An international team of astronomers has discovered that the supergiant star Zeta Puppis has bright spots on its surface that affect its stellar wind emission. These bright spots create a huge spiral pattern in the space environment around the star.
As reported in the Monthly Notices of the Royal Astronomical Society, the team noticed that both the star and its stellar wind rotate in less than two days. In particular, they observed some mysterious bright spots on the stellar surface that could be responsible for the spiral structure in the wind.
“The observations revealed a repeated pattern every 1.78 days, both at the surface of the star and in the stellar wind," lead author Tahina Ramiaramanantsoa, from the University of Montréal, said in a statement. "The periodic signal turns out to reflect the rotation of the star through giant ‘bright spots’ tied to its surface, which are driving large-scale spiral-like structures in the wind, dubbed ‘co-rotating interaction regions’ or ‘CIRs.’”
The observations were conducted with a series of nanosatellites known as BRITE (BRIght Target Explorers) and with ground-based professional and amateur observatories. The nanosatellites looked at the surface brightness from space, while the observatories looked at stellar wind behavior.
The team was able to link the spiral pattern to the bright spots and determine that the star surface changes every few hours, which leads to clump formations in the stellar wind.
“These results are very exciting because we also find evidence, for the first time, of a direct link between surface variations and wind clumping, both random in nature,” added Professor Anthony Moffat, also from the University of Montréal, and principal investigator for the Canadian contribution to the BRITE mission.
Zeta Puppis is an evolved star 60 times the mass of our Sun and seven times hotter. These characteristics already tell us that the star is pretty special, but it has another two qualities that intrigue astronomers. Unlike other supergiant stars, Zeta Puppis has no companion and it’s moving at 60 kilometers (37 miles) per second.
“One theory is that Zeta Puppis has interacted with a binary or a multiple system in the past, and been thrown out into space at an incredible velocity,” explained Professor Dany Vanbeveren from Vrije Universiteit Brussel.
The researchers have no explanation yet for the nature of the surface spots or its variation. More observations will be needed to untangle this mystery.