(ORDO NEWS) — Astronomers have observed a rare case of a change in the shape of a galaxy. Decades ago, PBC J2333.9-2343, about 630 million light-years away, was classified as a giant radio galaxy.
It projected large radio-emitting structures perpendicular to our line of sight, formed by colossal jets that once erupted from the galactic center.
However, more recent observations show that the core of the galaxy has turned on again, and is now directing its jet directly at us.
There is nothing wrong with that; in fact, it’s quite common. So common that we even have a name for it; blazar.
Thanks to a new classification, the blazar PBC J2333.9-2343 could give us a deeper understanding of how galaxies can transform, even on human timescales.
Galaxies come in all shapes and sizes, but they also have different levels of activity depending on the activity of the supermassive black hole at their core.
The Milky Way, for example, is a relatively peaceful galaxy; our supermassive black hole is fairly inactive, accreting only a small amount of material.
A supermassive black hole that literally swallows dust and gas from its surroundings looks very different.
This material forms the torus and disk surrounding the black hole; the extreme forces of gravity and friction cause this disk to shine with light across the entire electromagnetic spectrum.
From the inner edge of the disk, material falls into the black hole like water flowing down a sewer. But not all of this material is beyond the event horizon.
Some of it is guided and accelerated along the magnetic field lines outside the black hole.
Upon reaching the poles, this material is ejected into space at tremendous speed, forming jets of plasma that erupt into space at a significant percentage of the speed of light in a vacuum.
When the black hole finishes its meal and calms down again, what’s left of these jets can continue to travel through space, spreading out into lobes that continue to emit radio waves.
They are known as giant radio galaxies and they can be colossal. PBC J2333.9-2343 has such radio lobes, indicative 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 Hernandez-Garcia of the Millennium Institute of Astrophysics in Chile to conclude that PBC J2333.9-2343 could now be a blazar.
In 2017, they published an article outlining their arguments, and now they have obtained the relevant observational data.
“We started studying this galaxy because it showed special properties,” explains Hernandez-Garcia.
“Our hypothesis was that the relativistic jet of its supermassive black hole had changed its direction, and to confirm this idea, we had to make many observations.”
The research team has carried out an extremely thorough study, collecting observations in radio, infrared, optical, ultraviolet, X-ray and gamma wavelengths.
They then compared their observational data with a large database of blazar and non-blazar galaxies.
The results showed that the characteristics of J2333.9-2343 are more consistent with blazar galaxies, suggesting that the galaxy has changed significantly in some way. reorients up to 90 degrees so that its black hole sends one of its jets our way.
“The fact that we see that the core is no longer powering the shares means that they are very old. ”, says Hernandez-Garcia. “They are relics of past activity, while structures closer to the core are younger, more active jets.”
As to how the black hole could change position so dramatically, that is still unknown.
A clear lack of activity is found between the petals and the galaxy, suggesting that the black hole was thrown sideways during a major event such as a collision and merger with another galaxy.
In turn, this could mean that we are observing for the first time what the researchers call “an exceptional case of jet reorientation” transforming J2333.9-2343 and leading to its reclassification from a giant radio galaxy to a blazar.
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