For the first time, astronomers have mapped the surface of a massive hot star, proving a decades-long theory that hot spots on the star’s surface affect the behavior of stellar winds. A University of Toledo astronomer was a member of the international research team that made the groundbreaking discovery.
“We’re now better able to understand how massive stars send out material into space through their winds,” said Dr. Noel Richardson, postdoctoral research associate in the UT Department of Physics and Astronomy, who was a member of the research team. “This research gives us a better understanding of how stars lose material, which then forms new stars and planets.”
The team’s research appears in a paper recently published in the Monthly Notices of the Royal Astronomical Society, one of the world’s leading astronomy journals.
For decades, astronomers have theorized that there were hot spots on the surface of massive stars that affected stellar winds, but they didn’t know how those spots behaved or how they impacted the winds.
To test that theory, the research team chose as its test subject a supergiant called Zeta Puppis, a massive star 60 times larger than the sun and seven times hotter at the surface. Massive stars are rare and usually travel in pairs. But Zeta Puppis flies solo — and it flies fast. The star hurtles through space at 37 miles per second, 60 times faster than a speeding bullet.
Using a network of nanosatellites from the “BRIght Target Explorer” (BRITE) space mission, researchers monitored the surface brightness of Zeta Puppis every 100 minutes for six months in 2014. They simultaneously monitored the behavior of its stellar winds over time from several ground-based observatories.
After correlating the two sets of data, the team found that Zeta Puppis rotates at tremendous speed — once every 1.78 days. In comparison, our sun, which is 60 times smaller, takes almost a month to rotate once.
Astronomers in the past had never had enough data to verify their claims about hot spots and their effects on stellar winds. The new data allowed them to map the surface of Zeta Puppis. It proved what the astronomers suspected: The structures on the star’s surface were indeed there, and these hot spots did affect the star’s winds.
Astronomers have mapped the surfaces of cooler stars, Richardson said, but this is the first time they’ve mapped a hot star. They learned that a brighter, hotter spot creates huge spiral structures in stellar winds that scatter more material into space.
A team of more than 40 astronomers participated in the research. The group included six amateur astronomers in Australia, New Zealand and Brazil, who spent three to four hours every night for six months peering into their telescopes and collecting data.