Posts by HDE 226868
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 ...
This sort of scenario is quite possible, and would likely be the result of the merger of two supermassive black holes during the collision of the galaxies. We have evidence of this in the quasar 3C...
Yes, but for a different reason. This is basically what happened with the Cassini probe, which was sent to crash into Saturn in 2017. However, the reason the probe was successfully disposed of was...
Problem 1: The supernova The first concern I have is one that Zeiss Ikon's answer discusses. To form a black hole, you need some sort of energetic event, likely a supernova. However, a supernova r...
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...
Orbits Conventional wisdom says that terrestrial planets and hot Jupiters are not likely companions. These gas giants in close orbits aren't thought to form in situ, but rather to form further awa...
To determine the color of the plants most likely to arise on a planet orbiting the star, we have to consider the wavelengths of peak absorption of different photosynthetic pigments. I would argue t...
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 ...
Let me address your second paragraph: Upon thinking more about this, sight in the infrared band seems like it would come with several problems. This vision would be relying on the radiant emitt...
M. A. Golding's answer is correct, I think, but it's also a bit incomplete, because the exoplanets in the TRAPPIST-1 system are not equally unsuitable for hosting exomoons. In particular, their ind...
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...
AGN structure and emission Let's talk about the structure of an active galactic nucleus like a quasar, and the types of emission we see from it. The classic unified model of an AGN consists of a s...
Gravitational instabilities There's actually a second idea for planet formation that's been around for some time (see Kuiper 1951). It requires the nebula hypothesis, like accretion, but it's a to...
There are a number of ways a star can lose mass, and I think it's worth talking about them: A normal coronal mass ejection may contain $\sim10^{-18}M_{\odot}$, which is also extremely low. Eta Ca...
A naive first calculation The formulas for orbital velocity and escape velocity are $$v_o=\sqrt{\frac{GM}{r}},\quad v_e=\sqrt{\frac{2GM}{r}}$$ I get $v_o=9.6\text{ km/s}$ for Saturn. For this to e...
Transit simulation I simulated the transit of your spaceship in front of a Sun-like star. Besides the dimensions of your ship, I made the following assumptions: A roughly circular orbit, with se...
I would recommend looking at pre-existing numerical models, rather than computing your own. This has a couple of advantages: You don't need to use any approximations. Factors like metallicity, ro...
TL;DR: About 2150 light-years Here's the gist of my answer, for simplicity: The largest nebulae are HII regions, clouds of gas ionized by young hot stars forming inside them. We can calculate th...
Cave formation This setup reminds me of rhizomes, which are essentially underground root systems that can spread out underground, sending up new seedlings at various intervals. Rhizomatic root sys...
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...
In my story, reasonably far in the future, an intrepid group of explorers are on the first manned mission to the Andromeda galaxy, travelling close to the speed of light. They slumbered in suspende...
For Hawaii, $H\propto\sqrt{A}$. I looked at the islands on the Hawaiian-Emperor Seamount Chain with surface volcanoes, and plotted their surface area vs. their maximum elevation, using data from W...
Try the Kozai mechanism The basis for the Kozai mechanism is that in a binary system, a third orbiting body - with a much lower mass than the other two - has a quantity that doesn't change in time...
Calculating flux I think a slightly more helpful quantity to calculate is the flux received by the planet - the power per unit area from the star. The mean flux on Earth is the solar constant, $F_...
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 ...
