[填空题]
The Sun rotates around the center of the Milky Way Grm 60hb, m :wkwkx 3pb62nhj6jalaxy (sl,iv s +x 3t u4ob5wf8mibjpr6qs1j 5,iuk)3 Fig. 5-46) at a distance of about 30,000 light-years fro,k3 q5vjiom8fi)xr wsps t6s,b1+3 lujub 54 im the center $ \left(1 \mathrm{ly}=9.5 \times 10^{15} \mathrm{~m}\right)$ . If it takes about 200 million years to make one rotation, estimate the mass of our Galaxy. Assume that the mass distribution of our Galaxy is concentrated mostly in a central uniform sphere. If all the stars had about the mass of our Sun $\left(2 \times 10^{30} \mathrm{~kg}\right)$ , how many stars would there be in our Galaxy?$\approx$ $\times 10^{11}$
