Dark Matter Evidence From Galaxy Cluster Abell 1689
September 13, 2013

Hubble Discovers Largest Ever Globular Star Cluster Population

[ Watch the Video: Pan Across Galaxy Cluster Abell 1689 ]

redOrbit Staff & Wire Reports - Your Universe Online

Astronomers studying a new image of the massive galaxy cluster Abell 1689 have revealed the largest known population of globular clusters to date, NASA reported on Thursday.

In a study published earlier this week in the online edition of The Astrophysical Journal, Karla Alamo-Martinez of the Center for Radio Astronomy and Astrophysics of the National Autonomous University of Mexico and colleagues report that they located an estimated 160,000 of the dense bunches of hundreds of thousands of clusters using Hubble's Advanced Camera for Surveys (ACS).

Furthermore, Alamo-Martinez and her co-authors also found that those globular clusters can be used as reliable tracers for dark matter, which the US space agency dubs “the invisible gravitational scaffolding on which galaxies are built.” These groups of stars are home to some of the oldest surviving stars in the universe, with nearly 95 percent of globular cluster formation occurring within the first two billion years after the Big Bang occurred.

[ Listen to the Podcast: What Is Dark Matter?: Podcast Interview With Dr. Matthew Walker ]

“We show how the relationship between globular clusters and dark matter depends on the distance from the center of the galaxy grouping,” Alamo-Martinez, who part of a research team led by John Blakeslee of National Research Council Canada's Herzberg Institute of Astrophysics at the Dominion Radio Astrophysical Observatory, explained in a statement. "In other words, if you know how many globular clusters are within a certain distance, we can give you an estimate of the amount of dark matter."

According to a NASA statement, "Peering deep inside the heart of Abell 1689, Hubble detected the visible-light glow of 10,000 globular clusters, some as dim as 29th magnitude, which is 1 one-billionth the faintness of the dimmest star that can be seen with the naked eye. Based on that number, Blakeslee's team estimated that more than 160,000 globular clusters are huddled within a diameter of 2.4 million light-years."

Furthermore, at 2.25 billion light years away, they also are the farthest objects of their kind to ever be studied. Hubble was also able to determine that the majority of the globular clusters were formed near the center of the cluster, which is home to a deep well of dark matter. As the space telescope began moving further away from the core, the researchers observed fewer and fewer of the giant clusters, the US space agency added.

“The globular clusters are fossils of the earliest star formation in Abell 1689, and our work shows they were very efficient in forming in the denser regions of dark matter near the center of the galaxy cluster,” explained Blakeslee. “Our findings are consistent with studies of globular clusters in other galaxy clusters, but extend our knowledge to regions of higher dark matter density.”

The image captured by Hubble also contains several glowing golden clumps, bright stars, and distant, ethereal spiral galaxies. A number of “electric blue streaks” were also visible, encircling the galaxies in the center. Those streaks, NASA said, indicate a cosmic phenomenon known as gravitational lensing.

They explain that Abell 1689 is so massive that it actually bends and warps the space surrounding it, altering the way that light from objects behind the cluster travels through space. Those streaks are actually the distorted forms of galaxies that lie behind Abell 1689, the agency noted. The image combines visible and infrared data from the ACS, which used a combined total exposure time of more than 34 hours in the process.