SPACE
Supercomputer simulations reveal the nature of turbulence in black hole accretion disks
Tohoku University
image:
Artistic image of accretion disk turbulence. The inset is the magnetic field fluctuations computed by the simulation of this study.
view moreCredit: ©Yohei Kawazura
Researchers at Tohoku University and Utsunomiya University have made a breakthrough in understanding the complex nature of turbulence in structures called "accretion disks" surrounding black holes, using state-of-the-art supercomputers to conduct the highest-resolution simulations to date. An accretion disk, as the name implies, is a disk-shaped gas that spirals inwards towards a central black hole.
There is a great interest in studying the unique and extreme properties of black holes. However, black holes do not allow light to escape, and therefore cannot be directly perceived by telescopes. In order to probe black holes and study them, we look at how they affect their surroundings instead. Accretion disks are one such way to indirectly observe the effects of black holes, as they emit electromagnetic radiation that can be seen by telescopes.
"Accurately simulating the behaviour of accretion disks significantly advances our understanding of physical phenomena around black holes," explains Yohei Kawazura, "It provides crucial insights for interpreting observational data from the Event Horizon Telescope."
The researchers utilized supercomputers such as RIKEN's "Fugaku" (the fastest computer in the world up until 2022) and NAOJ's "ATERUI II" to perform unprecedentedly high-resolution simulations. Although there have been previous numerical simulations of accretion disks, none have observed the inertial range because of the lack of computational resources. This study was the first to successfully reproduce the "inertial range" connecting large and small eddies in accretion disk turbulence.
It was also discovered that "slow magnetosonic waves" dominate this range. This finding explains why ions are selectively heated in accretion disks. The turbulent electromagnetic fields in accretion disks interact with charged particles, potentially accelerating some to extremely high energies.
In magnetohydronamics, magnetosonic waves (slow and fast) and Alfvén waves make up the basic types of waves. Slow magnetosonic waves were found to dominate the inertial range, carrying about twice the energy of Alfvén waves. The research also highlights a fundamental difference between accretion disk turbulence and solar wind turbulence, where Alfvén waves dominate.
This advancement is expected to improve the physical interpretation of observational data from radio telescopes focused on regions near black holes.
The study was published in Science Advances on August 28, 2024.
The spatial structures of magnetorotational turbulence in an accretion disk (modeled). (A) shows the flow and (B) shows the magnetic field intensity. White lines represent typical magnetic field lines.
Credit
©Yohei Kawazura
Journal
Science Advances
Article Title
Inertial range of magnetorotational turbulence
Article Publication Date
28-Aug-2024
Dancing galaxies make a monster at the cosmic dawn
image:
Artist’s impression of the interacting galaxies observed in this research. The gravitational interactions during the merger trigger both starburst and quasar activity.
view moreCredit: Credit: ALMA (ESO/NAOJ/NRAO), T.Izumi et al.
Astronomers have spotted a pair of galaxies in the act of merging 12.8 billion years ago. The characteristics of these galaxies indicate that the merger will form a monster galaxy, one of the brightest types of objects in the Universe. These results are important for understanding the early evolution of galaxies and black holes in the early Universe.
Quasars are bright objects powered by matter falling into a supermassive black hole at the center of a galaxy in the early Universe. The most accepted theory is that when two gas-rich galaxies merge to form a single larger galaxy, the gravitational interaction of the two galaxies causes gas to fall towards the supermassive black hole in one or both of the galaxies, causing quasar activity.
To test this theory, an international team of researchers led by Takuma Izumi used the ALMA (Atacama Large Millimeter/submillimeter Array) radio telescope to study the earliest known pair of close quasars. This pair was discovered by Yoshiki Matsuoka, at Ehime University in Japan, in images taken by the Subaru Telescope. Located in the direction of the constellation Virgo, this pair of quasars existed during the first 900 million years of the Universe. The pair is dim, indicating that the quasars are still in the early stages of their evolution. The ALMA observations mapped the host galaxies of the quasars and showed that the galaxies are linked by a “bridge” of gas and dust. This indicates that the two galaxies are in fact merging.
