Topic: Mid November Astronomy Bulletin

[Clive]

LOST FRAGMENT OF THE MOON
University of Arizona

A near-Earth asteroid named Kamo`oalewa could be a fragment of our Moon, according to a new research. Kamo`oalewa is a quasi-satellite -- a subcategory of near-Earth asteroids that orbit the Sun but remain relatively close to Earth. Little is known about these objects because they are faint and difficult to observe. Kamo`oalewa was discovered by the PanSTARRS telescope in Hawaii in 2016, and the name -- found in a Hawaiian creation chant -- alludes to an offspring that travels on its own. The asteroid is roughly the size of a Ferris wheel -- between 150 and 190 feet in diameter -- and gets as close as about 9 million miles from Earth. Due to its orbit, Kamo`oalewa can only be observed from Earth for a few weeks every April. Its relatively small size means that it can only be seen with one of the largest telescopes on Earth. Using the UArizona-managed Large Binocular Telescope on Mount Graham in southern Arizona, a team of astronomers found that Kamo`oalewa's pattern of reflected light, called a spectrum, matches lunar rocks from NASA's Apollo missions, suggesting it originated from the Moon. The team can't yet be sure how it may have broken loose. The reason, in part, is because there are no other known asteroids with lunar origins. Kamo`oalewa's orbit is another clue to its lunar origins. Its orbit is similar to the Earth's, but with the slightest tilt. Its orbit is also not typical of near-Earth asteroids. It is very unlikely that a garden-variety near-Earth asteroid would spontaneously move into a quasi-satellite orbit like Kamo`oalewa's. It will not remain in this particular orbit for very long, only about 300 years in the future, and it is we estimated that it arrived in this orbit about 500 years ago. Kamo`oalewa is about 4 million times fainter than the faintest star the human eye can see in a dark sky.


SMALL ASTEROID PASSED VERY CLOSE TO EARTH LAST MONTH
NASA

NASA usually keeps an eye on every asteroid in space that has the potential to impact the Earth. It routinely says that most of these asteroids are small and pose no risk, but there’s always some fear that a large and unknown asteroid could be lurking in space. Recently, a small asteroid roughly the size of a refrigerator came extremely close to the Earth. It’s not the size of the asteroid that worries scientists so much. Rather it was that the asteroid came from the direction of the Sun, and scientists didn’t even know it was there. The asteroid is called Asteroid 2021 UA1 and is the third closest approach by an asteroid ever. A distance of 3000 kilometres is extremely close, but the asteroid’s small size meant it posed no risk. Astronomers say the asteroid approached the planet passing over Antarctica last month. While 3000 kilometers sounds very close, that puts it outside the orbit of the ISS. Despite being outside the orbit of the ISS, it was lower than the orbit of communications satellites. With a diameter of roughly 2 metres, had the asteroid entered the planet’s atmosphere, it would have burned up before hitting the ground. The flyby was so surprising because it came from behind the Sun coming from the daytime sky. Approaching in that manner made the asteroid invisible until its close approach. The only asteroids to have ever come closer to the Earth included 2020 QG, which came within 1830 miles of the planet. Asteroid 2020 VT4 passed by at a distance of only a few hundred miles away from the planet. All of those asteroids were too small to have caused harm to the planet.


JUNO PEERS DEEP INTO JUPITER
University of Leicester

Researchers studying data captured in orbit around Jupiter has revealed new insights into what's happening deep beneath the gas giant's distinctive and colourful bands. Data from the microwave radiometer carried by NASA's Juno spacecraft shows that Jupiter's banded pattern extends deep below the clouds, and that the appearance of Jupiter's belts and zones inverts near the base of the water clouds. Microwave light allows planetary scientists to gaze deep beneath Jupiter's colourful clouds, to understand the weather and climate in the warmer, darker, deeper layers. At altitudes shallower than five bars of pressure (or around five times the average atmospheric pressure on Earth), the planet's belts shine brightly in microwave light, whereas the zones are dark. But everything changes at higher pressures, at altitudes deeper than 10 bars, giving scientists a glimpse of an unexpected reversal in the meteorology and circulation. Among Jupiter's most notable attributes is its distinctive banded appearance. Planetary scientists call the light, whitish bands zones, and the darker, reddish ones belts. Jupiter's planetary-scale winds circulate in opposite direction, east and west, on the edges of these colourful stripes. A key question is whether this structure is confined to the planet's cloud tops, or if the belts and zones persist with increasing depth. An investigation of this phenomenon is one of the primary objectives of NASA's Juno mission, and the spacecraft carries a specially-designed microwave radiometer to measure emission from deep within the Solar System's largest planet for the first time.

