Some of the brightest cosmic objects are blazars. They consist of a supermassive black hole capable of generating two powerful jets perpendicular to the disk and feeding material swirling around it within a disk. A blazar looks unusually bright when viewed through our telescopes because one of its powerful jets of fast-moving particles is pointed directly at Earth. How the particles in these jets reach such high energies has long been a mystery to scientists.
Astronomers have made progress in their search for an explanation thanks to NASA's Imaging X-ray Polarimetry Explorer, or IXPE. The best explanation for particle acceleration is a shock wave in a jet, according to a new study published November 23 in the journal Nature by a large international team.
Yannis Liodakis, lead author of the study and an astronomer at ESO and the Finnish Center for Astronomy FINCA, said, “This is a 40-year-old mystery that we have answered. “When we finally put all the pieces of the puzzle together, the picture they drew was very clear.”
Launched on December 9, 2021, the IXPE satellite in Earth orbit, a joint project of NASA and the Italian Space Agency, offers a unique type of data never before obtained from space. In these new data, the polarization of X-ray light was measured, meaning the IXPE can now determine the average strength and direction of the electric field of X-ray light waves.
Because the atmosphere absorbs X-rays from space, telescopes on Earth cannot determine the direction of the electric field or degree of polarization in X-ray radiation.
Immacolata Donnarumma, IXPE project scientist at the Italian Space Agency, explained that he made a direct comparison with the models created by examining different frequencies of light, from radio to very high-energy gamma rays.
“IXPE will continue to provide new evidence as existing data are reviewed and new data collected in the future.”
The current study focused on Markarian 450, a blazar located about 501 million light-years from Earth in the constellation Hercules. He did this using IXPE. The active black hole system of this massive elliptical galaxy is located at its core.
In early March 2022, IXPE observed Markarian 501 for three days before returning two weeks later.
Other orbiting and Earth telescopes were used by astronomers during these observations to collect data about the blazar in a variety of light spectra, including radio, optical, and X-ray.
For the first time, researchers have been able to get this perspective on X-rays emitted closer to the particle acceleration source of a blazar. While other studies have previously examined the polarization of low-energy light from blazars, this is the first time scientists have been able to do so.
IXPE research team leader Alan Marscher of Boston University described the addition of X-ray polarization to the radio, infrared and optical polarization arsenal as a "game-changing development".
Researchers discovered that radio waves are more polarized than optical waves, which are more polarized than X-rays. However, the orientation of polarized light was consistent across all measured light wavelengths and coincided with the path of the jet.
After comparing their results with theoretical models, the team of astronomers discovered that their data most closely fits a scenario where a shock wave accelerates jet particles. A shock wave is produced when anything moves faster than the speed of sound in the surrounding material, for example when a supersonic airplane passes through Earth's atmosphere.
The aim of the research was not to examine the still unknown origins of the shock waves. But researchers believe it's a change in its flow that makes part of the jet supersonic. This may be the result of severe pressure surges in the jet barrier or high-energy particle collisions within the jet.
According to Marscher, when the shock wave passes through the region, the magnetic field gets stronger and the particle energy increases. “The material that creates the energy of motion of the shock wave is where the energy comes from.”
Because of their high energies, X-rays are initially produced as particles move outward. As they move away from the shock region through the turbulent region, they begin to lose energy, causing them to emit less energetic light such as optical and then radio waves. This is similar to how a waterfall makes the water flow more turbulent; however, in this case, the source of turbulence is magnetic fields.
The Markarian 501 blazar will continue to be observed by researchers to determine whether polarization has developed over time. During its main two-year mission, IXPE will also examine a wider range of blazars, uncovering more enduring mysteries about the universe. In Marscher's words, "this is part of humanity's evolution towards an understanding of nature and all of its exoticism."
Source: scitechdaily – DOI: 10.1038/s41586-022-05338-0
Günceleme: 25/11/2022 14:34