Pressures Inside A Proton Are Higher Than Those Inside A Neutron Star

  • Researchers measure the pressure distribution inside a proton for the first time.
  • The proton’s core, at its highest point, generates pressures of about 1035 pascals.
  • They used a Lattice QCD approach to achieve this feat and performed calculations on several supercomputers.

Neutron stars are one of the densest objects in the universe: they are so dense that one teaspoon of star’s material would weigh a billion tons. The gravitational field at their surface is approximately 200 billion times that of the Earth.

Yet protons — stable subatomic particles with a positive charge — consist of even higher pressures. They make up 90% of cosmic rays that propagate in vacuum for interstellar distances.

Recently, physicists at MIT measured the pressure distribution inside a proton for the first time. They discovered that the proton’s core, at its highest point, generates pressures of about 1035 pascals. This is 10x higher pressure than what is found inside a neutron star.

The core pushes out from the center of the proton while the outer regions push inward. You can imagine it as a tennis ball trying to expand inside a football that is shrinking. The resulting pressure stabilizes the overall structure of the proton.

Proton’s Pressure Distribution

To calculate proton’s pressure distribution, physicists took both quarks and gluons (subatomic constituents of larger particles such as protons and neutrons) into account.

Over the past 6 decades, scientists have acquired a lot of information about quarks’ behavior inside the proton. However, the structure of gluon is far difficult to measure and understand.

In this study, physicists were able to determine the contribution of both quarks and gluons, which continuously interact in a fluctuating and dynamic way inside the proton.

Reference: Phys. Rev. Lett. | doi:10.1103/PhysRevLett.122.072003 | MIT

They have achieved this feat by calculating the interactions between gluons and quarks on several supercomputers. There is a quantum vacuum of pairs of gluons as well as quarks and antiquarks inside a proton, which regularly appears and disappears. The computations performed on supercomputers include all these dynamic fluctuations.

Lattice Quantum Chromodynamics

To calculate such fluctuations, they used a well-established non-perturbative approach called lattice QCD (quantum chromodynamics). It represents a set of equations describing the strong force, which binds gluons and quarks inside the proton’s structure.

This approach uses a 4D grid (lattice), 3 of which represents dimensions of space and 1 represents the dimension of time. Physicists evaluated the pressure within a proton using QCD equations defined on the lattice.

Distribution of Pressures Inside A ProtonPressure distribution within a proton | Courtesy of researchers

Since the task demands a lot of computational resources, they used some of the most advanced supercomputers in the world to perform these calculations. Over one and a half years, they executed numerous configurations of gluons and quarks across different machines.

Eventually, the team calculated the average pressure at every single spot from the protons center out to its edge. As per results, the highest pressure inside the proton is nearly 1035 pascals and low-pressure region extends from the proton’s center.

Read: The Most Precise Measurement Of The Shape Of The Field Around An Electron

To confirm these measurements (would take at least 10 years), scientists will need to work on intensively powerful detectors like an Electron-ion collider, a proposed particle accelerator that could be used to collide spin-polarized beams of ions and electrons and obtain more insight about the particles’ inner structures.

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