Posts by HDE 226868
Supercritical carbon dioxide Once upon a time, Venus may have had seas of supercritical $\text{CO}_2$ ($\text{scCO}_2$) thanks to a higher surface temperature (by a few hundred Kelvin) and surface...
Stars that become Cepheid variables stay in this phase of their lives for only a short period of time, and after they leave the main sequence. While their properties vary (in particular, Cepheids a...
This scenario is quite problematic for two main reasons: evaporation and peak wavelength. The black hole's lifetime is too short We can make a rough estimate of the properties of the Hawking radi...
As the sphere is self-gravitating, it must be in hydrostatic equilibrium; that is, there must be a non-zero pressure gradient to balance the force of gravity. For a fluid of uniform density, you ca...
I don't have a solution; what I do have is a possible path to a numerical solution. For the sake of simplicity and sanity, I will consider the special case of a non-rotating, chargeless, spherical...
Carbon planets We typically expect a moon's composition to reflect the part of the protoplanetary disk it came from. If it's orbiting a planet close to the star, we'd expect it to be composed larg...
The five primary layers of the atmosphere are, with increasing, altitude, the troposphere, stratosphere, mesosphere, thermosphere, and exosphere. The corresponding boundaries are the tropopause, st...
We have plenty of examples where stars have been hidden by nebulae - and not just newborn stars. Typically, the gas and dust comes from mass loss from one of the stars in the system. Examples inclu...
TL;DR I'd propose that weak force life has a tiny change of existing in environments where particles travel at high speeds. A possible example is the jets produced by an active galactic nucleus. A...
Your environment is quite similar to that in a globular cluster. At its densest, a globular cluster may see peak stellar number densities of $\sim1000$ stars per cubic parsec, which implies a mean ...
TL;DR As most of the other answers say, the plants on this world would likely be purple-ish, using photosynthetic pigments that operate at the same wavelengths as bacteriochlorophylls. Chlorophyll...
Atmosphere loss As you've suggested in your question, once a Sun-like star leaves the main sequence, it begins losing mass through a strong stellar wind, a stream of charged particles driven by ph...
Not unless life evolves extremely quickly. There are two conditions for cosmic background radiation to be able to support life: It's partially composed of photons at wavelengths required by phot...
In my answer to another question, I suggested that the Super-Earth in question be tidally locked to its host star for a period of time while part of its surface experienced a bombardment. After tha...
Super-rotation As I wrote in an answer to another question about winds, studies of slow-rotating planets like Venus have yielded information about what we should expect for planets like this in ge...
Summary It turns out that even relatively low-mass ocean planets are capable of forming some of the exotic ices you name in their cores. Ice VII appears to form at the centers of planets of $0.015...
Tachyons are detectable. Fortunately, I believe your question is based on a mistaken premise. Tachyons, if they exist, would likely indeed be detectable. In fact, since they were initially theoriz...
Models of planetary structure indicate that ocean planets should reach peak size at a few hundred to a thousand Earth masses, reaching maximum radii of perhaps 4-5 Earth radii. Add in some iron and...
Equations of state The "ocean" should be described by an equation of state that relates thermodynamic variables (e.g. density $\rho$, temperature $T$, pressure $p$, etc.) to one another. Different...
Yup! This is possible, and a number of small bodies in the Solar System have rings: Haumea, a dwarf planet in the outer Solar System, was recently discovered to have rings, which lie inside its R...
What can a star be made of? A star's composition is limited by the elements that exist in significant quantities in the universe. These include primordial elements - hydrogen, helium and lithium -...
The answer to your question depends strongly on the supernova rate in the galaxy. The Milky Way currently is not an active galaxy - the supermassive black hole at its center is relatively quiescent...
Alexander's answer is completely correct; there is no way to split one black hole into smaller ones. I think, though, that it might be worth explaining why this is the case, particularly because th...
The situation you're considering involves a rotating black hole characterized by the parameters $M$ and $J$, the mass and angular momentum of the black hole. The two are encapsulated in something c...
No, wind patterns are not always going to be the same. Venus is a key counterexample here. Its Hadley cells extend to 60 degrees above and below the equator - double the size of Earth's Hadley cel...
