7 Mysteries About the Universe That Have Baffled Scientists - Newsweek

According to the European Space Agency (ESA), "although thought to be invisible, neither emitting nor absorbing light, dark matter can be detected through its gravitational influence on the movements and appearance of other objects in the Universe, such as stars or galaxies.".

And based on this indirect evidence, "astronomers believe that dark matter is the dominant type of matter in the Universe – yet it remains obscure," says ESA.

If dark matter seems to join galaxies together, dark energy wants to push everything apart.

However, no one is quite sure what dark matter or energy are comprised of.

According to the American Space Agency, "we know how much dark energy there is because we know how it affects the universe's expansion.

"Time, space and matter all began with the Big Bang," the European Space Agency explains.

Using the Hubble Space Telescope, scientists have been effectively able look back in time to shortly before the event, about 13.8 billion years ago, because light from the earlier universe taking so long to reach Earth.

In 2006 when scientists began to look for distant signals in the universe using a instrument fixed to a huge balloon that was sent to space, they detected a mysterious roar

Cosmic rays are high energy atom particles that rain down on the Earth from outer space at the speed of light