In a groundbreaking observation, scientists have witnessed a collision between giant clusters of galaxies that is so intense, the dark matter within them has detached from the normal matter and surged ahead. This phenomenon, likened to untethered cargo continuing forward during a car crash, could provide fresh insights into the mysterious behavior of dark matter, which remains one of the universe’s greatest enigmas.
Dark matter, though invisible and undetectable by conventional means, constitutes about 85% of the universe’s matter. It interacts with normal matter primarily through gravity, affecting the movement of stars and galaxies, and even the warping of space-time itself. However, its exact nature remains elusive.
In this recent cosmic event, normal matter and dark matter responded differently to the colossal forces at play. While normal matter, which interacts electromagnetically, slowed down due to shock and turbulence from the collision, dark matter continued on its path, unaffected by these forces. This decoupling has been observed before, but never in such a distinct manner.
The galactic clusters involved in this collision are known as MACS J0018.5+1626. Uniquely, their orientation allows for new measurements of the velocities of both dark and normal matter. Scientists used two main techniques to measure these speeds. The velocity of dark matter was inferred from the movement of galaxies within the clusters using the Doppler shift, which measures how light stretches or compresses as objects move towards or away from us. Since galaxies move similarly to dark matter during a collision, their speed serves as a proxy for the dark matter’s speed.
For the normal matter, scientists relied on the Sunyaev-Zeldovich effect, a warping of background cosmic light caused by electrons in space. By analyzing this effect, researchers could determine the speed and direction of the intracluster medium, revealing a distinct difference in velocity compared to the dark matter.
This thorough study not only highlights the differing behaviors of dark and normal matter during such cosmic events but also opens new avenues for understanding dark matter’s elusive properties. As researcher Silich noted, “This study is a starting point to more detailed studies into the nature of dark matter,” potentially bringing us closer to uncovering the secrets of this invisible force that shapes our universe.
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