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Discovery of the least 'metallic' stellar structure in the Milky Way – Phys.org

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This illustration shows the location of the C-19 stellar stream (orange, vertical stream of stars in lower left), which was recently discovered at the edge of our Milky Way Galaxy. Observations using the Gemini North telescope—part of the international Gemini Observatory, a program of NSF’s NOIRLab—reveal that the stars in this stream were once part of an ancient globular star cluster that was torn apart by gravitational interactions with our galaxy. The Large Magellanic Cloud and Small Magellanic Cloud (satellite galaxies of the Milky Way) appear in the lower right. Credit: International Gemini Observatory /NOIRLab / NSF / AURA/ J. da Silva / Spaceengine / M. Zamani (NSF’s NOIRLab)

A primordial stellar stream discovered in the outer reaches of the Milky Way has a lower proportion of heavy elements than any known stellar system in our galaxy. Observations with the Gemini Observatory, a Program of NSF’s NOIRLab, showed that the stars in this stream were torn from an ancient star cluster and are relics from the early days of the Milky Way, which could provide insights into the formation of the first stars.

An international team of researchers including members from Europe, Canada, and Russia has discovered a unique stream of stars orbiting the Milky Way. Called C-19, the stellar stream is south of the spiral of the Milky Way, and its orbit extends about 20,000 light-years from the galactic center at its closest approach and roughly 90,000 light-years at its farthest. The stellar stream stretches across an impressive expanse of the night sky—roughly 30 times the width of the full moon—although it isn’t visible to the naked eye.

Using the Gemini North telescope—located in Hawai’i as part of the international Gemini Observatory, a program of NSF’s NOIRLab—and the GRACES instrument, the team realized that C-19 is a remnant of a globular cluster. In addition, the stars in the stream possess a uniquely low proportion of heavy elements, or as astronomers phrase it, low “metallicity.” Globular clusters were previously thought to have metallicities no lower than 0.2%, but C-19 has an unprecedentedly low metallicity of less than 0.05%—lower than has ever been observed for a stellar system in the Milky Way or its surroundings.

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Astronomers have discovered the ruins of an ancient star cluster in the outer fringes of the Milky Way. This stellar stream, known as C-19, extends across a large area of the night sky, approximately 30 times the width of the full Moon. The stars in the stream have a uniquely low proportion of heavy elements—lower than any other stellar system in the Milky Way or its surroundings. This discovery was made using telescopes on the ground and in space, including the international Gemini Observatory, a Program of NSF’s NOIRLab. Credit: International Gemini Observatory / NOIRLab / NSF / AURA / J. da Silva / Spaceengine / M. Zamani (NSF’s NOIRLab)

The discovery that a low-metallicity stream originated from a globular cluster has implications for the formation of stars, star clusters, and galaxies in the early universe. The very existence of the stream proves that globular clusters and the first building blocks of the Milky Way must have been able to form in low-metal environments, before successive generations of stars supplied the universe with heavier elements.

“It was not known if globular clusters with so few heavy elements exist—some theories even hypothesized they couldn’t form at all,” commented Nicolas Martin of the Strasbourg Astronomical Observatory, who is the lead author of the Nature paper reporting this discovery. “Other theories suggest that they would all have long-since disappeared, which makes this a key discovery for our understanding of how stars form in the early universe.”

Discovery of the least 'metallic' stellar structure in the Milky Way
Distribution of very dense groups of stars in the Milky Way, called globular clusters, superimposed on a map of the Milky Way compiled from data obtained with the Gaia Space Observatory. Each dot represents a cluster of a few thousand to several million stars, as in the insert image of the Messier 10 cluster. The color of the dots shows their metallicity, in other words, their abundance of heavy elements relative to the Sun. The C-19 stars are indicated by the light blue symbols. Credit: N. Martin / Strasbourg Astronomical Observatory / CNRS; Canada-France-Hawaii Telescope / Coelum; ESA / Gaia / DPAC

Members of the team originally spotted C-19 in data from the Gaia mission using an algorithm they designed specifically to detect stellar streams. The stars in C-19 were also identified by the Pristine survey—a search for the lowest-metallicity stars in and around the Milky Way using the Canada-France-Hawaii Telescope in Hawai’i—as being interesting enough to merit follow-up observations. To identify the origin of C-19’s constituent stars, astronomers needed the detailed spectra from GRACES. The team also gathered data using a spectrograph mounted on the Gran Telescopio Canarias on La Palma in the Canary Islands.