The Juno team utilise data from this instrument to examine the nature of the belts and zones by peering deeper into the Jovian atmosphere than has ever previously been possible. Juno's microwave radiometer operates in six wavelength channels ranging from 1.4 cm to 50 cm, and these enable Juno to probe the atmosphere at pressures starting at the top of the atmosphere near 0.6 bars to pressures exceeding 100 bars, around 250 km deep. At the cloud tops, Jupiter's belts appear bright with microwave emission, while the zones remain dark. Bright microwave emission either means warmer atmospheric temperatures, or an absence of ammonia gas, which is a strong absorber of microwave light. This configuration persists down to approximately five bars. And at pressures deeper than 10 bars, the pattern reverses, with the zones becoming microwave-bright and the belt becoming dark. Scientists therefore believe that something -- either the physical temperatures or the abundance of ammonia -- must therefore be changing with depth. There are two possible mechanisms that could be responsible for the change in brightness, each implying different physical conclusions. One mechanism is related to the distribution of ammonia gas within the belts and zones. Ammonia is opaque to microwaves, meaning a region with relatively less ammonia will shine brighter in Juno's observations. This mechanism could imply a stacked system of opposing circulation cells, similar to patterns in Earth's tropics and mid-latitudes. These circulation patterns would provide sinking in belts at shallow depths and upwelling in belts at deeper levels -- or vigorous storms and precipitation, moving ammonia gas from place to place. Another possibility is that the gradient in emission corresponds to a gradient in temperature, with higher temperatures resulting in greater microwave emission. Temperatures and winds are connected, so if this scenario is correct, then Jupiter's winds may increase with depth below the clouds until we reach the jovicline, before tapering off into the deeper atmosphere -- something that was also suggested by NASA's Galileo probe in 1995, which measured windspeeds as it descended under a parachute into the clouds of Jupiter. The likely scenario is that both mechanisms are at work simultaneously, each contributing to part of the observed brightness variation. The race is now on to understand why Jupiter's circulation behaves in this way, and whether this is true of the other Giant Planets in our Solar System.


“EGGSHELL PLANETS” POSSIBLE
Washington University in St. Louis

Strange 'eggshell planets' are among the rich variety of exoplanets possible, according to a recent study. These rocky worlds have an ultra-thin outer brittle layer and little to no topography. Such worlds are unlikely to have plate tectonics, raising questions as to their habitability. Only a small subset of extrasolar planets are likely eggshell planets. At least three such worlds found during previous astronomical surveys may already be known. Scientists could use planned and future space telescopes to examine these exoplanets in greater detail and confirm their geological characteristics. To date, exoplanets have largely been the domain of astronomers, because space scientists rely on astronomical techniques and instruments to detect exoplanets. Planets have certain qualities that are inherent to the planets themselves, like their size, interior temperature and the materials that they are made of. Other properties are more of a function of the planet's environment, like how far it is from the sun. The planets that humans know best are those in our own solar system -- but these truths are not necessarily universal for planets that orbit other stars. The researchers wanted to see which planetary and stellar parameters play the most important role in determining the thickness of a planet's outer brittle layer, which is known as the lithosphere. This thickness helps determine whether, for example, a planet can support high topography such as mountains, or has the right balance between rigidity and flexibility for one part of the surface to dive down, or subduct, beneath another -- the hallmark of plate tectonics. It is this process that helps Earth regulate its temperature over geological timescales, and the reason why plate tectonics is thought to be an important component of planetary habitability. They discovered that surface temperature is the primary control on the thickness of brittle exoplanet lithospheres, although planetary mass, distance to its star and even age all play a role. The new models predict that worlds that are small, old or far from their star likely have thick, rigid layers, but, in some circumstances, planets might have an outer brittle layer only a few kilometres thick -- these so-called eggshell planets.


