Matthew Stepney and his team at the Center of Excellence in Astrophysics and Related Technologies in Chile have just doubled humanity's census of the universe's most elusive black holes—77 heavily reddened quasars captured in a single observation campaign, more than tripling the total known population in one stroke. These aren't new objects in the cosmos; they're newly visible ones, hidden behind thick clouds of dust that have made them invisible to conventional telescopes until now. NASA's SPHEREx telescope has changed that, revealing what astronomers believe is the smoking gun evidence for a crucial—and brief—chapter in how galaxies evolve.
At the heart of most large galaxies lurks a supermassive black hole, a monster millions or billions of times the mass of our sun. When these black holes begin gorging themselves on material, they blaze as quasars—among the brightest objects in the universe. But not all quasars shine openly. Some are wrapped so thickly in dust that ground-based telescopes see nothing at all. These heavily reddened quasars have long puzzled astronomers, but a leading theory suggests they're something precious: a window into galaxy evolution itself.
The theory goes like this: when two galaxies collide, chaos erupts. Gas streams inward, igniting explosive bursts of star formation while simultaneously feeding the central black hole. Dust surrounds this maelstrom, powered by radiation so intense it creates winds of devastating force. These are the dust-obscured growth phases—violent, temporary, and crucial. Yet finding them has been maddeningly difficult. Previous searches required hunting them down one at a time using infrared telescopes, a time-consuming process that had turned up only about 50 confirmed specimens. The small sample meant astronomers couldn't answer fundamental questions about this transitional phase with any real confidence.
Stepney's team changed the equation by using infrared spectrophotometry from SPHEREx to identify 77 new heavily reddened quasars lurking in the universe when it was between 1.6 billion and 4.3 billion years old. Even more striking, they discovered the first seven such objects at redshifts above 3—meaning they existed within just 2.1 billion years after the Big Bang itself, when the universe was still in its infancy.
What makes these objects truly remarkable is what they're not doing. Despite their extreme brightness once you correct for dust obscuration, they show surprisingly little infrared emission from the hot dust structures around their black holes. This seemingly contradictory combination—extreme luminosity but depleted dust—points to something extraordinary happening: a "blow-out" phase. Picture it as a cosmic cleaning event, where the black hole's devastating feedback winds are actively clearing away the dusty envelope that has cloaked the galaxy's core. The quasars are caught mid-sneeze, if you will, violently expelling the very material that's been obscuring them.
About three-quarters of the sample also showed an unexpected excess of ultraviolet light, possibly scattered around the edges of the dusty cocoon or produced by a final burst of star formation before the black hole clears house. Looking forward, Stepney's team plans to exploit SPHEREx's all-sky capabilities to expand these samples even further, hoping to finally answer how many of these "hidden monsters" actually dominate black hole growth during what astronomers call cosmic noon—the universe's most prolific epoch of galaxy formation.