar System, and all of them revealing higher proportions of deuterium to 'normal' hydrogen than that found in Earth's oceans. These results seemed to suggest that comets – icy leftovers of our ancient protoplanetary disc – could not have been the source of our planet's water, while a specific class of meteorites, called Cl carbonaceous chondrites, possessed the 'right' D/H ratio and thus seemed to be the main culprit.
In 2011, Herschel's observations of water in Comet 103P/Hartley 2 reopened this fascinating debate. This measurement was the first of its kind performed for a Jupiter-Family comet – a class of comets with orbits governed by Jupiter's gravity and with much shorter period with respect to their Oort-cloud counterparts – and revealed, for the first time, water with a deuterium to hydrogen proportion similar to that found on our planet.
Herschel contributed two more observations to the debate, finding a Jupiter-Family comet (45P/Honda-Mrkos- Pajdušáková) with Earth-like water, and an Oort-cloud comet (2009P1) with a different blend from that of our planet's water.
The plot thickened when ESA's Rosetta mission reached Comet 67P/Churyumov–Gerasimenko in 2014 and sampled the water content in its atmosphere. Rosetta's comet is also a Jupiter-Family one but, unlike the two observed by Herschel, it does not contain Earth-like water; on the contrary, it turned out to have the highest D/H ratio ever measured for a comet.
Herschel image and spectrum of Jupiter-Family comet 103P/Hartley 2 [Credit: ESA/AOES Medialab; Herschel/HssO Consortium]
While Rosetta revealed that not all Jupiter-Family comets contain water that is similar to that of our planet's oceans, Herschel's earlier detections had importantly pointed out that comets with the right composition do exist and some might indeed have contributed to Earth's water budget. In fact, current models indicate that a broad and diverse range of minor bodies contributed to the critical role of bringing water to our planet.
Elsewhere in the Solar System, Herschel has gone as far as confirming that at least one comet has contributed to enriching a different planet – Jupiter – with water. By investigating the distribution of water vapour in the stratosphere of the giant planet, astronomers found evidence that almost all of it was delivered by the famous impact of Comet Shoemaker-Levy 9 in 1994.
Following water throughout the Solar System, Herschel has found this molecule in many more places, from the dwarf planet Ceres, the largest body in the asteroid belt, to a giant torus of water vapour surrounding Saturn, which appears to be supplied by the planet's small moon Enceladus. As revealed by the NASA/ESA/ASI Cassini mission, Enceladus exhibits plumes of water drawing from the underground ocean lurking under its icy crust.
Farther away from the Sun, Herschel revealed highly reflecting surfaces on several Trans-Neptunian Objects (TNOs), indicating that water ice might be present even on these ancient, remote objects. While TNOs date back to the early formation of our Solar System, astronomers suspect that their bright icy coating may be more recent – a speculative but not unfeasible hypothesis given the availability of water on outer planets like Uranus and Neptune, and on their major moons. Such a recent coating might also suggest that the surface of these long-thought 'dead' objects can in fact be alive, as highlighted also by the in-situ observations performed in 2015 by NASA's New Horizon probe of another TNO, the dwarf planet Pluto.
Herschel's population of trans-Neptunian objects [Credit: ESA/Herschel/PACS/SPIRE; acknowledgements: M. Rengel and P. Lacerda (Max-Plack-Institute für Sonnensystemforschung, Germany), T. Müller (Max-Planck-Institut für extraterrestrische Physik) and the Herschel]
Outlook
Out to much grander scales, beyond our Solar System and the Galactic confines of the Milky Way, Herschel has detected water in many other galaxies. As already highlighted by some of its predecessors, the findings corroborate the crucial role of this all-important molecule in the processes that lead to the birth of stars throughout the cosmos.
Given its chemical composition, water unsurprisingly is ubiquitous in the Universe, and, after Herschel, there is no longer any doubt that cosmic water trails go a long way, from planets to stars, and even to the vastness of interstellar space.
However, Herschel has only begun scratching the surface of the proverbial iceberg, having spotted water in individual cosmic sources that are, in many cases, one of a kind. These exciting discoveries call for future surveys to follow up on Herschel's observations, collecting larger samples of each type of sources to scrutinise water and other molecules and delve into the physical mechanisms underlying their formation and delivery across the cosmos.