BLACK HOLE FOUND HIDING IN STAR CLUSTER
ESO

Using the Very Large Telescope (ESO’s VLT), astronomers have discovered a small black hole outside the Milky Way by looking at how it influences the motion of a star in its close vicinity. This is the first time this detection method has been used to reveal the presence of a black hole outside of our galaxy. The method could be key to unveiling hidden black holes in the Milky Way and nearby galaxies, and to help shed light on how these mysterious objects form and evolve. The newly found black hole was spotted lurking in NGC 1850, a cluster of thousands of stars roughly 160 000 light-years away in the Large Magellanic Cloud, a neighbour galaxy of the Milky Way. The object” tracked down by the team turned out to be roughly 11 times as massive as our Sun. The smoking gun that put the astronomers on the trail of this black hole was its gravitational influence on the five-solar-mass star orbiting it. Astronomers have previously spotted such small, “stellar-mass” black holes in other galaxies by picking up the X-ray glow emitted as they swallow matter, or from the gravitational waves generated as black holes collide with one another or with neutron stars. However, most stellar-mass black holes don’t give away their presence through X-rays or gravitational waves. The detection in NGC 1850 marks the first time a black hole has been found in a young cluster of stars (the cluster is only around 100 million years old, a blink of an eye on astronomical scales). Using their dynamical method in similar star clusters could unveil even more young black holes and shed new light on how they evolve. By comparing them with larger, more mature black holes in older clusters, astronomers would be able to understand how these objects grow by feeding on stars or merging with other black holes.

Furthermore, charting the demographics of black holes in star clusters improves our understanding of the origin of gravitational wave sources. To carry out their search, the team used data collected over two years with the Multi Unit Spectroscopic Explorer (MUSE) mounted at ESO’s VLT, located in the Chilean Atacama Desert. MUSE allowed the team to observe very crowded areas, like the innermost regions of stellar clusters, analysing the light of every single star in the vicinity. The net result is information about thousands of stars in one shot, at least 10 times more than with any other instrument. This allowed the team to spot the odd star out whose peculiar motion signalled the presence of the black hole. Data from the Optical Gravitational Lensing Experiment and from the NASA/ESA Hubble Space Telescope enabled them to measure the mass of the black hole and confirm their findings.


MOST DISTANT DETECTION OF FLUORINE
ESO

A new discovery is shedding light on how fluorine — an element found in our bones and teeth as fluoride — is forged in the Universe. Using the Atacama Large Millimeter/submillimeter Array (ALMA), a team of astronomers have detected this element in a galaxy that is so far away its light has taken over 12 billion years to reach us. This is the first time fluorine has been spotted in such a distant star-forming galaxy. The team spotted fluorine (in the form of hydrogen fluoride) in the large clouds of gas of the distant galaxy NGP–190387, which we see as it was when the Universe was only 1.4 billion years old, about 10% of its current age. Since stars expel the elements they form in their cores as they reach the end of their lives, this detection implies that the stars that created fluorine must have lived and died quickly. The team believes that Wolf–Rayet stars, very massive stars that live only a few million years, a blink of the eye in the Universe’s history, are the most likely production sites of fluorine. They are needed to explain the amounts of hydrogen fluoride the team spotted, they say. Wolf–Rayet stars had been suggested as possible sources of cosmic fluorine before, but astronomers did not know until now how important they were in producing this element in the early Universe. Besides these stars, other scenarios for how fluorine is produced and expelled have been put forward in the past. An example includes pulsations of giant, evolved stars with masses up to few times that of our Sun, called asymptotic giant branch stars. But the team believes these scenarios, some of which take billions of years to occur, might not fully explain the amount of fluorine in NGP–190387.

