The James Webb Space Telescope (JWST) has captured an image of a massive, dusty galaxy that existed when the universe was only a few hundred million years old. Dubbed the "AzTEC-C71 monster galaxy" by astronomers, this ancient galaxy has mystified scientists for over a decade since it seemed to appear and disappear from different telescope observations. JWST’s powerful infrared imaging has now conclusively revealed AzTEC-C71 in more detail than ever before, unlocking clues about the early days of galaxy formation.
The Hunt for AzTEC-C71: A Ghostly Galaxy
AzTEC-C71 was first detected in 2006 using the AzTEC camera installed on the James Clerk Maxwell Telescope in Hawaii. Astronomers spotted an extremely bright source of submillimeter radiation, indicating emission from huge amounts of dust. However, when they tried to observe AzTEC-C71 at other wavelengths, the galaxy seemed to vanish.
"For the next 15 years, this galaxy taunted astronomers." said Jeyhan Kartaltepe, an astronomer at the University of Rochester in New York who led studies trying to understand AzTEC-C71. "It seemed to appear and disappear from observations at different wavelengths."
Kartaltepe coined AzTEC-C71 the "disappearing monster galaxy" after spending years trying unsuccessfully to spot it with various ground and space based observatories including the Hubble Space Telescope and Atacama Large Millimeter Array (ALMA). The mystery only deepened when ALMA detected AzTEC-C71 but found it was forming stars at nearly one hundred times the rate of the Milky Way. Where were all these stars?
| Telescope / Observatory | Year Detected | Wavelength Detected | Notes |
|---|---|---|---|
| AzTEC Camera on James Clerk Maxwell Telescope | 2006 | 1100 microns | First detection as very bright submillimeter source |
| Hubble Space Telescope | N/A | Visible and ultraviolet light | No detection |
| Atacama Large Millimeter Array (ALMA) | 2017 | 1300 microns | Detected but fainter than expected |
"How could this invisible galaxy form stars at such an incredible rate?" said Kartaltepe. "Finding the truth behind AzTEC-C71 became an obsession of mine."
Webb Reveals the Disappearing Monster
The launch of the James Webb Space Telescope in 2021 provided astronomers with a new tool to solve the mystery of AzTEC-C71. As a large infrared observatory, JWST offered the perfect capabilities needed to pierce through the thick cosmic dust enshrouding AzTEC-C71.
In November 2022, an international team led by Ivo Labbé of the University of Texas at Austin aimed Webb’s powerful NIRCam instrument towards the last known location of AzTEC-C71. To the team’s delight, NIRCam’s images clearly revealed a massive galaxy brimming with astronomical activity.
"When I first saw the massive galaxy revealed in the Webb image I was awestruck," said Labbé. "JWST illuminated the monster for the first time allowing us to pinpoint the galaxy that had evaded astronomers for so long."
Webb’s detailed infrared spectra showed that AzTEC-C71 was not only dizzyingly massive with 1 trillion solar masses worth of stars, but the galaxy was furiously forming new stars at a rate of up to 1,000 solar masses per year. For comparison, the Milky Way forms just 1-2 solar masses of new stars per year. AzTEC-C71’s extreme stellar baby boom was likely triggered by a close collision with another smaller galaxy within the last 100 million years.
Peering Back to the Cosmic Dawn
Beyond solving a decade old mystery, astronomers are excited about what AzTEC-C71 can tell us about the earliest days of galaxy formation just a few hundred million years after the Big Bang. Current theories predict the first galaxies were small collections of stars tens of thousands of lightyears across. As these infant galaxies merged and grew, over billions of years they gradually built up massive galaxies like our own Milky Way.
However, AzTEC-C71 defies these theories by appearing as colossal galaxy just 870 million years after the birth of the universe. The galaxy is churning out stars faster than astronomers thought was possible for the era known as "cosmic dawn".
"JWST has shown us that AzTEC-C71 is a monster galaxy from the universe’s toddler years that grew up fast!" said Labbé. "It’s challenging our very ideas of how early galaxies could form."
The extreme size and star formation rate suggest AzTEC-C71 must have formed from an exceptionally large reservoir of cold hydrogen gas. Astronomers theorize this cosmic gas collapsed rapidly due to an earlier unknown population of stars or blackholes not yet seen. Upcoming Webb observations scanning AzTEC-C71’s surroundings may detect these mysterious initiators.
"We have seen some evidence of the monsters responsible for triggering the formation of AzTEC-C71." said Kartaltepe. "JWST has opened a new gateway to understanding the earliest massive galaxies when the universe was still very young"
The Future of AzTEC-C71 and Galaxy Formation Studies
Astronomers suspect that AzTEC-C71 may evolve into a giant elliptical galaxy containing over 1 trillion stars but little dust and gas. Over billions of years bursts of star formation could use up most of the remaining cosmic raw materials in AzTEC-C71 giving rise to an elliptical galaxy composed mostly of aging red giant stars.
Further observations by Webb’s detailed spectroscopy surveys could reveal wider clues about how common monster galaxy’s like AzTEC-C71 really are in the early universe. Astronomers are now racing to find more examples galaxies as massive as AzTEC-C71 less than 1 billion years after the Big Bang. Each new discovery will help unravel the mysteries of how galaxies manage grow so enormous in the cosmic blink of an eye.
"JWST has solved an over 15 year old mystery by finally showing AzTEC-C71 is an absolute monster galaxy seen at a time when the universe was still very young." said Kartaltepe. "But at the same time, this monster galaxy is already challenging our theories of how quickly early galaxies could form and grow. Solving the mystery of AzTEC-C71 has opened a new cosmic mystery about the emergence of massive galaxies across cosmic dawn."
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