Scientists Propose a New Kind of Matter Inside the Densest Stars

By Ryan F. Mandelbaum on at

You might have a pretty rigid understanding of the way stuff should look, at the most basic level. It should have a nucleus that is orbited by electrons. The nucleus should have protons and neutrons, inside each of which reside three quarks.

But experiment and theory have demonstrated a quirky nature to the most basic form of matter. Time and again, the largest colliders seem to have created matter at such high temperatures that quarks serve as the fundamental unit instead of atoms. Perhaps this matter could exist at the centre of neutron stars, too—and would be a lot less strange than scientists think.

There are six flavors of quarks—the up and down quarks that make up protons and neutrons, then four heavier ones that make up weirder particles, including the strange quarks. Some scientists, such as Edward Witten, have provided mathematical evidence that if you could get enough up, down, and strange quarks together, the resulting matter would prefer this quark-based state to the atomic one.

A new paper published by a team from the University of Toronto takes this idea even further. “Physicists have been searching for SQM for decades,” the researchers told “From our results, many searches may have been looking in the wrong place.”

Their calculations propose that maybe strange quarks aren’t required for quark-based matter to exist. Maybe, so long as the combined mass of the quarks is heavier than the heaviest elements in the periodic table, matter will prefer to exist in a state of solely up and down quarks. Such matter could possibly exist inside neutron stars, the incredibly dense stellar corpses thought to be made from neutrons. The team published their results recently in Physical Review Letters.

This new kind of strange-less quark matter is just a conjecture. One researcher not involved in the study, Kent State University associate professor Veronica Dexheimer, told Gizmodo that the work is unexpected and that the mathematics checks out. But she points out that the researchers include a few caveats where their theory might differ from more well-accepted ideas. It would require rejecting a more standard understanding of neutron stars, that they have an outer shell of quarks locked up in neutrons, for example.

“More investigation of the topic is necessary before turning two-flavoured quark matter into a strong candidate for what is in the interior of neutron stars,” Dexheimer said.

Perhaps such matter could be made in high-energy experiments by fusing together heavy atoms, the authors suggest, and maybe it would even be stable.

Whether they contain this quark matter or not, neutron stars hold many other mysteries. They glitch, they smash, they might be full of pasta. But at least they might not be “strange.” [Physical Review Letters]