Activity for HDE 226868
| Type | On... | Excerpt | Status | Date |
|---|---|---|---|---|
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How efficient can my neutrino detector be? In a class discussion last week, someone pointed out that a typical core collapse supernova releases $\sim10^{46}\text{ J}$ of energy in the form of (anti-)neutrinos while only radiating $\sim10^{44}\text{ J}$ in the form of photons. This then means that the energy flux from neutrinos is about two or... (more) |
— | almost 7 years ago |
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What wearable material do I need to survive a pyroclastic flow? This question is inspired by Green's Volcanoes in Orbit! The premise is that there is a 50-mile-high shield volcano (again, let's ignore the height implausibility) with a slope of about 2-3 degrees, at its base. In my case, this is a rare pyroclastic shield volcano. I calculated that if the mean slop... (more) |
— | about 7 years ago |
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A: Volcanoes in Orbit! What we're concerned with here is the eruption column and subsequent plume arising from the volcanic eruption. This is a shield volcano, so it's not going to erupt a la Mount St. Helens; rather, it will slowly spew out material. Granted, for a volcano this large that's still going to be quite the eru... (more) |
— | about 7 years ago |
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A: Exploration of a 50 mile high mountain TL;DR You'll see the development of both aerial vehicles and the means to survive in harsh spaces. Technology will develope faster in this world - at least, technology related to this mountain. All of that will in turn accelerate the drive to go to space. Going to space might be necessary to summit... (more) |
— | about 7 years ago |
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A: Can I overcome the bandwidth limitation on my photonic railways? Use a chain of ships. I'm imagining a pyramid setup, in a sense. Take $n$ ships. Send out the first one, of relatively low mass - Ship $1$. Then send out Ship $2$. Ship $2$ is now directly propelled by the laser on the base, and it in turn is propelled Ship $1$. Repeat by launching Ship $3$ to power... (more) |
— | about 7 years ago |
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A: Can a rational creature have a series of small brains instead of a large one? Yes. For large animals, octopuses are a possible source of inspiration. They have neurons in their arms, which lets them have a very large brain-to-body ratio. This does let their arms move without as much direct control from the brain. You could also argue that this sort of structure can be found ... (more) |
— | about 7 years ago |
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A: Is a bioluminescent analog to hemoglobin possible? You might consider adding luminol to the creatures' bloodstreams. When mixed with an oxidizer (like oxygen) and a catalyst, it becomes luminescent. It turns out that the iron in hemoglobin is a very good catalyst, which is why it's sometimes used at crime scenes to track blood. The glow dies away qu... (more) |
— | about 7 years ago |
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Could a large radio telescope survive interstellar spaceflight? I recently came across Could pulsars really act as "lighthouses" to help in interstellar travel?, asked a week ago. The author was trying to figure out if pulsars could be useful for interstellar FTL travel, because they could be used to find a craft's position; the answer was, of course, yes. I had ... (more) |
— | about 7 years ago |
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A: Goldplating Planets with Kilonovas How much gold are we talking about? Well, let's use the approximation $$\Delta V\approx4\pi r^2\Delta r$$ If $r$ is about the radius of Earth and $\Delta r$ is $1\text{ meter}$, then $\Delta V\approx5\times10^{14}\text{ m}^3$. The density of gold is $\rho\approx19320\text{ kg/m}^3$, and so $\Delta m... (more) |
— | about 7 years ago |
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A: Long-term memory loss The answer, as far as I can tell, is that there aren't any existing drugs that would do what you want. Drug-induced amnesia is, of course, a real thing. In your question, you alluded to drugs that cause anterograde amnesia, which involves a reduced ability to form new memories. Alcoholism can cause ... (more) |
— | about 7 years ago |
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A: pH Indicators and Fantastical Skin Colors What worries me about the bromothymol blue proposal is that it doesn't appear to be an organic chemical, i.e. no living organism produces it. This means that it's not possible (or at least unlikely) to be created in nature, and it would have to be artificially replenished. Those are obviously some bi... (more) |
— | about 7 years ago |
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A: O'Neill/McKendree Looping River The Coriolis acceleration is $$\mathbf{a}c=-2\mathbf{\Omega}\times\mathbf{v}$$ where $\mathbf{\Omega}$ is the angular velocity vector of the cylinder and $\mathbf{v}$ is the velocity vector of the river. $\mathbf{\Omega}$ is along the axis of rotation of the cylinder. Let's look at two cases: $\mat... (more) |
— | about 7 years ago |
