... everything except the black holes will have a tendency to "sublimate" or "ionize", gradually losing atoms or even electrons and protons, despite the low temperature. ... If you take a box of hydrogen and keep making the box bigger while keeping its temperature fixed, it will eventually ionize. This happens no matter how low the temperature is, as long as it's not exactly absolute zero — which is forbidden by the 3rd law of thermodynamics, anyway.
This may seem odd, but the reason is simple: in thermal equilibrium any sort of stuff minimizes its free energy, E - TS: the energy minus the temperature times the entropy. This means there is a competition between wanting to minimize its energy and wanting to maximize its entropy. Maximizing entropy becomes more important at higher temperatures; minimizing energy becomes more important at lower temperatures — but both effects matter as long as the temperature isn't zero or infinite.
Ionization at low densities refers to the process by which atoms or molecules lose one or more of their electrons, resulting in the formation of ions, in an environment where the number of particles per unit volume is relatively low.
Ionization at low densities can be caused by a variety of factors, including exposure to high-energy radiation, collisions with other particles, or chemical reactions. It can also occur naturally in outer space due to the presence of cosmic rays.
One common application of ionization at low densities is in plasma generation, which is used in many technologies such as fluorescent lighting, plasma TVs, and particle accelerators. It is also important to study in fields such as astrophysics, where ionization at low densities plays a significant role in the behavior of interstellar matter.
Ionization at low densities can be measured using a variety of techniques, depending on the specific environment being studied. Some common methods include using mass spectrometry to detect the presence of ions, or using spectroscopy to analyze the wavelengths of light emitted by ionized particles.
Ionization at low densities can have both beneficial and harmful effects on biological systems. On one hand, it is used in medical treatments such as radiation therapy to kill cancer cells. On the other hand, excessive exposure to ionizing radiation can lead to DNA damage and increase the risk of cancer. It is important to carefully control and monitor ionization levels to ensure the safety of living organisms.