For something that doesn’t emit light we can detect, black holes I just like to disguise themselves in sparkle.
In fact, some of the brightest light in the Universe comes from supermassive black holes. It’s not actually the black holes themselves; is the material around them while actively digesting large amounts of matter from their immediate environment.
Among the brightest of these swirling vortices of hot material are galaxies known as blazars. Not only do they glow with the heat of a rotating cladding, they also radiate electromagnetic radiation at inconceivable energies, directing matter into “glowing” rays converging across the cosmos.
Scientists have finally figured out the mechanism that produces the incredibly high-energy light that reached us billions of years ago: black holesjets that increase the speed of particles to mind-blowing speeds.
“This is a 40-year-old mystery we’ve solved” says astronomer Yannis Liodakis From the Finnish Center for Astronomy with ESO (FINCA). “We finally had all the pieces of the puzzle and the picture they formed was clear.”
Most galaxies in the universe are built around a supermassive black hole. These mind-blowingly large objects lie in the galactic center and sometimes do very little (for example, Bow A*The black hole at the heart of the Milky Way) and sometimes it does a lot.
This activity consists of deposition material. A huge cloud gathers around the black hole to form an equatorial disk and water around a drain. The friction and gravitational interactions active in the extreme space surrounding a black hole cause this material to heat up and shine brightly at a range of wavelengths. This is one of the sources of light from a black hole.
The other – playing in blazars – are twin jets of material ejected from the polar regions outside the black hole perpendicular to the disk. These jets are thought to be material from the inner edge of the disk, where instead of falling towards the black hole, they are ejected at very high speeds close to the speed of light, accelerating toward the poles along the outer magnetic field lines. .
For a galaxy to be classified as a blazar, these jets must be pointed almost directly at the viewer. This is us on Earth. Thanks to their extreme particle acceleration, they scatter light across the electromagnetic spectrum, including high-energy gamma and X-rays.
How exactly this jet accelerates particles to such high velocities has been a huge cosmic question mark for decades. But now, the Imaging X-ray Polarimetry Explorer (IXPE), launched in December 2021, gave scientists the key to solving the mystery. First space telescope to reveal the direction or polarization of X-rays.
“The first X-ray polarization measurements of sources in this class allowed for the first time a direct comparison with models developed by observing other light frequencies, from radio to very high-energy gamma rays.” says astronomer Immacolata Donnarumma of the Italian Space Agency.
Converted to IXPE brightest high-energy object a blazar called Markarian 501 located 460 million light-years away in the constellation of Hercules in our sky. The telescope collected data on the X-ray light emitted by the blazar jet for a total of six days in March 2022.
At the same time, other observatories were measuring light from other wavelength ranges, from radio to optics, which was the only data previously available for the Markarian 501.
The team soon noticed an interesting difference in the X-ray light. Its orientation is significantly more bent or polarized than low-energy wavelengths. And optical light became more polarized than radio frequencies.
However, the direction of polarization was the same for all wavelengths and aligned with the direction of the jet. The team found that this is consistent with models where shocks in jets produce shock waves that provide additional acceleration along the length of the jet. This acceleration, closest to the shock, is at its highest and produces X-radiation. Further along the jet, the particles lose energy, producing optics with lower energy and then radio emission with lower polarization.
“As the shock wave passes the region, the magnetic field gets stronger and the energy of the particles rises” says astronomer Alan Marscher from Boston University. “The energy comes from the energy of motion of the material that makes up the shock wave.”
It’s not clear what caused the shocks, but one possible mechanism is that the faster material in the jet traps the slower moving clumps, causing collisions. Future research may help confirm this hypothesis.
Because blazars are among the most powerful particle accelerators in the Universe and one of the best laboratories for understanding extreme physics, this research marks a very important piece of the puzzle.
Future research will continue to observe Markarian 501 and turn the IXPE to other blazars to see if similar polarization can be detected.
Research published Nature Astronomy.
