Astronomers have discovered propagating heat waves near a massive protostar. These waves became visible thanks to stellar masers - natural sources of microwave radiation in the molecular cloud surrounding the star. The results of the discovery are described in the journal Nature Astronomy.
Astronomers from the Maser Monitoring Organization, an international group for the study of M2O masers, using data from several radio telescopes, detected episodic heat waves propagating in the vicinity of the massive protostar G358-MM1. Subsequent observations confirmed that these waves were caused by a temporary increase in accretionary activity.
Although the basic principles of star formation are well known, it is still a mystery how supermassive stars manage to reach such large sizes. Due to the tremendous gravitational pressure inside the massive protostar, nuclear fusion in it should begin during the formation process. In this case, further growth will be difficult due to the strong radiation pressure of the young star.
Scientists assumed that the resistance of this pressure could be overcome if the accretion of material from the circumstellar disk occurs in discrete large batches (packets) of material. At such moments, the brightness of the star should increase greatly within a short time. Unfortunately, brightness fluctuations are very difficult to observe due to the fact that protostars are usually surrounded by dense clouds of dust.
Researchers from the M2O project used the observation of masers - bursts of microwave radiation in massive star-forming regions, the formation of which is associated with the process of molecular amplification of the signal - to record the activity of the nascent star.
In this case, the source of amplification was methanol molecules, which were excited by a thermal wave propagating from the protostar. The wave locally increases the temperature of the gas for a short time, causing the emission of methanol masers. As the wave propagates, the position of the maser emission changes.
The scientists recorded high spatial resolution radio interferometric data of 0.005 arc seconds (1 degree of arc = 3600 arc seconds) at intervals of several weeks and found that masers were spreading outward from the star. However, the speed of their propagation is too high to be compatible with the movement of the gas. From this, astronomers concluded that the maser activity was caused by a heat wave caused by gas accretion onto the protostar.
The episodic nature of heat waves confirms the hypothesis that massive protostars grow discretely.
"The observations of M2O are the first to provide detailed evidence for the effects of an accretion burst in a massive protostar in sufficient detail to support the theory of episodic accretion of massive star formation," the Max Planck Institute for Astronomy said in a press release from the Max Planck Institute of Astronomy, first author Ross Burns from the National Astronomical Observatory of Japan.
Hendrik Linz, another study author, adds: “Observing a real heat wave directly in the thermal infrared range would be very difficult. timescales after the outbreak."
Scientists plan to continue monitoring masers in other star-forming regions to learn more about the growth of massive protostars.
