Astrophysicists solve a supermassive black hole mystery

thinking black holes as dark voids — and technically, that’s true, but their impact on the space around them produces some of the brightest light in the universe. And physicists just got one step closer to understanding why.

The supermassive black hole called Markarian 501 lies at the heart of a galaxy 457 million light-years away and is spewing jets of charged particles into space at nearly the speed of light. In the process, these particles emit powerful X-rays, and because the jets happen to be pointed toward Earth, astronomers get an excellent view.

Recently, data from a fairly new space telescope helped a team of astrophysicists work out the mechanics that make these jets shine brighter than 100 billion Suns. A University of Turku team that observed the galaxy published their work in the journal Nature.

This image from the Sloane Digital Sky Survey shows Markarian 501.By Sloan Digital Sky Survey – Sloan Digital Sky Survey, CC BY 4.0, 70790790

What’s new – Shock waves can turn a black hole’s magnetic field into a giant particle accelerator, astrophysicist Ioannis Liodakis and his colleagues from the University of Turku (Finland) have discovered, and this fuels the massive X-ray emission.

Supermassive black holes like Markarian 501 are voracious but messy eaters. As they feast on gas and dust, they also throw some of their food aside, blasting electrically charged gas, called plasma, into space at enormous speeds. And when the fast-moving plasma plows into the slower gas clouds outside the black hole’s accretion disk, the collision produces powerful shock waves.

“The particles are basically trapped in the shock, bouncing back and forth in the shock’s magnetic field,” Liodakis tells Inverse. “Each bounce gives them a little more energy until they are energetic enough to escape the shock and start radiating.”

When electrons moving at nearly the speed of light are pushed in a different direction by a magnetic field, they emit what is called synchrotron radiation. That’s why the jets shine so brightly, according to Liodakis and his colleagues.

The X-rays in the jets turned out to be highly polarized, meaning all the light waves were oriented in the same direction. Imagine a light bulb. emits light waves, but the crests and troughs of these waves are all oriented in random directions. Some of them may wave up and down, while others may oscillate left to right or diagonally. This is what light usually does. Now picture a computer screen. It also emits light waves, but the screen polarizes this light so that all the waves oscillate in the same direction from left to right.

Liodakis and colleagues used data from NASA’s Imaging X-ray Polarimetry Explorer (IXPE) space telescope to measure how polarized the light from Markarian 501’s jets is. IXPE launched in early December, just weeks before James Webb Space Telescope. Because magnetic fields play a role in the polarization of light, measuring polarization is a good way to understand the structure of magnetic fields around objects such as pulsars, neutron stars, and supermassive black holes.

If the synchrotron radiation came from random turbulence in the jets, physicists would not expect the X-rays to be polarized. But the lightweight IXPE saw actually is very polarized. This suggests that the shock wave in the plasma created a magnetic field, which acts as a giant particle accelerator, accelerating the electrons in a new direction and causing them to emit X-rays in the process.

This artist’s impression shows IXPE in Earth orbit. Its mission is scheduled to continue until December 2023.

Here is the background – Most supermassive black holes lie dormant in the centers of their galaxies. Those still actively feasting on gas and dust are rare. And those that produce relativistic jets are even rarer. they are called quasars.

Only a few of these jets are directed toward Earth, making Markarian 501 part of a very small and very interesting group of supermassive black holes (to be fair, small in astronomical terms means that Markarian 501 is one of about 2,700 known blazars.a term for quasars that happen to be aimed in our direction).

What’s next – The IXPE mission will last for at least another year, and Liodakis and his colleagues plan to use the space telescope to learn more about the mechanics behind Markarian 501’s brilliant relativistic jets. They are watching closely for “bursts,” moments when in which the already bright jets flare even brighter than usual, indicating that the supermassive black hole is more active.

“Our observations were made when Markarian 501 was in a medium activity state. These sources are always active, but there are periods of time that go into these outbursts that can make them more than 100 times brighter,” says Liodakis. “We are not sure that our findings apply to these states.”

The researchers also want to learn more about the particles that are accelerated to nearly the speed of light to produce the jets. According to physicists’ current models of how the universe works, these particles should all be electrons — but we don’t know for sure.

“Generally speaking, we are also not sure what the composition of the jets is, that is, what is the mixture of particles that make up the jet, and how blazars produce gamma rays,” says Liodakis. “We hope that with our new observations we can solve these mysteries as well.”

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