Astronomers Just Found a Radio Galaxy That Turned Into a Blazar : ScienceAlert

Astronomers have observed a rare case of a galaxy changing shape.

A few decades ago, an object some 630 million light-years away named PBC J2333.9-2343 was classified as a giant radio galaxy. It hurled large radio-emitting structures perpendicular to our line of sight, formed by colossal jets that once erupted from the galactic center.

More recent observations, however, reveal that the galaxy’s core has reignited and is now directing its jet directly at us.

There is nothing to be alarmed about; in fact, it’s quite common. So common, in fact, we have a name for it; a joke. With its new classification, the PBC J2333.9-2343 blazar could give us a better understanding of how galaxies can transform, even on the scale of human times.

Galaxies come in different shapes and sizes, but they also have different levels of activity depending on the activity of the supermassive. black holes to their nuclei. The Milky Way, for example, is a relatively peaceful galaxy; our supermassive black hole is fairly inactive, accrete only a small amount of matter.

A supermassive black hole positively absorbing dust and gas from its surrounding space looks very different. This material forms a torus and a disk that surround the black hole; the extreme gravitational and frictional forces at play cause this disc to glow with light across the entire electromagnetic spectrum.

From the inner edge of the disc, matter falls onto the black hole, as water swirling in a sewer. But all this material does not end up beyond the event horizon. Some of it is channeled and accelerated along the magnetic field lines outside the black hole. When it reaches the poles, this material is launched into space at a phenomenal speed, forming plasma jets which burst into space at a significant percentage of the speed of light in a vacuum.

An image of PBC J2333.9-2343 obtained using Pan-STARRS. (University of Hawaii Institute of Astronomy)

When the black hole finishes its meal and calms down again, what remains of these jets may continue to travel through space, spreading out into lobes that continue to emit radio waves. These are known as giant radio galaxies, and they can be colossal. PBC J2333.9-2343 has such radio lobes, evidence of past black hole activity, spanning a total distance of 3.9 million light-years.

But the galaxy showed strange behavior at different wavelengths, leading a team of astronomers led by astrophysicist Lorena Hernández-García of the Millennium Institute of Astrophysics in Chile to believe that PBC J2333.9-2343 could now be a blazar. They published an article outlining their argument in 2017and now they got the corresponding observational evidence.

“We started to study this galaxy because it had special properties,” Hernández-García explains. “Our hypothesis was that the relativistic jet from its supermassive black hole had changed direction, and to confirm this idea we had to make many observations.”

The research team conducted an extremely thorough investigation, collecting observations in radio, infrared, optical, ultraviolet, X-ray and gamma wavelengths. Next, they compared their observational data to a large database of blazar and non-blazar galaxies.

The results showed that the features of J2333.9-2343 are more consistent with blazar galaxies, suggesting that the galaxy has dramatically reoriented up to 90 degrees, so that its black hole directs one of its jets in our direction.

“The fact that we see that the nucleus no longer nourishes the lobes means that they are very old”, said Hernandez-García. “These are relics of past activity, while structures closer to the core represent younger, active jets.”

As for how the black hole could have shifted position so dramatically, that remains unknown. There is a distinct lack of activity detected between the lobes and the galaxy, suggesting that the black hole was knocked over during a major event, such as a collision and merger with another galaxy.

In turn, that could mean we’re looking, for the first time, at what the researchers call a “very exceptional case of jet redirection,” transforming J2333.9-2343 and leading to its reclassification from a giant radio galaxy to a joke. .

The research was published in the Royal Astronomical Society Monthly Notices.

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