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Astronomers Locate the Source of High-Energy Cosmic Rays – Universe Today

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Roughly a century ago, scientists began to realize that some of the radiation we detect in Earth’s atmosphere is not local in origin. This eventually gave rise to the discovery of cosmic rays, high-energy protons and atomic nuclei that have been stripped of their electrons and accelerated to relativistic speeds (close to the speed of light). However, there are still several mysteries surrounding this strange (and potentially lethal) phenomenon.

This includes questions about their origins and how the main component of cosmic rays (protons) are accelerated to such high velocity. Thanks to new research led by the University of Nagoya, scientists have quantified the amount of cosmic rays produced in a supernova remnant for the first time. This research has helped resolve a 100-year mystery and is a major step towards determining precisely where cosmic rays come from.

While scientists theorize that cosmic rays originate from many sources – our Sun, supernovae, gamma-ray bursts (GRBs), and Active Galactic Nuclei (aka. quasars) – their exact origin has been a mystery since they were first discovered in 1912. Similarly, astronomers have theorized that supernova remnants (the after-effects of supernova explosions) are responsible for accelerating them to nearly the speed of light.

Showers of high-energy particles occur when energetic cosmic rays strike the top of the Earth’s atmosphere. Cosmic rays were discovered unexpectedly in 1912. Illustration Credit: Simon Swordy (U. Chicago), NASA.

As they travel through our galaxy, cosmic rays play a role in the chemical evolution of the interstellar medium (ISM). As such, understanding their origin is critical to understanding how galaxies evolve. In recent years, improved observations have led some scientists to speculate that supernova remnants give rise to cosmic rays because the protons they accelerate interact with protons in the ISM to create very high-energy (VHE) gamma rays.

However, gamma-rays are also produced by electrons that interact with photons in the ISM, which can be in the form of infrared photons or radiation from the Cosmic Microwave Background (CMB). Therefore, determining which source is greater is paramount to determining the origin of cosmic rays. Hoping to shed light on this, the research team – which included members from Nagoya University, the National Astronomical Observatory of Japan (NAOJ), and the University of Adelaide, Australia – observed the supernova remnant RX J1713.7?3946 (RX J1713).

The key to their research was the novel approach they developed to quantify the source of gamma-rays in interstellar space. Past observations have shown that the intensity of VHE gamma-rays caused by protons colliding with other protons in the ISM is proportional to the interstellar gas density, which is discernible using radio-line imaging. On the other hand, gamma-rays caused by the interaction of electrons with photons in the ISM are also expected to be proportional to the intensity of nonthermal X-rays from electrons.

For the sake of their study, the team relied on data obtained by the High Energy Stereoscopic System (HESS), a VHE gamma-ray observatory located in Namibia (and operated by the Max Planck Institute for Nuclear Physics). They then combined this with X-ray data obtained by the ESA’s X-ray Multi-Mirror Mission (XMM-Newton) observatory and data on the distribution of gas in the interstellar medium.

Cosmic rays produced by gamma-rays vs. electrons (Top), and data obtained by the HESS and XMM-Newton observations (Bottom). Credit: Astrophysics Laboratory/Nagoya University

They then combined all three data sets and determined that protons account for 67 ± 8% of cosmic rays while cosmic-ray electrons account for 33 ± 8% – roughly a 70/30 split. These findings are groundbreaking since they are the first time that the possible origins of cosmic rays have been quantified. They also constitute the most definitive evidence to date that supernova remnants are the source of cosmic rays.

These results also demonstrate that gamma-rays from protons are more common in gas-rich interstellar regions, whereas those caused by electrons are enhanced in the gas-poor regions. This supports what many researchers have predicted, which is that the two mechanisms work together to influence the evolution of the ISM. Said Emeritus Professor Yasuo Fukui, who was the study’s lead author:

“This novel method could not have been accomplished without international collaborations. [It] will be applied to more supernova remnants using the next-generation gamma-ray telescope CTA (Cherenkov Telescope Array) in addition to the existing observatories, which will greatly advance the study of the origin of cosmic rays.”

In addition to leading this project, Fukui has been working to quantify interstellar gas distribution since 2003 using the NANTEN radio telescope at the Las Campanas Observatory in Chile and the Australia Telescope Compact Array. Thanks to Professor Gavin Rowell and Dr. Sabrina Einecke of the University of Adelaide (co-authors on the study) and the H.E.S.S. team, the spatial resolution and sensitivity of gamma-ray observatories has finally reached the point where it is possible to draw comparisons between the two.

