The most powerful radio-sources in the southern hemisphere

Mon 2 July, 2018 @12:00 PM, level 7
Dr. Sarah White, Research Associate
Curtin University

Email:  Sarah.White1[at]


Powerful radio-galaxies feature heavily in our understanding of galaxy evolution. However, when it comes to studying their properties as a function of redshift and/or environment, the most-detailed studies tend to be limited by small-number statistics. In this talk, I will present a new sample of nearly 2,000 of the brightest radio-sources in the southern hemisphere (Dec. < 30 deg). These were observed at low radio-frequencies as part of the GaLactic and Extragalactic All-sky MWA (GLEAM) survey, conducted using the Murchison Widefield Array (MWA). Being brighter than 4 Jy at 151 MHz, we refer to these objects as “The GLEAM 4-Jy Sample”. Thanks to the location of the MWA in a protected, radio-quiet zone, we have excellent spectral coverage for these sources, with 20 radio flux-densities spanning a frequency range of 72-231 MHz. A key component of this project is identifying the appropriate host galaxy of the radio emission, with these positions feeding into target lists for the Taipan Galaxy Survey. Having 10 times as many sources as the most-prominent, low-frequency radio-source sample that is optically complete (the revised Third Cambridge Catalogue of Radio Sources; 3CRR), the GLEAM 4-Jy Sample will allow models of powerful active galactic nuclei to be tested more robustly.

Science vs Cinema: Apollo 13

Sun 17 Jun, 2018 @3.30 PM, NOVA cinema
Dr. Rachael Livermore, DECRA fellow
University of Melbourne

Email: rlivermore[at]

Celebrate space and stars with a fun event for the whole family! Revisit classic sci-fi films on the big screen, followed by fascinating presentation and discussion on how space is depicted in cinema with Astrophysicist Dr Rachael Livermore (The University of Melbourne).

More details are here: Apollo 13

Precession measurability in black hole binary coalescences

Wed 13 June, 2018 @12:00 PM, level 7
Dr. Grant David Meadors, Postdoctoral Researcher
Monash University

Email:  grant.meadors[at]


Rotating bodies precess, and black holes should be no exception. Black hole spin has so far been inferred largely from electromagnetic observations of surrounding matter. Gravitational-wave observations of coalescences can probe the spin and precession of the black holes themselves. Using a Bayesian parameter estimatin pipeline, we characterize a method for detecting evidence of precession. Precession might conceivably be seen in either high-signal-to-noise ratio events with favorably parameters, or in a statistical ensemble of many events. We use simulated events with numerical-relativity approximant waveforms to estimate the detectability of precession.

Enhancing EoR limits – spectral accuracy of the MWA

Wed 6 June, 2018 @12:00 PM, level 7
Dr. Nichole Barry, Postdoctoral Researcher
University of Melbourne 

Email:  nichole.barry[at]

Epoch of Reionization observations have the potential to be transformative in the field of cosmology, but this is impossible without unprecedented levels of accuracy in calibration. We enhance EoR upper limits from the Murchison Widefield Array through the improvement of instrumental calibration with in situ simulations, and the reduced limit highlights the precision and accuracy that we must achieve. An in situ calibration simulation verifies our experimental findings, and identifies the fundamental limits of sky-based calibration. We set a precedent for required bandpass accuracy to one part in 105

Our improved EoR upper limit is (80 mK)2 at k=0.2 h Mpc-1 for z=7, an improvement of over a factor of 4 compared to a previous analysis using the exact same data set. These spectral accuracy techniques will influence future pipeline advances in the search for the EoR.

The lithium-rich giant star puzzle

Wed 23 May, 2018 @12:00 PM, level 7
Dr. Andy Casey, Postdoctoral Fellow
Monash University

Email:  andrew.casey[at]


All theoretical models of stellar evolution predict that most of the lithium inside a star is destroyed as the star becomes a red giant. However, observations reveal that about 1% of red giants are peculiarly rich in lithium, often exceeding the amount in the interstellar medium or predicted from the Big Bang. With only 151 lithium-rich giants discovered in the past four decades, and no distinguishable properties other than lithium enhancement, the origin of lithium-rich giant stars is one of the oldest problems in stellar astrophysics. In this talk I will report on the discovery of 2,330 low-mass lithium-rich giant stars, and a likely solution to this longstanding puzzle.

