Webb Telescope Unveils 19 Galaxies in a New Light

The exquisitely detailed images of 19 nearby, face-on spiral galaxies come to you via the Physics at High Angular resolution in Nearby GalaxieS (PHANGS) program.More than 150 astronomers of the PHANGS team used the James Webb Space Telescope to study these galaxies.

While you may have seen an image or three over the past couple years, this is the first time all 19 images are being released at once a special issue of Astrophysical Journal, consisting of 21 separate papers. The images under study show off details as small as 100 light-years across, which means we're seeing structures smaller than massive star formation regions within the Orion Nebula in galaxies tens of millions of light-years away.

“They’re mind-blowing even for researchers who have studied these same galaxies for decades,” says Janice Lee (STSCI). “Bubbles and filaments are resolved down to the smallest scales ever observed, and tell a story about the star formation cycle.”

We'll Be Counting Stars

In these images, Webb's near-infrared camera sees fully formed stars as blue lights. Some of them are older stars gathered in the galaxies' central bulges, while others are scattered along the spiral arms.

Dust had hidden many of these clusters of stars from visible-light view, so astronomers had previously relied on counting the most massive ones and then making some assumptions about how many smaller ones would accompany them.

“Now we can go look for the actual embedded young stellar objects and count them up,” explained PHANGS member Karin Sandstrom (University of California, San Diego), who presented some of the collaboration's results at the recent meeting of the American Astronomical Society. A full stellar census will help astronomers understand the whole stellar lifecycle, which can last billions or even trillions of years.

Dusty Bubbles

The mid-infrared images, on the other hand, reveal the glow of dust — especially the presence of complex molecules known as polycyclic aromatic hydrocarbons. The presence of these molecules acts as a tracer of star formation. Massive newborn stars, still enshrouded in such dust, appear a bright red.

As striking as the light in these images is, darker regions also intrigue: The outer layers of exploding stars have plowed into the sparse gases between stars, creating dark bubbles large and small amidst the glowing dust.

In the spiral galaxy NGC 628, a Herculean effort by postdoctoral researcher Elizabeth Watkins (Heidelberg University, Germany) resulted in the identification of more than 1,700 bubbles. What's more, she found that a third of the bigger bubbles had smaller bubbles along their edges. That's a sign that new starbirth was triggered along the dusty bubble walls carved out by older stars' deaths. As stars both form from gas and expel gas when they die, the study of dust-embedded stars and dusty gas in these galaxies will give astronomers insight into how this feedback cycle operates.

Webb isn't the only powerful telescope to look at these galaxies, just the latest. Images of these galaxies are already available in visible and ultraviolet light from the Hubble Space Telescope as well as the European Southern Observatory's Very Large Telescope’s Multi-Unit Spectroscopic Explorer in Chile. Radio data comes from the Atacama Large Millimeter/submillimeter Array, also in Chile.

The full PHANGS archive is available here — it's worth exploring!