Have you ever played connect-the-dots in a magazine? At first, it looks like a mess - but after you figure out how to connect the points, a pattern appears out of the chaos. Recently, astronomers noticed a mysterious spiral pattern hiding around a baby star. But instead of  ‘dots’, the pattern was made up by strange kind of ‘space torches’ called “masers”! 

When young stars form, they are surrounded by a disk made of gas and dust. The disk provides a steady flow of nutrients for the baby star at its centre - the “protostar” - to grow up. For a massive protostar - more than 8 times heavier than our Sun, the flow of nutrients is not continuous. Instead, clumps of material fall onto the baby star only occasionally. This releases a burst of energy that heats up the disk as it moves outwards - and produces maser emissions on the way. Astronomers call these short bursts of energy release - ‘episodic bursts of growth’. 

Using the VLBI technique, an international team of astronomers at NAOJ studied the high-mass protostar G358-MM1 in utmost detail. By connecting the regions that fired a maser emission the researchers could map out the surface of the disk in G358-MM1. This new technique is called - heat-wave mapping. However, the surprise doesn’t end here!

As it turns out, this particular baby star doesn’t just have a simple disk around it! It has a rotating disk shaped like a spiral, like an octopus - only instead of 8 arms, the disk has 4. Astronomers think that a spiral pattern is a telltale sign of disturbances or “instabilities” in the disk due to gravity. This is usually the case where there is heavy star formation going on.

This discovery also connects spiral arm instabilities to the episodic growth bursts - a key factor for how high-mass stars form. To help with the further investigation, astronomers will now start  looking for other baby stars with masers around them - maybe they will find another spiral… or something entirely unexpected!

Image: Map of material distribution in the disk around protostar G358-MM1. The white “+” marks the location of the protostar. The contour lines indicate signal strength. The colours represent the line-of-sight velocities. Movement away from the viewer is shown in red/orange and movement towards the viewer is shown in blue/green, indicating that the disk is rotating. Overlaid gray lines indicate the spiral arms identified through data analysis. (Credit: R. A. Burns)