Astronomy and Cosmology

Does dark matter or dark energy, or dark stuff in general actually interact with gravity? I know modern interpretations of it hold that gravity is the only way currently to determine the existence of such stuff, and that such stuff does not interact with any other fundamental force, but in all reality is there actual science to prove that dark stuff actually does indeed physically interact with gravity, or could such a correlation be explained away by other means?

According to Wikipedia, the Raleigh Convection Index, for the onset of natural convection in systems heated from below (as w/ air heated from below by burning materials), due to Thermal Expansion, is: [math]Ra = \frac{\alpha}{\kappa \, \mu} \rho g \Delta T L^{3} = \frac{k}{\rho \, c_{p}} \frac{1}{\kappa \, \mu} \rho g \Delta T L^{3} = \frac{k \, \Delta T}{c_{p} \, \kappa \, \mu} \times g L^{3}[/math] Now, for "forest fires" on an hypothetical exoplanet, would not the characteristic convection length scale (L) basically be that world's Atmospheric Scale Height (Wiki.) ?? [math]H = \frac{k_{B} \, T}{\bar{m} \, g}[/math] If so, an exoplanet's convecti…

How can distinguish conves and concave gravitational lensing effect? Generally, it is possible to examine the existence of dark matter with the existence of additional mass with the effect of gravitational lensing. If negative mass is dark matter, so if we try to examine the effect of gravitational lensing, previously the gravity between positive mass is attraction, so it has the shape of convex lens to collect within the form, whereas the force between negative mass and positive mass is repulsion, so a set of massive negative mass can make the effect that distorts observation target in the form of concave lens. If existing measuring instrument recognizes the e…

The Inner Solar System is depleted in both Hydrogen*, and Carbon**. The chemical combination of Hydrogen & Carbon, Methane (CH4), was a principal component of Earth's Primordial Volcanic Degassings (~4.5 to 4.4 Ga)***. And, in the Proto-Solar Nebula, Methane Ices only froze-formed beyond about 30 AU#. So, surely, Methane only existed as a Gas, in the Inner Solar System. * W.T. Sullivan III & J.A. Baross. Planets and Life, pg. 88. See also: Attachment 1 ** ibid., pg. 463. See also: Attachment 2 *** ibid., pg. 101. # Carroll & Ostlie. Introduction to Modern Astrophysics (1996 ed.), pg. 893. CONCLUSION (?): During the Sun's T-Tauri Phase…

Can the infinite fractals be applied for our universe? If it does, will we find the same pattern if we zoom out of our universe/multiverses? Also if it applies, do we stop at string theory or can we go further?(stupid but crazy like infinity)

this is a piece of star's picture that was taken with using Optical Vortex Coronagraph by university arizona in 2006 If you compare this objects with planets around star beside their unusual form you can see they are very bright as if they have their own light source aside of star. and also both of them have a unusual loop. that's why i call them mysterious objects. some say this is "dust bunnies" if we had more picture from this star we could confirm or reject "dust bunnies"but if this objects really exist only explain i have is that''we are not only smart life in universe" the original picture is dark .i increase brightness and resolution original picture ,now y…

We know well the Sun emits solar wind and solar rays. And, the Earth is attracted by Sun's gravity. If there were no solar radiation, how much Earth orbit around the Sun would be changed? Are there any equations?

We know well the Earth gravity affects on the Moon surface. How to we calculate the Earth gravity effect on the Moon, i.e., like the tide on the Earth, as a function of time?

From the Feb. 2 New York Times: In a long-awaited announcement, scientists operating NASA’s Kepler planet-hunting satellite reported on Wednesday that they had identified 1,235 possible planets orbiting other stars, potentially tripling the number of known planets. Of the new candidates, 68 are one and a quarter times the size of the Earth or smaller — smaller, that is, than any previously discovered planets outside the solar system, which are known as exoplanets. Fifty-four of the possible exoplanets are in the so-called habitable zones of stars dimmer and cooler than the Sun, where temperatures should be moderate enough for liquid water. http://www.nytimes…

What are your favorite books in astronomy and cosmology? If you had to share one book on astronomy with a friend, what is that book?

Many SFN posters must be familiar with the usual models of stellar explosion---this "pair instability" mechanism is different, and far more powerful. If anyone is interested in a simple explanation of how these hyper-powerful explosions work, here's the SciAm article http://www.scientificamerican.com/article.cfm?id=the-biggest-bang-theory Here is the technical article: http://arxiv.org/abs/1001.1156 from a team led by Avishay Gal-Yam. Usual supernovae result in two ways: One way is from a binary star where one partner is burnt-out and modest-size (like around 1.4 solar mass). The small burnt-out partner explodes when the large active partner dumps mass on …

Hello! I have a question. We know TEGR is obtained when we choose f(T) = T. I think it means this case is identical with f® = R, i.e. we obtain the same friedmann equations in both models. Also, we know that if we want to study a \Lambda CDM model in f® theory the Lagrangian density is something like R - 2*\Lambda. I need to know is there a similar Lagrangian density for \Lambda CDM model in f(T) gravity or not. I think it has a form like T-2*\Lambda. Am I wrong?

