For the first time, astronomers have observed how certain supermassive black holes launch jets of high-energy particles into space — and the process is shocking.
Shock waves propagating along a jet of such blazar Convert magnetic fields to accelerate escaping particlesAstronomers report November 23rd at almost the speed of light Nature. Studying such extreme acceleration can help probe fundamental physics questions that can’t be studied any other way.
Blazars are black holes that are actively active. Send high-energy particles in jets towards EarthThey can appear bright spots even from billions or millions of light-years distant, thus making them look like bright spots.SN: 7/14/15). Astronomers knew that the jets’ extreme speeds and tight columnated beams had something to do with the shape of magnetic fields around black holes, but the details were fuzzy.
The Imaging X-Ray Polarimetry Explorer (or IXPE), an orbiting telescope that was launched in December 2021, is now available. Its mission is to determine X-ray polarization. This is how Xray light travels through space. However, previous blazar observations Polarized radio waves and optical lights probed parts of jets days to years after they’d been accelerated, polarized X-rays can see into a blazar’s active core (SN: 3/24/21).
“In X-rays, you’re really looking at the heart of the particle acceleration,” says astrophysicist Yannis Liodakis of the University of Turku in Finland. “You’re really looking at the region where everything happens.”
IPXE viewed Markarian 501 in March 2022. It is approximately 450 million light years from Earth.
Liodakis and colleagues had two main ideas for how magnetic fields might accelerate Markarian 501’s jet. The magnetic reconnection process, in which magnetic field lines are broken, reform, and connect to other lines nearby, could increase particle kinetic energy. Similar process Plasma accelerates on the sun (SN: 11/14/19). If this was the particle acceleration engine then the polarization should be the same along all wavelengths of the jet, radio waves and X-rays.
A shock wave can also shoot particles down the jet. The shock causes the magnetic fields to suddenly change from chaotic and ordered. The switch could cause particles to zoom away like water passing through a nozzle. Turbulence should then take control as the particles leave the shock area. If the shock caused acceleration, shorter wavelength Xrays should be more Polarized than radio and optical light of longer wavelengths, as measured by other telescopes.
That’s exactly what the researchers saw, Liodakis says. “We got a clear result,” he says, that favors the shock wave explanation.
James Webb, an astrophysicist from Florida International University in Miami says that it is still difficult to determine how the particles flow. For one, it’s not clear what would produce the shock. But “this is a step in the right direction,” he says. “It’s like opening a new window and looking at the object freshly, and we now see things we hadn’t seen before. It’s very exciting.”
