What is Dark Matter ?

Despite decades of search, nobody has ever directly detected a dark matter particle and the only evidence we have is still indirectly inferred from gravitational pull. Physicists have been looking for the rare interactions of proposed dark matter candidates in many Earth-based experiments starting already in the 1980s. They are also on the lookout for astrophysical evidence of dark matter, such as signals from the mutual annihilation of dark matter particles. There have been some intriguing findings, such as the PAMELA positron excess, the DAMA annual modulation, or the Fermi gamma-ray excess, but physicists haven’t been able to link any of these convincingly to dark matter.

After everything the Universe has told us about itself, we’re convinced that some type of dark matter must exist: matter that’s different from any of the known particles in the Standard Model. This dark matter outmasses all other particles and radiation in the Universe by a factor of five or so, but has yet to be directly detected. We know it exists, but we don’t know exactly what it’s made of. Until we do, this will remain a mystery in need of a more complete solution.

One of the Dark Matter facts is that it is not in the form of stars and planets that we see. Observations show that there is far too little visible matter in the universe to make up the 27% required by the observations.

Second, it is not in the form of dark clouds of normal matter, matter made up of particles called baryons.

Third, Dark Matter is not antimatter, because scientists do not see the unique gamma rays that are produced when antimatter annihilates with matter.

Most experts consider Dark Matter to be ubiquitous in the universe and has strongly affected its structure and evolution.

The first person who suggested the existence of Dark matter was Dutch astronomer Jacobus Kapteyn in 1922.

In the early 1990s, one thing was fairly certain about the expansion of the universe.

The name Dark Matter refers to the fact that it does not appear to interact with observable electromagnetic radiation, such as light, making it extremely difficult to detect using usual astronomical equipment.

It might have enough energy density to stop its expansion and recollapse, it might have so little energy density that it would never stop expanding, but gravity was certain to slow the expansion as time went on. Granted, the slowing had not been observed, but, theoretically, the universe had to slow

One of the Dark Matter facts is that 68% of the universe is dark energy, so Dark matter makes up about 27%. The rest – everything on Earth, everything ever observed with all of astronomer’s instruments, all normal matter – adds up to less than 5% of the universe.

The universe is full of matter and the attractive force of gravity pulls all matter together.

Dark matter is classified as cold, warm, or hot according to its velocity. Current models favor a cold Dark Matter scenario, in which structures emerge by gradual accumulation of particles.

There are still many mysteries about Dark Matter that need to be unfolded, but astronomers and physicists have gathered evidence about its presence.

the expansion of the universe has not been slowing due to gravity, as everyone thought, it has been accelerating. No one expected this, no one knew how to explain it. But something was causing it.

Astronomers have also considered that Dark Matter may be supermassive black holes (single points of infinite mass and gravity formed from the collapse of burned-out massive stars) at the centers of galaxies.

Eventually theorists came up with three sorts of explanations. Maybe it was a result of a long-discarded version of Einstein's theory of gravity, one that contained what was called a "cosmological constant." Maybe there was some strange kind of energy-fluid that filled space

there is something wrong with Einstein's theory of gravity and a new theory could include some kind of field that creates this cosmic acceleration. Theorists still don't know what the correct explanation is, but they have given the solution a name. It is called dark energy.

More is unknown than is known. We know how much dark energy there is because we know how it affects the universe's expansion. Other than that, it is a complete mystery.

Planets, stars, asteroids, galaxies – the things that we can actually see – constitute less than 5% of the total universe. So what makes up the rest? Therein lies the mystery.

it is an important mystery. It turns out that roughly 68% of the universe is dark energy. Dark matter makes up about 27%. The rest - everything on Earth, everything ever observed with all of our instruments, all normal matter - adds up to less than 5% of the universe.

Dark matter is the name we give to all the mass in the universe that remains invisible, and there’s a whole lot of it. Research suggests that about 70% of the universe is composed of dark energy, whilst the remaining 25% is composed of a mysterious substance known as dark matter. We can’t see it, we don’t understand it, but we know it’s out there.

Come to think of it, maybe it shouldn't be called "normal" matter at all, since it is such a small fraction of the universe.

Dark matter is really hard to study, because we have no way of seeing it. This weird substance doesn’t interact with light, so it’s totally invisible.

So how do we know it exists? Well, because it affects the universe in strange ways; and that’s something we can see.

explanation for dark energy is that it is a property of space. Albert Einstein was the first person to realize that empty space is not nothing. Space has amazing properties, many of which are just beginning to be understood.