Stars are born from clouds of gas and dust in space. Elements like hydrogen, helium, and lithium come together at the center of the cloud, and the whole thing starts to spin. As gravity takes over, these lighter elements start to fuse together, forming heavier elements. This process releases radiation from the core, which takes thousands of years to reach the surface and create pressure on the outer layers, leading to more radiation emission. This is the moment when we see the first light from the gas cloud, and we call this stage a protostar. Protostars are like the babies of the stars.
In some regions of galaxies, we can still observe these stellar nurseries where stars are forming, and this process will continue until there is no interstellar matter left for stars to form. Once a star forms, there is a struggle between two opposing pressures at the surface - the gravity that pulls everything toward the center of the star and the Pauli pressure that pushes the radiation out. When the fuel in the core of the star runs out, radiation stops being produced, causing a sudden implosion of the core. The outer layers of the star are ejected due to the conservation of momentum, resulting in the explosion of a supernova. The core of the star remains lifeless, and if it is heavy enough, it can curve space-time fabric enough to form a black hole. The gravity of a black hole is so strong that even light cannot escape, and we call the point of no return the event horizon.
Our Sun is a middle-sized star and will not form a black hole after it explodes in around 5 billion years. It will instead become a white dwarf, which will eventually become a black dwarf after a long time. A star needs to have a mass greater than 1.4 times that of the Sun to become a black hole or a neutron star. Stars can also become subgiants and then red supergiants before becoming black holes.
Unfortunately, the pervasive dark energy in space and time causes the accelerated expansion of the universe, leading to the decline of the rate of star formation over time. This is like cosmic climate change in a way, as the favorable conditions for star formation are changing. If every single star in the universe exhausts its fuel, we will enter an era called the black hole era, where the universe will be filled with black holes. The black holes may eventually collide and form even larger black holes, ultimately leading to the formation of a cosmological singularity. From this point, the second generation of the universe could form, and the cycle of birth and death of the universe could repeat in this way.