SPHEREx has opened a much wider window onto one of the dustiest phases of black hole growth. In a new all-sky infrared analysis, researchers confirmed 77 new heavily reddened quasars, more than doubling the known number of confirmed examples at redshifts above 1.5.
These objects are not quiet. They are luminous, dust-obscured quasars powered by supermassive black holes feeding at enormous rates. The new sample suggests many may sit in a short-lived “blow-out” phase, when feedback from the active black hole has begun clearing the obscuring material around it.
The blow-out phase comes into focus
Quasars are the bright cores of galaxies, powered by supermassive black holes pulling in surrounding matter. Many catalogued quasars look blue and relatively unobscured. Heavily reddened quasars, or HRQs, are different. Their visible and ultraviolet light is heavily dimmed by dust, leaving them far easier to identify in infrared light.
The new SPHEREx work, posted on arXiv as “Hidden Monsters with SPHEREx I”, used SPHEREx spectrophotometry to confirm 77 new HRQs across redshifts from 1.5 to 3.9. The authors report that this more than doubles the number of confirmed HRQs at redshift greater than 1.5 and includes the first seven found beyond redshift 3.
That matters because HRQs are thought to trace a brief but important stage in galaxy evolution. A dust-rich galaxy can funnel gas toward its center, feeding a supermassive black hole while still wrapping the quasar in obscuring material. As the quasar grows more powerful, radiation pressure and winds may begin pushing gas and dust outward. That is the blow-out phase: the moment when the hidden engine starts reshaping its surroundings.
The SPHEREx sample strengthens that picture. The researchers found that HRQs are hot-dust poor compared with blue quasars of similar luminosity and redshift. They also found weaker mid-infrared emission at fixed optical luminosity, suggesting a deficit of both hot and warm dust. In plain terms, the central dust reservoir appears thinner than expected for objects this luminous.
That combination supports the idea that HRQs are not simply ordinary quasars viewed through a thicker curtain. They may be quasars in transition, still reddened by dust but already beginning to clear the central regions around the black hole.
Why SPHEREx changes the scale of the search
Before wide infrared surveys, HRQ hunting was slow and uneven. These objects are rare, spread across the sky, and often missed by optical surveys because dust dims the very wavelengths those surveys rely on.
SPHEREx changes the scale of the work. The observatory maps the entire sky in infrared, splitting light into many narrow wavelength bands. That allows astronomers to identify and confirm large numbers of dust-obscured quasars far more efficiently than one-object-at-a-time follow-up campaigns.
The result is not just a longer list of exotic objects. It is the beginning of a population study. With 77 new confirmed HRQs, researchers can begin asking how common this phase is, how long it lasts, and how much hidden black hole growth optical surveys have missed.
A clue in the ultraviolet
One of the more intriguing findings is that many HRQs show an ultraviolet excess. That is surprising because heavy dust should strongly suppress ultraviolet light from the central quasar.
The study reports that 50 of the 66 SPHEREx HRQs with sufficient ultraviolet coverage show this excess. The authors model it as consistent with scattered quasar light, although they note that star formation in the host galaxy cannot be ruled out.
Both possibilities point to a messy, changing environment. Scattered light would suggest that the obscuring dust is not a smooth shell but a patchy structure with some sightlines opening. Host-galaxy starlight would suggest that star formation is still active while the black hole is beginning to affect the surrounding gas. Either way, the systems look less like static buried quasars and more like objects caught during a transitional phase.
How black hole feedback enters the story
The broader idea behind the discovery is feedback: the process by which energy from an active supermassive black hole changes the galaxy around it. In extreme cases, quasar winds can drive gas out of a galaxy and make future star formation harder.
That mechanism is not unique to this SPHEREx sample. Separate JWST work reported by AZoQuantum described powerful quasar winds in the early universe, including galaxy-scale outflows that could remove large amounts of gas from host galaxies over relatively short cosmic timescales.
The HRQ study is not measuring the same objects or proving that every newly confirmed HRQ is shutting down its host galaxy. Its importance is more specific. It identifies a large population of luminous, dust-obscured quasars whose dust properties fit the picture of feedback beginning to clear the central regions.
Follow-up will decide how dramatic the phase really is
SPHEREx is built for breadth. It can find and confirm large samples across the sky. Deeper follow-up will be needed to understand individual host galaxies and the gas around them.
The James Webb Space Telescope can help test whether the ultraviolet excess is scattered quasar light or star formation. It can also examine the host galaxies in more detail, including their gas motion and structure. The Nancy Grace Roman Space Telescope should add wide-field infrared imaging with much sharper angular resolution than SPHEREx.
Together, those instruments could turn the new HRQ catalogue into a clearer timeline. Astronomers want to know how long the blow-out phase lasts, how much material is removed, whether star formation actually shuts down, and how often this stage leads to the ordinary blue quasars that dominate optical catalogues.
The hidden monsters of cosmic noon
The demographic implication is the most important one. Cosmic noon, roughly the era when the universe was forming stars and growing black holes at especially high rates, is also a period when dust can hide some of the most active systems from optical surveys.
If HRQs are common but hard to see, then older quasar censuses have likely missed part of the story. The universe’s biggest black holes did not grow only in the systems easiest to spot. Some were working behind a curtain of dust, luminous in their own right but filtered out by the methods used to count them.
SPHEREx has now more than doubled the confirmed high-redshift HRQ sample in one study. That does not settle every question about how black holes and galaxies regulate each other. But it sharply expands the number of objects caught in the phase where that relationship may be changing.
The picture of black hole growth at cosmic noon was missing many of its reddest subjects. SPHEREx has started bringing them into view.