Closing in on the HIdden universe

Thurs 17 May, 2018 @12:00 PM, level 7
Dr. Michelle Cluver, ARC Future Fellow
Swinburne University

Email:  mcluver[at]


As the experiments looking to detect dark matter close in (coming from different directions on the Feynman Diagram), a small fraction of the baryon community is quietly anticipating a window on the universe (21cm neutral hydrogen) to de-fog a little. While theoretical simulators continue to grapple with the challenges of “mocking the universe”, observers can focus on refining (or even just beginning to understand) the prescriptive, previously sub-grid, physics and chemistry that made the universe great. I will talk about how star formation and stellar mass in galaxy groups can possibly make more sense if we can see the faint stuff (stars and gas) that everyone assumed was unimportant.

[CII] as a SFR tracer in M31 and M51: A ~constant photoelectric heating efficiency links [CII] 158 um with young stars

Wed 9 May, 2018 @12:00 PM, level 7
Dr Maria Kapala, SARChI Postdoctoral Fellow
University of Cape Town

Email:  kapala[at]


The energy balance sets the structure of the interstellar medium (ISM) phases, which in turn control the processes of star-formation (SF). We investigate the balance between the heating by stellar radiation, and neutral gas cooling dominated by [CII] emission line. [CII] is typically the brightest far-IR emission line from star-forming galaxies, and it has been proven to be a useful SFR tracer, both locally and at high redshifts, however, with some vital caveats. Specifically, we are interested wheather there are any changes in the efficiency of the photoelectric heating (PEeff), the dominant heating mechanism of the neutral gas, that might affect reliability of the [CII] as a SFR tracer.

To address these issues, we have assembled a unique set of observations in two nearby galaxies, M31 and M51. Multi wavelength FUV-FIR photometric coverage enables a well constrained SED modelling. Key observations of [CII] emission at high, 50pc, resolution in five SF regions in M31 (Herschel), and the first fully mapped galaxy at ~650pc resolution in M51 (SOFIA), enable a local and a global studies. Finally, we model individually resolved stars with 6 band HST photometry down to spectral type F0 with PHAT survey in M31 using BEAST (Bayesian Extinction and Stellar Tool) for an independent measurement of the heating at smallest scales.

A commonly used ratio [CII]/TIR (total IR emission), fails as a proxy for PEeff, because the TIR measures all dust heating, not just the FUV photons capable of ejecting electrons from dust grains (Kapala et al. 2017). We find [CII]/TIR to be strongly correlated with UVatt/TOTatt (inferred from MAGPHYS SED fitting), indicating that, in M31 at least, one of the dominant drivers for [CII]/TIR variation is the relative hardness of the absorbed stellar radiation field. We define PEeff(UV), [CII]/UVatt which should be more closely related to the true PE efficiency, which we find to be essentially constant (1.85 ± 0.8%) in all explored 700x700pc fields in M31, regardless of the value of [CII]/TIR (varying by a factor of 3).

I will present the above findings and the preliminary results of the [CII] – SFR relation, and the PEeff(UV) on 650pc scales in M51. I will also explore environmental dependencies on those relations.


When Galaxy Clusters Collide: Shocking tales of structure formation

Wed 2 May, 2018 @12:00 PM, level 7
Dr Andra Stroe, European Southern Observatory,

Email:  astroe[at]


Red weather alert: dangerous cosmic weather forecast, in light of galaxy cluster mergers! Clusters grow through mergers with other clusters, events which give rise to the largest cosmic shock waves. Shocks travel like giant tsunamis through the electron plasma and shape the evolution of the intra-cluster medium. Giant radio relics trace these shock fronts and are thought to form when accelerated electrons emit synchrotron radiation in the presence of a magnetic field. I will present results from the widest frequency study of radio relics, where we combine, for the first time, data covering more than 2 order of magnitude in radio frequency. Our very low and very high radio frequency data challenge the simple, widely accepted model for relic formation. Using unique observations spanning the 150 MHz to 30 GHz range, I will derive physical parameters, such as Mach numbers and electron ages, as well as constrain injection mechanisms. I will also discuss how new models involving re-acceleration of aged seed electrons or evolving magnetic fields can alleviate the discrepancies between observations of relics and theory.

Science vs Cinema: Galaxy Quest

Sun 29 Apr, 2018 @3.30 PM, NOVA cinema
Dr. Rachael Livermore, DECRA fellow
University of Melbourne

Email: rlivermore[at]

Celebrate space and stars with a fun event for the whole family! Revisit classic sci-fi films on the big screen, followed by fascinating presentation and discussion on how space is depicted in cinema with Astrophysicist Dr Rachael Livermore (The University of Melbourne).

