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Starts With A Bang

A quasar-galaxy hybrid could be astronomy’s “missing link”

Single objects rarely change the course of an entire scientific field. Distant object GNz7q, a galaxy-quasar hybrid, might do exactly that.
quasar-galaxy hybrid
This tiny sliver of the GOODS-N deep field, imaged with many observatories including Hubble, Spitzer, Chandra, XMM-Newton, Herschel, the VLT, and more, contains a seemingly unremarkable red dot. That object, a quasar-galaxy hybrid from just 730 million years after the Big Bang, showcases how bright and powerful quasars can be. However, despite their early presence and remarkable luminosities, they cannot account for all or even most of the reionizing photons needed to render the Universe transparent to optical light.
Credit: NASA, ESA, G. Illingworth (UCSC), P. Oesch (UCSC, Yale), R. Bouwens (LEI), I. Labbe (LEI), Cosmic Dawn Center/Niels Bohr Institute/University of Copenhagen, Denmark
Key Takeaways
  • In the distant Universe, objects are either dominated by starlight or from the emission of the central, supermassive black hole.
  • The regions of sky with the deepest, best multiwavelength coverage, from X-rays through UV, optical, infrared, and more, have been the GOODS-N and GOODS-S fields.
  • And yet, for over a decade, everyone missed this one quasar-galaxy hybrid: GNz7q. It could be the astronomical key that unlocks the secret to galaxy evolution.

Out in the distant Universe, a cosmic mystery awaits a solution.

Galaxies comparable to the present-day Milky Way are numerous, but younger galaxies that are Milky Way-like are inherently smaller, bluer, more chaotic, and richer in gas in general than the galaxies we see today. For the first galaxies of all, this effect goes to the extreme. As far back as we’ve ever seen, galaxies obey these rules.
Credit: NASA, ESA, P. van Dokkum (Yale U.), S. Patel (Leiden U.), and the 3-D-HST Team

The first star-forming galaxies are the most distant objects yet discovered.

James Webb Hubble
Only because the most distant galaxy spotted by Hubble, GN-z11, is located in a region where the intergalactic medium is mostly reionized, was Hubble able to reveal it to us at the present time, breaking the prior record held by EGSY8p7. Other galaxies that are at this same distance but aren’t along a serendipitously greater-than-average line of sight as far as reionization goes can only be revealed at longer wavelengths, and by observatories such as JWST. At present, GN-z11 has been relegated to the 9th most distant galaxy known as of 2024: in the JWST era.
Credit: NASA, ESA, P. Oesch and B. Robertson (University of California, Santa Cruz), and A. Feild (STScI)

Intrinsically bright and blue, many appear in our deepest views of space.

An artist’s conception of what a region within the Universe might look like as it forms stars for the first time. As they shine and merge, radiation will be emitted, both electromagnetic and gravitational. But the conversion of matter into energy does something else: it causes an increase in radiation pressure, which fights against gravitation. Surrounding the star-forming region is darkness, as neutral atoms effectively absorb that emitted starlight, while the emitted ultraviolet starlight works to ionize that matter from the inside out.
Credit: Pablo Carlos Budassi/Wikimedia Commons

They’re very dusty, as copious neutral matter is required to rapidly form hot, newborn stars.

Galaxies undergoing massive bursts of star formation expel large quantities of matter at great speeds. They also glow red, covering the whole galaxy, thanks to hydrogen emissions. This particular galaxy, M82, the Cigar Galaxy, is gravitationally interacting with its neighbor, M81, causing this burst of activity. Although the winds and ejecta are copious, this episode is not expected to completely “kill” the galaxy, as some gas will still persist after this episode completes.
Credits: NASA, ESA and the Hubble Heritage Team (STScI/AURA); Acknowledgment: J. Gallagher (University of Wisconsin), M. Mountain (STScI) and P. Puxley (National Science Foundation)

Later, the first quasars appear, dominated by central, supermassive black holes.

This 20-year time-lapse of stars near the center of our galaxy comes from the ESO, published in 2018. Note how the resolution and sensitivity of the features sharpen and improve toward the end, all orbiting our galaxy’s (invisible) central supermassive black hole. Practically every large galaxy, even at early times, is thought to house a supermassive black hole, but only the one at the center of the Milky Way is close enough to see the motions of individual stars around it, and to thereby accurately determine the black hole’s mass. The actual number density of black holes in the Universe, and their number density as a function of mass, remains only poorly estimated, with large uncertainties remaining.
Credit: ESO/MPE

These supermassive black holes reach billions of solar masses in relatively short order.

If you begin with an initial, seed black hole when the Universe was only 100 million years old, there’s a limit to the rate at which it can grow: the Eddington limit. If seeds of several tens-of-thousands of solar masses arise early on and these SMBH seeds grow rapidly thereafter, there may be no conflict with what’s observed, after all.
Credit: F. Wang, image taken at AAS237

Both jets and luminous accretion disks, in X-ray and ultraviolet light, reveal these black holes’ properties.

