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  2. Negative temperature - Wikipedia

    en.wikipedia.org/wiki/Negative_temperature

    The possibility of negative temperatures was first predicted by Lars Onsager in 1949. [4] Onsager was investigating 2D vortices confined within a finite area, and realized that since their positions are not independent degrees of freedom from their momenta, the resulting phase space must also be bounded by the finite area.

  3. Bohr radius - Wikipedia

    en.wikipedia.org/wiki/Bohr_radius

    In Schrödinger's quantum-mechanical theory of the hydrogen atom, the Bohr radius is the value of the radial coordinate for which the radial probability density of the electron position is highest. The expected value of the radial distance of the electron, by contrast, is ⁠ 3 2 a 0 {\displaystyle {\tfrac {3}{2}}a_{0}} ⁠ .

  4. Crystallographic database - Wikipedia

    en.wikipedia.org/wiki/Crystallographic_database

    The space group of a crystal is a mathematical description of the symmetry inherent in the structure. The motif of the crystal structure is given by the asymmetric unit, a minimal subset of the unit cell contents. The unit cell contents can be fully reconstructed via the symmetry operations of the space group on the asymmetric unit.

  5. White dwarf - Wikipedia

    en.wikipedia.org/wiki/White_dwarf

    In this case, only a fraction of the star's mass will be ejected during the collapse. [50] If a white dwarf star accumulates sufficient material from a stellar companion to raise its core temperature enough to ignite carbon fusion, it will undergo runaway nuclear fusion, completely disrupting it.

  6. Pea galaxy - Wikipedia

    en.wikipedia.org/wiki/Pea_galaxy

    The Pea galaxies, also known as Green Peas (GPs), are compact oxygen-rich emission line galaxies that were discovered at redshift between z = 0.112 and 0.360. [1] These low-mass galaxies have an upper size limit generally no bigger than 16,300 light-years (5,000 pc) across, and typically they reside in environments less than two-thirds the density of normal galaxy environments. [1]

  7. Seyfert galaxy - Wikipedia

    en.wikipedia.org/wiki/Seyfert_galaxy

    The Circinus Galaxy, a Type II Seyfert galaxy. Seyfert galaxies are one of the two largest groups of active galaxies, along with quasar host galaxies. They have quasar-like nuclei (very luminous sources of electromagnetic radiation that are outside of our own galaxy) with very high surface brightnesses whose spectra reveal strong, high-ionisation emission lines, [1] but unlike quasars, their ...

  8. h-index - Wikipedia

    en.wikipedia.org/wiki/H-index

    The h-index is an author-level metric that measures both the productivity and citation impact of the publications, initially used for an individual scientist or scholar. The h-index correlates with success indicators such as winning the Nobel Prize, being accepted for research fellowships and holding positions at top universities. [1]