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Physics, Astronomy & Cosmology / Can Dark Matter Make Dark Stars?

« on: 02/04/2009 19:18:17 »

With regard dark matter, I had not come across that Cambridge research. That makes dark matter even stranger - interacts with gravity but stays apart. hmmmmm...

http://arxiv.org/abs/astro-ph/0608528

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Physics, Astronomy & Cosmology / Can dark matter be a simple thing?

« on: 02/04/2009 19:14:49 »

E = mc² meaning longer wavelength light (ie lower energy) must have less gravity than higher energy light.

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Physics, Astronomy & Cosmology / Re: The truth is out there, in pictures.

« on: 31/03/2009 01:57:41 »

This has to be my all time favourite photo from Hubble. The so-called Pillars Of Creation where stars are being formed.

This is the picture that had such a huge effect on me I became an astronomer! I think I was about 10-12 years old at the time and just imagining the fact that each of the little bits poking out were whole solar systems forming blew my mind!

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Physics, Astronomy & Cosmology / Can Dark Matter Make Dark Stars?

« on: 31/03/2009 01:46:07 »

So - two questions here which i will tackle one at a time:

1 - the sun will not get to the point of burning up to iron, it takes a star at least a few time heavier than ours - the red giant phase is just part of the running-out-of-hydrogen effect and we will burn helium and little more to get a C-O white dwarf. However - for all stars, even the really big ones that explode (supernova) and fuse all elements bigger than iron during that explosion, the Hydrogen is never completely depleted. Enough is fused that the density decreases below what can be pushed together to fuse. This still leaves most of the star as Hydrogen - especially in the outer layers. In most supernovae you can still see the lines from hydrogen showing a significant mass left in hydrogen (the exception being stars that have 'blown-off' most of their outer layers before exploding).

2 - dark matter -> dark stars. There seems to be an interesting property to dark matter (if it exists) in that it doesn't clump together much. Sure it concentrates to form the large scale structure we see as galaxy clusters etc. but never more than that. There was some work done by some Cambridge astronomers looking at dark matter distribution in ver small galaxies suggesting the density flattened toward the centre - as if the dark matter particles (or what ever it is made of) do not like to get too close together.

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Physics, Astronomy & Cosmology / Re: Can dark matter be a simple thing?

« on: 31/03/2009 01:34:54 »

My main concern for you theory is that extreemly long wavelength radiation has very little energy (since energy is proportional to frequency) and as "dark matter" seems to have many times the mass of "light matter" within our galaxy that would require a huge huge huge source of these low frequency photons. Also if so much of such long wavelength light existed then there would be a noticeable effect of the photons up-scattering off electrons in the galaxy and halo (known as the inverse Compton effect).

Also if it were electrons or any other type of matter we know about it we would be able to detect the absorption of distant light by them.

I think we just don't understand gravity yet but am hoping the dark matter people will finally find something to prove their theory right....

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Physics, Astronomy & Cosmology / Neptune's distance

« on: 31/03/2009 01:26:49 »

Neptune was discovered nearly 160 years ago meaning it has completed almost a full orbit since its discovery. There have been many, many observations of it since that date so we have a very accurate orbit, and more importantly orbital period. Given its orbital period it is easy to calculate its distance relative to the Earth-Sun distance (= 1 AU) by using Kepler's third law. Since both the Earth and Neptune are orbiting the same object, the Sun, their relative periods (P_E for the Earth and P_N for Neptune) give their relative distances (a_E for the Earth, a_N for Neptune) by:
               (P_N / P_E)² = (a_N / a_E)³.
Thus:
               a_N = a_E (P_N / P_E)^2/3.
I hope that helps!