Astronomy and Cosmology

With Hobson's notation: H=(da/dt)/a dH/dt = ((d2a/dt2)/a) - ((da/dt)/a)2 If ((d2a/dt2)/a) is negative, (dH/dt) is certainly negative. But if ((d2a/dt2)/a) is positive, (dH/dt) can be positive or negative. What is your interpretation?

Are there, or is it possible that clouds or regions in space can drop hundreds of degrees below absolut zero?

What is the exact calculation of Particle horizon in Lemaître model? Does it exist? Is it finite or infinite? Can anyone calculate that integral? Thanks

If space-time "sags" under the influence, of massive objects: and if matter "grips" space-time, so as to "curl space-time up", i.e. induce positive "contractile" curvature (Wheeler. Journey into Gravity & Spacetime); then might relativistically-dense black-holes be able to "curl the fabric of space-time all the way around", and "pinch off" (vaguely resembling a rain-drop) ??

There may be an easy answer for this, but, if there is please forgive me. I have posted previously about the supposed graviton, thanks for those that replied. I understand that this graviton is the particle responsible for the effects of gravity. Is there a particle that is responsible for the effect of magnetism?

Hello everybody! First of all, please ignore my language mistakes, cause I'm non native speaker. My question is this: is it possible that a telescope in space (located at low orbit, high orbit or somewhere in space) which is mounted on spy satellite or ufo can discern (recognize) human's faces (i.e. "see", that is detect reflected light photons) and simultaneously be invisible (that is do not reflect light photons) for the ground telescopes and let's say hubble telescope? Take into account rotation of The Earth about it's axis and rotation around the Sun. Any corrections of my thoughts are welcomed. Many thanks in advance.

http://www.dailygalaxy.com/my_weblog/2011/12/-from-the-x-files-dept-could-the-newly-discovered-gigantic-black-holes-harbor-life-.html Check this article out.

http://www.examiner.com/paelenotology-science-news-in-national/4-5-billion-year-old-concrete-from-space

every one saying that source of dark energy is black hole ,big bang,etc.. but they aren't true.since its so powerful i can't be created by black hole or from left out big bang.hence there is a central force is creating it from center of universe

I can't be the first person to think of this but here it is anyway. If you took a golf ball sized chunk out of a neutron star, or quazar and threw it into outerspace, it would probably have enough weight to cause a gravitational time dialation strong enough to warp the fabric of space time and cause light to bend around it's gravity well field. Some of these molecules might be escaping through the jets of energy that form from time to time at the polar regions. I don't know, what do you think?

Can some one please briefly explain why natural cosmological events are unlikely to generate prime numbers.

Hubble's observations of distant galaxies showed an increase in redshift with distance which is conventionally interpreted as an accelleration in expansion with distance. This has led to all sorts of speculation as to what might be causing such an effect. I have a problem with the statement that distant galaxies are moving away faster. Not the faster bit, but the word "are". In truth we have no idea what they are doing at this point in time, we only know that they were moving away faster when the light which left them billons of years ago started its journey to us. Our view of the universe is down a cone through time with events happening further back in time the fur…

Cluster cores contain anomalously low amounts of baryonic matter, b/c "in the central regions [of galaxy clusters], the gas is repeatedly whipped up and smoothed out by passing galaxies" (daily galaxy 2011). And, shock-heating "sound waves" have been observed, in the ICM, in the cores of nearby clusters, e.g. Perseus, Virgo (Wikipedia). Such shock-waves could, conceivably, have been caused, by the "wakes" of galaxies passing through the cluster core. Therefore, could "galactic stirring", of ICMs, inject sufficient heat, into the ICMs, to prevent "cooling collapse", i.e. to offset observed x-ray emissions of Lx ~ 300 MLsol - 300 GLsol (irwin) ?

People seem to say, that WMAP "proves" that our spacetime "is" flat; for, curved spacetime would lens and distort, our view, of the CMB. But, CMB photons, observed by WMAP, have traveled across our cosmos, from the distant past, i.e. from "way over there, way back then"; to our modern earth, i.e. to "here, now". Thus, the flatness implied, by those un-lensed, un-distorted CMB photons, reflects their inbound, earth-bound, sightlines, from far far away, over the past ~10 Gyr. Er go, WMAP proves that our space-time HAS BEEN flat, along the light-like null-geodesics, along which those photons HAVE traveled, over the PAST billions of years, from the last-scattering-surf…

Entropy = chaos. Chaos theory dictates that it can generate order, e.g. forget the name but those solutions that oscillate between two equilibrium states in rythmical manor. So if chaos can generate or foster order then how is that entropy only ever increase in theory?

