GWSkyNet, developed by [1], is a machine learning classifier designed to facilitate potential EM follow-up observations. It is capable of separating astrophysical events and instrumental artifacts. GWSkyNet can be operated in low-latency and provide, in seconds after an alert is published, information complementary to that released by the LIGO-Virgo-KAGRA (LVK) via the open public alerts (OPA).
The current classifier needs only the publicly available information from the OPA system. However, it can be expanded easily to intake other properties of a GW candidate. Of the 77 OPA* alerts published during O3, GWSkyNet has correctly classified 61, showing great scientific potential.
In preparation of O4, GWSkyNet is currently being developed as a low-latency annotation pipeline. It will be incorporated into the LVK low-latency framework. Another independent and separate pipeline with GWSkyNet, planned to run on the Treasure Map [2], is also being developed.
The success of GWSkyNet has motivated the development of an extension to a multi-class classifier, known as GWSkyNet-Multi [3], which is capable of determining whether the source of an OPA contains a neutron star. It has correctly classified 64 of 77 OPAs correctly for O3.
* In total, 80 OPAs were released during O3, but GWSkyNet was only applied to OPAs with FITS files generated with Bayestar [4, 5].
This workshop brings together experts on gravitational wave astronomy, multi-messenger astronomy with gravitational waves and machine learning to explore possible paths for the further development of GWSkyNet beyond O4, as well as novel applications of machine learning techniques to the study of gravitational waves. In particular, the workshop will have a focus on electromagnetic follow-up observations of gravitational wave events. This workshop will be more discussion-focused where attendees are encouraged to participate in a series of related discussions related and to come up with new ideas.
This workshop is generously supported by the McGill Space Institute, the University of British Columbia, and the New Frontiers in Research Fund. Thanks to this funding, there will not be a registration fee for this workshop, but registration by May 18th is highly encouraged. The registration form is available near the top of the page. Coffee, breakfast and lunch will be provided on June 2nd and 3rd, and a dinner on June 2nd. Attendees are responsible for their travel expenses and accommodations.
For any questions or concerns, please do not hesitate to contact Mervyn Chan at mervync[at]phas.ubc.ca
PHAS Assistant Professor Dr. Jess McIver, was appointed Tier 2 Canada Research Chair in Gravitational Wave Astrophysics. Twenty-two UBC researchers were appointed as new and renewed Canada Research Chairs in the latest round of appointments announced on January 12, 2022. The new and renewed UBC chairholders being announced represent an investment of $19.5 million through the Canada Research Chairs program.
Jess’ research involves working with the Laser Interferometer Gravitational-wave Observatory (LIGO) in measuring the ripples in spacetime produced by gravitational waves. She recently received funding from the federal New Frontiers in Research Fund (NFRF) 2020 Exploration Stream to employ a novel machine learning approach to leverage information reported by LIGO-Virgo to identify kilonovae events, and from the BC Knowledge Development Fund (BCKDF) to provide critical infrastructure to support scientific collaboration in gravitational waves detection.
About the Canada Research Chairs Program
This year, the Canada Research Chairs Program is investing more than $151 million to support 188 new and renewed Canada Research Chairs at 43 institutions. The Canada Foundation for Innovation (CFI), a partner with the Canada Research Chairs Program, will invest more than $9.5 million to support 43 chairholders at 19 institutions across the country through its John R. Evans Leaders Fund for the cutting-edge labs and equipment they need to pursue their important work.
The Canada Research Chairs Program enables Canadian universities to achieve the highest levels of research excellence and become world-class research centres. Chairholders improve our depth of knowledge and quality of life, strengthen Canada’s international competitiveness, and help train the next generation of highly skilled people through student supervision, teaching and the coordination of other researchers’ work.
“The Canada Research Chairs announced this week comprise the full diversity of Canada, both in terms of their backgrounds and training, as well as the broad range of disciplines they represent,” says Ted Hewitt, Chair of the Canada Research Chairs Program Steering Committee. “This, in turn, helps to drive the research excellence we have come to expect from these outstanding scholars, as well as their contributions to the well-being and prosperity of Canadians.”
A global team of scientists, including researchers at the University of British Columbia (UBC), have detected thirty-five new gravitational wave events, including colliding black holes and neutron stars. The new events, detailed in today’s paper, bring the total number of observed events to 90 since the first detection of gravitational waves in 2015.
Gravitational waves are tiny ripples in the fabric of spacetime that carry information about the movement of massive objects in the Universe, like black holes and neutron stars. “As the number of detections grows, we can learn more about these objects, including how massive they are when they form, how quickly they are spinning, and how far from Earth they are,” says Alan Knee, a UBC doctoral student in astronomy, who contributed to the analysis of the events. “In doing so, we can better understand how they form and evolve.”
The catalogue and three companion papers, published on arXiv and soon to appear in Physical Review X and other journals, updates the list of all gravitational-wave events observed to date, using three international detectors: the two Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors in Louisiana and Washington state in the US, and the Advanced Virgo detector in Italy.
This diagram shows the estimated masses of all known dead stars, as measured by telescopes and by gravitational waves. The dead stars observed with telescopes (black holes in red and neutron stars in yellow), are all within or very near our own Milky Way galaxy. The dead stars observed with gravitational waves (black holes in blue and neutron stars in orange) are mostly very distant – some were detected billions of light years away! Objects in the “mass gap” between neutron stars and black holes, where there are few definitive measurements, are marked as half blue and half orange. (Credit: Aaron Geller/ Northwestern/ LIGO-Virgo-KAGRA)
Data taken during the last half of the most recent observing run (November 2019 to March 2020) have been analysed by scientists from the LIGO Scientific Collaboration, the Virgo Collaboration and the Kamioka Gravitational Wave Detector (KAGRA) collaboration. Of the 35 events detected, 32 were most likely to be black hole mergers, where two black holes spiral around each other and finally crash together, emitting a burst of gravitational waves.
