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

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, and their star-formation histories evolve over time. This was not discovered or well-known until the 1960s, when we began to see large numbers of galaxies from much earlier in our cosmic history.

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

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. Other high-redshift galaxy candidates have not yet been spectroscopically confirmed.

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 that we’ve seen are all very bright and intrinsically blue, but not quite pristine, still coming to us from several hundred million years after the start of the hot Big Bang.

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 located just outside of the Local Group, being the closest one with those properties. The radiation from hot, young stars ionizes a variety of atomic and molecular gases, particularly in the galaxy’s central region. Flares, supernovae, and radiation will be common in these environments.

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.

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.

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.

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.

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.

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.

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

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.

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

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.

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

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.

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.

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

A portion of the Hubble eXtreme Deep Field that’s been imaged for 23 total days, as contrasted with the simulated view expected by James Webb in the infrared. With large-area mosaics such as COSMOS-Web and PANORAMIC, the latter of which takes advantage of pure parallel observing, upcoming, we should not only shatter the cosmic record for most distant galaxy, but should learn about what the earliest luminous objects in the Universe looked like.

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