More details are here: Galaxy Quest

Vesta and the Chaotic Formation of Planets

Thurs 26 Apr, 2018 @12:00 PM, level 7
Brother Guy Consolmagno, Director of the Vatican Observatory
Vatican Observatory

Email:  director[at]


NASA’s Dawn mission was sent to asteroid 4 Vesta to inspect, close up, “an intact protoplanet from the origin of the solar system”. But the Dawn data have revealed that Vesta’s overall density is too low, and its core and crust too big, to resemble anything like an intact protoplanet. Was Vesta ripped apart and re-assembled? It looks like Vesta is giving us new clues to planet formation and evolution in a violent early solar system.

The growing field of post-main-sequence exoplanetary science

Wed 18 Apr, 2018 @12:00 PM, level 7
Dr. Dimitri Veras, STFC Ernest Rutherford Fellow
University of Warwick

Email: d.veras[at]


Connecting planetary systems at different stages of stellar evolution helps us understand their formation, evolution and fate, as well as provides us with crucial insights about their dynamics and chemistry. Post-main-sequence stars — pulsars, white dwarfs and giant branch stars — all host planetary systems, which often include remnant debris discs. Here I provide a review of our current knowledge of these systems. I show how this interdisciplinary field incorporates several facets of stellar physics and chemistry as well as solar system physics and chemistry, and detail simulation-based efforts to understand the big picture.

Small scale structure of the IGM: A Dark Matter Tale

Wed 11 Apr, 2018 @12:00 PM, level 7
Dr. Vid Irsic, Postdoctoral Fellow
University of Washington

Email: irsic[at]


The intergalactic medium (IGM) plays a unique role in constraining the (small scale) matter power spectrum, since the low-density, high redshift IGM filaments are particularly sensitive to the small scale properties of dark matter. The main observable manifestation of the IGM, the Lyman-alpha forest, has provided important constraints on the linear matter power spectrum, especially when combined with cosmic microwave background data. This includes, most notably, the tightest constraints on warm dark matter (WDM) and fuzzy dark matter (FDM) models, that I will present in this talk.

The Hubble Space Telescope: 28 Years of Cosmic Discovery

Thu 29 Mar, 2018 @14:30 PM, level 7
Dr. Jennifer Wiseman, Senior Project Scientist for the Hubble Space Telescope
NASA Goddard Space Flight Center

Email: jennifer.j.wiseman[at]


The Hubble Space Telescope is operating at peak scientific capability even 28 years after its launch, thanks to successful astronaut servicing missions and operations that keep the observatory in top condition.  I will review the premiere scientific advancements achieved by Hubble, including both those that were planned at launch (e.g. measuring the Hubble constant) and many that were never dreamed of at launch (e.g. finding evidence for dark energy; analyzing exoplanet atmospheres).  Hubble observations are now helping prepare for JWST and other future missions, and are contributing critical complementary observations for solar system probes like JUNO and New Horizons.  I will discuss how Hubble can be used in its coming final years to provide the best science return, complementing other space-based and ground-based observatories and setting the stage for future flagship missions.

Parameter Estimation and Model Selection of Gravitational Wave Signals Contaminated by Transient Detector Noise Glitches

Wed 28 Mar, 2018 @12 PM, level 7
Dr. Jade Powell, Postdoctoral Fellow
Swinburne University

Email: jpowell[at]


The number of astrophysical sources detected by Advanced LIGO and Virgo is expected to increase as the detectors approach their design sensitivity. Gravitational wave detectors are also sensitive to transient noise sources created by the environment and the detector, known as ‘glitches’. As the rate of astrophysical sources increases, the probability that a signal will occur at the same time as a glitch also increases. This has occurred previously in the gravitational wave binary neutron star merger detection GW170817. In this talk, we examine the effect of glitches on the measurement of signal parameters and Bayesian model selection. We include binary black holes similar to current detections, sine Gaussian bursts, and core-collapse supernovae. We examine if the effects of glitches are worse when there is a mis-match between the signal model and the data.

