(ORDO NEWS) — New observations reveal a spiral pattern in a disk of material around a still-forming but already massive young star.
This indicates that there is a gravitational instability in the disk that influences the formation of a large mass star.
The protostellar disk helps supply material to the nascent star. Instead of a continuous stream, clumps of material from the disk are thought to fall onto high-mass protostars (which have 8 times the mass of the Sun and continue to grow), causing short, episodic bursts of growth.
An international research team led by NAOJ’s Ross A. Burns used VLBI techniques, integrating arrays of radio telescopes around the world, to map the maser emission in the disk around the high-mass protostar G358-MM1.
This protostar is the third observed growth spurt in history. It has been carefully studied by the Maser Monitoring Organization.
The team was able to investigate this phenomenon in detail for the first time.
Observations show a clear rotation around the central protostar and a spiral pattern with four arms. Spiral arms in rotating protostellar disks are a sign of instability.
For a long time it was assumed that this feature is associated with massive star formation, but it has not been proven by observations.
This discovery not only revealed the first spiral accretion disk in a high-mass protostar, but also linked spiral arm instability to the episodic growth bursts that are central to the theory of high-mass star formation.
This study used a new heat wave mapping technique.
When a clump of material falls from the disk onto the protostar, it releases a burst of energy that heats up the interior of the disk, causing a methanol maser to emit.
This heat wave then travels outward, heating more and more distant parts of the disk over time.
By observing the regions that caused the maser emission, the scientists were able to map the surface of the disk in G358-MM1.
A team of more than 90 astronomers from around the world now hope to apply this technique to observing the disks of other high-mass protostars that will experience growth bursts in the future.
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