Hen 2-428 is a planetary nebula with a binary double white dwarf system core.

This core star system is the first discovered candidate for Type Ia supernova through binary white dwarf merger process.

[2][3][4][5] The pair are expected to merge into a single star in about 700 million years, whereupon they will explode in a Type Ia supernova.

The inspiralling of the stars is caused by the emission of gravitational waves, resulting in the loss of orbital energy.

The system is important to astrophysicists as Type Ia supernovae are used as standard candles to measure the distance to faraway objects, thus understanding the process is important to regularize and quantify the variations in the standard candle to reduce the error uncertainty in determining distance.