Surveying black holes and neutron stars with gravitational waves

Lead Research Organisation: University of Glasgow
Department Name: School of Physics and Astronomy

Abstract

Black holes and neutron stars are some of the strangest objects in our universe, formed in the supernova explosions at the end of the lives of the most massive stars. Neutron stars contain the mass of the Sun compressed into a sphere only a few tens of kilometres across; so dense that atoms can no longer exist, so the entire star consists of neutrons packed together by gravity. Black holes are thought to be more massive still, and so dense that not even light can escape from beyond their event horizons. These fascinating objects are a physicist's dream laboratory: a place where all our theories are pushed to their limits and beyond. Understanding how they are formed can also shed light on the evolution of the stars that they came from.
When two of these objects are found in a binary system, their small size allow them to orbit each other in a few hours or less.
According to Einstein's general theory of relativity these systems have so much matter in such a small space that they distort the space-time around them, whipping up gravitational waves that extract energy from the orbit and change the dimensions of everything they pass through. Luckily, by the time they reach us at Earth, these gravitational waves are so weak that the changes in length are equivalent to changing the distance between the Sun and Saturn by one hair's width, far too small to notice. Eventually so much energy is extracted that the objects orbit each other hundreds of times a second before they finally collide, releasing a huge amount of energy that can produce the brightest explosions in the universe if a neutron star is involved, but are completely invisible if only black holes are. Invisible that is, except to gravitational wave observatories, which are designed to measure the distortion of space-time produced by these events throughout the universe. The second generation of these observatories, called Advanced LIGO and Advanced Virgo, will come online in 2015 and start to make detections of binary collisions soon afterwards. By precisely measuring the distortions produced as a gravitational wave passes by, it will be possible to measure the nature of the binary system that produced it, even when no electromagnetic signal can be seen. Gravitational waves form in effect an entirely new spectrum with which we can observe the universe, opening up new avenues for discovery.
The hunt for these gravitational waves is an incredibly exciting field of science. It pushes the limits of what is technologically possible in every part of its design. Knowing that we will soon be observing black holes and neutron stars fuels the curiosity that drives this global effort forward. We are about to open up a new tool that will allow us to observe space-time itself, and will eventually lead to a better understanding of the nature and evolution of the universe.

Publications

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Goldstein J (2019) Associating host galaxy candidates to massive black hole binaries resolved by pulsar timing arrays in Monthly Notices of the Royal Astronomical Society

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Goldstein J (2018) Null-stream analysis of Pulsar Timing Array data: localization of resolvable gravitational wave sources in Monthly Notices of the Royal Astronomical Society

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Goldstein J (2019) Associating host galaxy candidates to massive black hole binaries resolved by pulsar timing arrays in Monthly Notices of the Royal Astronomical Society

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Hayes F (2020) Comparing Short Gamma-Ray Burst Jet Structure Models in The Astrophysical Journal

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LIGO Scientific Collaboration And The Virgo Collaboration (2017) A gravitational-wave standard siren measurement of the Hubble constant. in Nature

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Neijssel C (2019) The effect of the metallicity-specific star formation history on double compact object mergers in Monthly Notices of the Royal Astronomical Society

Related Projects

Project Reference Relationship Related To Start End Award Value
ST/K005014/1 01/02/2014 30/04/2017 £438,661
ST/K005014/2 Transfer ST/K005014/1 01/05/2017 31/01/2019 £158,580
 
Description Work has proceeded along the path outlined in my research plan in the STFC ERF case for support. During the first part of 2015 this focused on the finalisation of parameter estimation in preparation for the first observing run of Advanced LIGO (O1). This was documented in the published paper "Parameter estimation for compact binaries with ground-based gravitational-wave observations using the lalinference software library" (Veitch et al Phys. Rev. D 91 (4) 2015) which describes the LALInference software used for parameter estimation. Additionally I continued examining the science potential of gravitational wave detectors across the compact binary search space with several publications:
* Measuring intermediate-mass black-hole binaries with advanced gravitational wave detectors. (Veitch et al, Phys. Rev. Lett. 115 (14) 2015)
* Parameter estimation for binary neutron-star coalescences with realistic noise during the advanced ligo era (Berry et al Ap. J. 804 (2) 2015)
* Inference on gravitational waves from coalescences of stellar-mass compact objects and intermediate-mass black holes (Haster et al MNRAS in press 2016)

