B How black hole Sgr-A* Was Found

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The supermassive black hole Sagittarius A* at the center of the Milky Way has a mass of approximately 4.3 million solar masses, equivalent to 1.4 trillion Earths. Its discovery involved a combination of observational techniques over several decades, culminating in significant advancements in technology and data analysis. The black hole's presence was hinted at through the movement of nearby stars, which indicated a massive, invisible object exerting gravitational influence. Observations from various telescopes, including radio and infrared, played a crucial role in confirming its existence. Sagittarius A* remains a focal point for ongoing research in astrophysics and our understanding of galaxy formation.
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Some astronomy history on the discovery of the black hole at the center of our galaxy.
https://www.astronomy.com/science/5...-beast-lurking-in-the-heart-of-the-milky-way/

The supermassive black hole in our Milky Way weighs about 4.3 million solar masses, equal to 1.4 trillion Earths

Finding the Milky Way in the night sky is fairly easy. A short stroll to a dark, isolated location affords a ready snapshot of its splendor, as a small fraction of its 100 billion to 400 billion stars blaze overhead like a sprawling celestial stream.
 
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