Astronomers may have finally cracked the enigma of why the universe's brightest galaxies are so incredibly luminous.

Over the past 50 years or so, astronomers have observed certain galaxies in our universe—called submillimeter galaxies (SMGs)—that outshine other galaxies by hundreds of times over. These rabid, glowing galaxies also give birth to stars thousands of times faster than our own Milky Way does. But ever since their discovery, exactly what exactly causes these ultra-bright galaxies to become so radiant has been a longstanding mystery.

One prevailing theory is that SMGs are cosmic car crashes—the fiery result of two disc galaxies like the Milky Way colliding. But in simulation after simulation, nobody's ever been able to plug in the physics and explain what we see in real life. But today, a team of astronomers—led by Desika Narayanan at Haverford College—has announced the first working model of SMGs and the first conclusive answer of why they're so radiant. They published their work today in the journal Nature.

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Based on Narayanan's new model, SMGs are not the result of spectacular crashes. Rather, something much more interesting is going on: SMG galaxies are strange, long-lived convection ovens driven by gravity.

Narayanan's new model shows that despite their ample reservoirs of gas and dust, SMGs don't leak gas (what astronomers call galactic outflow) at all the way Milky Way-type galaxies do. Instead, because of the tight grip of gravity in these hugely massive galaxies, as stars die and go nova the stellar gas is recycled back inward, continually fueling the formation of new stars and future supernova. That recycling process forms a feedback loop that jets out crazy amounts of light while keeping the mass trapped inside the galaxy.

According to Narayanan and his team, their model owes its accuracy to a newly developed computer code that describes how light escapes the complex maze of dust and gas in an SMG. Romeel Davé, an astronomer at the University of the Western Cape who specializes in supercomputer galactic models (and was not involved in the research), says that thanks to this breakthrough, Narayanan and his team have "presented the first impressively viable model of SMG formation, allowing us a tantalizing glimpse behind the mask of these behemoths of deep space."

According to Davé, Narayanan's new model "offer[s] unprecedented clarity in understanding the origins of such deep-space monsters."

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