Here’s Why Some Supermassive Black Holes Shine So Brightly

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 the jet of such a blazar distort magnetic fields that accelerate the escape of particles almost at the speed of light, astronomers report on November 23 at Nature. Studying such extreme accelerations can help probe fundamental questions in physics that cannot be studied otherwise.

Blazars are active black holes that shoot jets of high-energy particles toward Earthcausing them to appear as points of light millions or even billions of light-years away (SN: 07/14/15). Astronomers knew the jets’ extreme speeds and tight columnar beams had something to do with the shape of the magnetic fields around black holes, but the details were hazy.

Enter Imaging X-Ray Polarimetry Explorer, or IXPE, an orbiting telescope launched in December 2021. Its mission is to measure the polarization of X-rays, or how light from X-rays is oriented as it travels through space . While previous bland observations of polarized radio waves and optical light probed parts of jets days to years after their acceleration, polarized X-rays can see into the active core of a blazar (SN: 03/24/21).

“In X-rays, you’re really looking at the heart of particle acceleration,” says astrophysicist Yannis Liodakis from the University of Turku in Finland. “You really look at the area where everything is happening.”

In March 2022, IPXE examined a particularly bright blazar called Markarian 501, located about 450 million light-years from Earth.

Liodakis and his colleagues had two main ideas for how magnetic fields could accelerate Markarian 501’s jet. The particles could be stimulated by magnetic reconnection, where magnetic field lines break, reform and connect with other other lines nearby. The same process accelerates plasma on the sun (SN: 11/14/19). If this were the particle acceleration engine, the polarization of light should be the same along the jet in all wavelengths, from radio waves to X-rays.

Another option is a shock wave throwing particles into the jet. At the shock site, the magnetic fields suddenly change from turbulent to orderly. This switch could send particles flying away, like water through the nozzle of a hose. As the particles move away from the shock site, the turbulence should take over. If a shock was responsible for the acceleration, the short-wavelength X-rays should be more polarized than the longer-wavelength optical and radio light, as measured by other telescopes.

An illustration of the IXPE spacecraft observing polarized X-rays from a blazar and its jet
The IXPE spacecraft (shown) observed polarized X-rays from a blazar and its jet. The inset illustrates how the particles in the jet strike a shock wave (white) and are propelled at extreme speeds, emitting high-energy X-rays. As they lose energy, the particles emit lower energy light in the visible, infrared, and radio (violet and blue) wavelengths, and the jet becomes more turbulent.Pablo Garcia/MSFC/NASA

That’s exactly what the researchers saw, says Liodakis. “We got a clear result,” he says, which favors the shock wave explanation.

There is still work to be done to understand the details of particle circulation, says astrophysicist James Webb of Florida International University in Miami. On the one hand, it is unclear what would produce the shock. But “it’s a step in the right direction,” he says. “It’s like opening a new window and looking at the object freshly, and now we see things that we hadn’t seen before. It’s very exciting.”

Leave a Reply

Your email address will not be published. Required fields are marked *