Cosmic lens reveals a galaxy cradle

Press release written by The National Radio Astronomy Observatory with contributions from Kim Baptista at Arizona State University’s School of Earth and Space Exploration

Astronomers at Arizona State University are helping reveal how some of the universe’s largest structures began.

Using the National Science Foundation’s Very Large Array (VLA) and the Atacama Large Millimeter/submillimeter Array (ALMA), those astronomers found a group of galaxies called protoclusters — tightly packed, young galaxies growing quickly — and observed them as they appeared more than 11 billion years ago.

The results of the recent paper published in The Astrophysical Journal detailing the finding were presented at the 247th meeting of the American Astronomical Society held in Phoenix. The research was led by Nicholas Foo and included co-authors Patrick S. Kamieneski, Allison Noble and Seth H. Cohen of Arizona State University's School of Earth and Space Exploration.

The newly studied protocluster, known as PJ0846+15 (or J08), was first spotted by the Planck space telescope because it appeared unusually bright in infrared light across the sky. However, Planck’s limited resolution made it difficult to study. Follow-up observations with ALMA and the VLA provided higher-resolution data and revealed a surprising result.

Instead of being one object, J08 is made up of 11 separate galaxies, all packed closely together to form a classic protocluster. For perspective, all these galaxies would fit within the space between the Milky Way and our nearest large neighbor, the Andromeda Galaxy.

“Galaxy clusters are akin to a sprawling modern metropolis that was built upon an ancient civilization from the past. For example, if an archaeologist digs deeper into the ground, then they uncover an earlier civilization. Similarly, when astronomers observe objects farther away, they can look farther back in time. In this way, the study of this distant protocluster gives us a glimpse into how one of the earliest ‘settlements’ of galaxies grew and evolved into the mature structures such as that foreground galaxy cluster that we observe today,” said lead author Foo, a graduate student at ASU.

Inside the J08 protocluster, these young galaxies are making new stars quickly, making J08 one of the fastest growing protoclusters found so far. When stars form in bursts, they create dust, much like fireworks leave behind clouds of smoke. This dust blocks visible light, so regular telescopes can’t see these galaxies well. But ALMA and the VLA can detect longer wavelengths that pass through the dust, allowing astronomers to find and study these hidden galaxies.

By checking how bright the dust is, researchers can estimate how fast new stars are forming, and by measuring how much gas remains they can tell how long this star-forming burst might continue.

The light from the young galaxies in J08 happens to pass through an unrelated foreground galaxy cluster before reaching Earth, acting like a natural cosmic lens. According to Einstein’s theory of general relativity, the gravity of this foreground cluster bends and magnifies the light from J08. This effect, known as gravitational lensing, can make distant galaxies appear larger, distorted or even doubled, helping astronomers study extremely faint and distant objects in much greater detail.

Because of this rare alignment, astronomers can study both a young protocluster and an older galaxy cluster simultaneously. Since light takes time to reach us, looking farther into space also means looking further back in time. This idea, called look-back time, allows scientists to observe different stages of galaxy cluster growth in a single system.

“These data and Nick Foo's paper on this very dusty protocluster show how important NRAO's ground-based radio and millimeter images are to interpret what we see with Hubble and Webb. I have very high hopes that this combination will unravel the hidden modes of star formation in the first few billion years,'' said Rogier Windhorst, a Regents Professor at ASU.

Protoclusters like J0846 are the precursors of today’s massive galaxy clusters, representing adolescent "cradles" where gravity rapidly assembles gas, galaxies and dark matter into the largest structures in the cosmos. By combining ALMA’s view of dust and molecular gas with the NSF VLA’s maps of radio emission, astronomers obtained a multi-wavelength picture of how galaxies in this dense environment grew, interacted and transformed over time. Its rare alignment with a foreground galaxy cluster produced a gravitational lens, making J08 an exceptional laboratory for testing models of cluster formation and the co‑evolution of galaxies and their environments. As the NSF VLA and ALMA continue to target this field, the system will serve as a benchmark for connecting today’s mature clusters to their compact, dust‑rich, star‑bursting ancestors in the early universe.

Additional researchers on this study include: Kevin C. Harrington, Brenda L. Frye, Min S. Yun, Massimo Pascale, Ilsang Yoon, James D. Lowenthal, Melanie Kaasinen, Belén Alcalde Pampliega, Daizhong Liu, Olivia Cooper, Carlos Garcia Diaz, Anastasio Díaz-Sánchez, Jose Diego, Nikhil Garuda, Eric F. Jiménez-Andrade, Reagen Leimbach, Amit Vishwas, Q. Daniel Wang, Dazhi Zhou, and Adi Zitrin.