Posts by HDE 226868
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...
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, ...
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...
I'm reminded strongly of Iapetus, a moon of Saturn that has a dramatic two-tone coloring. One hemisphere is quite light, while the other is dark. It almost looks like you dunked half of the moon in...
With the naked eye, humans can see approximately 6th-magnitude objects. We can compute the apparent magnitude of a planet at a given distance, and find the distance corresponding to an apparent mag...
Pressure is important here. It's both a problem and a solution. As expected in giant planets, the atmospheric pressure and temperature change with altitude and depth. By the time you get to the ba...
Backwards running will almost certainly never be as fast or efficient as regular running. A study back in 2011 showed that it should takes about 30% more energy to run backwards at a given speed. W...
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...
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...
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...
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...
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...
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...
