Astrophysicists test their hypothesis by using

For much of astrophysics
Newton’s theory of gravity is perfectly adequate to predict how things behave.
However
In instances of strong gravity or very large scales
Astrophysicists use Albert Einstein’s theory of general relativity.
Those cases include
Gravitational waves
And the structure of the universe as a whole.

Theorists in the astrophysics division use combinations of calculations
And observations to characterize and understand astrophysical phenomena on a wide range of scales
Ranging from exoplanets
And neutron stars
To the dynamics of stars and galaxies
All the way to the universe at large.

Quite a lot of physics started out as astrophysics originally.
Many colleges offer courses in astronomy aimed at non-physicists.
This may include
Planetary science
Observational astronomy
And the study of the structure of stars
And planetary systems.

The astrophysicist is concerned not just with the motion of the star
But its properties - things such as :
Chemical and metallic composition
Luminosity - all those things that make up the modern study.

Astrophysicists studying galactic dynamics model the disks, spiral arms, and other features of galaxies, to compare with observations

Other research simulates galaxy collisions and galaxy formation

[ link to “galaxy formation and evolution” page ]