PLANCK STARS
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Black bodyA black body or blackbody is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. The radiation emitted by a black body in thermal equilibrium with its environment is called black-body radiation. The name "black body" is given because it absorbs all colors of light. In contrast, a white body is one with a "rough surface that reflects all incident rays completely and uniformly in all directions." A black body in thermal equilibrium (that is, at a constant temperature) emits electromagnetic black-body radiation. The radiation is emitted according to Planck's law, meaning that it has a spectrum that is determined by the temperature alone (see figure at right), not by the body's shape or composition. An ideal black body in thermal equilibrium has two main properties: It is an ideal emitter: at every frequency, it emits as much or more thermal radiative energy as any other body at the same temperature. It is a diffuse emitter: measured per unit area perpendicular to the direction, the energy is radiated isotropically, independent of direction. Real materials emit energy at a fraction—called the emissivity—of black-body energy levels. By definition, a black body in thermal equilibrium has an emissivity ε = 1. A source with a lower emissivity, independent of frequency, is often referred to as a gray body. Constructing black bodies with an emissivity as close to 1 as possible remains a topic of current interest. In astronomy, the radiation from stars and planets is sometimes characterized in terms of an effective temperature, the temperature of a black body that would emit the same total flux of electromagnetic energy.
Planck's lawIn physics, Planck's law (also Planck radiation law: 1305 ) describes the spectral density of electromagnetic radiation emitted by a black body in thermal equilibrium at a given temperature T, when there is no net flow of matter or energy between the body and its environment. At the end of the 19th century, physicists were unable to explain why the observed spectrum of black-body radiation, which by then had been accurately measured, diverged significantly at higher frequencies from that predicted by existing theories. In 1900, German physicist Max Planck heuristically derived a formula for the observed spectrum by assuming that a hypothetical electrically charged oscillator in a cavity that contained black-body radiation could only change its energy in a minimal increment, E, that was proportional to the frequency of its associated electromagnetic wave. While Planck originally regarded the hypothesis of dividing energy into increments as a mathematical artifice, introduced merely to get the correct answer, other physicists including Albert Einstein built on his work, and Planck's insight is now recognized to be of fundamental importance to quantum theory.
Exotic starAn exotic star is a hypothetical compact star composed of exotic matter (something not made of electrons, protons, neutrons, or muons), and balanced against gravitational collapse by degeneracy pressure or other quantum properties. Types of exotic stars include quark stars (composed of quarks) strange stars (composed of strange quark matter, a condensate of up, down, and strange quarks) § Preon stars (speculative material composed of preons, which are hypothetical particles and "building blocks" of quarks and leptons, should quarks be decomposable into component sub-particles). Of the various types of exotic star proposed, the most well evidenced and understood is the quark star, although its existence is not confirmed. In Newtonian mechanics, objects dense enough to trap any emitted light are called dark stars,, as opposed to black holes in general relativity. However, the same name is used for hypothetical ancient "stars" which derived energy from dark matter. Exotic stars are hypothetical – partly because it is difficult to test in detail how such forms of matter may behave, and partly because prior to the fledgling technology of gravitational-wave astronomy, there was no satisfactory means of detecting compact astrophysical objects that do not radiate either electromagnetically or through known particles. While candidate objects are occasionally identified based on indirect evidence, it is not yet possible to distinguish their observational signatures from those of known objects.
Planck unitsIn particle physics and physical cosmology, Planck units are a system of units of measurement defined exclusively in terms of four universal physical constants: c, G, ħ, and kB (described further below). Expressing one of these physical constants in terms of Planck units yields a numerical value of 1. They are a system of natural units, defined using fundamental properties of nature (specifically, properties of free space) rather than properties of a chosen prototype object. Originally proposed in 1899 by German physicist Max Planck, they are relevant in research on unified theories such as quantum gravity. The term Planck scale refers to quantities of space, time, energy and other units that are similar in magnitude to corresponding Planck units. This region may be characterized by particle energies of around 1019 GeV or 109 J, time intervals of around 5×10−44 s and lengths of around 10−35 m (approximately the energy-equivalent of the Planck mass, the Planck time and the Planck length, respectively). At the Planck scale, the predictions of the Standard Model, quantum field theory and general relativity are not expected to apply, and quantum effects of gravity are expected to dominate. One example is represented by the conditions in the first 10−43 seconds of our universe after the Big Bang, approximately 13.8 billion years ago. The four universal constants that, by definition, have a numeric value 1 when expressed in these units are: c, the speed of light in vacuum, G, the gravitational constant, ħ, the reduced Planck constant, and kB, the Boltzmann constant. Variants of the basic idea of Planck units exist, such as alternate choices of normalization that give other numeric values to one or more of the four constants above.
