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Zooming In on Dark Matter Haloes – SciTechDaily

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An artist’s impression of dark matter haloes with various mass in the Universe. Credit: YU Jingchuan, Beijing Planetarium

Most matter in the Universe is dark and completely different in nature from the matter that makes up stars, planets and people. Galaxies form and grow when gas cools and condenses at the center of enormous clumps of this dark matter, the so-called dark matter haloes.

An international research team led by Prof. WANG Jie from the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC) used supercomputers in China and Europe to zoom in on a typical region of a virtual universe as if zooming in on an image of the Moon to see a flea on its surface.

The study was published in Nature on September 2, 2020.

The biggest dark matter haloes in today’s universe contain huge galaxy clusters, collections of hundreds of bright galaxies. The properties of such clusters, which weigh over a quadrillion (a million billion) times as much as our Sun, are well studied.

On the other hand, the masses of the smallest dark matter haloes are unknown. They are hypothesized to be about the mass of the Earth, according to currently popular theories.

Such small haloes would be extremely numerous, containing a substantial fraction of all the dark matter in the universe. However, they would remain dark throughout cosmic history because stars and galaxies grow only in haloes more than a million times as massive as the Sun.

“These small haloes can only be studied by simulating the evolution of the Universe in a large supercomputer,” said Prof. WANG.

Projected Dark Matter Density

Simulations of formation of dark matter haloes ranging in size from Earth mass to clusters of galaxies find a universal halo density structure spanning 20 orders of magnitude in mass. Credit: Dr. Sownak Bose, Center for Astrophysics, Harvard University

The research team, based at the National Observatory of the Chinese Academy of Sciences in China, Durham University in the UK, the Max Planck Institute for Astrophysics in Germany, and the Center for Astrophysics in the USA, took five years to develop, test and carry out their cosmic zoom.

It enabled them to study the structure of dark matter haloes of all masses between that of the Earth and that of a big galaxy cluster. In number, the zoom covers a mass range of 10 to the power 30 (that is a one followed by 30 zeroes), which is equivalent to the number of kilograms in the Sun.

By zooming-in on the virtual universe in such microscopic detail, the researchers were able to study the structure of dark matter haloes ranging in mass from that of the Earth to a big galaxy cluster.

“Surprisingly, we find that haloes of all sizes have a very similar internal structure, i.e., they are extremely dense at the center, become increasingly spread out, and have smaller clumps orbiting in their outer regions,” said Prof. WANG. “Without a measure scale it was almost impossible to tell an image of a dark matter halo of a massive galaxy from one whose mass is a fraction of the Sun.”

Particles of dark matter can collide near the centers of haloes, and may, according to some theories, annihilate in a burst of energetic (gamma) radiation.

Co-author, Prof. Carlos Frenk from Durham University said: “By zooming in on these relatively tiny dark matter haloes, we can calculate the amount of radiation expected to come from different sized haloes.”

Most of this radiation would be emitted by dark matter haloes too small to contain stars and future gamma-ray observatories might be able to detect these emissions, making these small objects individually or collectively “visible.”

“This would confirm the hypothesized nature of the dark matter, which may not be entirely dark after all,” said co-author Simon White from the Max Planck Institute of Astrophysics. “Our research sheds light on these small haloes as we seek to learn more about what dark matter is and the role it plays in the evolution of the universe.”

Read Zooming In Tight on Dark Matter for more on this research.

Reference: “Universal structure of dark matter haloes over a mass range of 20 orders of magnitude” by J. Wang, S. Bose, C. S. Frenk, L. Gao, A. Jenkins, V. Springel and S. D. M. White, 2 September 2020, Nature.
DOI: 10.1038/s41586-020-2642-9

The simulations were carried out in the Cosmology Machine supercomputers in Guangzhou, China, Durham, England of the UK, and Munich, Germany.

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NASA Publishes Artemis Plan to Land First Woman, Next Man on Moon in 2024 – Stockhouse

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WASHINGTON , Sept. 21, 2020 /PRNewswire/ — Following a series of critical contract awards and hardware milestones, NASA has shared an update on its Artemis program, including the latest Phase 1 plans to land the first woman and the next man on the surface of the Moon in 2024.

In the 18 months since NASA accepted a bold challenge to accelerate its exploration plans by more than four years and establish sustainable exploration by the end of the decade, the agency has continued to gain momentum toward sending humans to the Moon again for the first time since the last Apollo lunar mission in 1972.

“With bipartisan support from Congress, our 21st century push to the Moon is well within America’s reach,” said NASA Administrator Jim Bridenstine . “As we’ve solidified more of our exploration plans in recent months, we’ve continued to refine our budget and architecture. We’re going back to the Moon for scientific discovery, economic benefits, and inspiration for a new a generation of explorers. As we build up a sustainable presence, we’re also building momentum toward those first human steps on the Red Planet.”

In its formal plan, NASA captures Artemis progress to date, identifying the key science, technology and human missions, as well as the commercial and international partnerships that will ensure we continue to lead in exploration and achieve our ambitious goal to land astronauts on the Moon.

