Astrophysics: The Universe

The Universe includes everything that exists: galaxies, stars, planets, space, time, energy, and matter.
There are billions of galaxies in the Universe, each containing billions of stars. Our galaxy is called the Milky Way.
Astronomers use different types of telescope to observe the Universe. Visible light telescopes allow us to see celestial bodies, while radio telescopes let us detect radio waves from space.
The Universe began with the Big Bang - a colossal explosion from a tiny, extremely hot and dense point around 13.8 billion years ago.
Cosmic Microwave Background Radiation gives evidence for the Big Bang. It is radiation left over from shortly after the Big Bang, showing the Universe was very hot and dense.
Redshift is another evidence for the Big Bang, enabling us to estimate the age of the Universe. It shows galaxies are moving away from us, indicating the Universe is expanding.
The lifecycle of stars depends on their mass. Stars begin as a nebula, eventually becoming a main sequence star. High mass stars may end their lifecycle as a supernova and then into a neutron star or black hole. Low mass stars like our Sun become red giants and then white dwarfs, before ending as a black dwarf.
The electromagnetic spectrum is used to study the Universe. Different parts of the spectrum give different information about the Universe.
The Hubble constant helps us calculate the age and size of the Universe. It is used to work out how fast the Universe is expanding by observing the redshift of galaxies.
Some theories suggest the Universe will continue to expand forever, while others suggest gravity will eventually slow and reverse the expansion, resulting in a Big Crunch.
The Universe contains dark matter and dark energy. Dark matter doesn’t emit light or energy, and we can only detect it due to its gravitational effects on visible matter. Dark energy is hypothesised to be driving the accelerated expansion of the Universe.
A black hole is an object in space with gravity so strong that nothing, not even light, can escape from it. They form from the remnants of massive stars.
While understanding of the Universe grows, there are still many unanswered questions, such as the nature of dark matter and dark energy, the fate of the Universe, and the possibility of life beyond Earth.