2025-03-10 ミシガン大学（UMich）
炎星雲は星形成が活発な領域で、年齢は100万年未満と推定されています。この星雲内には、褐色矮星と呼ばれる、核での水素融合が起こらないほど小さな天体が存在します。褐色矮星は時間とともに暗く冷たくなるため、観測が困難ですが、若い段階では比較的明るく、JWSTの赤外線観測能力を活用することで検出が可能となります。
研究チームは、JWSTを用いて、木星の2～3倍の質量を持つ自由浮遊天体を発見しました。これは、星や褐色矮星が形成される際の質量の下限に関する理解を深めるものです。これらの発見により、星形成過程や惑星の研究において、褐色矮星が重要な情報源となることが示唆されています。
＜関連情報＞
- https://news.umich.edu/u-m-astronomers-peer-deeper-into-mysterious-flame-nebula/
- https://iopscience.iop.org/article/10.3847/2041-8213/adb96a
若い恒星群の初期質量関数における0.5 MJまでのターンオーバーの同定 Identification of a Turnover in the Initial Mass Function of a Young Stellar Cluster Down to 0.5 MJ
Matthew De Furio, Michael R. Meyer, Thomas Greene, Klaus Hodapp, Doug Johnstone, Jarron Leisenring, Marcia Rieke, Massimo Robberto, Thomas Roellig, Gabriele Cugno,…
The Astrophysical Journal Letters Published: 2025 March 10
DOI:10.3847/2041-8213/adb96a
Abstract
A successful theory of star formation should predict the number of objects as a function of their mass produced through star-forming events. Previous studies in star-forming regions and the solar neighborhood have identified a mass function increasing from the hydrogen-burning limit down to about 10 MJ. Theory predicts a limit to the fragmentation process, providing a natural turnover in the mass function down to the opacity limit of turbulent fragmentation, thought to be near 1–10 MJ. Programs to date have not been sensitive enough to probe the hypothesized opacity limit of fragmentation. We present the first identification of a turnover in the initial mass function below 12 MJ within NGC 2024, a young star-forming region. With JWST/NIRCam deep exposures across 0.7–5 μm, we identified several free-floating objects down to roughly 3 MJ with sensitivity to 0.5 MJ. We present evidence for a double power-law model increasing from about 60 MJ to roughly 12 MJ, consistent with previous studies, followed by a decrease down to 0.5 MJ. Our results support the predictions of star and brown dwarf formation theory, identifying the theoretical turnover in the mass function and suggesting the fundamental limit of turbulent fragmentation to be near 3 MJ.
