Researchers using NASA’s Hubble Space Telescope have discovered that the accretion disk around the young star FU Orion is much hotter than previously thought, reaching nearly three times the temperature of our Sun. This discovery challenges existing models and suggests a more complex interaction at the star-disk interface that emits unexpected levels of ultraviolet light.

Unprecedented heat in a young star’s accretion disk

NASA’s Hubble Space Telescope has revealed surprising new details about FU Ori, a young star surrounded by a disk of extremely hot material. The temperature of the disc was measured at 16,000 Kelvin; This is nearly three times the surface temperature of our Sun and nearly twice as high as scientists had previously estimated.
Young stars such as FU Ori often experience sudden and sharp increases in brightness caused by explosions. These stars grow by pulling material from surrounding disks and nebulae through a process known as accretion. However, the accretion disk around FU Ori is extremely unstable, leading to unpredictable fluctuations in the inlet flow rate.

Surprising findings in Stellar Interface

“By measuring ever closer to the inner edge of the accretion disk, we hoped to validate the hottest part of the accretion disk model to determine its maximum temperature,” says Lynn Hillenbrand, a professor of astronomy at Caltech and second author of the new study. article, published Astrophysics Journal Letters, explains the results.

“I think there was some hope that we would see something extra, like the interface between the star and its disk, but we certainly didn’t expect that. “It was a big surprise how much we saw – much brighter in ultraviolet light than we expected.”

To address the large temperature difference between past models and recent Hubble observations, the team proposes a revised interpretation of the geometry of the inner FU Ori region: accretion disk material approaches the star and a hot shock occurs when it reaches the star’s surface. It emits high levels of ultraviolet light.

Implications for planet formation and survival

Understanding the mechanisms of FU Ori’s rapid accretion process is more relevant to ideas of planet formation and survival.

“Our revised model, based on Hubble data, is not bad news for planetary evolution; that’s something different,” explains Adolfo Carvalho, a Caltech graduate student and lead author of the study. “If the planet was far outside the disk when it formed, flares from the FU Ori object should affect the chemicals the planet eventually inherits. However, if the planet formed is very close to the star, then the situation is slightly different. After several explosions, planets formed very close to the star can rapidly move inward and eventually merge with it. “You could lose, or at least completely destroy, rocky planets that form near such a star.”