Water snow line around young star seen for the first time

In a first, scientists have spotted a water snow line surrounding a young star that is about 400 times brighter than our Sun and is undergoing a stellar outburst.
Scientists using Atacama Large Millimetre/submillimetre Array (ALMA) located in Chile have produced the first image of a water snow line within a protoplanetary disk.
The line marks where the temperature in the disk surrounding the star drops sufficiently low for snow to form.
A dramatic increase in the brightness of the young star V883 Orionis flash heated the inner portion of the disk, pushing the water snow line out to a far greater distance than is normal for a protostar, and making it possible to observe it for the first time.

Young stars are often surrounded by dense, rotating disks of gas and dust, known as protoplanetary disks, from which planets are born.
Snow lines are the regions in those disks where the temperature reaches the sublimation point for most of the volatile molecules.

In the inner disk regions, inside water snow lines, water is vaporised, while outside these lines, in the outer disk, water is found frozen in the form of snow.
These lines define the basic architecture of planetary systems like our own and are usually located at around 3 astronomical units (au) for a typical solar-type star.
However, the recent ALMA observations show that the water snow line in V883 Orionis is currently at more than 40 au of the central star, greatly facilitating its detection.

This star is only thirty per cent more massive than the Sun, but its luminosity is 400 times brighter as it is currently experiencing what is known as a FU Ori outburst, a sudden increase in temperature and luminosity due to large amounts of material being transferred from the disk to the star.
This explains the displaced location of its water snow line: the disk has been flash-heated by the stellar outburst.
"Our observations were designed to look for disk fragmentation leading to planet formation," said Lucas Cieza, from the Protoplanetary Disks Nucleus and University Diego Portales in Chile.
"Instead, we found what looks like a ring at 40 au. This illustrates well the transformational power of ALMA, which delivers exciting results even if they are not the ones we were looking for," said Cieza.

The discovery that these outbursts may blast the water snow line to about 10 times its typical radius is very significant for the development of good planetary formation models.
Such outbursts are believed to be a stage in the evolution of most planetary systems, so this may be the first observation of a common occurrence.
In that case, this observation from ALMA could contribute significantly to a better understanding of how planets form and evolve throughout the Universe.
The findings were published in the journal Nature.