“GRACES provided the critical clues that C-19 is a disrupted globular cluster and not the more common disrupted dwarf galaxy,” explained Kim Venn of the University of Victoria, the lead investigator for the GRACES observations. “We already knew that this was a very metal-poor stream, but identifying it as a globular cluster required the precision metallicities and detailed chemical abundances only available with high-resolution spectra.”

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This animation shows how a globular star cluster, orbiting a still-forming Milky Way Galaxy, can get torn apart by the gravity of the developing galaxy to become the C-19 stellar stream that now orbits the present-day Milky Way. Credit: Gabriel Pérez Díaz, SMM (IAC)

The Gemini observations suggest that the cluster must have formed from very early generations of stars, making C-19 a remarkable relic from the time when the very first groups of stars were being formed. Consequently, this discovery improves our understanding of the formation of stars and star clusters that arose shortly after the Big Bang, and provides a close-to-home natural laboratory in which to study the oldest structures in galaxies.

“This artifact from ancient times opens a direct and unique window onto the early epochs of star formation in the universe,” concluded co-investigator Julio Navarro of the University of Victoria. “While astronomers can look at the most distant galaxies to study the early universe, we now know that it is possible to study the oldest structures in our own galaxy as fossils from those ancient times.”

“This international collaboration reveals startling new insight into the structure, evolution, and formation of our galaxy,” added Martin Still, Gemini Program Director at the National Science Foundation. “The Gemini observatories continue to demonstrate key advances in the understanding of our night sky, concerning the cosmic ecosystem and our own place in the universe.”


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Cosmic galaxy assembly and the evolution of metals


More information:
Nicolas Martin, A stellar stream remnant of a globular cluster below the metallicity floor, Nature (2022). DOI: 10.1038/s41586-021-04162-2

Citation:
Discovery of the least ‘metallic’ stellar structure in the Milky Way (2022, January 5)
retrieved 5 January 2022
from https://phys.org/news/2022-01-discovery-metallic-stellar-milky.html

This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no
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Shattered 'alphabet soup' iceberg flushed a lot of fresh water into the ocean – Space.com

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A rogue iceberg that drifted dangerously close to an Antarctic penguin population in 2020 and 2021 released billions of tons of fresh water into the ocean during its breakup.

A new study, based on satellite data, tracks the aftermath of the once-mighty iceberg A-68a, which held the title of world’s largest iceberg for more than three years before shattering into a dozen pieces. (NASA’s Earth Observatory once dubbed the various mini-bergs “alphabet soup.”)

For a while, there were worries the iceberg might threaten a penguin-filled island called South Georgia, located about 940 miles (1,500 kilometers) northeast of the Antarctic Peninsula. Happily, that never came to pass, but the new research shows that the iceberg flooded the region with fresh water, potentially affecting the local ecosystem and providing yet another example of the effects of global warming on the oceans.

Related: Watch this giant iceberg break off from Antarctica

The research consulted data gathered by missions including Sentinel-1 (operated by European Space Agency, or ESA), Sentinel-3 (ESA), CryoSat-2 (ESA) and ICESat-2 (NASA), as well as the Moderate Resolution Imaging Spectroradiometer, or MODIS, instrument that flies aboard two NASA satellites, Aqua and Terra.

The satellite data shows that during the iceberg’s three-month melting period in late 2020 and early 2021, the former A-68a flushed into the ocean about 162 billion tons (152 billion metric tonnes) of fresh water — equivalent to 61 million Olympic-sized swimming pools, according to a press release from United Kingdom study participant University of Leeds.

“The berg had melted enough as it drifted to avoid damaging the sea floor around South Georgia by running aground,” the university stated. “However, a side effect of the melting was the release of a colossal 152 billion tonnes of fresh water in close proximity to the island — a disturbance that could have a profound impact on the island’s marine habitat.”

Fresh meltwater and nutrients tend to flow from melting icebergs. The freshwater flooding alters ocean circulation and the ocean ecosystem nearby the glacier fragment, the university noted.