If time is truly a dimension and is integral to the concept of space-time, time must be much more than the 'arrow of time' we experience. If all other directions of time exist, could our limited experience of time be similar to how our eyes can only sense a very narrow band of the electromagnetic spectrum? As I read about Einstein's theories of time-space, I kept turning to such thoughts. In addition, I recently came across a news item concerning dark matter. As I recall, it stated that dark matter is not concentrated as scientists had speculated, but was dispersed consistently through space. I was struck by a correlation that space is primarily (80 percent?) c…

What was the Size of the universe right after inflation?

Is the accelerating expansion of the universe only experienced between superclusters? Do superclusters also fall apart, or do they remain gravitationally bound? If the expansion is only between superclusters of gallaxies, then it almost seems irrelevant to us, since our supercluster dominates our local experience. Our universe, out to the edge of our supercluster (10s or 100s of light years out) is not expanding at all.

If anyone can help me, I am looking for the %s of the dark matter, atoms and "dark energy or/and photons" in a 6x10^9 years old universe‏. I need the %s to verify my calculations: 50.165% Dark Matter, 40.28% Dark Energy/photons and 9.552% Atoms Plz note I need the % of Atoms and % dark matter been separated from the % of photons and neutrinos. In the Cosmology standard model, Dark Energy only appeared 7billion years ago, but I have hard time to believe it, Dark Energy cannot just appeared out of nowhere. So I came up with a hypothesis where Dark Energy existed from the beginning of the universe and photons aka light or/and matter with no mass conceal th…

I've read that the voyager has encounted magnetic fields at the edge of our solar system. I'm wondering if these magnetic fields might exist around all or most solar systems, and if they might or probably exist in denser quantites around the edge of a galaxie? I wonder if the dynamics of these fields might create some kind of algorythmic structure of energy flow, and how or if the energy builds and releases in some fashion.

You must know this representation of the expansion of the universe. It is published in several places on the web. In fact, this representation is a Space-Time diagram. WMAP is the point where we are today as observers of the Universe. _The Big Bang happened 13,7 billions years ago, in the past. The past is on the left side of the diagram. The present time is where the WMAP sattelite is pictured. The future is on the right side. Time goes from left to right. _Each slice of the diagram represents space at a specific period. 3d space has been reduced to a 2d surface. What part of the diagram are we looking at when focusing with our telescopes? Roughly, it …

Presumably, when the universe formed from Alan Guth's inflaton, its hyperbolic gravitational field began to collapse into a parabolic one (see post of Sept. 19, 2011). That collapse continues to this day. But, the process is almost done. There cannot be an infinite amount of gravitational energy sequestered in the hyperbolic field that would be available to fuel acceleration of the expansion rate via such a transformation. That is, transition to a lower energy parabolic field must provide a distinctly limited supply of extra impetus. Surely, after 13.72 billion years, the spring has almost run down by now. If the expansion rate is called h, and its present value is ca…

First, in a flat, matter-dominated cosmos, the age of the universe is 2/3 H0-1. For H0 ~ 70 km/s/Mpc, that age is cosmologically calculated to be >9 Gyr. Second, our sun has a B-V color index of ~0.6, approximately the MS Turn-Off, of the Globular Cluster 47 Tucanae: And, GCs are nearly as old as our universe, i.e. ~9 Gyr for a flat, matter-dominated cosmology. QUESTIONS: First, if our cosmos turns out to be nearly flat, and mostly matter-dominated; then, would not GCs be ~9 Gyr old; and would not our sun's MS lifetime be about ~9 Gyr as well ? Second, if our sun's MS lifetime is typically predicted to be ~10 Gyr; and, if our sun represents …

Please consider a spheroidal 'Dark Matter' (DM) halo, of total mass M; characteristic scale radius R; and, a power-law DM 'particle' Initial Mass Function (IMF), i.e. [math]N(m) \propto m^{-\alpha}[/math] (cp. galaxy luminosity function, star IMF). We shall require that the DM IMF be 'steep', i.e. [math]\alpha > 2[/math] (see below). Normalizations: W.h.t.: [math]M = \int_{m_0}^{\infty} m N(m) dm[/math] [math] = C \times \int_{m_0}^{\infty} m^{1-\alpha} dm[/math] [math] = C \times \frac{1}{\alpha - 2} \frac{1}{m_0^{\alpha-2}}[/math] [math]\therefore C = (\alpha-2) M m_0^{\alpha-2}[/math] Thus: [math]N = \int_{m_0}^{\infty} N(m) d…

The conversational theory of what constitutes a black hole core has resulted in many non-answers, some even dealing with an "infinitesimal singularity" which I find ridiculous. Why not just take a logical step back and conclude that a black hole, and its core, is simply a very large, dense neutron star! That would also keep current laws of physics intact, without all those hypothetical black hole hyperboles. Or has this neutron star thing been rebuffed already? Thanks.