Record-making vorticity found in quark-gluon plasma
Brookhaven National Laboratory
High-energy ion collisions have produced the swirliest fluid ever discovered, in a state of matter that mimics the early universe.
To create the überwhirly liquid, scientists slammed gold ions together at velocities approaching the speed of light at Brookhaven National Laboratory in Upton, N.Y. Such collisions, performed in Brookhaven’s Relativistic Heavy Ion Collider, cook up an ultrahot fluid, re-creating the state of the universe millionths of a second after the Big Bang, before protons and neutrons had formed. In this fluid, known as a quark-gluon plasma, the constituents of protons and neutrons — quarks and gluons — intermingle freely (SN: 12/10/16, p. 9).
Scientists already knew that this fluid is the hottest ever produced in a laboratory, and that it has almost no viscosity. Now, physicists can add one more unusual property to the list. The quark-gluon plasma created in such collisions has an average vorticity — or swirliness — of about 9 billion trillion radians per second, researchers from the STAR Collaboration report online January 23 at arXiv.org. That’s vastly more than other known fluids. Even the core of a supercell tornado has a vorticity of only 0.1 radians per second.
To measure vorticity, the scientists studied a quantum mechanical property called spin from particles produced in the collision known as lambda baryons. The spin, an intrinsic type of angular momentum, tends to align with the vorticity of the fluid, providing a window into the plasma’s gyrations.
STAR Collaboration. Global Λ hyperon polarization in nuclear collisions: evidence for the most vortical fluid. arXiv:1701.06657. Posted online January 23, 2017.
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