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Our planet is constantly bombarded by particles from outer space. While most of us are familiar with the sight of rocky meteorites - those shooting stars that light up the night sky - it's the smaller particles that hold the key to unlocking the mysteries of the universe. Cosmic rays, which include high-speed subatomic particles like electrons and protons from interstellar space and beyond, are by Robert Schreiber
Berlin, Germany (SPX) Jan 30, 2025
Our planet is constantly bombarded by particles from outer space. While most of us are familiar with the sight of rocky meteorites - those shooting stars that light up the night sky - it's the smaller particles that hold the key to unlocking the mysteries of the universe. Cosmic rays, which include high-speed subatomic particles like electrons and protons from interstellar space and beyond, are among the fastest particles known to humankind.
The origins and acceleration processes behind the most energetic cosmic rays remain a significant enigma in astrophysics. One possible source of these fast-moving particles lies in the powerful jets ejected from black holes. However, the precise mechanisms that allow these jets to accelerate particles remain unclear. These jets are most commonly observed in microquasars, binary systems consisting of a stellar-mass black hole and a companion star. As the black hole draws in matter from the star, it launches these jets, which could potentially accelerate particles to extremely high energies.
Recent research has suggested that the jets produced by microquasars could be significant accelerators of cosmic rays, but it was uncertain how much these systems contribute to the total cosmic ray flux in the Milky Way. To answer this, researchers need to determine whether all microquasars are capable of accelerating particles, or if only certain systems are efficient at doing so.
Microquasars are typically classified based on the mass of the star in the system, with low-mass systems being much more common than high-mass systems. For a long time, evidence of particle acceleration had only been observed in high-mass microquasars. One example is SS 433, a microquasar containing a star roughly ten times the mass of our Sun, which had been identified as one of the most powerful cosmic ray accelerators in the galaxy. This led to the assumption that low-mass microquasars simply didn't have the necessary power to produce gamma rays.
However, a groundbreaking discovery by Dr. Laura Olivera-Nieto from the Max-Planck-Institut fur Kernphysik (MPIK) in Heidelberg, Germany, and Dr. Guillem Marti-Devesa from the Universita di Trieste, Italy, challenges this assumption. By analyzing 16 years of data from NASA's Fermi Large Area Telescope, the researchers identified a faint gamma-ray signal associated with GRS 1915+105, a microquasar with a star smaller than the Sun. The detected gamma rays have energies exceeding 10 GeV, suggesting that this system could accelerate particles to even higher energies.
The researchers believe that protons are being accelerated in the jets of GRS 1915+105, where they escape and interact with nearby gas, producing gamma-ray photons in the process. This hypothesis is supported by additional data from the Nobeyama 45-meter radio telescope in Japan, which indicates that there is sufficient surrounding gas to facilitate this interaction.
This discovery proves that low-mass microquasars can also act as efficient particle accelerators, a finding that could have significant implications for our understanding of cosmic ray sources. Because low-mass systems are far more common than their high-mass counterparts, this could mean that microquasars as a whole contribute more to the cosmic ray content of our galaxy than previously thought. However, further observations and multi-wavelength studies will be needed to understand why only certain systems accelerate particles effectively.
Research Report:Persistent GeV Counterpart to the Microquasar GRS 1915+105
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Max-Planck-Institut fur Kernphysik
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