Jul 16, 2022 - Science

Astronomers search for light that holds answer to how earliest galaxies formed

Photo illustration of a black and whtie galaxy with a spotlight revealing a brightly colored area.
Photo illustration: Aïda Amer/Axios. Photo: NASA, ESA, CSA, and STScI

Features of some of the earliest galaxies in the universe are coming into sharper focus.

The big picture: Data from telescopes in space and on Earth — including the powerful new James Webb Space Telescope (JWST) — will give astronomers their best shot yet of figuring out how the first stars and galaxies in the universe formed and evolved.

  • The several hundred million years after the Big Bang are a mysterious and critical moment in the cosmos. During that time, the first stars were born from gas largely made of hydrogen and helium. Those stars died and produced heavier elements that were strewn across the universe, seeding the next generation of stars.
  • One billion years after the Big Bang, galaxies and supermassive black holes existed across the universe. The universe was also reionized by then, transforming it from a place filled with dark, dense primordial gas into a place where light could shine.
  • Astronomers want to know what role the first stars and galaxies played in that critical process — and how these early astronomical objects came to be.

Driving the news: NASA released a stunning image showing thousands of galaxies — some of which formed less than 1 billion years after the Big Bang — this week as part of the JWST's first five scientific photos.

  • The telescope is also designed to piece together the elements that made up the earliest galaxies to understand their evolution.
  • "This is how the oxygen in our bodies was made — in stars in galaxies. And we're seeing that process get started," says Jane Rigby, an astrophysicist at NASA's Goddard Flight Center and the operations project scientist for JWST.

How it works: JWST looks at the universe in infrared (IR) light, giving astronomers access to distant stars and galaxies that emit light typically obstructed by cosmic dust.

  • As the universe expands, the wavelength of optical light from early galaxies increases and is shifted into the IR spectrum as it moves through space and time. These galaxies are too faint for us to see with the naked eye, but they can still be captured by the lenses and detectors of sensitive telescopes.
  • Data from JWST will be combined with optical observations from the Hubble Space Telescope, radio data from the Atacama Large Millimeter/submillimeter Array (ALMA) and the Very Large Array (VLA) telescopes, and measurements from the Chandra X-ray Observatory to give scientists a more holistic view of the universe.

The big question: In combining that data, astronomers are searching for clues about how the first galaxies ever formed.

One theory suggests early galaxies were born from massive clouds of gas and dust that collapsed in on themselves, creating dense clouds that began to coalesce and spin — forming galaxies.

  • Another theory, supported by Hubble data, says smaller masses of gas and dust merged to form larger galaxies and clusters bound together by immense gravity.
  • Mounting evidence points to mergers as the dominant way galaxies grow but observations are still sparse and the details aren't clear.
  • “Galaxy formation is just a messy process,” says Chris Carilli, a radio astronomer who works on the National Science Foundation’s ALMA observatory and studies early galaxy formation.
  • “[It’s] more like weather,” he says. Like studying clouds, the goal is to identify essential physical phenomena seen across galaxies and separate them from the details of an individual galaxy to understand when and how the universe turned primordial gas into stars.

Between the lines: About 10 billion years ago, the mass of galaxies appears to have been dominated by gas rather than stars, according to data from ALMA. In newer galaxies, the opposite is true.

  • This molecular inventory provides clues about how galaxies — and their star-forming activities — change over time. The rise and fall in the amount of gas in galaxies over the history of the universe parallels the rate at which stars were formed in them, Carilli says.

Where it stands: Scientists were able to use the JWST to parse out the molecules — including oxygen, neon and hydrogen — that made up one of the galaxies in this week's deep field image as it existed 13.1 billion years in the past.

  • "The spectra are the astronomer's equivalent of the DNA swabs," tweeted Jonathan McDowell, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics. "What the galaxies were up to is encoded in their light."

What to watch: Comparing the properties of gas in galaxies near and far can help astronomers study how the interstellar medium itself changed over time.

  • “I think we'll be able to better understand that evolution in the coming years, especially with JWST,” says Bryan Terrazas, an astrophysicist and postdoctoral fellow at the Center for Astrophysics.
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