Free Astronomy Magazine September-October 2015

SPACE CHRONICLES carried out over years using the po- werful DEIMOS multi-object spec- trograph fitted on Keck II, which is capable of obtaining spectra of one hundred globular clusters in a single exposure. DEIMOS breaks the visible wavelengths of objects into spectra, which the team used to reverse-en- gineer the ages of the globular clusters by comparing their chemi- cal composition with the chemical composition of the Universe as it changes with time. “The Universe is now well known to be 13.7 bil- lion years old,” research team mem- ber and Professor Jean Brodie said. “We determined globular clusters form on average some 1.2 and 2.2 billion years after the Big Bang.” “Our age measurements indicate that globular clusters managed to avoid the period, called cosmic reionization, in which the Universe was bathed in ultra-violet radiation which could have destroyed them” said fellow team member, Professor Aaron Romanow- sky. “Now that we have estimated when globular clusters form, we next need to tack- le the questions of where and how they formed.” For- bes said. The SLUGGS sur- vey is comprised of an internation- al team of astro- nomers who aim to understand the formation and evo- lution of galaxies and their globular cluster systems. Globular clusters are tightly bound clusters of around a million stars. Most large galaxies, including the Milky Way, host a sys- tem of globular clusters. Although the Universe itself, and galaxies within it, has evolved over cosmic time, globular clusters are very ro- bust and many have survived intact for over 10 billion years. Fossil star clusters reveal their age by Keck Observatory U sing a new age-dating meth- od and the W. M. Keck Obser- vatory on Maunakea, an in- ternational team of astronomers have determined that ancient star clusters formed in two distinct ep- ochs – the first 12.5 billion years ago and the second 11.5 billion years ago. Although the clusters are almost as old as the Uni- verse itself, these age measurements show the star clus- ters – called glob- ular clusters – are actually slightly younger than pre- viously thought. “We now think that globular clus- ters formed along- side galaxies rath- er than significant- ly before them,” research team lead- er, Professor Dun- can Forbes of Swin- burne University of Technology said. The new estimates of the star cluster average ages were made possible using data obtained from the SAGES Legacy Unifying Globulars and GalaxieS (SLUGGS) survey, which was carried out on Keck Observatory’s 10-meter, Keck II telescope. Observations were C osmic timeline showing the birth of the Universe in a Big Bang 13.7 billion years ago to the present day. Using the Keck Observatory, an international team of researchers led by Professor Forbes of Swin- burne University of Technology has determined ancient star clusters, known as globular clusters, formed in two epochs – 12.5 and 11.5 bil- lion years ago. They formed alongside galaxies, rather than prior to galaxies, as previously thought. [NASA/CXC/SAO and A. Romanowsky] n