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March 8, 2020 at 10:22 am #10024Anonymous
THE SOCIETY FOR POPULAR ASTRONOMY Electronic News Bulletin No. 510 2020 March 8
Here is the latest round-up of news from the Society for Popular Astronomy. The SPA is arguably Britain's liveliest astronomical society, with members all over the world. We accept subscription payments online at our secure site and can take credit and debit cards. You can join or renew via a
secure server or just see how much we have to offer by visiting http://www.popastro.com
PROTO-EARTH FORMED VERY QUICKLY
University of Copenhagen
The precursor of our planet, the proto-Earth, formed within a time span of approximately five million years, according to a new study from the Centre for Star and Planet Formation (StarPlan) at the Globe Institute at the University of Copenhagen. On the astronomical scale, this is extremely fast, the researchers explain. If you compare the solar system's estimated 4.6 billion years of existence with a 24-hour period, the new results indicate that the proto-Earth formed in what corresponds to about a minute and a half. Thus, the results from StarPlan break with the traditional theory that the proto-Earth formed by random collisions between larger and larger planetary bodies throughout several tens of millions of years — equivalent to about 5-15 minutes out of the above-mentioned fictional 24 hours of formation. Instead, the new results support a more recent, alternative theory about the formation of planets through the accretion of cosmic dust. The key to the new finding came in the form of the most
precise measurements of iron isotopes that have so far been published scientifically. By studying the isotopic mixture of the metallic element in different meteorites, the researchers found only one type of meteoritic material with a composition similar to Earth: the so-called CI chondrites. The researchers behind the study describe the dust in that fragile type of meteorite as our best equivalent to the bulk composition of the solar system itself. It was dust like that combined with gas that was funnelled via a
circumstellar accretion disc onto the growing Sun. This process lasted about five million years and our planets were made from material in that disc. Now, the researchers estimate that the proto- Earth's ferrous core also formed already during that period, removing early accreted iron from the mantle.
Other meteorites, for example from Mars, tell us that at the beginning the iron isotopic composition of material contributing to the growing Earth was different — most likely due to thermal processing of dust close to the young Sun, the researchers from StarPlan explain. After our solar system's first few hundred thousands of years it became cold enough for unprocessed CI dust from further out in the system to enter the accretion region of the proto-Earth. That added CI dust overprinted the iron composition in the Earth's mantle, which is only possible if most of the previous iron was already removed into the core. That is why the core formation must have happened early. If the Earth's formation was a random process where you just smashed bodies together, you would never be able to compare the iron composition of the Earth to only one type of meteorite — you would get a mixture of everything. On the basis that the evidence for the theory that planets form through the accretion of cosmic dust, the researchers believe that the same process may occur elsewhere in the Universe. That means that also other planets may form much faster than if they grow solely from random
collisions between objects in space. That assumption is corroborated by the thousands of exoplanets — planets in other galaxies — that astronomers have discovered since the mid- nineties. Now we know that planet formation happens everywhere. That we have generic mechanisms that work and make
planetary systems. When we understand these mechanisms in our own solar system, we might make similar inferences about other planetary systems in the galaxy. Including at which point and how often water is accreted. If the theory of early planetary accretion really is correct, water is probably just a by-product of the formation of a planet like the Earth — making the ingredients of life, as we know it, more likely to be found elsewhere in the Universe.
POSSIBLE NEW MINI MOON ORBITING EARTH
Astronomers from the Catalina Sky Survey say they have detected a rare mini-moon around Earth. Sadly, we shouldn't get too attached to our new natural satellite, as the rock — if that is indeed what it is — will only hang around for a few months. The mini-moon, dubbed 2020 CD3 and also known as
C26FED2, was seen by astronomers from the Catalina Sky Survey at the University of Arizona on 2020 February 15. Further observations are required to confirm the object as a mini-moon, or a Temporary Captured Orbiter (TCO).
