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Sagittarius A or Sgr A is a complex radio source at the center of the Milky Way. It is located in the Sagittarius constellation, and is hidden from view at optical wavelengths by large clouds of cosmic dust in the spiral arms of the Milky Way. It consists of three components, the supernova remnant Sagittarius A East, the spiral structure Sagittarius A West, and a very bright compact radio source at the center of the spiral, Sagittarius A *. These three overlap: Sagittarius A East is the largest, West appears off-center within East, and A * is at the center of West. ==Two-dimensional size== The two-dimensional size of Sagittarius A * has been determined, based on Very Long Baseline Array observations, which helps explain the context of jet disk and accretion disk models on the radio emission spectrum. These measurements were made through the use of a wavelength of 7 mm, enabling the size to be determined. The result was that Sagittarius A * was determined to be an elliptical Gaussian with a semi-major axis size of 35.4×12.6 Rs with an inclination of 95 degrees east of north. The observations for this finding were found from the detection of NIR (near infrared) flares, and X-ray flares that were spotted by NuSTAR. Both flares come from electron excitation, not an enhanced accretion rate onto the black hole, which means that not all high energy events produce variability at radio wavelengths. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Sagittarius A」の詳細全文を読む スポンサード リンク
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