The solar system is 25,000 light years from the center of our Milky Way galaxy. One light year is the distance light travels in one year at a speed of 3.0 x 10⁸ m/s . Astronomers have determined that the solar system is orbiting the center of the galaxy at a speed of 230 km/s . (b) Our solar system was formed roughly 5 billion years ago. How many orbits has it completed?

Astronomers have observed an otherwise normal star, called S2, closely orbiting an extremely massive but small object at the center of our Milky Way Galaxy called SgrA. S2 moves in an elliptical orbit around SgrA with a period of 15.2 yr and an eccentricity e = 0.87 (Fig. 6–17). In 2002, S2 reached its closest approach to SgrA, a distance of only 123 AU ( 1 AU = 1.50 x 10¹¹m is the mean Earth–Sun distance). Determine the mass m of SgrA, the massive compact object (believed to be a supermassive black hole) at the center of our Galaxy. State m in kg and in terms of the mass of our Sun.

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