The black holes have a wide range of masses, with the most massive around 90 times the mass of our sun. Several of the resulting black holes that formed from these mergers exceed 100 times the mass of our sun and are classed as intermediate-mass black holes. Black holes of this mass were only predicted theoretically before LIGO-Virgo’s latest observing run, and have been proven to exist thanks to gravitational wave observations.
“These catalogues are hotly anticipated by astrophysicists because with enough detections we can start to see patterns,” says co-author Dr. Jess McIver, assistant professor of physics and astronomy at UBC, who led the data quality sections of the analysis. “One detection of a new type of source is a discovery, two is confirmation, and the more we observe, the better we can measure how common or rare newly observed objects like intermediate mass black holes are.”
Two of the 35 events spotted were likely to be neutron stars and black holes merging – a much rarer event, and one that was only discovered in the most recent observing run of LIGO and Virgo. The masses of black holes and neutron stars are clues to how massive stars live their lives and die in supernova explosions.
“It is exciting to find more surprising gravitational wave sources that help reveal what is happening in some of the most cataclysmic astrophysical events. Our measurements offer a unique probe that would otherwise be invisible to scientists,” says Dr. Evan Goetz, research associate in physics and astronomy at UBC, who contributed to calibrating and characterizing the LIGO data for astrophysical analysis.
This calendar shows all gravitational wave events detected by LIGO and Virgo so far, starting from the first observing run (O1), through this latest catalog release of the last half of the most recent observing run (O3b). (Credit: Carl Knox/ OzGrav/ Swinburne University of Technology)
Of these rare neutron star and black hole mergers, one event shows a massive black hole (about 33 times the mass of our sun) with a very low-mass neutron star (about 1.17 times the mass of our sun). This is one of the lowest-mass neutron stars ever detected, including by radio astronomers using data from observatories like the Canadian Hydrogen Intensity Mapping Experiment (CHIME).
Dr. Christopher Berry, a lecturer at the University of Glasgow, explains: “Only now are we starting to appreciate the wonderful diversity of black holes and neutron stars. Our latest results prove that they come in many sizes and combinations—we have solved some long-standing mysteries, but uncovered some new puzzles too. Using these observations, we are closer to unlocking the mysteries of how stars, the building blocks of our Universe, evolve.”
One notable gravitational wave event in the new catalogue came from two objects merging, one almost certainly a black hole and the other either a very light black hole or a very heavy neutron star of around 2.8 times the mass of our sun. The mass of the lighter object is puzzling, as scientists expect that the most massive a neutron star can be before collapsing to form a black hole is around 2.5 times the mass of our sun. Observations with electromagnetic radiation have revealed an apparent ‘mass gap’ between the lightest black holes and the heaviest neutron stars, where objects seem to be missing, says Alan Knee. “The two new objects provide further insight into this elusive mass gap, and highlight the role that gravitational waves will play in studying these exotic phenomena.”
Einstein’s predictions are still right
Identifying signals in the detector data requires careful analysis to distinguish real gravitational waves from noise. UBC researchers played a crucial role in this area, identifying data anomalies with the potential to make the data appear inconsistent with Einstein’s theory of general relativity that were actually detector noise. “Careful understanding of noise is crucial for such complex detectors, especially when we’re conducting very sensitive measurements,“ says Dr. McIver. “As the detectors improve, we’ll keep looking for signs of new physics, but so far Einstein’s predictions are still right!”
UBC developing new quantum materials to improve detectors
Gravitational wave detectors operate by using high power lasers to carefully measure the time taken for light to bounce between mirrors. In the third observing run, the gravitational wave detectors reached their best ever performance thanks to a program of upgrades and maintenance.
One such upgrade in future will be the use of new materials for optical coatings, to expand the reach of the detectors. A team of researchers at the Stewart Blusson Quantum Matter Institute is working to develop these materials, which will allow LIGO scientists to not only identify more distant events but also to observe them in sharp detail, says Dr. Kirsty Gardner, postdoctoral research fellow at the Institute. “Improved detectors will unlock a census of dead stars in our local Universe and new tests of Einstein’s relativity.”
For the first time, researchers have confirmed the detection of a collision between a black hole and a neutron star. In fact, the scientists – including those at the University of British Columbia – detected not one but two such events occurring just ten days apart in January 2020. The extreme events made splashes in space that sent gravitational waves rippling across 900 million light-years to reach Earth. In both cases, the neutron star was likely swallowed whole by its black hole partner.
Artwork of a neutron star–black hole merger. Credit: Carl Knox, OzGrav-Swinburne University.
Gravitational waves are disturbances in the curvature of space-time created by massive objects in motion. During the five years since the waves were first measured, a finding that led to the 2017 Nobel Prize in Physics, researchers have identified more than 50 gravitational-wave signals from the merging of pairs of black holes and pairs of neutron stars. Black holes and neutron stars are both the corpses of massive stars, with black holes being even more massive than neutron stars.
Results from the new study were published today in The Astrophysical Journal Letters. The gravitational waves were detected by the National Science Foundation’s (NSF’s) Laser Interferometer Gravitational-Wave Observatory (LIGO) in the United States and by the Virgo detector in Italy.
The first merger, detected on Jan. 5, 2020, involved a black hole about nine times the mass of our sun, or nine solar masses, and a 1.9-solar-mass neutron star. The second merger was detected 10 days later on Jan. 15, and involved a six-solar-mass black hole and a 1.5-solar-mass neutron star.
