Young stars, so-called protostars, grow by clumps of matter falling onto them from their surroundings. However, this process does not occur evenly, but in boosts. During such a growth boost, the protostars light up brightly - they experience an accretion burst. Researchers have already been able to observe low-mass stars, which have a similar mass to our sun, several hundred times during their growth phases. High-mass stars (heavier than 8 solar masses) are much rarer and only live for a comparatively short period of time. This is why astronomers were only able to observe the first outburst of radiation from a massive star in 2016 (see DSI News of November 14, 2016). Overall, only a handful of outbursts of such heavyweights are known to date. A team led by Verena Wolf from the Thuringian State Observatory (TLS) has now been able to detect the sixth, strongest growth boost of such a massive young star to date. Far-infrared data from SOFIA, the Stratospheric Observatory for Infrared Astronomy, allowed a more precise estimation of the total energy released by the associated accretion burst. The results of this study were published on July 30st in the journal Astronomy & Astrophysics.
SOFIA was operated by the German and American space agencies (DLR and NASA) and the German SOFIA Institute (DSI) at the University of Stuttgart coordinates the activities of SOFIA on the German side.
Infrared images confirm the growth boost
In 2019, radio data indicated an increase in microwave radiation in the star-forming region G323.46-0.08 (G323 for short), which is located in the southern sky in the constellation Circinus. Together with her colleague Bringfried Stecklum, also from the TLS, Verena Wolf set out to find the cause of this increased microwave radiation. Was a growth boost the reason? Star formation takes place well hidden inside cold, dusty molecular clouds, which absorb visible light and only become transparent at longer wavelengths. In the archive of the VISTA telescope (Visible and Infrared Survey Telescope for Astronomy) of the European Southern Observatory (ESO) the scientists found what they were looking for. Numerous near-infrared images of the star-forming region G323 at various dates made it possible to reconstruct a light curve. “With the VISTA images, we were able to confirm the accretion burst beyond a doubt,” says Bringfried Stecklum. “It lasted around eight years - from 2012 to 2020.”

SOFIA data confirm the model
In addition, for the first time the researchers used time depending models to analyze how the thermal radiation of the dust around the young star changes during its growth boost. The simulation predicted that the afterglow of the burst should still be measurable in the far infrared wavelength range in 2022, although the burst already ended in 2020. Far-infrared observations of G323 with the HAWC+ instrument on board SOFIA at wavelengths of 53, 62, 89, 154 and 214 μm indeed showed a slight increase in brightness and confirmed this prediction.
Seven times the mass of Jupiter
With the help of the computer simulation, Wolf's team was able to model the progression of the outburst and to precisely investigate the interplay between the dust distribution around the young star and the strength of the outburst for the first time: How much does the luminosity change during the outburst? How long exactly does the outburst last? How much energy is released? How much mass has fallen onto the protostar? The combination of the VISTA and SOFIA data with the models provided the breakthrough: “This allowed us to reliably determine the energy that G323 released during the growth spurt and estimate the accreted mass,” explains Wolf. “Presumably a huge lump with about seven times the mass of Jupiter fell onto the star. In the eight years of the outburst, the star released as much energy as the sun emits in 740,000 years.”
Original Publication:
- The accretion burst of the massive young stellar object G323.46−0.08, A&A July 30th, 2024
Futher Links to the News:
- Researches at the Thuringian State Observatory find proof of the most energetic accretion burst of a massive young star, Press release of the Thuringian State Observatory (TLS), 30. Juli 2024
Contact:
Thuringian State Observatory (TLS):
Dr. Verena Wolf |
Dr. Bringfried Stecklum |
German SOFIA Institute (DSI):
Dörte Mehlert (mehlert@dsi.uni-stuttgart.de)
Further SOFIA Links:
- SOFIA Science Center
- NASA SOFIA Missions Page
- NASA SOFIA blog
- SOFIA Mission Page of DLR Space Agency (German)
- DSI Image Galery (German)
- News Overview (partly in German)
- Project Chronicle (German)
SOFIA, the "Stratospheric Observatory for Infrared Astronomy" is a joint project of the Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR; German Aerospace Center, grant: 50OK0901, 50OK1301, 50OK1701, and 50OK2002) and the National Aeronautics and Space Administration (NASA). It is funded on behalf of DLR by the Federal Ministry for Economic Affairs and Climate Action based on legislation by the German Parliament, the State of Baden-Württemberg and the University of Stuttgart. SOFIA activities are coordinated on the German side by the German Space Agency at DLR and carried out by the German SOFIA Institute (DSI) at the University of Stuttgart, and on the U.S. side by NASA and the Universities Space Research Association (USRA). The development of the German instruments was funded by the Max Planck Society (MPG), the German Research Foundation (DFG) and DLR.
The Thuringian State Observatory is a non-university research institution of the Free State of Thuringia. It conducts basic research in astrophysics. The researchers at the TLS use various telescopes around the world to observe galaxies, stars, the sun, gamma-ray bursts and extrasolar planets.
The Thuringian State Observatory operates and uses the 2-meter Alfred Jensch Telescope for observations in the optical spectral range and a station of the European Low Frequency Array (LOFAR) radio telescope. It is also setting up a solar laboratory to develop a prototype of an automated telescope for continuous observations of the sun.