In the constellation Orion, in the cloud of gas and dust L1641, the young star PR Ori B suddenly flared up like a furnace that someone had thrown fuel into. Its brightness rose fivefold, and astronomers watched for the first time as a fuor was born, a rare event in which a star begins greedily swallowing material from the surrounding disk.
Until now, little was known about such outbursts, because almost all fuors are far away, and no one had studied them before they erupted. PR Ori B turned out to be the exception: it is close, and decades of archival observations of it have survived. Astronomers compared images from before and after and saw how a cool late-K-class star turned into a scorching disk with deep absorption bands of carbon monoxide and water.
The most curious discovery is the crystallization of silicates. The dust in the disk, made of amorphous silicates, rearranged itself into crystals of forsterite when heated. It is as if powdered sugar in hot caramel suddenly turned into hard candy. This process had only been hypothesized before, and now it has been seen in action.
PR Ori B will now become a benchmark for studying outbursts of young stars. Its proximity makes it possible to examine the disk at high resolution and to check exactly how outbursts reprocess the dust from which planets will later assemble.
PR Ori B is only the second-brightest known FU Orionis-type outburst in the optical, falling roughly one magnitude short of the prototype of the FU Orionis class. What's more, the PR Ori system was already observed as a variable star back in 1888, and complaints about funding for astronomical observations can be found in publications from that era.
Outbursts of young stars like PR Ori B bring to mind the plot of Stanisław Lem's novel Solaris, in which the planet's ocean responds to the star's radiation: here the star's disk responds to the outburst by reprocessing dust and heating up, which alters the chemistry of the future planetary system.