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A: How would gravity on a moon be affected based on orientation relative to its parent planet? Let's make some assumptions: The moon is essentially spherical symmetric, with uniform density. There are no other gravitational effects from other celestial bodies. Denote the position of the center of the planet by Cartesian coordinates $(xp,0,0)$ and the position of the center of the moon by $... (more) |
— | over 7 years ago |
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A: Do stars in a binary star system fall along the ecliptic? Most likely, yes. I wrote an answer here discussion how binary stars are born. The relevant part here is that there are several main theories for how binary stars form: Capture: In an interaction between three stars, two become bound together while the third one is ejected away. This is unlikely t... (more) |
— | over 7 years ago |
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A: How To Make Lightning Building from scratch weather.gov gives three cases where lightning can suddenly become more intense or common in an area: "High instability" release: In this case, there is a large negative vertical temperature gradient (a.k.a. the lapse rate) in the atmosphere, i.e. temperature rapidly decreases... (more) |
— | over 7 years ago |
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A: What happens to asteroids when heated into a plasma? Asteroid Laser Ablation is a related technique, where a set of lasers heats up part of an asteroid, applying a torque that can change its orbit and (hopefully) send it moving away from Earth. Looking at that might be helpful. Here are some statistics: Temperatures needed: 3000 K, at the most.1 Powe... (more) |
— | over 7 years ago |
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A: How many moons can form around this alternate Earth? The number of moons Sean Raymond wrote a great answer to a similar question, and I'd like to base my answer on his. He used the following technique to estimate the total number of moons orbiting a planet, assuming all the moons are in mean motion orbital resonances with one another. Calculate the ... (more) |
— | over 7 years ago |
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A: How do I explain the formation of my world scientifically? The formula for the time a body $B1$ orbiting another body $B2$ of mass $m2$ will become tidally locked to $B2$ is (see Gladman et al. (1996), Equation 9) $$t=\frac{\omega a^6I1Q}{3Gm2^2k2R1^5}$$ where $\omega$ is the initial spin rate, $a$ is the semi-major axis, $Q$ is something called the dissipat... (more) |
— | over 7 years ago |
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A: What parameters are necessary to generate a plausible star in line with a spectral classification? The spectral type of a star tells you, in general, its surface temperature. Unfortunately, there's one main issue here. Each spectral type can give way to a range of luminosities and properties (see any Hertzsprung"“Russell diagram). This can be rectified if you just want to create a star as it enter... (more) |
— | over 7 years ago |
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A: Gravitational lenses for focusing giant lasers Probably not. After some more consideration, I'm less confident that the proposal could work. There are two reasons: No guarantee of focusing at any one point, and an inability to control the parameters of the lens. 1. A gravitational lens has no focal point. The analogy to a traditional lens does... (more) |
— | over 7 years ago |
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A: What kind of stellar core or degenerate material would be needed to create a survivable explosion? Interesting question. I'm reasonably certain that the answer boils down to a property of matter called the equation of state. An equation of state is a relation between several thermodynamic variables, typically pressure ($P$), density ($\rho$), and temperature ($T$). You might have heard of some si... (more) |
— | over 7 years ago |
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A: Effects of powerful superconducting rings on humans? I'm reasonably sure that the $5\text{ G}$ there refers to $5$ Gauss. The Gauss is a unit of magnetic flux (named, of course, after Carl Friedrich Gauss). The $5\text{ G}$ figure makes sense, too; it lines up with the recommendations in this Cornell recommended safety guide for public areas (Section 5... (more) |
— | over 7 years ago |
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A: Can gamma radiation be used to generate electricity on earth? Yes, it's been tried. Hashizume et al. attempted to use semiconductors (variants of which are also used in normal solar cells) which were subjected to gamma radiation from a radioactive isotope of cobalt. They generated up to 0.2"‰Watts/meter² "” certainly not a lot. The energy conversion efficienc... (more) |
— | over 7 years ago |
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A: Smallest Black Hole to 'heat' a Gas Giant 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 mass of the black hole is; this is incorrect because accretion would probably be prevented because o... (more) |
— | over 7 years ago |
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A: Can stars that are not powered by nuclear fusion exist? 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 $10M{\odot}\text{-}100M{\odot}$ surrounded by a gas envelope of up to $1000\text{-}10000M{\odot}$. These objects generated energy from g... (more) |
— | over 7 years ago |
