銀河中心のブラックホールが常に光を放出していることを発見 (Flickers and flares: Milky Way’s central black hole constantly bubbles with light)

2025-02-19

2025-02-18 ノースウェスタン大学

ノースウェスタン大学が主導する天体物理学者のチームは、NASAのジェームズ・ウェッブ宇宙望遠鏡（JWST）を用いて、天の川銀河中心部の超大質量ブラックホール「いて座A*」を詳細に観測しました。その結果、周囲の降着円盤が絶え間なくフレアを放出していることが明らかになりました。これらのフレアは、数秒間の微弱なものから、毎日発生する非常に明るい爆発、さらには数ヶ月にわたる微かな揺らぎまで、多様な時間スケールで観測されています。この研究は、ブラックホールの本質や周囲環境との相互作用、そして銀河の進化に関する理解を深める可能性があります。

＜関連情報＞

JWSTによるSgr Aの波長2.1μmと4.8μmの非停止変動：微弱な変動発光と明るい変動発光の異なる集団の証拠 Nonstop Variability of Sgr A Using JWST at 2.1 and 4.8 μm Wavelengths: Evidence for Distinct Populations of Faint and Bright Variable Emission

F. Yusef-Zadeh, H. Bushouse, R. G. Arendt, M. Wardle, J. M. Michail, and C. J. Chandler
The Astrophysical Journal Letters Published: 2025 February 18
DOI:10.3847/2041-8213/ada88b

Abstract

We present the first results of JWST Cycle 1 and 2 observations of Sgr A* using NIRCam taken simultaneously at 2.1 and 4.8 μm for a total of ~48 hr over seven different epochs in 2023 and 2024. We find correlated variability at 2.1 and 4.8 μm in all epochs, continual short-timescale (a few seconds) variability, and epoch-to-epoch variable emission implying long-term (~days to months) variability of Sgr A*. A highlight of this analysis is the evidence for subminute, horizon-scale time variability of Sgr A*, probing inner accretion disk size scales. The power spectra of the light curves in each observing epoch also indicate long-term variable emission. With continuous observations, JWST data suggest that the flux of Sgr A* is fluctuating constantly. The flux density correlation exhibits a distinct break in the slope at ~3 mJy at 2.1 μm. The analysis indicates two different processes contributing to the variability of Sgr A*. Brighter emission trends toward shallower spectral indices than the fainter emission. Cross-correlation of the light curves indicates for the first time a time delay of 3–40 s in the 4.8 μm variability with respect to 2.1 μm. This phase shift leads to loops in plots of flux density versus spectral index as the emission rises and falls. Modeling suggests that the synchrotron emission from the evolving, age-stratified electron population reproduces the shape of the observed light curves with a direct estimate of the magnetic field strengths in the range between 40 and 90 G and an upper cutoff energy, E_c, between 420 and 720 MeV.