During early 2015 I was elected as co-chair of the LIGO-Virgo compact binary coalescence (CBC) working group, which recognises my leadership within the collaboration. This placed additional constraints on my time and has led to me becoming more involved in the broader aspects of LIGO-Virgo data analysis. The recruitment of Sebastian Gaebel using the additional grant secured through ERF funding has helped reinforce the research programme, and together we are continuing the development of hierarchical statistical models for analysing populations of sources.

In Sept 2015 the initial observing run of the detectors began, and on Sept 14th the first direct detection of GWs from the binary black hole GW150914 was made. The discovery itself was presented on Feb 11th, with the detection paper Observation of gravitational waves from a binary black hole merger (Abbot et al, Phys. Rev. Lett. 116 2016). Additionally, 13 companion papers looking at difference aspects of the detection are at various stages in the publication pipeline at this time (March 2016). As co-chair I was also responsible for setting the scope of the publications and coordinating the various group activities to ensure the timely delivery of the results. I was closely involved in all aspects of the data analysis of this event, contributing especially to the CBC search, parameter estimation, testing general relativity, electromagnetic followup and rate estimation papers, all of which which made use of the LALInference software mentioned earlier or its data products.

The second observing run took place in 2017, with myself as co-chair of the analysis group. As well as detecting black holes, on 17th August 2017 we detected the first binary neutron star coalescence, which was associated with the short gamma ray burst GRB170817A, proving the long-supposed link between these two phenomena. This event was successfully localised, and later found by electromagnetic observations as a kilonova, making it one of the most studied astronomical transients ever. The combined analysis paper was co-authored by several thousand astronomers, indicating the scope of the followup. Implications of this observation continue to be felt across the field.
Exploitation Route The outcomes of this grant are evident in the broad range of compact binary science that has been enabled by the first gravitational wave detections. As the field continues to grow, with improved detector sensitivity, and more observations, we will be able to use the populations of sources discovered to place constraints on the evolution of massive stars into black holes and neutron stars, and use these signals to probe general relativity, dense neutron star matter, and even the cosmological history of the universe through multi-messenger observations.
Sectors Digital/Communication/Information Technologies (including Software),Education

 
Description The opening of the field of gravitational wave astronomy has had a primarily cultural and educational impact. The excitement generated by the new way of doing astronomy has prompted great interest in the field in the last few years, and this has translated to increased interest in studying STEM subjects (particularly astronomy) which are of national importance in providing a trained workforce. This includes the training of postgraduate students who have gone on to research careers in the UK and abroad.
First Year Of Impact 2016
Sector Digital/Communication/Information Technologies (including Software),Education
Impact Types Cultural,Societal

 
Description Simulating the universe of binary black hole gravitational wave detections for cosmological inference
Amount £1,200 (GBP)
Organisation Royal Astronomical Society 
Sector Academic/University
Country United Kingdom
Start 07/2019 
End 09/2019
 
Description Tests of General Relativity with Gravitational Waves (Joint with Taiwan Ministry of Science and Technology)
Amount £12,000 (GBP)
Organisation Royal Society of Edinburgh (RSE) 
Sector Charity/Non Profit
Country United Kingdom
Start 10/2019 
End 09/2021
 
Description The spatial distribution of binary black hole gravitational wave sources
Amount £1,200 (GBP)
Organisation Royal Astronomical Society 
Sector Academic/University
Country United Kingdom
Start 07/2018 
End 09/2018
 
