BAS Observer July 2017

2 BAS OBSERVER RETHINKING GALACTIC EVOLUTION The image above ( courtesy of NASA, ESA, and Z. Levy (STScI) ) is an artist’s concept showing what the ‘dead’ galaxy MACS212 9 -1 (right) would look like when compared with our Milky Way Galaxy (left). Although three times as massive as the Milky Way, MACS212 9 -1 is only half its size and spins more than twice as fast. MACS212 9 -1 was detected by the Hubble Space Telescope via the light-bending power of a gravitational lens . The Hubble image can be viewed here . So what’s so exciting about this long-dead galaxy? MACS212 9 -1 is a compact yet massive galaxy that stopped making stars only a few billion years after the Big Bang – but its features are very much at odds with our current understanding of galactic formation. Astronomers distinguish between two main types of galaxies: disc-shaped spiral ones (e.g. our Milky Way) and elliptical-shaped ones. One of the main differences between the two types is that while new stars are still being born in disc-shaped galaxies, elliptical-shaped galaxies stopped doing this long ago – hence their ‘dead’ monicker. Another difference is that the stars in a disc-shaped galaxy rotate around its centre in a regular, predictable fashion – unlike those in the elliptical variety, which move every which way. Given the currently accepted model of galactic formation, an early dead galaxy like MACS212 9 -1 should be a chaotic, elliptical ball of stars, but instead the Hubble image revealed a regularly rotating disc! This discovery contradicts prevalent theory regarding the formation of elliptical-shaped galaxies shortly after the Big Bang. ‘This new insight may force us to rethink the whole cosmological context of how galaxies burn out early on and evolve into local elliptical-shaped galaxies,’ said study leader Sune Toft of the Dark Cosmology Center at the Niels Bohr Institute, University of Copenhagen, Denmark. ‘Perhaps we have been blind to the fact that early “dead” galaxies could in fact be discs, simply because we haven’t been able to resolve them.’ But how do these young, massive, compact discs evolve into the chaotic elliptical galaxies we see in the present-day Universe? ‘Probably through mergers,’ Toft said. ‘If these galaxies grow through merging with minor companions, and these minor companions come in large numbers and from all sorts of different angles onto the galaxy, this would eventually randomize the orbits of stars in the galaxies. You could also imagine major mergers. This would definitely also destroy the ordered motion of the stars.’ The findings are published in the June 22nd issue of the journal Nature . Toft and his team hope to use NASA’s upcoming James Webb Space Telescope to look for a larger sample of such galaxies. Darryl Nixon Club representatives PRESIDENT Peter Allison Ph: 0488 140 755 Email: president@bas.asn.au VICE-PRESIDENT Les Csibi SECRETARY Mike Lewis TREASURER Subbarao (Siva) Sivakumar GENERAL COMMITTEE MEMBERS Caroline Williams, Stephanie Williams and Ken Wishaw ASTRO-IMAGING OFFICER Tony Surma-Hawes CATERING OFFICER Caroline Williams DEEP SKY OFFICER Vacant EDUCATION OFFICER Arthur Theodoropoulos EQUIPMENT OFFICERS Cheryl-Ann Tan and Ashley Ruaux FUNDRAISING/GRANTS OFFICER Mike Lewis LIBRARIAN Stephanie Williams LUNAR AND PLANETARY OFFICER Stephanie Williams MEMBERSHIP OFFICER Caroline Williams MERCHANDISE/SALES OFFICER Vacant PUBLICITY OFFICER Tony Surma-Hawes WEBMASTER/FACEBOOK ADMIN Ashley Ruaux and Peter Allison NEWSLETTER EDITOR Darryl Nixon Ph: (07) 3219 3839 Email: darryl@sunsetdigital.com.au Layout and design: Sunset Publishing Services Pty Ltd ABN 90 130 679 791 POSTAL ADDRESS PO Box 15892 City East, QLD 4002 WEBSITE www.bas.asn.au EMAIL info@bas.asn.au No material may be reproduced from this publication without the written permission of the Brisbane Astronomical Society Inc. © BAS 2017 Cover image: An artist’s concept of the pair of supermassive black holes at the centre of galaxy 0402+37 9 , 750 million light-years from Earth – see full story at https://www.sciencedaily.com/releases/2017/06/ 170627114815.htm . ( Image courtesy of Josh Valenzuela/University of New Mexico )