A gigantic collision between two clusters of galaxies has yielded possible new evidence in the search for dark matter.

“Dark matter is said to be material that can only be detected gravitationally and does not emit radiation at any wavelength,” said Charles Kerton, assistant professor of physics and astronomy. “It seems to have no other readily visible reaction besides with gravity.”

The theory of dark matter is one explanation scientists have offered to explain the discrepancies between the effects of gravity on Earth and its effects on a larger scale out in space.

Motion and rotation of large interstellar bodies such as galaxies don’t follow the same rules as small objects on Earth do, and many scientists think this difference is because of the amounts of “dark” material that may be present, but unseen in huge cosmic masses.

The evidence that points toward the existence of dark matter was found when two huge clusters of galaxies collided nearly 100 million years ago. As the light reached Earth, NASA researchers documented the collision and noticed the phenomenon of light from behind the galaxy clusters being bent around them by gravity, otherwise known as “gravitational lensing.”

Gravitational lensing can only occur to such a huge degree when a giant amount of mass is present. The normal matter detectable in the collision, in the form of hot gases that slowed as their masses struck each other, did not account for the shape of the bent light.

NASA calculated that dark matter, which had probably passed through the collision without any sort of interaction, was causing the gravitational lensing.

“The ordinary matter seemed to separate from the dark matter in the collision,” said Curtis Struck, professor of physics and astronomy. “The hot gases were visible by X-ray, but the gravity from just the normal matter didn’t account for all of the lensing.”

The composite image constructed from NASA’s data shows the gases of the clusters slowing down because of the drag during the crash, while a representation of dark matter appears to have passed through the collision unhindered and stretches beyond the roiling gases.

Many scientists, however, remain skeptical about the discovery and are waiting for more solid evidence. Some believe the current gravitational knowledge may simply need modifications in order to be universally correct, and others are examining myriad alternatives.

“There are many theories about what hasn’t been seen or studied closely,” said John Hauptman, professor of physics and astronomy. “I don’t doubt the measurements of the gravitational effects, but there are still many possibilities.”

Hauptman said there are still too many possible explanations surrounding the phenomena.

“There’s nothing wrong with good ideas,” Hauptman said. “But a physicist should remain skeptical.”