3 ms·

> Magnetic fields fall off with the inverse square law. Inverse cube: the simplest magnets are dipoles. > It's pretty easy to construct a light bulb with a fi

> Magnetic fields fall off with the inverse square law. Inverse cube: the simplest magnets are dipoles. > It's pretty easy to construct a light bulb with a filament which is hotter than the surface of the sun The surface of the sun is about 10,000 F, well above the melting point of tungsten. Maybe there's some exotic ceramic that can survive those temperatures, but I'm not aware of any.

Groxx 3y ago
Seems like ceramics have hit ~7,000F: https://en.wikipedia.org/wiki/Ultra-high_temperature_ceramic https://en.wikipedia.org/wiki/Ultra-high_temperature_ceramic But yeah. No filaments at that temperature, though 10,000F is rather easy to hit if you're not trying to keep whatever you're heating. Though this does make me wonder how hot a star can get. Stable states are likely not all that hot, but what about supernova?
- ben_w 3y ago
  My favourite type of supernova is the pair-instability collapse, where it's hot enough that, thanks to the Maxwell-Boltzman distribution and Stefan–Boltzmann law, a nontrivial fraction of the photons spontaneously turn into positron-electron pairs, causing a runaway loss of pressure, leading to collapse, leading to more heat, leading to more sufficiently energetic photons… leading very quickly to multiple tens of solar masses of hydrogen turning directly into nickel-56 in a matter of seconds.
  - gus_massa 3y ago
    It sounds very interesting, like a scenario from https://what-if.xkcd.com/ https://what-if.xkcd.com/ but in real life. Do you know a good (not specialized) article/blog post/Wikipedia article about it? Something at the ELI25 level.
    - dustingetz 3y ago
      https://en.m.wikipedia.org/wiki/Pair-instability_supernova https://en.m.wikipedia.org/wiki/Pair-instability_supernova
- gattr 3y ago
  Check out Wolf-Rayet stars ([1]); effective surface temperature from 10,000 to 210,000 K. Tungsten melts at 3956 K, hafnium carbonitride ([2]) at 4370 K. [1] https://en.wikipedia.org/wiki/Wolf%E2%80%93Rayet_star https://en.wikipedia.org/wiki/Wolf%E2%80%93Rayet_star [2] https://en.wikipedia.org/wiki/Hafnium_carbonitride https://en.wikipedia.org/wiki/Hafnium_carbonitride
- MereInterest 3y ago
  > Stable states are likely not all that hot, but what about supernova? As context first, at some point temperature just sort of, stops being useful as a comparison. Not because it can't be computed, but because there really isn't any point of comparison for it. The coldest temperature in Antarctica was -89.2 Celsius [0]. The hottest day in Death Valley was 56.7 Celsius [1]. Tungsten melts at 3400 Celsius [2]. And papers about supernova will casually throw around phrases like "for temperatures exceeding a few 100 keVs" [3], to state that pretty much everything that happens in a supernova will be hotter than that. That's an energy measurement equivalent to about 1 trillion kelvin. The second piece of context, for anything that deals with energy output, supernova are basically the "I win." answer. XKCD's "What If?" series has a good comparison for this, that for pretty much any comparison you can conceive, if the question is about energy output, the supernova wins. > Which of the following would be brighter, in terms of the amount of energy delivered to your retina: (1) A supernova, seen from as far away as the Sun is from the Earth, or (2) The detonation of a hydrogen bomb pressed against your eyeball? ... [The supernova] is ... by nine orders of magnitude. [4] So when temperatures are reported as 100 billion kelvin for the neutron star remnant [5], those are the cold (by comparison only) embers of a dying fire. The supernova itself has a "typical core temperature of 1 MeV" [3], which translates to about 10 trillion kelvin. [0] https://en.wikipedia.org/wiki/Lowest_temperature_recorded_on_Earth https://en.wikipedia.org/wiki/Lowest_temperature_recorded_on... [1] https://en.wikipedia.org/wiki/Highest_temperature_recorded_on_Earth https://en.wikipedia.org/wiki/Highest_temperature_recorded_o... [2] https://en.wikipedia.org/wiki/Tungsten https://en.wikipedia.org/wiki/Tungsten [3] https://arxiv.org/abs/astro-ph/0612072 https://arxiv.org/abs/astro-ph/0612072 [4] Xkcd, What If, #73: https://what-if.xkcd.com/73/ https://what-if.xkcd.com/73/ [5] https://en.wikipedia.org/wiki/Supernova#Detailed_process https://en.wikipedia.org/wiki/Supernova#Detailed_process

