The protocluster of very early galaxies is centered on a source dubbed AzTEC 3, after the millimeter-wave instrument that first detected it. The full collection of galaxies, called the COSMOS-AzTEC protocluster, has been caught in the act of formation when the universe was only 1 billion years old. So dusty that most of the light it emits is trapped, AZTEC 3 would be nearly invisible to even the most powerful optical instruments such as the Hubble Space Telescope.
Wilson calls the observation surprising, given that current theory suggests that finding such a nascent cluster of galaxies in the early stages of formation should be very difficult. “Clusters, which are some of the biggest structures in the universe, are relatively rare. If galaxies spread through the universe are like towns dotting the Earth, clusters would be like the biggest cities,” he notes. And the discovery of the COSMOS-AzTEC protocluster would be like looking back in time to peer at the first houses on Manhattan Island, destined to be one of the most populous places on the planet.
Yet AzTEC 3 was one of the very first objects discovered by the team using the AzTEC camera. Wilson led an international team of astronomers who designed and built the special millimeter wave-detecting camera, funded in part by the National Science Foundation and to be installed at the Large Millimeter Telescope in Mexico, a joint project between the university and Mexico expected to be completed later this year.
Most astronomers believe that such a massive cluster as the COSMOS-AzTEC protocluster should not be mature until 2 to 3 billion years later, explains Yun. “Such a young cluster is really interesting. The computer simulations of the universe suggest we were extremely fortunate to find it.” The protocluster also contains a galaxy harboring a super massive black hole and several other interesting galaxies. The AzTEC-3 galaxy itself is extraordinary in that it appears to be generating 1,000 new stars annually, compared to the Milky Way’s one to three. “This protocluster is a real collection of odd and intriguing sources, all congregating when the universe was in its infancy,” Yun adds.
Astronomers Grant Wilson (left) and Min Yun with the AzTEC camera’s detector array, tuned to detect the radiation from cold dust in the universe.