How do we image dark matter?
(a) We see light from galaxies behind the bullet cluster that is bent (gravitationally lensed)
due to the matter (regular and dark) in the bullet cluster.
(b) We see light from the gas in the two bullet cluster galaxies and we observe that the gas
is moved due to the pull of dark matter.
(c) We see light from dark matter annihilation to photons (or to other particles which
subsequently produce light).
(d) We see light from Type-1a supernovas which resulted from two stars being pulled close
to each other due to dark matter.
Final exam-find by yourself
The correct answer is (b) We see light from the gas in the two bullet cluster galaxies and we observe that the gas is moved due to the pull of dark matter.
When we observe the bullet cluster, we can see that the gas in the two galaxies is being displaced from the cluster center. This displacement is caused by the gravitational pull of the dark matter present in the cluster. By studying the motion of the gas, scientists can indirectly infer the presence and distribution of dark matter in the cluster.
Option (a) is related to gravitational lensing, which does provide evidence for the presence of dark matter. However, it does not directly image dark matter itself.
Option (c) refers to the potential detection of light from dark matter annihilation, but this method has not been conclusively proven or observed so far.
Option (d) is not a valid method for imaging dark matter as Type-1a supernovas are not caused by dark matter interactions.
The correct answer is (a) We see light from galaxies behind the bullet cluster that is bent (gravitationally lensed) due to the matter (regular and dark) in the bullet cluster.
To image dark matter, we rely on its gravitational effects on visible matter. Dark matter does not interact directly with light, which makes it difficult to observe directly. However, its presence can be inferred from its gravitational pull on visible matter.
In the case of the bullet cluster, astronomers observed the light from galaxies behind the cluster being gravitationally lensed or bent. This lensing effect is caused by the mass of both regular and dark matter in the cluster. By carefully studying the distribution of this lensing effect, scientists were able to map out the invisible dark matter present in the cluster.
This method provides indirect evidence of dark matter's existence and helps us understand its distribution in the universe.