MARTIAN MAGNETIC FIELD MUCH STRONGER THAN EXPECTED
University of British Columbia
New data gleaned from the magnetic sensor aboard NASA's InSight spacecraft are offering an unprecedented close-up of magnetic fields on Mars. Scientists reveal that the magnetic field at the InSight landing site is ten times stronger than anticipated, and fluctuates over time-scales of seconds
to days. Before the InSight mission, the best estimates of Martian magnetic fields came from satellites orbiting high above the planet, and were averaged over distances of more than 150 kilometres. Scientists have known that Mars had an ancient global magnetic field billions of years ago that
magnetized rocks on the planet, before mysteriously switching off. Because most rocks at the surface are too young to have been magnetized by this ancient field, the team thinks it must be coming from deeper underground from much older rocks that are buried up to ten kilometres below ground. The team hopes that by combining these InSight results with satellite magnetic data and future studies of Martian rocks, they can identify exactly which rocks carry the magnetization and how old they are. The magnetic sensor has also provided new clues about phenomena that occur high in the upper atmosphere and the space environment around Mars. Just like Earth, Mars is exposed to solar wind, which is a stream of charged particles from the Sun that carries an interplanetary magnetic field (IMF) with it, and can cause disturbances like solar storms. But because Mars lacks a global magnetic field, it is less protected from solar weather. The sensor captured fluctuations in the magnetic field between day and night and short, mysterious pulsations around midnight, confirming that events in and above
the upper atmosphere can be detected at the surface. The team believes that the day–night fluctuations arise from a combination of how the solar wind and IMF drape around the planet, and solar radiation charging the upper atmosphere and producing electrical currents, which in turn generate
WATER IN JUPITER'S ATMOSPHERE
The Juno mission has provided its first science results on the amount of water in Jupiter's atmosphere. The results estimate that at the equator, water makes up about 0.25% of the molecules in Jupiter's atmosphere — almost three times that of the Sun. These are also the first findings on the gas giant's abundance of water since the agency's 1995 Galileo mission suggested Jupiter might be extremely dry compared to the Sun (the comparison is based not on liquid water but on the presence of its components, oxygen and hydrogen, present in the Sun). An accurate estimate of the total amount
of water in Jupiter's atmosphere has been on the wish lists of planetary scientists for decades. The figure in the gas giant represents a critical missing piece to the puzzle of our solar system's formation. Jupiter was probably the first planet to form, and it contains most of the gas and dust that wasn't incorporated into the Sun. The leading theories about its formation rest on the amount of water the planet soaked up. Water abundance also has important implications for the gas giant's meteorology (how wind currents flow on Jupiter) and internal structure. While lightning — a phenomenon typically fuelled by moisture — detected on Jupiter by Voyager and other spacecraft implied the presence of water, an accurate estimate of the amount of water deep within Jupiter's atmosphere remained elusive.
Before the Galileo probe stopped transmitting 57 minutes into its Jovian descent in December 1995, it radioed out spectrometer measurements of the amount of water in the gas giant's atmosphere down to a depth of about 120 kilometres, where the atmospheric pressure reached about 22 bar. The scientists working on the data were dismayed to find ten times less water than expected. Even more surprising: the amount of water the Galileo probe measured appeared to be still increasing at the greatest depth measured, far below where theories suggest the atmosphere should be well mixed. In a well-mixed atmosphere, the water content is constant across the region and more likely to represent a global average; in other words, it's more likely to be representative of water planet-wide. When combined with an infrared map obtained at the same time by a ground-based telescope, the results suggested the probe mission may have just been unlucky, sampling an unusually dry and warm meteorological spot on Jupiter. A rotating, solar-powered spacecraft, Juno launched in 2011. Because of the Galileo probe experience, the mission seeks to obtain water abundance readings across large regions of the immense planet. A new kind of instrument for deep space planetary exploration, Juno's Microwave Radiometer (MWR) observes Jupiter from above using six antennae that measure atmospheric temperature at multiple depths simultaneously. The Microwave Radiometer takes advantage of the fact that water absorbs certain wavelengths of microwave radiation, the same trick used by microwave ovens to heat food quickly. Measured temperatures are used to constrain the amount of water and ammonia in the deep atmosphere, as both molecules absorb microwave radiation.
