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Scientists Explore Differences in Extragalactic Jets Emerging From Black Holes

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A team of international astrophysicists have uncovered new insights into the mystery behind the differences in the appearances of extragalactic jets emerging from the environments of supermassive blackholes. They showed that the plasma composition can affect the appearances of these jets. This may help to unravel the mystery of matter content of relativistic jets.

At the centers of many distant galaxies reside supermassive black holes with masses millions to billions of times that of our Sun. These black holes don’t just eat everything, but can also act like powerful engines, launching narrow beams of plasma and energy known as “jets” that shoot into space at nearly the speed of light. These extragalactic jets can travel for thousands of light-years and emit radiation ranging from low-energy radio waves to high-energy gamma rays.

For a long time, astronomers have been wondering about a noticeable difference in radio images of extragalactic jets, first identified by Fanaroff & Riley in 1974. They broadly classified radio jets into two main categories: FR I & FR II. The FR I jets are “core-brightened,” meaning they are brightest near the core and gradually fade into diffuse structures as they move outward. The FR II jets, on the other hand, are “edge-brightened,” meaning they are fainter near the core but stay tightly focused over long distances until they hit the surrounding gas, creating giant “hot spots” at their tips.

Scientists have for long continued to debate whether this difference is due to the black hole itself, the environment around it, or the intrinsic properties of the jet, such as its speed, temperature, and magnetic strength, etc.

A new research published in The Astrophysical Journal by Mr. Priyesh Kumar Tripathi, Dr. Indranil Chattopadhyay, and Mr. Sanjit Debnath from Aryabhatta Research Institute of Observational Sciences (ARIES), Dr. Raj Kishore Joshi from the Nicolaus Copernicus Astronomical Center, Poland, Dr. Ritaban Chatterjee from Presidency University, Kolkata, and Dr. M. Saleem Khan from MJPRU Barelly, used advanced computer simulations to reveal that the secret to these differences may be due to the jet’s composition and the environment it travels through. The research team performed large 3D magnetohydrodynamic (MHD) simulations of these jets at kiloparsec scales using a numerical simulation code developed by the Numerical and Theoretical Astrophysics Group at ARIES. Notably, this code incorporates a relativistic equation of state, which can accurately handle a very large range of temperatures encountered at different regions of the jet.

The team discovered that a phenomenon called the “kink instability” is a major player in shaping these powerful, narrow jets, causing wiggles (small bend). In space, if this wiggle grows faster than the jet can flow forward, the jet beam disrupts, spreading its energy into a faint, diffuse cloud – the classic look of an FR I jet. Astrophysical jets aren’t made of ordinary matter. Instead, they are composed of plasma, a soup of charged particles including electrons, positrons (the antimatter twin of electrons), and sometimes heavier particles like protons. One of the study’s most significant findings is that the composition of jet plasma can determine its fate.

Jets can be made of mostly electrons and protons (Hadronic plasma), a mixture that includes positrons (the antimatter twin of the electron– Leptonic/Mixed plasma).

Fig: 3D Volume rendering of the jet tracer for electron-proton and mixed plasma jet

The simulations showed that jets rich in positrons (lepton-rich) are relatively hotter, causing them to expand and slow down. They often can’t stay straight and get twisted by the kink instability. As a result, they form a diffuse, FR I–like structure, where the jet gradually fades instead of ending in a bright hotspot. In contrast, jets composed primarily of electrons and protons were more likely to transition between morphologies, thereby changing their identity. This suggests that what we see through our telescopes might just be a snapshot of a long, evolving cosmic process.

 

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Where do high-energy particles that endanger satellites, astronauts, airplanes come from?

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For decades, scientists have been trying to solve a vexing problem about the weather in outer space: At unpredictable times, high-energy particles bombard the earth and objects outside the earth’s atmosphere with radiation that can endanger the lives of astronauts and destroy satellites’ electronic equipment. These flare-ups can even trigger showers of radiation strong enough to reach passengers in airplanes flying over the North Pole. Despite scientists’ best efforts, a clear pattern of how and when flare-ups will occur has remained enduringly difficult to identify.

This week, in a paper in The Astrophysical Journal Letters, authors Luca Comisso and Lorenzo Sironi of Columbia’s Department of Astronomy and the Astrophysics Laboratory, have for the first time used supercomputers to simulate when and how high-energy particles are born in turbulent environments like that on the atmosphere of the sun. This new research paves the way for more accurate predictions of when dangerous bursts of these particles will occur.

“This exciting new research will allow us to better predict the origin of solar energetic particles and improve forecasting models of space weather events, a key goal of NASA and other space agencies and governments around the globe,” Comisso said. Within the next couple of years, he added, NASA’s Parker Solar Probe, the closest spacecraft to the sun, may be able to validate the paper’s findings by directly observing the predicted distribution of high-energy particles that are generated in the sun’s outer atmosphere.

NASA/Photo: Nasa.gov

In their paper, “Ion and Electron Acceleration in Fully Kinetic Plasma Turbulence,” Comisso and Sironi demonstrate that magnetic fields in the outer atmosphere of the sun can accelerate ions and electrons up to velocities close to the speed of light. The sun and other stars’ outer atmosphere consist of particles in a plasma state, a highly turbulent state distinct from liquid, gas, and solid states. Scientists have long believed that the sun’s plasma generates high-energy particles. But particles in plasma move so erratically and unpredictably that they have until now not been able to fully demonstrate how and when this occurs.

Using supercomputers at Columbia, NASA, and the National Energy Research Scientific Computing Center, Comisso and Sironi created computer simulations that show the exact movements of electrons and ions in the sun’s plasma. These simulations mimic the atmospheric conditions on the sun, and provide the most extensive data gathered to-date on how and when high-energy particles will form.

The research provides answers to questions that scientists have been investigating for at least 70 years: In 1949, the physicist Enrico Fermi began to investigate magnetic fields in outer space  as a potential source of the high-energy particles (which he called cosmic rays) that were observed entering the earth’s atmosphere. Since then, scientists have suspected that the sun’s plasma is a major source of these particles, but definitively proving it has been difficult.

Aldrin walks on the surface of the Moon during Apollo 11(NASA)

Comisso and Sironi’s research, which was conducted with support from NASA and the National Science Foundation, has implications far beyond our own solar system. The vast majority of the observable matter in the universe is in a plasma state. Understanding how some of the particles that constitute plasma can be accelerated to high-energy levels is an important new research area since energetic particles are routinely observed not just around the sun but also in other environments across the universe, including the surroundings of black holes and neutron stars.

While Comisso and Sironi’s new paper focuses on the sun, further simulations could be run in other contexts to understand how and when distant stars, black holes, and other entities in the universe will generate their own bursts of energy.

“Our results center on the sun but can also be seen as a starting point to better understanding how high-energy particles are produced in more distant stars and around black holes,” Comisso said. “We’ve only scratched the surface of what supercomputer simulations can tell us about how these particles are born across the universe.”