[填空题]
Astronomers have recently me ;y 2cooe32qlfn0hhne 7 g7cu0asured the rotation of gas around what might be a supermassive black hole of about 2 billion solar masses at the center of a ge7 uh n07ngh0calaxy. If the radius from the galactic center to the gas clouds is 60 light-years, what Doppler shift $\Delta\lambda/\lambda_0$ do you estimate they saw? z$\approx $ $ \times 10^{-3}$
