A stormy glow in a distant galaxy could change our view of black holes

(ORDO NEWS) — Something strange is happening in the galaxy known as 1ES 1927+654: in late 2017, for reasons scientists could not explain, the supermassive black hole at the center of this galaxy experienced a massive identity crisis.

Within a few months, this already bright object, belonging to a class of black holes known as active galactic nuclei (AGNs), suddenly became much brighter – in visible light, it glowed almost 100 times brighter than normal.

An international team of astrophysicists, including scientists from the University of California at Boulder, may have identified the reason for this change.

It appears that the magnetic field lines passing through the black hole have flipped upside down, causing a rapid but brief change in the object’s properties. It was as if the compasses on Earth suddenly started pointing south instead of north.

“Normally, we expect black holes to evolve over millions of years,” Stsepi said. “But these objects, which we call shapeshifting AGNs, evolve on very short time scales. Their magnetic fields could be the key to understanding this rapid evolution.”

Stsepi, as well as JILA fellows Mitchell Begelman and Jason Dexter, first suggested that such a magnetic somersault is possible in 2021.

A new study supports this idea. In it, a team led by Sibasish Lah of NASA’s Goddard Space Flight Center collected the most comprehensive data on this distant object.

The team used observations from seven telescopes on the ground and in space, tracking the radiation from 1ES 1927+654 as the AGN flashed bright and then dimmed again.

Observations show that the magnetic fields of supermassive black holes may be much more dynamic than scientists previously thought. And, as Begelman pointed out, this AGN is probably not alone.

“If we saw it in one case, then we will definitely see it again,” said Begelman, professor in the Department of Astrophysical and Planetary Sciences (APS). “Now we know what to look for.”

An unusual black hole

Begelman explained that AGNs are generated by one of the most extreme physics in the known universe.

These monsters arise when supermassive black holes begin to draw in huge amounts of gas from the galaxies around them.

Like water swirling around a drain, this material spins faster and faster the closer it gets to the black hole, forming a bright “accretion disk” that generates intense and varied radiation that scientists can observe from billions of light-years away.

These accretion disks also give rise to a curious feature: They generate strong magnetic fields that wrap around the central black hole and, like the Earth’s own magnetic field, point in a certain direction, such as north or south.

“The Event Horizon Telescope and other observations are increasingly suggesting that magnetic fields may play a key role in how gas falls into black holes,” says APS assistant professor Dexter.

It could also affect how bright the AGN is. similar to the one at the center of 1ES 1927+654 appears in telescopes.”

By May 2018, this object’s burst of energy had peaked, throwing out more visible light, but also many times more ultraviolet radiation than usual. Around the same time, AGN X-ray emissions began to dim.

“Typically, if ultraviolet increases, then X-rays also increase,” Stsepi said. “But here the ultraviolet has gone up and the X-rays have gone down a lot. It’s very unusual.”

Researchers at JILA proposed a possible response to this unusual behavior in a paper published last year.

Begelman explained that these objects are constantly drawing in gas from outer space, and some of that gas also carries magnetic fields.

If the AGN attracts magnetic fields that point in the direction opposite to its own to the south instead of the north, for example then its own field is weakened. This is similar to how a tug-of-war team in one direction can negate the efforts of opponents pulling in the other direction.

According to the JILA team’s theory, the black hole’s magnetic field became so weak that it flipped it upside down.

“Essentially, you’re completely destroying the magnetic field,” Begelman said.

In the new study, NASA-led scientists set out to collect as many observations of 1ES 1927+654 as possible.

The gap between ultraviolet and X-ray radiation turned out to be a “smoking gun”. Astrophysicists suspect that the weakening of the magnetic field could cause just such a change in the physics of AGN – shifting the accretion disk of a black hole so that it throws out more ultraviolet and visible light and, paradoxically, less X-rays. No other theory could explain what the researchers observed.

AGN itself went silent and returned to normal by the summer of 2021. But Szepi and Begelman see the event as a natural experiment – a way to get close to a black hole to learn more about how these objects feed bright beams of radiation.

This information, in turn, could help scientists know which signals they should look for in order to detect more strange AGNs in the night sky.

“Perhaps there are some similar events that have already been observed – we just don’t know about them yet,” Stsepi said.

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