The agency’s powerful new rocket, the Space Launch System (SLS), and the Orion spacecraft are closer than ever to their first integrated launch. The spacecraft is complete while the core stage and its attached four engines are undergoing a final series of tests that will culminate in a critical hot fire test this fall.

Early Artemis Missions

Following a successful hot fire test, the core stage will be shipped to the agency’s Kennedy Space Center in Florida for integration with the spacecraft. NASA will launch an SLS and an Orion together on two flight tests around the Moon to check performance, life support, and communication capabilities. The first mission – known as Artemis I – is on track for 2021 without astronauts, and Artemis II will fly with crew in 2023.

In the Phase 1 plan, NASA notes additional details about conducting a new test during the Artemis II mission – a proximity operations demonstration. Shortly after Orion separates from the interim cryogenic propulsion stage, astronauts will manually pilot Orion as they approach and back away from the stage. This demonstration will assess Orion’s handling qualities and related hardware and software to provide performance data and operational experience that cannot be readily gained on the ground in preparation for rendezvous, proximity operations, and docking, as well as undocking operations in lunar orbit beginning on Artemis III.

While preparing for and carrying out these flight test missions, NASA already will be back on the Moon robotically – using commercial delivery services to send dozens of new science investigations and technology demonstrations to the Moon twice per year beginning in 2021.

In 2024, Artemis III will be humanity’s return to the surface of the Moon. After launching on SLS, astronauts will travel about 240,000 miles to lunar orbit aboard Orion, at which point they will directly board one of the new commercial human landing systems , or dock to the Gateway to inspect it and gather supplies before boarding the landing system for their expedition to the surface.

Wearing modern spacesuits that allow for greater flexibility and movement than those of their Apollo predecessors, astronauts will collect samples and conduct a range of science experiments over the course of nearly seven days. Using the lander, they will return to lunar orbit before ultimately heading home to Earth aboard Orion.

Work is progressing rapidly on the Gateway. NASA will integrate the first two components to launch – the power and propulsion element and the habitation and logistics outpost – in 2023. This foundation for the Gateway will be able to operate autonomously, conducting remote science experiments when astronauts are not aboard. NASA has selected the first two science instrument suites to conduct space weather investigations in lunar orbit before crew visits.

While NASA has not made a final decision to use the Gateway for Artemis III, Artemis IV and beyond will send crew aboard Orion to dock to the Gateway, where two crew members can stay aboard the spaceship in orbit while two go to the surface. Over time, the outpost will evolve, with new modules added by international partners, allowing crew members to conduct increasingly longer lunar missions.

As detailed in the agency’s concept for surface sustainability earlier this year, an incremental buildup of infrastructure on the surface will follow later this decade, allowing for longer surface expeditions with more crew. That concept calls for an Artemis Base Camp that would include new rovers, power systems, habitats, and more on the surface for long-term exploration of the Moon.

Throughout the Artemis program, robots and humans will search for, and potentially extract, resources such as water that can be converted into other usable resources, including oxygen and fuel. By fine-tuning precision landing technologies as well as developing new mobility capabilities, astronauts will travel farther distances and explore new regions of the Moon.

Learn more about NASA’s Artemis program at:

www.nasa.gov/artemis

Cision View original content to download multimedia: http://www.prnewswire.com/news-releases/nasa-publishes-artemis-plan-to-land-first-woman-next-man-on-moon-in-2024-301135059.html

SOURCE NASA

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Arctic ice melt doesn't boost sea levels, so do we care? – FRANCE 24

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Paris (AFP)

US government scientists reported Monday that the Arctic Ocean’s floating ice cover has shrivelled to its second lowest extent since satellite records began in 1979.

Until this month, only once in the last 42 years has Earth’s frozen skull cap covered less than four million square kilometres (1.5 million square miles).

The trend line is clear: sea ice extent has diminished 14 percent per decade over that period. The Arctic could see it’s first ice-free summer as early as 2035, researchers reported in Nature Climate Change last month.

But all that melting ice and snow does not directly boost sea levels any more than melted ice cubes make a glass of water overflow, which gives rise to an awkward question: who cares?

Granted, this would be bad news for polar bears, which are already on a glide path towards extinction, according to a recent study.

And yes, it would certainly mean a profound shift in the region’s marine ecosystems, from phytoplankton to whales.

But if our bottom-line concern is the impact on humanity, one might legitimately ask, “So what?”.

As it turns out, there are several reasons to be worried about the knock-on consequences of dwindling Arctic sea ice.

– Feedback loops –

Perhaps the most basic point to make, scientists say, is that a shrinking ice cap is not just a symptom of global warming, but a driver as well.

“Sea ice removal exposes dark ocean, which creates a powerful feedback mechanism,” Marco Tedesco, a geophysicist at Columbia University’s Earth Institute, told AFP.

Freshly fallen snow reflects 80 percent of the Sun’s radiative force back into space.

But when that mirror-like surface is replaced by deep blue water, about the same percentage of Earth-heating energy is absorbed instead.