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“The next thing we want to learn is whether it had a positive or negative impact on the ecosystem around South Georgia,” Leeds lead author and Ph.D. candidate Anne Braakmann-Folgmann said in the same statement. 

She noted the iceberg moved across a common ocean “highway” known as the Drake Passage, so the fate of A68-A may help understand how icebergs in that zone influence the ocean in general.

A study based on the research was published in the forthcoming March 1 issue of Remote Sensing of Environment.

Follow Elizabeth Howell on Twitter @howellspace. Follow us on Twitter @Spacedotcom and on Facebook

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Robot dog that can hike peaks in the Swiss Alps unaided could be used on other planets – Euronews

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This robot dog hiked over a steep mountain in Switzerland – and it didn’t need the help of its humans to overcome the many obstacles of the rough terrain.

The skilled dog bot could be used to reach areas that are too dangerous or inaccessible to humans, including other planets, according to its creators.

The research by ETH Zurich effectively allows ANYmal, a four-legged robot dog, to move quickly over rough terrain while still taking care – a new trait for robots.

The robot dog is able to work out how to walk over any terrain by combining what its sensors can “see” with what it knows about its surroundings, just like people or animals.

“Until now when a robot used perception mostly they were just assuming that the map is always correct,” said Takahiro Miki, a PhD student at the Robotics Systems Lab at ETH Zurich.

“But often when we go outdoors this doesn’t happen, like when you go into the tall grass”.

The team used landscapes with visual obstacles like deep snow and tall grass as an example of when a robot’s camera systems produce a map of the landscape that doesn’t work when the robot puts its foot down.

ANYmal’s control system allows it to prioritise its sense of touch over its visual perception.

The team put the ability to the test on a hiking route up Mount Etzel in the Swiss Alps which stands 1,098 metres above sea level.

“The slope was quite steep, like it was even hard sometimes for us. It was quite exhausting but the robot could go over all of these obstacles and we didn’t need to help the robot,” Miki said.

The scientists hope the new skill could allow ANYmal to be deployed anywhere on Earth and on space missions to other planets.

Hundreds of four-legged robots, many of them made by Hyundai-owned Boston Dynamics, are already in use, some in hostile industrial environments, including one performing survey work in Chernobyl and another working on a BP oil rig in the Gulf of Mexico.

For more on this story, watch the video in the media player above.

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Satellites show 'mega-iceberg' released 152 billion tons of fresh water into ocean as it scraped past South Georgia – Phys.org

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Image 1: The A68A iceberg with some smaller parts of ice that have broken off around it (21 November 2020). Credit: MODIS image from NASA Worldview Snapshots.

152 billion tons of fresh water—equivalent to 20 times the volume of Loch Ness or 61 million Olympic-sized swimming pools, entered the seas around the sub-Antarctic island of South Georgia when the megaberg A68A melted over three months in 2020/2021, according to a new study.

In July 2017, the A68A snapped off the Larsen-C Ice Shelf on the Antarctic Peninsula and began its epic 3.5-year, 4,000-km journey across the Southern Ocean. At 5719 square kilometers in extent—one-quarter the size of Wales—it was the biggest iceberg on Earth when it formed and the sixth largest on record. Around Christmas 2020, the berg received widespread attention as it drifted worryingly close to South Georgia, raising concerns it could harm the island’s fragile ecosystem.

Researchers from the Centre for Polar Observation and Modelling (CPOM) and British Antarctic Survey (BAS) used to chart the A68A iceberg’s area and thickness change throughout its life cycle. The authors show that the berg had melted enough as it drifted to avoid damaging the sea floor around South Georgia by running aground. However, a side effect of the melting was the release of a colossal 152 billion tons of fresh water in to the island—a disturbance that could have a profound impact on the island’s marine habitat.

For the first two years of its life, A68A stayed close to Antarctica in the cold waters of the Weddell Sea and experienced little in the way of melting. However, once it began its northward journey across Drake Passage, it traveled through increasingly warm waters and began to melt. Altogether, the iceberg thinned by 67 meters from its initial 235-meter thickness, with the rate of melting rising sharply as the berg drifted in the Scotia Sea around South Georgia.

Animation 2: Thinning and breakage of the A68A iceberg over time. Melt rates increase sharply once the iceberg is drifting in open ocean north of the Antarctic peninsula. Iceberg thickness was derived from satellite altimetry data from Cryosat-2 and ICESat-2. Iceberg shape and size were sourced from Sentinel-1, Sentinel-3 and MODIS satellite data. Credit: Credit: Anne Braakmann-Folgmann CPOM.