Groxx 3y ago

Seems like ceramics have hit ~7,000F: https://en.wikipedia.org/wiki/Ultra-high_temperature_ceramic https://en.wikipedia.org/wiki/Ultra-high_temperature_ceramic But yeah. No filaments at that temperature, though 10,000F is rather easy to hit if you're not trying to keep whatever you're heating. Though this does make me wonder how hot a star can get. Stable states are likely not all that hot, but what about supernova?

ben_w 3y ago
My favourite type of supernova is the pair-instability collapse, where it's hot enough that, thanks to the Maxwell-Boltzman distribution and Stefan–Boltzmann law, a nontrivial fraction of the photons spontaneously turn into positron-electron pairs, causing a runaway loss of pressure, leading to collapse, leading to more heat, leading to more sufficiently energetic photons… leading very quickly to multiple tens of solar masses of hydrogen turning directly into nickel-56 in a matter of seconds.
- gus_massa 3y ago
  It sounds very interesting, like a scenario from https://what-if.xkcd.com/ https://what-if.xkcd.com/ but in real life. Do you know a good (not specialized) article/blog post/Wikipedia article about it? Something at the ELI25 level.
  - dustingetz 3y ago
    https://en.m.wikipedia.org/wiki/Pair-instability_supernova https://en.m.wikipedia.org/wiki/Pair-instability_supernova
gattr 3y ago
Check out Wolf-Rayet stars ([1]); effective surface temperature from 10,000 to 210,000 K. Tungsten melts at 3956 K, hafnium carbonitride ([2]) at 4370 K. [1] https://en.wikipedia.org/wiki/Wolf%E2%80%93Rayet_star https://en.wikipedia.org/wiki/Wolf%E2%80%93Rayet_star [2] https://en.wikipedia.org/wiki/Hafnium_carbonitride https://en.wikipedia.org/wiki/Hafnium_carbonitride
MereInterest 3y ago
> Stable states are likely not all that hot, but what about supernova? As context first, at some point temperature just sort of, stops being useful as a comparison. Not because it can't be computed, but because there really isn't any point of comparison for it. The coldest temperature in Antarctica was -89.2 Celsius [0]. The hottest day in Death Valley was 56.7 Celsius [1]. Tungsten melts at 3400 Celsius [2]. And papers about supernova will casually throw around phrases like "for temperatures exceeding a few 100 keVs" [3], to state that pretty much everything that happens in a supernova will be hotter than that. That's an energy measurement equivalent to about 1 trillion kelvin. The second piece of context, for anything that deals with energy output, supernova are basically the "I win." answer. XKCD's "What If?" series has a good comparison for this, that for pretty much any comparison you can conceive, if the question is about energy output, the supernova wins. > Which of the following would be brighter, in terms of the amount of energy delivered to your retina: (1) A supernova, seen from as far away as the Sun is from the Earth, or (2) The detonation of a hydrogen bomb pressed against your eyeball? ... [The supernova] is ... by nine orders of magnitude. [4] So when temperatures are reported as 100 billion kelvin for the neutron star remnant [5], those are the cold (by comparison only) embers of a dying fire. The supernova itself has a "typical core temperature of 1 MeV" [3], which translates to about 10 trillion kelvin. [0] https://en.wikipedia.org/wiki/Lowest_temperature_recorded_on_Earth https://en.wikipedia.org/wiki/Lowest_temperature_recorded_on... [1] https://en.wikipedia.org/wiki/Highest_temperature_recorded_on_Earth https://en.wikipedia.org/wiki/Highest_temperature_recorded_o... [2] https://en.wikipedia.org/wiki/Tungsten https://en.wikipedia.org/wiki/Tungsten [3] https://arxiv.org/abs/astro-ph/0612072 https://arxiv.org/abs/astro-ph/0612072 [4] Xkcd, What If, #73: https://what-if.xkcd.com/73/ https://what-if.xkcd.com/73/ [5] https://en.wikipedia.org/wiki/Supernova#Detailed_process https://en.wikipedia.org/wiki/Supernova#Detailed_process