Using Composite Spectral Energy Distributions to Characterize Galaxy Populations at 1 < z < 4

Thu 21 Mar, 2018 @12 PM, level 7
Ben Forrest, PhD student
Texas A&M University

Email: bforrest[at]


Ben Forrest Ben Forrest, PhD student
Texas A&M University
Email: bforrest[at]
With increasing sample sizes and multiwavelength photometric coverage of distant galaxies through surveys such as CANDELS, NMBS, and ZFOURGE, the available data at high redshift has grown significantly in the last decade. By de-redshifting and scaling photometry of many tens to hundreds of galaxies with similar spectral energy distributions, we can create low resolution spectra (R~50), quantifying features such as emission line equivalent widths with more precision than possible for a single galaxy without spectroscopy. In this talk I will detail the use of this method with ~7000 high signal to noise galaxies from the ZFOURGE survey. This allows us to identify and characterize populations of galaxies in the green valley, which show morphologies, dust content, and star formation rates between those of star-forming and quenched populations. I will also discuss those galaxies with extreme nebular emission in the young universe, which may be analogs to those which played a role in cosmic reionization.

Simulating GENESIS: The ASTRO 3D Theory programme

Thu 15 Mar, 2018 @12 PM, level 7
Dr. Pascal Elahi, Postdoctoral Fellow
The University of Western Australia

Email: pascal.elahi[at]


I will discuss the ASTRO 3D theoretical programme, which aims to follow galaxy formation and evolution across key epochs in cosmic time, from the EoR to the present-day, producing synthetic skies for ongoing and upcoming surveys. I will present current and near future simulations, how they compare to state-of-the-art work done else where, I will also discuss how we will tackle the variety of large scientific questions in ASTRO 3D’s other programmes. I will end with a taster of several specific scientific questions we seek to answer in the near term.

The fast radio bursts population as observed by the Australian Square Kilometre Array Pathfinder

Wed 28 Feb, 2018 @12 PM, level 7
Dr. Ryan Shannon, Postdoctoral Fellow
Swinburne University

Email: Ryan.Shannon[at]


Fast radio bursts (FRBs) remain one of the most exciting and confounding classes of astronomical transients. There is mounting evidence that these bright, dispersed pulses of radio emission originate at cosmological (gigaparsec) distances. Not only do the energetics of the events point to a new radiative process, but the pulses are imprinted with propagation through the ionised intergalactic medium and cosmic web, making them invaluable probes of media invisible to most other types of observations. Despite considerable effort to detect additional bursts, the yields have been low because of relatively narrow fields of view of most searches. Here I will present the discovery of 20 FRBs from a wide-area survey conducted with the Australia Square Kilometre Array Pathfinder (ASKAP), nearly doubling the total number of known FRBs in only one year of surveying. The burst properties suggest a cosmologically evolving population with a wide luminosity function. I will then discuss future plans to develop interferometric fast transient capabilities with ASKAP, necessary to harness the full value of FRBs. To conclude, I will present the very recent discovery of two FRBs with the Parkes telescope, one of which is the highest signal-to-noise ratio burst seen to date.

Pulsar timing arrays

Wed 07 Mar, 2018 @12 PM, level 7
Dr. Stefan Oslowski, Laureate Fellowship Postdoctoral Research Fellow
Swinburne University

Email: stefanoslowski[at]


The gravitational wave spectrum spans a large range of frequencies with various experiments covering different parts of the spectrum. At the low end of the spectrum, in the nanoHertz regime, we use so-called Pulsar Timing Arrays (PTAs) to try and detect gravitational waves. PTAs observe tens of millisecond pulsars spread throughout our Galaxy to form a galactic-scale detector. The primary signal PTAs attempt to detect are mergers of supermassive blackholes but we are also sensitive to more exotic sources like cosmic strings. During this talk I’ll provide you with an overview of the history of PTAs, current efforts and struggles, as well as the outlook into the bright future.

Neutrino cosmology

Wed 28 Feb, 2018 @12 PM, level 7
Dr. Yvonne Wong, Senior Lecturer
University of New South Wales

Email: yvonne.y.wong[at]


Neutrinos are the most weakly interacting and one of the lightest particles in the standard model of particle physics. Ironically, while these characteristics make the neutrino elusive in the laboratory, they are precisely what makes neutrinos the most abundant known subatomic particle in the universe, averaging about 300 particles per cubic centimetre today. The sheer number of these particles makes them an important participant in many cosmological processes, from the primordial synthesis of light elements, to the formation of the cosmic microwave background anisotropies and the large-scale cosmic structures. In this talk I will review the role played by neutrinos in these processes.

