An international group of scientists, including dozens of Australians, this weekend announced the detection of the most massive binary black hole merger yet witnessed in the universe. The black hole that resulted from this cataclysmic event is more than 80 times as massive as our Sun.
The discovery of GW170729 – along with evidence of nine other black hole mergers – comes just over one year since scientists announced they had witnessed, for the first time, the violent death spiral of two dense neutron stars via gravitational waves, another set of major astrophysical discoveries have been announced in the US.
The series of papers including the work of the Australians, all from the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav), present the full catalogue of observations of binary black hole and binary neutron star mergers from the first two observing runs (2015, 2016-17) of the Advanced LIGO (US) and Advanced Virgo (Italy) gravitational-wave detectors.
According to Dr Meg Millhouse, from OzGrav and the University of Melbourne, the papers outline a catalogue of all gravitational wave signals "heard" by the Advanced LIGO detectors in the last three years. “These signals are generated by some of the most violent events in the universe, when pairs of neutron stars and black holes – each with many times more mass than our sun – come crashing together,” she said.
Dr Simon Stevenson, from OzGrav and Swinburne University, said that the additional information of the other nine binary black holes, “means we are learning things about the population, such as how frequently binary black holes merge in the universe (once every few hundred seconds somewhere in the universe) and whether small (low mass) or large (high mass) black holes are more common -- there are many more light black holes (around 5-10 times the mass of the sun) in the universe than heavy black holes (around 30-40 times the mass of the sun), but the heavy ones are ‘louder’ in gravitational-waves, and easier to ‘hear’ colliding,” he said.
“With each new detection we learn something more about how these extraordinary objects came to be. The detections also help to answer questions about the theory of gravity, the formation of galaxies, and how heavy elements (including gold and platinum) are produced”, said co-author Dr Xu (Sundae) Chen from OzGrav and the University of Western Australia.
Another author, student Colm Talbot from OzGrav and Monash University, in a separate paper describes how the detection of these new black holes will assist in understanding the Universe’s entire population of black holes. “Each of these black holes formed from huge stars which died in violent explosions called supernovae. By studying these black holes, we act as black hole archaeologists to learn how these cosmic giants die,” he said.
Last year Dr Paul Altin from OzGrav and the Australian National University was part of LIGO's "rapid response team", whose job it is to be ready to receive a detection alert at any time, day or night, in order to quickly analyse the data and decide whether the event is significant enough for an alert to be sent to our partner astronomers for follow-up observations. According to Dr Altin, in 2019 Advanced LIGO comes back online with even higher sensitivity, in part due to the use of quantum squeezing. “Squeezing allows us to get around noise that comes from quantum mechanics, the fundamental theory that governs microscopic particles,” he said. The Advanced LIGO squeezer was designed at ANU and is currently being installed in the US.
Several OzGrav members are currently in the US at LIGO Hanford installing upgrades to the detector. According to Dr Dan Brown, from OzGrav and the University of Adelaide, the next observation run aims to use squeezed light to reach the target sensitivity to look for extreme events. “With OzGrav's expertise in squeezed light and adaptive optics for compensating thermal effects from the increased laser power we're making significant contributions towards improving LIGO for the next run,” he said.
The ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) is funded by the Australian Government through the Australian Research Council Centres of Excellence funding scheme. OzGrav is a partnership between Swinburne University of Technology (host of OzGrav headquarters), the Australian National University, Monash University, University of Adelaide, University of Melbourne, and University of Western Australia, along with other collaborating organisations in Australia and overseas. LIGO is funded by the NSF, and operated by Caltech and MIT, which conceived of LIGO and led the Initial and Advanced LIGO projects. Financial support for the Advanced LIGO project was led by the NSF with Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council) and Australia (Australian Research Council) making significant commitments and contributions to the project. More than 1,200 scientists and some 100 institutions from around the world participate in the effort through the LIGO Scientific Collaboration, which includes the GEO Collaboration and the Australian collaboration OzGrav. Additional partners are listed at http://ligo.org/partners.php. The Virgo collaboration consists of more than 280 physicists and engineers belonging to 20 different European research groups: six from Centre National de la Recherche Scientifique (CNRS) in France; eight from the Istituto Nazionale di Fisica Nucleare (INFN) in Italy; two in the Netherlands with Nikhef; the MTA Wigner RCP in Hungary; the POLGRAW group in Poland; Spain with the University of Valencia; and the European Gravitational Observatory, EGO, the laboratory hosting the Virgo detector near Pisa in Italy, funded by CNRS, INFN, and Nikhef
Dr Aidan Brooks (LIGO Laboratory Caltech) visited Australia in Aug-27 through Sep-21 2018 to visit the University of Adelaide (UoA) with additional short trips to UWA, ANU and Monash. The focus of the trip was divided into three main research areas with different time horizons:
Advanced LIGO support
Extensive discussions were held with Dan and Peter on how Adelaide can continue to support the Hartmann sensor (HWS) code for LIGO. I also discussed the cavity eigenmode modulation (CEM) technique for cavity mode-matching and alignment that Alexei has developed.
