Topic: Late April Astronomy Bulletin

[Clive]

FIRST KNOWN INTERSTELLAR OBJECT ON EARTH
United States Space Command

A small meteor that hit Earth in 2014 was from another star system, and may have left interstellar debris on the seafloor. The meteor ignited in a fireball in the skies near Papua New Guinea, the memo states, and scientists believe it possibly sprinkled interstellar debris into the South Pacific Ocean. The confirmation backs up the breakthrough discovery of the first interstellar meteor—and, retroactively, the first known interstellar object of any kind to reach our solar system—which was initially flagged by Harvard University researchers. The discovery of the meteor, which measured just a few feet wide, follows recent detections of two other interstellar objects in our solar system, known as ‘Oumuamua and Comet Borisov, that were much larger and did not come into close contact with Earth. There are nearly 1,000 impacts logged in the database, but a fireball that exploded near Manus Island on January 8, 2014 jumped out at researchers owing to an unusually swift speed exceeding 130,000 miles per hour. This breakneck pace hinted at “a possible origin from the deep interior of a planetary system or a star in the thick disk of the Milky Way galaxy of the solar system.”

Some of the sensors that detect fireballs are operated by the U.S. Department of Defense, which uses the same technologies to monitor the skies for nuclear detonations. As a result, the team couldn’t directly confirm the margin of error on the fireball’s velocity. The secret data threw the paper into limbo as the researchers sought to get confirmation from the U.S. government. The newly released memo, which is dated March 1 of this year, reveals that the velocity estimate reported to NASA is sufficiently accurate to indicate an interstellar trajectory. Any information about the light emitted by the object as it burned up in the atmosphere could yield insights about the interior composition of the interstellar visitor. While this was an incredibly small object, it indicates that the solar system may be awash in material from other star systems, and indeed even other galaxies, that could be turned up by future searches. Such efforts could offer a glimpse of the worlds beyond the Sun right here on Earth, and perhaps even unearth bonafide interstellar meteorites.


RELIC FROM EARLY SOLAR SYSTEM TO VISIT
University of California - Los Angeles


An enormous comet -- approximately 80 miles across is heading our way at 22,000 miles per hour from the edge of the solar system. Fortunately, it will never get closer than 1 billion miles from the Sun, which is slightly farther from Earth than Saturn; that will be in 2031. Comets, among the oldest objects in the solar system, are icy bodies that were unceremoniously tossed out of the solar system in a gravitational pinball game among the massive outer planets. The evicted comets took up residence in the Oort cloud, a vast reservoir of far-flung comets encircling the solar system out to many billions of miles into deep space. A typical comet's spectacular multimillion-mile-long tail, which makes it look like a skyrocket, belies the fact that the source at the heart of the fireworks is a solid nucleus of ice mixed with dust -- essentially a dirty snowball. This huge one, called Comet C/2014 UN271 and discovered by astronomers Pedro Bernardinelli and Gary Bernstein, could be as large as 85 miles across. This comet has the largest nucleus ever seen in a comet by astronomers. I ts nucleus is about 50 times larger than those of most known comets. Its mass is estimated to be 500 trillion tons, a hundred thousand times greater than the mass of a typical comet found much closer to the Sun. The researchers used Hubble to take five photos of the comet on Jan. 8, 2022, and incorporated radio observations of the comet into their analysis.

The comet is now less than 2 billion miles from the Sun and in a few million years will loop back to its nesting ground in the Oort cloud, Comet C/2014 UN271 was first serendipitously observed in 2010, when it was 3 billion miles from the Sun. Since then, it has been intensively studied by ground and space-based telescopes. The challenge in measuring this comet was how to determine the solid nucleus from the huge dusty coma -- the cloud of dust and gas -- enveloping it. The comet is currently too far away for its nucleus to be visually resolved by Hubble. Instead, the Hubble data show a bright spike of light at the nucleus' location. Astronomers compared the brightness of the nucleus to earlier radio observations from the Atacama Large millimeter/submillimeter Array, or ALMA, in Chile. The new Hubble measurements are close to the earlier size estimates from ALMA, but convincingly suggest a darker nucleus surface than previously thought. The comet has been falling toward the Sun for well over 1 million years. The Oort cloud is thought to be the nesting ground for trillions of comets. It is believed the Oort cloud extends from a few hundred times the distance between the Sun and the Earth to at least a quarter of the way out to the distance of the nearest stars to our sun, in the Alpha Centauri system. The Oort cloud's comets were tossed out of the solar system billions of years ago by the gravitation of the massive outer planets, according. The far-flung comets travel back toward the Sun and planets only if their orbits are disturbed by the gravitational tug of a passing star. First hypothesized in 1950 by Dutch astronomer Jan Oort, the Oort cloud still remains a theory because the comets that make it up are too faint and distant to be directly observed. This means the solar system's largest structure is all but invisible.


