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The Starry Sky Just Got Starrier
An anonymous reader writes "Astronomers have surveyed eight elliptical galaxies, and found that we've vastly underestimated the number of dim red dwarf stars in these giant galaxies. When they used the new number of red dwarfs in their calculations, they tripled the total number of known stars in the universe."
No, it's out there. Things like the bullet cluster pretty much prove that there must be large amounts of some sort of weakly interacting matter. Basically, two galaxies collide. Normal matter in one galaxy interacts with normal mater in the other, slowing it down. But something massive wasn't slowed down and kept right on trucking along the same path at the same speed as before. We only know it is there because of the gravitational lensing it produces. So, we have direct evidence of matter that we can not see, and that does not interact with other stuff except through gravity. Call it whatever you like, it's out there. And that is just one piece of evidence. Galaxy rotation and the CMB are others.
- None can love freedom heartily, but good men; the rest love not freedom, but license. -- John Milton
Dark matter and dark energy are two totally different things. They're placeholders for vastly different phenomena. Dark matter explains why galaxies rotate at the speeds they do, even though their visible mass is much, MUCH, lower than the spinning speed shows it should be. Dark energy is the pressure that's causing the universe to accelerate outward. The universe isn't just expanding, the rate of the expansion is increasing, not decreasing as you would expect. Some force is being exerted on the fabric of the universe that's causing it to expand at a faster rate every second.
So, to recap:
Dark matter = mass that's causing galaxies to spin faster than they should be
Dark energy = force that's pushing the universe apart
Learn something new.