Almost 50 years after it was first predicted that rapidly rotating stars would emit polarised light, a UNSW Sydney-led team of scientists has succeeded in observing the phenomenon for the first time.
August's total eclipse of the sun with the star Regulus visible as a blue dot in the lower left corner. The photograph was taken in Casper, Wyo. [Credit: jmsands57]
They used a highly sensitive piece of equipment designed and built at UNSW and attached to the Anglo-Australian Telescope at Siding Spring Observatory in western NSW to detect the polarised light from Regulus, one of the brightest stars in the night sky.
The research has provided unprecedented insights into the star, which is in the constellation Leo, allowing the scientists to determine its rate of spinning and the orientation in space of the star's spin axis.
The study, by a team at UNSW, University College London, University of Washington and University of Hertfordshire, is published in the journal Nature Astronomy.
"We found Regulus is rotating so quickly it is close to flying apart, with a spin rate of 96.5 per cent of the angular velocity for break-up," says study first author and UNSW scientist Dr Daniel Cotton, of the School of Physics.
"It is spinning at approximately 320 kilometres per second -- equivalent to travelling from Sydney to Canberra in less than a second."
Indian astrophysicist and Nobel laureate Subrahmanyan Chandrasekhar first predicted the emission of polarised light from the edges of stars in 1946, prompting the development of sensitive instruments called stellar polarimeters to try and detect this effect.
Optical polarisation is a measure of the orientation of the oscillations of a light beam to its direction of travel.
In 1968, other researchers built on Chandrasekhar's work to predict that the distorted, or squashed shape, of a rapidly rotating star would lead to the emission of polarised light, but its detection has eluded astronomers until now.
"The instrument we have built, the High Precision Polarimetric Instrument, HIPPI, is the world's most sensitive astronomical polarimeter. Its high precision has allowed us to detect polarised light from a rapidly spinning star for the first time," says Dr Cotton.
"We have also been able to combine this new information about Regulus with sophisticated computer models we have developed at UNSW to determine the star's inclination and rotation rate.
"It has previously been extremely difficult to measure these properties of rapidly rotating stars. Yet the information is crucial for understanding the life cycles of most of the hottest and largest stars in the galaxies, which are the ones that produce the heaviest elements, such as iron and nickel, in interstellar space."
Regulus is about 79 light years away. During the total solar eclipse in the US in August, Regulus was just 1 degree away from the Sun and was, to many people, the only star visible during the eclipse.
A study using multiple radio telescopes confirms that supermassive black holes found in the centers of galaxies can form gravitationally bound pairs when galaxies merge.
The two compact radio sources separated by less than a light year at the center of the galaxyNGC7674. The two sources correspond to the location of the two active supermassive blackholes which form a binary and orbit around each other [Credit: TIFR-NCRA and RIT, USA]
The paper published in Nature Astronomy sheds light on a class of black holes having a mass upwards of one million times the mass of the sun. Supermassive black holes are expected to form tightly bound pairs following the merger of two galaxies.
"The dual black hole we found has the smallest separation of any so far detected through direct imaging," said David Merritt, professor of physics at Rochester Institute of Technology, a co-author on the paper.
The supermassive black holes are located in the spiral galaxy NGC 7674, approximately 400 million light years from earth, and are separated by a distance less than one light year. The study was led by Preeti Kharb, from the National Center for Radio Astrophysics at Pune University in India and co-authored by Dharam Vir Lal, also at Pune University and Merritt at RIT.
"The combined mass of the two black holes is roughly 40 million times the mass of the Sun, and the orbital period of the binary is about 100,000 years," Merritt said.
A class of smaller black holes form when massive stars explode as supernovae. A collision of stellar mass black holes led to the landmark discovery of gravitational waves in 2015 using the Laser Interferometer Gravitational-wave Observatory. The black holes were approximately 29 and 36 times the mass of the sun and collided 1.3 billion light years away
"A supermassive binary generates gravitational waves with much lower frequency than the characteristic frequency of stellar-mass binaries and its signal is undetectable by LIGO," Merritt said.
To simulate a highly sensitive detector, the researchers used a method to make radio telescopes around the world work together as a single large telescope and achieve a resolution roughly 10 million times the angular resolution of the human eye.
