'Time machine' reveals hidden structures in the universe's first galaxies

Astronomers have turned the Atacama Large Millimeter/submillimeter Array (ALMA) into a time machine to peer back in cosmic time to 1 billion years after the Big Bang.

This has revealed previously hidden structures within the universe's first galaxies, which could help us understand how the modern cosmos, including our galaxy, the Milky Way, took shape.

The data was collected as part of the CRISTAL survey ([CII] Resolved ISM in STar-forming galaxies with ALMA), which zoomed in on 39 typical star-forming galaxies in the infancy of the 13.8 billion-year-old universe. ALMA had infrared assistance from the James Webb Space Telescope (JWST) and Hubble. The target galaxies were selected to represent the main population of galaxies shortly after the Big Bang.

"Thanks to ALMA’s unique sensitivity and resolution, we can resolve the internal structure of these early galaxies in ways never possible before," CRISTAL principal investigator Rodrigo Herrera-Camus said in a statement. "CRISTAL is showing us how the first galactic disks formed, how stars emerged in giant clumps, and how gas shaped the galaxies we see today."

How ancient structures were revealed by CRISTAL

The CRISTAL findings were possible thanks to the sensitivity of ALMA, consisting of 66 radio antennas in the Atacama desert region of northern Chile, to a specific emission of ionized carbon atoms in cold interstellar gas. This is called the [CII] line emission, and it acts as a tracer of cold gas and dust.

Thus, the CRISTAL team was able to create a complex and detailed map of interstellar gas, the nebulous matter between stars, in galaxies.

One of the key things this cosmic map revealed was stars being born in vast clumps, each stretching for several thousand light-years. Additionally, in many of the CRISTAL galaxies, the [CII] emission was seen to extend far beyond the population of stars of those galaxies.

That indicates the presence of more cold gas that could go on to form more stars or could be driven out of these galaxies by the powerful stellar winds of infant stars. This hints at how star-forming regions gather and evolve.

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Several of the galaxies seen by CRISTAL seemed to be spinning, which indicates how they could eventually flatten out into disk-like structures. These disk-shaped galaxies are thought to be the progenitors of spiral galaxies like the Milky Way.

"What's exciting about CRISTAL is that we are seeing early galaxies not just as points of light, but as complex ecosystems," team member and National Radio Astronomy Observatory (NRAO) scientist Loreto Barcos-Muñoz said. "This project shows how ALMA can resolve the internal structure of galaxies even in the distant universe — revealing how they evolve, interact, and form stars."

Two CRISTAL galaxies are real gems

As stunning and scientifically important as these 37 galaxies are, two seem to be something really special.

One galaxy that really stood out from these ALMA observations was CRISTAL-13 which is shrouded in vast and massive clouds of dust that block the visible light from its newborn stellar population.

These clouds absorb this light and reemit it in wavelengths that ALMA can detect, allowing it to see structures that would be hidden from telescopes observing CRISTAL-13 in visible light or even in infrared light as used by the JWST and Hubble.

Also exceptional, but arguably more mysterious, is CRISTAL-10. This ancient galaxy has ionized carbon that seems to be unusually faint compared to how bright the galaxy is in infrared.

This is a characteristic usually only seen in galaxies that are heavily obscured, like the local galaxy Arp 220. The fact that it is seen for CRISTAL-10 implies there are extreme physical conditions at work within its interstellar medium. Another possibility is that there is something within the interstellar medium of CRISTAL-10 that is pumping out energy.

"These observations highlight ALMA’s potential as a time machine, allowing us to peer into the early ages of the Universe," ALMA head of science operations Sergio Martín said. "Programs like CRISTAL demonstrate the power of ALMA's Large Programs to drive high-impact science. They allow us to tackle the big questions of cosmic evolution with the unprecedented depth and resolution that only a world-class observatory like ALMA can provide."

The CRISTAL survey hasn't just opened a new view of cosmic history by conducting the interstellar medium that can be compared with galaxies' stars and dust content, but it has set the stage for future surveys.

These could eventually reveal how the turbulent, violent, and chaotic early galaxies transformed into well-ordered and structurally well-defined modern galaxies like our own.

"CRISTAL provides the kind of multi-wavelength data that allows us to test and refine our theories of galaxy evolution," Herrera-Camus concluded. "This is a major step toward understanding how galaxies like our Milky Way came to be."

The team's research was published on June 30 in the journal Astronomy & Astrophysics.

This article was originally published on Space.com.