SOAR telescope time exposure image

SOAR Telescope Time Exposure Image
[Pin It] A time exposure view of the SOAR telescope observing at Cerro Pachon in Chile.
CREDIT: Daniel Maturana/NOAO/AURA/NSF

A powerful new ultraviolet laser that fires into the night sky is helping scientists take their most detailed look yet at a distant star cluster.

A team of astronomers at the Southern Observatory for Astrophysical Research (SOAR) and the Cerro Tololo Inter-American Observatory (CTIO) in Cerro Pachon in Chile used an instrument called SOAR Adaptive Module, or simply SAM, to peer deep inside the crowded NGC 6496 cluster to understand how its stars evolved.

The researchers measured the color and brightness of over 7,000 stars in NGC 6496, and determined that the star cluster is 10.5 billion years old and 32,600 light years away from Earth — the most exact measurement yet of the star cluster’s key parameters. [Starry Night: Take Our Star Quiz]

The study also suggests that NGC 6496’s stars have a much higher proportion of elements heavier than hydrogen and helium than most clusters of its kind. The research will be detailed in an upcoming edition of the Astronomical Journal.

Star clusters across the universe come in two types:  globular clusters, which are home to hundreds of thousands of gravitationally bound and very ancient stars, many of them nearly 10 billion years old; and open star clusters, which are normally very young and contain only a few hundred stars.

NGC 6496 is a globular cluster. According to study team member Andrea Kunder of CTIO, such clusters are “some of the most interesting objects in the Milky Way, because they are so old, and also because they are some of the few visible objects in the galactic halo.”

The galactic halo extends beyond the visible part of a galaxy and is composed mainly of dark matter, which cannot be observed directly, researchers said.

“Just like archaeologists use fossils to reconstruct the history of the Earth, astronomers use globular clusters to reconstruct the history of the galaxy,” Kunder said. “There are only about 150 globular clusters known in the Milky Way Galaxy, so each of these globular clusters is an important tracer of the galactic halo and the formation of the Milky Way Galaxy.”

NGC 6496 lies on the other side of Milky Way’s center, so when you look at it from Earth, you have to peer through a lot of gas and dust. That is why during previous ground-based observations it was tricky to measure with certainty its basic parameters, such as its distance from the Earth and precise age, said study team member Luciano Fraga from the National Astrophysics Laboratory (LNA) in Brazil. In 2003 the cluster had been studied with the Hubble Space Telescope, and the new observations using SAM have made it possible to improve the original measurements.

It took a decade to develop and build SAM, at a cost of $4.5 million. And on its very first use it already helped to improve the image quality from observations.

“Quite honestly, this cluster was chosen because it was visible in the night sky when SAM was being commissioned.  We needed a target to observe, and this cluster was up at the right time. We also knew that it hadn’t been studied very extensively, so we thought we could contribute to a further understanding of the properties of this cluster,” Kunder said.