JUPITER’S MOON HAS SPLENDID DUNES
Rutgers University

Scientists have long wondered how Jupiter's innermost Moon, Io, has meandering ridges as grand as any that can be seen in movies like "Dune." Now, a research study has provided a new explanation of how dunes can form even on a surface as icy and roiling as Io's. The study is based on the physical processes controlling grain motion coupled with an analysis of images from the 14-year mission of NASA's Galileo spacecraft, which allowed the creation of the first detailed maps of Jupiter's moons. The new study is expected to expand our scientific understanding of the geological features on these planet-like worlds. Current scientific understanding dictates that dunes, by their nature, are hills or ridges of sand piled up by the wind. And scientists in previous studies of Io, while describing its surface as containing some dune-like features, concluded the ridges could not be dunes since the forces from winds on Io are weak due to the moon's low-density atmosphere. The Galileo mission, which lasted from 1989 -- 2003, logged so many scientific firsts that researchers to this day are still studying the data it collected. One of the major insights gleaned from the data was the high extent of volcanic activity on Io -- so much so that its volcanoes repeatedly and rapidly resurface the little world. Io's surface is a mix of black solidified lava flows and sand, flowing "effusive" lava streams, and "snows" of sulphur dioxide. The scientists used mathematical equations to simulate the forces on a single grain of basalt or frost and calculate its path. When lava flows into sulphur dioxide beneath the moon's surface, its venting is "dense and fast moving enough to move grains on Io and possibly enable the formation of large-scale features like dunes. Once the researchers devised a mechanism by which the dunes could form, they looked to photos of Io's surface taken by the Galileo spacecraft for more proof. The spacing of the crests and the height-to-width ratios they observed were consistent with trends for dunes seen on Earth and other planets.


NEPTUNE’S SURPRISING TEMPERATURE CHANGES
ESO

Astronomers have used ground-based telescopes, including the European Southern Observatory’s Very Large Telescope (ESO’s VLT), to track Neptune’s atmospheric temperatures over a 17-year period. They found a surprising drop in Neptune’s global temperatures followed by a dramatic warming at its south pole. Like Earth, Neptune experiences seasons as it orbits the Sun. However, a Neptune season lasts around 40 years, with one Neptune year lasting 165 Earth years. It has been summertime in Neptune’s southern hemisphere since 2005, and the astronomers were eager to see how temperatures were changing following the southern summer solstice. Astronomers looked at nearly 100 thermal-infrared images of Neptune, captured over a 17-year period, to piece together overall trends in the planet’s temperature in greater detail than ever before. These data showed that, despite the onset of southern summer, most of the planet had gradually cooled over the last two decades. The globally averaged temperature of Neptune dropped by 8 °C between 2003 and 2018. The astronomers were then surprised to discover a dramatic warming of Neptune’s south pole during the last two years of their observations, when temperatures rapidly rose 11 °C between 2018 and 2020. Although Neptune’s warm polar vortex has been known for many years, such rapid polar warming has never been previously observed on the planet.

The astronomers measured Neptune’s temperature using thermal cameras that work by measuring the infrared light emitted from astronomical objects. For their analysis the team combined all existing images of Neptune gathered over the last two decades by ground-based telescopes. They investigated infrared light emitted from a layer of Neptune’s atmosphere called the stratosphere. This allowed the team to build up a picture of Neptune’s temperature and its variations during part of its southern summer. Because Neptune is roughly 4.5 billion kilometres away and is very cold, the planet’s average temperature reaching around –220°C, measuring its temperature from Earth is no easy task. Around one third of all the images taken came from the VLT Imager and Spectrometer for mid-InfraRed (VISIR) instrument on ESO’s VLT in Chile’s Atacama Desert. Because of the telescope’s mirror size and altitude, it has a very high resolution and data quality, offering the clearest images of Neptune. The team also used data from NASA’s Spitzer Space Telescope and images taken with the Gemini South telescope in Chile, as well as with the Subaru Telescope, the Keck Telescope, and the Gemini North telescope, all in Hawai‘i. Because Neptune’s temperature variations were so unexpected, the astronomers do not know yet what could have caused them. They could be due to changes in Neptune’s stratospheric chemistry, or random weather patterns, or even the solar cycle. More observations will be needed over the coming years to explore the reasons for these fluctuations. Future ground-based telescopes like ESO’s Extremely Large Telescope (ELT) could observe temperature changes like these in greater detail, while the NASA/ESA/CSA James Webb Space Telescope will provide unprecedented new maps of the chemistry and temperature in Neptune’s atmosphere.