The discovery in NGP–190387 marks one of the first detections of fluorine beyond the Milky Way and its neighbouring galaxies. Astronomers have previously spotted this element in distant quasars, bright objects powered by supermassive black holes at the centre of some galaxies. But never before had this element been observed in a star-forming galaxy so early in the history of the Universe. The team’s detection of fluorine was a chance discovery made possible thanks to the use of space and ground-based observatories. NGP–190387, originally discovered with the European Space Agency’s Herschel Space Observatory and later observed with the Chile-based ALMA, is extraordinarily bright for its distance. The ALMA data confirmed that the exceptional luminosity of NGP–190387 was partly caused by another known massive galaxy, located between NGP–190387 and the Earth, very close to the line of sight. This massive galaxy amplified the light enabling astronomers to spot the faint radiation emitted billions of years ago by the fluorine in NGP–190387. Future studies of NGP–190387 with the Extremely Large Telescope (ELT) — ESO’s new flagship project, under construction in Chile and set to start operations later this decade — could reveal further secrets about this galaxy.


EXPANSION OF UNIVERSE IMPACTS BLACK HOLE GROWTH
University of Hawaii at Manoa

Over the past 6 years, gravitational wave observatories have been detecting black hole mergers, verifying a major prediction of Albert Einstein's theory of gravity. But there is a problem -- many of these black holes are unexpectedly large. Now, a team of researchers has proposed a novel solution to this problem: black holes grow along with the expansion of the Universe. Since the first observation of merging black holes by the Laser Interferometer Gravitational-Wave Observatory (LIGO) in 2015, astronomers have been repeatedly surprised by their large masses. Though they emit no light, black hole mergers are observed through their emission of gravitational waves -- ripples in the fabric of spacetime that were predicted by Einstein's theory of general relativity. Physicists originally expected that black holes would have masses less than about 40 times that of the Sun, because merging black holes arise from massive stars, which can't hold themselves together if they get too big. The LIGO and Virgo observatories, however, have found many black holes with masses greater than that of 50 suns, with some as massive as 100 suns. Numerous formation scenarios have been proposed to produce such large black holes, but no single scenario has been able to explain the diversity of black hole mergers observed so far, and there is no agreement on which combination of formation scenarios is physically viable. This new study is the first to show that both large and small black hole masses can result from a single pathway, wherein the black holes gain mass from the expansion of the Universe itself. Astronomers typically model black holes inside a Universe that cannot expand. Because the individual events detectable by LIGO -- Virgo only last a few seconds, when analyzing any single event, this simplification is sensible. But these same mergers are potentially billions of years in the making. During the time between the formation of a pair of black holes and their eventual merger, the universe grows profoundly. If the more subtle aspects of Einstein's theory are carefully considered, then a startling possibility emerges: the masses of black holes could grow in lockstep with the Universe, a phenomenon that the team call cosmological coupling.

The most well-known example of cosmologically-coupled material is light itself, which loses energy as the Universe grows. To investigate this hypothesis, the researchers simulated the birth, life, and death of millions of pairs of large stars. Any pairs where both stars died to form black holes were then linked to the size of the Universe, starting at the time of their death. As the universe continued to grow, the masses of these black holes grew as they spiralled toward each other. The result was not only more massive black holes when they merged, but also many more mergers. When the researchers compared the LIGO -- Virgo data to their predictions, they agreed reasonably well. According to the researchers, this new model is important because it doesn't require any changes to our current understanding of stellar formation, evolution, or death. The agreement between the new model and our current data comes from simply acknowledging that realistic black holes don't exist in a static universe. The researchers were careful to stress, however, that the mystery of LIGO -- Virgo's massive black holes is far from solved. Many aspects of merging black holes are not known in detail, such as the dominant formation environments and the intricate physical processes that persist throughout their lives. As gravitational-wave observatories continue to improve sensitivities over the next decade, the increased quantity and quality of data will enable new analysis techniques. This will be measured soon enough.'


