April 24 (UPI) -- Scientists say they've discovered a secret law of galaxy cluster evolution.
Galaxy clusters are the largest objects in the universe held together by gravity, but because they're made up of mostly dark matter, they're difficult to measure.
In a new study, published this week in the Astrophysical Journal, a team of researchers from Taiwan, Italy, Japan and the United States detailed their discovery of a law they believe governs the evolution of all galaxy clusters.
Because dark matter can't be directly observed -- at least, not yet -- the best way to study it is measure its gravitational influence. Thus, the best way to image and analyze galaxy clusters and their massive amounts of dark matter is by studying gravitational lensing data.
Gravitational lensing describes the bending of distant light as it is warped by the gravitational pull of an intermediary object. By measuring how the intermediary cluster warps the light of a faraway galaxy on its trek to the lens of a telescope, scientists can yield new insights into their nature.
While a single gravitational lensing event can't uncover many secrets of galaxy clusters, a survey of many gravitational lensing events can yield patterns. By studying how multiple clusters distort the light of distant galaxies, scientists were able to estimate each cluster's gravitational field, as well as each cluster's size and mass.
Data recorded by the National Astronomical Observatory of Japan's Subaru Telescope and NASA's Hubble Space Telescope helped scientists calculate the distortion effect of the galaxy clusters.
When astronomers combined their calculations with gas temperature measurements recorded by NASA's Chandra X-ray Observatory, they found a rather simple law dictating the relationship between each cluster's size, mass and gas temperature.
The law suggests that while galaxy clusters have been growing for between 4 and 8 billion years, they're still in adolescence.
"We've discovered the law that regulates the growth of clusters of galaxies," Yutaka Fujita, an astronomer at Osaka University, said in a news release. "Clusters have an internal structure uniquely created in an early growth spurt."
The newly discovered law could help scientists unravel the complex relationships between the thousands of galaxies that make up galaxy clusters. Understanding the dynamics of cluster relations is essential to studying the cosmological laws of the universe.
"Our research draws us closer to explaining the evolutionary history of clusters and the universe," Fujita said.