Photo: B. Marcote (JIVE/ASTRON)
Astronomers have identified the first convincing example of a microblazar in the Milky Way, a black-hole-powered particle accelerator that produces relativistic plasma jets aimed almost directly toward Earth. The system, known as IRAS 18293−0941, is located about 12,000 light-years away.
IRAS 18293−0941 is a binary system consisting of a stellar-mass black hole and a massive companion star. The black hole pulls material from the star, with some of that matter being channeled toward its poles and expelled in the form of twin jets travelling at about three-quarters of the speed of light. The two objects orbit each other every 11.38 days.
Microblazars are considered smaller versions of blazars. Ordinary blazars are powered by supermassive black holes millions or billions of times more massive than the Sun, while microblazars contain much smaller stellar-mass black holes. In the case of IRAS 18293−0941, the black hole is estimated to have a mass of up to a few hundred solar masses.
The existence of microblazars in the Milky Way had been predicted for decades, but finding one proved difficult because the system is hidden behind a dense layer of interstellar gas and dust.
“Everything about IRAS 18293−0941 was hiding in plain sight,” said Josep Martí of the University of Jaén, who led the research. “It sits behind so much dust that it is essentially invisible in ordinary optical images. It was catalogued decades ago and then more or less forgotten.”
How the microblazar was identified
Astronomers first detected a subtle variation in the light of the system’s companion star. The periodic flickering revealed the binary orbit and indicated that researchers were viewing the system almost face-on.
Radio observations then revealed a bright one-sided jet. The second jet could not be seen directly because it was moving away from Earth, while the approaching jet was enhanced by relativistic effects.
High-resolution observations with the European VLBI Network (EVN) confirmed the jet’s orientation and showed that it originated from IRAS 18293−0941 rather than from a distant background galaxy that happened to lie in the same direction. Gaia observations provided an additional confirmation of the system’s position.
Further observations with the MeerKAT radio telescope in South Africa revealed a much larger structure surrounding the system. The jet has created a roughly 100-light-year-wide bubble in the interstellar medium, with a bright hotspot where the receding jet interacts with surrounding material.
A natural particle accelerator
The system is of particular interest because its jets can accelerate particles to extremely high energies. Researchers believe the nearby high-energy gamma-ray source LHAASO J1831-1007u* may be connected to the same activity.
The discovery provides astronomers with a relatively nearby laboratory for studying relativistic jets and how black holes transfer enormous amounts of energy into their surroundings.
The research has been accepted for publication in Astronomy & Astrophysics and is also available as a preprint on arXiv.
