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January 5, 2020 at 8:32 pm #9987Anonymous
THE SOCIETY FOR POPULAR ASTRONOMY Electronic News Bulletin No. 506 2020 January 5
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/
“ONCE IN A LIFETIME” STRATOSPHERIC CLOUDS
A spectacular outbreak of polar stratospheric clouds (PSCs) is under way around the Arctic Circle. Polar stratospheric clouds are newsworthy because normally the stratosphere has no clouds at all. Home to the ozone layer, the stratosphere is arid and almost always transparent. Only when the temperature drops to a staggeringly cold -85C can sparse water molecules
assemble themselves into icy stratospheric clouds. PSCs are far more rare than aurorae. At one point villagers reported that close to 25% of the sky was filled with the clouds. PSCs in previous winters have been closer to 1% or 2%. PSCs are intensely colourful because they are made of a special type of ice. High-altitude sunlight shining through microscopic crystals only ~10 microns across produce a bright iridescent glow unlike the lesser iridescence of ordinary tropospheric clouds.
PLANET AND STAR GIVEN MANX NAMES
A star and planet will be given Manx Gaelic names for the first time after being chosen in an international competition. The star WASP-13 will be known as Gloas (which means 'to shine') and the planet WASP-13b as Cruinlagh ('to orbit'). A class of Manx eight and nine-year-olds came up with the names for a competition run by the International Astronomical Union (IAU).
The names were chosen due to their “sense of mystery” after taking 20% of 15,000 votes cast by members of the public. The naming competition was held by the IAU as part of a larger worldwide event to celebrate its 100th anniversary. More than 110 countries were given an opportunity to name a star and an exoplanet (a planet outside of the solar system), with each
winning entry being rec gnised internationally. WASP-13, a star within the Lynx constellation that was first observed in 1997, is 1.5 times bigger than the Sun and is visible with the naked eye from the British Isles. WASP-13b, which was discovered in 2009, orbits the star every four days and is bigger than Jupiter.
BETELGEUSE NOTICEABLY DIMMER
The red supergiant star Betelgeuse, in the shoulder of the constellation Orion, is one of the easiest-to-recognize stars in the night sky. It is also one of the biggest stars we know, with a radius extending out to the distance of Mars from our Sun, and possibly Jupiter. This star is also famous for the fact that it will someday explode and appear in our sky as a supernova, becoming visible in daytime. In recent weeks astronomers have become excited about the fact that this bright star has become noticeably dimmer and is now well below magnitude 1. Could it be a sign that Betelgeuse is about to explode as a supernova? Astronomers say probably
not. Betelgeuse is normally one of 2 very bright stars in the constellation Orion; the other one is Rigel.
DISTANT MILKY-WAY-LIKE GALAXIES
National Radio Astronomy Observatory
To learn about the star-formation history of the Universe, we need to look back in time. Galaxies throughout the Universe have been forming stars for the past 13 billion years. But most stars were born between 8 and 11 billion years ago, during an era called “cosmic noon”. It has been a challenge for astronomers to study the faint light coming from that era. Optical telescopes can see very distant galaxies, but new stars are largely hidden inside dusty clouds of gas. Radio telescopes can see through the dust and observe the rare, bright starburst galaxies, but until now have not been sensitive enough to detect the signals from distant Milky Way-like galaxies that are responsible for most of the star formation in the Universe. An international team of astronomers using the South African Radio Astronomy Observatory (SARAO) MeerKAT telescope recently made the first radio observation sensitive enough to reveal such galaxies. To make the image, they selected an area in the southern sky that contains no strong radio sources whose glare could blind a sensitive observation. The team used the 64 MeerKAT dishes to observe the area for a total of 130 hours. The resulting image shows a region of the sky that is comparable in area to five full Moons, containing tens of thousands of galaxies.
Because radio waves travel at the speed of light, the image is a time machine that samples star formation in those distant galaxies over billions of years. Only short-lived stars that are less than 30 million years old send out radio waves, so astronomers know that the image is not contaminated by old stars. The radio light we see from each galaxy is therefore proportional to its star-forming rate at that moment in time. The astronomers want to use the image to learn more about star formation in the entire Universe. These first results indicate that the star-formation rate around cosmic noon is even higher than was originally expected. Previous
images could only detect the tip of the iceberg, the rare and luminous galaxies that produced only a small fraction of the stars in the Universe. What can be seen now is the complete picture: these faint dots are the galaxies that formed most of the stars in the Universe.
