Advancing the Search for Gravitational Waves with Next-Generation Citizen Science

by Michael Zevin.


martin-zevin

Michael Zevin is a third-year doctoral student in astrophysics at Northwestern University. He is a member of the LIGO Scientific Collaboration, and in addition to citizen science and LIGO detector characterization his research focuses on utilizing gravitational-wave detections to learn about binary stellar evolution and the environments in which compact binaries form.

With the first observations of gravitational waves and the discovery of binary black hole systems, LIGO has unveiled a new domain of the universe to explore. Though the recent signals persisted in LIGO’s sensitive band for a second or less, these last words of the binary that were spewed into the cosmos provided an unprecedented test of general relativity and insight into the progenitor stars that subsequently formed into the colliding black holes. However, the hunt is far from over. With LIGO’s second observing run underway, we can look forward to many more gravitational-wave signals, and as is true with any new mechanism for studying the cosmos, we can also expect to find the unexpected.

The extreme sensitivity required to make such detections was acquired through decades of developing methods and machinery to isolate the sensitive components of LIGO from non-gravitational-wave disturbances. Nonetheless, as a noise-dominated experiment, LIGO is still susceptible to Continue reading

Tails from Eccentric Encounters

by Nicholas Loutrel.


loutrel-pic

Nicholas Loutrel is a Graduate Student in the eXtreme Gravity Institute at Montana State University.

A new method of computation aims to fill in the gaps in our knowledge of gravitational waves from eccentric binaries.

The modeling of gravitational waves (GWs) suitable for detection with ground-based detectors has been mostly focused on binary systems composed of compact objects, such as neutron stars (NSs) and black holes (BHs). Binaries that form with wide orbital separations are expected to have very small orbital eccentricity, typically less than 0.1, by the time their GW emission enters the detection band of these instruments. However, in dense stellar environments, unbound encounters between multiple compact objects can result in the formation of binaries with high orbital eccentricity (close to, but still less than unity) and whose GW emission is in band for ground-based detectors. Such systems are expected to be Continue reading

Pulsed Gravitational Waves

timothyjwalton

Timothy J. Walton occupies some quantum state between a physicist and a mathematician, having obtained his PhD from the physics department at Lancaster University in 2008 but now masquerading as a lecturer in mathematics at the University of Bolton.

by Timothy J. Walton.


Applying techniques from classical electrodynamics to generate new gravitational wave perturbations

I must begin with a confession: I don’t view myself as a gravitational physicist. Despite my PhD at Lancaster University involving a formulation of relativistic elasticity and an awful lot of differential geometry, my research thus far has been within the realm of classical and quantum electrodynamics. But it was precisely within that domain, along one particular avenue of investigation, where the first seeds of an idea were sown. Following my earlier work on a class of exact finite energy, spatially compact solutions to the vacuum source-free Maxwell equations – pulsed electromagnetic waves – describing single cycle pulses of laser light [1], together with Shin Goto at Kyoto University in Japan and my former PhD supervisor Robin Tucker at Lancaster University, a new question arose: “do pulsed gravitational waves exist?’’

As I recall, this question was posed and began to take root during one of the regular meetings I have with Robin. Within my institution, I am fortunate enough Continue reading

Pushing post-Newtonian theory even further!

by Tanguy Marchand, Luc Blanchet and Guillame Faye.


With the spectacular discoveries by the LIGO/VIRGO collaboration of gravitational waves from the coalescence of black-hole binaries, we foresee the possibility of extremely accurate measurements of the so-called post-Newtonian (PN) coefficients that describe the gravitational waveform of these systems in the inspiral phase prior to the final coalescence. The PN coefficients are especially important because they probe the non-linear structure of general relativity (GR) and provide thus very constraining tests of this theory. In turn, they permit accurate measurements of the physical parameters of the binary, essentially the mass of the compact objects and their moment of rotation or spin.


Continue reading

Tilting laser beams in LISA

by Michael Tröbs.


Michael Troebs in the lab

Michael Tröbs in the lab. Michael Tröbs is an experimental physicist at Max Planck Institute for Gravitational Physics (AEI). The LISA optical bench test bed was built in collaboration with Airbus DS and University of Glasgow. At AEI Michael is responsible for the project.

A testbed to experimentally investigate tilt-to-length coupling for LISA, a gravitational-wave detector in space.

The planned space-based gravitational-wave detector LISA will consist of three satellites in a triangle with million kilometer long laser arms. This constellation will orbit the Sun, following the Earth. LISA is expected to be laser shot-noise limited in its most sensitive frequency band (in the Millihertz range). The second largest contribution to the noise budget is the coupling from laser beam tilt to the interferometric length measurement, which we will call tilt-to-length (TTL) coupling in the following.

