10 Jan. () –
Our galaxy has significantly less “regular” or baryonic matter -the same type of matter that forms stars, planets and living things- than expected.
Astronomers have used an intense burst of radio waves originating from a nearby galaxy to inspect the halo of gas that surrounds our own galaxy, the Milky Way. Scientists studied the way light from the so-called fast radio burst, or FRB, scattered as it traveled from deep space toward our galaxy as a means of estimating how much matter resides in the galaxy’s halo. This is a bit like shining a flashlight through the fog to see how thick the cloud is; the more matter there is, the more the light will be scattered.
The results show that our galaxy has significantly less “regular” or baryonic matter (the same type of matter that makes up stars, planets, and living things) than expected. This, in turn, supports theories that matter is regularly thrown out of galaxies by powerful stellar winds, exploding stars, and actively feeding or accumulating supermassive black holes.
“These results strongly support the scenarios predicted by galaxy formation simulations where feedback processes push matter out of galaxy halos,” he says. it’s a statement Vikram Ravi, assistant professor of astronomy at Caltech, who presented the results at the 241st meeting of the American Astronomical Society (AAS) in Seattle. “This is critical for galaxy formation, so matter is funneled in and ejected from galaxies in cycles,” says Ravi.
The latest findings, submitted to The Astrophysical Journal, are part of a series of new results from Caltech’s Deep Synoptic Array (DSA), a National Science Foundation (NSF)-funded collection of radio antennas located in the high desert at the Owens Valley Radio Observatory, east of the mountains from the Sierra Nevada of California. The purpose of the DSA is to discover and study FRBs, mysterious flashes of radio waves that usually originate in the depths of the cosmos. The first FRB was discovered in 2007 and hundreds are now observed every year.
One of the challenges in the study of FRBs lies in identifying their place of origin. Knowing where the FRBs originate helps astronomers determine what may be triggering the intense cosmic flares. Identifying their locations is also essential for using FRBs to study how baryonic matter is distributed in the universe. Of the several hundred FRBs discovered to date, only 21 have been identified as known galaxies. The DSA, which began operating in February 2022, it has already discovered and identified the locations of 30 new FRBs.
In addition to finding less matter than expected in our Milky Way galaxy, other preliminary results from the array have raised new questions about the leading candidate for the cause of FRBs.
Previous findings have indicated that recently deceased stars with extreme magnetization, called magnetars, may be the source of FRBs. For example, in 2020, several telescopes, including Caltech’s STARE2 (Survey for Transient Astronomical Radio Emission 2), caught a red-handed magnetar firing an intense FRB in our own galaxy.
However, the new DSA observations show that FRBs originate from a diverse variety of galaxies, including older galaxies within rich galaxy clusters. These results suggest that if magnetars do emit FRBs, they form through multiple, potentially unknown pathways.
“Magnetars like those in the Milky Way form during episodes of intense star formation,” says Ravi. “Finding FRBs from galaxies that have mostly stopped forming stars was surprising.”
