An example of the new type of star cluster discovered (left), and an example of a previously known globular star cluster (right). The images were taken with the Hubble Space Telescope and their distances from Earth confirmed by the Keck II telescope. (Image courtesy of Swinburne/Forbes)

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Star clusters with properties not seen before have been discovered by an international team of astrophysicists, led by Swinburne University of Technology’s Professor Duncan Forbes.

Using data from the Hubble Space Telescope and the W. M. Keck Observatory in Hawaii, the researchers found several star clusters with sizes and masses that were previously not known to exist.

“Old, compact star clusters, such as globular clusters, are well known to amateur astronomers,” Forbes said. “Although globular star clusters were first discovered in 1665, it has taken more than 340 years to fully appreciate all the different types of star clusters that are made in the Universe.”

The researchers confirmed the existence of a number of different star clusters, overturning the idea that star clusters only come in certain types.

“We now know that star clusters have a rather continuous range of size and mass without any gaps in their properties,” Forbes said.

“Our discovery was made possible by using the Hubble Space Telescope to measure the sizes of the star clusters and long exposures on the Deep Extragalactic Imaging Multi-Object Spectrograph fitted to the Keck II telescope to obtain distances and confirm their status.” Professor Jean Brodie, a team member from the University of California, said.

They also measured the color of the star clusters, finding the lower mass ones to be red and the higher mass ones to be blue in color, suggesting differences in their chemical composition.

“No single model for the formation of these star clusters can currently reproduce the diversity of structural properties we have observed for old star clusters,” Forbes said. “Our observations present a challenge to researchers aiming to reproduce star clusters in computer simulations.”

The research team included Vincenzo Pota and Christopher Usher (Swinburne University of Technology), Jay Strader (Michigan State University), Aaron Romanowsky (San Jose State University), Jean Brodie and Jacob Arnold (University of California), and Lee Spitler (Macquarie University).

The paper has been accepted for publication in the Monthly Notices of the Royal Astronomical Society, published by Oxford University Press

The Keck II telescope’s DEIMOS instrument is capable of gathering spectra from 130 galaxies or more in a single exposure. In “Mega Mask” mode, DEIMOS can take spectra of more than 1,200 objects at once, using a special narrow-band filter.

The W. M. Keck Observatory operates the largest, most scientifically productive telescopes on Earth. The two, 10-meter optical/infrared telescopes on the summit of Mauna Kea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectroscopy and a world-leading laser guide star adaptive optics system.

The Observatory is a private 501(c) 3 non-profit organization and a scientific partnership of the California Institute of Technology, the University of California and NASA.

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