Astronomers have had to reclassify a bright radio galaxy in the sky after it was found to have redirected a jet of radiation straight towardsEarth. The event marks the first observation of a reorientation so dramatic that it changes the category a galaxy fits into.
At the heart of most galaxies lies a supermassive black hole, and in some cases these monsters are busily chowing down on material and emitting higher levels of radiation. A region undergoing this process is called an active galactic nucleus (AGN) or a quasar. Some of them are such messy eaters that they’re spewing off huge jets of charged particles traveling close to the speed of light. These jets can point away from the home galaxy in any direction, and if one just so happens to be pointing towards Earth, it appears as a very bright object called a blazar.
Now, astronomers have discovered a bizarre galaxy that seems to have switched from a quasar to a blazar, in a transition that’s never been seen before. At some point in its past, the galaxy’s jet seems to have changed direction by as much as 90 degrees, so that it flipped from running across the sky to pointing directly at Earth.
Known as PBC J2333.9-2343, the galaxy is located 656.8 million light-years away, and when observed on a large scale with certain types of instruments, what look like jets can be seen stretching across the sky. This led it to being originally classed as a radio galaxy with an AGN at its center.
But the galaxy seemed to have some other strange properties, so the astronomers examined it closer using radio, optical, infrared, X-ray, ultraviolet and gamma ray telescopes. These comprehensive studies revealed a blazar in the center of the galaxy – the signature of a jet seen head-on. So what of the old jets? The astronomers also saw two lobes of material, which are relics of these old jets that are no longer being fed by the AGN’s activity.
The study allowed the team to better estimate the galaxy’s size, and it turns out it’s a giant, spanning roughly 4 million light-years in diameter. For reference, our own Milky Way is a mere 100,000 light-years wide.
The team says that other AGNs have been seen to redirect their jets in the past, but this was always from one perpendicular part of the sky to another. PBC J2333.9-2343 marks the first time a jet has moved into a direct line with Earth, causing the object’s classification to change. However, similar events have seen presumed-quiet galaxies suddenly fire up into quasars.
Exactly what caused the shift remains unexplained, but the team speculates that it may have merged with another galaxy, collided with another large object, or the black hole fired back up again after a period of laying dormant.
The research was published in the journal Monthly Notices of the Royal Astronomical Society.
**By Michael Irving