Astronomers have spent decades searching for neutron stars orbiting black holes in the Milky Way, our home galaxy, but have found none so far. These extragalactic events are our first confident detection of these systems.
“These detections offer valuable insight into how often neutron star-black hole mergers occur in our region of the Universe, as well as how these systems form,” said co-author Yannick Lecoeuche, a master’s student at UBC physics and astronomy.
The first of the two events, GW200105, was detected as a strong signal by the LIGO detector in Livingston, Louisiana, while the Virgo detector was also observing. Given the nature of the gravitational wave signal, the team inferred that the source was a black hole colliding with a 1.9-solar-mass compact object, later identified as a neutron star, 900 million light-years from Earth.
“It’s exciting to see how gravitational waves emitted in just the last few seconds of these neutron star black hole mergers can give us information about where these stellar remnants might have come from and how they might have been formed, helping us to constrain their histories over millions of years,” said co-author Nayyer Raza, a master’s student at UBC physics and astronomy.
Because the signal was strong in only one detector, the location of the merger on the sky remains uncertain, lying somewhere in an area that is 34,000 times the size of a full moon.
The UBC LIGO team played a major role in LIGO data quality investigations, LIGO-Virgo candidate event validation, and LIGO data calibration, which is used to infer the true nature of the source.
“Building confidence that a candidate signal is truly astrophysical is especially important for discoveries of new sources of gravitational waves,” said co-author Dr. Jess McIver, an assistant professor at UBC physics and astronomy. “This discovery was a tricky case – we needed to remove glitches from the LIGO Livingston detector data before analyzing the signal. But GW200105 was a strong signal, and we can be confident it originated from the merger of a black hole and a neutron star.”
The second event, GW200115, was detected by both LIGO detectors and the Virgo detector. GW200115 comes from the merger of a black hole with a 1.5-solar mass neutron star that took place roughly 1 billion light-years from Earth. Using information from all three instruments, scientists were better able to narrow down the part of the sky where this event occurred. Nevertheless, the localized area is almost 3,000 times the size of a full moon.
Astronomers were alerted to both events soon after they were detected in gravitational waves and subsequently searched the skies for associated flashes of light. They found none but this is not surprising due to the very large distance to these mergers, which means that any light coming from them, no matter what the wavelength, would be very dim and hard to detect with even the most powerful telescopes. Additionally, researchers think that the mergers did not give off a light show because their black holes are big enough to have most likely swallowed the neutron stars whole.
Having confidently observed two examples of gravitational waves from black holes merging with neutron stars, researchers now estimate that, within one billion light-years of Earth, roughly one such merger happens per month.
The UBC LIGO team, working with the Stewart Blusson Quantum Matter Institute at UBC, is also researching new thin materials for gravitational wave detector mirror coatings that would allow instruments like LIGO and Virgo to sense much further into space.
“Mirror coatings on the current LIGO detectors represent one of the largest sources of noise and actually limit our ability to detect these types of neutron star – black hole collisions,” said David Dvorak, a research technician at Blusson QMI. “We are working on developing the next generation of mirror coatings which will, like a new pair of glasses, allow us to see both further and with greater clarity.”
Artist’s illustration of a merging black hole and neutron star. Credits: LIGO-India/Soheb Mandhai
Numerical-relativity simulation: S.V.Chaurasia (Stockholm University), T. Dietrich (Potsdam University and Max Planck Institute for Gravitational Physics). Scientific visualization: T. Dietrich (Potsdam University and Max Planck Institute for Gravitational Physics), N. Fischer, S. Ossokine, H. Pfeiffer (Max Planck Institute for Gravitational Physics), T. Vu.
PHAS recipients of the NFRF. L-R: David Jones, Jess McIver, Joerg Rottler, and Jeff Young.
UBC Physics & Astronomy researchers David Jones, Jess McIver, Joerg Rottler, and Jeff Young have been awarded the federal New Frontiers in Research Fund (NFRF) 2020 Exploration Stream. This funding, each in the amount of $250K, will support high-risk, high-reward and interdisciplinary research. Their three projects are among the 7 projects awarded at UBC, and 117 projects awarded across Canada. Their projects will have potentially game-changing impacts in mining, machine learning, and event detection in astrophysics.
“Research that takes great risks advances the way we think about the issues that impact Canadians,” said the Honourable François-Philippe Champagne, Minister of Innovation, Science and Industry. “The Government of Canada is supporting researchers who are exploring bold new directions that could change lives and position Canada at the forefront of global research and innovation.”
Prof. Jess McIver, leader of the UBC gravitational-wave astrophysics group and the UBC LIGO Scientific Collaboration group, will lead an interdisciplinary project that harnesses the power of machine learning to search for electromagnetic counterparts to gravitational wave events, in partnership with Canadian astronomers Prof. Maria Drout and Prof. Daryl Haggard:
First Light: Unleashing Machine Learning for Multi-Messenger Discovery
Principal Investigator: Jess McIver
Co-applicants: MariaDrout (University of Toronto); Daryl Haggard (McGill University)
In a game-changing 2017 discovery, gravitational waves (GWs) were observed in concert with light for the first time. A burst of gamma-rays was observed within seconds of a GW signal from the merger of two neutron stars, but the glow of the resulting “kilonovae” explosion was not detected until nine hours later. The project will employ a novel machine learning (ML) approach to leverage information reported by LIGO-Virgo to identify kilonovae events. Understanding the complete evolution of kilonovae will unlock new insights into some of the most important outstanding questions about our Universe, including the structure of extremely dense matter and the origin of heavy elements like gold. In addition to advancing AI methods, we will enable Canadian telescope assets located around the world to swiftly slew toward a true astrophysical GW signal, reject noise events, and unlock the potential for new cosmic discoveries led by Canadian astronomers.
