SAO 2020, Подбор за GeCAA · структурирани задачи — Задача 3. Galaxies
GeCAA Selection Test Structured Question Paper · 9 т.
Условие
Figure 1 shows the measured rotation velocity of hydrogen gas around the centre of galaxy NGC4565 as a function of angular separation from the galaxy. NGC4565 is located 10.2 MPc away from Earth.
1. Estimate the total mass within the galaxy within the largest radius for which the data is available. [5 т.]
2. Assume that the mass of galaxy is dominated by axions of rest energy having a lifetime of decay into two photons of seconds. Calculate the power from photons incident on a 100 cm diameter radio dish here due to axion decay. [4 т.]
Отговори
1. kg
Official accepted range: 6.4 × 10⁴¹ kg – 7.3 × 10⁴¹ kg.
2. W
Official accepted range: 2.5 × 10⁻³⁰ W – 2.9 × 10⁻³⁰ W.
Решение
3a
From the graph, we deduce the maximum angular distance to be , with a rotational velocity of (a value will be accepted as well)
M1
M1
Under the general assumption of radial symmetry,
M2
A1
3b
The power emitted is derived from the rate of axion mass decay into photons/energy
M1
M1
M1 A1
(accepted range: )
Оригинал в Архива: GeCAA Selection Test Structured Question Paper.pdf · официални решения: GeCAA Selection Test Structured Question Solutions.pdf