In a remarkable development, NASA’s Hubble Space Telescope has provided unprecedented insights into the young star FU Orionis, located in the constellation of Orion. Astronomers observed an unexpected increase in brightness of FU Orionis in 1936, and the star has continued to intrigue scientists due to its unique characteristics.
Hubble’s latest observations, utilizing its ultraviolet capabilities, have unveiled intricate details about the interaction between FU Orionis and its accretion disk, which has been depositing material onto the star for nearly 90 years. The findings challenge existing models of stellar accretion, particularly regarding the temperature of the inner disk. Using the Cosmic Origins Spectrograph and the Space Telescope Imaging Spectrograph, scientists obtained the first far-ultraviolet and new near-ultraviolet spectra of FU Orionis.
Lynne Hillenbrand from Caltech, a co-author of the study, expressed surprise at the results. “We were hoping to validate the hottest part of the accretion disk model, to determine its maximum temperature, by measuring closer to the inner edge of the accretion disk than ever before,” she said. The team found the inner disk touching the star to be alarmingly hot, challenging previous assumptions. It was much brighter in the ultraviolet spectrum than anticipated, which was an unexpected revelation for the researchers.
Originally considered an anomaly among young stars, FU Orionis belongs to a class of stars known for their dramatic fluctuations in brightness. These stars, a subset of T Tauri stars, are in the early stages of development and gain mass by absorbing material from their surrounding disk. Unlike typical T Tauri stars, whose disks are held back by stellar magnetic fields, the disks of FU Orionis objects frequently interact with the star, sometimes due to their massive size or interactions with a binary companion.
The astronomers discovered that the temperature of the inner disk of FU Orionis reaches approximately 16,000 kelvins, significantly hotter than previously estimated. This temperature is almost three times that of the Sun’s surface and nearly twice the amount prior models predicted. Such a high temperature in the impact region between the star and disk defies earlier theories and prompts further investigation into this dynamic.
Understanding these mechanisms not only helps in comprehending the processes around FU Orionis but also has broader implications for planet formation theories. As Adolfo Carvalho from Caltech explained, the revised model suggests a mixed impact on developing planets. While an FU Orionis outburst could alter the chemical composition of a distant planet, planets forming close to the star might face detrimental effects or even merge with the star due to increased accretion activity.
Further analysis of the ultraviolet data is underway, focusing on the spectral lines from various elements within the inner regions of the star. This analysis aims to shed light on the gas movements and environmental conditions surrounding FU Orionis. Hillenbrand noted that the wealth of ultraviolet data provided by Hubble allows scientists to explore previously inaccessible areas of stellar dynamics.
Such groundbreaking research continues to emphasize the Hubble Space Telescope’s critical role in advancing astrophysical knowledge. Operated jointly by NASA and ESA, the telescope remains a pivotal tool for unraveling the mysteries of the universe.
The discoveries made by the Hubble Telescope regarding FU Orionis offer valuable insights into the behavior of early-stage stars and their accretion processes. These findings not only challenge existing models but also open up new avenues for understanding stellar and planetary formation dynamics. Continued research in this field is essential for refining our comprehension of the universe and the formation of celestial bodies.
Source: Science.Nasa
