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Dr. Cabero Müller receives 2020 Killam Postdoctoral Fellow Research Prize

Congratulations to our team member Dr. Miriam Cabero Müller, who is receiving the 2020 Killam Postdoctoral Fellow Research Prize!

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.

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Scientists detect 39 new gravitational wave events

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.

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The results are reported in a series of four papers published on the arXiv:

The most massive black hole merger detected

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.

Find out more

No mountains detected yet on millisecond pulsars

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.

Find out more

Discovery of the heaviest neutron star, or lightest black hole, ever observed

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.

BH and mystery object

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.

Find out more

UBC gravitational wave astrophysics group participates in the #Strike4BlackLives

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!

UBC GW astrophysics group research continues remotely

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.

Zoom_meeting

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.

Farewell_to_Maryum

The UBC GWs astro group virtually celebrate’s Maryum’s last group meeting before starting her new job after graduation.

LIGO-Virgo ends third observing run early

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.

LIGO detectors and sunset

LIGO Image Credit: LIGO-Virgo Collaboration. Sunset Credit: Getty Images.

Detector characterization at LIGO Livingston

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.

Read more about their findings on the public LIGO-Livingston alog.

DetChar_f2f

LIGO detector characterization members tackle noise sources during the Jan 2020 noise sprint workshop.

Harmonics in gravitational wave signals observed from collision of black holes for the first time

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.

GW Harmonics

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.

 

 

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