Using Globular Cluster Stellar Populations to Understand Galaxy Formation

Wed 21 Feb, 2018 @12 PM, level 7
Dr. Christopher Usher, Postdoc
Liverpool John Moores University

Email: c.g.usher[at]


Globular clusters are important tools to help us understand how galaxies form and evolve. Globular cluster formation tells us about the conditions of extreme star formation while their survival from high redshift tell us about the processes of galaxy assembly. Being much brighter than red giant stars, globular clusters allow the stellar populations of galaxies to be studied at much greater distances. Thus a wider range of galaxy masses, environments and morphologies to be studied than can be with resolved stars. Using data from the WAGGS survey of massive star clusters in the Milky Way and its satellite galaxies and the SLUGGS survey of the globular cluster systems of massive early-type galaixes, I will talk about how we can measure the metallicities of globular clusters using the strength of the calcium triplet in integrated light. Using globular cluster metallicity distributions and the relationships between globular cluster colour and metallicity, I will present evidence that different galaxies with similar masses experienced different formation histories. I will compare these observations with the predictions of the E-MOSAICS cosmological simulations of the formation of globular cluster systems. I will also talk about how the E-MOSAICS simulations have allowed to us to understand how globular cluster colour distributions vary with globular cluster luminosity (the ‘blue tilt’).

Hunting for the first stars I: Attempts to demystify He II with MUSE

Wed 14 Feb, 2018 @12 PM, level 7
Dr. Themiya Nanayakkara, Postdoc
Leiden Observatory

Email: nanayakkara[at]


In the quest for identifying pop-III stars, the most sought-after emission line is He II, however, stellar population models are unable to accurately predict the He II features while being consistent with other emission line diagnostics. To produce He II ionizing photons, stellar populations require sources of hard ionizing radiation with energies >= 54.4 eV and sources such as AGN, shocks, X-Ray binaries, stellar rotation and/or binary stellar evolution, and post-AGB stars have been suggested as possible contributors. To accurately identify relative contributions from these wide variety of sources, high signal-to-noise spectra with rest-frame UV/optical coverage and advanced stellar population/photoionization models are required.

The VLT/MUSE GTO program has obtained deep ≈10-30h exposures of the Hubble legacy fields yielding rest-UV spectra of galaxies at z≈2-6. In this talk I will present recent results of the MUSE program, where we compare the z=2-4 He II emitters with expectations from photoionization modelling to explore their stellar population and ISM conditions. I will compare our results with recent results from local samples of high-redshift ‘analogues’ to show the different parameter spaces probed by local and high-redshift galaxies in the rest-UV. I will address the necessity to obtain high signal-to-noise spectra of individual galaxies to model rest UV emission and absorption systems along with auxiliary rest-NIR lines to constrain stellar population properties of galaxies at high-z, which will be aided by combined studies by MUSE and JWST in future.

Hierarchical Star Formation Across Space and Time with Star Clusters from LEGUS

Wed 7 Feb, 2018 @3PM, level 7
Kathryn Grasha, PhD student
University of Massachusetts

Email: kgrasha[at]


A key missing piece in a predictive theory of star formation is the link between scales of individual stars and star clusters up to the scales of entire galaxies. LEGUS, a HST Treasury program of 50 nearby galaxies imaged at UV and optical wavelengths, is now providing us the information to test the overall organization and spatial evolution of star formation. I will present my latest findings of using star clusters from LEGUS combined with millimeter observations to trace the hierarchy of the entire star-forming process to improve our understanding of the evolution of star formation, stellar populations, and the natal molecular gas in galaxies.

Stars and scintillations

Tue 23 Jan, 2018 @12PM, level 7
Mark Walker, Director
Manly Astrophysics, NSW

Email: Mark.Walker[at]


Our understanding of radio-wave propagation through interstellar space is evolving rapidly in response to new observational results. It now appears that radio-wave scattering is caused primarily by dense plasma organised in radial filaments around hot stars. The resulting picture of the circumstellar plasma environment looks much like the Helix Nebula, where ionised filaments arise as the cometary tails of tiny molecular clouds. I’ll describe the observational developments and their interpretation, and I’ll sketch some broad astrophysical implications.

Searching for cosmic dawn from the sub-Antarctic

Mon 11 Dec, 2017 @2.15PM, level 6
Liju Philip, PhD student
University of KwaZulu-Natal

Email: lijuphil[at]


Observations of the redshifted 21-cm signal of neutral hydrogen can potentially help us probe the uncharted epochs in the universe’s history. One such epoch is “cosmic dawn,” when the first luminous objects lit up the universe, a few hundred million years after the big bang. The radiation from first stars heated the intergalactic medium, imprinting a characteristic signature in the evolution of the globally averaged 21-cm signal when observed as a function of frequency. The 21-cm spectrum is expected to have a ~100 mK absorption feature at a redshift of approximately 20 (frequency of ~70 MHz). This dip corresponds to the heating of the ambient neutral hydrogen by the first stars and is observationally undetected to date.