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A: Effect of Hot/Warm Jupiter atmosphere loss on Habitable Zone As you've stated, the paper you cited gives the rate of atmospheric mass loss as approximately $\dot{M}=10^9\text{-}10^{11}\text{ g/s}=10^{6}\text{-}10^8\text{ kg/s}$ of hydrogen. We can convert this to mass flux as $$Fm(r)=\frac{\dot{M}}{2\pi r^2}$$ a distance $r$ from the Hot Jupiter because the at... (more) |
— | over 7 years ago |
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A: Formation of a planet with a mercury core You want a cold disk. Mercury is an example of a volatile, which, for our purposes, means that it exists as a solid only at very low temperatures. One thesis (Funk (2015)) classifies it as "moderately volatile" (Table 1.1), also noting that its 50% condensation temperature, $T{c}$1, is less than tha... (more) |
— | over 7 years ago |
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A: What is the habitable zone around my star? Short answer You have the two equations you need on the linked page under the heading "Stage two": $$ri=\sqrt{\frac{L{\text{star}}}{1.1}},\quad ro=\sqrt{\frac{L{\text{star}}}{0.53}}$$ where $ri$ and $ro$ are the inner and outer radii of the habitable zone, in astronomical units and $L{\text{star}}$ ... (more) |
— | over 7 years ago |
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A: Would a large, close-by, molten moon be able to support photosynthesis at night? Let's assume that the Moon is roughly a black body. Therefore, its luminosity can be approximated by the Stefan-Boltzmann law: $$L=4\pi\sigma R^2T^4$$ As you've said, $T=1100^\circ\text{ C}=1373\text{ K}$. $R$ is related to mass, $M$, by $$\rho=\frac{M}{\frac{4}{3}\pi R^3}\to R\propto M^{1/3}$$ Doubl... (more) |
— | over 7 years ago |
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A: Would it be possible to punch someone into space? On Earth, escape velocity is about 11 km/s, or 11,000 m/s. Assuming the opponent weighs around 70 kg (maybe more), that's a kinetic energy of at least $$\text{KE}=\frac{1}{2}mv^2=\frac{1}{2}\cdot70\cdot(11000)^2=4.235\times10^9\text{ Joules}$$ Furthermore, the opponent would have a momentum of $$p=mv... (more) |
— | over 7 years ago |
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A: Which factors are more dominant when it comes down to atmospheric escape? I wrote an answer on Physics Stack Exchange that discussed this a bit. I'll present a shorter and more focused version here. There are two main processes by which a planet can lose atmosphere: Jeans escape (for lighter particles) and dissociation/non-thermal escape (for heavier particles). Jeans es... (more) |
— | over 7 years ago |
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A: How long before we're stuck on Earth due to Space Debris? (Kessler syndrome) A couple hundred years. In 2013, the Inter-Agency Space Debris Coordination Committee (IASDCC) published a report detailing comparisons of several independent models (one each from ASI, ESA, ISRO, JAXA, NASA, and UKSA) for how the amount of space debris will evolve over time. This was then translate... (more) |
— | over 7 years ago |
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A: In an elliptical orbit, where should a rocket fire its engines for maximum efficiency? Fire the engines closer to the Sun for maximum efficiency. This is due to the Oberth effect. Assume the spacecraft undergoes a burn when it is farther away from the Sun. The expelled propellant will have a certain amount of kinetic and potential energy, $Ep$. If an energy of $\Delta E$ is released d... (more) |
— | over 7 years ago |
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A: Do different star types produce plants with different properties? Let's think about this in terms of peak emission. Wien's displacement law tells us that the peak emission wavelength of a black body, $\lambda{\text{max}}$, is inversely proportional to its temperature, $T$: $$\lambda{\text{max}}=\frac{b}{T}$$ where $b$ is Wien's displacement constant; $b\simeq2.9\ti... (more) |
— | over 7 years ago |
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Is it possible to surf a solar flare? I was rereading The Restaurant at the End of the Universe, the sequel to The Hitchhiker's Guide to the Galaxy, and I came across an interesting passage: Flare riding is one of the most exotic and exhilarating sports in existence, and those who can dare and afford to do it are among the most lioni... (more) |
— | over 7 years ago |
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A: Is a bigger planet than Earth with the same density possible? That's no planet! Let's say that the radius is $18R{\oplus}$, where $R{\oplus}$ is Earth's radius. The volume will then be $$\frac{4}{3}\pi(18R{\oplus})^3\bar{\rho}=5832\left(\frac{4}{3}\pi R{\oplus}^3\bar{\rho}\right)=5832M{\oplus}$$ where $M{\oplus}$ is the mass of Earth and we assume the same mea... (more) |
— | over 7 years ago |
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A: Escaping a pair of orbiting black holes through the saddle So . . . modeling the space near two close black holes is actually a really, really tough task. Numerical relativity is extremely challenging; a good example is the intense computations it took to finally create an excellent simulation of GW150914, the source of the first directly detected gravitatio... (more) |
— | over 7 years ago |
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A: Which major solar system body could most realistically be artificial? Consider a short-period comet (specifically, Comet Encke). Pros: Very short-period comets can have orbital periods of only a few years, with approaches relatively close to Earth ($\sim0.1\text{ AU}$) happening every couple of decades. Comets will spend some time away from Earth, and may thus escap... (more) |
