BAS Observer March 2018

2 BAS OBSERVER GLIMPSING THE COSMIC DAWN No, you’re not looking at a coffee table sitting in the middle of a desert; the object pictured above is actually one of three radio astronomy antennas in the outback of Western Australia. In a project known as the Experiment to Detect the Global Epoch of Reionization Signature (EDGES), the array was used to search for signs that the hydrogen atoms pervading the newborn universe had absorbed microwaves left over from the Big Bang. This absorption marks the moment when the very first stars began to glow – the dawn of the cosmos. This is the first time anyone has been able to gather and analyse data from the period between the creation of the cosmic microwave background (380 000 years after the Big Bang) and the formation of the oldest known galaxies (400 000 000 years later). As EDGES lead researcher Judd Bowman puts it, ‘This is really the only possible probe that we have of the time before the stars.’ The detection of the tiny absorption signal was no small task. To achieve it, Bowman and his team had to subtract the radio noise from our galaxy, which is 30 000 times stronger than the signal they were seeking. Nevertheless, they were successful and concluded that they had detected the shadows of hydrogen clouds that existed between 180 million and 250 million years after the Big Bang. The researchers’ results, published in this month’s edition of Nature , are intriguing, to say the least. The absorption turned out to be more than twice as strong as predicted, indicating that the hydrogen’s temperature was far lower than previously thought. And here’s where it gets really interesting . . . The hydrogen must have lost its heat to something even colder, and the only colder particles in existence at the time were those of dark matter. In another paper published in Nature , Tel Aviv physicist Rennan Barkana suggests that the dark matter particles would need to have been less than five times as massive as the hydrogen atoms in order to act as a cooling agent. There have been numerous unsuccessful searches for hypothetical weakly interacting massive dark matter particles, but it has been assumed that they would weigh hundreds of times as much as hydrogen atoms. As a result, some physicists have started looking for much lighter dark matter particles, and no doubt the results of the EDGES experiment will encourage more such searches. However, a word of caution is in order: the EDGES measurements relied on very fine calibrations with a margin for error of just a few hundredths of one per cent. It’s therefore a little early to make any definitive statement on the properties of the elusive dark matter particle. Darryl Nixon No material may be reproduced from this publication without the written permission of the Brisbane Astronomical Society Inc. © BAS 2018 Cover image: Duelling Bands in the Night. The more commonly seen band on the right is the central band of our Milky Way galaxy, but the band on the left is the less commonly seen zodiacal light (sunlight reflected from dust orbiting the Sun in our Solar System). Image Credit & Licence : Ruslan Merzlyakov ( RMS Photography ) Club representatives PRESIDENT Peter Allison Ph: 0488 140 755 Email: president@bas.asn.au VICE-PRESIDENT Stephanie Williams SECRETARY Syed Uddin TREASURER Subbarao (Siva) Sivakumar GENERAL COMMITTEE MEMBERS Ken Wishaw and Caroline Williams ASTRO-IMAGING OFFICER Tony Surma-Hawes CATERING OFFICER Caroline Williams DEEP SKY OFFICER Stephanie Williams EDUCATION OFFICER Peter Allison 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