Tracking down a kilonova: The story of how thousands of scientists decoded the year’s biggest discovery

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This is the backstory to the biggest scientific discovery of 2017.

It began, as most things do these days, with a notification on phones and computers. Scientists working on the LIGO and Virgo collaboration stared at their screens, expecting the same sort of news push alert or unremarkable data filing they got all the time. But after a few seconds, it dawned on them that these data were different. It was what they had been waiting for all these years. The time, 8:41am eastern standard time on Aug. 17, would go down in history as the moment when physicists and astronomers enjoyed a collective intellectual orgasm.

An almost failure

LIGO and Virgo comprise more than 1,500 scientists, all of whom are working towards a single goal: to capture signs of gravitational waves and decode their meaning. The data gathering happens at massive observatories in the US and Italy, but the analysis is done in countries all over the world.

Gravitational waves are generated when massive, violent events occur in our universe—such as the collision of two black holes, which these scientists have seen four times since 2015. Three leading LIGO scientists were awarded this year’s Nobel Prize in Physics for their contributions to these observations.

But LIGO was almost never built. One of the Nobel winners, Rainer Weiss, conceived the basic idea of how to “listen” to gravitational waves back in 1967. The first large prototype of a lab that could observe these phenomena was built in 1980 by another of the 2017 Nobel winners, Kip Thorne; the success of the prototype suggested that laboratories large enough to actually capture proof of gravitational waves were feasible. Despite lots of political pressure, the US government at the time chose to not fund the proposed large-scale construction, which would have cost hundreds of millions of dollars.

LIGO in Hanford, Washington.
LIGO in Hanford, Washington.
Image: CalTech

It would’ve ended there if not for Barry Barish, professor of physics at California Institute of Technology, who took over the collaboration in 1994. Because Barish had a track record of success with big science projects in the field of particle physics, the US National Science Foundation trusted him more than any of the previous directors of the project. In Barish’s first year in charge, the government approved the construction of two labs: one in Hanford, Washington and another in Livingston, Louisiana, at a total cost of $400 million.

In 2002, the Laser Interferometer Gravitational-wave Observatory (LIGO) started listening—on time and on budget.

Albert Einstein had predicted that whenever huge celestial events occur, they create gravitational waves. The waves, originating light years away from Earth, would be faint by the time they got here. The instruments to search for them had to be so sensitive that they could filter out interference from trucks on nearby roads, winds outside the building, and even molecular vibrations in the mirrors used in the instrument. Having two labs thousands of miles apart meant that if one detected something but another didn’t, then the signals could be safely discarded as noise. In addition, if a signal was detected first in Hanford, then seconds later in Livingston, scientists could calculate the speed at which it traveled—if it was traveling at light speed, it’d be proof that it was in fact a gravitational wave.

In parallel, scientists from a handful of European countries were collaborating to get their own gravitational wave-listening project off the ground. The Virgo interferometer near Pisa, Italy—named for the Virgo cluster of galaxies—was initially completed in 2003. In its first phase, it wasn’t sensitive enough to detect gravitational waves. So it was decommissioned and given a massive overhaul. The upgrades were completed Aug. 1, 2017—just in time to help LIGO make the most important detection of gravitational waves yet.

Wooing the astronomers

Gravitational waves offered astronomers a new way to look at the celestial world. No longer did they have to depend on just looking at the sky; they could also “listen” to some of the most spectacular, distant cosmic events.

The scientists who first saw the notification on Aug. 17 belonged to a “rapid response team” whose job was to discern whether the signals their instruments were hearing weren’t noise or a computer bug. Once those doubts were out of the way—21 minutes later—they issued a global notification; something to the effect of, “All astronomers should point their telescopes towards these coordinates in the sky.”

An artist’s imagination of a kilonova.
An artist’s imagination of a kilonova.
Image: Dana Berry, SkyWorks Digital, Inc.

This sort of global notification has been going out about once a month for years. But before 2015, it always turned out to be a dud. That’s when the collaboration upped its game and upgraded its instrument. A gravitational wave from a source four light years away will cause a perturbation of no more than a thousandth of the width of an atomic nucleus, and the improved instruments can measure that. After years of never hearing any actual gravitational waves, LIGO managed to record four black hole mergers in a space of less than two years. But LIGO could see other phenomena too—from exploding stars to mergers of collapsed stars. Astronomers remained excited for those, because alongside gravitational waves, these other events would also release visible light in real-time. LIGO could detect these faint events, too.