"Using very long baseline interferometry techniques, two compact sources of radio emission were detected at the center of NGC 7674; the two radio sources have properties that are known to be associated with massive black holes that are accreting gas, implying the presence of two black holes," Merritt said.
The galaxy hosting the binary supermassive black hole loudly emits radio waves. The detection confirms a theory predicting the presence of a compact binary in a radio galaxies bearing a "Z" shape.
"This morphology is thought to result from the combined effects of the galaxy merger followed by the formation of the massive binary," Merritt said.
River deposits exist across the surface of Mars and record a surface environment from over 3.5 billion years ago that was able to support liquid water at the surface. A region of Mars named Aeolis Dorsa contains some of the most spectacular and densely packed river deposits seen on Mars.
The dotted white arrow points to curved strata recording point bar growth and river migration. The boundaries of ancient valley walls are defined by textural and albedo changes and are also associated with lateral river migration. Stacked above the point bars and completely confined within the dotted white and black lines are topographically inverted river deposits outcropping as ridges (e.g., black arrow). In places (e.g., south of the dotted white arrow), the ridges run against the dotted boundaries, suggesting flow was once redirected along a valley wall [Credit: B.T. Cardenas et al., Geological Society of America Bulletin]
These deposits are observable with satellite images because they have undergone a process called "topographic inversion." where the deposits filling once topographically low river channels have been exhumed in such a way that they now exist as ridges at the surface of the planet.
With the use of high-resolution images and topographic data from cameras on orbiting satellites, B.T. Cardenas and colleagues from the Jackson School of Geosciences identify fluvial deposit stacking patterns and changes in sedimentation styles controlled by a migratory coastline. They also develop a method to measure river paleo-transport direction for a subset of these ridges.
Together, these measurements demonstrate that the studied river deposits once filled incised valleys. On Earth, incised valleys are commonly cut and filled during falling and rising eustatic sea level, respectively.
Cardenas and colleagues conclude that similar falling and rising water levels in a large water body forced the formation of the paleo-valleys in their study area. Cross-cutting relationships are observed at the valley-scale, indicating multiple episodes of water level fall and rise, each well over 50 meters, a similar scale to eustatic sea level changes on Earth.
The conclusion that such large water level fluctuations and coastline movements were recorded by these river deposits suggests some long-term stability in the controlling, downstream water body, which would not be expected from catastrophic hydrologic events.
For decades, astronomers have known about irregular outbursts from the double star system V745 Sco, which is located about 25,000 light years from Earth. Astronomers were caught by surprise when previous outbursts from this system were seen in 1937 and 1989. When the system erupted on February 6, 2014, however, scientists were ready to observe the event with a suite of telescopes including NASA’s Chandra X-ray Observatory.
Figure 1 [Credit: Chandra X-ray Center]
V745 Sco is a binary star system that consists of a red giant star and a white dwarf locked together by gravity. These two stellar objects orbit so closely around one another that the outer layers of the red giant are pulled away by the intense gravitational force of the white dwarf. This material gradually falls onto the surface of the white dwarf. Over time, enough material may accumulate on the white dwarf to trigger a colossal thermonuclear explosion, causing a dramatic brightening of the binary called a nova. Astronomers saw V745 Sco fade by a factor of a thousand in optical light over the course of about 9 days.
Astronomers observed V745 Sco with Chandra a little over two weeks after the 2014 outburst. Their key finding was it appeared that most of the material ejected by the explosion was moving towards us. To explain this, a team of scientists from the INAF-Osservatorio Astronomico di Palermo, the University of Palermo, and the Harvard-Smithsonian Center for Astrophysics constructed a three-dimensional (3D) computer model of the explosion, and adjusted the model until it explained the observations. In this model they included a large disk of cool gas around the equator of the binary caused by the white dwarf pulling on a wind of gas streaming away from the red giant.
The computer calculations showed that the nova explosion’s blast wave and ejected material were likely concentrated along the north and south poles of the binary system. This shape was caused by the blast wave slamming into the disk of cool gas around the binary. This interaction caused the blast wave and ejected material to slow down along the direction of this disk and produce an expanding ring of hot, X-ray emitting gas. X-rays from the material moving away from us were mostly absorbed and blocked by the material moving towards Earth, explaining why it appeared that most of the material was moving towards us.
