Discovery of an Accretion Streamer and a Slow Wide-angle Outflow around FU Orionis

Left: optical RGB composite image of LBN 878 (the red and brown nebula dominating the field) obtained by astrophotographer Jim Thommes. FU Ori (with its reflection nebula) is the bright object located at the center of the image. The inset shows the integrated intensity 12CO(2–1) maps as traced by the ALMA observations . Redshifted and blueshifted 12CO integrated intensity maps of FU Ori are plotted over the optical emission (color scale). The blueshifted moment 0 map (blue contours) was constructed including emission from 8.0 to 11.5 km s−1, while the redshifted integrated emission (red contours) includes the emission between 12.7 and 17.5 km s−1. Credit: The Astrophysical Journal (2024). DOI: 10.3847/1538-4357/ad31a1

A rare star cluster in the constellation Orion has revealed its secret. FU Orionis, a binary star system, first attracted the attention of astronomers in 1936 when its central star suddenly became 1,000 times brighter than its normal size. This behavior is expected from a dying star and has never been observed before in a young star like FU Orionis. This strange phenomenon inspired a new classification of the star of the same name (FUor star). Four stars suddenly flare up, grow brighter and brighter, and then dim again after many years. It is now known that this brightening is due to stars absorbing energy from their surroundings through gravitational accretion, the main force that forms stars and planets. But how and why this happens remains a mystery, thanks to astronomers’ use of the Atacama Large Millimeter/Submillimeter Array (ALMA). “The FU Ori has been devouring matter for almost 100 years to keep it going,” said the study, published today in the journal Astrophysical Journal, and the deputy director of ALMA’s North American Regional Center and a scientist at the National Radio Astronomy Observatory. “We have finally found the answer to how these young eruptive Mars replenish their mass,” said Antonio Hales, lead author of the study. journal. “For the first time, we have direct observational evidence of what is causing the eruption,” Hales said. ALMA observations showed that a long, thin jet of carbon monoxide rains down on FU Orionis. It appears that this gas did not contain enough fuel to sustain the current eruption. Rather, this accretion stream is thought to be a remnant of an earlier, much larger phenomenon that entered this young star system. “Interactions with larger gas flows in the past could have destabilized the system, causing an increase in brightness,” Hales explains. Astronomers used the ALMA antennas in different configurations to detect different types of emission from FU Orionis and detect the flow of mass into the star system. They also combined new numerical methods to model the mass flow as an accretion flow and estimate its properties. “We compared the shape and speed of the observed structures with what we would expect from a signature of incoming gas, and the numbers made sense,” says Aashish Gupta, a graduate student and candidate at the European Southern Observatory (ESO) and co-author of the study, who developed the method to model the accretion streamers. “The range of angular scales that can be investigated with a single instrument is truly amazing. ALMA gives us a comprehensive overview of the dynamics of star and planet formation, from large molecular clouds where hundreds of stars are born to our more familiar scale solar system,” adds Sebastián Pérez of the Universidad Santiago de Chile (USACH), director of Chile’s Millennium Emplacement on Young Exoplanets and Moons (YEMS) and co-author of the study.

These observations also indicated a slow-moving carbon monoxide efflux from FU Orionis. This gas is not related to recent outbreaks. Rather, it resembles outflows observed around other protostars. Mr Hales added: “Understanding how these strange FUor stars form can confirm what we know about the formation of different stars and planets. We believe that all stars I believe we will experience an eruption.” These eruptions are important because they affect the chemical composition of the accretion disks around the forming stars and the planets they eventually form. ” “We have been studying FU Orion since its first observation with ALMA in 2012,” Hales added. It will be interesting to finally get an answer. ”