EXOCOMETS FOUND AROUND ANOTHER STAR
Science

When a comet dives near the Sun, it’s a spectacular and rare sight from here on Earth. Our solar system, however, is full of these tiny chunks of ice, spinning far from the Sun in the distant Oort cloud. Given the ubiquity of comets here, scientists think other planetary systems probably have them too. Ukrainian recently published a discovery of five new exocomets — comets that orbit a star other than the Sun. They also independently confirmed a handful of exocomets previously detected by other researchers. Within our solar system, comets are studied as remnants of the past and provide clues to the chemistry of the formation of Earth and its neighbouring planets. They are also a particularly important part of Earth’s story, as comets are believed to have brought water to Earth, making our planet bursting with life. These newly discovered exocomets orbit the star Beta Pictoris, a well-studied favourite of astronomers that is only about 65 light-years from Earth. Beta Pictoris is much younger than the Sun, only 10 to 40 million years old compared to the solar system’s 4.5 billion years, making it a useful snapshot of what happens during its youth. a planetary system. This star orbits a gas giant planet 11 times larger than Jupiter (called Beta Pic b) and a huge disk of dust nearly 40 billion miles in diameter, known as a debris disk.

Debris disks represent the “older” era of planet-forming disks — the later stage in the complex dance of dust and gas that form full-fledged planets like those around the Sun. These disks are often chaotic and violent places, with chunks of rock and protoplanets flying around and colliding. That’s where exocomets come in. In younger planetary systems like Beta Pic, comets are much more likely to dive near their stars because everything on the disk is still shifting before objects settle into their final configuration. In fact, this discovery isn’t even the first time exocomets have been seen around Beta Pic — the first detection with TESS occurred in 2019, and previous studies inferred that Beta Pic actually has two distinct groups of exocomets with different properties. The new exocomets add to a growing stack of exocomet discoveries around multiple stars from both TESS and its predecessor, the planet-hunting Kepler Space Telescope. While these observatories aren’t the first to spot exocomets in one form or another, they’re the first to detect them directly through transits — tiny dips in the amount of light we see from a star as a comet passes in front. First observed in Kepler data in 2017, comet transits are steeper and skewed than exoplanet transits, due in part to the comet’s long tail. Transits show how big the exocomet is, while other discovery methods can measure the comet’s speed and orbit. When combined, all of this information provides a more complete picture of what’s going on with exocomets — how they’re born and how they change. By building a large catalogue of exocomet transits around many different stars, astronomers can discover patterns in the data, potentially revealing trends caused by the process of planet formation.


NOVA OUTBURSTS ARE SOURCE OF COSMIC RAYS
Max Planck Institute for Physics

Every 15 years or so, a dramatic explosion occurs in the constellation of Ophiuchus. Birthplaces of a nova are systems in which two very different stars live in a parasitic relationship: A white dwarf, a small, burned-out and tremendously dense star -- a teaspoon of its matter weighs about 1 ton -- orbits a red giant, an old star that will soon burn up. The dying giant star RS Ophiuchi (RS Oph) feeds the white dwarf with matter shedding its outer hydrogen layer as the gas flows onto the nearby white dwarf. This flow of matter continues, until the white dwarf overheats itself. The temperature and pressure in the newly gained stellar shells become too large and are flung away in a gigantic thermonuclear explosion. The dwarf star remains intact and the cycle begins again -- until the spectacle repeats itself. It had been speculated that such explosions involve high energies. The two MAGIC telescopes recorded gamma rays with the value of 250 gigaelectronvolts (GeV), among the highest energies ever measured in a nova. By comparison, the radiation is a hundred billion times more energetic than visible light. MAGIC was able to make its observations following initial alerts from other instruments measuring at different wavelengths. "The spectacular eruption of the RS Ophiuchi shows that the MAGIC telescopes' fast response really pays off: It takes them no more than 30 seconds to move to a new target," said David Green, a scientist at the Max Planck Institute for Physics and one of the authors of the paper. After the explosion, several shock fronts propagated through the stellar wind from the Red Giant and the interstellar medium surrounding the binary system. These shock waves work like a giant power plant in which particles are accelerated to near the speed of light. The combined measurements suggest that the gamma rays emanate from energetic protons, nuclei of hydrogen atoms. To fully understand the complicated interplay of violent events with the interstellar medium in the Milky Way, more observations like those reported now will be necessary. The MAGIC collaboration will therefore continue to look for "restless" objects in our Galaxy and beyond.