And the signal astronomers were really waiting for was finally heard on Aug. 17. Many in the LIGO and Virgo collaboration had been trained for years to look for a characteristic signal that would likely be produced when two neutron stars merge. When they saw the data on Aug. 17, they were pretty sure this was it—and that the celestial event was happening now, in real time.

As Quartz explained previously:

The drama of a neutron-star merger is due to the fact that it involves one of the most extreme objects in the universe. Neutron stars are some of the smallest, densest stars we know. They do not have much more mass than our sun, but all of it is compressed into a ball no bigger than the width of a mid-sized city (about 15 km, or 9 miles). That’s a lot of compression. A teaspoon of neutron star would weigh 10 billion kg (or 22 billion lbs)—about the same as 1 million very large elephants.

“What followed was a whirlwind of activities,” says Kenneth Strain of the University of Glasgow, a LIGO-Virgo collaborator. “We may be thousands of people, but we were barely enough to get all the work done.”

Big Science

We live in an era of big science. For the past two decades, collaborations involving hundreds of scientists have been commonplace and there are even some involving thousands. These big projects have achieved great things that wouldn’t have been possible without the ability of large groups to communicate and share data, from decoding the human genome to revealing the Higgs boson. Even by these standards, however, what happened on Aug. 17 and the days that followed was special.

Starting with a few scientists at first, slowly hundreds and then thousands joined in, pointing every ground-based and space-based telescope they could spare to a small patch in the sky. None of the previous big science projects required this sort of coordination in real time, and none produced their results in less than two months after getting their data.

The flurry of news that resulted from the project might have obscured one amazing thing about the process: Scientists are almost always strapped for funding, and time using expensive astronomy instruments is extremely limited. Though some instruments are on call for what astronomers call “transient events,” most are not. For each of the 70 ground-based and space-based observatories, there were dozens of people involved in deciding whether it was worth stopping the observations they were making to capture some of the light coming from the merger.

Scientists of the CMS group at CERN.
Scientists of the CMS group at CERN.
Image: CMS

When so many were willing to stop doing what they were doing—what their PhD funding is for, what their grants demand of them—to record an event, you can be certain it was something unique, and important. The event, also called a “kilonova,” didn’t just emit gravitational waves. It put out electromagnetic radiation in every spectrum: X-rays, gamma rays, ultraviolet, visible, and radio waves. The scientists were presented with an all-you-can-eat buffet after a long fast.

Of course, not everyone could free their instruments immediately. The first telescope to capture light from the gravitational waves did so 12 hours after they were detected, and NASA’s peerless Hubble telescope couldn’t be pointed in the right spot in the sky until days later—just barely in time to catch the fading light of the event.

Recording the data is only half the job. The way the second phase of the kilonova work went down is a master class in project management. In the weeks that followed, scientists openly shared their data with each other and began analyzing what it meant. Their aim was to publish the results as soon as possible, so that even more people would begin dissecting the data in new ways. Some 3,500 people, who have never worked together at such a scale, had to all of a sudden figure out how to collaborate.

The single-most observed celestial phenomenon in human history has already yielded many new discoveries. First, the data from the event was an independent verification that the speed of gravitational waves is the same as the speed of light. Second, the way gravitational waves traveled from the event also proved to be an independent confirmation of the age and the rate of expansion of the universe. Finally, scientists confirmed a suspicion they’d been harboring for some time: that heavy elements in the periodic table are created during violent celestial events, like kilonovas.

This is just a tip of the iceberg. What’s next? “It’s like asking Galileo: ‘What else can you see with your telescope?'” quipped LIGO collaborator Andreas Freise of the University of Birmingham.

None of this would have happened without spending billions of dollars to build the most advanced instruments in human history and billions more to train experts to capture and decode the data those tools would gather. Often, when “Big” is attached to the name of a field, it’s meant as a pejorative. Big Pharma. Big Tobacco. Big Business. Not, however, in the case of Big Science, which has helped us decode the mysteries of nature and, perhaps, provided a blueprint for addressing other planetary challenges, from curing diseases to mitigating climate change.