Planets or no planets?

NASA artists have released a video exploring an alternative hypothesis to explain the existence of disks comprising dust and gas often observed around young stars.

The standard theory for the lines and apparent currents swirling through these disks is that they are wakes and eddies left by the movement of newly formed planets. 

And while NASA scientists are happy to embrace this idea, the organisation’s astronomers are also (as all good scientists are) prepared to embrace alternative explanations.

Much of the groundwork for one such explanation was laid in 2013, with the publication in the journal Nature of a paper by astrophysicists from NASA’s Goddard Flight Centre and the California Institute of Technology’s Jet Propulsion Laboratory.

The paper revealed modelling that produced the same kind of disturbances in the dust-and-gas clouds without planets being present.

The suggested mechanism is called the photoelectric instability cycle (Pel). When ultraviolet light from the star hits dust grains in the disk, electrons are stripped away which then collide with the gas, producing heat. 

As the gas warms, its pressure increases, which traps more dust, which produces more heat and so on. 

Taking these calculations, as well as more recent refinements – especially constraints on the influence of radiation pressure – NASA has now produced new visualisations exploring the predicted role of Pel influencing the disks.

It will require much more data, and many more papers, before the mystery of what is causing disturbances in the dust disks is finally resolved. In the meantime, however, the latest images make for most fascinating, and relaxing, diversions.