MICRONOVAE, A NEW KIND OF STELLAR EXPLOSION
ESO

A team of astronomers using the Very Large Telescope (ESO’s VLT), have observed a new type of stellar explosion — a micronova. These outbursts happen on the surface of certain stars, and can each burn through around 3.5 billion Great Pyramids of Giza of stellar material in only a few hours. Micronovae are extremely powerful events, but are small on astronomical scales; they are much less energetic than the stellar explosions known as novae, which astronomers have known about for centuries. Both types of explosions occur on white dwarfs, dead stars with a mass about that of our Sun, but as small as Earth. A white dwarf in a two-star system can steal material, mostly hydrogen, from its companion star if they are close enough together. As this gas falls onto the very hot surface of the white dwarf star, it triggers the hydrogen atoms to fuse into helium explosively. In novae, these thermonuclear explosions occur over the entire stellar surface. Micronovae are similar explosions that are smaller in scale and faster, lasting just several hours. They occur on some white dwarfs with strong magnetic fields, which funnel material towards the star’s magnetic poles. These new micronovae challenge astronomers’ understanding of stellar explosions and may be more abundant than previously thought. The team first came across these mysterious micro-explosions when analysing data from NASA’s Transiting Exoplanet Survey Satellite (TESS). It observed three micronovae with TESS: two were from known white dwarfs, but the third required further observations with the X-shooter instrument on ESO’s VLT to confirm its white dwarf status.The discovery of micronovae adds to the repertoire of known stellar explosions.


ORIGINS OF SUPERMASSIVE BLACK HOLES
NASA/Goddard Space Flight Center

Astronomers have identified a rapidly growing black hole in the early Universe that is considered a crucial "missing link" between young star-forming galaxies and the first supermassive black holes. They used data from NASA's Hubble Space Telescope to make this discovery. Until now, the monster, nicknamed GNz7q, had been lurking unnoticed in one of the best-studied areas of the night sky, the Great Observatories Origins Deep Survey-North (GOODS-North) field. Archival Hubble data from Hubble's Advanced Camera for Surveys helped the team determine that GNz7q existed just 750 million years after the big bang. The team obtained evidence that GNz7q is a newly formed black hole. Hubble found a compact source of ultraviolet (UV) and infrared light. This couldn't be caused by emission from galaxies, but is consistent with the radiation expected from materials that are falling onto a black hole. Rapidly growing black holes in dusty, early star-forming galaxies are predicted by theories and computer simulations, but had not been observed until now. One of the outstanding mysteries in astronomy today is: How did supermassive black holes, weighing millions to billions of times the mass of the Sun, get to be so huge so fast? Current theories predict that supermassive black holes begin their lives in the dust-shrouded cores of vigorously star-forming "starburst" galaxies before expelling the surrounding gas and dust and emerging as extremely luminous quasars. While extremely rare, both these dusty starburst galaxies and luminous quasars have been detected in the early Universe.

The team believes that GNz7q could be a missing link between these two classes of objects. GNz7q has exactly both aspects of the dusty starburst galaxy and the quasar, where the quasar light shows the dust reddened colour. Also, GNz7q lacks various features that are usually observed in typical, very luminous quasars (corresponding to the emission from the accretion disk of the supermassive black hole), which is most likely explained that the central black hole in GN7q is still in a young and less massive phase. These properties perfectly match with the young, transition phase quasar that has been predicted in simulations, but never identified at similarly high-redshift Universe as the very luminous quasars so far identified up to a redshift of 7.6. While other interpretations of the team's data cannot be completely ruled out, the observed properties of GNz7q are in strong agreement with theoretical predictions. GNz7q's host galaxy is forming stars at the rate of 1,600 solar masses per year, and GNz7q itself appears bright at UV wavelengths but very faint at X-ray wavelengths. Generally, the accretion disk of a massive black hole should be very bright in both UV and X-ray light. But this time, although the team detected UV light with Hubble, X-ray light was invisible even with one of the deepest X-ray datasets. These results suggest that the core of the accretion disk, where X-rays originate, is still obscured; while the outer part of the accretion disk, where UV light originates, is becoming unobscured. This interpretation is that GNz7q is a rapidly growing black hole still obscured by the dusty core of its star-forming host galaxy. Finding GNz7q hiding in plain sight was only possible thanks to the uniquely detailed, multiwavelength datasets available for GOODS-North. Without this richness of data GNz7q would have been easy to overlook, as it lacks the distinguishing features usually used to identify quasars in the early Universe. The team now hopes to systematically search for similar objects using dedicated high-resolution surveys and to take advantage of the NASA James Webb Space Telescope's spectroscopic instruments to study objects such as GNz7q in unprecedented detail.


