An international team of astronomers has discovered the smallest and heaviest white dwarf yet. The stellar remnant, called ZTF J1901+1458, is a truly extreme object with an incredible magnetic field and fast rotation.
As reported in Nature, the white dwarf has a radius of 2,140 kilometers and a mass 1.327 times that of our Sun. This makes it very close to the maximum possible mass for such a stellar object. A little bit more and the white dwarf would explode into a supernova, an ironic fate given that white dwarfs are the end product of stars that couldn’t go supernova in the first place, not being massive enough to collapse destructively on themselves.
This white dwarf is also a fast spinner, rotating on its axis every 6 minutes 57 seconds, not quite as quick as EPIC 228939929, the fastest spinning star observed, which rotates every 5.3 minutes. ZTF J1901+145 also has an incredible magnetic field, several hundred times stronger than the most powerful non-destructive magnetic fields we can create on Earth.
This exceptional stellar remnant might dramatically change what we know of white dwarfs and more. "We caught this very interesting object that wasn't quite massive enough to explode," lead author Dr Ilaria Caiazzo from Caltech said in a statement seen by IFLScience. "We are truly probing how massive a white dwarf can be."
A possibility is that white dwarfs might not have to go through an explosive event to turn into a neutron star, the collapsed core of a massive star. The complex physics happening inside these objects might be sufficient (when the mass is high enough) to make them implode into a neutron star.
"This is highly speculative, but it's possible that the white dwarf is massive enough to further collapse into a neutron star," said Caiazzo. "It is so massive and dense that, in its core, electrons are being captured by protons in nuclei to form neutrons. Because the pressure from electrons pushes against the force of gravity, keeping the star intact, the core collapses when a large enough number of electrons are removed."
The newly found white dwarf is just 130 light-years away, very close to Earth in galactic terms. It is also young, less than 100 million years in age. This suggests that exceptionally small and heavy objects might be more common than thought.
The stellar remnant was discovered by the Zwicky Transient Facility, or ZTF, which operates at Caltech's Palomar Observatory. Many more extreme white dwarfs such as this might soon be found, and scientists may be able to start answering pressing questions about the nature of these objects.
"The discovery of this unique object illustrates the power of ZTF. By making hundreds of observations of the entire northern sky spread over several years, we can continue to identify exotic objects like this one," says co-author Tom Prince, the Ira S. Bowen Professor of Physics at Caltech.