And we’re not talking about a postage stamp area here: the difference between the average ice cap minimum from 1979 to 1990 and the low point reported today — more than 3 million km2 — is twice the size of France, Germany and Spain combined.

The oceans have already soaked up 90 percent of the excess heat generated by manmade greenhouse gases, but at a terrible cost, including altered chemistry, massive marine heatwaves and dying coral reefs.

And at some point, scientists warn, that liquid heat sponge may simply become saturated.

– Altering ocean currents –

Earth’s complex climate system includes interlocking ocean currents driven by wind, tides and something called the thermohaline circulation, which is itself powered by changes in temperature (“thermo”) and salt concentration (“haline”).

Even small changes in this Great Ocean Conveyor Belt — which moves between poles and across all three major oceans — can have devastating climate impacts.

Nearly 13,000 years ago, for example, as Earth was transitioning out of an ice age into the interglacial period that allowed our species to thrive, global temperatures abruptly plunged several degrees Celsius. They jumped back up again about 1,000 years later.

Geological evidence suggests a slowdown in the thermohaline circulation caused by a massive and rapid influx of cold, fresh water from the Artic region was partly to blame.

“The fresh water from melting sea ice and grounded ice in Greenland perturbs and weakens the Gulf Stream,” part of the conveyor belt flowing in the Atlantic, said Xavier Fettweis, a research associate at the University of Liege in Belgium.

“This is what allows western Europe to have a temperate climate compared to the same latitude in North America.”

The massive ice sheet atop Greenland’s land mass saw a net loss of more than half-a-trillion tonnes last year, all of it flowing into the sea.

Unlike sea ice, which doesn’t increase sea levels when it melts, runoff from Greenland does.

That record amount was due in part to warmer air temperatures, which have risen twice as fast in the Arctic as for the planet as a whole.

But it was also caused by a change in weather patterns, notably an increase in sunny summer days.

“Some studies suggest that this increase in anticyclonic conditions in the Arctic in summer results in part from the minimum sea ice extent,” Fettweis told AFP.

– Bears on thin ice –

The current trajectory of climate change and the advent of ice-free summers — defined by the UN’s IPCC climate science panel as under one million km2 — would indeed starve polar bears into extinction by century’s end, according to a July study in Nature.

“Human-caused global warming means that polar bears have less and less sea ice to hunt on in the summer months,” Steven Amstrup, lead author of the study and chief scientist of Polar Bears International, told AFP.

“The ultimate trajectory of polar bears with unabated greenhouse gas emissions is disappearance.”

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Arctic sea ice shrinks to 2nd lowest level in 4 decades – CBC.ca

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Warming in the Arctic shrank the ice covering the polar ocean this year to its second-lowest extent in four decades, scientists announced Monday, yet another sign of how climate change is rapidly transforming the region.

Satellites recorded this year’s sea ice minimum at 3.74 million square kilometres on Sept. 15, only the second time the ice has been measured below 4 million square kilometres in 40 years of record keeping, said researchers at the National Snow and Ice Data Center

“It’s fairly devastating that we’ve had such consistently low sea ice. But unfortunately, it’s not surprising,” said Twila Moon, a glaciologist at the research centre in Boulder, Colorado.

The record low of 3.41 million square kilometres, reached in 2012 after a late-season cyclonic storm broke up the remaining ice, is not much below what researchers see today.

This year’s decline was especially fast between Aug. 31 and Sept. 5, thanks to pulses of warm air coming off a heat wave in Siberia, according to the NSIDC. The rate of ice loss during those six days was faster than during any other year on record. Another team of scientists found in July that the Siberian heat wave would have been all but impossible without human-caused climate change.

As the Arctic sea ice vanishes, it leaves patches of dark water open. Those dark waters absorb solar radiation rather than reflecting it back out of the atmosphere, a process that amplifies warming and helps to explain why Arctic temperatures have risen more than twice as fast as the rest of the world over the last 30 years.

Arctic sea ice at the North Pole is seen from the German icebreaker RV Polarstern, on Aug. 19, 2020. The voyage made an unplanned detour because of lighter-than-usual sea ice conditions. (Markus Rex/Alfred Wegener Institute via AP)

The loss of sea ice also threatens Arctic wildlife, from polar bears and seals to plankton and algae, said Tom Foreman, a polar wildlife expert and Arctic guide.

“The numbers that we’re getting in terms of extent of sea ice decrease each year put us pretty much on red alert in terms of the level of worry that we have, our concern for the stability of this environment,” Foreman said.

The same warming that is opening summertime Arctic waters is also eating away at the ice sheets covering Arctic lands in Canada and Greenland. The faster those ice sheets melt into surrounding ocean, the faster sea levels will rise worldwide.

Given that a warmer Arctic could impact weather patterns worldwide, Moon said the world should not wait for another new record sea ice low before taking action to limit climate change.

“We should work very hard to make differences in our emissions of polluting gases so that we do not see so many records created in the future,” Moon said.

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