http://www.physicsforums.com The application of physics to astronomy en Sun, 19 May 2013 01:27:39 GMT vBulletin 60 http://www.physicsforums.com/images/physicsforums/misc/rss.jpg http://www.physicsforums.com http://www.physicsforums.com/showthread.php?t=692339&goto=newpost Sat, 18 May 2013 12:07:42 GMT Hello
Dark matter is presumed.... to balance the sums... as visible matter doesn't work out (apparently) to a high enough value.....

.... What part of the calculations was evaluated as being too high.... to warrant the need for more matter to be 'somewhere'.

Thanks for thoughts ]]> Astrophysics stephenn http://www.physicsforums.com/showthread.php?t=692339 http://www.physicsforums.com/showthread.php?t=692183&goto=newpost Fri, 17 May 2013 10:57:23 GMT Why do we talk about dark matter rather than dark mass? Where does the necessity for matter stem from? Why do we talk about dark matter rather than dark mass?

Where does the necessity for matter stem from? ]]> Astrophysics Philosopha http://www.physicsforums.com/showthread.php?t=692183 http://www.physicsforums.com/showthread.php?t=692177&goto=newpost Fri, 17 May 2013 09:52:54 GMT I'm sorry if I posted this is the wrong section, but I was wondering if fundamental forces evolve? In other words, can universes evolve. Since stagnant ones eventually die out. And the successful ones produce black holes; transferring matter into a whole new beginning. ]]> Astrophysics Lyre http://www.physicsforums.com/showthread.php?t=692177 http://www.physicsforums.com/showthread.php?t=691940&goto=newpost Wed, 15 May 2013 23:17:44 GMT I'm working on a video game set in space, and I'd like my portrayal of the galaxy to be as scientifically accurate as is feasible.

I've been looking into metallicity functions, but I can't make any sense of what I'm seeing, and I don't even know where to start on the subject of algorithms for star position and planet properties.

To boil it down to a single statement, I need help finding an algorithm or series of algorithms that can procedurally generate the positions of 100,000 stars, their basic parameters, and a rough estimate of the mineral content of the planets that orbit them, giving results that are at least not blatantly impossible. I don't really care much about the simulation methods being right (as in, how these things actually came about) as much as them being simple and resembling real data. I realize this might be a tall order, and I don't expect to be spoon-fed, but I'm pretty much totally lost here. Can anyone point me in the right direction? ]]> Astrophysics Schilcote http://www.physicsforums.com/showthread.php?t=691940 http://www.physicsforums.com/showthread.php?t=691922&goto=newpost Wed, 15 May 2013 21:10:06 GMT Have a homework question about power law density distributions that I could use a little help on...

Given a power-law distribution, ρ(R) [itex]\propto[/itex] [itex]R^{-\propto}[/itex], show that a flat rotation curve can be obtained if [itex]\propto[/itex] = 2 and that solid body rotation is obtained if [itex]\propto[/itex] = 0.

Also, I'm really not sure what this next question is asking for... Any help?

Suppose the rotation curve of the Milky Way is flat out to 2[itex]R_{0}[/itex]. What mass does that imply out to that distance? If all the luminosity of the Milky Way is contained inside 2[itex]R_{0}[/itex] what is the mass-to-light ratio of the Milky Way in solar units? What is the significance of this value? ]]> Astrophysics sfbsoccer25 http://www.physicsforums.com/showthread.php?t=691922 http://www.physicsforums.com/showthread.php?t=691694&goto=newpost Tue, 14 May 2013 17:09:22 GMT hi guys, i have an elementary question about the blackhole..recently i have read in a science magazine that even the lights from other stars can not... hi guys, i have an elementary question about the blackhole..recently i have read in a science magazine that even the lights from other stars can not reach to the blackhole ( event horizon) rather bends in other direction due to its gravitational force..now my question is if i point a light source towards a blackhole , will it not hit the blackhole (event horizon ) and never return to me ? or it will just bend tangent to the horizon and go to some other space ...

previously i thought blackholes just grab light and never returns it ...but grabs actually...is it wrong thinking ?
plz help me
regards ]]> Astrophysics cooper607 http://www.physicsforums.com/showthread.php?t=691694 http://www.physicsforums.com/showthread.php?t=691560&goto=newpost Mon, 13 May 2013 20:44:00 GMT I was watching a popular TV series on the Universe which briefly described super novae. Here are two naive questions not well answered in the... I was watching a popular TV series on the Universe which briefly described super novae.

Here are two naive questions not well answered in the video.

1) When a white dwarf becomes a super nova through accretion of gas from a companion star. the pressure from the accreted material ignites carbon-carbon fusion which explodes the star into a super nova. Why does this carbon-carbon fusion release so much energy and blow the star?

2) For huge stars carbon-carbon fusion apparently is no problem and in fact fusion is able to form elements all the way up to iron. At some point the iron core implodes from its own weight.
Why is this? Is this saying that if one builds up an iron ball in space - slowly adding more iron - until the ball is enormous that at some point it will no be able to support itself? Secondly, why is the implosion so violent and where does the energy come from? ]]> Astrophysics lavinia http://www.physicsforums.com/showthread.php?t=691560 http://www.physicsforums.com/showthread.php?t=691473&goto=newpost Mon, 13 May 2013 08:44:58 GMT I see there have been many postings about this topic in this forum. The formula for this relation is Luminosity = Mass^3.5 Taking logs of both... I see there have been many postings about this topic in this forum.

