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A White Dwarf in a Lab (Science Advent 21)

(Every day until Christmas, I’ll be posting a science-related image.)

Day 21

The Z-machine at Sandia National Laboratory in Albuquerque, New Mexico (don't make a wrong turn there!) uses intense pulses of electrical energy to make gamma rays and X-rays. These in turn are used to study nuclear fusion - and to simulate certain astrophysical systems, like white dwarfs. [Credit: Sandia Corporation]

The Z Machine at Sandia National Laboratory in Albuquerque, New Mexico (don’t make a wrong turn there!) uses intense pulses of electrical energy to make gamma rays and X-rays. These in turn are used to study nuclear fusion – and to simulate certain astrophysical systems, like white dwarfs. [Credit: Sandia Corporation]

Many objects we see in space have no corresponding phenomena on Earth. Consider white dwarfs: the cores of star like our Sun after they have exhausted their usable nuclear fuel and shed their outer layers. These remnants are extremely dense and hot, a combination difficult to achieve in the lab! A typical white dwarf is about the physical size of Earth, but a mass comparable to the Sun, and surface temperatures far hotter than an average star. White dwarfs also are challenging theoretically, since the force holding them together is gravitation, while the force preventing them from collapsing arises from a quantum mechanical principle: the Pauli exclusion principle. More challenging still are neutron stars, which have larger masses compressed to spheres about 10 to 20 kilometers across—the size of a large city. The combination of strong gravity, high temperatures, and condensed matter is what makes these objects interesting, but very hard to model theoretically or reproduce in the lab.

The Z Machine at Sandia National Laboratory in New Mexico offers some of the best hope of experimental extreme astrophysics. Technically known as the Z Pulsed Power Facility, the Z Machine was constructed for nuclear fusion research. It uses powerful pulses of electricity to generate gamma rays and X-rays; the bright arcs in the image above come from ionizing molecules in the water tank used to keep things cooled and under control. When materials are subjected to this intense energy, researchers are able to determine certain properties: something known as a material’s equation of state. The Ideal Gas Law (which you  might remember from chemistry or physics classes) is a particularly simple and well-known equation of state describing the relationship between density, pressure, and temperature of a gas. The equations of state for a white dwarf or neutron star are far more complicated, involving specifically quantum and gravitational properties, along with magnetic effects. The Z Machine has provided some fascinating insights into the equation of state of a white dwarf, which is exciting since we can’t study one up close.

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