A+ is a medium-scale upgrade to Advanced LIGO (aLIGO) that will introduce frequency dependent squeezing and new coatings to the aLIGO test masses. Much of the trip was focused on development of adaptive optics, designed at Adelaide, for use in A+. Successful deployment of these optics will significantly reduce the complexity of the A+ adaptive optics system and could potentially reduce the budget for this system by $200k or more.
The third generation of LIGO will be called LIGO-Voyager and will require, amongst other large-scale upgrades, a 2-micron laser source so Seb showed me the one that UoA are developing.
Work at other OzGrav Nodes
At UWA, I had long discussions with Zhao and gave some input on their plans to develop technologies for Voyager. The Gingin facility is potentially the only site in the next few years to have a suspended Fabry-Perot cavity with silicon optics and two micron lasers and thus could be valuable for testing.
I spent two days at ANU (overlapping with Rana Adhikari during that time). We provided input on the OzGrav proposal to build a high-frequency GW detector in Australia, and Bram and I discussed the requirements for two-stage tip-tilt.
Postdoctoral research position at Monash University.
Theoretical Astrophysics for 3 years full-time. Applications close 30 November 2018 to start in September 2019 (the start date is flexible). I welcome applications from candidates with broad interests connected to any of the following areas of theoretical astrophysics:
*Gravitational-wave astrophysics and the astrophysical interpretation of exciting new data on binary neutron star and black hole mergers
* Modelling massive stellar and binary evolution
* The interpretation of high-energy astrophysical transients, including tidal disruption events and gamma ray bursts
* Stellar dynamics
Enquiries: Professor Ilya Mandel, Ilya.Mandel@monash.edu
Researchers are applying big data analysis techniques used in astronomy to better understand diseases of the eye and brain.
The team, led by ophthalmologist Dr Peter van Wijngaarden (CERA) and astrophysicist Associate Professor Christopher Fluke (Centre for Astrophysics and Supercomputing at Swinburne University and OzGrav), will be working together to apply the same big data analysis used by astronomers in their study of the universe, to the field of ophthalmology.
The collaboration will be formalised thanks to a generous donation from Australian entrepreneur Dr Steven Frisken, CEO of ophthalmic tech company Cylite, who was one of four people jointly awarded the Prime Minister’s Prize for Innovation last night in Canberra.
Daniel Brown from OzGrav’s team at the University of Adelaide travelled to MIT for the A+ Balanced Homodyne Workshop, 11-12 Oct, 2018. Overall this was a productive meeting which favourably demonstrated how the research being undertaken here in the Adelaide node of OzGrav is pushing the future detectors forward.
Recently the next iteration of the LIGO experiment was announced, named A+. This upgrade takes us from Advanced LIGO and further improves the sensitivity. One of the more involved upgrades is to change the gravitational wave readout scheme, from what is currently used and is called “DC Readout” to “Balanced Homodyne Readout” (BHD). Both of these techniques are employed to provide a strong optical field, called a local oscillator, at the output port, which beats with the optical fields generated by a gravitational wave and allows us to measure them on a photodiode.
For A+ the plan is pick off a small amount of light from the power recycling cavity through one of its mirrors. We then have to shape and align this light correctly and combine it with the signal coming out of the detector. This beam shaping and designing of optical control systems is some of the core OzGrav research Daniel is undertaking at the University of Adelaide.
The outcome of this meeting was that much work still needs to be done. The output part of LIGO is having a complete redesign. New suspension stages must be designed to accommodate the adaptive optic elements being developed at Adelaide. There is also scope for our new beam shape sensing technique to also be employed for controlling these adaptive elements. Next a control system must be designed and modelled for all this, which is being simulated in my modelling software Finesse. In the coming months we aim to write several design documents outlining all the new elements for the BHD system of A+.
