BULLETIN
Stellar smoke rings shaped by starlight
Back in July this year, astronomers were baffled by the discovery of 17 concentric rings around a binary star system, WR140, in images taken by the James Webb Space Telescope. Though some wondered if it could be signs of an alien megastructure, recent simulations have found that the most likely explanation is dust blown out from a dying star being sculpted not just by stellar winds, but by the push of starlight – the first time the latter has been seen as it is happening.
WR140 is a blue supergiant star orbited every eight years by a Wolf–Rayet, a dying star with extremely strong winds. When the pair get close, the Wolf–Rayet star briefly produces dust that is then pushed outwards by stellar winds.
“Eight years later, as the binary returns in its orbit, another ring appears, the same as the one before, streaming out into space inside the bubbles of the previous one, like a set of giant nested Russian dolls,” says Peter Tuthill from the University of Sydney, who took part in the study.
However, the pattern of rings only matches their simulations precisely when they included not just the solar wind, but the push of starlight on the dust. Though the after-effects of this ‘radiation pressure’ have been seen many times, this is the first time that it has ever been directly observed.
“When it catches the photon wind streaming from the star, like a yacht catching a gust, it makes a sudden leap forward,” says Tuthill. “In one sense, we always knew this must be the reason for the outflow, but I never dreamed we’d be able to see the physics at work like this.” webb.nasa.gov
Comment by Chris Lintott
Since their discovery back in the 19th century, astronomers have wondered how Wolf–Rayets fit into the lives of stars. They’re thought to be produced when the most massive blue stars use up their hydrogen fuel, and have long been blamed for many Type 1b and 1c supernovae. But nagging doubts remained. We’d simply never seen an explosion that looked like it had been affected by the material we see surrounding Wolf–Rayets like WR140. But earlier this year Israeli astronomers showed that supernova 2019hgp took place inside a nebula like WR140’s. While it’s too early to say that WR140 will definitely end its life in a bang, we now know at least one of its cousins did.
Chris Lintott co-presents The Sky at Night