Figure 2 [Credit: Chandra X-ray Center]
In Figure 1 which shows the new 3D model of the explosion, the blast wave is yellow, the mass ejected by the explosion is purple, and the disk of cooler material, which is mostly untouched by the effects of the blast wave, is blue. The cavity visible on the left side of the ejected material is the result of the debris from the white dwarf's surface being slowed down as it strikes the red giant. Below is an optical image from Siding Springs Observatory in Australia.
An extraordinary amount of energy was released during the explosion, equivalent to about 10 million trillion hydrogen bombs. The authors estimate that material weighing about one tenth of the Earth’s mass was ejected.
While this stellar-sized belch was impressive, the amount of mass ejected was still far smaller than the amount what scientists calculate is needed to trigger the explosion. This means that despite the recurrent explosions, a substantial amount of material is accumulating on the surface of the white dwarf. If enough material accumulates, the white dwarf could undergo a thermonuclear explosion and be completely destroyed. Astronomers use these so-called Type Ia supernovas as cosmic distance markers to measure the expansion of the Universe.
The scientists were also able to determine the chemical composition of the material expelled by the nova. Their analysis of this data implies that the white dwarf is mainly composed of carbon and oxygen.
A 3D print of the model was also created (Figure 2). This 3D print was simplified and printed in two parts, the blast wave (shown here in grey) and the ejected material (shown here in yellow).
Surveying the sky for almost four years to observe the glow of cold cosmic dust embedded in interstellar clouds of gas, the Herschel Space Observatory has provided astronomers with an unprecedented glimpse into the stellar cradles of our Galaxy. As a result, giant strides have been taken in our understanding of the physical processes that lead to the birth of stars and their planetary systems.
Herschel's view of the W3/W4/W5 complex [Credit: ESA/Herschel/NASA/JPL-Caltech, CC BY-SA 3.0 IGO; Acknowledgement: R. Hurt (JPL-Caltech)]
"We are made of star stuff," the astronomer Carl Sagan famously said, as the atoms that make us – our bodies, our homes, our planet – come largely from previous generations of stars.
Indeed, stars and planets are continually born in the densest and coldest pockets of molecular clouds, where they take shape from a mixture that consists largely of gas but also contains small amounts of dust mixed in.
As part of a cosmic recycling process, stars also return their re-processed material after their demise, enriching this interstellar medium that pervades all galaxies, including our Milky Way, with heavy elements produced in their nuclear furnaces and during the violent explosions that end the lives of the most massive stars.
Herschel: star formation [Credit: ESA/Herschel/NASA/JPL-Caltech;
acknowledgement: T. Pyle & R. Hurt (JPL-Caltech)]
Astronomers have long been aware that stars take shape as interstellar material comes together and condenses, then breaks up into fragments – the seeds of future stars – but many details of this complex process remained unclear until not so long ago.
What turned the tables in the understanding of how stars are born was ESA's Herschel Space Observatory, a trailblazing mission that was launched in 2009 and operated until 2013.
A unique observatory
Making sense of the Universe we live in is a fascinating endeavour forged over thousands of years by the incessant work of countless dedicated early thinkers, philosophers, and more recently, by scientists. This continuous process is punctuated by major discoveries, often made possible by the onset of new instrumentation that opens another window on the world, amplifying or expanding our senses.
Artist's impression of the Herschel spacecraft [Credit: ESA]
Enabling astronomers to observe farther and in greater detail for the past four centuries, the telescope has been key to establishing our physical understanding of the cosmos. Similarly, the progress in astronomical detectors – from the human eye to photographic plates, a couple of hundred years ago, and to a wide variety of electronic devices over the past century – has been just as revolutionary for the development of these investigations.
The discovery of light at wavelengths other than the visible band, in the nineteenth century, and its application to astronomy in the twentieth, have furthered this process, revealing entirely new classes of cosmic sources and phenomena, as well as unexpected aspects of known ones.
The cooler an object is, the longer the wavelengths of light it emits, so observing the sky in the far-infrared and sub-millimetre domains provides access to some of the coldest sources in the Universe, including cool gas and dust with temperatures of 50 K and even less.
