According to the Cosmological principle, the Universe is isotropic, homogeneous and the laws of physics are universal. State what is meant by the term isotropic.
Astronomers often use absorption spectral lines to determine the relative velocity of distant galaxies. The wavelength of a specific absorption spectral line measured in a laboratory on Earth is 450 nm450\text{ nm}450 nm.
A distant galaxy, Markarian 421, is at a distance of 180 Mpc180\text{ Mpc}180 Mpc from the Earth and contains a massive black hole at its core.
Calculate, in nm\text{nm}nm, the wavelength λ\lambdaλ of this same spectral line when observed in the light coming from Markarian 421. Assume the Hubble constant is 70 km s−1 Mpc−170\text{ km s}^{-1}\text{ Mpc}^{-1}70 km s−1 Mpc−1 and the speed of light in a vacuum is 3.00×108 m s−13.00 \times 10^8\text{ m s}^{-1}3.00×108 m s−1.
State one defining physical characteristic of a black hole.
