Saturday, December 30, 2023

SPACE

FASHI releases the largest extragalactic HI catalog with FAST

Peer-Reviewed Publication

SCIENCE CHINA PRESS

The promotional image of FASHI 

IMAGE: 

THE PROMOTIONAL IMAGE SHOWS THE PROJECT ABOUT THE FIVE-HUNDRED-METER APERTURE SPHERICAL RADIO TELESCOPE (FAST) ALL SKY HI SURVEY (FASHI). AS THE IMAGE ILLUSTRATES, THE POWERFUL FAST TELESCOPE IS OBSERVING DISTANT GALAXIES, RECORDING THEIR HI EMISSION, AND REVEALING THE DETAILED PHYSICAL PROPERTIES OF THE GALAXIES.

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CREDIT: ©SCIENCE CHINA PRESS




The FAST All Sky HI survey (FASHI) was designed to cover the entire sky observable by the Five-hundred-meter Aperture Spherical radio Telescope (FAST), spanning approximately 22000 square degrees of declination between -14 deg and +66 deg, and in the frequency range of 1050-1450 MHz, with the expectation of eventually detecting more than 100000 HI sources. Between August 2020 and June 2023, FASHI had covered more than 7600 square degrees, which is approximately 35% of the total sky observable by FAST. FASHI team has detected a total of 41741 extragalactic HI sources in the frequency range 1305.5-1419.5 MHz. When completed, FASHI team will provide the largest extragalactic HI catalog and an objective view of HI content and large-scale structure in the local universe.

Lister Staveley-Smith, a professor at the University of Western Australia and a peer reviewer of the paper, called their work: “That’s an impressive milestone. That’s is an extremely important contribution to astronomical research, particularly in the field of galaxy evolution.”

Hélène Courtois, a professor at the University of Lyon 1, called their work: “The paper is a fantastic news for projects like Cosmic Flows!! I didn’t know that the FASHI survey was already going so strongly since 3 years!! The quality of the spectra that are shown is exquisite, the completeness of the sample is amazing and showing the excellent sensitivity of the instrument. The area surveyed in just 3 years gives high hopes that the full sky that can be accessed by the FAST will be covered in a record of time! The paper was a total surprise to me , and reading page after page of the article was just like being a child unwrapping slowly and with delight a Christmas gift.”

The work was recently published in the journal SCIENCE CHINA Physics, Mechanics and Astronomy. Researchers from Guizhou University, the National Astronomical Observatories under the Chinese Academy of Sciences, and Peking University in China contributed to the study.

  

FASHI sky distribution of the currently released 41741 H I sources (in blue dots) in the galactic hemispheres, showing the coarseness of the limits imposed by practical and scheduling constraints. For comparison, ALFALFA α100 (Haynes et al., 2018) and HIPASS galaxies (Koribalski et al., 2004; Meyer et al., 2004; Wong et al., 2006) are also shown with red and green points, respectively. The two black dashed lines indicate the position of the of the galactic plane at galactic latitude b = ±10deg.

CREDIT

©Science China Press

See the article and download the catalog:

The FAST all sky HI survey (FASHI): The first release of catalog

https://zcp521.github.io/fashi

https://fast.bao.ac.cn/cms/article/271/

https://ui.adsabs.harvard.edu/abs/2023arXiv231206097Z

http://engine.scichina.com/doi/10.1007/s11433-023-2219-7


Sodium’s high-pressure transformation can tell us about the interiors of stars, planets


Scientists reveal how the element’s electrons chemically bond when under pressures like those found below Earth’s crust


Peer-Reviewed Publication

UNIVERSITY AT BUFFALO



Travel deep enough below Earth’s surface or inside the center of the Sun, and matter changes on an atomic level. 

The mounting pressure within stars and planets can cause metals to become nonconducting insulators. Sodium has been shown to transform from a shiny, gray-colored metal into a transparent, glass-like insulator when squeezed hard enough. 

Now, a University at Buffalo-led study has revealed the chemical bonding behind this particular high-pressure phenomenon.

While it’s been theorized that high pressure essentially squeezes sodium’s electrons out into the spaces between atoms, researchers’ quantum chemical calculations show that these electrons still very much belong to the surrounding atoms and are chemically bonded to each other.

“We’re answering a very simple question of why sodium becomes an insulator, but predicting how other elements and chemical compounds behave at very high pressures will potentially give insight into bigger-picture questions,” says Eva Zurek, Ph.D., professor of chemistry in the UB College of Arts and Sciences and co-author of the study, which was published in Angewandte Chemie, a journal of the German Chemical Society. “What’s the interior of a star like? How are planets’ magnetic fields generated, if indeed any exist? And how do stars and planets evolve? This type of research moves us closer to answering these questions.”

The study confirms and builds upon the theoretical predictions of the late renowned physicist Neil Ashcroft, whose memory the study is dedicated to.

It was once thought that materials always become metallic under high pressure — like the metallic hydrogen theorized to make up Jupiter’s core — but Ashcroft and Jeffrey Neaton’s seminal paper two decades ago found some materials, like sodium, can actually become insulators or semiconductors when squeezed. They theorized that sodium’s core electrons, thought to be inert, would interact with each other and the outer valence electrons when under extreme pressure. 

“Our work now goes beyond the physics picture painted by Ashcroft and Neaton, connecting it with chemical concepts of bonding,” says the UB-led study’s lead author, Stefano Racioppi, Ph.D., a postdoctoral researcher in the UB Department of Chemistry. 

Pressures found below Earth’s crust can be difficult to replicate in a lab, so using supercomputers in UB’s Center for Computational Research, the team ran calculations on how electrons behave in sodium atoms when under high pressure. 

