Canada solid gold in G-Wave breakthrough
GW170817 sheds light on nuclear physics, relativity, cosmology, and origin of gold
The discovery of a new kind of gravitational wave announced last month is an astronomical breakthrough as significant as any in history, and Canadians played crucial roles. Indeed, a former Canadian astronomer played two crucial roles. So did more than two dozen scientists at several Canadian research centres.
“Where observation is concerned, chance favours only the prepared mind,” said Barry Madore, an astronomer with the Carnegie Observatories, who was involved in the discovery of the gravitational wave’s point of origin in the galaxy NGC 4993. Canadian born Madore began his career as an astronomer in Canada, and earned his doctorate in the field at the University of Toronto (U of T).
What Madore’s team found in that galaxy happened when two neutron stars crashed into one another. Neutron stars have a little more mass than our Sun. All that mass is contained within a tiny diameter compared to our Sun, however. So neutron stars are ultracompact stars of unimaginably high density.
When the neutron stars involved here collided, the resulting explosion released more energy in a single second than our Sun will produce over most of its existence. The explosion also released a gravitational wave. Scientists knew right away that this wave was different in two important ways from the previous five, including the first gravitational wave ever discovered that made headlines in 2016. First, neutron stars were involved. All waves detected previously were produced by colliding black holes. Second, and crucially, this explosion happened at a distance 10 times closer to Earth.
“When alerts were sent out to the LIGO/VIRGO gravity wave detection consortium on the night of Aug. 17, 2017, our team of astronomers was indeed prepared,” added Madore.
Because it happened as close as it did to our planet, light from the explosion was seen within seconds when a burst of gamma-rays was detected by two orbiting space telescopes. The discovery of a Gamma-Ray Burst (GRB), and its coincidence with the discovery of a gravitational wave, was a first. No other gravitational wave had ever been confirmed by independent observations. Best of all for astronomers, their odds of also discovering the explosion’s point of origin by photographing its visible afterglow, were exponentially higher. The gravitational wave gave the distance. The gamma-rays gave an approximate position on the sky. So a call to astronomical arms went out to observatories worldwide and in space. As a result, the largest number of astronomers ever involved in the search for a single object began diligently scanning the sky, frantically searching for a cosmic needle in an extragalactic haystack with an area the size of 144 full moons.
“With a previously-compiled list of nearby galaxies having positions and distances culled from the massive online archive of the NASA/IPAC Extragalactic Database (NED), our team rapidly zeroed in on the host galaxy of the event,” Madore explained.
Using the Swope, one-metre diameter telescope, at the Las Campanas Observatory in Chile, Madore’s team became the first ever to discovery a gravitational wave’s point of origin. They found it in the galaxy NGC 4993, the ninth galaxy on their list, and captured the very first photograph of the explosion’s afterglow.
“There will be more such events, no doubt; but this image taken at the Henrietta Swope 1-m telescope at the Las Campanas Observatory in Chile was the first in history, and it truly ushered in the Era of Multi-Messenger Astronomy,” Madore noted.
Swope’s team attributes part of their success in the discovery to their use of the world’s largest database of galaxies, which helped narrow down the number of galaxies in the search. Madore also contributed to the discovery, decades before it was made, because he co-founded the NED galaxy database in the late 1980s, with George Helou and Marion Schmitz at the California Institute of Technology. It was then when Madore was lured to Pasadena, Calif., along with fellow astronomer and his Toronto-born wife Wendy Freedman, also a U of T grad and now with the University of Chicago. At Caltech and at the Carnegie Observatories, they were co-leaders of the Key Project conducted by the NASA Hubble Space Telescope, which established our universe’s size is around 14 billion light-years.
Canadian scientists were among the first to discover the explosion’s afterglow in X-rays. Astronomer Daryl Haggard, along with fellow researchers Melania Nynka and John Ruan, all with McGill University, began observing with the Chandra X-ray space telescope two days after the explosion. Nothing unusual appeared. Over the next two weeks however, Haggard’s team was among the first to capture Xray images of the event.
The Laser Interferometer Gravitational-wave Observatory (LIGO) and VIRGO observatories discovered the gravitational wave itself on Aug. 17. Thousands of scientists from around the world are involved with the LIGO and VIRGO teams, and contribute as co-authors to their scientific papers. Two-dozen Canadian scientists were involved in this discovery, including teams from the U of T and University of Alberta. So too was physicist Ken Clark, with SNOLAB, the expanded Solar Neutrino Laboratory at the Sudbury Neutrino Observatory (SNO).
