Some scientists question whether dark matter is even real, and suggest that the mysteries it was conjured to solve could be explained by a better understanding of gravity.

Antimatter

Like Superman's alter-ego, Bizzaro, the particles making up normal matter also have their opposite versions. An electron has a negative charge, for example, but its anti-matter equivalent, the positron, is positive. Matter and anti-matter annihilate each other when they collide and their mass is converted into pure energy.

Mini black holes

If a radical new “braneworld” theory of gravity is correct, then scattered throughout our solar system are thousands of tiny black holes, each about the size of an atomic nucleus. Unlike their larger brethren, these mini-black holes are primordial leftovers from the Big Bang and affect space-time differently because of their close association with a fifth dimension.

Microwave background

Cosmic microwave background — also known as the CMB — this radiation is a primordial leftover from the Big Bang that birthed the universe. It was first detected during the 1960s as a radio noise that seemed to emanate from everywhere in space. The CMB is regarded as one of the best pieces of evidence for the theoretical Big Bang. Recent precise measurements by the WMAP project place the CMB temperature at -455 degrees Fahrenheit (-270 Celsius).

Dark Matter

Scientists think it makes up the bulk of matter in the universe, but it can neither be seen nor detected directly using current technologies. Candidates range from light-weight neutrinos to invisible black holes. Some scientists question whether dark matter is even real, and suggest that the mysteries it was conjured to solve could be explained by a better understanding of gravity.

Exoplanets

Until about the early 1990s, the only known planets in the universe were the familiar ones in our solar system. Astronomers have since identified more than 190 extra solar planets (as of June 2006). They range from gargantuan gas worlds whose masses are just shy of being stars to small, rocky ones orbiting dim, red dwarfs. Searches for a second Earth, however, have so far turned up empty.

Gravity waves

Gravity waves are distortions in the fabric of space-time predicted by Albert Einstein’s theory of general relativity. The waves travel at the speed of light, but they are so weak that scientists expect to detect only those created during colossal cosmic events, such as black hole mergers like the one shown above.

Galactic Cannibalism

Like life on Earth, galaxies can ‘eat’ each other and evolve over time. The Milky Way's neighbour, Andromeda, is currently dining on one of its satellites. More than a dozen clusters are scattered throughout Andromeda, some cosmic remains. The image above is from a simulation of Andromeda and our galaxy colliding, an event that will take place in about 3 billion years.