INTRODUCTION
In astronomy, dark matter is an invisible and form of matter that
does not interact with light or other
electromagnetic radiation. Dark matter is implied by gravitational effects that cannot be explained by general
relativity unless more matter is present than can be observed. Such effects occur in the context
of formation and evolution of galaxies,
gravitational lensing, the observable universe's current structure, mass
position in galactic collisions, the
motion of galaxies within galaxy clusters, and cosmic microwave background anisotropies.
Dark matter is a form of matter that does not emit, absorb or
reflect light making it invisible (or
"dark") to electromagnetic observations (like telescopes). We cannot
see it directly, but scientists infer
its presence from its gravitational effects on visible matter, light, and the structure of the universe.
HISTORY OF DARK MATTER
The theory of dark matter has a complex history. Wm. Thomson, Lord
Kelvin, discussed the number of stars
around the Sun in the appendices of a book based on a series of lectures given in 1884 in Baltimore. He investigated
their density using the observed velocity
dispersion of the stars near the Sun, assuming that the Sun was 20–100
million years old. He posed what would
happen if there were a thousand million stars within 1 kiloparsec of the Sun (at which distance their parallax
would be 1 milli-arcsecond).
THEORETICAL CLASSIFICATIONS
Dark matter can be divided into cold, warm, and hot categories.
These categories refer to velocity
rather than an actual temperature, and indicate how far corresponding
objects moved due to random motions in
the early universe, before they slowed due to cosmic expansion. This distance is called the free
streaming length. The categories of dark matter
are set with respect to the size of the collection of mass prior to
structure formation that later collapses
to form a dwarf galaxy. This collection of mass is sometimes called a protogalaxy. Dark matter particles are
classified as cold, warm, or hot if their free
streaming length is much smaller (cold), similar to (warm), or much
larger (hot) than the protogalaxy of a
dwarf galaxy. It also makes up 27% total energy content
DARK ENERGY
INTRODUCTION
Dark energy is a mysterious form of energy thought to be
responsible for the accelerating
expansion of the universe. Unlike dark matter, which pulls things
together via gravity, dark energy pushes
space apart.
dark energy is a proposed form of energy that affects the universe
on the largest scales. Its primary
effect is to drive the accelerating expansion of the universe. Dark energy's
density is very low: 7×10−30 g/cm3, much less than the density of ordinary matter or dark matter
within galaxies.
THE NATURE OF DARK ENERGY
The nature of dark energy is more hypothetical than that of dark
matter, and many things about it remain
in the realm of speculation. Dark energy is thought to be very homogeneous and not dense, and is not known to interact
through any of the fundamental forces other
than gravity. Since it is rarefied and un-massive—roughly 10−27 kg/m3—it is unlikely to be
detectable in laboratory experiments. The reason dark energy can have
such a profound effect on the universe,
making up 68% of universal density in spite of being so dilute, is that it is believed to uniformly fill otherwise
empty space.
CONCLUSION
Dark matter and dark energy are two of the most mysterious and
dominant components of our universe, yet
they play very different roles.
• Dark matter acts as an
invisible glue, holding galaxies and galaxy clusters together through its gravitational pull. Although we
can't see it directly, we observe its effects
on the motion of stars and galaxies.
• Dark energy, in contrast,
works as a repulsive force, driving the accelerating expansion of the universe. While dark matter
pulls things together, dark energy
pushes them apart.
Together, they make up about 95% of the universe's total content —
with dark matter accounting for 27% and
dark energy 68%. This leaves only 5% for all visible matter (like stars, planets, and humans).
Despite decades of study, the true nature of both dark matter and
dark energy remains unknown. Solving
these cosmic puzzles is one of the greatest challenges in modern physics and astronomy, with the potential to reshape
our understanding of the universe, gravity, and
the fundamental laws of nature.
Both dark
matter and dark energy are still being intensely researched, and solving
these mysteries could lead to
breakthroughs in our understanding of physics and the universe.
WRITTEN BY:
SRIWANT ARYAN VASI
BATCH NO:27