Galaxies change at every possible timescale. From the billion year-long slow mergers of massive systems to the minute-to-minute flickers of active galactic nuclei, they are always changing in a myriad of different ways. 

In a startling-to-me story from radio astronomy, the new Very Large Array Sky Survey (VLASS) catalog of radio galaxies is allowing astronomers to see galactic jets turning on. VLASS is working to map 80% of the sky. This kind of survey was done at a smaller scale twenty-some-odd years ago with the VLA FIRST, or Faint Images of the Radio Sky at Twenty centimeters, survey. The similarities in data quality of these two surveys and their separation in time means astronomers can search through the data for objects that have changed in those twenty years, and, remarkably, it turns out that roughly 2000 galaxies appear in VLASS that weren’t in FIRST. 

Initial follow-up observations of fourteen of these objects found that these systems were AGN lighting up and sending out new jets of material.

According to Kristina Nyland, the lead author of this new study which appears in The Astrophysical Journal: Jets like these can strongly affect the growth and evolution of their galaxies, but we still don’t understand all of the details. Catching newborn jets with surveys like VLASS provides a measure of the role of powerful radio jets in shaping the lives of the galaxies over billions of years.

People often talk about how the universe doesn’t do things on timescales humans can see, but it turns out that sometimes we can get lucky and catch the start or finish of the civilization spanning activities.

More Information

National Radio Astronomy Observatory press release 

“Quasars That Have Transitioned from Radio-Quiet to Radio-Loud on Decadal Timescales Revealed by VLASS and FIRST,” Kristina Nyland et al., 2020, to appear in the Astrophysical Journal (preprint on arxiv.org)