A nova occurs in a binary star system consisting of a white dwarf and a companion star, usually a main-sequence star or a red giant. The white dwarf, which is the remnant of a star that has exhausted its nuclear fuel, has a strong gravitational pull. This gravitational force draws hydrogen-rich material from the companion star onto its surface via an accretion disk. When the accumulated material reaches a critical density and temperature, it ignites in a thermonuclear explosion, producing the nova.