SUB-NEPTUNE-SIZED PLANET VALIDATED
A signal originally detected by the Kepler spacecraft has been validated as an exoplanet using the Habitable-zone Planet Finder (HPF), an astronomical spectrograph recently installed on the 10m Hobby-Eberly Telescope at McDonald Observatory in Texas. The HPF provides the highest-precision
measurements to date of infrared signals from nearby low-mass stars, and astronomers used it to validate the candidate planet by excluding all possibilities of contaminating signals to a very high level of probability. The planet, called G 9-40b, is about twice the size of the Earth, but likely closer in size to Neptune, and orbits its low-mass host star, an M dwarf star, only 100 light years from Earth. Kepler detected the planet by observing a dip in the host star's light as the planet crossed in front of
— or transited — the star during its orbit, a trip completed every six Earth days. This signalas then validated using precise observations from the HPF, ruling out the possibility of a close stellar or substellar binary companion. Observations from other telescopes, including the 3.5m telescope
at Apache Point Observatory and the 3m Shane Telescope at Lick Observatory, helped to confirm the identification. G 9-40b is amongst the top twenty closest transiting planets known. Further, owing to its large transit depth, G 9-40b is an excellent candidate exoplanet to study its atmospheric composition with future space telescopes. The spectroscopic observations from HPF allowed astronomers to place an upper bound of 12 Earth masses on the mass of the planet. That demonstrates that a planet is causing the dips in light from the host star, rather than another astrophysical object such as a background star. Astronomers hope to obtain more observations with HPF to precisely measure its mass, which will allow them to constrain its bulk composition and differentiate between a predominantly rocky or gas-rich composition.
BETELGEUSE BEGINS TO BRIGHTEN
Call off the supernova watch! Betelgeuse is brightening again. Researchers from Villanova University, who have been leading the study of Betelegeuse's decline, have confirmed that the star has reversed itself. The turnaround was actually predicted, and suggests that the recent dimming was an unusually
deep excursion of the star's natural 430-day periodicity. According to the light curve, Betelgeuse hit bottom during the week of Feb. 7 to 13 with a V magnitude slightly greater than +1.6.
STUDENT DISCOVERS 17 NEW PLANETS
University of British Columbia
Astronomy student Michelle Kunimoto has discovered 17 new planets, including a potentially habitable, Earth-sized world, by combing through data gathered by NASA's Kepler mission. Over its original four-year mission, the Kepler satellite looked for planets, especially those that lie in the “Habitable Zones” of their stars, where liquid water could exist on a rocky planet's surface. The new findings include one such particularly rare planet. Officially named KIC-7340288 b, the planet discovered by Kunimoto is just 1.5 times the size of Earth — small enough to be considered rocky, instead of gaseous like the giant planets of the Solar System — and in the habitable zone of its star. This planet is about a thousand light years away and has a year that is 142 days long,orbiting its star at a distance of 0.444 Astronomical Units – just bigger than Mercury's orbit in our Solar System, and gets about a third of the light Earth gets from the Sun. Of the other 16 new planets discovered, the smallest is only two-thirds the size of Earth — one of the smallest planets to be found with Kepler so far. The rest range in size up to eight times the size of Earth. Kunimoto is no stranger to discovering planets: she previously discovered four during her
undergraduate degree. Now working on her PhD, she used what is known as the “transit method” to look for the planets among the roughly 200,000 stars observed by the Kepler mission. Every time a planet passes in front of a star, it blocks a portion of that star's light and causes a temporary decrease in the star's brightness. By finding these dips, known as transits, you can start to piece together information about the planet, such as its size and how long it takes to orbit.
