Figure 1: Artist’s impression of a ‘sneeze’ of magnetic field lines, dust, and gas ejected from a baby star.　(c) ALMA (ESO/NAOJ/NRAO)

A star forms from a cloud of gas and dust. Interstellar magnetic field lines pass through these clouds. As the cloud contracts to form the star, the magnetic field lines get pulled along. But observations of young stars show that most of this magnetic energy is lost during the formation process. The question is, where does it go?

Looking for the answer to this question, a team led by Kazuki Tokuda, an astronomer affiliated with NAOJ and Kyushu University, used ALMA (Atacama Large Millimeter/submillimeter Array) to study a group of young stars called Taurus Dense Core MC 27. This stellar nursery is located approximately 450 light-years from Earth in the direction of the constellation Taurus.

One of the leading theories was that the magnetic field gradually weakened over time as the baby star grew. But as Tokuda explains, “As we analyzed our data, we found something quite unexpected. There were these ‘spike-like’ structures extending a few astronomical units from the protostellar disk. As we dug in deeper, we found that these were spikes of expelled magnetic flux, dust, and gas.”

Tokuda continues, “”This is a phenomenon called ‘interchange instability’ where instabilities in the magnetic field react with the different densities of the gases in the protostellar disk, resulting in an outward expelling of magnetic flux. We dubbed this a baby star’s ‘sneeze’ as it reminded us of when we expel dust and air at high speeds.”

Additionally, other spikes were observed several thousands of astronomical units away from the protostellar disk. The team hypothesizes that these were indications of past ‘sneezes.’ And similar spike-like structures have been observed in other young stars, indicating that they may be ubiquitous. These sneezes could help explain how baby stars shed excess magnetic energy and might be a vital part of the star formation process.

Figure 1: Artist’s CG movie of  ejection of dust and gas from a baby star by relasing magnetic field lines. (c) ALMA (ESO/NAOJ/NRAO)

Figure 2 (a) Bow shaped gas clouds surrounding a protostar, as revealed by previous observations. The image shows the radio wave intensity from HCO+ molecules. (b) A more detailed observation of the vicinity of the protostar by the highest resolution observation of the ALMA telescope. The image shows radio emissions from dust in the dense gas. Spine-like features associated with the protostellar disk are seen. (c) Comparison and correspondence between the imaginary image in Figure 1 and the observation in (b), with explanations for each region superimposed.
Credit: (a), (b) ALMA (ESO/NAOJ/NRAO), K. Tokuda et al.(c) ALMA (ESO/NAOJ/NRAO)

Paper(s)

Kazuki Tokuda et al. “Discovery of Asymmetric Spike-like Structures of the 10 au Disk around the Very Low-luminosity Protostar Embedded in the Taurus Dense Core MC 27/L1521F with ALMA”, in The Astrophysical Journal, DOI: 10.3847/1538-4357/ad2f9a

These works were supported by ALMA Joint Scientific Research Program (2022-22B), and JSPS KAKENHI grants (JP18H05436, JP18H05437, JP20H01945, JP20H05645, JP21H00046, JP21H00049, JP21K03617, JP21K13962, JP23K03464, and JP23H00129).

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Organisation for Astronomical Research in the Southern Hemisphere (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science and Technology Council (NSTC) in Taiwan and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).
ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.