BLACK HOLES AT THE COSMIC DAWN
Astronomers using the Very Large Telescope have observed reservoirs of cool gas around some of the earliest galaxies in the Universe. Those gas haloes are the perfect food for supermassive black holes at the centres of those galaxies, which are now seen as they were over 12.5 billion years ago. This food storage might explain how these cosmic monsters grew so fast during a period in the Universe's history known as the Cosmic Dawn. Astronomers have wondered how supermassive black holes were able to grow so large so early on in the history of the Universe. The presence of these early monsters, with masses several billion times the mass of our Sun, is a big mystery for astronomers. It means that the first black holes, which might have formed from the collapse of the first stars, must have grown very fast. But, until now, astronomers had not observed black hole food — gas and dust — in large enough quantities to explain this rapid growth. To complicate matters further, previous observations with ALMA, the Atacama Large Millimeter/submillimeter Array, revealed a lot of dust and gas in these early galaxies that fuelled rapid star formation. Those ALMA observations suggested that there could be little left over to feed a black
To solve this mystery, astronomers used the MUSE instrument on the Very Large Telescope (VLT) in the Chilean Atacama Desert to study quasars — extremely bright objects powered by supermassive black holes which lie at the centre of massive galaxies. The study surveyed 31 quasars that are seen as they were more than 12.5 billion years ago, at a time when the Universe was still an infant, only about 870 million years old. This is one of the largest samples of quasars from so early on in the history of the Universe to be surveyed. The astronomers found that 12 quasars were surrounded by enormous gas reservoirs: haloes of cool, dense hydrogen gas extending 100000 light-years from the central black holes and with billions of times the mass of the Sun. The team also found that the gas haloes were tightly bound to
the galaxies, providing the perfect food source to sustain both the growth of supermassive black holes and vigorous star formation. While quasars are bright, the gas reservoirs around them are much harder to observe. But MUSE could detect the faint glow of the hydrogen gas in the haloes, allowing astronomers finally to reveal the food stashes that power supermassive black holes in the early Universe. In the future, ESO's Extremely Large Telescope (ELT) will help scientists reveal even more details about galaxies and supermassive black holes in the first couple of billion years after the Big Bang.
VIEW OF UNIVERSE UNDER THREAT
A campaign to launch thousands of new satellites has begun in earnest, offering high-speed internet access from space. But the first fleets of these spacecraft, which have already been sent into orbit by US company SpaceX, are affecting images of the night sky. They are appearing as bright white streaks, so dazzling that they are competing with the stars.
Scientists are worried that future “mega-constellations” of satellites could obscure images from optical telescopes and interfere with radio astronomy observations. To give you an idea of the numbers, there are currently just 2,200 active satellites flying around the Earth. But now the Starlink constellation – a project by US company SpaceX – will start sending batches of 60 telescopes into orbit every few weeks. This will mean about 1,500 satellites have been launched by the end of next year, and by the mid-2020s there could be a fleet of 12,000. UK company OneWeb are aiming for about 650 satellites — but this could rise to 2,000 if there is enough customer demand. Amazon have a constellation of 3,200 spacecraft planned. These satellites are about the size of a table, but they're very reflective, and their panels reflect lots of the Sun's light, which means that we can see them in images that we take with telescopes.
The satellites are also big radiowave users — and that means that they can interfere with the signals that astronomers using. So it also affects radio astronomy as well. The satellites could have a real impact on observations, as they present a foreground between what we're observing from the Earth and the rest of the Universe. So they get in the way of everything. It would be particularly troublesome for telescopes taking large surveys of the sky, such as the future Large Synoptic Survey Telescope (LSST) in Chile. For their next launch, SpaceX are trialling a special coating that is designed to make the spacecraft less bright to see if that will help. OneWeb said they wanted to be a “thought leader in responsible space” and were putting
their satellites into an orbit of 1,200km so they would not interfere with astronomical Observations.
Bulletin compiled by Clive Down
(c) 2020 The Society for Popular Astronomy
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