Given all the information about the workings
of our planets and the solar system, and even how the universe and
life as we know it formed, one would assume that scientists seemed
to understand exactly how the universe worked. Everything – that
is us, the earth, the stars, the supernovas, are all made up of
atoms, which were all created at time zero – the Big
Bang. In between these atoms was
literally nothing, a void, a space. However recent discoveries have
led to an unraveling (or further complication) of the mystery –
there is a lot more to the universe than meets the eye. According
to the best estimates of scientists these days we only know what
about 4% of the universe is made up of...but if this 4% is made
up of only atoms what is the rest made of? Well 'the rest' is made
of mysterious entities about which very little is understood – dark
matter and dark energy.
In 1974 the astronomer, Vera Rubin, was working
on a project involving the investigation of stars on the outer edges
of galaxies – and what she actually discovered came as a great surprise
to the scientific community. Before we discuss what she found let
us remember Newton's discovery, that is gravity is universal. An
apple falling on his head on earth obeys the same mathematical laws
as an apple falling on the other side of the universe. In the same
way that the sun controls the orbiting planets by exerting gravity
on them, a spiral galaxy must be controlled by the gravity giving
black hole at it centre. It has long been known that Pluto, which
is at the edge of our solar system, travels slower then Mercury,
which is closest to the sun. Essentially it was observations like
these which allowed Newton to finalise his laws in the 17th century.
When Rubin carried out her work on galaxies she expected to find
that as you reach the edge of the galaxy the stars would be moving
much slower than those close to the centre – but in actual fact
it didn't work out like that at all.
She found that almost all of the stars in
spiral galaxies are racing around the centre at approximately the
same speed. This finding was to say the least a contradiction of
the laws proposed by Newton – laws that had come to be universally
accepted by many. Questioning Newton seemed unthinkable so scientists
went down a different route altogether – rather than variable gravity
they argued that there had to be something else in galaxies, something
that was providing extra gravity. With extra gravity, the stars
would be pulled harder and would travel faster, as Rubin's observations
suggested. So the name they gave to this extra something – Dark
Matter.
Two professors at Princeton University –
Peebles and Ostriker – looked further into the issue of dark matter,
suggesting that there was at least ten times more of it than there
was ordinary matter. Yet despite this growing acceptance as to the
existence of Dark Matter, its real identity remained completely
unknown. Nothing that particle physics came up with appeared to
fit the bill, and even the discovery of the neutrino could not put
together the missing pieces of the jigsaw. What was needed was something
with mass but also something which does not interact with ordinary
matter. Professor Sumner proposed a possible answer – a new hypothetical
particle called the neutralino. It is thought to have the right
mass and exist in suitably vast quantities – but has never been
detected.
If dark matter in our galaxy is everywhere
in our galaxy, then it must be present here on our earth, in fact
thousands of tonnes of the stuff must pass through the earth everyday.
As it doesn't interact with ordinary matter it can pass straight
through us, the earth, everything we are familiar with.
Of course not everyone was as keen to pursue
the ideas underpinning dark matter. In 1974 an Israeli astrophysicist,
Professor Milgrom, tried something even more audacious by attempting
to re–write Newton's laws of gravity. Of course knowing such a move
would not be wholly welcomed by the scientific community he worked
in private until he was ready to reveal his ideas in 1981. He called
his ideas the Modified Newtonian Dynamics (MOND), and used it to
show how gravity could be a little stronger than previously thought,
across the huge distances that galaxies cover.
In 1997 another can of worms was opened when
Professor Perlmutter discovered that not only were stars and galaxies
moving away from each other, but they were doing so at greater and
greater speeds. This could mean that one day in the future we could
look up to the sky and see no stars as they are all too far away
from us. However it also meant that something was pushing the stars
apart. This anti–gravity force was completely new to science, but
again what it actually was remained a mystery. It was given a name
though–Dark Energy.
When we bring these things together it appears
that the universe comprises of 4% ordinary matter, 21% dark matter
and 75% dark energy. Whilst there are skeptics who ask where the
evidence exists for such views, supporters (including myself) believe
that dark matter and dark energy have been vital to the development
of the universe. The results of the WMAP satellite survey appear
to confirm the quantity of each of the dark components.
So where are we at now? Well astronomers
cannot detect dark matter directly because it emits no light or
radiation, yet its presence can be inferred from the way galaxies
rotate: their stars move so fast they would fly apart if they were
not being held together by the gravitational attraction or some
unseen material. However the institute of astronomy at Cambridge
university have provided further information with a study of 12
dwarf galaxies that skirt the edge of our own milky way. Using some
of the most technical and largest telescopes available the team
made detailed 3D maps of the galaxies, using the movement of their
stars to trace the impression of the dark matter among them and
weigh it very precisely. With the aid of 7,000 separate measurements
the researchers have been able to establish that the galaxies contain
about 400 times the amount of dark matter as they do normal matter.
It also comes in a 'magic volume' which happens to correspond to
an amount which is 30 million times the mass of the sun. According
to Professor Nichol you cannot 'ever pack it smaller than about
300 parsecs–1000 light years, this stuff will not let you. That
tells you a speed at which dark matter particles are moving (Approx.
9km/s).' These are the first properties other than existence that
the scientific community have been able to determine.
The issue of speed is a huge surprise – with
current theory predicting dark matter particles being extremely
cold and moving at a few millimetres per second. However these observations
prove the particles must actually be quite warm at around 10,000
degrees. The most likely candidate for dark matter is the so called
weakly interacting massive particle
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