Description:
Forum in astronomy/astrophysics research. (Moderated)
|
|
|
Visible Horizons
|
| |
Visible Horizons as Gravitational Potential Wells Take a sphere of Radius R and uniform Density D imbedded in a background Density D1 [Where D>D1]. Lets set the background Density equal to critical density or 10^-29 gms/cm^3, so what we have is a sphere located at any point within the universe, but at the... more »
|
|
|
ARXA and Milliquas catalogs available on-line
|
| |
The Atlas of Radio/X-ray Associations (ARXA) has been in submission for the past two months, but no reply yet from the referee. This catalog has 602,570 optical objects with X-ray associations listed from Chandra, XMM-Newton, ROSAT RASS, HRI, PSPC and WGA, and radio associations from NVSS, FIRST, and SUMSS. Also, existing... more »
|
|
|
Graviton Ques?
|
| |
While I am aware that gravitons are still hypothetical under QM [not yet di= scovered],,,,, Would gravitons [wavelength] undergo a red or blueshift if the 2 interactin= g masses were moving away or towards each other at high speeds? As opposed to 2 interacting masses which are stationary wrt each other.... more »
|
|
|
QUESTION: if a planet explodes, which parts spread away faster
|
| |
Hi all I wanted to ask a question about the physics related to the explosion of a planet. Lets say that there was a planet with 2 "layers": A. solid core (with density something similar to the average density of our moon), having diameter of around 10000 kilometers B. around the core, a layer of water vapor, having a diameter of... more »
|
|
|
neophyte question about hubble's law
|
| |
The 'Hubble's law' Wikipedia article states '...that the velocity at which various galaxies ARE receding from the Earth IS proportional to their distance from us.' (emphasis added) My question is about the tense of the two verbs in all caps above. Aside from assuming things are orderly, do we have any way of inferring that a galaxy that was moving away... more »
|
|
|
Betelgeuse as possibly pre supernova - what are the closest and most
|
| |
I notice from APOD that Betelgeuse is ~640 l.y. away, and from Wikipedia that it is possibly in a pre supernova stage, perhaps to explode in a few thousand years. In thinking about the ecological consequences of this, being mindful that Betelgeuse's spin axis is not pointed toward the solar system, I still would like to estimate the... more »
|
|
|
The origin of spiral arms
|
| |
A little while back I announced on s.a.r. the explanation as to why Newtonian gravity causes galaxies to form logarithmic spirals, and in particular bisymmetric spirals. Readers may like to know that this explanation has now been published in a peer reviewed journal. [link]... more »
|
|
|
Movie "Knowing"
|
| |
The end of the 2009 movie "Knowing" shows Earth destroyed by a solar flare. [link] Is this even remotely possible? [[Mod. note -- No. Contrary to how Holywood portrays them, actual solar flares involve only very small changes in the Sun's overall energy output, and are many orders of magnitude too weak to destroy... more »
|
|
|
Two considerations for Fermi's Paradox
|
| |
A recent paper, astro-ph/0907.3432 by Milan Cirkovic, reviews the arguments surrounding Fermi's Paradox. There is a good discussion of how quickly the galaxy would be completely colonized by any spacefaring civilization -- a negligably short time span in cosmological terms -- and that Earth is if anything a late comer to... more »
|
|
|
|
