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)