More about NFRF
The New Frontiers in Research Fund (NFRF) 2020 Exploration competition has awarded funds to support 117 research projects across Canada that bring diverse disciplines together in pursuit of breakthrough ideas and high-reward outcomes. The NFRF program, a federal research funding initiative, mobilizes cutting-edge interdisciplinary, international, and transformative research that strengthens Canadian innovation and benefits Canadians.
The fund’s Exploration stream specifically targets interdisciplinary, high-risk, high-reward research that defies current models, bridges disciplines in novel ways, or tackles fundamental problems from new perspectives. The stream’s design recognizes that interdisciplinary research is often risky, but worthwhile given the potential for significant groundbreaking impact. All funded teams must demonstrate commitment to equity, diversity and inclusion in the research environment.
The Killam Postdoctoral Fellow Research Prize is awarded annually for excellence in research. Established in 2011, the Killam PDF Prize is in memory of Izaak Walton Killam and his wife, Dorothy Johnston Killam, who together created the Killam trusts. Two prizes in the amount of $5,000 each are awarded to full-time Postdoctoral Fellows at UBC in recognition of outstanding research and scholarly contributions while at UBC.
Miriam is recognized for her work in developing a new machine learning approach to distinguish between gravitational wave (GW) signals and detector noise. “This revolutionizes multi-messenger astrophysics by increasing the discovery likelihood of kilonova GW-counterparts, unlocking the origin of heavy elements, the rate of expansion of the Universe, and the physics of extremely dense matter,” according to her award citation.
In addition to her research achievement, Miriam is also known for her equity and inclusion work in the department; she is currently the Equity and Inclusion in PHAS Coordinator. She has also served as the VP Operations (2020 – 2021) for the UBC Postdoctoral Association.
“Receiving the Killam Postdoctoral Fellow Research Prize is a great honour and I am extremely grateful for this recognition,” said Miriam. “This prestigious award is an inspiring achievement for my research that will expand my career opportunities in Canada. It is encouraging that my work has been selected as a highlight of outstanding research at UBC and it provides a much needed confidence boost.”
The other recipient of the 2020 Killam Postdoctoral Fellow Research Prize is Dr. Ryan Hoiland from the Faculty of Medicine.
A schematic of estimated masses of black holes and neutron stars measured with electromagnetic radiation (yellow, purple) and gravitational waves (orange, blue). Image credit: Frank Elavsky, Aaron Geller, Northwestern University
(via UBC News) The LIGO-Virgo Collaboration, including UBC Department of Physics & Astronomy researchers, has confirmed 39 new gravitational wave event detections, more than quadrupling the total known gravitational wave events from 11 to 50.
The results, published in four papers on arXiv, and soon to appear in Physical Review X and other journals, were collected from the first half of the most recent LIGO-Virgo observing run, O3. The two LIGO detectors in the U.S. and the Virgo detector in Italy gathered the data from April to October 2019.
Gravitational waves are tiny ripples in the fabric of spacetime that carry information about the movement of massive objects in the Universe, like black holes and neutron stars.
The results feature what may be the first gravitational-wave observation of a neutron star colliding with a black hole, black holes spinning faster than ever before measured, and black holes with spin that likely doesn’t align with their orbit.
“From these results, we’re starting to see hints that there may be a population of black holes that form orbiting pairs after stellar collapse,” said LIGO team member Jess McIver, an assistant professor in the department of physics and astronomy at UBC. “Now that we’re beginning to see the true picture of black hole populations with gravitational waves, clearly we still have a lot to learn about how stars live and die.”
McIver and her research lab are involved in leading the LIGO detector characterization effort, which distinguishes between true gravitational wave signals and the detector noise quirks that can mask or mimic them. Data recalibration, conducted in part by UBC research associate Evan Goetz, also reveals more distant gravitational wave sources.
“Data from LIGO and Virgo has to be processed and analyzed very carefully to confirm new and varied gravitational wave signals coming from many different astrophysical events,” said Goetz. “We calibrate the data and characterize noise sources, which requires us to understand all the strange ways noise can impact our analyses. Without this careful, patient understanding, we might otherwise miss these signals.”
The improved data quality and calibration allowed LIGO-Virgo researchers to conduct improved tests of Einstein’s theory of general relativity with the recovered gravitational wave signals – with all results so far consistent with Einstein’s predictions.
The increase in detections is due in part to a significant improvement in detector sensitivity in O3. Relative to the prior observing run, O2, the median detector sensitivity, averaged over LIGO and Virgo, increased by over 60 percent.
“That increase in detector reach translates to a huge improvement in the observed volume and rate of gravitational wave detections,” said McIver.
Data from the second half of the O3 observing run is still being analyzed. Gravitational wave discoveries reported from O3 have included a few surprises, including the first definitive measurement of an intermediate mass black hole – between stellar-mass black holes that form from collapsed stars and supermassive holes at the centers of galaxies. A ‘mystery compact object’ was also observed between the lowest mass scientists have measured for a black hole and the highest mass we would expect for a neutron star, an extremely dense core of a dead star. The second detection of gravitational waves from a binary neutron star merger, revealed a potentially new extra-galactic population of neutron stars orbiting each other.
The LIGO and Virgo detectors are currently undergoing upgrades to prepare for the next observing run, O4.
Read more
The results are reported in a series of four papers published on the arXiv:
Mark Myers, ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav)
An international team of researchers, including scientists with the University of British Columbia’s gravitational wave astrophysics group, has detected a signal from the most massive black hole merger yet observed. The discovery, outlined in papers published today in Physical Review Letters and The Astrophysical Journal, raises a slew of new questions about the nature of black-hole formation, and upends previously held theories about how big holes can get.