Description LSC 
Organisation LIGO
Country United States 
Sector Academic/University 
PI Contribution I am a member of the LIGO Scientific Collaboration (LSC), preparing for the analysis of Advanced LIGO and Advanced Virgo data. As the co-chair of the compact binary coalescence working group, I have led the search for compact binaries of neutron stars and black holes, which made the first direct detection of gravitational waves from a binary black hole GW150914. I coordinated the analysis and publication of multiple papers on this discovery. As an LSC member I also participate in service activities, examples of which are: - Reviewer for the BAYESTAR rapid sky localization code - Internal refereeing of papers
Collaborator Contribution Building and operating the LIGO and Advanced LIGO detectors. Organisation of LIGO Scientific Collaboration and its associated working groups. Internal review of publications, code, etc Co-authorship of papers Access to Data Collaborative Research Computing Resources Data Processing Scientific Support
Impact Publications - Multiple publications on GW150914 Technical Reports - Search plans for compact binaries - Studies of ability to localise sources with future networks
 
Title CPNest 
Description A generic nested sampling tool for bayesian model selection and parameter estimation. 
Type Of Technology Software 
Year Produced 2017 
Open Source License? Yes  
Impact Recently released, but intend it to be useful in population modelling and signal extraction, within the gravitational wave and wider community. 
URL https://github.com/johnveitch/cpnest
 
Title LALInference 
Description A toolkit for performing inference on gravitational wave signals. Along with co-authors, we have released an internally reviewed version of this software during 2014. 
Type Of Technology Software 
Year Produced 2014 
Open Source License? Yes  
Impact This software has enabled several of the studies listed in the list of publications. 
URL https://www.lsc-group.phys.uwm.edu/daswg/projects/lal/nightly/docs/html/group__pkg___l_a_l_inference...
 
Description Ayrshire Astronomical Society 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact In April 2019 I was invited to give a public talk at the April meeting of the Ayrshire Astronomical Society, a group of enthusiasts. The talk was followed by many questions and discussion, and the organisers reported that it was one of the best-received by the society in recent years.
Year(s) Of Engagement Activity 2019
 
Description Binary Neutron Star press conference 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Media (as a channel to the public)
Results and Impact At a press conference at the Royal Society, London, I led a panel of experts in making the UK announcement of the discovery of the binary neutron star coalescence GW170817, along with its electromagnetic counterpart. This was attended by reporters from TV, print, and new media. This was followed up by an interview for Sky News.
Year(s) Of Engagement Activity 2017
 
Description Festival of Physics 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Festival of Physics was a two-day event at the Dynamic Earth museum in Edinburgh. It drew a large audience from the general public, mostly from children and adults who were enthusiastic about science. My research group ran a stall with interactive demonstration, including a gravitational-wave alarm that was developed by myself and a student. Additionally I gave a public talk to an audience of ~30 people.
Year(s) Of Engagement Activity 2019
URL http://www.festivalofphysics.org/
 
Description Festival of Physics 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Festival of Physics was a two-day event at the Dynamic Earth museum in Edinburgh. It drew a large audience from the general public, mostly from children and adults who were enthusiastic about science. We had a stall with practical demonstrations, and I gave one of the public talks.
Year(s) Of Engagement Activity 2018
URL http://www.festivalofphysics.org/
 
Description Glasgow Science Festival Panel 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Around 70 members of the public attended a Q&A event where I was one of three panel members fielding questions and talking about research.
Year(s) Of Engagement Activity 2017
URL http://www.whatsonglasgow.co.uk/event/038602-glasgow-science-festival-presents:-chasing-the-waves/
 
Description Interview on BBC Scotland's "The Nine" 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Media (as a channel to the public)
Results and Impact I was invited to the BBC Scotland evening news television show "The Nine" to give a broadcast interview about the Event Horizon Telescope results, as an expert in black hole physics. The interview has given me a contact with journalist/researcher covering science topics at BBC Scotland.
Year(s) Of Engagement Activity 2019
 
Description RAS group prize talk 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact The Royal Astronomical Society awarded its 2017 Group Achievement prize to the LIGO Collaboration. In recognition of this I was invited to speak at the Feb 2018 Ordinary Meeting. The talk was very well received, with follow-up questions, and a request for a written report to be published in Observatory magazine.
Year(s) Of Engagement Activity 2018