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July 7, 2019 at 4:05 pm #9864Anonymous
THE SOCIETY FOR POPULAR ASTRONOMY Electronic News Bulletin No. 493 2019 July 7
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
MOULD ON SPACE STATION HARD TO KILL
It seems that fungus might be better suited for space travel than people are. New research has found that mould can survive incredibly high doses of ionizing radiation, which means that we may have to keep a very careful eye out for spores that might hitch a ride to Mars. Blasted with radiation in a controlled setting, the two mould genera Aspergillus and Pennicillium were
able to survive up to 200 times the fatal human dose of X-rays. That means that they could survive radiation conditions on the outside of a spacecraft. Humans are pretty moist creatures. Put us in an enclosed box, and sooner or later the moisture from our sweat and breath is going to be running down the walls. The International Space Station may be climate- and humidity-controlled, but it is still, indeed, an enclosed box — and there's enough damp that mould keeps growing on the walls. Aspergillus and Pennicillium are among the two most common space-station invaders. They can also cause some pretty nasty respiratory infections, when fungal filaments are breathed in and lodge themselves in the airways. Obviously, that's not ideal when you're orbiting 400 kilometres above Earth with limited medical supplies, not to even mention being en route to, say, Mars.
So these two mould genera seemed like pretty good candidates to blast with large amounts of ionizing radiation and see what would happen. The spores of the moulds were suspended in a saline solution, and scientists deployed three kinds of radiation: X-rays, heavy ions, and high-frequency ultraviolet radiation that is stopped by Earth's atmosphere, but propagates freely in
space. The moulds survived incredibly high doses — 500 gray of heavy ions and 1,000 gray of X-rays. The gray is a unit of ionizing radiation dose, defined as the absorption of one joule of radiation energy per kilogram of tissue. Half a gray, delivered in one blast, is enough to give a person radiation sickness, and five gray is fatal to a human being. The spores also survived 3,000 joules per metre squared of the ultraviolet radiation. So, given radiation alone, one ought to expect mould spores could survive a space trip, even to another planet. But the research team hasn't yet tested other space conditions, such as vacuum and extreme temperature,
although previous research conducted by researchers at DLR found that other organisms could survive those, housed in a special unit attached to the outside of the space station. Similar research would need to be done to see if this applies to common mould spores as well, and whether we need to worry about, for example, contaminating the Moon next time we visit. But mould in space wouldn't be all bad, the researchers note. Mould can be used to produce important things, compounds like antibiotics and vitamins.
UNUSUALLY HIGH METHANE LEVELS ON MARS
The Curiosity Mars rover has found a surprising result: the largest amount of methane ever measured during the mission — about 21 parts per billion units by volume (ppbv). The finding came from the rover's Sample Analysis at Mars (SAM) tunable laser spectrometer. It's exciting because microbial life is an important source of methane on Earth, but methane can also be
created through interactions between rocks and water. Curiosity doesn't have instruments that can definitively say what the source of the methane is, or even if it's coming from a local source within Gale Crater or elsewhere on the planet. The Curiosity team has detected methane many times over the course of the mission. Previous papers have documented how
background levels of the gas seem to rise and fall seasonally. They've also noted sudden spikes of methane, but the science team knows very little about how long these transient plumes last or why they're different from the seasonal patterns.
The SAM team organized a different experiment to gather more information on what might be a transient plume. Whatever they find — even if it's an absence of methane — will add context to the recent measurement. Curiosity's scientists need time to analyze these clues and conduct many more methane observations. They also need time to collaborate with other
science teams, including those with the European Space Agency's Trace Gas Orbiter, which has been in its science orbit for a little over a year without detecting any methane. Combining observations from the surface and from orbit could help scientists locate sources of the gas on the planet and understand how long it lasts in the Martian atmosphere. That might explain
why the Trace Gas Orbiter's and Curiosity's methane observations have been so different.