On May 21, 2019, the Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors in the U.S. and the Virgo interferometer in Italy picked up the signal of a gravitational wave—a ripple in the curvature of spacetime caused by a cataclysmic cosmic event. The signal, named GW190521, was shorter in duration, and peaked at a lower frequency, than any other binary black hole merger observed to date.
Analysis of the data revealed that the 0.1-second signal came from the merger of two black holes—the first about 85 times as massive as the sun, and the second measuring about 65 times the sun’s mass. The spectacular smash-up created an even more massive black hole, of about 142 solar masses, along with an enormous amount of energy equivalent to around 8 solar masses, that was shot across the universe in the form of gravitational waves.
“When I first saw the shape of this signal I was a bit worried. It looked quite similar to common LIGO detector noise,” said co-author Jess McIver, assistant professor of physics and astronomy, who leads UBC’s gravitational wave astrophysics group and the international LIGO Detector Characterization team. “But as we analyzed it and saw how consistent the data between the detectors, and as we worked through all of our environmental sensors and our usual checks to make sure that there was nothing that could have possibly propagated across the earth that might mimic this, we were able to confirm it.”
GW190521 was generated by a source that is about 5 gigaparsecs away, or about 17 billion light years from Earth, making it the most distant gravitational-wave source detected so far. The source has a red shift of 0.8, meaning that since the gravitational waves were first produced, the universe has expanded by a factor of 1.8, almost doubling in size.
A cosmic holy grail
The discovery of GW190521 means that scientists have detected what, for many years, has been considered an astronomical holy grail: an intermediate mass black hole, larger than a stellar-mass black hole and smaller than a supermassive black hole.
All of the black holes observed prior to this discovery fit within either of two categories: stellar-mass black holes, which measure tens of solar masses and are thought to form when massive stars die; or supermassive black holes, such as the one at the center of the Milky Way galaxy, that have masses from hundreds of thousands to billions of times that of our sun. In the case of GW190521, the final 142-solar-mass black hole lies within an intermediate mass range between stellar-mass and supermassive black holes.
To find GW190521, McIver’s group had to analyze mountains of data to confirm its astrophysical nature. For previously reported gravitational-wave merger events, the LIGO and Virgo detectors registered many cycles of the compact objects orbiting each other in space before colliding. However, GW190521 is so heavy that its signal rose above the lowest sensitive frequencies of the detectors only tenths of a second before coalescence, making it much harder to distinguish from transient noise in the LIGO and Virgo detectors, which can also appear as short bursts in the data.
In a previous paper, UBC postdoctoral fellow Dr. Miriam Cabero Mueller investigated an insidious source of glitches in the Advanced LIGO detectors that don’t register in environmental or detector sensors and tend to have a very similar morphology to high mass signals like GW190521. Researchers at UBC and around the world have leveraged this improved understanding of glitches and their properties in order to extend the reach of searches for gravitational waves further into deep space.
“We have to establish a high level of confidence in this discovery, since this is the first time a system like this has been observed,” said Evan Goetz, research associate at UBC who has worked with LIGO for 15 years. “We find that GW190521 is the first conclusive observation of an intermediate mass black hole. In order to make a confident detection, we need a deep understanding of LIGO and Virgo noise sources that could mimic a signal like this.”
What’s more, the two progenitor black holes that produced the final black hole are so massive that scientists suspect they may not have formed from a collapsing star, as most stellar-mass black holes do. According to the physics of stellar evolution, stars between 60 and 130 times the mass of the Sun—a range that is known as the pair instability mass gap—are predicted to die in a pair instability supernova, in which the star completely blows apart with no black hole remaining.
“The fact that we’re seeing a black hole in this mass gap will make a lot of astrophysicists scratch their heads and try to figure out how these black holes were made,” said Virgo member Nelson Christensen, director of the Artemis Laboratory at the Nice Observatory in France.
LIGO/Caltech/MIT/R. Hurt (IPAC)
More questions than answers
These findings may indicate that massive stars can collapse into high-mass black holes after all—or whether a cascade of black hole mergers has occurred. One possibility proposed by the researchers is that is of a hierarchical merger, in which the two progenitor black holes themselves may have formed from the merging of two smaller black holes. The two black holes may also have formed in separate systems before migrating together and eventually merging.
Scientists are also considering the possibility that GW190521 isn’t from a binary black hole merger at all. As LIGO and Virgo detectors listen for gravitational waves passing through Earth, automated searches comb through the incoming data for interesting signals. These searches can use two different methods: algorithms that pick out expected wave patterns in the data produced by compact binary systems; and more general “burst” searches, which essentially look for any signal that stands out above detector noise.
In the case of GW190521, it was the burst searches that picked up a slightly clearer signal, opening the small chance that the binary event has previously unobserved properties that are not well described by current models—or even that the gravitational waves arose from something other than a binary merger.
Other sources for the signal put forward by the researchers include the possibility that the gravitational waves were emitted by a collapsing star in our galaxy. The signal could also be from a cosmic string produced as the universe inflated in its earliest moments. Or it could be the product of two (hypothetical) “primordial” black holes, formed in the Big Bang, and merging billions of years later.
“It’s just a really astounding discovery,” said McIver. “Not only is this going to change the way that we’re thinking about black holes, but it demonstrates the capacity for gravitational waves to discover new phenomena in the Universe that we can’t see with light.”
The gravitational wave research team at the University of British Columbia played a key role in the detection of GW190521. UBC assistant professor Dr. Jess McIver leads the international LIGO Detector Characterization team responsible for understanding noise in the LIGO detectors. Her team’s work allows searches for gravitational waves to make confident distinctions between extremely short high mass signals like GW190521 and common blips and glitches in detector data.
