Shining a light on planetary processes
Wed 13 Sep, 2017 @12PM, level 7
Dr. Helen Brand, Scientist - Powder Diffraction
Jarosites and related minerals are of great importance to a range of mineral processing and research applications. They are used in the removal of iron species from smelting processes; they occur in metal bioleaching systems, and in the desulphurisation of coal; they are present in acid mine drainage environments.
There has been a recent resurgence in interest in jarosite and associated minerals since their detection on Mars by the MER rover Opportunity. In this context, the presence of jarosite has been recognised as a likely indicator of liquid water at the surface of Mars in the past and it is hoped that their study will provide insight into the environmental history of Mars.
Acid sulfate soils cover large areas of the Australian coastline and are likely to be a major constituent of the Martian environment. The oxidation of acid sulfate soils, coupled with potential release of heavy metals and acidic groundwaters, can have serious consequences for fragile ecosystems. Understanding these sediments will provide insight into the biogeochemical processes that affect the lifetimes of transient mineral species on Earth, and may be used to better understand soil acidification, contaminant mobility at sites affected by acid and metalliferous drainage, and even constrain past weathering and putative biosignatures on Mars.
Knowledge of the behaviour of jarosite minerals under the actual conditions that they are found in is crucial to understanding their potential environmental impacts on both Earth and Mars. To this end, we are engaged in a program to study the formation, stability and alteration of jarosite minerals using a complementary suite of in situ synchrotron and neutron techniques.
After GW150914: gravitational-wave astronomy in the era of routine detection
Wed 30 Aug, 2017 @12PM, level 7
Dr. Eric Thrane, Senior Lecturer
The first detection of gravitational waves from merging black holes (dubbed GW150914) ushered in the era of observational gravitational-wave astronomy. Since this seminal discovery, Laser Interferometer Gravitational-wave Observatory (LIGO) has announced the detection of three additional confirmed merger events—four if we include the marginal LVT151012. As the sensitivity of our detector network improves, detections will become routine. Indeed, at design sensitivity, LIGO may be detecting several events every week. This glut of gravitational waves presents us with new opportunities. I discuss a few of the research directions that have emerged in the wake of LIGO’s first detections including observationally-driven analysis of binary black hole formation channels, measurements of gravitational-wave memory, and tests of the famed no-hair theorem.
Modelling thermonuclear supernovae: how to blow up a white dwarf star
Wed 09 Aug, 2017 @12PM, level 7
Dr. Stuart Sim, Lecturer/Associate Investigator (SkyMapper)
Queen's University Belfast, UK
Aside from being spectacular displays in their own right, Type Ia supernova explosions have a key role in measuring the expansion history of the Universe and synthesizing the iron group elements. But what is their origin? That Type Ia supernovae arise from exploding white dwarfs is relatively well-established but the manner in which the explosion is ignited and how this can be determined from what we observe remain hotly debated issues.
I will discuss the theoretical modelling of Type Ia supernovae with particular focus on how radiative transfer simulations can be used to test explosion scenarios. I will argue that understanding the diversity of thermonuclear supernovae requires us to investigate a variety of different progenitor scenarios. Specifically, I will present recent results from our work on both Chandrasekhar mass white dwarf explosion scenarios and sub-Chandrasekhar mass models.
Galaxies at Cosmic Dawn: Exploring the First Billion Years with Hubble and Spitzer – Implications for JWST
Wed 02 Aug, 2017 @12PM, level 7
Prof. Garth Illingworth, Professor
University of California Santa CruzEmail: gedi[at]ucolick.org
Hubble has revolutionized the discovery and study of very distant galaxies through its deep imaging surveys. Together the HST WFC3/IR and ACS cameras have opened up the exploration of the universe in the first billion years after the Big Bang. I will discuss what we have learned about the earliest galaxies during the reionization epoch at z>6 from the remarkable HST and Spitzer imaging surveys (e.g., HUDF/XDF, GOODS, HUDF09/12 and CANDELS), as well as surveys of galaxy clusters like the Frontier Fields (HFF). Lensing clusters provide extraordinary opportunities for characterizing the faintest earliest galaxies, but also present extraordinary challenges. Together these surveys have reliably established the volume density of galaxies in the first billion years down to extremely faint levels around -14.5 mag. The results from deep UV luminosity functions from Hubble, combined with the recent results from Planck, indicate that galaxies dominate the UV ionizing flux that reionized the universe. Some of the greatest surprises have come from the discovery of very luminous galaxies at z~8-11, around 400-650 million years after the Big Bang. Spectroscopic followup of these very rare, bright galaxies has confirmed redshifts from z~7 to z~11, and revealed, surprisingly, strong Lyα emission near the peak of reionization when the HI fraction in the IGM is high. The small sizes of galaxies at high redshifts, from analysis of the HFF cluster samples, reveal objects that, remarkably, are as small as globular clusters and dwarf galaxies. The recent confirmation of a z=11.1 galaxy, just 400 million years after the Big Bang, by a combination of Hubble and Spitzer data, pushed Hubble into JWST territory, far beyond what we ever expected Hubble could do. Twenty years of astonishing progress with Hubble and Spitzer leave me looking to JWST to provide even more remarkable exploration of the realm of the first galaxies at "Cosmic Sunrise". The latest results on the sizes of distant galaxies, on the star formation rate density at z~10 and from Planck indicating that reionization began around z~10 together have significant implications for the detectability of the "first galaxies" with JWST.
A list of recent colloquia, with slides in some cases, can be found here.