Quote:
Originally Posted by Pluto
I thought the mass of 95% is found as compact matter through out the galaxy.
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I believe you're confusing a few different things. It's possible to roughly determine the mass of the Milky Way by measuring the velocity of stars and dwarf galaxies at the perimeter of our galaxy. Doing this shows a mass of at least 600 billion solar masses, and more-likely one trillion solar masses.
(1)(2).
Only about 200 billion solar masses of that total mass is definitively accounted for as "visible" matter. That is a very rough estimate because there is a lot of uncertainty regarding the number of low-mass stars. But, it's generally agreed that there is some form of hidden or invisible mass which is (at this point) only detectable through its gravitational effects.
That hidden matter goes by the name
dark matter. The term "dark" refers to our inability to see it which mostly reflects our ignorance regarding what exactly it is. The search is on and some dark matter candidates have been convincingly ruled out.
Where you say "95% is found as compact matter", I believe you are recalling the dark matter candidate MACHOs (massive astrophysical compact halo object). It is NOT the same thing as degenerate matter (which you often call compact matter). MACHOs are planet-sized or star-sized chunks of normal matter which do not emit much (if any) light. These might include black holes, neutron stars, white dwarfs, or red dwarfs.
Studies have shown that MACHOs are not likely to account for large amounts of dark matter. Astrophysicist seem more-convinced that dark matter consists of fundamental non-baryonic (non-relativistic) particles. You can think of these as invisible subatomic particles floating around everywhere, but they are invisible and don't interact with normal baryonic matter (the stuff you and I are made of). This
cold dark matter is NOT the same thing as degenerate matter (or compact matter).
The
current big bang theory proposes that there is five and a half times as much cold dark matter as there is normal visible matter. This could be consistent with the missing mass in galaxies. I believe the number you gave of 95% was meant to be 96% which is the proposed percentage of the universe's energy density which is not normal visible matter. However, only 22% is cold dark matter. The other 74% is dark energy which is a whole different subject (again—*not* degenerate or compact matter).
So, I think your quote above probably meant to say that 96% of our universe (not galaxy) is dark matter and dark energy—which I would agree, that is the current model which cosmologists use to describe our universe. But, as Coldcreation said, those numbers represent something we believe is there, but we know very little about.
Quote:
Originally Posted by Pluto
Eg Our Sun has 99% mass compared to the remaining solar system.
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I believe strongly that you're confusing the sun (which is normal baryonic matter like you and I are made of) with
degenerate matter (such as you would find in a neutron star) and dark matter / dark energy (neither of which make up stars).
Quote:
Originally Posted by Pluto
Yes I know that the sun is not all compact. But! The core is.
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Yes, when the sun runs out of stuff to fuse then thermal pressure will give way to degenerate pressure and it will collapse into a white dwarf composed of "degenerate matter" and considered a "compact object". You can read about the sun's core in its current condition in this article:
Solar core - Wikipedia, the free encyclopedia
It is not currently degenerate matter but that is very far off the topic of cold dark matter.
~modest
