Cosmic Drift Captured Before Star Birth

Cosmic Drift Captured Before Star Birth

Astronomers have detected a phenomenon known as ambipolar diffusion within a prestellar core for the first time, providing a new look at the mechanisms that trigger the birth of stars. The discovery, published in Astronomy & Astrophysics, reveals how the weakening of magnetic support leads to the gravitational collapse of cold, dense concentrations of gas and dust into protostars.

Researchers from Kyushu University and the Max Planck Institute for Extraterrestrial Physics focused their study on L1544, a prestellar core located in the Taurus molecular cloud. Using the Institute for Radio Astronomy in the Millimetre Range (IRAM) 30 m telescope, the team sought to understand how these cores reduce the strength of their magnetic fields, which can otherwise delay the formation of a star.

Because the extreme cold of prestellar cores causes common molecular tracers to freeze onto dust grains, the team identified a new set of tracers: the ion Diazenylium‑d1 (N2D+) and the neutral molecule para‑monodeuterated ammonia (para‑NH2D). By modeling the velocity of these two molecules, the researchers found a difference of about 0.05 km/s.

This velocity gap is evidence of ion-neutral drift. In these environments, ions remain tied to magnetic fields, while neutral particles eventually decouple and drift inward due to gravity. As these neutral particles accelerate toward the core center, they create the observed velocity difference.

"As ambipolar diffusion continues, the strength of the magnetic field decreases. Eventually, gravity becomes the primary driving force in the core, resulting in its gravitational collapse into a protostar."

Doris Arzoumanian, Associate Professor at Kyushu University's Institute for Advanced Study, via miragenews.com

While this research examines the precursors to star birth, the James Webb Space Telescope (JWST) has captured the violent aftermath of the process. In the Chamaeleon I Cloud complex, located approximately 625 to 630 light-years from Earth, JWST imaged a Herbig-Haro object known as HH 49/50. This object, nicknamed the cosmic tornado due to its helical shape, consists of ionized gas and debris whipped into a tower by plasma jets blasting from a baby protostar.

The source of these jets is believed to be a Class I protostar named Cederblad 110 IRS4 (or CED 110 IRS4), located about 1.5 light-years away from HH 49/50. These jets travel at speeds between 100 and 300 kilometers per second, plowing through surrounding clouds to form shock waves. The JWST used its Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI) to resolve details that were blurry in 2006 observations from the Spitzer Space Telescope.

The new imagery revealed that a fuzzy patch previously thought to be part of the jet is actually a distant, unrelated spiral galaxy. This chance alignment creates a visual illusion of the galaxy sitting atop the cosmic tornado. Other dots in the image were identified as entire galaxies or lone stars.

Beyond individual star births, the interaction between entire galaxies can also drive stellar creation. Data from the JWST and Hubble Space Telescope shows two spiral galaxies, IC 2163 and NGC 2207, undergoing a merger described as galactic cannibalism. Located about 114 light-years away in the Eridanus and Canis Major constellations, the galaxies are experiencing intense bursts of star formation due to their gravitational interaction.

The pair produces roughly two dozen new stars the size of the sun every year, a rate approximately eight times higher than that of the Milky Way. The duo has also seen about seven supernovas over the last few decades, compared to an average of two per century in the Milky Way.

The research team studying ambipolar diffusion intends to further confirm their findings by observing more prestellar cores and seeking higher-angular resolution observations to map the velocity drift of ion and neutral molecules.