USAAAO 2022, I кръг — Задача 29
USAAAO 2022 - First Round · 5 февруари 2022 г.
Условие
An astronomer takes a spectrum of a galaxy and observes that the hydrogen-alpha emission line is at a wavelength of 721.9 nanometers. In a laboratory on Earth, this same emission line is observed at a wavelength of 656.3 nanometers. Approximately what is the (proper) distance to this galaxy?
(a) 66 Mpc
(b) 430 Mpc
(c) 480 Mpc
(d) 3900 Mpc
(e) 4700 Mpc
Отговори
- B
Решение
The redshift of this galaxy is
According to Hubble’s law, for small redshifts the proper distance to a galaxy is related to its redshift by
where is the Hubble constant, 70 (km/s)/Mpc. Therefore, 430 Mpc.
Answer: B
Оригинал в Архива: usaaao_first_exam_2022_problems.pdf · официални решения: usaaao_first_exam_2022_solutions-1.pdf