Shining Light of Dark Matter and a peek into Gravitational Lensing

Bosco Noronha

What is dark matter?

Matter causes a curvature in space-time according to general relativity. Light from a large source, such as a quasar or pulsar, even other galaxies or point masses, propagating through space-time can be curved, magnified or distorted by gravity. The General Theory of Relativity predicted that massive objects such as stars could bend light rays passing nearby. It was later verified by the observation of light from distant stars, which bent around the Sun, in 1919. That year, an English physicist, Sir Oliver Lodge, suggested that this phenomenon could produce a gravitational lens.

 

(Source: http://www.nature.com/nature/journal/v417/n6892/fig_tab/417905a_F1.html)

The multiple blue lights in the corner image is a result of gravitational lensing of a quasar.

How bending/lensing is determined:

There are 4 factors which determine the formation of the image: Source, lens, distance from lens and magnitude of light projection.

Maximum bending and distortion occurs when the source light is closer to the large mass, while minimum bending occurs as the source of light is further away from the large mass in front of it.

Lensing can be separated into three classes: Strong lensing, weak lensing and micro lensing.

The first image proving this was found in 1979, of a quasar.

Accepting Dark Matter:

Here’s what grips the minds of many astronomers. In the late 1930s two astronomers, Fritz Zwiky and Sinclair Smith made a peculiar observation when studying and measuring the velocities of galaxies in the Virgo clusters. They observed the galaxies travelling at speeds orbiting around each other through Doppler shifting.

The mass of the cluster from the derived formula of their velocities; m=(rV²)/G

When they added the mass of all the galaxies together and compared it to the derived mass formula from their velocities, the numbers were nowhere close to what they were supposed to equal to each other.

How could this be? According to Newton the greater the mass of a cluster, the greater its gravitational pull. The estimated mass is measured by combining the mass of all the visible gas and light in that cluster. The numbers didn’t make sense to them. There had to be more mass present, but they didn’t know where or how it could be present.

This led to the theory that there was a presence of a “matter-like” substance which has the effect of gravity, but doesn’t produce or absorb light. Today there’s major speculation among many mathematicians and physicists that the dark matter particle is one of super symmetry. If this is true this could open a new branch of physics in which the study of matter can be conducted. 

  

(Source: http://www.astronomy.ohio-state.edu/~pogge/TeachRes/Ast162/Clusters/index.html)

Gravitational lensing by dark matter can be observed through the famous Abell 2218 cluster by the HST.

Gravitational lensing is a way that dark matter can be studied more intently. Dark matter’s interaction with light through gravity keeps me thinking. What possibilities can humans create if we had a greater understanding of this strange, natural, product of nature?

Will we ever be capable of harnessing this matter and manipulating it?

Bibliography:

Discovery of the First "Einstein Ring" Gravitational Lens. (n.d.). The First Einstein Ring. Retrieved

November 16, 2013, from http://www.nrao.edu/pr/2000/vla20/background/ering/

  Gravitational Lensing. (n.d.). Gravitational Lensing. Retrieved November 16, 2013, from

http://imagine.gsfc.nasa.gov/docs/features/news/grav_lens.html

  Gravitational lensing. (n.d.). Gravitational lensing. Retrieved November 16, 2013, from

http://astro.berkeley.edu/~jcohn/lens.html

 Moffat, J. W. (2008). Reinventing gravity: a physicist goes beyond Einstein.

New York: Smithsonian Books/Collins.

Images:

(http://www.nature.com/nature/journal/v417/n6892/fig_tab/417905a_F1.html)

(http://www.astronomy.ohio-state.edu/~pogge/TeachRes/Ast162/Clusters/index.html)