Ar-Rehman

First Microblazar discovered in The Milky Way, may produce the fastest particles in the Galaxy

Astronomers have found, for the first time, a microblazar in our own galaxy. The object is a miniature version of what happens when a supermassive black hole produces an energetic jet and shoots right towards Earth. It is made of a star and a black hole with a jet pointing right at Earth. The impression shows a jet pointing to the side and another invisible to us slamming into a gas cloud. An international team of astronomers from ASTRON, JIVE, the University of Amsterdam and other institutions has found the first so-called "microblazar" in the Milky Way. This stellar system is composed of a massive star and a black hole with a jet that is pointed toward Earth. The researchers also identified the region where the jet hits a molecular cloud as a place where particles are accelerated to ultra-high energies, likely up to petaelectronvolts. This would make microblazars one of the most powerful particle accelerators in the galaxy. First convincing microblazar, an orbiting system featuring a star and a black hole named IRAS 18293−0941, it fires a jet of matter nearly straight toward Earth at three-quarters the speed of light. Located in our galaxy, it consists of a companion star and a stellar-mass black hole pulling in material and shooting twin jets. One jet points almost directly at Earth (brightened by relativistic effects), while the opposite, invisible jet slams into a dense molecular cloud.

The object, called IRAS 18293−0941, also has a black hole, but a stellar-mass one. It weighs about 10 times the mass of our Sun, and it has a stellar companion that goes around it every 11 days. The black hole steals material from the companion, which first ends up in an accretion disk and eventually in the black hole. Part of that material is shot out into the galaxy as two jets shooting in in opposite directions. As luck would have it, one points almost right at us. Black holes can attract matter from their surroundings, powering jets of matter and radiation which escape from their poles with extremely high energies. When such a jet is pointed toward Earth, it makes the object appear much brighter. In the case of supermassive black holes, which are found at the center of many galaxies, such blazars have been studied for a long time. Now, for the first time, astronomers have identified a stellar-sized black hole in the Milky Way whose jet is pointed toward Earth. It is the first microblazar found. Where that rear jet impacts the gas and dust cloud, it creates a brilliant gamma-ray hotspot which accelerates particles to nearly the speed of light with energies up to peta electron volts.

Radio imaging has revealed not only the jet but also its interaction with its surroundings. First, the jet crosses a region of about 100 light-years (590 trillion miles), where it has already "cleared" the so-called interstellar medium. After that, it hits a relatively dense molecular cloud, which consists mainly of molecular hydrogen and dust. The ones from regular blazars can extend for millions of light-years, but they are also at an enormous distance away. This one is roughly 12,000 light-years from Earth. The inforgraphic shows the black hole stealing material, producing two jets and one of them hitting a gas cloud where particles are accelerated to incredible energies. The interaction creates a bright spot on the cloud where the interstellar material is ionized and the dust is heated. Here, particles are accelerated to nearly the speed of light, with energies up to petaelectronvolts. This makes the microblazar one of the most powerful particle accelerators in the Milky Way, about 100 times stronger than the Large Hadron Collider, the strongest particle accelerator on Earth. Microblazars have been predicted for about 30 years. This discovery not only sheds new light on the origins of the most energetic particles in the Milky Way, but it also teaches astronomers about similar but larger systems already found in other galaxies. "This discovery allows us to study remote blazars created by distant supermassive black holes," says Benito Marcote, senior support scientist at ASTRON and JIVE and one of the paper's authors. "Those blazars are too remote to be resolved in our images. Having an analog object in our galaxy allows for detailed study of blazar physics."

This particle acceleration is roughly 100 times more powerful than Earth's Large Hadron Collider, making it a premier candidate for producing the fastest particles in the Milky Way. Because full-scale supermassive blazars in distant galaxies are too remote to image clearly, having a close-range analog allows astronomers to study blazar physics and galaxy evolution in fine detail. The object, IRAS 18293−0941, consists of a black hole about 10 times the mass of our sun and a hot, massive star orbiting each other every 11 days. The jets are produced by matter that the black hole attracts from the star. First, this matter is "collected" in a disk surrounding the black hole. Just before it finally falls into the black hole, part of the matter is ejected through powerful jets at both poles of the black hole. This microblazar is not the most powerful particle accelerator in the universe, but it might be one of the most powerful in our galaxy, since there is no blazar at the center of the Milky Way. The particles are moving just a tiny fraction slower than the speed of light, and they might well be the fastest particles in the galaxy. It is only the microblazar nature of IRAS 18293−0941 that is newly discovered. The object itself was spotted in 1983 by the now many-decades-defunct IRAS satellite, an early infrared space telescope. Astronomers' attention was drawn to the object because, in many radio observations, it appeared to have a bright, compact core and radio emission on one side only, hinting at the existence of such a jet.

An extensive observational campaign was launched using radio telescopes (for high-resolution images and showing jet interactions), optical telescopes (for spectra and measuring velocities in the system), X-ray and gamma-ray telescopes (for probing the hot plasma around the black hole), and infrared images (showing the warm dust around the system). "This was a genuinely multiwavelength observational campaign," Marcote says. All of this was key to fully capturing its behavior and its environment. Cosmic particles with energies reaching up to petaelectronvolts have been detected by cosmic ray observatories on Earth, but for more than a century, it has remained unclear where these particles are accelerated to such high energies. One candidate accelerator is the shock wave created by a powerful black hole jet hitting the interstellar medium, as seen in the microblazar. In this study, the scientists found that the bright spot in the molecular cloud coincides with a gamma-ray signature of high-energy particles. Marcote is excited that the microblazar's jet can be associated with this elusive class of particles. "We are planning more observations of the hot spot where the jet hits the interstellar medium," Marcote says. "Better characterizing this region and how the material gets heated and ionized would have strong implications for galactic star formation, which happens in molecular clouds. It can also teach us how microblazars affect the structure and evolution of galaxies like the Milky Way."

“This discovery highlights the power of studying the Universe with different kind of telescopes at the same time, because none of the individual telescopes could have told the entire story,” added coauthor Jakob van den Eijnden, from the University of Amsterdam. "It is a great showcase of the international team effort that is at the core of modern astronomy." Alfredo has a PhD in Astrophysics and a Master's in Quantum Fields and Fundamental Forces from Imperial College London.