Posts by HDE 226868
Directly? No. Indirectly? Yes. As Renan indicated in their answer, material that enters a black hole cannot leave; the only way around this is through evaporation. Even then, the Hawking radiation...
Black body radiation The Sun is, approximately, a black body. That means that the light it emits follows a particular spectrum according to Planck's law, with the shape of the spectrum determined ...
TMM;DR (Too Much Math, Didn't Read): For anyone who doesn't want to go through the derivations and calculations below, here are the important points from my answer: We're not working with the sa...
The setup and the equation Let's look at the geometry involved here. I created two diagrams: On the left, we have the star of radius $R$. On the right, we have a cross-section of the ring. The ...
Jim2B beat me to the best answer, but there are more solutions. Analyzing a system like this is called the three-body problem, a case of the n-body problem. There are not many stable solutions to ...
A key part of the plot in a story I'm working on revolves around the main region being on top of volcano that is set to erupt. The trouble is that the region in question in my setting is roughly th...
Gawiser & Silk (2000) provide a nice overview of the CMB (possibly better than Wikipedia). The paper is a bit outdated - after all, they use a figure of 15 billion years as the age of the unive...
Special cases Tectonically-locked Mostly Frozen Surface Water-free (Dune) Or, no/very-little free water. All Water (Europa) Currently, by question definition, this is non-habitable. (Orig...
Atmosphere, surface temperature and other properties directly related to life Magnetosphere: Magnetospheres are thought to be driven by a dynamo process driven by internal circulation in the ...
Orbit, rotation, mass and other properties not directly related to life A planet is a rotating mass (larger than ~500km in diameter) in orbit around the star of normal material becomes an oblate s...
The question: What characteristics are necessary for a planet to be habitable for humans? What should the generic star and planet be like? The life forms are human, so they Need to have access ...
Age: The time a star spends on the main sequence is roughly inversely proportional to the luminosity, as given by the formula $$T \approx \ 10^{10} \text{years} \cdot \left[ \frac{M}{M_{\bigodot}...
The question: What characteristics are necessary for a planet to be habitable for humans? What should the generic star and planet be like? The life forms are human, so they Need to have access ...
A decent proxy for habitability and long-term colonizability is the effective temperature of the planet - essentially the surface temperature. A planet's effective temperature scales as $T\propto (...
The Copernican principle As L.Dutch pointed out, this would violate the Copernican principle, which essentially states that there's nothing special about observing the universe from any one place....
This is actually a really interesting question. While there are many stars with orbits outside the galactic plane ("halo stars"), these tend to be old and metal-poor, as star formation in the halo ...
The Alcubierre drive not only allows but actually necessitates the production of event horizons at superluminal speeds - but not necessarily the sort you're looking for. It's been shown (Finazzi e...
The Alcubierre drive works by distorting space around a bubble: expanding space behind it and contracting space in front of it. It's a nice way to get faster-than-light travel without, well, techni...
This wouldn't work. The big issue is that stars make up only a few percent of the Milky Way's total mass - estimates vary by a bit, but I've heard numbers in the 3-5% range. For instance, McMillan...
The simple answer is a no. We've gotten some pretty good constraints from the Planck satellite; their final results indicated a dark energy density of $\rho\approx6\times10^{-30}\text{ g cm}^{-3}$....
I agree largely with Matthew's answer; this is intended to put everything on a more quantitative footing. The answer to your question primarily depends on three things: the mass of molecules in th...
Sort of. A structure similar to the one you describe can in fact form. Triple-stranded DNA can be stable under certain conditions. Two bases bond via slightly different structures, and a third bas...
Sure. Not a whole lot, but you'll get a decent number. Beer et al. 2004 present a formula for calculating the mean time before a star passes within a distance $b_{\text{min}}$ of another star: $$...
Just reduce the rate at which you lose entanglement (The paper, for anyone wanting to read it, is Humphreys et al. 2018.) The hey problem here isn't entangling particles, per se - the problem is ...
Based on the current state of thinking, somewhere in the vicinity of a couple hundred kilometers. This particular formation theory (Zhang & Lin 2020) is a variant of an idea that's been kicked...
