Researchers have made a groundbreaking discovery showing that microquasars with low-mass stars can effectively accelerate particles, which significantly alters how scientists interpret the presence of gamma rays in the universe.
Researchers have made a groundbreaking discovery showing that microquasars with low-mass stars can effectively accelerate particles, which significantly alters how scientists interpret the presence of gamma rays in the universe.
Our planet is constantly bombarded by particles from space. While we’re typically aware of rocky meteorites from our solar system that create spectacular shooting stars, it’s the tiniest particles that are crucial for scientists to comprehend the universe. Subatomic particles like electrons and protons that travel from interstellar space are among the fastest particles recorded and are referred to as cosmic rays.
The origins and acceleration mechanisms behind the most intense of these cosmic particles remain one of astrophysics’ greatest enigmas. High-speed matter jets produced by black holes are considered ideal locations for particle acceleration, yet the specifics of how and under which conditions this occurs are still unclear. The strongest jets found within our Galaxy are produced by microquasars, which consist of a stellar-mass black hole and a standard star orbiting together. When they come close, the black hole begins to gradually consume its companion star, generating jets from the area surrounding it.
Recent years have seen increased evidence suggesting that jets from microquasars serve as effective particle accelerators. However, it remains uncertain how much these systems collectively contribute to the overall quantity of cosmic rays in the Galaxy. Understanding whether all microquasars can accelerate particles or if only a select few can is key to answering this question.
Microquasars are usually categorized based on the mass of the star in the system as either “low-mass” or “high-mass,” with lower-mass types being far more common. Until now, evidence for particle acceleration had only been observed in high-mass microquasars. For instance, SS 433, a well-known microquasar, has been found to be one of the Galaxy’s strongest particle accelerators and contains a star roughly ten times heavier than the Sun. As a result, it was widely assumed that low-mass microquasars lacked the power to generate gamma rays. However, Dr. Laura Olivera-Nieto from the Max-Planck Institute for Nuclear Physics in Heidelberg, Germany, alongside Dr. Guillem Martí-Devesa from the University of Trieste, Italy, have challenged this assumption. They utilized 16 years’ worth of data from the Large Area Telescope aboard NASA’s Fermi satellite to detect a faint gamma-ray signal in line with the location of GRS 1915+105, a microquasar featuring a star lighter than the Sun. This gamma-ray signal is recorded with energies exceeding 10 GeV, suggesting the system could accelerate particles to even greater energies.
The findings propose a scenario where protons gain speed within the jets, after which they escape and interact with surrounding gas to create gamma-ray photons. In their study, published in the Astrophysical Journal Letters, they also reference data from Japan’s Nobeyama 45-meter radio telescope, indicating that there is sufficient gas surrounding the source to support this theory.
This discovery demonstrates that even microquasars with low-mass stars can engage in particle acceleration. Given that this is the most common type of microquasar, this finding has significant ramifications for the anticipated contribution of these systems to the cosmic ray population in our Galaxy. However, further detections and multi-wavelength studies will be necessary to clarify why certain systems can effectively accelerate particles while others cannot.
