The most massive and luminous stars in the universe are known as hypergiants or supergiants. These stars are extremely rare and represent some of the most massive objects in the cosmos. Here are a few examples:
R136a1: Located in the Tarantula Nebula within the Large Magellanic Cloud, R136a1 is one of the most massive and luminous stars discovered so far. It has an estimated mass of about 265 times that of the Sun.
Eta Carinae: Eta Carinae is a binary star system located in the Carina Nebula. It consists of two massive stars, with the primary star having a mass estimated to be around 100 times that of the Sun. Eta Carinae has exhibited dramatic outbursts and is one of the most luminous stars in our galaxy.
Pistol Star: The Pistol Star is another luminous and massive star located in the Milky Way galaxy. It has a mass estimated to be about 100 times that of the Sun and is one of the brightest known stars, radiating an enormous amount of energy.
WR 25: WR 25 is a binary star system in the constellation Carina. The primary star is a massive Wolf-Rayet star, with a mass around 70 times that of the Sun. It is one of the most luminous stars in the Milky Way.
It's worth mentioning that these stars are incredibly rare and short-lived. Their immense mass leads to a rapid consumption of fuel, resulting in intense energy output and often culminating in explosive events such as supernovae or gamma-ray bursts.