A purple haze shows dark matter flanking the "Bullet Cluster."

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WASHINGTON, 22 August 2006: A huge collision between two clusters of galaxies has provided the first direct evidence of the existence of the universe's mysterious dark matter, researchers said on Monday.

"This is the most energetic cosmic event, besides the Big Bang, which we know about," said Maxim Markevitch of the Harvard-Smithsonian Centre for Astrophysics in Cambridge, Massachusetts.

The impact forced apart dark and normal matter, offering the strongest evidence yet that most of the matter in the universe is dark, researchers said.

Dark matter has long been a puzzling enigma, and has threatened to unhinge our best models of how the universe works.

According to observations, only around four per cent of the mass in the universe is visible in the form of stars and galaxies. The question is: where is the rest?

Scientists can determine that the other 96 per cent must exist due to the gravitational forces it exerts: without dark matter, galaxies would fly apart.

The problem is, dark matter is, well, dark. While there is ample indirect evidence of the influence of dark matter on large structures, such as galaxies, dark matter has never been directly observed.

Until now.

"We've come closer than ever to seeing this invisible matter," University of Arizona researcher Doug Clowe, a leader of the study, said in a statement.

"This provides the first direct proof that dark matter must exist and must make up the majority of the matter in the universe," Clowe said.

The new evidence of dark matter's existence was discovered with NASA's Chandra X-ray Observatory, the Hubble Space Telescope, the European Southern Observatory's Very Large Telescope and the Magellan optical telescopes, researchers said.

Sadly, even in light of these new observations, scientists are still left in the dark about what dark matter actually is.

Some theories propose that dark matter consists of innumerable sub-atomic particles that sport mass, but don't interact with other matter – the so-called WIMPs (Weakly Interactive Massive Particles).

Alternative theories suggest that dark matter is actually macroscopic, but in the form of large objects that aren't easily visible at astronomical distances, such as proto-stars, planets or clouds of non-luminous gas.

Other theories suggest that dark matter is an anomaly caused by a faulty understanding of gravity itself. However, these theories have yet to present a consistent alternative picture of the fundamental forces of the universe.

This latest finding reinforces the existence of dark matter, but the quest to determine its true nature continues.