Credit: NASA, ESA, Yu-Ching Chen (UIUC), Hsiang-Chih Hwang (IAS), Nadia Zakamska (JHU), Yue Shen (UIUC)
The two quasars are found in the central region, denoted with “NE” and “SW.”
Credit: Adapted from Ishikawa et al. 2025
Title: VODKA-JWST: Synchronized Growth of Two Supermassive Black Holes in a Massive Gas Disk? A 3.8 kpc Separation Dual Quasar at Cosmic Noon with the NIRSpec Integral Field Unit
Authors: Yuzo Ishikawa et al.
First Author’s Institution: Johns Hopkins University and MIT Kavli Institute for Astrophysics and Space Research
Status: Published in ApJ
First Author’s Institution: Johns Hopkins University and MIT Kavli Institute for Astrophysics and Space Research
Status: Published in ApJ
Binary supermassive black holes are an interesting phenomenon, with implications for galaxy evolution and gravitational wave observations.
It is thought that these supermassive black hole pairs most often arise
from galaxy mergers, during which gas accretion can spark active galactic nucleus activity. Today’s article analyzes JWST observations of one particular pair of quasars
(a type of active galactic nucleus) with the lovely poetic name of
J0749+2255. As shown in Figure 1, these quasars (observed at a redshift of z
= 2.17) are quite close together, separated by only 12,300 light-years.
They find that the southwest quasar is about three times brighter than
its partner in the northeast, but the real interesting stuff is found in
the spectral analysis.
Figure 2: Spectral observations of the two quasars, vertically offset
for clarity. The blue and red curves represent JWST observations, with
the gray lines representing observations from previous works with other
telescopes. The JWST results shown here demonstrate the remarkable
similarity between the two quasars. Adapted from Ishikawa et al. 2025
Seeing Double?
Figure 3: Maps of Hɑ emission with the quasar contributions removed. Left panel shows the flux, middle shows the velocity dispersion, and right the radial velocity. The radial velocity measurements provide strong evidence for a disk with gas rotation and relatively little disturbance, which is not usually the case for merger environments. Credit: Ishikawa et al. 2025
Disk Gas Enters the Chat
Original astrobite edited by Hillary Andales
About the author, Skylar Grayson:
Seeing Double?
Figure 2 shows the spectra for the SW and NE quasars, and the first thing that is impossible to ignore is just how similar they are. There are some small differences; for example, the NE quasar is
slightly redder than the SW quasar, and some emission lines have
different shapes and are a smidge offset from one another. But the
general similarity brings up the possibility that what we’re looking at
isn’t two separate quasars, but rather one object that’s being gravitationally lensed!
The small differences in the spectra could be consistent with a lensing
scenario, as they could be explained by time delays in the lensing or
foreground contamination. A major problem with this idea, however, is
that no observations of this system have provided evidence for a lens:
we have not seen the massive foreground object that would actually be
causing the gravitational lensing. While it’s possible that the lens is
just incredibly faint, there’s no smoking gun for lensing happening
here.
Disk Gas Enters the Chat
The story becomes even more complicated when you look beyond the quasars, as JWST observations also detected diffuse emission from gas as shown in Figure 3. This gas is at the same redshift as the quasars, and can thus be associated with their host galaxy. And crucially, this gas doesn’t show any signs of lensing, such as the distinct arcs or symmetry you find in other lensed systems. This, coupled with the differences in the quasar spectra, suggests that this is not a lensed system, and that in fact we are looking at two different quasars.
But even within this model there are mysteries afoot! It’s generally thought that dual quasar systems are found in galaxy mergers, and there is some evidence that we’re seeing that here. The region labeled T1 in Figure 1 is one such piece of evidence, thought to be a tidal tail formed by gravitational disruptions during a merger event. It’s also generally thought that mergers provide a key way to trigger active galactic nucleus activity, where the two supermassive black holes of the merging galaxies become fed by the same gas reservoir. This could explain why the two quasars in J0749+2255 are so similar, as they may have undergone very similar accretion histories.
However, this story is complicated by the dynamics within the gas surrounding the quasars. As shown in the rightmost panel of Figure 3, the quasars are embedded in a gas disk that’s rotating, with one half of the gas being redshifted and the other half blue shifted. The quasars aren’t separated into these two regions, but are rather both found at the center of the disk. And the gas is showing none of the kinematic disturbance we would expect during a major merger, as the disk seems to be relatively stable. So maybe we’re not witnessing a merger in progress, but rather a disk galaxy that is playing host to two quasars! Based on simulations, one way this could happen is if a major merger takes place at an earlier time, and two black holes form from the resulting instabilities. This is another possible explanation for why the quasars are so similar.
Overall, this work points to the complicated nature of dual quasar systems. Is this one quasar being lensed or two different quasars? If they are distinct objects, are we witnessing a merger of galaxies, or did they both form in one galaxy? Future observations may be the key to answering these questions, but for now it remains a very interesting system.
But even within this model there are mysteries afoot! It’s generally thought that dual quasar systems are found in galaxy mergers, and there is some evidence that we’re seeing that here. The region labeled T1 in Figure 1 is one such piece of evidence, thought to be a tidal tail formed by gravitational disruptions during a merger event. It’s also generally thought that mergers provide a key way to trigger active galactic nucleus activity, where the two supermassive black holes of the merging galaxies become fed by the same gas reservoir. This could explain why the two quasars in J0749+2255 are so similar, as they may have undergone very similar accretion histories.
However, this story is complicated by the dynamics within the gas surrounding the quasars. As shown in the rightmost panel of Figure 3, the quasars are embedded in a gas disk that’s rotating, with one half of the gas being redshifted and the other half blue shifted. The quasars aren’t separated into these two regions, but are rather both found at the center of the disk. And the gas is showing none of the kinematic disturbance we would expect during a major merger, as the disk seems to be relatively stable. So maybe we’re not witnessing a merger in progress, but rather a disk galaxy that is playing host to two quasars! Based on simulations, one way this could happen is if a major merger takes place at an earlier time, and two black holes form from the resulting instabilities. This is another possible explanation for why the quasars are so similar.
Overall, this work points to the complicated nature of dual quasar systems. Is this one quasar being lensed or two different quasars? If they are distinct objects, are we witnessing a merger of galaxies, or did they both form in one galaxy? Future observations may be the key to answering these questions, but for now it remains a very interesting system.
Original astrobite edited by Hillary Andales
About the author, Skylar Grayson:
Skylar Grayson is an astrophysics PhD candidate and NSF Graduate Research Fellow at Arizona State University. Her primary research focuses on active galactic nucleus feedback processes in cosmological simulations. She also works in astronomy education research, studying online learners in both undergraduate and free-choice environments. In her free time, Skylar keeps herself busy doing science communication on social media, playing drums and guitar, and crocheting!
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