STRANGE GAS MOVEMENTS NEAR MILKY WAY CENTRE
Astronomers have detected unusual movements of gas clouds near the centre of our galaxy, and they could be pointing the way to the most elusive species of black hole, according to a new study. For the longest time, we weren't even sure if these types of black holes existed. Researchers tracking the
gasses in the middle of the Milky Way have concluded the clouds are orbiting an object 10,000 times the mass of the Sun – and yet, when they look at where that object should be, nothing is there. The most obvious explanation is a quiescent black hole, one that isn't actively feeding, and therefore is
emitting no detectable radiation. It is, the researchers say, the fifth such candidate in the galactic centre, mounting evidence that not only do intermediate mass black holes exist, but that they're abundant in the heart of the Milky Way. Intermediate mass black holes are exactly what they sound
like. We know stellar mass black holes, up to 100 times the mass of the Sun, exist. The biggest black hole we've detected in this mass range is 62 solar masses, created by the merger of two black holes in the gravitational wave event GW150914. We also know supermassive black holes exist, like those
that power galaxies. They start at around 100,000 solar masses, but they can get almost incomprehensibly massive, by means we have yet to discover. The class that sits in between them — between 1,000 and 100,000 solar masses — is called intermediate mass black holes. They have remained extraordinarily elusive. This raises questions such as “do they exist?” and “if they don't
exist, why?” and “if they do exist, why can't we find them?”
Because black holes don't emit any detectable radiation of their own, scientists have to get creative in their search. Instead of looking for the black holes, they look for the effects black holes would have on other objects in nearby space. Astrophysicists of the National Astronomical Observatory of Japan have been studying the motion of the high-velocity clouds of gas in the centre of the Milky Way to help answer these questions. Previously, they used the gas-tracking method to identify an intermediate
-mass lack hole candidate clocking in at around 32,000 solar masses, which would produce an event horizon – the spherical region of space around a black hole past which light cannot escape – roughly the size of Jupiter. Now, they've applied it to a high-velocity gas cloud called HCN-0.085-0.094. It mainly consists of three smaller clumps; one of those clumps seems to be swirling around – but not being accreted by – a black hole. One of the three clumps has a ring-like structure with a very steep velocity gradient. This kinematical structure suggests an orbit around a point-like object with a mass of 104 solar masses. The absence of stellar counterparts indicates that the point-like object may be a quiescent black hole. For a handy comparison, at that mass range, the black hole's event horizon would be a little bigger than Uranus or Neptune. Oddly behaving clumps of gas and dust aren't the only way to find intermediate mass black holes. Amongst other candidate observations is a star caught moving at
incredible speed from the centre of the Milky Way, on a trajectory into intergalactic space. Analysis has shown that an intermediate mass black hole is the most likely thing to have given that star the punt it needed to achieve such velocity. There was also a tremendous flare of multi-wavelength radiation that started in 2003, and gradually died down over the course of a decade. The distribution of the photons suggested that it was an intermediate mass black hole, a few tens of thousands of solar masses.
Newly released analysis of follow-up observations supports this, making it one of the best candidates yet, but it's 740 million light-years away. The galactic centre is a lot closer, which means if we find any intermediate mass black holes there, they may be easier to study. That could help us figure out such questions as – how do they form? And how do supermassive black holes form? A census could help us to understand how common or rare intermediate mass black holes are, and how they are distributed across galaxies. So far, the results of the research indicate that looking at swirling gas at the heart of the Milky Way is a reliable method to search for intermediate mass black hole candidates; but we are yet to confirm one of them for sure.
GALAXY'S HALO SUGGESTS TURBULENT PAST
NASA/Goddard Space Flight Center
Surprising new data from NASA's Hubble Space Telescope suggests the smooth, settled “brim” of the Sombrero galaxy's disk may be concealing a turbulent past. Hubble resolves tens of thousands of individual stars in the Sombrero's vast, extended halo, the region beyond a galaxy's central portion, typically made of older stars. These latest observations of the Sombrero are turning conventional theory on its head, showing only a tiny fraction of older, metal-poor stars in the halo, plus an unexpected abundance of metal-rich stars typically found only in a galaxy's disk, and the central bulge. Past major galaxy mergers are a possible explanation, though the stately Sombrero shows none of the messy evidence of a recent merger of massive galaxies. Long a favourite of astronomers and amateur sky watchers alike for its bright beauty and curious structure, the Sombrero galaxy (M104) now has a new chapter in its strange story — an extended halo of metal-rich stars with barely a sign of the expected metal-poor stars that have been observed in the halos of other galaxies. Researchers, puzzling over the data from Hubble, turned to sophisticated computer models to suggest explanations for the perplexing inversion of conventional galactic theory. Those results suggest the equally surprising possibility of major mergers in the galaxy's past, though the Sombrero's structure bears no
evidence of recent disruption.