The electrons become trapped within the interspatial regions between atoms, known as an electride state. This causes sodium’s physical transformation from shiny metal to transparent insulator, as free-flowing electrons absorb and retransmit light but trapped electrons simply allow the light to pass through. 

However, researchers’ calculations showed for the first time that the emergence of the electride state can be explained through chemical bonding.

The high pressure causes electrons to occupy new orbitals within their respective atoms. These orbitals then overlap with each other to form chemical bonds, causing localized charge concentrations in the interstitial regions.

While previous studies offered an intuitive theory that high pressure squeezed electrons out of atoms, the new calculations found that the electrons are still part of surrounding atoms.

“We realized that these are not just isolated electrons that decided to leave the atoms. Instead, the electrons are shared between the atoms in a chemical bond,” Racioppi says. “They're quite special.”

Other contributors include Malcolm McMahon and Christian Storm from the University of Edinburgh’s School of Physics and Astronomy and Center for Science at Extreme Conditions.

The work was supported by the Center for Matter at Atomic Pressure, a National Science Foundation center led by the University of Rochester that studies how pressure inside stars and planets can rearrange materials’ atomic structure. 

“Obviously it is difficult to conduct experiments that replicate, say, the conditions within the deep atmospheric layers of Jupiter,” Zurek says, “but we can use calculations, and in some cases, high-tech lasers, to simulate these kinds of conditions.”

JOURNAL

DOI

METHOD OF RESEARCH

SUBJECT OF RESEARCH

ARTICLE TITLE

Further evidence for quark-matter cores in massive neutron stars


New theoretical analysis places the likelihood of massive neutron stars hiding cores of deconfined quark matter between 80 and 90 percent. The result was reached through massive supercomputer runs utilizing Bayesian statistical inference.

Peer-Reviewed Publication

UNIVERSITY OF HELSINKI

Layers inside a massive neutron star 1 

IMAGE: 

ARTIST’S IMPRESSION OF THE DIFFERENT LAYERS INSIDE A MASSIVE NEUTRON STAR, WITH THE RED CIRCLE REPRESENTING A SIZABLE QUARK-MATTER CORE.

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CREDIT: JYRKI HOKKANEN, CSC



New theoretical analysis places the likelihood of massive neutron stars hiding cores of deconfined quark matter between 80 and 90 percent. The result was reached through massive supercomputer runs utilizing Bayesian statistical inference.

Neutron-star cores contain matter at the highest densities reached in our present-day Universe, with as much as two solar masses of matter compressed inside a sphere of 25 km in diameter. These astrophysical objects can indeed be thought of as giant atomic nuclei, with gravity compressing their cores to densities exceeding those of individual protons and neutrons manyfold.

These densities make neutron stars interesting astrophysical objects from the point of view of particle and nuclear physics. A longstanding open problem concerns whether the immense central pressure of neutron stars can compress protons and neutrons into a new phase of matter, known as cold quark matter. In this exotic state of matter, individual protons and neutrons no longer exist.

”Their constituent quarks and gluons are instead liberated from their typical color confinement and are allowed to move almost freely,” explains Aleksi Vuorinen, professor of theoretical particle physics at the University of Helsinki.

A Strong Phase Transition May Still Ruin the Day

In a new article just published in Nature Communications, a team centred at the University of Helsinki provided a first-ever quantitative estimate for the likelihood of quark-matter cores inside massive neutron stars. They showed that, based on current astrophysical observations, quark matter is almost inevitable in the most massive neutron stars: a quantitative estimate that the team extracted placed the likelihood in the range of 80-90 percent.

The remaining small likelihood for all neutron stars to be composed of only nuclear matter requires the change from nuclear to quark matter to be a strong first-order phase transition, somewhat resembling that of liquid water turning to ice. This kind of rapid change in the properties of neutron-star matter has the potential to destabilize the star in such a way that the formation of even a minuscule quark-matter core would result in the star collapsing into a black hole.

The international collaboration between scientists from Finland, Norway, Germany, and the US was able to further show how the existence of quark-matter cores may one day be either fully confirmed or ruled out. The key is being able to constrain the strength of the phase transition between nuclear and quark matter, expected to be possible once a gravitational-wave signal from the last part of a binary neutron-star merger is one day recorded.

Massive Supercomputer Runs Using Observational Data

A key ingredient in deriving the new results was a set of massive supercomputer calculations utilizing Bayesian inference – a branch of statistical deduction where one infers the likelihoods of different model parameters via direct comparison with observational data. The Bayesian component of the study enabled the researchers to derive new bounds for the properties of neutron-star matter, demonstrating them to approach so-called conformal behavior near the cores of the most massive stable neutron stars.

Dr. Joonas Nättilä, one of the lead authors of the paper, describes the work as an interdisciplinary effort that required expertise from astrophysics, particle and nuclear physics, as well as computer science. He is about to start as an Associate Professor at the University of Helsinki in May 2024.

”It is fascinating to concretely see how each new neutron-star observation enables us to deduce the properties of neutron-star matter with increasing precision.”

Joonas Hirvonen, a PhD student working under the guidance of Nättilä and Vuorinen, on the other hand emphasizes the importance of high-performance computing:

”We had to use millions of CPU hours of supercomputer time to be able to compare our theoretical predictions to observations and to constrain the likelihood of quark-matter cores. We are extremely grateful to the Finnish supercomputer center CSC for providing us with all the resources we needed!”

Original publication: Annala, E., Gorda, T., Hirvonen, J. et al. Strongly interacting matter exhibits deconfined behavior in massive neutron stars. Nat Commun 14, 8451 (2023). https://doi.org/10.1038/s41467-023-44051-y

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