This illustration shows the rapidly rotating, highly magnetized white dwarf with the smallest radius ever found, with Earth’s moon shown nearby for a size comparison. With a radius of ~2,140 km, just about 20% larger than the Moon’s radius, this marks the smallest and most massive white dwarf whose parameters were ever measured this accurately. (GIUSEPPE PARISI)

What The Heaviest, Smallest White Dwarf Ever Found Means For Science

The new record-holder opens up a literal Universe full of possibilities.

Someday, even our own Sun will eventually run out of hydrogen fuel in its core, bringing a tremendous set of changes to our Solar System. Its core will contract and heat up while its outer layers expand and slowly get expelled, signifying our transition into a red giant. When the helium in the core is exhausted, the core will contract further, becoming a carbon/oxygen white dwarf, while the remainder of our star gets blown back into interstellar space in a spectacular planetary nebula. For practically every star born with 40% to 800% of our Sun’s mass, the same fate awaits them all.

The white dwarf that we’re left with is always much less massive than the star it originated from, and never more massive than about 1.4 solar masses. Above this mass limit — known as the Chandrasekhar mass — a spontaneous thermonuclear reaction will occur: a type Ia supernova, destroying the white dwarf entirely. Driven by a series of curious observations, a team of scientists just discovered the most massive white dwarf ever robustly measured: between 1.327 and 1.365 solar masses, and it’s only 2,140 kilometers in radius, or barely larger than the Moon. It’s a fascinating find, but what it teaches us is truly phenomenal.

Normally, a planetary nebula will appear similar to the Cat’s Eye Nebula, shown here. A central core of expanding gas is lit up brightly by the central white dwarf, while the diffuse outer regions continue to expand, illuminated far more faintly. The white dwarf at the center contracts but remains very hot, with some white dwarfs reaching temperatures of 60,000 K or more at the extremes. (NORDIC OPTICAL TELESCOPE AND ROMANO CORRADI / WIKIMEDIA COMMONS / CC BY-SA 3.0)

While we might look at our Solar System and our Sun as a “typical” example of what’s out there, it’s important to recognize that we’re only a sample size of 1, and that nature comes in all sorts of varieties. 95% of the stars in our galaxy are less massive than our Sun, but that remaining 5% means that approximately 20 billion stars in the Milky Way are more massive than we are. Additionally, about half of all the stars we know of are part of a system with two or more stars in them; singlet systems like our own are extremely common, but binaries, trinaries, and other multi-star configurations are quite common as well.

The reason this matters is that many binary systems are born with stars of similar masses, and hence they have similar fates. If one…