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| An illustration of a blazar -- a ravenous, supermassive black hole shooting radiation toward Earth at near-light-speed (Image credit: NASA/ JPL-Caltech) |
An object once thought to be a radio galaxy is actually an active black hole
that changed angles to point directly at Earth, new research suggests.
In a distant galaxy, a supermassive black hole spewing radiation at near light
speed has shifted its angle by a whopping 90 degrees to point directly toward
Earth — a sharp turn that's puzzling physicists.
Active galactic nuclei (AGN) are the hungry black holes at the cores of many
other galaxies, and they accrete matter and spew powerful jets of
high-energy particles known as relativistic jets. AGN are classified
according to what part of the AGN is pointed toward Earth.
PBC J2333.9-2343, a large galaxy about 4 million light-years across, was
previously classified as a radio galaxy, meaning its AGN's gargantuan jets
of radiation were pointed perpendicular to our line of sight. But new
research published March 20 in the journal Monthly Notices of the Royal
Astronomical Society reclassifies the galaxy as a blazar, meaning the black
hole's jets are now pointed directly at Earth. This means the galaxy's jets
shifted by a "dramatic" degree, the researchers wrote in the study.
"Our hypothesis was that the relativistic jet of its supermassive black hole
had changed its direction, and to confirm that idea we had to carry out a
lot of observations," lead study author Lorena Hernández-García, an
astrophysicist at the Millennium Institute of Astrophysics, said in a
statement.
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| The galaxy PBC J2333.9-2343 is the bright spot at the center of this image, taken by the Institute for Astronomy at the University of Hawaii's Pan-STARRS survey. (Image credit: Institute for Astronomy at the University of Hawaii) |
Hernández-García and colleagues observed PBC J2333.9-2343 across nearly the
entire electromagnetic spectrum, from radio waves to gamma-rays. Their
observations showed that this galaxy had characteristics typical of blazars:
It brightened and dimmed like a blazar, and it had similar jets. Thus, they
concluded that the object was most likely a blazar.
The researchers also observed two lobes — areas where an AGN's jets interact
with surrounding gas — where some jets had previously made their mark. This
blazar's lobes are "very old," however, Hernández-García said, adding that
"they are the relics of past activity, whereas the structures located closer
to the nucleus represent younger and active jets."
These dormant lobes are evidence that the jets have, in fact, changed
direction. It's not totally unprecedented for a galaxy's jets to appear in
different places. But in prior examples, there were two sets of lobes,
meaning two separate jets turning on and off. For PBC J2333.9-2343, it
appears that there is only one source of activity, and it has changed tack.
What caused this great shift? Astronomers are still working that out.
Current theories include a galaxy merger, where another large galaxy
collided with PBC J2333.9-2343, jostling the orientation of everything
within it. More observations are needed to figure out this mystery.
Reference:
L Hernández-García et al, Multiwavelength monitoring of the nucleus in PBC
J2333.9-2343: the giant radio galaxy with a blazar-like core, Monthly Notices
of the Royal Astronomical Society (2023).
DOI: 10.1093/mnras/stad510
Tags:
Space & Astrophysics