The ALMA observations also allowed the team to measure the amount of gas, the material for new star formation. The team found that the two galaxies are very rich in gas, suggesting that in addition to more vigorous quasar activity in the future, the merger will also trigger a rapid increase in star formation, known as a “starburst.” The combination of starburst activity and vigorous quasar activity is expected to create a super-bright object in the early Universe known as a monster galaxy.
Journal
The Astrophysical Journal
Method of Research
Observational study
Subject of Research
Not applicable
Article Title
Merging Gas-rich Galaxies that Harbor Low-luminosity Twin Quasars at z = 6.05: A Promising Progenitor of the Most Luminous Quasars
Article Publication Date
29-Aug-2024
International consortium with NASA reveals hidden impact of spaceflight on gut health
International team led by UCD and McGill University reveals previously unknown effects on physiology that could shape the future of long-duration space missions.
UCD Research & Innovation
UNIVERSITY COLLEGE DUBLIN: Scientists have uncovered how spaceflight profoundly alters the gut microbiome, revealing previously unknown effects on host physiology that could shape the future of long-duration space missions.
Led by University College Dublin (UCD) and McGill University, Canada, in collaboration with NASA and an international consortium, the research offers the most detailed profile to date of how space travel impacts the gut microbes we carry into space.
Published in npj Biofilms and Microbiomes, the study used advanced genetic technologies to examine changes in the gut microbiome, colons, and livers of mice aboard the International Space Station (ISS) over three months. The findings reveal significant shifts in specific bacteria and corresponding changes in host gene expression associated to immune and metabolic dysfunction commonly observed in space, offering new insights into how these changes may affect astronaut physiology during extended missions.
Dr Emmanuel Gonzalez, McGill University, and first author of the study, said: "Spaceflight extensively alters astronaut physiology, yet many underlying factors remain a mystery. By integrating new genomic methods, we can simultaneously explore gut bacteria and host genetics in extraordinary detail and are beginning to see patterns that could explain spaceflight pathology. It’s clear we’re not just sending humans and animals to space, but entire ecosystems, the understanding of which is crucial to help us develop safeguards for future space exploration."
The international collaboration, spearheaded by UCD with NASA GeneLab’s Analysis Working Groups, is part of the recent Nature Portfolio package: The Second Space Age: Omics, Platforms and Medicine across Space Orbits - the largest coordinated release of space biology discoveries in history. These findings highlight Ireland's growing role in microbiome and space life sciences research and demonstrate how understanding biological adaptations to spaceflight can not only advance aerospace medicine but also have significant implications for health on Earth.
Professor Nicholas Brereton, UCD School of Biology and Environmental Science, and senior author of the study, said: "These discoveries highlight the intricate dialogue between specific gut bacteria and their mouse hosts, critically involved in bile acid, cholesterol, and energy metabolism. They shed new light on the importance of microbiome symbiosis to health and how these Earth-evolved relationships may be vulnerable to the stresses of space. We hope this research exemplifies how cooperative Open Science can drive discoveries with clear medical benefits on Earth, while also supporting the upcoming Artemis missions, the deployment of the Gateway deep space station, and a crewed mission to Mars."
Ames Space Biology Portfolio Scientist, NASA Ames Research Center, Jonathan Galazka said: "These discoveries are an important piece in our understanding of how spaceflight impacts astronauts and will aid the design of safe and effective missions to Earth orbit, the Moon, and Mars. Moreover, the collaborative nature of this project is a blueprint for how Open Science can accelerate the pace of discovery.”
Read the paper: 'Spaceflight alters host-gut microbiota interactions' in npj Biofilms and Microbiome.
Journal
npj Biofilms and Microbiomes
Article Title
Spaceflight alters host-gut microbiota interactions
Article Publication Date
29-Aug-2024
NASA, ESA missions help scientists uncover how solar wind gets energy
Since the 1960s, astronomers have wondered how the Sun’s supersonic “solar wind,” a stream of energetic particles that flows out into the solar system, continues to receive energy once it leaves the Sun. Now, they may have discovered the answer
NASA/Goddard Space Flight Center
image:
This conceptual image shows Parker Solar Probe about to enter the solar corona.
view moreCredit: NASA/Johns Hopkins APL/Ben Smith
Since the 1960s, astronomers have wondered how the Sun’s supersonic “solar wind,” a stream of energetic particles that flows out into the solar system, continues to receive energy once it leaves the Sun. Now, thanks to a lucky lineup of a NASA and an ESA (European Space Agency)/NASA spacecraft both currently studying the Sun, they may have discovered the answer — knowledge that is a crucial piece of the puzzle to help scientists better forecast solar activity between the Sun and Earth.