Planck starIn loop quantum gravity theory, a Planck star is a hypothetical astronomical object, theorized as a compact, exotic star, that exists within a black hole's event horizon, created when the energy density of a collapsing star reaches the Planck energy density. Under these conditions, assuming gravity and spacetime are quantized, a repulsive "force" arises from Heisenberg's uncertainty principle. The accumulation of mass–energy inside the Planck star cannot collapse beyond this limit because it violates the uncertainty principle for spacetime itself. The key feature of this theoretical object is that this repulsion arises from the energy density, not the Planck length, and starts taking effect far earlier than might be expected. This repulsive "force" is strong enough to stop the star's collapse well before a singularity is formed and, indeed, well before the Planck scale for distance: for a stellar mass black hole the Planck star would be of the order of 10−12 m - for a primordial black hole, the order of 10−16 m.: whilst tiny, these scales are many orders of magnitude larger than the Planck length of 10−35 m. Then too, this allows adequate room for all the information captured inside a black hole to be encoded in the star, thus avoiding information loss. While it might be expected that such a repulsion would act very quickly to reverse the collapse of a star, it turns out that the relativistic effects of the extreme gravity of such an object slow down time for the Planck star to a similarly extreme degree. Seen from outside the star's Schwarzschild radius, the rebound from a Planck star takes approximately fourteen billion years, such that even primordial black holes are only now starting to rebound from an outside perspective. Furthermore, the emission of Hawking radiation can be calculated to correspond to the timescale of gravitational effects on time, such that the event horizon that "forms" a black hole evaporates as the rebound proceeds. Carlo Rovelli and Francesca Vidotto, who first proposed the existence of Planck stars, theorized in 2014 that Planck stars form inside black holes as a solution to the black hole firewall and the black hole information paradox. Confirmation of emissions from rebounding black holes could provide evidence for loop quantum gravity. Recent work demonstrates that Planck stars may exist inside black holes as part of a cycle between black and white holes. A somewhat analogous object theorized under string theory is the fuzzball, which similarly eliminates the singularity within a black hole and accounts for a way to preserve the quantum information that falls into a black hole's event horizon.
Francesca VidottoFrancesca Vidotto (born November 22, 1980) is an Italian theoretical physicist.
Planck StarsPLANCK STARS (プランクスターズ) is a Japanese idol girl group from Hiroshima. They made their debut in 2018 and reached mainstream success in 2021. Their music is a mix of Rock and electronic dance music. The concept behind them is described as "free-spirited delinquents." The name sounds like "pranksters", which describes many controversies in which the group has been involved. Their antics have ranged from a member exiting the stage mid-song to buy a churro (and not returning until the very end of the concert), to releasing 300 live crickets in the audience. Members have also hammered the ceiling of a venue; slept on stage; stepped on a fan; thrown ink and soy sauce at the audience; spit watermelon seeds into a fan's mouth; and made a fan drink detergent. The concept was born from a desire to go against Japanese idol girl groups culture, who tend to face a lot of boundaries on who they can be and how they must act in public. Members perform wearing extravagant clothing, sing foulmouthed lyrics, and even have a monkey and a dog as official members. One of their most famous pranks happened in 2022, when they held a competition to see which member could sell more tickets to a concert, with the winner getting a bike and the one who sold the least tickets having to make an "AV", which many assumed to stand for "adult video". However, the member who had to star in the video was Puri-chan, the dog, who obviously didn't sell a single ticket. Puri-chan then starred in a video playing in a park, an "Animal Video". In 2022, they released their first mini-album, called Ochi Omega Rema, which reached the 1st place on the Oricon Albums Chart. They have toured in countries like Thailand, United States, England, Taiwan and South Korea. They have made songs inspired by these places. In 2024, they performed in Brazil for the first time at Anime Summit, in Brasília. The group disbanded in February 9, 2025, but announced their reformation in July.
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