The stars at the edges of a galaxy are rotating around the galaxy’s center at the same speed as the stars in the middle of the galaxy. How does this provide evidence of dark matter? Dark matter absorbs light from outside the galaxy, allowing the light of the stars in the galaxy to show the orbital speeds of the stars.

Dark matter emits the light that astronomers need to see the orbital speeds of the stars.

Dark matter subtracts gravity, which allows the stars to rotate at the same speed.

Dark matter provides the gravity that allows the stars to rotate at the same speed.

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Explanation:

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relative dating involves things like higher layers are most recent than rocks lower in the sequence. this can be extended to the known sequence of fossils. rocks containing rabbit fossils are later than those containing dinosaur fossils.  

absolute dating methods mainly use radioactive elements that have known rates of decay and produce recognizable products. for example potassium 40 decays to produce argon. once a rock has solidified the argon is trapped. by measuring the argon and potassium0 you can get an accurate number for the age.  

some other methods are good for archaeological ages. dendrochronology involves recognizing the sequence of tree rings. the orientation of magnetized particles in baked clay can be used to date a fire.

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