Herschel's view of Orion B [Credit: ESA/Herschel/NASA/JPL-Caltech, CC BY-SA 3.0 IGO; Acknowledgement: R. Hurt (JPL-Caltech)]
Boasting a telescope with a 3.5-metre primary mirror – the largest ever to observe at far-infrared wavelengths – and detectors cooled to just above absolute zero, Herschel could perform observations with unprecedented sensitivity and spatial resolution at the wavelengths that are crucial to delve into the tangle of star-forming clouds.
This made Herschel much more capable of mapping the direct emission from cold dust than its predecessors, which include the US-Dutch-British Infrared Astronomical Satellite (IRAS), ESA's Infrared Space Observatory (ISO), NASA's Spitzer Space Telescope, and JAXA's Akari satellite.
Dust is a minor but crucial component of the interstellar medium that obscures observations at optical and near-infrared wavelengths. As such, it had long stood in the way of astronomers getting to the bottom of star formation, in our Milky Way as well as in other, more distant galaxies.
Herschel's view of Rho Ophiuchi [Credit: ESA/Herschel/NASA/JPL-Caltech, CC BY-SA 3.0 IGO; Acknowledgement: R. Hurt (JPL-Caltech)]
Herschel turned the situation around completely. Rather than being a problem, the dust became a crucial asset for astronomers: shining brightly at the long wavelengths probed by the observatory, dust could be used as a tracer of interstellar gas across the Galaxy and, most importantly, of its densest regions – the molecular clouds – where star formation unfolds.
In addition, Herschel provided the unique possibility to observe, with unprecedented spectral coverage and resolution, a vast number of lines in the spectra of gas clouds produced by atoms and molecules that are present, albeit in small amounts, in the gas. Together with the observation of dust, these atomic and molecular lines were instrumental in tracking down the properties of gas in a vast number of star-forming clouds.
Several of Herschel's Key Programmes were dedicated to studying the birth of stars in molecular clouds, near and far, in our Galaxy.
The filamentary structure of the Galactic Plane [Credit: ESA/PACS & SPIRE Consortium, S. Molinari, Hi-GAL Project]
Prominently among them, the Herschel Gould Belt Survey concentrated on areas close to home, gathering exceptionally detailed observations of the nearest star-forming regions, which are located in clouds collectively forming a giant ring out to 1500 light-years from the Sun. Another project, the Herschel imaging survey of OB Young Stellar objects, looked specifically at how massive stars are born. And finally, the Herschel infrared Galactic Plane Survey performed a complete census of stellar nurseries across the Milky Way by collecting a 360-degree view of the Galactic Plane. These three observing programmes alone spent over 1500 hours of observations to investigate star formation.
Filaments galore
The most striking discovery that emerged from these extensive surveys was a vast and intricate network of filamentary structures weaving their way through the Galaxy.
Herschel's view of the Taurus molecular cloud [Credit: ESA/Herschel/NASA/JPL-Caltech, CC BY-SA 3.0 IGO; Acknowledgement: R. Hurt (JPL-Caltech)]
Finding filaments per se was not a novelty – similar structures had already been detected in previous decades – but their ubiquitous presence was definitely remarkable.
Herschel was the first observatory to reveal filaments nearly everywhere in the interstellar medium, from small ones, only a few light-years long, to giant threads extending over hundreds of light-years.
Such structures were spotted in all types of clouds, also in those with no ongoing star formation. Astronomers wondered: why do some filaments produce stars, while others do not?
Herschel image of the Polaris Flare [Credit: ESA/Herschel/SPIRE/Ph. André (CEA Saclay) for the 'Gould Belt survey' Key Programme Consortium and A. Abergel (IAS Orsay) for the 'Evolution of Interstellar Dust' Key Programme Consortium]
The bounty of new data revealed not only that filaments are omnipresent, but also that they seem to have very similar properties, at least in our local neighbourhood. Regardless of their length, all filaments observed in nearby clouds have a universal width – about one third of a light-year.
The origin of these interstellar filaments and of their universal width is likely linked to the turbulent dynamics of gas in interstellar clouds. In fact, the width corresponds to the typical scale where gas undergoes the transition from supersonic to subsonic state, suggesting that filaments arise as a result of supersonic turbulence in the clouds.
Low-mass star formation
After 2010, when the first studies of Herschel observations were published, it became clear that interstellar filaments are crucial elements in the process of star formation. Evidence from Herschel observations continued to pile up over the following years.