Meanwhile, co-author Dr. Hidetoshi Sano of the NAOJ led the analysis of archival datasets from the XMM-Newton observatory. In this respect, this study also shows how international collaborations and data-sharing are enabling all kinds of cutting-edge research. Along with improved instruments, improved methods and greater opportunities for cooperation are leading to an age where astronomical breakthroughs are becoming a regular occurrence!

Further Reading: Nagoya University, The Astrophysical Journal

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Ancient Jordanian town destroyed by a meteor blast may have inspired Biblical stories, scientists say – CBC.ca

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A thriving town in the Jordan River valley was utterly annihilated by the explosion of a meteor 3,600 years ago, which produced a flash and shock wave that scorched and shattered buildings, animals and people.

That’s the scenario painted by a large collaboration of archaeologists, earth and space scientists who have been studying the remains of the Bronze Age town at a site called Tall el-Hammam in Jordan, not far from the Dead Sea.

Before its destruction, Tall el-Hammam was a bustling town of perhaps 8,000 people, with mud-brick buildings and a four-story palace. There is evidence that the site of the town had been occupied for several thousand years.

Archaeologists have been excavating the ruins of the town for more than 15 years, revealing a rich history during its long occupation that included ruins from fires, warfare and earthquakes.  

Their findings were published this month in the journal Scientific Reports.

The ‘destruction layer’

But their excavations also revealed destruction that didn’t have any ordinary explanation: a one-and-a-half-metre-thick layer of debris the team dubbed the “destruction layer,” encompassing the whole settlement, and dated to 1650 BC. This layer showed signs of an incredibly violent event.

It included melted pottery and bricks, soot, melted plaster and metal, that only could have resulted from temperatures approaching 2,000 C. It also contained ruins of flattened buildings, including the town’s palace and four metre-thick outer wall.

“The city was built with millions of mud bricks, in the walls, the ramparts, the buildings,” space physicist Malcolm LeCompte, who was part of the research team, told Quirks & Quarks host Bob McDonald. “Much of the mud brick was just disintegrated and blown away off the upper stories of these structures into the next valley.” 

Researchers stand at the Tall el-Hammam archaeological site in Jordan. (Phil Silvia)

Most gruesomely, the debris also contained the remains of humans and animals that had been burned and torn apart.

“The human remains and bones were abundant. There’s very few total skeletal remains. Those that do remain are pretty disarticulated — just shattered,” said LeCompte. “It’s pretty horrifying, actually.” 

The extreme temperatures and the widespread and violent destruction began to point the research team to a culprit. But microscopic examination of the debris also helped build the case. They found sand grains with unique cracks and fractures within them called “shocked quartz,” which are often found in the debris from super-high velocity impacts, like those generated by a meteor strike.

This led them to conclude that the best fit for what they were seeing was an “air burst” by meteor likely composed of rock and ice. The object, perhaps 50 metres across, would have hit the Earth’s atmosphere above the town travelling at perhaps 60,000 km/h. At that speed the atmosphere would have behaved as if it was almost solid, causing the meteor to explode violently.

“The evidence we have suggests that it was something like … a megaton-yield event in terms of its equivalent in atomic or nuclear bombs.” said LeCompte.

On the ground, the flash of heat from the explosion would have caused hair and textiles to burst into flame, and melted metal and brick. Moments later, a shock wave would have hit, causing winds that researchers estimate reached speeds of up to 1,200 km/h — knocking structures in the town flat and killing every living thing in the town.

“The shock wave would have come and just torn them apart,” said LeCompte.

Tall el-Hammam is located just north of the Dead Sea in the Joran River valley. (NASA)

It will happen again, LeCompte warns

The researchers point out that there are modern precedents for an event like this. In 1908 a similar-sized object is thought to have exploded in the atmosphere over Siberia, in what is known as the Tunguska event. It flattened 2,000 square kilometres of forest, and started a huge forest fire.

In 2013 a roughly 200-metre meteor exploded over Chelyabinsk in Russia, shattering windows and causing more than 1,000 injuries.

So far the team has found some material they think could be from the meteor, including tiny samples of rare metals often found in meteorites, but need to do more work to confirm their origin. LeCompte points out that excavation in the area can be difficult, particularly as much of the local landscape is currently occupied by Syrian refugees.

One intriguing, if speculative, possibility that the researchers have suggested is that the destruction of Tall el-Hammam might be the inspiration behind Biblical legends like the destruction of Sodom — in what is described as a “rain” of “fire and brimstone” — or the destruction of the walls of Jericho.

But LeCompte says those that look at Tall el-Hammam as a historical curiosity are missing the point. Instead, he said, they should look at it as a warning.

“The significance to its past pales in what it foretells for the future, because this is going to happen again,” he said. The Tunguska event shows that the Earth can still be struck by destructive objects from space, and if something similar were to happen over a city or populated region, the devastation would be enormous.

