Astronomers Using ALMA Telescope Discover ‘Gas Waterfalls’ Orbiting Young Stars
Scientists have observed the 3D motion of a protoplanetary disc for the first time according to a CNN report on the study, which was published yesterday in the international science journal Nature.
A protoplanetary disc is the billowing cloud of dust and gas that orbits a newborn star. This material collides and binds together by sheer physical force to eventually form a planet's rocky core. According to Phys.org, a protoplanetary disc is 99% gas. Of that gas, carbon monoxide is brightest and emits a particular wavelength that the ALMA Telescope can observe. New high-resolution data meant they could observe it in 3D.
This gas waterfall phenomenon has been theoretically modeled since the '90s but had never been confirmed by direct observation – until now. According to Richard Teague from the University of Michigan and lead author of the study, "…It was a big surprise to actually see these gas flows so clearly. The disks appears to be much more dynamic than we thought."
Teague went on to explain the rest of their findings:
"Planets form in the middle layer of the disk, the so-called midplane. This is a cold place, shielded from radiation from the star…We think that the gaps caused by planets bring in warmer gas from the more chemically active outer layers of the disk."
"What most likely happens is that a planet in orbit around the star pushes the gas and dust aside, opening a gap…The gas above the gap then collapses into it like a waterfall, causing a rotational flow of gas in the disk."
The team saw this phenomenon at three different points in the protoplanetary disc orbiting the star HD 163296, located almost 400 light-years away.
Despite this very plausible-sounding hypothesis, scientists cannot rule out other possible causes until we directly observe these planets (or whatever else). It could be, for example, due to the star's magnetic field – but researchers are fairly confident in their data. According to Jaehan Bae, the study's coauthor: "The patterns of these gas flows are unique and it is very likely that they can only be caused by planets."
Cover image: NRAO/AUI/NSF, S. Dagnello