In a previous paper, UBC postdoctoral fellow Dr. Miriam Cabero Mueller investigated an insidious source of glitches in the Advanced LIGO detectors that don’t register in environmental or detector sensors and tend to have a very similar morphology to high mass signals like GW190521.
Miriam: “For heavy black holes mergers, current gravitational-wave detectors can only measure the final moments of the binary. Hence, the observable signal is very short. Blip glitches are a type of terrestrial detector noise of short duration, similar in shape to the signal from heavy black holes merging.”
Researchers at UBC and around the world have leveraged this improved understanding of glitches and their properties in order to extend the reach of searches for gravitational waves further into deep space. UBC students are also making key contributions to exciting results from LIGO and Virgo’s recent observing run, including current UBC student Robert Beda and recent alumni Katie Rink and Maryum Sayeed.
What are gravitational waves?
Gravitational waves are tiny ripples in the fabric of spacetime that carry information about the movements of massive objects in the Universe, like black holes.
Gravitational waves are a unique way to explore the dark, hidden Universe. Since their Nobel-prize winning discovery in 2015, researchers have used gravitational waves to begin mapping dead stars in nearby galaxies, measure the expansion of the Universe in new ways, and test Einstein’s relativity.
A recently released pre-print by the LIGO Scientific Collaboration and Virgo Collaboration reports the most sensitive test yet of the ellipticity of millisecond pulsars. Researchers in the gravitational-wave astrophysics group at UBC played a key role in new results for five known pulsars using data from the most recent LIGO and Virgo observing run.
“This result is very exciting because the detectors are finally sensitive enough for us to learn something new about the structure of these rapidly spinning neutron stars,” said Dr. Evan Goetz, a research associate at UBC and co-chair of the LIGO Scientific Collaboration continuous waves working group.
Neutron stars–the relic cores of massive stars–can be observed with light as “pulsars” when strong electromagnetic emission (radio waves, for example) sweeps across the Earth as the dead star spins, like a lighthouse.
Non-axisymmetric, rapidly spinning neutron stars are also predicted to emit continuous (persistent) gravitational waves as they rotate. These gravitational waves can allow scientists to measure deviations from axial asymmetry, or ellipticity, of spinning neutron stars. For example, a mountain on the surface of a neutron star could create such a deviation. Detection of continuous gravitational waves will allow us to infer how tall a mountain the crust of a neutron star could support, which will yield new insight on how the extremely dense matter of neutron stars is structured.
Observations of the pulsar light waves, like those collected by CHIME, can tell scientists how quickly the neutron stars are spinning, and how their spins change over time. Researchers can use pulsar data to accurately predict what the gravitational wave signal of a neutron star would look like, permitting more sensitive gravitational waves searches.
This is an artist’s impression of millisecond pulsar PSR J1023+0038 (white object on the right with magnetic field lines). It extracts matter from its companion star (red object on the left) via an accretion disk (also shown in red). Image credit: European Space Agency (ESA).
Millisecond pulsars are especially intriguing because they have likely undergone accretion from a binary companion at some point in their history. Accretion “spins up” the rotation to high levels–the fastest observed pulsar to date spins over 716 times in 1 second! Some theories predict that this process may introduce asymmetries.
This new paper reports updated search results for three millisecond pulsars as well as the slower spinning Crab and Vela pulsars. Although no signals were detected from these five pulsars, the results are the most sensitive to date. For the first time, the spin down limit of a millisecond pulsar was exceeded–a milestone achievement.
The spin down limit is the amount of gravitational wave energy that would need to be emitted in order to account for the very slow decrease in rotation speed observed in pulsars. The sensitivity of previous gravitational wave searches exceeded the spin down limit for a handful of isolated, more slowly spinning neutron stars (the Crab and Vela pulsars most notably). Millisecond pulsars are more interesting because their very rapid spin rate can be used to better test the physics of dense matter.
“We still don’t know that much about neutron star composition,” said Dr. Goetz. “Detecting continuous gravitational waves from even a single source would enable a host of discoveries and new understanding. This result brings us one step closer to those discoveries.”
What are gravitational waves?
Gravitational waves are tiny ripples in the fabric of spacetime that carry information about the movements of massive objects in the Universe, like black holes or neutron stars.
Gravitational waves are a unique way to explore the dark, hidden Universe. Since their Nobel-prize winning discovery in 2015, researchers have used gravitational waves to begin mapping dead stars in nearby galaxies, measure the expansion of the Universe in new ways, and test Einstein’s relativity.
An international team of astrophysicists, including researchers at UBC, have detected the ‘extremely loud’ merger of a black hole with a mystery compact object—the most asymmetric gravitational-wave source yet observed.
Artist’s impression of the merger of a black hole and a mystery compact object. Image credit: Carl Knox/OzGrav
GW190814, the merger of a heavy black hole with an unidentified compact object about nine times smaller, was reported today in Astrophysical Journal Letters.
When stars die, they can collapse into black holes or explode in a supernova that leaves behind dense, dead remnant star cores called neutron stars. For decades, astronomers have been puzzled by the observed gap between measured neutron star masses and black hole masses. Past observations that used light to measure black hole companions orbiting stars yielded neutrons stars with masses no more than 2.5 times our own Sun, and black holes with masses no less than five times that of our Sun. The question has remained: Could any stellar remnant could form in this ‘mass gap’?
The mass of the lighter compact object in the GW190814 system lies between 2.5 and three solar masses, placing it confidently within the ‘mass gap’. This makes it heavier than nearly every neutron star observation reported to date, or an unusually light black hole, consistent only with the remnant black hole from the binary neutron star merger observed in 2017, GW170817.
The heavier compact object in the GW190814 system had a mass of approximately 23 solar masses (23 times the mass of the Sun) and is consistent with the population of black holes observed by a network of gravitational wave detectors, including LIGO and Virgo.
