Posts by HDE 226868
Galaxy size The first question is whether such a galaxy (less than 3000 stars) is possible. The clear answer is yes; Segue II already satisfies those requirements. Segue I and Willman I appear qui...
Mass The big issue here lies in determining the mass of these black holes. On the one hand, the traditional primordial black holes you mention - formed by density perturbations - occupy a relative...
The Earth-like planet I'm working on is the culmination of years of labor by the galaxy's best scientists. It consists of fully artificial ecosystems, and is, for all intents and purposes, like Ear...
TL;DR Your world will experience constant, uniform gravity. Everything is accelerating upward at the same rate - but this isn't the case in our universe, as gravity follows (approximately) an inve...
TL;DR There are several important factors considered when trying to determine if a group of stars are actually from the same stellar cluster, moving group, or association: Kinematics. Do the sta...
Let's look at two key equations: $$F_i=\frac{L_i}{4\pi r_i^2},\quad \lambda_{\text{max,i}}=\frac{b}{T_i},\tag{1, 2}$$ For a given star with luminosity $L_i$ and surface temperature $T_i$ a distance...
In response to a question about an asteroid filled with degenerate matter, Ender Look suggested that using matter from a black dwarf would be better than using matter from a white dwarf since black...
A first approximation Let's calculate surface gravity. Assuming an object of density $\rho$ and radius $R$, the surface gravity is $$g=\frac{4\pi}{3}G\rho R\tag{1}$$ For a white dwarf, $\rho\sim10...
Greater endurance/stamina: A thicker atmosphere/higher oxygen levels Try a thicker atmosphere - or rather, a planet where the humans largely live at higher elevations. Altitude training is useful ...
This isn't going to happen, for a number of reasons (all of which boil down to "It's dangerous, and these bacteria will kill their hosts"). Organic materials may "spontaneously ignite" when they ...
The time it takes a moon to become tidally locked to a planet depends on a number of factors. In particular, $$t_{\text{lock}}\propto\frac{\omega a^6}{m_p^{2}}$$ where $\omega$ is the moon's initia...
Deriving the radius The heliopause is a place of equilibrium, where the ram pressure from the solar wind is equal to the pressure of the interstellar medium (ISM). There are a number of sources of...
Massive objects beyond the frost line are likely giant planets. Let's talk about the frost line, which you helpfully specified (3.94 AU). For anyone not familiar with the term, the frost line is t...
Reverse the War of the Currents. In the late 19th century, Thomas Edison supported the use of direct current, and his company, Edison General Electric, attempted to use it on a large scale. A majo...
The redness of Mars' surface comes from the large quantities of iron in its crust. Other terrestrial planets in the Solar System also contain iron, but not at their surfaces. Mars in particular has...
For waves that have small heights relative to the water depth ($H\ll a$), we can use Airy wave theory. This works well for waves that are far out at sea, and can include tsunamis, in deep water. I ...
The Moon can appear to be different colors, as seen from Earth: A red, orange, or yellow moon can appear when the moon is near the horizon, and light has to travel through more of the atmosphere,...
Optical depth Let's start by looking at the idea of optical depth. Optical depth is a quantity that describes how light is attenuated as it travels through a medium. There are two commonly used eq...
Coboglobin is one of the main iron- and copper- free proteins that can be used for oxygen transport. It was first synthesized by humans in 1970, where cobalt was intentionally substituted for iron ...
I actually figured this out shortly after beginning the story, and I'm going to therefore post a self-answer, because it might be useful to others. Obviously, I'm still open to more ideas if this o...
About 5 billion years from now, the Sun will begin to swell into a red giant. This will cause some problems, because life on a planet orbiting a red giant is hard. Even if Earth isn't engulfed by t...
Yes. You want a hornet-like platypus in the rainforest. Hear me out. Water conducts electricity substantially better than air, salt water in particular. Therefore, electroreception - the ability ...
First, I suppose I should define what a "theory of everything" actually is. I'd describe it as a mathematical model that predicts the behavior of any object under any given set of conditions. It sh...
Temperature and luminosity Let's start with some calculations. For the sake of argument, I'll assume that we're talking about a planet that's identical to Earth orbiting a star that's identical to...
Robots can do jobs humans can't. In fact, they can do a lot of jobs humans can't. They can Explore and clean up after a nuclear accident Go into a volcano to explore Travel the universe without w...