ASTRONOMERS SEE 'WARM' GLOW OF URANUS'S RINGS
University of California — Berkeley
Two telescopes have measured the faint heat from the main, or epsilon, ring, of Uranus, enabling astronomers for the first time to determine its temperature: a cool 77 Kelvin. Earlier images of the rings came from reflected light only. The observations also show that the rings lack dust, which is common in the rings of other planets, and are composed of centimetre-sized particles and larger. The rings of Uranus are invisible to all but the largest telescopes — they weren't even discovered until 1977 — but they're surprisingly bright in new heat images of the planet taken by two large telescopes in the high deserts of Chile. The thermal glow gives
astronomers another window onto the rings, which have been seen only because they reflect a little light in the visible, or optical, range and in the near-infrared. The new images taken by the Atacama Large Millimeter/ submillimeter Array (ALMA) and the Very Large Telescope (VLT) allowed the team for the first time to measure the temperature of the rings: a cool 77 Kelvin, or 77 degrees above absolute zero — the boiling temperature of liquid nitrogen and equivalent to 320 degrees below zero Fahrenheit. The observations also confirm that Uranus's brightest and densest ring, called the epsilon ring, differs from the other known ring systems within our solar system, in particular the spectacularly beautiful rings of Saturn. Saturn's mainly icy rings are broad, bright and have a range of particle sizes, from micron-sized dust in the innermost D ring, to tens of metres in size in the main rings. The small end is missing in the main rings of Uranus; the brightest ring, epsilon, is composed of golf-ball-sized and larger rocks. By comparison, Jupiter's rings contain mostly small, micron-sized particles (a micron is a thousandth of a millimetre). Neptune's rings are also mostly dust, and even Uranus has broad sheets of dust between its narrow main rings.
Rings could be former asteroids captured by the planet's gravity, remnants of moons that crashed into one another and shattered, the remains of moons torn apart when they got too close to Uranus, or debris remaining from the time of formation 4.5 billion years ago. The lack of dust-sized particles in Uranus's main rings was first noted when Voyager 2 flew by the planet in 1986 and photographed them. The spacecraft was unable to measure the temperature of the rings, however. To date, astronomers have counted a total of 13 rings around the planet, with some bands of dust between the rings. The rings differ in other ways from those of Saturn.
EARTH-LIKE PLANETS FOUND NEAR TEEGARDEN'S STAR
University of Gottingen
Astronomers have discovered two new Earth-like planets near one of our closest neighbouring stars. “Teegarden's star” is only about 12.5 light years away from Earth and is one of the smallest known stars. It is only about 2,700 C warm and about ten times lighter than the Sun. Although it is so close to us, the star wasn't discovered until 2003. The scientists observed the star for about three years. Their data clearly show the existence of two planets that resemble the inner planets of our solar system. They are only slightly more massive than the Earth and are located in the so-called habitable zone, where water can be present in liquid form. The astronomers suspect that the two planets could be part of a larger system. Although planetary systems around similar stars are known, they have always been detected using the 'transit method' — the planets have to pass visibly in front of the star and darken it for a moment, which only happens in a very small fraction of all planetary systems. Such transits have not yet been found for the new planets. But the system is located at a special place in the sky: from Teegarden's star you can see the planets of the solar system passing in front of the Sun.
ASTRONOMY BOT SEARCHES FOR JUPITER'S TWINS
University of California – Riverside
Astronomers have a new tool in their search for extraterrestrial life — a sophisticated bot that helps identify stars hosting planets similar to Jupiter and Saturn. These giant planets' faraway twins may protect life in other solar systems, but they aren't bright enough to be viewed directly.
Scientists find them based on properties they can observe in the stars they orbit. The challenge for planet hunters is that in our galaxy alone, there are roughly 200 billion stars. The astronomy bot is a machine-learning algorithm designed by the Southwest Research Institute. Using data produced by the bot, scientists have discovered three stars that have strong evidence of harbouring giant, Jupiter-like planets about 100 light years away. The algorithm uses information about the chemical composition of stars to predict whether it is surrounded by planets. Scientists can use spectroscopy to measure the elements inside it such as carbon, iron, and oxygen. Those elements are key ingredients in making planets, since stars
and planets are made at the same time and from the same materials.