The large asymmetry in masses modifies the gravitational-wave signal in such a way that enables scientists to leverage a fundamental prediction of Albert Einstein’s General relativity—that gravitational waves ‘ring’ at more than one fundamental frequency, so-called higher multipoles.
These harmonics in the gravitational wave signature allow researchers to better distinguish between the effect of the distance and the inclination of the orbit of the two objects relative to the Earth. Researchers estimate GW190814 occurred roughly 800 million lightyears away, 800 million years ago.
For some systems, astrophysicists are able to infer whether a compact object in a merger is a neutron star or a black hole by looking for a unique signature imprinted on the gravitational wave signal. For neutron stars, which are composed of extremely dense matter, the gravitational force exerted by its companion raises, similar to the ocean tides on Earth due to the Moon. However, for a system as massive and asymmetric as GW190814, the tidal imprint is too small to measure.
GW190814 is the most extreme mass-ratio merger observed so far, adding to the growing number of gravitational wave signals observed by the National Science Foundation’s Laser Interferometer Gravitational-Wave Observatory (LIGO) and the European Virgo detector. LIGO is a network of two gravitational wave detectors with four-kilometer arms located in Hanford, Washington and Livingston, Louisiana in the US. The three-kilometer Virgo detector is located in Cascina, Italy.
LIGO at UBC
A broad team of researchers at UBC are advancing gravitational wave science as part of the global LIGO Scientific Collaboration. Minkyun Noh, an assistant professor in the Department of Mechanical Engineering, and his lab are pursuing designs which will support quantum light squeezing in the planned LIGO A+ upgrade.
Researchers in the Quantum Matter Institute, including Curtis Berlinguette, Joerg Rottler, Jeff Young, Ke Zou and their labs, are developing new materials that will allow future gravitational wave detectors to sense far into deep space.
The GW astrophysics group at UBC, led by McIver, contributes to searches for gravitational wave signals from spinning neutron stars and recovering signals like GW190814 in addition to improving and calibrating the Advanced LIGO detectors.
What are gravitational waves?
Gravitational waves are tiny ripples in the fabric of spacetime that carry information about the movements of massive objects in the Universe, like black holes.
Gravitational waves are a unique way to explore the dark, hidden Universe. Since their Nobel-prize winning discovery in 2015, researchers have used gravitational waves to begin mapping dead stars in nearby galaxies, measure the expansion of the Universe in new ways, and test Einstein’s relativity.
Read a related paper about the search for an electromagnetic counterpart: A Deep CFHT Optical Search for a Counterpart to the Possible Neutron Star by Vieira et al, arXiv
The UBC gravitational wave astrophysics group joins the American Physical Society, the AAAS, the LIGO Scientific Collaboration, the journals Science and Nature, and the arXiv in participating in the strike organized on June 10, 2020.
Patrick Brady, the LIGO Scientific Collaboration spokesperson, said of the strike:
It’s a call to set aside our usual scholarly activities for a day to focus on the pervasive racism in our institutions, learn, and plan for a change in STEM and academia, while also providing a day of rest for our Black colleagues.
We devoted our working hours on June 10 to educating ourselves on anti-Black racism, discussing what we learned, and developing an anti-racism action plan for our research group. Please get in touch with us if you’d like to collaborate!
The UBC gravitational-wave astrophysics group has been researching remotely since March 16, 2020. Zoom and slack have been invaluable tools to keep us connected with each other and with our colleagues in the LIGO Scientific Collaboration, as well as Virgo and KAGRA.
Robert Beda, a UBC student studying Mathematical Physics, has remotely joined the group for the summer working on LIGO detector characterization research.
The UBC GW astro team holding a weekly group meeting on zoom.
The group congratulates members Katie Rink and Maryum Sayeed for graduating from UBC with their Bachelor’s degrees in June 2020! Katie will be continuing her work on detector characterization with the group through the summer and transition to a graduate program at UMass Dartmouth. Maryum will be using her physics and coding skills at a new job.
The UBC GWs astro group virtually celebrate’s Maryum’s last group meeting before starting her new job after graduation.
In response to the COVID-19 pandemic, LIGO and Virgo decided to suspend their third observing run (O3) roughly a month ahead of schedule. The observing run will end on March 27th instead of the original planned end date, April 30, 2020.
From a statement released by the LIGO Laboratory on ligo.caltech.edu:
In spite of the early suspension, the O3 run has been a tremendous success. We are grateful to everyone in the LIGO Lab, the LSC, and Virgo for their work during this very successful observing run, and we look forward to both bringing the results to publications as quickly as feasible, and getting back to work on the A+ upgrade.
Researchers in the UBC GW astrophysics team will continue their work from off-campus until the fall.
Group members Jess McIver, Evan Goetz, and student Katie Rink visited the LIGO-Livingston detector in Livingston, Louisiana for the LIGO Detector Characterization meeting and noise sprint in January 2020.
Jess led the meeting, which focused on plans for LIGO detector noise studies and supporting validation of event candidates in the remainder of the current LIGO-Virgo observing run, O3. and Katie and Evan participated in the noise sprint workshop, which matched junior researchers with mentors to tackle a series of LIGO detector characterization projects.
Astrophysicists including a team at UBC have observed gravitational waves from the collision of two black holes with distinctly different masses, dubbed GW190412. This discovery gives us a glimpse of subtle harmonics in gravitational wave signals for the first time. These harmonics not only allow improved tests of Einstein’s theory of general relativity, they also allow researchers to better resolve how far away black holes are and how fast they are spinning before merging.
A still frame from a numerical simulation of a black hole system similar to GW190412 that emits gravitational waves as it inspirals and merges into a larger black hole. Image credit: N.L. Fischer, H. Pfeiffer, MPI, SXS.
