Bright infrared light emanating from two merging galaxies has just been brought out of hiding. Using the JWST, astronomers have pinpointed the exact location of the light, behind a thick wall of dust that obscures it at other wavelengths. It’s still unknown what is producing the light, but narrowing down its location will help figure out what it is and how it shines much brighter than expected. “The James Webb Space Telescope has given us completely new views of the Universe thanks to its highest spatial resolution and infrared sensitivity.” says astrophysicist Hanae Inami of the Hiroshima Center for Astrophysical Sciences at Hiroshima University in Japan.
“We wanted to find the ‘engine’ that drives this galaxy merging system. We knew this source was deeply hidden by cosmic dust, so we couldn’t use visible or ultraviolet light to find it. Only in the mid-infrared, observed with the James Webb Space Telescope, we now see this source dwarfing everything else in these merged galaxies.”
Although the Universe is mostly empty space, mergers between galaxies are not uncommon. Massive galaxies are pulled together by the inexorable pull of gravity, combining to form larger galaxies. It’s not even something remote that only happens to other galaxies in other places: the Milky Way itself is a cosmic Frankenstein’s monster, partially made up of all the other galaxies it has included during its billions of years of life. Many examples of galactic mergers at various stages have been found in the wider Universe, but it is a slow process that can take millions to billions of years.
Scientists have to take the examples we have and reconstruct the timeline around them, like a single frame from a movie, and the only other examples are single frames from similar, but different movies. It’s painstaking work, but it’s one of the best tools we have for understanding galaxy mergers.
We also know from the light emitted by these mergers that they are quite animated. Although galaxies are mostly space, stars can collide with each other or interact gravitationally to disrupt each other’s orbits. Clouds of star-forming gas between stars can also collide with each other, generating shocks that can unleash furious waves of star formation known as starbursts, visible as infrared light shining off the dust clouds.
This is what scientists expected to see when they switched the infrared Spitzer Space Telescope to a merger of galaxies 500 million light-years away called IIZw096 in 2010. Instead, they found bright infrared light shining through the midst of the ongoing collision. Unfortunately, Spitzer did not offer a high enough resolution to find the exact location of the light source, and the mystery had to be put aside. That’s because the longer wavelengths of infrared light don’t scatter dust the way shorter wavelengths do, and Spitzer was top-of-the-line in its time, so no other telescope could hope to come close. . Then the JWST arrived, and Inami and his colleagues went to watch closer