How does tilt-to-length coupling come about? Continue reading

OK, so what happens now?

Written by Michael Coughlin


The future of gravitational-wave astronomy after the first detection

Michael Coughlin is currently a post-doctoral fellow at Harvard University with Prof. Christopher Stubbs. In September 2016, he successfully defended his Harvard Physics PhD, titled "Gravitational-wave astronomy in the LSST era". He began researching gravitational waves with LIGO over eight years ago as a college freshman at Carleton College in Northfield, MN and it was very exciting for him to be part of LIGO’S historical confirmation in February 2016. At Harvard, he added the Large Synoptic Survey Telescope (LSST), Pan-STARRS, and ATLAS to his research areas, including designing and building a prototype calibration system, which he nicknamed "CaBumP". Coughlin dances on the Harvard ballroom dance team and enjoys the chaos of teaching 3rd and 4th graders in an after-school math and science program at a local elementary school.

Michael Coughlin is currently a post-doctoral fellow at Harvard University with Prof. Christopher Stubbs. In September 2016, he successfully defended his physics PhD at Harvard, titled “Gravitational-wave astronomy in the LSST era”. He began researching gravitational waves with LIGO over eight years ago as a college freshman at Carleton College in Northfield, MN and it was very exciting for him to be part of LIGO’s historical confirmation in February 2016. At Harvard, he added the Large Synoptic Survey Telescope (LSST), Pan-STARRS, and ATLAS to his research areas, including designing and building a prototype calibration system, which he nicknamed “CaBumP”.

Since LIGO announced the detection of gravitational waves from binary black hole mergers in its first observing run [1-2], the most common question I have received is “What was it like to be part of such a historic scientific discovery?” The second most common question has been: “So what happens now?” The answer is a lot of stuff! Here I’ll focus on three main goals:

  1. Using LIGO to detect other sources of gravitational-waves
  2. Improving the gravitational-wave detectors in order to probe farther into the cosmos
  3. Electromagnetic follow-up of gravitational-wave events with telescopes to get a more complete picture

What else does nature have in store for us?

The detection of gravitational waves from binary black hole mergers has been incredibly exciting, and we look forward to the detection of more such systems. Of course, there are many other sources (pulsars, supernovae, binary neutron stars, etc.) that we hope to detect as well. As a member of the group in LIGO searching for a stochastic background of gravitational waves, I am particularly interested in the processes that could create such a signal. This includes backgrounds from compact binary coalescences, pulsars, magnetars, or core-collapse supernovae. A cosmological background (such as from inflation!) could be generated by various physical processes in the early universe. In particular, with the recent discovery of binary black-hole mergers, there is a really good chance of observing a stochastic gravitational-wave background from these systems [3].

There are other sources that are likely to produce long-lived transients, including emission from rotational instabilities in proto-neutron stars and black-hole accretion disk instabilities. There is ongoing significant effort to improve Continue reading

LIGO’s gravitational wave detection is Physics World 2016 Breakthrough of the Year

by Clifford M Will.


Physics World breakthrough of the year prize

The Physics World 2016 Breakthrough of the Year goes to the LIGO Scientific Collaboration for their revolutionary, first ever direct observations of gravitational waves.

Long awaited direct detection of Einstein’s gravitational-waves tops Physics World’s list of the 10 key breakthroughs in physics in 2016

It give me great pleasure to report that the LIGO Scientific Collaboration are to receive Physics World’s Breakthrough of the year award.  At the end of every year, the Physics World editorial team reveals what it believes to be the top 10 research breakthroughs for the past year and one of these is selected to be the Physics World Breakthrough of the year.

In recognition of this achievement, the Physics World team have created a short documentary movie with the assistance of members of the LIGO collaboration from Cardiff University.

The video features Samantha Usman, who recently wrote an excellent CQG+ entry about the discovery.
Continue reading

“There’s no way it’s real”

Written by Samantha Usman, who is currently pursuing an MPhil at Cardiff University, UK under the supervision of Prof. Stephen Fairhurst. She graduated in May 2016 with a BS in Mathematics and Physics at Syracuse University. While at Syracuse, Usman worked with Prof. Duncan Brown on improving LIGO’s sensitivity to gravitational waves from binary star systems. In her spare time, Usman trains in Brazilian jiu jitsu and Muay Thai kickboxing and enjoys walks with her Australian Shepherd, Marble.


The discovery of gravitational waves from an undergraduate’s perspective

Author Samantha Usman training for competition in Brazilian jiu jitsu.

Author Samantha Usman training for competition in Brazilian jiu jitsu.

The first time I learned LIGO might have detected a gravitational wave, I was listening in on a conference call on September 16, 2015. Two days earlier, ripples in the fabric of space from massive black holes crashing into each other at half the speed of light had passed through the Earth. The LIGO detectors picked up these faint changes in the length of space, but they pick up all sorts of extra noise that you’d never expect; how could we be sure this was really a gravitational wave?