The formula for this relation is Luminosity = Mass^3.5
Taking logs of both sides we get log (lum) = 3.5 * log (mass)
and using a little algebra we find that the exponent (3.5) should equal log (lum) ÷ log (mass)

I have selected stars from a table located here: http://www.essex1.com/people/speer/main.html
and I have computed what the exponent value should be in each case.
STAR   Lum   Mass   EXP
Orionis C 30,000.00   18.00  3.566653
Becrux   16,000.00   16.00   3.491446
Spica   8,300.00   10.50   3.837759
Achernar   750.00   5.40   3.925568
Rigel   130.00   3.50   3.885439
Sirius A   63.00   2.60   4.336039
Fomalhaut   40.00   2.20   4.678604
Altair   24.00   1.90   4.951367
Polaris A   9.00   1.60   4.674910
Eta Scorpii   6.30   1.50   4.539354
Procyon A   4.00   1.35   4.619371
Alpha Centauri A   1.45   1.08   4.827943
The Sun   1.00   1.00
Mu Cassiopeiae   0.70   0.95   6.953637
Tau Ceti   0.44   0.85   5.051600
Pollux   0.36   0.83   5.483033
Epsilon Eridani   0.28   0.78   5.123395
Alpha Centauri B   0.18   0.68   4.446371
Lalande 21185   0.03   0.33   3.162872
Ross 128   0.0005   0.20   4.722706
Wolf 359   0.0002   0.10   3.698970


No matter whether we concentrate on low mass or high mass stars, we see that the exponent value varies quite a bit .
Does anyone know why there is so much variance in the mass luminosity relation? ]]> Astrophysics wolf1728 http://www.physicsforums.com/showthread.php?t=691473 http://www.physicsforums.com/showthread.php?t=691167&goto=newpost Sat, 11 May 2013 17:15:24 GMT As the expansion of space accelerates, space is created and this seems to break the conservation of energy law. I've googled this but have not found a really good explanation of this.

Imagine for a moment we're so far into the future that there are vast vast voids between what remains of galaxies. Some of these voids may be larger than the current known universe. Background radiation from the big bang has red-shifted to the point that it's wavelength is longer than the size of the known universe.

How is the expansion of space at some mind-boggling rate with nothing in it and no background radiation not breaking the law of conservation of energy?

Second question: Can light actually stretch that far or will it eventually be absorbed into the background quantum fluctuations and "die" so to speak?

Thanks for helping me with my curiosity! ]]> Astrophysics typical guy http://www.physicsforums.com/showthread.php?t=691167 http://www.physicsforums.com/showthread.php?t=690769&goto=newpost Thu, 09 May 2013 14:56:38 GMT "...... the first direct evidence of pear shaped nuclei in exotic atoms. The findings could advance the search for a new fundamental force in nature that could explain why the Big Bang created more matter than antimatter—-a pivotal imbalance in the history of everything."

Any insights.

http://phys.org/news/2013-05-exotic-...ysics.html#jCp ]]> Astrophysics julcab12 http://www.physicsforums.com/showthread.php?t=690769 http://www.physicsforums.com/showthread.php?t=690518&goto=newpost Wed, 08 May 2013 11:15:40 GMT Hi, I am a Mechanical engineer from India. I want to do my Masters and Phd. in Astrophysics or cosmology.Can anyone suggest me some good... Hi,
I am a Mechanical engineer from India. I want to do my Masters and Phd. in Astrophysics or cosmology.Can anyone suggest me some good universities (all over the world) that allow mechanical engineers to pursue graduate studies in Astrophysics ? My GRE score is 313 & 3.5 and TOEFL score is 110. ]]> Astrophysics varun.kalra13 http://www.physicsforums.com/showthread.php?t=690518 http://www.physicsforums.com/showthread.php?t=690436&goto=newpost Wed, 08 May 2013 02:20:08 GMT If the universe is expanding at less than the speed of light, what happens to EM radiation that is emitted from stars at the edge of the universe? If the universe is expanding at less than the speed of light, what happens to EM radiation
that is emitted from stars at the edge of the universe? ]]> Astrophysics yoyopizza http://www.physicsforums.com/showthread.php?t=690436 http://www.physicsforums.com/showthread.php?t=690358&goto=newpost Tue, 07 May 2013 18:17:09 GMT hello I amm trying to understand the difference between flux and specific intensity of radiation. I understand that one is dependent on distance... hello
I amm trying to understand the difference between flux and specific intensity of radiation.
I understand that one is dependent on distance the other is not, but
can you make it more tangible with an example? ]]> Astrophysics alkmini http://www.physicsforums.com/showthread.php?t=690358 http://www.physicsforums.com/showthread.php?t=690141&goto=newpost Mon, 06 May 2013 17:08:06 GMT I hear that black holes evaporate, but does it all get converted into Hawkins radiation? And what role do white holes play in evaporation? I hear that black holes evaporate, but does it all get converted into Hawkins radiation? And what role do white holes play in evaporation? ]]> Astrophysics Geordie Ross http://www.physicsforums.com/showthread.php?t=690141 http://www.physicsforums.com/showthread.php?t=690017&goto=newpost Mon, 06 May 2013 01:34:09 GMT Hello everyone!

Just something I was thinking about today that I haven't been able to shake. I recently read that space is not actually a perfect vacuum, but that it contains low density particles, plasma, electromagnetic fields and so on. Is 'hard vacuum' the correct definition, or is it okay just to use vacuum?

I'd like to know why these low density particles, fields, and plasma don't interact with the light or slow it down in any way (or do they?) While I'm on the subject of particles, do virtual particles exist in space, and do they interact with light?

Thanks! ]]> Astrophysics Thomas1989 http://www.physicsforums.com/showthread.php?t=690017