We present a new global signal experiment called Probing Radio Intensity at high-Z from Marion (PRIZM). PRIZM consists of two antennas with center frequencies of 70 and 100 MHz operating in the 30–200 MHz frequency band. The instrument observes from Marion Island in the southern Indian ocean, halfway between the continents of Africa and Antarctica. The pristine radio-quiet environment of Marion makes it an excellent location for low-frequency observations. PRIZM observes in dual-polarization mode and uses a Smart Network ADC Processor (SNAP) FPGA board for backend digital signal processing. I will discuss the deployment of PRIZM to Marion during the three-week relief voyage in April 2017. I will present the challenges and lessons learned during the deployment, our assessment of the RFI environment on Marion Island, and preliminary science results from the data collected during the relief voyage. I will also discuss prospects for future radio measurements from Marion that will extend to even lower frequencies.


Wed 7 Mar, 2018 @12PM, level 7
Dr. Stefan Oslowski, Laureate Fellowship Postdoctoral Research Fellow
Swinburne University

Email: stefanoslowski[at]



Weak Lensing in the Dark Energy Survey

Tue 14 Nov, 2017 @3PM, level 7
Dr. Daniel Gruen, Einstein Postdoctoral Fellow
SLAC / KIPAC / Stanford University

Email: dgruen[at]


The Dark Energy Survey has combined analyses of galaxy clustering and weak gravitational lensing two-point correlation functions in its first year (Y1) of observations. The goal of this is to constrain cosmological parameters from lensing measurements of structure in the evolved Universe. The combination of two-point correlation functions provides information on the amplitude of density fluctuations (S8=0.794+0.029-0.027) and the dark energy equation of state (w=-0.80+0.20-0.22) that is competitive with Planck CMB data. When joint with probes of cosmic geometry, it yields the best measurement of these parameters to date. Besides reviewing these results and the technical advances that facilitated them, I will also present work that provides a DES lensing view of higher than second moments of the matter density field.

Harnessing the Power of Gravitational Lensing

Wed 08 Nov, 2017 @12PM, Geoff Opat room, level 6
Dr. Rachael Livermore, Postdoctoral fellow
University of Melbourne

Email: r.c.livermore[at]


The magnifying power of gravitational lensing allows us to study distant galaxies in unprecedented detail. At moderate redshifts (1 < z < 5) the spatial magnification allows us to examine the kinematics and morphologies of ‘normal’ star-forming galaxies, revealing the processes that lead to the clumpy star formation observed in this epoch. At the highest redshifts (6 < z < 10), the flux magnification from lensing allows us to directly observe dwarf galaxies in the first billion years of the Universe, probing the faint end of the luminosity function where the majority of the ionizing photons that contribute to reionization originate. I will also discuss prospects for JWST in studying the first galaxies and the epoch of reionization.

Insights into binary black hole formation from gravitational waves

Wed 01 Nov, 2017 @12PM, Level 7
Dr. Simon Stevenson, OzGrav postdoctoral fellow
Swinburne University
Email: spstevenson[at]

In its first observing run (O1), Advanced LIGO detected gravitational waves from two binary black hole mergers, GW150914 and GW151226, along with a statistically less significant candidate LVT151012. The Advanced LIGO detectors were joined by the Advanced Virgo detector in the recently concluded second observing run (O2). Another two binary black hole mergers, GW170104 and GW170814, have been announced so far from this analysis, with the analysis of the data ongoing. These observations confirmed the existence of merging stellar mass black hole binaries originating in low metallicity environments. How to form merging binary black holes remains an open question theoretically. There are many proposed mechanisms, falling broadly into two families: 1) Isolated binary evolution and 2) dynamical formation in dense stellar environments. We show that comparing the distribution of observed black hole masses and spins to those predicted from population models will allow us to gain insight into how binary black holes form. We examine the measurements of the effective spin parameters for the 5 binary black hole observations published thus far and show that the data already exhibit a mild (2.7 sigma) preference for an isotropic distribution of spins over spins aligned with the binary orbital angular momentum. Alternatively, dimensionless black hole spin magnitudes in these systems could be intrinsically small (average spin magnitude < 0.2), at odds with measurements of black hole spin magnitudes in high mass X-ray binaries. Both of these conclusions have implications for the formation of binary black holes, and the formation of heavy black holes in supernovae.

Number of posts found: 140