Posts by HDE 226868
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 ...
This is a classic problem in electrostatics - that is, in an analogous situation where we care about calculating the electric force on an object inside some cavity. The same solution technique appl...
7110 Earth masses and a surface temperature of 1700 K aren't unreasonable for a brown dwarf. The lower mass limit is thought to be around 13 Jupiter masses (or 4100 Earth masses) (see e.g. Spiegel ...
A star's life ends when it can no longer undergo fusion at its core. For massive stars, this often happens when the core is made largely of iron, which can be fused (and is) in small amounts, but o...
Introduction In our universe, the cosmic microwave background was formed approximately 400,000 years after the Big Bang. It was hot, but within a few million years after the Big Bang, it would no ...
This star would not fuse gold. Fusion reactions producing elements beyond zinc-60 are not energetically favorable; they are endothermic, and so consume energy. Several elements heavier than iron a...
The collapse of bubbles on various scales has actually been an area of research for quite some time. Analyses are typically numerical, and rely on something known as the Rayleigh-Plesset equation, ...
Here's a first-order approximation based on a fundamental limit: diffraction and angular resolution. How far someone can see of course depends on the size of the object they're looking at, because...
There are a whole bunch of different ways to determine the thickness of a planet's ice sheets; over the decade, dozens have been tried on Europa and other icy bodies. Broadly speaking, as we're wor...
Apologies for taking a while to respond to this. When I used the phrase "hasn't been discussed", I was talking about the meta discussion at hand, rather than prior discussions. I rejected the edit,...
I agree with Tim B's assessment that this is a complicated question. However, I disagree on just why this is the case. The characteristics of the star are well defined, given that it's a solar anal...
This is essentially a partial answer, insofar as it's a series of loosely chained together critiques. Sometime in the future, I'll revise it so it's more organized, but for now, it's a work in prog...
Using Kepler's third law, I get $$a=\sqrt[3]{\frac{P^2G\times(M+M)}{4\pi^2}}=5.32\times10^4\text{ kilometers}$$ where $a$ is the semi-major axis, $P$ is the time it takes the planets to orbit each ...
First, let's look at the different types of trajectories a solar sail can take. They differ mainly based on something called the lightness number, $\beta$, which depends on the composition and stru...
Wikipedia gives the formula for the tidal heating $\dot{E}$ as $$\dot{E}=-\text{Im}(k_2)\frac{21}{2}\frac{R^5n^5e^2}{G}\tag{1}$$ where $R$ is the radius of the satellite, $n$ is something weird cal...
Apparently, this was investigated by NASA in the early 2000s in what became known as The Caves of Mars Project. Its goal was to find possible places for humans to live over extended periods of time...
Models of such planets exist, courtesy of Unterborn et al. (2014). They discuss planets of similar composition to yours - looking at the value of the mass fraction given by $(\text{Mg}+2\text{Si}+\...
Your main problem is that the planets will comprise a chaotic system. This is why the stability of the Solar System is so difficult (possibly impossible) to determine. Our best models are valid for...
I decided to start answering this question by building a galaxy (well, a model of a galaxy, but it sounds cooler the first way). A lot of research has already been done in this area, specifically, ...
Use a Quasi-star. The solution I think will finally work is to use a quasi-star, a theoretical object from the early universe consisting of a black hole of perhaps $10M_{\odot}\text{-}100M_{\odot}...
I went about this a bit differently than kingledion, and got a different answer (off by $\sim6$ orders of magnitude!). The difference is that I assumed that there would be accretion no matter what ...
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 ...
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 thing about planetary systems - and many $N$-body systems in general - is that they are fundamentally chaotic. That is, small changes grow over time, eventually creating wildly divergent result...
