Navarre Pratt
English Section E
Science Section C
Space Research
Dark Matter
Everything in the universe is held together with a special type of glue. Gravity is space’s
glue, and this glue is making sure that everything does not fly apart from its neighbors. Recently,
scientists have found an invisible glue acting upon all objects in space. Scientists call this
invisible glue, “dark matter”. Regular matter follows many guidelines, and by studying these
guidelines, scientists can answer many questions about the objects they are studying just by
looking at them. All regular matter gives off light, and by studying light, scientists can figure out
mass. Then by studying mass, scientists can find gravity. So when scientists find that there is
more gravity than the given light suggests, they know that something is missing. Scientists can
search for dark matter by observing its effects on the surrounding objects.
The discovery of dark matter was actually an accident. Fritz Zwicky, a Swiss astronomer,
was the first to theorize that there was an unseen matter in the Universe. In the 1930s, Zwicky
was watching the movement of galaxies in the Coma galaxy cluster. He noticed that the galaxies
were moving too fast to be still held together. There was not enough gravity coming from the
visible mass of the galaxies, so he knew there there must have been extra gravity coming from
somewhere unseen. He called this theory the “Missing Particle” theory. The theory states that
there is an invisible particle with a massive amount of gravity that holds galaxy clusters together.
He was right. In the 1970s, “U.S. astronomer Vera Rubin and her colleagues” (Hooper)
confirmed Zwicky’s findings when they noticed the same missing particle, in other galaxy
clusters. They also found that single galaxies and not just clusters are spinning faster than their
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visible light suggests. Galaxies themselves would be unraveling if just their gravity was holding
them together (Hooper).
Somewhere out there in space lies an invisible particle thought to comprise “22% of the
Universe’s energy contents,” (Clark) and we cannot even see it. This type of matter has a
massive gravitational field that is big enough to hold entire galaxy clusters together. It emits no
light (Woo), and Fritz Zwicky only discovered it by accidently finding its effects (Hooper). Since
we cannot observe dark matter directly, we have to look for how dark matter affects its
surroundings. To do this, scientists search for a massive gravitational field coming from what
looks like nowhere. A gravitational field coming from dark matter should be strong enough to
hold whole galaxy clusters together.
Gravitational lensing is now being used to find dark matter clumps. Einstein first
described gravitational lensing in his theory of relativity.
He predicted that the “gravitational field of any massive
object would act as a lens and bend light that passes by the
object” (Wilkuns). Any massive object that eclipses the
light source and the destination can act as a gravitational
lens (Silberg).The first gravitational lens observed by
Einstien is now called the Huchra’s Lens, more commonly
know as Einstein’s Cross. In Huchra’s Lens, light was bent
from a distant quasar. The field of gravity from the
This graphic depicts Huchra’s Lens, otherwise
known as Einstien’s Cross, as seen from earth.
We see five different light sources, but there is
really only one, as Einstein predicted. This
warp in light is calle gravitational lensing.
eclipsing galaxy formed what seemed like five quasars from an observatory on earth, instead of
one (Wilkuns).
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Scientists know that gravitational lensing is caused by gravity bending light, so if light is
being bent somewhere in space, there must be a super massive object with a super massive
gravitational field. The Optical Gravitational Lensing Experiment, or OGLE, uses this form of
gravitational lensing called “micro lensing” to look for dark matter. This project first began in
1992 as a “cooperative effort coordinated by the Warsaw University in Poland” (Irwin). It looks
for occurences of micro lensing, and by studying how big the lens is and how long it lasts, they
can determine how far away the light and lens sources are. Once they have found this, they
search for the lens source. If they do not find anything, they know they have probably found dark
matter. They can assume this because we know that dark matter does not interact with light. If
there is nothing seen where the lens source is supposed to be, but there there is gravity coming
from that spot, the only possible explanation is dark matter. OGLE has not found any invisible
lens sources yet, but it has found many events of micro lensing. Scientists working with OGLE
are able to measure objects based on their mass instead of their light (Irwin).
A more direct approach to finding dark matter is by searching for medium-energy gamma
ray radiation. Gamma rays are the highest-energy
form of light. This radiation is caused by many
things, but in dark matter it occurs when WIMPs,
or Weakly Interacting Massive Particles, collide.
WIMPs are the leading theory of the make up of
dark mattter. They are called weakly interacting
because they very rarely interact with regular
matter. WIMPs do not emit or absorb light, but
according to the theory of supersymmetry,
This grahpic shows what happens when neutralinos, more
commonly known as WIMPS, annihilate each other. When
they touch, they blow up creating many praticles, including a
special type of radiation, medium-energy gamma rays. GLAST
searched thorugh the cosmos looking for this special type of
radiaiton
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WIMPs act as their own antimatter. When they encounter each other, they annihilate each other.
This creates medium-energy gamma ray radiation (Woo) that scientists can find with a satellite
called the Fermi Gamma-ray Space Telescope, formaly known as GLAST (Gamma-ray Large
Area Space Telescope). Started by NASA’s astrophysics team and launched in 2008, GLAST
has discovered many things about the gamma-ray universe. To find dark matter, GLAST zeros in
on galaxies called dwarf spheroidals. These tiny galaxies are thought to have impressive amounts
of dark matter, and few gamma-ray emiting objects to interfere with GLAST’s findings. By
studying ten of these dwarf spheroidals during the first two years of GLAST’s launch, scientists
have now eliminated some possible particles from the list of what WIMPS exactly are (Reddy).
With projects like this, NASA is coming closer and closer to figuring out what dark matter is
really made of.
When scientitsts learn more about dark matter by observing its effects, many other
discoveries will be made that affect the numerous theories about how our universe works. For
example, scientists’ leading theory about the reason why the universe is accelerating is dark
energy. Dark energy is “the energy in empty space causing the expanding universe to accelerate”
(Ryba). Dark energy was created in the Big Bang, including all other particles, so if scientists
can recreate the Big Bang with information found from studying dark matter, they will be able to
zero in on the properties of dark energy and its effects on the expanding universe. Scientists
cannot prove these theories yet, but with new projects like OGLE and GLAST, scientists hope to
soon change the way humans look at the universe.
Scientists can search for dark matter by observing its effects on the surrounding objects.
Scientists throughout the years have found a missing particle by observing a massive amount of
gravity seemly coming from nowhere. Later called dark matter, this particle has been theorized
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to be twenty two percent or more of all matter and has a major gravitational effect on galaxies
and galaxy clusters (Clark). Scientists are trying to find dark matter in many ways, including
gravitational micro lensing (Irwin) and gamma-ray radiation (Woo), and one day scientists will
be able to prove that dark matter exists. When this happens, it will change the world. Scientists
will understand a lot more about the creation of our universe and the world of gamma-ray
energy. We might also one day be able to harness the power of dark matter and use its massive
gravitational power to our advantages.
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