We humans may be even more of the universe than we imagined. According to a study published in the journal Physical Review C, neutron stars and cell cytoplasm have something in common: structures that resemble multi-story garages. In 2014, soft condensed matter physicist Greg Huber and colleagues investigated the biophysics of these shapes - spirals connecting evenly spaced sheets - in the endoplasmic reticulum. Huber and his colleagues named them Terasaki Ramps after their discoverer Mark Terasaki, a cell biologist at the University of Connecticut.
Huber thought these "parking garages" were unique to soft matter (like the inside of cells) until he stumbled upon the work of nuclear physicist Charles Horowitz of Indiana State University. Using computer simulations, Horowitz and his team found similar shapes deep in the crust of neutron stars.
“I called Chuck and asked if he was aware that we saw such structures in cells and came up with a model for them,” says Huber, deputy director of the Kavli Institute for Theoretical Physics at the University of California, Santa Barbara. "This was news to him, so I realized that we could have a fruitful cooperation."
As a result of their collaborative work, as noted in Physical Review C, they investigated the relationship between two completely different models of matter.
Nuclear physicists have a very precise terminology for the entire class of figures they observe in their computer models of neutron stars: nuclear paste. It consists of tubes (spaghetti) and parallel sheets (lasagne), connected by spiral shapes reminiscent of Terasaki ramps.
“They observe the shapes we see in the cell,” explains Huber. “We see a tubular network, we see parallel sheets. We see sheets interconnected by topological defects, which we call Terasaki ramps. Therefore, the parallels are very deep."
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Nevertheless, their physics is different. Usually a substance is characterized by its phase, a state that depends on thermodynamic variables: density (or volume), temperature and pressure - factors that differ significantly at the nuclear and intracellular levels.
“For neutron stars, strong nuclear and electromagnetic forces pose a quantum mechanical problem,” explains Huber. - In the interior of the cell, the forces holding the membranes together are fundamentally entropic and are related to minimizing the total free energy of the system. At first glance, these are completely different things."
Another difference is scale. In the nuclear case, these structures are based on nucleons such as protons and neutrons, and these building blocks are measured with femtometers (10-15). In the case of intracellular membranes, the scale length is measured in nanometers (10-9). The difference between them is quite large (10-6), but at the same time they have days and the same forms.
“This means that there is something deeper than we understand about how to model a nuclear system,” Huber says. "When you have a dense collection of protons and neutrons, like on the surface of a neutron star, strong nuclear forces and electromagnetic forces together slip you into phases of matter that you cannot predict by looking at small collections of neutrons and protons."
The similarity of structures excited theoretical physicists and nuclear physicists. Martin Savage, for example, stumbled upon charts from a new work on arXiv and became very interested. “I was very surprised that such a state of matter occurs in biological systems,” says Savage, a professor at the University of Washington. "There's definitely something about that." In addition, the similarity is also very mysterious. This is just the beginning.
ILYA KHEL