Markarian 421, a supermassive black hole situated in the constellation Ursa Major and positioned around 400 million light-years away from Earth, has become a subject of fascination for astronomers. Firing a high-energy particle jet aimed directly at our planet, this enigmatic entity has been at the center of attention for NASA’s IXPE (X-ray Polarimetry Explorer), which has recently unveiled several mysteries surrounding it. Supermassive black holes like Markarian 421 are colossal objects found at the hearts of galaxies, exhibiting gravitational forces so intense that even light cannot escape. These cosmic giants, millions or billions of times the mass of our Sun, are thought to have grown over billions of years through the merging of smaller black holes and the accretion of gas. They are often associated with powerful phenomena such as active galactic nuclei (AGNs) and quasars, which release vast amounts of energy as matter falls into the black hole and emits intense radiation.
The high-speed stream of matter and radiation ejected from the vicinity of Markarian 421, known as its jet, is a result of the interaction between the black hole’s strong magnetic field and the surrounding rotating disk of material, known as the accretion disk. Remarkably, Earth finds itself in the line of sight of this jet, making Markarian 421 a special type of supermassive black hole system called a blazar. Blazars are distinguished by their brightness and variability, emitting copious amounts of gamma rays and X-rays due to the phenomenon of relativistic beaming, which boosts the radiation from the jet.