Gravitational waves are tiny ripples in the fabric of spacetime that carry information about the movements of massive objects in the Universe, like black holes. In 2016, the LIGO-Virgo collaboration announced the first direct detection of gravitational waves, and the first observation of two black holes orbiting each other. This system, detected in the two Advanced LIGO detectors on September 14, 2015, was composed of two black holes roughly 30 times the mass of our sun, that collided 1.4 billion light years away, released more than three solar masses of energy in a fraction of a second. In comparison, the newly discovered GW190412 was produced when black holes roughly 8 and 30 times the mass of our sun merged into a heavier black hole.
Several UBC researchers made critical contributions to the discovery of GW190412. Jess McIver, an assistant professor in Physics and Astronomy at UBC, co-leads the international LIGO Detector Characterization team responsible for data quality and verifying that events like GW190412 are truly astrophysical. “GW190412 is an exciting discovery,” said Jess. “Adding this one event to the ten previously known LIGO-Virgo binary black hole mergers tells us much more about how these systems form and evolve than we knew before.”
A broad team of researchers at UBC are advancing gravitational wave science as part of the global LIGO Scientific Collaboration. Minkyun Noh and his lab are engineering components that will support quantum light squeezing in the planned LIGO A+ upgrade. Researchers in the Quantum Matter Institute, including Curtis Berlinguette, Joerg Rottler, Jeff Young, Ke Zou and their labs, are developing new materials that will allow future gravitational wave detectors to sense far into deep space. McIver’s group contributes to searches for gravitational wave signals from spinning neutron stars and recovering signals like GW190412 in addition to improving and calibrating the Advanced LIGO detectors.
Evan Goetz, a research associate in McIver’s group, played a key role in calibrating the Advanced LIGO detector data for this discovery. “The high precision calibration of Advanced LIGO detector data allowed us to observe higher-order modes in a gravitational wave signal for the first time and perform additional tests of general relativity than we could for previously discovered signals,” said Evan.
Thursday: the McGill Space Institute.
Friday: the InterContinental Hotel Montreal, 360 Rue St-Antoine Ouest, Montreal
Internet connections
The following information is relevant for the Thursday sessions:
Wifi networks are available for attendees:
eduroam : accounts from attendees’ affiliated institutions will be needed.
guest.mcgill.ca: social network (Facebook, Google, etc.) accounts will be needed.
Discussion
On Thursday, the workshop will have a focus on discussion on topics that are related to multi-messenger astronomy with gravitational waves, especially electromagnetic follow-up observations and the applications of machine learning algorithm to gravitational wave astronomy. On Friday, we will have a joint session with the CIFAR Machine Learning Meeting. Please refer to the agenda for a list of discussion topics. If you would like to suggest topics for discussion during our discussion sessions, please also add them to the agenda.
The McGill Space Institute (MSI) is located at 3550 University Street, next to the Rutherford Physics Building. The front door is usually not locked from 9:00 am to 5:00 pm. But the door is heavy and sticks a little, a good pull may be needed before it will open.
Transportation:
The following options are available for travel from the airport to the MSI:
the STM 747 bus is the cheapest option at a $10 fare (see http://www.stm.info/en/info/networks/bus/shuttle/747-yul-montreal-trudeau-airport-downtown-shuttle). A ticket can be bought at the automated STM machine inside the airport with a debit or credit card, or on the bus but changes will not be available. Two route options are available:
Destination Terminus Lionel-Groulx
A single stop
Travel time from 25 to 35 minutes, depending on traffic
Get off the bus at Lionel-Groulx, and then take the subway (metro).
Travel time from 45 to 70 minutes, depending on traffic
Get off the bus, and then take the subway (metro).
Uber is also an option for going between the Montreal Trudeau Airport and McGill ($35-40, 30-45min).
Train: If taking a VIA rail train into Montreal Gare Central is preferred, McGill Campus is approximately a 15min walk north.
Metro: McGill campus is a block away from a Montreal Metro subway stop (Metro McGill on the Green Line), which is connected to most places in the city (but not to the airport).
Accommodation
All attendees are expected to arrange for their own accommodations. There are many hotels in downtown Montreal near the MSI. These include the Delta Hotel, Hotel Omni Mont-Royal, Sofitel Golden-Mile, and the Best Western Ville-Marie.
Food
Lunches will be provided on June 2nd and 3rd, and a formal dinner on June 2nd. But information about must-try food specialties in Montreal are given below in case attendees would like to explore Montreal prior and/or after the workshop:
Montreal-style bagels: Fairmount Bagel in Mile End and St-Viateur are the most famous. St-Viateur in some locations and Fairmount are open 24/7.
Montreal smoked meat sandwiches: Schwartz’s deli in the Plateau is the most famous. So famous that there is often a line. If the line is too long, the smoked meat sandwiches served right across the street at The Main deli are also just as good.
Poutine: the most famous is La Banquise in the Plateau. It is also open 24/7. But again a line often gathers outside. The Montreal Pool Room, Chez Claudette, and Poutineville are some other very classic spots.
Closer to McGill, other restaurant options for dinner: Lola Rosa (vegan), Reuben’s (American), Le Taj (Indian), Moleskine (pizza), La Capital Tacos (tacos). If uncertain, Le Central is recommended, a gourmet food court featuring: poutine, ramen, Portuguese chicken, seafood caught right here in Québec, delicious churros, and beyond.
Drinks are also served around McGill at Benelux (brewery), and Pullman (wine bar). If a longer (~30 min) walk is not a problem, Else’s is also recommended, a unique pub with a Scandinavian motif and excellent food options, from smoked salmon on potato latkes to spicy wings with a side of cold sesame noodles.
