A James Webb Space Telescope survey known as PHANGS has revealed exquisite details in 19 nearby galaxies.

Gallery of 19 PHANG galaxy images
The PHANGS survey has collected observations of 19 face-on spiral galaxies in near- and mid-infrared light using the James Webb Space Telescope. Near-infrared light reveals light (old stars in the core appear blue). Dust appears in mid-infrared wavelengths, colored red and orange in this image. Dust-encased stellar newborns appear bright red.
NASA / ESA / CSA / STScI / Janice Lee (STScI) / Thomas Williams (Oxford) / PHANGS Team; Designer: Elizabeth Wheatley (STScI)

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

Webb's image at top left is blended with a Hubble image at bottom right. The comparison shows that Webb picks up what Hubble can't see
Face-on spiral galaxy, IC 5332, is split diagonally in this image: The James Webb Space Telescope’s observations appear at top left, and the Hubble Space Telescope’s at bottom right. Dust that appears dark to Hubble's visible-light and ultraviolet cameras instead appears bright to Webb's infrared detectors. IC 5332 has low surface brightness, making it almost a dwarf galaxy, Sandstrom says.
NASA / ESA / CSA / STScI / Janice Lee (STScI) / Thomas Williams (Oxford) / Rupali Chandar (UToledo) / PHANGS Team;

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.

Spiral galaxy with a bustling core, Webb's view shows orange-bright dust at top left, Hubble's view shows stars at bottom right
Face-on spiral galaxy, NGC 628, is split diagonally in this image: The Webb’s observations appear at top left, and Hubble’s on bottom right. The JWST image reveals more than 1,700 bubbles.
NASA / ESA / CSA / STScI / Janice Lee (STScI) / Thomas Williams (Oxford) / PHANGS Team

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!


You must be logged in to post a comment.