Laura Gerrish, GIS and mapping specialist at BAS and co-author of the study said, “A68 was an absolutely fascinating iceberg to track all the way from its creation to its end. Frequent measurements allowed us to follow every move and break-up of the berg as it moved slowly northward through iceberg alley and into the Scotia Sea, where it then gained speed and approached the island of South Georgia very closely.”

If an iceberg’s keel is too deep, it can get stuck on the sea floor. This can be disruptive in several ways: The scour marks can destroy fauna, and the berg itself can block and predator foraging routes. All of these potential outcomes were feared when A68A approached South Georgia. However, this new study reveals that it collided only briefly with the sea floor and broke apart shortly afterward, making it less of a risk in terms of blockage. By the time it reached the shallow waters around South Georgia, the iceberg’s keel had reduced to 141 meters below the , shallow enough to avoid the seabed which is around 150 meters deep.

Nevertheless, the ecosystem and wildlife around South Georgia will certainly have felt the impact of the colossal iceberg’s visit. When icebergs detach from ice shelves, they drift with the ocean currents and wind while releasing cold fresh meltwater and nutrients as they melt. This process influences the local ocean circulation and fosters biological production around the iceberg. At its peak, the iceberg was melting at a rate of 7 meters per month, and in total, it released a staggering 152 billion tons of fresh water and nutrients.

Animation 4: Journey of the A68A iceberg from the Larsen C Ice Shelf at the Antarctic Peninsula, across the Weddell Sea, through the deep ocean of Scotia Sea and approaching South Georgia at the end of its lifetime. The warming ocean conditions led to the thinning and shrinking of the berg. Elevation and ocean depth are based on IBCSO and GEBCO data (Arndt et al., 2013; GEBCO Compilation Group, 2019) and ocean temperature is derived from the World Ocean Atlas (WOA, Boyer et al., 2018). Iceberg positions and length are taken from the Antarctic Iceberg Tracking Database (Budge and Long, 2018) and iceberg thickness is calculated from satellite altimetry data. Credit: Anne Braakmann-Folgmann CPOM

Anne Braakmann-Folgmann, a researcher at CPOM and Ph.D. candidate at the University of Leeds’ School of Earth and Environment, is lead author of the study. She said, “This is a huge amount of melt water, and the next thing we want to learn is whether it had a positive or negative impact on the ecosystem around South Georgia. Because A68A took a common route across the Drake Passage, we hope to learn more about icebergs taking a similar trajectory, and how they influence the polar oceans.”

The journey of A68A has been charted using observations from five satellites. The iceberg’s area change was recorded using a combination of Sentinel-1, Sentinel-3 and MODIS imagery. Meanwhile, the iceberg’s thickness change was measured using CryoSat-2 and ICESat-2 altimetry. By combining these measurements, the iceberg’s area, thickness, and volume change were determined.

Satellites reveal world's most famous 'mega iceberg' released 152 billion tonnes of fresh water into ocean as it scraped past So
Image 2: A68A iceberg approaching the island of South Georgia (14 December 2020). The left hand part of the image are clouds. Credit: MODIS image from NASA Worldview Snapshots.

Tommaso Parrinello, CryoSat Mission Manager at the European Space Agency, said, “Our ability to study every move of the iceberg in such detail is thanks to advances in satellite techniques and the use of a variety of measurements. Imaging satellites record the location and shape of the iceberg and data from altimetry missions add a third dimension as they measure the height of surfaces underneath the satellites and can therefore observe how an iceberg melts.”


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Iceberg A-68A: hit or miss?


More information:
A. Braakmann-Folgmann et al, Observing the disintegration of the A68A iceberg from space, Remote Sensing of Environment (2022). DOI: 10.1016/j.rse.2021.112855

Citation:
Satellites show ‘mega-iceberg’ released 152 billion tons of fresh water into ocean as it scraped past South Georgia (2022, January 20)
retrieved 20 January 2022
from https://phys.org/news/2022-01-satellites-mega-iceberg-billion-tons-fresh.html

This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no
part may be reproduced without the written permission. The content is provided for information purposes only.

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