Question

We’ve learned in class that most of the gravitating mass in the Milky Way is in some form of “dark matter”. In a few paragraphs below, briefly describe how we measure the presence and properties of this dark matter in our galaxy, and discuss at least one possible 'solution' to the mystery of what dark matter is.

Answer 1

Inside the galaxies most of the matter is invisible which is not measured directly till now-the so called dark matter that constitutes the most mass of the universe. Dark matter cant be detected/measured directly but its effects are being interferred gravitationally and the technique used is known as gravitational lensing.

As we are aware about the theory of relativity that the gravitation changes its path of massive objects as suggested by Einstin the pull of gravity is actually caused by bending of the space. In gravitational lensing big mass objects(galaxies) discomfort the image of distant light source similar to the manner of that of magnifying glass.The galaxies lies between us and light sources. When the lensing occur there is formation of multiple number of images around the lensing galaxies. This technique is mass sensitive hence tells us about the matter in galaxy including dark matter and gives total mass of galaxies. After subtracting the mass of starr and gas it is possible to label out the properties of dark matter in galaxies.

PROPERTIES:

The dark matter is made of particles which don't absorb, emit or reflect the light hence the possibility of measuring them with usual electromegnitic radiation is null. Scientists believe that dark matter is responsible for the motion of stars inside the galaxies.

There have been many concepts relating to dark matter and theories are being produced by the scientists about "what exactly the dark matter is?" Some theories believes that dark matter may be the normal objects such as the cold gases, massive compact halo objects, dark galaxies, black holes.Others believe that dark matter may be made of strange particles like axions, weakly interacting massive particles which were created in early universe.