On September 16th, I was an undergraduate starting my senior year at Syracuse University. I’d been doing LIGO research with my advisor, Prof. Duncan Brown, for almost two and a half years. Since LIGO had yet to start an observing run, my research had been focused on testing improvements to the codes that we use to search for gravitational waves. I’d been told in those two and a half years that it would take a few years to get our detectors to design sensitivity and not to expect a detection until I was well into graduate school.

So when I sat in my boss’ office listening to a colleague in Germany say he thought we’d really seen something, I rolled my eyes and muttered, “There’s no way it’s real.” I was convinced people were Continue reading

CQG+ Insight: Spectral Cauchy Characteristic Extraction of strain, news and gravitational radiation flux

Written by Casey Handmer, a postdoctoral scholar at the California Institute of Technology. Bela Szilagyi is a researcher at NASA’s Jet Propulsion Laboratory. Jeffrey Winicour is a professor at the University of Pittsburg. Find out more on their group website at www.black-holes.org.


Casey Handmer (postdoctoral scholar at Caltech), Bela Szilagyi (researcher at JPL) and Jeffrey Winicour (professor at Pittsburg) reprise their former stance discussing asymptotically time-like inertial scri+ foliations, now with even better CGI. Image credit: Photo manipulation by Annie Handmer, background image by SXS Collaboration: Andy Bohn et al 2015 Class. Quantum Grav. 32 065002.

Casey Handmer (Caltech), Bela Szilagyi (JPL) and Jeffrey Winicour (Pittsburg) reprise their former stance discussing asymptotically time-like inertial scri+ foliations, now with even better CGI. Image credit: Photo manipulation by Annie Handmer, background image by SXS Collaboration: Andy Bohn et al 2015 Class. Quantum Grav. 32 065002.

Gravitational waves were detected in 2015. GW150914 wiggled LIGO’s mirrors and shook the whole world, except perhaps Stockholm. The opening paragraph of our previous CQG+ article was rendered obsolete:

“Colliding black holes create powerful ripples in spacetime. Of this we are certain. Directly detecting these ripples, or gravitational waves, is one of the hardest unsolved problems in physics.”

That article presented the evolution algorithm that simulates gravitational waves from compact object binaries in computational general relativity. The evolution algorithm is the powerful engine that drives the present work: extraction of all radiative energy-momentum flux in addition to the usual strain and gravitational news.

How did this come about? At APS April 2014, my coauthor Bela and I were approached by Jeffrey Winicour: Bela’s doctoral advisor and, we learned, a referee of our first paper. He excitably described how we could use our evolution algorithm to compute the gravitational wave flux. I schemed to co-opt all other possible referees in the same way.

What is the flux? The ten Poincaré symmetries of asymptotically flat spacetime generate respective conserved Noether momenta: linear momentum, angular momentum, energy, and three boost momenta corresponding to Lorentz transforms. Supertranslations, a possible solution to the Firewall Paradox, also generate momenta that are calculated using this method.

Along the way we discovered a number of surprises. Did you know that spherical foliations of future null infinity in inertial coordinates are actually asymptotically time-like? Read more in our CQG paper.


Read the full article in Classical and Quantum Gravity:
Spectral Cauchy characteristic extraction of strain, news and gravitational radiation flux
Casey J Handmer et al 2016 Class. Quantum Grav. 33 225007


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Inspiral into Gargantua; where science meets science-fiction

Niels Warburton from the Massachusetts Institute of Technology shares an insight into his latest work with Sam Gralla and Scott Hughes published in Classical and Quantum Gravity.


Niels Warburton

Niels Warburton is a Marie Curie postdoctoral fellow currently working at the Kavli Institute for Astrophysics and Space Research at the Massachusetts Institute of Technology. He works on calculating gravitational waveforms from the capture of compact objects by black holes ranging from hundreds to millions of solar masses. Outside of research he often encounters other types of waves on the waters around Boston where he is a keen sailor. Niels co-authored the article recently published in CQG with Sam Gralla of the University of Arizona and Scott Hughes at the Massachusetts Institute of Technology.

The first merging black holes recently detected by LIGO were strange objects indeed. Torturing reality so that even light cannot escape from their interiors, as they whirled around each other at over half the speed of light, the disturbances they induced in space and time propagated outwards as gravitational waves. The measured characteristic chirp, an upsweep in frequency and amplitude of the waves, signaled that the two black holes had merged into a single, larger black hole. Amazingly, though this remnant was more than sixty times as massive as our sun it could be described by just two numbers – its mass and its spin. This is an unusual property for any macroscopic object as they usually require Continue reading