Birth of a Supernova Type 1a Page 5 of 6 | Next page Now being fed by its companion star, the white dwarf pulls more and more stellar material into itself. When the mass of the white dwarf reaches 1.4 solar masses (40% more mass than that of our sun), a runaway nuclear chain reaction causes the entire white dwarf to explode. Because Type Ia supernovae always explode at 1.4 solar masses, they all have more or less the same characteristics, including how brightly they shine. Previous page | Next page History of the Universe | Birth of a Supernova | Tour the Universe Moving Targets | How Big is the Universe? | Spin a Spiral Galaxy Resources | Transcript | Site Map | Runaway Universe Home Editor's Picks | Previous Sites | Join Us/E-mail | TV/Web Schedule About NOVA | Teachers | Site Map | Shop | Jobs | Search | To print PBS Online | NOVA Online | WGBH © | Updated December 2000