Strange matter is, well, strange. And terrifying. It's a type of quark matter (matter at such extreme conditions that the normal rules break down) that could theoretically act like a combination of Kurt Vonnegut's ice-nine and the nanobot "gray goo" apocalypse scenario. Strange matter is a hyper-dense type of matter that does one thing: turn everything it touches into strange matter. Under the right conditions. Scientists have created strange matter in particle accelerators but the lab-grown strange matter quickly decays with no threat to us or the planet. Yet. But research has suggested that strange matter may be able to exist in a stable state inside the hyper-dense, hyper-weird interiors of neutron stars, and new research suggests that there may be entire star systems composed entirely of strange matter.
Research suggests that neutron stars may be so dense that the neutrons they're made of could break down into a soup of quarks (the constituent parts of sub-atomic particles). It's theorized that at the center of these weirdos, the pressure may cause half of the "down-quarks" to convert into strange-quarks (hey, I didn't make up these names) which, in turn instantly convert the entire neutron star into a strange soup. Further it's believed that these strange quark stars could periodically spit out a clump of strange matter that, if pulled into the gravity of another neutron star in a binary star system, would change that entire neutron star into a strange quark star in just one millisecond.
Scientists in China have recently detected multiple candidates they say might be potential "strange planets" orbiting pulsars (an even weirder type of rapidly spinning neutron star). Normal planets have a density no more than 1,870 lbs. per cubic foot, while strange planets would have an average density of 25 million billion lbs. per cubic foot. Million billion, that's right. So heavy it makes you sound like a babbling infant. These extreme densities would make it so strange planets could come close enough to the pulsar they orbit around to nearly skim the surface without being ripped apart by the pulsar's extreme gravity.
It's this characteristic that the scientists used to identify these potential strange planets. A series of potential candidates were found orbiting their stars much closer, and in two cases slower, than they should be able to if they were normal exoplanets.
Another series of potential strange planets were found orbiting what may be "strange quark dwarf stars", which are the strange-matter-assimilated versions of white dwarf stars, stars that have burned out most of their fuel and collapsed into compact, white-hot retirement.
But until they can measure potential gravity wave emissions from these strange planet candidates, researchers say that there's a chance they may just be looking at other white dwarf stars. It seems unlikely, though, as white dwarfs range from 150 to 1,200 times the mass of Jupiter, and these potential strange planets all have less than 10 Jupiter masses.
To know for sure, the scientists propose using the ongoing Advanced LIGO (Laser Interferometer Gravitational-Wave Observatory) project and the future Einstein Telescope to measure their gravitational waves. Anything as dense as strange planets would be would cause rippling warps in the space-time continuum that should be able to be detected. Until then though we'll probably continue to try making strange matter in the Large Hadron Collider and hope we don't all turn into strange soup.