Galactic Ghost

“A whole population of galaxies... have been hiding from us.”

Scientists first glimpsed the glowing blob from ground-based telescopes. Then it disappeared in images from the Hubble Space Telescope taken, apparently, of that same spot in the universe. 

Now, astronomers from UT Austin, working with the COSMOS-Web project, have used images from the James Webb Space Telescope to identify the mysterious reappearing object. AzTECC71 turns out to be a dusty star-forming galaxy, or a galaxy that’s still forming new stars but is concealed in a dusty veil. Previously, these galaxies were believed to be very rare in the early universe. The new detection indicates they may be far more common than expected.

“Even though (the galaxy) looks like a little blob, it’s actually forming hundreds of new stars every year,” said Jed McKinney, a UT postdoctoral researcher. “It’s potentially telling us there’s a whole population of galaxies that have been hiding from us.”

The COSMOS Web project, co-led by UT astronomer Caitlin Casey, hopes to map up to 1 million distant galaxies.

The James Webb Space Telescope has revolutionized the ability of scientists to study dusty star-forming galaxies. Previously, researchers struggled to see them in optical light as a lot of the light from such galaxies’ stars are absorbed by dust veils and then re-emitted at redder wavelengths, the type detectable with JWST. The telescope has revolutionized scientists’ ability to find previously hidden galaxies like these ones. 

“It’s so sensitive,” McKinney said, “not only can it stare back into the farthest reaches of the universe, but it can also pierce the thickest of dusty veils.”