Strangelets are cosmological objects that, as the name implies, are made of strange matter (also known as quark matter).
Scientists believe that strange matter is made in one of the universe’s hottest furnaces: the cores of very massive neutron stars. Neutron stars are actually the fragments of stars that have collapsed, and can be up to eight times larger than the Earth’s sun. The sheer pressure and temperature of those stars reached such intense proportions that the atomic nuclei soldered to form neutrons. Some scientists call these new matter neutronium, an ocean of neutrons packed in far greater density than ordinary matter.
Neutronium inside the center of the neutron star can collapse, due to the pressure and gravity in its center. This releases quarks, which then bond to each other again, forming quark matter. It’s considered to be a phase change, a lot like the way water freezes into ice, but of course with greater density and magnitude.
Scientists believe that quark matter can exist outside of quark stars, and dub these strangelets. These can be one cause of dark matter, which swallows ordinary matter when it comes in contact with it. Scientists theorize that it is possible for strangelets to eventually swallow all conventional matter—but this is not going to happen for a very, very long time.
Though scientists have not yet been able to present indisputable proof of the existence of strangelets, there have been observations of stars that are denser than neutron stars but have more volume than black holes.
Strangelets cannot be proven with existing instruments.