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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, may be key to unlocking the mystery of galaxy-black hole evolution. Once speculative, the evidence for the physical existence and ubiquity of black holes is now overwhelming.
(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 throughout cosmic time, having grown in mass and with more evolved structure at present. Younger, galaxies are inherently smaller, bluer, more chaotic, richer in gas, and have lower densities of heavy elements than their modern-day counterparts.
(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 this distant galaxy, GN-z11, is located in a region where the intergalactic medium is mostly reionized, can Hubble reveal it to us at the present time. To see further, we require a better observatory, optimized for these kinds of detection, than Hubble. Although the galaxy appears very red, that’s only due to the redshifting effect of the expanding Universe. Intrinsically, the galaxy itself is very blue.
(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.

The very first stars and galaxies that form should be home to Population III stars: stars made out of only the elements that first formed during the hot Big Bang, which is 99.999999% hydrogen and helium exclusively. Such a population has never been seen or confirmed, but some are hopeful that the James Webb Space Telescope will reveal them. In the meantime, the most distant galaxies are all very bright and intrinsically blue, but not quite pristine.
(Credit: Pablo Carlos Budassi/Wikimedia Commons)

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

Most galaxies contain only a few regions of star-formation: where gas is collapsing, new stars are forming, and ionized hydrogen is found in a bubble surrounding that region. In a starburst galaxy, pretty much the entire galaxy itself is a star-forming region, with M82, the Cigar Galaxy, being the closest one with those properties. The radiation from hot, young stars ionizes a variety of atomic and molecular gases, creating emission signatures that can be revealed visually with the right astronomical filters.
(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.

supermassive
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.
(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. Either these black holes start off bigger than our theories expect, form earlier than we realize, or they grow faster than our present understanding allows to achieve the mass values we observe. Examining quasar-galaxy hybrids may hold the key to unraveling this mystery.
(Credit: F. Wang, 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.
(Credit: ESA/C. Carreau)

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

This image is the full field Hubble view of the GOODS-N survey area. This area has also been imaged by NASA’s Spitzer, Chandra, ESA’s XMM-Newton, Herschel, and a series of large ground-based telescopes, the latter of which were vital for determining the object of interest GNz7q’s spectroscopic properties in the optical and near-infrared. GNz7q is found at the center of the red circle.
(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.

GNz7q
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.
(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
A portion of the Hubble eXtreme Deep Field that’s been imaged for 23 total days, as contrasted with the simulated view expected by the JWST in the infrared. By choosing its targets judiciously, the James Webb Space Telescope should be able to reveal extraordinary details about the most distant objects in the Universe that no other observatory could hope to reveal. Once calibration is complete, this type of science work can commence.
(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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