HUNTING FOR GRAVITATIONAL WAVES FROM MONSTER BLACK HOLES
NASA/Goddard Space Flight Center

Our Universe is a chaotic sea of ripples in space-time called gravitational waves. Astronomers think waves from orbiting pairs of supermassive black holes in distant galaxies are light-years long and have been trying to observe them for decades, and now they're one step closer thanks to NASA's Fermi Gamma-ray Space Telescope. Fermi detects gamma rays, the highest-energy form of light. An international team of scientists examined over a decade of Fermi data collected from pulsars, rapidly rotating cores of stars that exploded as supernovae. They looked for slight variations in the arrival time of gamma rays from these pulsars, changes which could have been caused by the light passing through gravitational waves on the way to Earth. But they didn't find any. While no waves were detected, the analysis shows that, with more observations, these waves may be within Fermi's reach. When massive objects accelerate, they produce gravitational waves travelling at light speed. The ground-based Laser Interferometer Gravitational Wave Observatory -- which first detected gravitational waves in 2015 -- can sense ripples tens to hundreds of miles long from crest to crest, which roll past Earth in just fractions of a second. The upcoming space-based Laser Interferometer Space Antenna will pick up waves millions to billions of miles long. Researchers are searching for waves that are light-years, or trillions of miles, long and take years to pass Earth. These long ripples are part of the gravitational wave background, a random sea of waves generated in part by pairs of supermassive black holes in the centres of merged galaxies across the Universe. To find them, scientists need galaxy-sized detectors called pulsar timing arrays. These arrays use specific sets of millisecond pulsars, which rotate as fast as blender blades. Millisecond pulsars sweep beams of radiation, from radio to gamma rays, past our line of sight, appearing to pulse with incredible regularity -- like cosmic clocks.

As long gravitational waves pass between one of these pulsars and Earth, they delay or advance the light arrival time by billionths of a second. By looking for a specific pattern of pulse variations among pulsars of an array, scientists expect they can reveal gravitational waves rolling past them. Radio astronomers have been using pulsar timing arrays for decades, and their observations are the most sensitive to these gravitational waves. But interstellar effects complicate the analysis of radio data. Space is speckled with stray electrons. Across light-years, their effects combine to bend the trajectory of radio waves. This alters the arrival times of pulses at different frequencies. Gamma rays don't suffer from these complications, providing both a complementary probe and an independent confirmation of the radio results. The Fermi results are already 30% as good as the radio pulsar timing arrays when it comes to potentially detecting the gravitational wave background. With another five years of pulsar data collection and analysis, it'll be equally capable with the added bonus of not having to worry about all those stray electrons. Within the next decade, both radio and gamma-ray astronomers expect to reach sensitivities that will allow them to pick up gravitational waves from orbiting pairs of monster black holes.


BIGGEST REVOLUTION IN PHYSICS SINCE EINSTEIN
Science

Scientists outside Chicago, USA, have discovered that the mass of a subatomic particle is not what it should be – a surprising discovery that could revolutionize physics and our understanding of the Universe. The measurement is the first conclusive result of an experiment that is at odds with one of the most important and successful theories in modern physics. The team found that the particle, known as the W boson, has more mass than theories predicted. The discovery could lead to the development of a new and more complete theory of how the Universe works. Scientists at the CDF (Fermilab Collider Detector) in the US state of Illinois found only a small difference in the mass of the W boson compared to what theory says it should be — just 0.1% . But if this is confirmed by other experiments, the implications are enormous. The so-called Standard Model of particle physics has predicted the behaviour and properties of subatomic particles without any discrepancy for 50 years. So far. The conclusion may be linked to clues from other experiments at Fermilab and the Large Hadron Collider on the Swiss-French border. These as-yet-unconfirmed conclusions also suggest deviations from the Standard Model, possibly as a result of an as-yet-undiscovered fifth force of nature at play. Physicists have known for some time that the theory needs updating. The concept is not able to explain the presence of invisible material in space, called Dark Matter, nor the continuous accelerated expansion of the Universe by a force called Dark Energy. Neither does gravity. But despite the enthusiasm, the physical community remains cautious. While the Fermilab result is the most accurate measurement of the W boson mass to date, it is at odds with two of the next most accurate measurements from two separate experiments that conform to the Standard Model. All eyes are now on the Large Hadron Collider, which is set to restart its experiments after a three-year renovation. The hope is that these tests will provide the results that will lay the groundwork for a more complete new theory of physics.