Astronomers are excited because the discovery confirms two long-held ideas that were impossible to prove until now. First, pairs of neutron stars that collide and explode are now known to produce gravitational waves, confirming an idea that had only been theorized before. Second, explosions from colliding neutron stars are now also known to produce Short GammaRay Bursts (SGRBs). Those cosmic explosions were unexplained previously.
Nuclear physicists are excited because explosions from colliding neutron stars are now confirmed to produce elements heavier than iron, including gold, platinum, and uranium. Until now, the origin of these elements had been hotly debated.
Cosmologists are excited because the discovery has confirmed two important predictions from Einstein’s theory of general relativity. First, gravitational waves are now known to travel at the speed of light, exactly as predicted. Second, the theory’s central idea was confirmed. Gravitational energy is equivalent to inertial energy. While that idea had already been confirmed based on previous observations, this proves it true to within parts per billion. Einstein’s theory is the blueprint scientists use to explain our universe’s age, size and makeup, and cosmologists are now more confident than ever that the theory is sound.
“This is quite literally a physics gold mine!” exclaimed Masao Sako, with the University of Pennsylvania and a co-author on 10 scientific papers regarding the discovery. “With GW170817, we can learn about nuclear physics, relativity, stellar evolution, and cosmology all in one shot. And we now know how all of the heaviest elements in the universe are created [including gold].”
The impact of gravitational wave research on science was recognized with the Nobel Prize in physics for 2017. Now, with GW170817, comes one of the most important astronomical breakthroughs in history. Other astronomical advances of consequence include Galileo’s discovery of the moons orbiting Jupiter. That confirmed planets in our solar system orbit the Sun. Sir Arthur Eddington’s discovery that light rays passing close to the Sun from distant stars are bent by the Sun’s gravity was a game changer. That confirmed Einstein’s theory of general relativity provides a realistic picture of our universe.
In terms of the number of discoveries from a single astronomical event, as well as the number of scientists involved, not to mention the number of people informed, including those reading this, nothing like this astronomical breakthrough has ever happened. It’s big, and with more still to come, only getting bigger, and Canadians have played and will continue to play important roles in this breakthrough.
More scientists have published more papers on this than for any astronomical discovery in history. A technical synopsis by this writer based on review of 96 papers, 1,552 pages, and 8,223-plus authors published from one to four days after the public announcement Oct. 16 is available online at Universe Today (four pages plus referenc- es).
Even “The Big Bang Theory” television series, created by Chuck Lorre, gave a nod. In the episode aired Nov. 16, check out the white board near the door in the first scene. One month exactly after the discovery was made public, there it was, writ large for millions to see. Plus, did they get it right? They nailed it!
“GW170817 brings a long awaited era of multi-messenger astronomy, by adding gravitational waves to the light studied by astronomers,” according to astrophysicist J. Craig Wheeler, with the University of Texas at Austin.
“A precursor was supernova 1987A, discovered by University of Toronto graduate student Ian Shelton, that brought both neutrinos and light,” Wheeler added. “Some day we will see all three messengers from a single event. While a triumph of observational astronomy, GW170817 also represented a proud moment for theory. Without Einstein’s 100-year-old theory, LIGO would never have been built. While observational confirmation is vital, it is also remarkable how thoroughly theorists predicted what we would see when neutron stars merged. They got it right!”
“This achievement comes from weaving together resources and capabilities ranging from small groups of observers using modest aperture telescopes such as SWOPE, to databases and archives representing the distillation of tremendous effort of curating data over many years such as NED, to the individual researcher with a theory insight,” summed Helou, who is also the executive director of Caltech’s Infrared Processing and Analysis Center (IPAC), which operates NED.
“This will be remembered as one of the events that truly revolutionized the modern fields of astronomy and astrophysics, and Canadian researchers were central to its success,” imparted Darren Grant, a physicist with the University of Alberta. Grant is also head of the Deep Core project at the ICE Cube neutrino detector located in Antarctica, and co-authored two papers on their collaboration with LIGO to search for neutrinos associated with GW170817. Grant summed Canada’s role as follows.
“Particularly noteworthy are the contributions of the LIGO team members at the University of Toronto and Canadian Institute for Theoretical Astrophysics, who have led the developments that make it possible to quickly identify the LIGO events in order to provide rapid alerts to the broad astronomical community, as well as key electromagnetic measurements of the event at multi-wavelengths, including those from team members at McGill (xrays), Toronto (optical and radio) and IceCube researchers at Alberta and SNOLAB (neutrinos). Researchers in Canada and around the world will clearly benefit from this scientific advancement for years to come.”
This is quite literally a physics gold mine! … we can learn about nuclear physics, relativity, stellar evolution, and cosmology all in one shot.