To train and test the algorithm, scientists fed it a publicly available database of stars that had been developed. The database has allowed the algorithm to look at the elements that make up more than 4,200 stars and assess their likelihood of hosting planets. In addition, they looked at
different combinations of those ingredients to see how they influenced the algorithm. The team used the algorithm specifically to help them identify giant planets like Jupiter that are hard to find because they are farther from their host stars. Distant giant planets are likely to protect the Earth-like rocky planets near them, and any life they could be home to. Jupiter-like planets pull meteors, comets and other flying space objects out of their trajectories before they can smash into their smaller planet neighbours.
OUTERMOST EDGE OF MILKY WAY
A team of researchers has identified the outermost edge of the Milky Way galaxy. The ultimate size of the galaxy is 520,000 light years in radius, 20 times larger than the distance between the galactic centre and our solar system (26,000 light years). Stars that reach the outermost regions of the Galaxy during their orbital motions are ancient stellar populations with ages as old as 12 billion years. The spatial extent in which these ancient stars wander is, therefore, important for understanding the Milky Way's formation. The Galaxy holds a broadly extended halo component, in addition to the bright Milky Way in the form of the stellar disc component. The halo contains about 1 billion ancient stars and 150 globular clusters with ages as old as 12 billion years. The halo thus contains the remnants of long-lived stars and star clusters that formed in the first stage of the Galaxy. That suggests that the Galaxy was quite large in its beginning before the later formation of the younger, disc component. Investigating the extent of
the halo component in the Galaxy is similar to identifying the outer boundary of a forest from inside the forest and observing the trees. In other words, it is an arduous task. So-called blue horizontal branch (BHB) stars as well as RR Lyr variables are ideal indicators for tracing the halo component. That is because they are naturally bright enough to determine the distance to and from them. However, the Galaxy is so large that it is impossible to identify the halo traces located at the outer boundary using 2.5- to 4-metre telescopes. The team of researchers used the Hyper Suprime-Cam (HSC) digital camera on the 8.2 metre-diameter Subaru Telescope.
It enabled them to capture remote, very faint halo tracers at the outer edge of the Galaxy. The team carefully selected the BHB stars from the on-going survey program (SSP: Subaru Strategic Program) data against other contaminants having similar colours such as blue-straggler stars, white dwarfs, quasars and distant galaxies. Using the data from HSC-SSP, the team derived the spatial density of the BHB stars over the Galaxy halo. While that density generally decreases the further you go from the galactic centre, the team discovered a sharp drop in density at around 520,000 light years away from the galactic centre. Thus, the team had finally observed the outermost edge of the galaxy. That is about 20 times larger than the
distance between our Solar System and the Galaxy centre. Twelve billion years ago, successive merging of small galaxies confined by dark matter halos occurred. Key to understanding that is measuring the distribution of the halo component to ascertain the volume. The merging process differs from galaxy to galaxy. Our neighbour, the Andromeda galaxy, is reported to have an extended halo component as large as 538,000 (at the very least) light-years in radius. It is, therefore, systematically larger when compared to the galaxy halo. The researchers are planning to map out further that ancient component of the galaxy after the final completion of the HSC-SSP.