Can x-rays be reflected? I thought x-rays can be neither reflected nor focused (such as light with a lens). I found this quote from an article from the link below: "Scientists have long been aware of the advantages of X-ray imagers, but they have been difficult to build. X-rays have enough energy to pass right through an ordinary mirror instead of being reflected off it. However, lower-energy or "soft" X-rays can be reflected if the mirror is stood on edge so that the incoming radiation just grazes the surface." http://imagine.gsfc....ray_mirror.html So, if x-rays really can be reflected off a mirror, how exactly does it work? Are the optical properties of the mirr…

According to the accepted theories: If we were sitting still in a space ship watching a galaxie move away from us, and then fired up the engine and started traveling towards this same galaxie, would we be able to watch the red shift turn to blue? Would we see the light in it's "natural" color when we reached a velocity of zero? Is it possible that we, (in the space ship) could be observing a blue shift while beings on a planet, that we were passing, could be experiencing the same light as a red shift?

It takes a lot of power for rockets to leave Earth, so wouldn't it take more power for a spacecraft to leave the galaxy? I ask because in our solar system, it's puzzling that we'd be able to escape a star whose gravity holds in large planets. Along that reasoning, how can we escape a galaxy that holds in ? Unrelated, but...I'm also thinking, if the ride into our solar system's edge has a nasty bump near the heliosheath, then perhaps the Milky Way has its own analogous "galaxy wind" that ends up in a galaxial-sheath with a devastating bumpiness.

I saw a globe of the comsic radiation background left over from the big bang. How faraway is this from earth? How can we see anything beyond the big bang?

Hi All, I Am Looking for a bit of information, as you might note my name i am At the moment attempting to write a book, and am researching for said novel, although it is Sci-Fi/Fantasy in Genre. For The Field of Astrophysics I am asking all those with knowledge of or theories on the behavior of gravity well when, or more importantly the plausibility of two same sized masses (eg. Two Earth Sized Planets) existing in the same gravity well without collision and at a close enough range so that their atmosphere's can at some points join, even if this is not possible at such a close range information on two same or very similar mass planetoids existing in orbit of each othe…

If dark matter would be actual matter that can block/filter light, would it not be possible that the measurements of the distance of stars is wrong? And would it not be possible that the theory of dark matter is wrong? Interstellar matter has a known composition. (Link to wikipedia). It can be relatively easily calculated that even if all dark matter is completely transparent, the actual dust and other matter in the universe becomes of significance when we talk about the brightness of the furthest objects. But if we're wrong in any of the assumptions in the interstellar matter table that I just linked to, and there is some real matter hanging somewhere in space…

Could it be possible nowadays to observe a large number of objects in the universe, at various distances from us, and keep track of the redshift that we measure to see if the objects are actually accelerating? I know that the acceleration will be difficult to measure, because in the course of a human lifetime, the relative change in velocity of the stars/galaxies will hardly be measureable. I know that we would be looking for tiny changes... But the possible data set is nearly infinite. If the dataset is large enough, even small changes can be determined with some degree of certainty. Imho, this would be a more direct method to support the theory of the accel…

Hi, I'm a sophomore in college, but credit wise still a freshman I believe. I really love Astronomy and Physics but I'm just not much of a math guy. However I do really LOVE the science aspects of studying planets. I would love to study things such as the composition of planets when I get out of school, including our own planet. But I'd also really like to be able to for instance study the proposed sub-surface oceans on Titan and other planets, and their moons, asteroids and so on (quite the ambitious, perhaps unrealistic expectations I know.) Considering that, would I be better off studying Environmental Science as a major while I'm in school, or should I major in As…

We have atmosphere which covers our solid Earth. And sea water height is affected by the gravity of the Sun and moon. But till now, I have never heard about atmosphere thickness is affected by the gravity of the Sun and moon. Is our Earth atmosphere thickness not affected by the Sun and moon?

I read it all of the time in articles, about stars that "are from a time right after the big bang'. With so many tens and hundreds of billions of light years of space outside the visible universe, just how is it that anybody is able to see what should be dead information? If a star is supposedly 13b lya now, then it was probably 7b lya when a given snapshot was taken, give or take a few, and the difference is made up by the expansion of space over time. And if we can't see them now, then supposedly the james webb will help us see this first generation of occurrences, but i just don't see it because these things that happened 13b ya happened when the universe was only a…

How would the gravitational influence of the [relatively] nearby passage of a stellar mass affect our system? As a system, rather than as individual components (I imagine the direct effect on Sol would be moderately significant ). Would the system possibly precess under the right circumstances? Thanks!

We've heard that the size amplification of the far away galaxys is the cause of the DM existence. How to make this phenomena? Any good opinion?

I have heard there are many dust wind in the desert. At that time , I think, fine and dry particles are floating around in the air. Are there any record about dust explosion in the desert?