General Meeting Report September 1999
The Mass(if) Mystery.
Speaker Dr. Michael Drinkwater, Dept. of Physics University of Melbourne.
Looking at Dr. Drinkwater you would not think he had a weight problem. Young, trim, in jeans and sweater, he is the epitome of the new generation PhD graduate. It wasn’t losing a few kilos around the waist though that Michael Drinkwater and his group at Melbourne Uni. are worried about They have a massive mystery, they lost 90% of the weight of our Milky-way Galaxy. They don’t know where it is! It’s a calamity. They are looking for it everywhere, amongst the wimps, the machos, in cold and in hot dark matter; all-the-while searching. If we include the two nearest Galaxy Clusters, Fornax and Virgo, in the equation the problem becomes even worse. Astronomers can only see 1% of all (what measurements in stellar movement tell us) that should be there.
Are the measurements wrong? Or are there more things in the heavens, more galaxies and stars we do not see, contributing to the total mass? Things we have missed so far? That is where Dr. Drinkwater and his team come into the picture. They are concentrating on classifying (or re-defining) low luminosity galaxies of the Fornax Cluster, which may have been overlooked due to their faintness, or misplaced by assuming a greater distance for their dim light. Perhaps by sheer number these could balance the scales? So far the group have collected data from thousands of faint, dwarf and brown galaxies, made spectral analysis and, by applying the standard redshift formula, they finished up with a three-dimensional wedge of space in proper perspective.
This sounds deceptively simple. You don’t see all the sleepless nights that went into collecting 14,000 spectra, the painstaking computer programming, the endless setting-up periods, and you don’t see the frustrations with fickle weather and equipment failure. You skip over months of planning and preparing submissions, competing for telescope time, and the painstaking work of sorting the mountains of data collected. But then, when it is all done, when you have analysed the results, when you have built representative computer models, when it all starts to come together and make sense, then you suddenly get this rush of adrenalin in the realisation: This is it! Never before has anyone presented that type of information in this way.
“I let you in on a secret” Michael said, as he, somewhat self-conscious in the significance of the moment, rotated the cube of cosmic space on the screen before our eyes, “this is the very first time this information is shown in public. You are witnessing a preview of material not yet published.” It was awe-inspiring. Here was the Fornax cluster of galaxies, 65 million light-years away right in front of us, suspended in space, dynamically distributed in width, height and depth according to the speed of recession of individual galaxies. There were the normal views as seen from Earth in the familiar arrangement, the bottom up view, the side and top views, showing the full extend of the 1014 solar-mass cluster stretching across cosmological distances.
Did they solve the mystery of the missing mass? No, but they have shown there is a lot more diversity in galaxies than was previously thought. The missing mass problem (if there is one) is still out there, staring every astronomer in the face, waiting to be recognised.