Surveying black holes and neutron stars with gravitational waves

Lead Research Organisation: University of Birmingham
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

10 25 50

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.

Looking forward, the analysis of the remainder of the O1 data is currently underway, and I expect this will result in several more publications in 2016 before the 2nd science run begins later this year. I will continue to coordinate the efforts of the collaboration to prepare for the analysis of this data, in which we expect to make several more detections of binary black holes. This will give us the first look at the astrophysical distribution of binary black hole masses, and development of the hierarchical model for this by myself, my student in collaboration with other LIGO-Virgo members will play a key part.
Exploitation Route The detection of GW150914 has already resulted in multiple papers by collaboration and non-collaboration members. The masses, spins, distance, rates and constraints on general relativity provided input to many different studies beyond the scope of my own research.

The LALInference software has attracted attention from other data analysts. I was invited to Tokyo where I took part in an interesting workshop and discussed how these methods could be used with the Japanese KAGRA detector data.
Sectors Aerospace, Defence and Marine,Digital/Communication/Information Technologies (including Software)

URL http://papers.ligo.org
 
Description The detection of gravitational waves in 2015 has been one of the major milestones of 21st Century astrophysics, and led to worldwide attention, especially from media and higher education institutions. The award has enabled me to take a leading role in this discovery as co-chair of the compact binary coalescence working group within the LIGO-Virgo Collaboration (2015-2018), where I had responsibility for ensuring analysis and publication was completed in a timely fashion. The first discovery, GW150914, was announced at a press conference in Washington DC, where I was interviewed by members of the media. The 2017 discovery of GW170817 was announced by simultaneous press-conferences in major participating countries, and I led the UK panel at a press event at the Royal Society in 2017.
First Year Of Impact 2015
Sector Education,Other
Impact Types Cultural

 
Description Scientific Cooperation Agreements between the Sao Paulo Research Foundation (FAPESP), Brazil and the University of Birmingham, UK
Amount £6,300 (GBP)
Funding ID FAPESP 2014/50259-3 
Organisation São Paulo Research Foundation (FAPESP) 
Sector Public
Country Brazil
Start 09/2014 
End 09/2016
 
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 Big Data Seminar Series 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Postgraduate students
Results and Impact Gave presentation on gravitational wave searches to an academic audience as invited speaker at the first of a seminar series whose purpose was to better utilise Big Data. The other workshop participants were from other disciplines in the University of Birmingham (Computer Science, Geographical Sciences, Social Sciences & Urban planning etc). The talk and discussion session allowed us to share insights into using our data.

After the talk, I had a fruitful conversation with members of the Computer Science dept, which we have continued since, with the aim of collaborating on interdisciplinary research.
Year(s) Of Engagement Activity 2014
 
Description Discovery Days 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Schools
Results and Impact Talk and demonstrations provoked interest from visitors and teachers.

Pupils who visited reported an increased likelihood of applying to study physics at university.
Year(s) Of Engagement Activity 2014,2015
URL http://www.birmingham.ac.uk/Documents/students/advice/Discovery-Day-and-Subject-Experience-Day-broch...
 
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 Interview by Guardian 
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 Interviewed by The Guardian newspaper.
Year(s) Of Engagement Activity 2016
URL https://www.theguardian.com/science/2016/jun/15/gravitational-waves-detected-from-collision-of-secon...
 
Description Interview by Science Studio 
Form Of Engagement Activity A broadcast e.g. TV/radio/film/podcast (other than news/press)
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact Interviewed for Science Studio programme on KTEP radio station, Texas plus their podcast.
Year(s) Of Engagement Activity 2017
URL http://ktep.org/post/science-studio-ligo
 
Description LIGO 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 Attended LIGO Press Conference on Feb 11th announcing detection of gravitational waves. Interviews with print and radio journalists.
Year(s) Of Engagement Activity 2016
URL http://www.ligo.org/news/media-advisory.php
 
Description Pint of Science 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact Public talk "Einstein's Last Quest" on gravitational waves as part of the Pint of Science nation-wide event.
Year(s) Of Engagement Activity 2016
URL https://pintofscience.co.uk/
 
Description Public lecture (National Astronomy Meeting Schools Day) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Schools
Results and Impact Was invited to give a talk at the National Astronomy Meeting Schools Day 2016 to around 300 school-children (ages 16+).
Year(s) Of Engagement Activity 2016
URL https://www.nam2016.org/public-and-schools-events/schools-and-teachers
 
Description School visit (Queensbridge) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact I was invited to talk to around 50 secondary students (ages 14-16) about my research, the discovery of gravitational waves, choosing a career in science and studying at university. Feedback from teachers suggests it was very well received by students.
Year(s) Of Engagement Activity 2016
 
Description Tutorials in Statistical Inference 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Postgraduate students
Results and Impact Delivered first lecture in series "Tutorials in Statistical Inference" to audience of students and academics from Birmingham and neighbouring universities.
Year(s) Of Engagement Activity 2015