ASTRONOMERS CAPTURE FLEETING RADIO BURST
Association of Universities for Research in Astronomy (AURA)
Australian astronomers using the Gemini South telescope in Chile have successfully confirmed the distance to a galaxy hosting an intense radio burst that flashed only once and lasted but a thousandth of a second. The team made the initial discovery of the fast radio burst (FRB) using the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope. The
critical Gemini observations were key to verifying that the burst left its host galaxy some 4 billion years ago. Since the first FRB discovery in 2007, these mysterious objects have played a game of cosmic cat-and-mouse with astronomers — with astronomers as the sharp-eyed cats! Fleeting radio outbursts, lasting about a millisecond, are difficult to detect, and even
more difficult to locate precisely. In this case, the FRB, known as FRB 180924, was a single burst, unlike others that can flash multiple times over an extended period. The momentary pulse was first observed in September 2018 during a dedicated search for FRBs using ASKAP — a 36-antenna array of radio telescopes working together as a single instrument in Western Australia — which also pinpointed the signal's location in the sky. The researchers used the miniscule differences in the amount of time it takes for the light to reach different antennae in the array to zoom in on the host galaxy's location. From those tiny time differences — just a fraction of a billionth of a second — they identified the burst's home galaxy. Once it was pinpointed, the team enlisted the Gemini South telescope, along with the W.M. Keck Observatory and European Southern Observatory's Very Large Telescope (VLT) to determine the FRB's distance and other characteristics by carefully observing the galaxy that hosted the outburst. The Gemini South data absolutely confirmed that the light left the galaxy about 4 billion years ago.
Localizing FRBs is critical to understanding what causes the flashes, which is still uncertain: to explain the high energies and short time-scales, most theories invoke the presence of a massive yet very compact object such as a black hole or a highly magnetic neutron star. Finding where the bursts occur would tell us whether it is the formation, evolution, or collision and destruction of these objects that is generating the radio bursts. Much like gamma-ray bursts two decades ago, or the more recent detection of gravitational wave events, astronomers stand on the cusp of an exciting new era where we are about to learn where fast radio bursts take place. The goal is to use FRBs as cosmological probes, in much the same way that we use gamma ray bursts, quasars, and supernovae. Such a map could pinpoint the
location of the 'missing baryons' (baryons are the subatomic building blocks of matter), which standard models predict must be out there, but which don't show up using other probes. By pinpointing the bursts and how far their light has travelled, astronomers can also obtain 'core samples' of the intervening material between us and the flashes. With a large sample of FRB
host galaxies, astronomers could conduct 'cosmic tomography', to build the first 3D map of where baryons are located between galaxies. To date, only one other fast radio burst (FRB 121102) has been localized, and it had a repeating signal that flashed more than 150 times. While both single and multiple flash FRBs are relatively rare, single FRBs are more common than repeating ones. The discovery of FRB 180924, then, could lead the way for future methods of localization.
QUANTUM GRAVITY HAS NO SYMMETRY
Kavli Institute for the Physics and Mathematics of the Universe
A new study by researchers in the US and Japan has found that, when gravity is combined with quantum mechanics, symmetry is not possible. Many physicists believe that there must a beautiful set of laws in Nature and that one way to quantify the beauty is by symmetry. Some of the symmetries may be hidden in our world, but they should manifest themselves if we look at Nature at a more fundamental level. The team showed that this expectation is wrong once we take into account the gravity. There are four kinds of fundamental forces in Nature: electromagnetism, strong force, weak force, and gravity. Of the four, gravity is the only one still unexplainable at the quantum level. Researchers believe the holographic principle is an
important hint to combine the gravity and quantum mechanics successfully. A hologram makes three-dimensional images pop out from a two-dimensional screen. Similarly, the holographic principle allows physicists to study gravitational systems by projecting them on a boundary that surrounds the entire Universe. The AdS/CFT (anti-de Sitter/conformal field theory)
correspondence, developed in the late 1990s by Juan Maldacena, has been particularly useful because it gives a precise mathematical definition of the holographic principle. This research has proved that symmetry is not possible in a gravitational theory if it obeys the holographic principle. Previous work had found a precise mathematical analogy between the holographic principle and quantum error correcting codes, which protects information in a quantum computer. Now scientists have shown such quantum error correcting codes are not compatible with any symmetry, meaning that symmetry would not be possible in quantum gravity. Their result has several important consequences. In particular, it predicts that the protons are stable against decaying into other elementary particles, and that magnetic
Bulletin compiled by Clive Down
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