Wow - evidence that very massive neutron stars may have cores made of deconfined quark matter! The idea of a 'quark star' is not new, but I didn't know it was a serious possibility.
An ordinary neutron star has a core made mostly of densely packed neutrons. A matchbox-sized chunk of this stuff weighs about 3 billion tonnes. But if you squeeze this stuff hard enough, eventually the neutrons break. Each neutron consists of 3 quarks held together by gluons. So when the neutrons break you get 'quark matter' - a sea of quarks and gluons, no longer confined in neutrons.
We've made something similar here on Earth: at CERN and Brookhaven, physicists smack atomic nuclei at each other so hard that the protons and neutrons break and momentarily form a 'quark-gluon plasma'. But the conditions in a neutron star core are different: cooler, but more pressure - and not just temporary.
This new paper tries to take the measured properties of massive neutron stars and see if they fit a model where the inner core is made of deconfined quark matter. They say it does with about 80% probability! I'd take this with a grain of salt, but it's an exciting possibility. It's not every day we find quintillions of tonnes of a new state of matter.
For me, the coolest part is that deconfined quark matter may have an extra symmetry, called 'conformal symmetry'. This means that if you zoom in on it, it looks almost the same. An atom looks like a blob with some specific size. So does a neutron. But a system with conformal symmetry is just a blur spread out everywhere - and if you zoom in or zoom out, you see something very similar. This is crazy.