In a galaxy's halo astronomers expect to find earlier generations of stars with less heavy elements, called metals, as compared to the crowded stellar cities in the main disk of a galaxy. Elements are created through the stellar “lifecycle” process, and the longer a galaxy has had stars going through this cycle, the more element- rich the gas and the higher- metallicity the stars that form from that gas. These younger, high-metallicity stars are typically found in the main disk of the galaxy where the stellar population is denser — or so goes the conventional wisdom. Complicating the facts is the presence of many old, metal-poor globular clusters of stars. These older, metal-poor stars are expected eventually to move out of their clusters and become part of the general stellar halo, but that process seems to have been inefficient in the Sombrero galaxy. The team compared their results with recent computer simulations to see what could be the origin of such unexpected metallicity measurements in the galaxy's halo. The results also defied expectations, indicating that the unperturbed Sombrero had undergone major accretion, or merger, events billions of years ago. Unlike our Milky Way galaxy, which is thought to have swallowed up many small satellite galaxies in so-called “minor” accretions over billions of years, a major accretion is the merger of two or more similarly massive galaxies that are rich in later-generation, higher-metallicity stars.
The satellite galaxies only contained low-metallicity stars that were largely hydrogen and helium from the big bang. Heavier elements had to be cooked up in stellar interiors through nucleosynthesis and incorporated into later-generation stars. This process was rather ineffective in dwarf galaxies such as those around our Milky Way, and more effective in larger, more evolved galaxies. The results for the Sombrero are surprising because its smooth disk shows no signs of disruption. By comparison, numerous interacting galaxies, like the iconic Antennae galaxies, get their name from the distorted appearance of their spiral arms due to the tidal forces of their interaction. Mergers of similarly massive galaxies typically coalesce into large, smooth elliptical galaxies with extended halos — a process that
takes billions of years. But the Sombrero has never quite fitted the traditional definition of either a spiral or an elliptical galaxy. It is somewhere in between — a hybrid. For this particular project, the team
chose the Sombrero mainly for its unique morphology. They wanted to find out how such “hybrid” galaxies might have formed and assembled over time. Follow-up studies for halo metallicity distributions will be done with several galaxies at distances similar to that of the Sombrero.
BIGGEST EXPLOSION SINCE BIG BANG
International Centre for Radio Astronomy Research
Scientists studying a distant galaxy cluster have discovered the biggest explosion seen in the Universe since the Big Bang. The blast came from a supermassive black hole at the centre of a galaxy hundreds of millions of light-years away and released five times more energy than the previous record holder. The explosion occurred in the Ophiuchus galaxy cluster, about 390 million light-years from Earth. It was so powerful it punched a cavity in the cluster plasma — the super-hot gas surrounding the black hole. Fifteen galaxies as large as the Milky Way could fit into the crater this eruption punched into the cluster's hot gas. The cavity in the cluster plasma had been seen previously with X-ray telescopes but scientists initially dismissed the idea that it could have been caused by an energetic outburst, because it would have been too big. The researchers only realised what they had discovered when they looked at the Ophiuchus galaxy cluster with radio telescopes. The radio data fit inside the X-rays like a hand in
a glove. The discovery was made using four telescopes; NASA's Chandra X-ray Observatory, ESA's XMM-Newton, the Murchison Widefield Array (MWA) in Western Australia and the Giant Metrewave Radio Telescope (GMRT) in India.
Bulletin compiled by Clive Down
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