— | over 7 years ago |
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A: Does gravity converge in a wrap-around universe? I can give you a Newtonian analysis of the situation, which may or may not be correct. If you want a Newtonian universe, then great. If you want a general relativistic one, you'll need something more complicated. Example 1: Square domain As a simple introductory example, let's say your universe is ... (more) |
— | over 7 years ago |
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A: If an Earth sized planet had 1.5-5x more or less gravity than that of the Earth, how would it affect the shape of waves in water bodies? The best way to study water waves of many sizes is to use Airy wave theory (see also here), a mathematical model using several simplifications that nonetheless produces reasonable results. The linear theory works best when the amplitude ($a$) is small in comparison to the water depth ($h$) and the wa... (more) |
— | over 7 years ago |
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A: The (Alternative) Reason for the Seasons, Part 2: Variable Star Let's look at the two extremes: $\Delta T=15^{\circ}\text{F}$ and $\Delta T=40^{\circ}\text{F}$. In the first case, I'll say $T{\text{min}}=50^{\circ}\text{F}$ ($283.2\text{ K}$) and $T{\text{max}}=65^{\circ}\text{F}$ ($291.5\text{ K}$). This gives us $$\frac{T{\text{max}}}{T{\text{min}}}=1.03$$ Let'... (more) |
— | over 7 years ago |
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A: Can quantum spin be converted to macro systems? Have you ever heard of the Einstein-de Haas effect? Take a large piece of iron, cylindrically shaped. Now, put it in an external magnetic field. The bar should become magnetized. Given that magnetization arises from the orientation of electron spins inside the bar, there's a change of spin angular m... (more) |
— | almost 8 years ago |
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A: Can twin stars be born? Although astronomers have considered this phenomenon in the past, the data indicates that this isn't how stars are born. That said, yes, your premise works. Here's how you make a star, in a nutshell: Take a big cloud of gas and dust. Have the cloud grow until it reaches roughly the Jeans length, a... (more) |
— | almost 8 years ago |
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A: Could animal life develop on the TRAPPIST-1 planets? As I'm sure you know, four more exoplanets were recently discovered around TRAPPIST-1 (Gillon et al. (2017)), bringing the total to seven "” all, amazingly, presumably rocky and near the star's habitable zone. There has been recent work, of course, about the system's habitable zone and whether any of... (more) |
— | almost 8 years ago |
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Is it safe to orbit HDE 226868? I'm considering a story where an exploration is devised to explore a binary system containing a black hole; the choice is Cygnus X-1, with its companion supergiant star HDE 226868. It would likely be dangerous to orbit the black hole, as the accretion disk means that there will be high emission of po... (more) |
— | almost 8 years ago |
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A: Quantum Based AI getting around Isaac Asimov's "Three Laws of Robotics" Asimov's laws of robotics are not technical laws; they're societal laws, imposed by humans to ensure that robots don't destroy mankind. You can make a robot that breaks any of them, still using ordinary computer chips, although really, the laws as they are are just fine, thank you very much. Silicon... (more) |
— | almost 8 years ago |
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A: How would a planetary ring react to a magnetic field? This has indeed been investigated. I found a thesis by Daniel Jontof-Hutter (2012) that did a stability analysis of particles in rings orbiting, among other bodies, Saturn. One important quantity he studied was the ratio of electric force to gravity, $L$. When $L\gg1$, the electric force dominated (t... (more) |
— | almost 8 years ago |
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A: What effect would liquid sulfur oceans, sulfur dioxide in the atmosphere have on visibility, sound propagation and other environmental information? How far and how well will sound travel through the sea? First, we need to figure out exactly what the sea is made out of. You've indicated that it's sulfur, but what kind of sulfur? Lopes & Williams (2005) is an excellent review article on Io that has a section discussing this. They identify differe... (more) |
— | almost 8 years ago |
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A: Creating a realistic world(s) map - Stars 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, in density wave theory, which explains the winding arms of spiral galaxies. Before we begin, here's your... (more) |
— | almost 8 years ago |
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What are the main problems with beaming light from the Sun to Saturn? I recently finished reading the Kim Stanley Robinson novel 2312 - set, of course, in the year 2312. Part of the background to the political negotiations and ongoing terraforming in the outer Solar System involves the transfer of energy to Titan, one of Saturn's moons, from the Vulcanoids, a populatio... (more) |
— | almost 8 years ago |