“It just took it out in an instant, so that’s a serious warning of what could happen — what will happen — in the future.”


Written by Jim Lebans. Produced by Mark Crawley.

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Archaeologists find oldest known human footprints in the Americas – HeritageDaily

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Archaeologists conducting research in the White Sands National Park in New Mexico has identified the oldest known human footprints in the Americas.

The findings provide the earliest unequivocal evidence of human activity in the Americas from over 23,000 years ago, a period during the height of the last glacial cycle, known as the Last Glacial Maximum.

Archaeologists have debated for decades when the first people arrived in the Americas, but Vance T. Holliday from the UArizona School of Anthropology and Department of Geosciences said: “Few archaeologists see reliable evidence for sites older than about 16,000 years. Some think the arrival was later, no more than 13,000 years ago by makers of artefacts called Clovis points. The White Sands tracks provide a much earlier date. There are multiple layers of well-dated human tracks in streambeds where water flowed into an ancient lake. This was 10,000 years before Clovis people.”

 

The team used radiocarbon dating of seed layers above and below the footprints to determine their age, which showed human presence at the site lasting two millennia, and the oldest track dating back 23,000 years.

Kathleen Springer from the U.S. Geological Survey said: “Our dates on the seeds are tightly clustered and maintain stratigraphic order above and below multiple footprint horizons – this was a remarkable outcome”.

An analysis on the size of the human footprints suggests that they were mainly teenagers and younger children, whilst other tracks indicate that they were left by mammoths, giant ground sloths, dire wolves, and birds.

“It is an important site because all of the trackways we’ve found there show an interaction of humans in the landscape alongside extinct animals, like mammoths and giant sloths.” said Sally Reynolds of Bournemouth University. “We can see the co-existence between humans and animals on the site as a whole, and by being able to accurately date these footprints, we’re building a greater picture of the landscape.”

 

The University of Arizona

Header Image Credit : David Bustos – White Sands National Park

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Bird reports rose during lockdowns | Cornell Chronicle – Cornell Chronicle

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Around 80% of bird species examined in a new study were reported in greater numbers in human-altered habitats during pandemic lockdowns, according to new research based on data from the eBird program at the Cornell Lab of Ornithology.

In the paper, “Reduced Human Activity During COVID-19 Alters Avian Land Use Across North America,” published Sept. 22 in Science Advances, researchers compared online eBird observations from the United States and Canada from before and during the pandemic. They focused on areas within about 100 km of urban areas, major roads, and airports.

Vast amounts of data from a likewise vast geographic area were vital for this study. The researchers used more than 4 million eBird observations of 82 bird species from across Canada and the U.S.

“A lot of species we really care about became more abundant in human landscapes during the pandemic,” said study senior author Nicola Koper of the University of Manitoba, which led the research. “I was blown away by how many species were affected by decreased traffic and activity during lockdowns.”

Reports of bald eagles increased in cities with the strongest lockdowns. Ruby-throated hummingbirds were three times more likely to be reported within a kilometer of airports than before the pandemic. Barn swallows, a threatened species in Canada, were reported more often within a kilometer of roads than before the pandemic.

A few species decreased their use of human-altered habitat during the pandemic. Red-tailed hawk reports decreased near roads, perhaps because there was less roadkill when traffic declined. But far more species had increased counts in these human-dominated landscapes.

The authors filtered pandemic and pre-pandemic eBird reports so that the final data sets had the same characteristics, such as location, number of lists, and level of birdwatcher effort.

“We also needed to be aware of the detectability issue,” said co-author Alison Johnston, assistant director of the Center for Avian Population Studies and Ecological Data in the Lab of Ornithology. “Were species being reported in higher numbers because people could finally hear the birds without all the traffic noise, or was there a real ecological change in the numbers of birds present?”

The study tested whether better detectability might be a factor in the larger bird numbers reported. If it was, the scientists expected that to be more noticeable for smaller birds, which are harder to detect beneath traffic noise. However, effects were noticed across many species, from hawks to hummingbirds, suggesting that the increased numbers were not only caused by increased detectability in the quieter environments.

“Having so many people in North America and around the world paying attention to nature has been crucial to understanding how wildlife react to our presence,” says lead author Michael Schrimpf, a postdoctoral fellow at the University of Manitoba. “Studies such as this one rely on volunteer birdwatchers, so if you enjoy watching wildlife, there are many projects out there, like eBird and iNaturalist, that can use your help.”

The study was funded by Natural Sciences and Engineering Research Council of Canada with in-kind support provided by Environment and Climate Change Canada and the Cornell Lab of Ornithology.

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