Herschel image of IC 5146 [Credit: ESA/Herschel/SPIRE/PACS/D. Arzoumanian (CEA Saclay) for the 'Gould Belt survey' Key Programme Consortium]
Filaments appear to precede the formation of stars in our Galaxy and, in some cases, they facilitate it. But only filaments that exceed a minimum density threshold seem to be active in the production of stars.
Taking account of the accumulating evidence, astronomers developed a new model to explain how stars of low mass, like our Sun, are born. In this two-step scenario, first a web of filaments arises from turbulent, supersonic motions of gas in the interstellar material. Later, but only in the densest filaments, gravity takes over: filaments then become unstable and fragment into clumps which, in turn, start to contract and eventually create pre-stellar cores – the seeds of future stars.
Even if ubiquitous, filaments represent a small fraction of the total mass that makes up the Galaxy's interstellar medium, and only the densest of them partake in the highly inefficient process of star formation. While dense filamentary structures are beyond doubt the preferred sites for stellar birth, Herschel also observed some stars that appear to be forming in regions where filaments have not been identified.
High-mass star formation
Massive stars, exceeding several times the mass of the Sun, are rare but extremely bright and powerful objects that have a significant impact on their environment. Their formation has been a conundrum that has eluded explanation for many decades because of the difficulty in reconciling the enormous radiation pressure that arises as they take shape with the fact that this is sufficient to disperse the material and stop the accretion process entirely.
Massive stars forming in Cygnus X [Credit: ESA/PACS/SPIRE/Martin Hennemann & Frédérique Motte, Laboratoire AIM Paris-Saclay, CEA/Irfu - CNRS/INSU - Univ. Paris Diderot, France]
Because of the larger masses and energy outputs involved, these stars must come to life in conditions that are quite different from those found in the birthplaces of their lower-mass counterparts. As revealed by Herschel's observations, massive stars appear to form in the vicinity of gigantic structures such as ridges (massive, high-density filaments) and hubs (spherical clumps of matter) that may arise at the intersection of ordinary filaments.
With their enormous reservoirs of gas and dust, ridges and hubs can provide the sustained flow of material needed to support the growth of huge stellar embryos. In these extreme environments, also called 'mini-starbursts', star formation can reach very intense levels, eventually giving rise to stellar clusters hosting primarily massive stars.
While highlighting the different phenomena that lead to the formation of high- and low-mass stars, Herschel has also brought them together within a common framework. As part of a continuous process taking place on all scales, the interstellar material is stirred up, compressed and confined in a variety of filamentary structures, whose later collapse under gravity and subsequent fragmentation gives rise to a multiplicity of different stars.
From new answers to new questions
Within less than a decade, astronomers using Herschel's extraordinary data have shown how the seemingly complex phenomenon of star formation can be understood in terms of simple and universal processes. Observations of nearby galaxies indicate that similar processes might be at play also beyond the confines of our Milky Way.
Intense star formation in the Westerhout 43 region [Credit: ESA/Herschel/PACS, SPIRE/Hi-GAL Project. Acknowledgement: UNIMAP / L. Piazzo, La Sapienza – Università di Roma; E. Schisano / G. Li Causi, IAPS/INAF, Italy]
During its surveys of star-forming regions, Herschel has also observed many protoplanetary disks around very young stars, providing a glimpse into the raw material that will eventually build up these stars' planetary systems.
However, as new observations offer an answer to old questions, many new questions arise, some of which remain unanswered. Astronomers are still investigating a number of crucial aspects of star formation, such as the origin of filaments in molecular clouds, the dynamics of matter accretion, and the role of magnetic fields in the process.
To address some of these questions, in particular the formation of filaments, Herschel observations of various molecular clouds have been compared with measurements of the magnetic field in these clouds, obtained using ESA's Planck satellite and ground-based observatories, as well as with predictions of numerical simulations. The comparisons show that the magnetic fields tend to be perpendicular to the densest, star-forming filaments and parallel to lower-density filaments, known as striations, that flow into the denser ones, contributing to their growth.
Future studies and even more detailed observations will be needed to confirm and elucidate how magnetic fields do, as suggested, play a strong role in the process of star formation, contributing to deepening our understanding of this fascinating phenomenon.