A paper published in the Aug. 30, 2024, issue of the journal Science provides persuasive evidence that the fastest solar winds are powered by magnetic “switchbacks,” or large kinks in the magnetic field, near the Sun.
“Our study addresses a huge open question about how the solar wind is energized and helps us understand how the Sun affects its environment and, ultimately, the Earth,” said Yeimy Rivera, co-leader of the study and a postdoctoral fellow at the Smithsonian Astrophysical Observatory, part of Center for Astrophysics | Harvard & Smithsonian. “If this process happens in our local star, it’s highly likely that this powers winds from other stars across the Milky Way galaxy and beyond and could have implications for the habitability of exoplanets.”
Previously, NASA’s Parker Solar Probe found that these switchbacks were common throughout the solar wind. Parker, which became the first craft to enter the Sun's magnetic atmosphere in 2021, allowed scientists to determine that switchbacks become more distinct and more powerful close to the Sun. Up to now, however, scientists lacked experimental evidence that this interesting phenomenon actually deposits enough energy to be important in the solar wind.
“About three years ago, I was giving a talk about how fascinating these waves are,” said co-author Mike Stevens, astrophysicist at the Center for Astrophysics. “At the end, an astronomy professor stood up and said, ‘that's neat, but do they actually matter?’”
To answer this, the team of scientists had to use two different spacecraft. Parker is built to fly through the Sun’s atmosphere, or “corona.” ESA's and NASA’s Solar Orbiter mission is also on an orbit that takes it relatively close to the Sun, and it measures solar wind at larger distances.
The discovery was made possible because of a coincidental alignment in February 2022 that allowed both Parker Solar Probe and Solar Orbiter to measure the same solar wind stream within two days of each other. Solar Orbiter was almost halfway to the Sun while Parker was skirting the edge of the Sun's magnetic atmosphere.
“We didn't initially realize that Parker and Solar Orbiter were measuring the same thing at all. Parker saw this slower plasma near the Sun that was full of switchback waves, and then Solar Orbiter recorded a fast stream which had received heat and with very little wave activity,” said Samuel Badman, astrophysicist at the Center for Astrophysics and the other co-lead of the study. “When we connected the two, that was a real eureka moment.”
Scientists have long known that energy is moved throughout the Sun‘s corona and the solar wind, at least in part, through what are known as "Alfvén waves.” These waves transport energy through a plasma, the superheated state of matter that makes up the solar wind.
However, how much the Alfvén waves evolve and interact with the solar wind between the Sun and Earth couldn't be measured — until these two missions were sent closer to the Sun than ever before, at the same time. Now, scientists can directly determine how much energy is stored in the magnetic and velocity fluctuations of these waves near the corona, and how much less energy is carried by the waves farther from the Sun.
The new research shows that the Alfvén waves in the form of switchbacks provide enough energy to account for the heating and acceleration documented in the faster stream of the solar wind as it flows away from the Sun.
“It took over half a century to confirm that Alfvenic wave acceleration and heating are important processes, and they happen in approximately the way we think they do,” said John Belcher, emeritus professor from the Massachusetts Institute of Technology who co-discovered Alfvén waves in the solar wind but was not involved in this study.
In addition to helping scientists better forecast solar activity and space weather, such information helps us understand mysteries of the universe elsewhere and how Sun-like stars and stellar winds operate everywhere.
“This discovery is one of the key puzzle pieces to answer the 50-year-old question of how the solar wind is accelerated and heated in the innermost portions of the heliosphere, bringing us closer to closure to one of the main science objectives of the Parker Solar Probe mission,” said Adam Szabo, Parker Solar Probe mission science lead at NASA.
By Megan Watzke
Center for Astrophysics | Harvard & Smithsonian
An artist’s concept shows Solar Orbiter near the Sun.
Credit
NASA's Goddard Space Flight Center Conceptual Image Lab
Journal
Science
Article Title
In situ observations of large-amplitude Alfvén waves heating and accelerating the solar wind
Article Publication Date
30-Aug-2024
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