A Carnegie Institution of Science-led team has found one of the most elusive objects in the universe: a fully formed galaxy just a few hundred million years after the Big Bang.

It’s a true rarity. Astronomers have only ever discovered one object of comparable size in this era of the early universe. The results were published today in papers in Nature and Astrophysical Journal Letters.

“The number of quasars as luminous and as distant as we’ve just found … there should be between 20 and 100 over the entire sky,” Eduardo Bañados of Carnegie and lead author of the study says. “This is really like finding a needle in the haystack.”

The galaxy J1342+0928—and its supermassive black hole—appear just 690 million years after the Big Bang during a time in the universe known as the Epoch of Reionization. For some time, the universe was “cloudy” with neutral hydrogen, creating a dense fog that blocked most light. Then, the neutral hydrogen was ionized by the first quasars, which are supermassive black holes at the center of galaxies.

But most galaxies we’ve seen from that era are very, very small. Dwarf galaxies nicknamed “green pea galaxies” are believed to dominate the Epoch of Reionization, making this one—for now at least—quite the bright, active outlier. (Two other larger galaxies near the Epoch were also reported today in Nature.)

It was found by combing over data from three different sky surveys: the Wide-Field Infrared Survey Explorer, the United Kingdom Infrared TElescope Infrared Deep Sky Survey, and DECam Legacy Survey to identify early galaxy candidates.

"This object gives us a picture of how the universe was when it was only five percent of its present age," Bañados says.

MPIA / Venemans et al.

The research paper focuses on a different facet of the galaxy: star formation. Any element higher than helium on the periodic table is regarded as a “metal” by astronomers studying this period. The galaxy, for its age and time period, is far more rich in metals than it should be, considering the first generation of stars were comprised almost entirely of hydrogen and helium.



The abundance of metals likely means a clip of star formation unlike anything we’ve seen. The stars and interstellar dust are dominated by carbon, but heavier materials like magnesium, silicon, and nitrogen are also seen accreting into the black hole at the center.

Venemans Bram of the Max Planck Institute and an author on the paper says it’s likely the early universe favored the formation of massive, unstable stars that exploded after a few million years, producing metals more rapidly than our present universe. As more stars formed from the remains of first-generation stars, they became “polluted” with heavier elements and in turn produce even heavier elements when they explode in supernovae.

“[Given] the short lifetimes of the first generation of stars, it’s very likely that there were at least several generations of stars,” Bram says. “Estimating the number of generations is virtually impossible.”

Future telescopes like the James Webb Space Telescope and upgrades to existing ones like the Atacama Large Millimeter/submillimeter Array will help find more of these ancient galaxies and study star formation during this era, as well as how the formation of supermassive black holes might have occurred so early in the history of the universe. But for now, astronomers have a true jewel from the early universe to study.

“If we keep finding objects like this at even further distances, then the problem will get even harder, to find a way to explain this that physically possible,” Bañados says.

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