STRANGE SHAPE AT CENTRE OF ANDROMEDA GALAXY
University of Colorado at Boulder

When two galaxies collide, the supermassive black holes at their cores release a devastating gravitational "kick," similar to the recoil from a shotgun. New research suggests that this kick may be so powerful it can knock millions of stars into wonky orbits. The research helps solve a decades-old mystery surrounding a strangely-shaped cluster of stars at the heart of the Andromeda Galaxy. It might also help researchers better understand the process of how galaxies grow by feeding on each other. In the 1970s, scientists launched balloons high into Earth's atmosphere to take a close look in ultraviolet light at Andromeda, the galaxy nearest to the Milky Way. The Hubble Space Telescope followed up on those initial observations in the 1990s and delivered a surprising finding: Like our own galaxy, Andromeda is shaped like a giant spiral. But the area rich in stars near that spiral's centre doesn't look like it should -- the orbits of these stars take on an odd, ovalish shape like a stretched out a wad of putty. In the new study, the team used computer simulations to track what happens when two supermassive black holes go crashing together -- Andromeda likely formed during a similar merger billions of years ago. Based on the team's calculations, the force generated by such a merger could bend and pull the orbits of stars near a galactic centre, creating that telltale elongated pattern. The team's findings help to reveal some of the forces that may be driving the diversity of the estimated two trillion galaxies in the Universe today -- some of which look a lot like the spiral-shaped Milky Way, while others look more like footballs or irregular blobs.

Mergers may play an important role in shaping these masses of stars: When galaxies collide, the black holes at the centres may begin to spin around each other, moving faster and faster until they eventually slam together. In the process, they release huge pulses of "gravitational waves," or literal ripples in the fabric of space and time. Those gravitational waves will carry momentum away from the remaining black hole, and you get a recoil, like the recoil of a gun. The team wanted to know what such a recoil could do to the stars within 1 parsec of a galaxy's centre. Andromeda, which can be seen with the naked eye from Earth, stretches tens of thousands of parsecs from end to end. The team used computers to build models of fake galactic centres containing hundreds of stars -- then kicked the central black hole to simulate the recoil from gravitational waves. The gravitational waves produced by this kind of disastrous collision won't affect the stars in a galaxy directly. But the recoil will throw the remaining supermassive black hole back through space -- at speeds that can reach millions of miles per hour, not bad for a body with a mass millions or billions of times greater than that of Earth's Sun. A supermassive black hole can start moving at thousands of kilometres per second and can actually escape the galaxy in which it resides. When black holes don't escape, however, the team discovered they may pull on the orbits of the stars right around them, causing those orbits to stretch out. The result winds up looking a lot like the shape scientists see at the centre of Andromeda.


DISTANT PROTO GALAXY SUPERCLUSTER
FOUND

University of Arizona

Astronomers have discovered a structure thought to be a 'protocluster' of galaxies on its way to developing into a galaxy supercluster. Observations show the protocluster, which is located 11 billion light-years from Earth, as it appeared when the Universe was 3 billion years old, when stars were produced at higher rates in certain regions of the cosmos. Initially discovered by the European Space Agency's Planck telescope as part of an all-sky survey, the protocluster described in the new paper showed up prominently in the far-infrared region of the electromagnetic spectrum. Sifting through a sample of more than 2,000 structures that could be in the process of becoming clusters, researchers came across a protocluster designated as PHz G237.01+42.50, or G237 for short. The observations looked promising, but to confirm its identity required follow-up observations with other telescopes. The team conducted observations using the Large Binocular Telescope in Arizona, and the Subaru Telescope in Japan. They identified 63 galaxies belonging to the G237 protocluster.

At first, observations of G237 implied a total star formation rate that was unrealistically high, and the team struggled to make sense of the data. The G237 protocluster seemed to be forming stars at a rate of 10,000 times that of the Milky Way. At that rate, the protocluster would be expected to rapidly use up its stellar fuel and subsequently settle down into a complex system similar to the Virgo supercluster. Such high yields could only be maintained by a continuous injection of fuel, which for stars is hydrogen gas. Later, the team discovered that some of what it was seeing came from galaxies unrelated to the protocluster, but even after the irrelevant observations were removed, the total star formation rate remained high, at least 1,000 solar masses per year. In comparison, the Milky Way produces about one solar mass each year. All galaxies in the Universe are part of a giant structure that resembles a three-dimensional spider web shape called the cosmic web.