- Daniel Brown, Postdoctoral Researcher at University of Adelaide
From March to June 2018 Sebastian (postdoc), Alexei (PhD student), and Daniel (postdoc) from the OzGrav team at the University of Adelaide travelled to the USA to attend the LIGO-Virgo Collaboration (LVC) meeting along with further trips to LIGO Hanford and the California Institute of Technology (Caltech).
One of Daniel’s main research topics is the creation of numerical simulation software, called
Finesse, which is used for understanding the complex optical interferometers that are at the core of gravitational wave detectors; we use this for design and commissioning work.
Sebastian's main research focus is 2µm fiber laser development which is one of the core research topics for OzGrav instrumentation. His research is in the development of lasers for the third generation of gravitational wave detectors. Sebastian spent time during the LVC engaging with research groups focussed on the current and future laser systems. Following the LVC he travelled south to Pasadena to visit the Caltech arm of LIGO Lab. This gave him an opportunity to examine the material and detector technologies being developed for the future detectors. While there he helped design the optical layout for the signal recycling heater and characterise the CO2 laser.
After this Sebastian joined Alexei and Daniel in Hanford and participated in the mode matching of the 70W upgrade to the prestabilised laser and helped with the implementation of the CO2 laser heater.
Arriving at the LIGO site at first is nothing short of daunting. Usually we work on small table-top optics experiments. The physical size of the LIGO experiment always blows me away, from the size of the vacuum chambers to the arms that shoot out into the desert.
The team at LIGO was amazing; their patience in teaching us how it all works and trust in us to let us work on the experiment really made the trip.
During our time there we all worked on several parts. First, we helped design and construct the new prototype adaptive optic system. This system uses a CO2 laser to heat the signal
recycling mirror to induce a small lens on its surface. This then shapes the beam exiting
the interferometer and will be used to better shape it for extracting the signal. This involved a lot of plumbing work (getting covered in aged coolant left in old pipes...) and aligning the CO2 laser into the vacuum chamber to correctly deform the mirror.
Alexei also looked into how we can better interpret cavity mode scans to infer the correct way to shape the laser beam. From this we found that we can actually extract more information than we expected previously, such as the astigmatism of the beam. Using this knowledge he wrote a new commissioning tool for analysing the output mode cleaner scans in a more automated and easier to use fashion.
We also helped in mode matching the squeezer beam to the interferometer and develop better Finesse models of the output path. Before we left we then also helped test the new Hartmann sensor system for sensing the deformations in the end test mass mirrors, something that previously had not worked optimally.
PhD scholarship at ANU!
See your future career in Gravitational Physics. Apply for admission at ANU by 31 October.
The neutron star merger, known as GW170817, occurred 130 million light-years from Earth and sent a burst of both gravitational and electromagnetic waves rippling through space that reached the Earth one year ago.
In the aftermath of the violent collision, GW170817 was observed worldwide by telescopes across the electromagnetic spectrum. By tracking changes in the optical, radio, and X-ray emission of the afterglow, scientists including Swinburne's Dr Adam Deller, from OzGrav, were able to study how the material flung out during the merger interacted with its surroundings.
Read more here.
OzGrav is delighted to be involved in a new art-science planetarium show that will have its world premier at the Melbourne International Arts Festival from October 6-13, 2018.
Particle/Wave sees poets, musicians, sound and video artists joining forces with renowned scientists to interpret the theories of gravitational waves, which Stephen Hawking has called “a completely new way of looking at the universe.”
Particle/Wave is directed by Alicia Sometimes, and includes narration by OzGravers Kendall Ackley, Lilli Sun, and Alan Duffy, along with video contributions from our own Mark Myers and Carl Knox.
OzGrav Associate Investigator Dr Adam Deller has helped test Einstein’s theory of general relativity and shown it still can’t be proven wrong, using the complicated orbital dance of three compact stars. Einstein’s strong equivalence principle says all objects should fall the same way in a gravitational field, regardless of their composition or how dense they are.
After five years of intensive observation of a triple stellar system, the international team of nine astronomers was able to conclude that the theory of general relativity is still relevant, as seen in the research paper published in the prestigious international science journal, Nature.
“This particular system consists of one ultra-dense neutron star and two less-dense white dwarf stars, which makes these stars the dream team for testing relativity,” Dr Deller says.
Read the press release here.