The universe's most extreme dead stars can form from vampire white dwarfs — and scientists finally know how

When stars the size of our sun die, they leave behind powerful stellar remnants called white dwarfs — and these white dwarfs can transform into even more extreme objects called neutron stars, composed of the densest material in the universe.

However, scientists have found that conditions must be "just right" for the major makeover to occur.

You can think of it like a cosmic "Goldilocks" situation.

As it turns out, the white dwarf has to be feeding on a companion star like some kind of cosmic vampire.

Neutron stars and white dwarfs are both born when stars run out of the fuel supplies needed for nuclear fusion happening in their cores, but the difference between the two lies with their masses.

Stars with masses similar to that of the sun end their lives when they run out of hydrogen in their cores.

This halts the nuclear fusion process — which involves converting that hydrogen to helium — leading to the stars collapsing and shedding their outer layers to become a white dwarf with around the mass of the sun crammed into the width of Earth.

When stars with masses around eight times that of the sun collapse after running out of hydrogen in their cores, they generate enough pressure and heat in these cores to fuse the produced helium into even heavier elements.

This process only ends when the star attains a core of iron.

The final collapse results in a supernova explosion and creates a neutron star with a mass between one and two times that of the sun.

That's the usual way neutron stars form.

However, what if there's a bridge between the white dwarf scenario and neutron star scenario? Scientists have long suspected there is indeed a pathway for a white dwarf to become a neutron star.

This new work maps out that pathway, calling it accretion-induced collapse (AIC).

"In AIC, the progenitor is already a stellar remnant, and the trigger is not its own evolution but material handed to it by a companion," team leader Laurenz Thümmler of ETH Zurich told Space.com.