To better understand the Universe, it is often necessary to estimate the mass of an astrophysical object. Those objects span a vast range of sizes, from the Sun, to the solar system, to the Milky Way, and even up to the entire Universe.
Researchers use a number of techniques to measure the mass of extremely large objects. One way to estimate an object’s mass is by observing its light output. If the object does not emit its own light, researchers can examine the way in which the light of background sources bends around it. Another technique is to examine the dynamic motion of objects around it.
It was long believed that the estimated masses coming from these techniques would agree with one another. However, over the past 80 years, it has become apparent that for objects the size of our galaxy and larger, the amount of mass contained exceeds the mass of its luminous constituents. This additional mass, which cannot be accounted for by the luminous matter we know about, has been coined “dark matter.”
From our understanding of how matter was created in the early universe, we now believe that dark matter is composed of fundamentally new particles