These two quasar pairs don’t possess a single supermassive black hole at the core of each, but rather two supermassive black holes separated by about 10,000 light-years apiece. The multiwavelength emission properties of these objects are required for unveiling the physical processes occurring inside.
(Credit: NASA, ESA, H. Hwang and N. Zakamska (Johns Hopkins University), and Y. Shen (University of Illinois, Urbana-Champaign))

Dust-rich starburst galaxies should evolve into quasars, feeding and growing their central black holes.

This artist’s impression shows how J043947.08+163415.7, a very distant quasar powered by a supermassive black hole, might look close up. This object is representative of the most luminous quasars in the early Universe, having evolved from a starburst galaxy but only shining at its brightest once the star-forming material has been blown and ionized away.
(Credit: ESA/Hubble & NASA, M. Kornmesser)

But such objects were always either galaxy or quasar, never a hybrid of the two.

This illustration of a radio-loud quasar that is embedded within a star-forming galaxy gives a close-up look of how giant radio galaxies are expected to emerge. At the center of an active galaxy with a supermassive black hole, jets are emitted that slam into the larger galactic halo, energizing the gas and plasma and causing radio emissions in the form of jets close by the black hole, and then plumes and/or lobes farther away. Both supermassive and stellar-mass black holes have overwhelming evidence supporting their existence, but supermassive black holes may heat matter to the highest temperatures of all, accelerating particles to even beyond the GZK cutoff set by particle physics.
Credit: ESA/C. Carreau

Until, in the GOODS-N deep field, the object GNz7q was discovered.

The GOODS-North survey, shown here, contains some of the most distant galaxies ever observed, a great many of which are over 30 billion light-years away already. The fact that galaxies at different distances exhibit different properties was our first clue that led us toward the idea of the Big Bang, but the most important evidence supporting it didn’t arrive until the mid-1960s.
(Credit: NASA, ESA, G. Illingworth (UCSC), P. Oesch (UCSC/Yale), R. Bouwens and I. Labbé (Leiden University), and the Science Team)

The GOODS fields contain multiwavelength data from ground and space-based observatories, providing our deepest wide-field views.

quasar-galaxy hybrid
The quasar-galaxy hybrid GNz7q is seen here as a red dot in the center of the image, reddened because of the expansion of the Universe and its great distance from us. Although it’s been exposes in the GOODS-N field for over 13 years, it was only flagged as an object of interest in 2022, as its spectrum reveals properties of both galaxy and quasar.
(Credit: NASA, ESA, G. Illingworth (UCSC), P. Oesch (UCSC, Yale), R. Bouwens (LEI), I. Labbe (LEI), Cosmic Dawn Center/Niels Bohr Institute/University of Copenhagen, Denmark)

GNz7q is a bright, dust-rich, star-forming galaxy, also possessing many quasar features.

quasar-galaxy hybrid
The distant object GNz7q possesses properties that don’t align with either the other galaxies or quasars seen from its epoch, just 730 million years after the Big Bang, but rather with a hybrid interpretation, as it has some, but not all, of the properties of both.
(Credit: S. Fujimoto et al., Nature, 2022)

The “disk emission” light is missing, while the total quasar light is severely reddened.

galaxy-quasar hybrid
Of all the distant quasars ever found in the Universe, GNz7q is by far, intrinsically, the reddest. The object has a supermassive black hole of a few tens of millions of solar masses, but lacks the characteristic X-ray disk emission normally seen: indicating this is our first galaxy-quasar hybrid.
(Credit: S. Fujimoto et al., Nature, 2022)

This indicates the quasar-containing core is dust-obscured, alongside extraordinarily high star-formation rates.

This artist’s impression of the dusty core of the galaxy-quasar hybrid object, GNz7q, shows a supermassive, growing black hole at the center of a dust-rich galaxy that’s forming new stars at a clip of some ~1600 solar masses worth of stars per year: a rate that’s about 3000 times that of the Milky Way. If the early JWST galaxies are “polluted” by an active galactic nucleus, that could be biasing our inferred masses for these galaxies.
Credit: ESA/Hubble, N. Bartmann

From just 750 million years after the Big Bang, GNz7q makes a perfect target for the JWST.

james webb hubble
This animation showcases a portion of the Hubble eXtreme Deep Field, with 23 days of cumulative data, and a simulated view of what scientists expected JWST might see when it viewed this region. This simulation predates JWST’s launch, and has since been spectacularly superseded by actual JWST data.
Credit: NASA/ESA and Hubble/HUDF team; JADES collaboration for the NIRCam simulation

Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.


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