What is the evidence for the existence of Dark Matter? Explain
a
There is not enough mass in galaxies to produce the gravitational force that exists, so Dark Matter must make up the difference
b
The galaxies are too bright for the total amount of energy they produce, meaning Dark Matter must exist to amplify the reflections of the light
c
The momentum of galaxies is too high to match their current moving velocities, meaning that there must be Dark Matter to increase the momentum of those galaxies
d
The largest galaxy was made of combined other galaxies, but the sum of its masses is not equal to the masses of the other galaxies, meaning that Dark Matter must make up that difference
The correct answer is a.
The evidence for the existence of Dark Matter primarily comes from the observation of the gravitational effects it has on visible matter. Dark Matter does not emit, absorb, or reflect light, which is why it is called "dark." However, its presence can be inferred by its gravitational influence on visible matter.
One piece of evidence is the observation of galaxy rotation curves. Based on the visible matter within galaxies, astronomers would expect the rotational velocities of stars and gas to decrease as they move farther from the center of the galaxy, following Kepler's laws. However, observations have shown that the rotation curves remain flat or even increase with distance from the galactic center. This indicates the presence of additional mass that is not accounted for by visible matter. Dark Matter is believed to provide this additional mass and thus explain the observed rotation curves.
Another piece of evidence comes from gravitational lensing. When light from distant galaxies passes through a massive object, such as a galaxy cluster, its path is bent due to the gravitational pull of the mass. This bending of light can be observed as a distortion or magnification of the background galaxy's image. By studying the gravitational lensing effects, scientists can determine the distribution of mass in the lensing object. Observations of gravitational lensing have shown that there is more mass than can be accounted for by the visible matter in galaxy clusters, indicating the presence of Dark Matter.
Furthermore, observations of the cosmic microwave background radiation, which is the remnant radiation from the early universe, also provide evidence for Dark Matter. The patterns observed in the cosmic microwave background can be explained by the presence of Dark Matter affecting the growth of cosmic structures over time.
Overall, the evidence for Dark Matter is based on its gravitational effects on visible matter and its influence on large-scale structures in the universe. While there is still much to learn about Dark Matter, its existence is strongly supported by the observed phenomena in astrophysics.
I agree that answer "a" is most relevant:
a
There is not enough mass in galaxies to produce the gravitational force that exists, so Dark Matter must make up the difference