It was the mid-afternoon, but astronomer Benjamin Shappee was just waking up. In a remote building, high above the floor of the arid Atacama desert in Chile, he had to get ready for the night shift on one of the telescopes at the Las Campanas Observatory.
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Everything he needed to do had been planned out for months. Telescopes had been reserved for specific tasks by institutions from around the world. He had grad students who’d flown in to learn how to operate the delicate equipment. And before it all began, he expected to take a nice walk from where he was staying to where he’d be working for the night. But then, as any modern story goes, he looked at his phone.
It was flooded with messages from colleagues around the world. A sense of urgency among a crowd used to dealing with slow moving or at least highly anticipated astronomical events. Gravitational waves and a gamma ray burst from a nearby galaxy had just been detected, and the messages were saying if he and his team wanted to study the source of the waves, they were going to have to move fast.
It was August 17, and the Laser Interferometer Gravitational-Wave Observatory (LIGO) had picked up the waves. Groundbreaking technology from CalTech and MIT, the instrument uses lasers reflected off of mirrors to detect when gravitational waves pass through. The ripples in space time, posited by Albert Einstein more than a century ago, have become the latest observational tool for deep-space astronomers.
LIGO had been triggered before, but by gravitational waves from black holes. This time though, things were different. The mass of the objects involved were smaller, which led the scientists to believe that they might get to see something they’d been waiting for: the merging of two neutron stars.
Coupled with a burst of gamma rays detected by NASA’s Fermi space telescope, scientists were able to use the data to narrow down the place in the universe where the event occurred. They knew that it was only observable from the Southern Hemisphere, and that there was likely only a short period of time that they'd be able to see it before it slipped from view.
The bat signal was sent out to about 100 astronomers at 18 telescopes around the world.
Shappee and his colleagues from the Carnegie Institution for Science, located in Pasadena, and UC Santa Cruz, were in that group. Their telescopes were in an ideal spot; at nearly 7500 feet, the atmosphere at Las Campanas is a bit thinner (less atmospheric distortion), the air is dry (humidity is bad for telescopes) and it’s isolated (there is little light pollution).
"Astronomers who I typically am very competitive with and have disagreements with, even they were emailing me and asking me to take observations," Shappee said. "I immediately started doing the arithmetic. How many galaxies there are within this distance range and how many telescopes on the mountain I can get to observe this particular look for this particular source."
He and his team had a chance to be the first people in the world to see two neutron stars merge togethert. But they were in a race against an event that would eventually fade from view, as well as other observatories.
It was a mad rush.
A needle in a haystack would’ve been easy. They had to find a single point of light in a sky with trillions of them, and quickly.
"Neutron stars … they’re the dead cores of stars after they explode as supernovae," said Tony Piro a theoretical astrophysicist with Carnegie. "And these stars are about one and a half times the mass of our sun … so they're very very dense objects."
To visualize just how dense they are, Piro said, imagine everyone on planet Earth gathered up and crushed down to the size of a sugar cube. Neutron stars are about 10 to 2o kilometers in diameter, and they bend spacetime with their intense gravity – the sort of extreme objects needed to make gravitational waves. Actually, they’re probably one of the most perfect spheres in the universe, said Piro, given their extreme gravity.
Scientists had been waiting to see two neutron stars rip each other apart for decades.
For years, we’ve understood where elements lighter than iron came from. Helium and hydrogen are remnants of the Big Bang, and the elements up to iron are created within stars. The origin of heavier elements has been a mystery, but it’s been hypothesized that they're created when two neutron stars merge.
"When you have these environments with very neutron rich material, those neutrons can bombard each other and because they're not charged you can build up really heavy nuclei," said Piro. "There's fission, things splitting and eventually this kind of radioactive waste goes back to the stable elements we know in our periodic table – things like gold, platinum and uranium."
Meaning, that gold ring on your finger might be neutron star ejecta.
One hundred and thirty million years before Ben Shappee awoke to a flurry of e-mails, two neutron stars smashed together, releasing 50 times more energy in gravitational waves in one moment than our sun will radiate in its entire lifetime, according to Piro. The material was thrown out greater than 20 percent the speed of light.
They still had to figure out where it was coming from, so they and others devised a plan to look at about 50 select galaxies that they believed the event could’ve taken place in. They tore apart a schedule of observations that had been planned for months and eventually started taking photos with the three telescopes they had available on the mountain.
"There was two grad students and an undergrad in the room," said Shappee. "I was just telling them, everything you see that I’m doing right now, don’t mimic this. This is exactly what you don’t want to do. You should be prepared and this should be boring, this should never be exciting like this."
At UC Santa Cruz, post doc Charlie Kilpatrick was receiving the images, cleaning them up and comparing them by flipping back and forth between the new ones and the old ones they had on file.
"I looked through all of the galaxies in each image. There wasn't anything there," he said. "But then I get to the ninth image and in the second galaxy in that image that I looked at, there was something."
It was a bright point of light from galaxy NGC 4993, 130 million light years from Earth.
"I couldn't believe that it was so bright," said Shappee.
For a moment, Shappee and his colleagues were the first people ever to witness a neutron star merger.
"I’m very very honored to be able to be a part of a discovery that future undergrads will be forced to read a couple of sentences about," Shappee said.
Other telescopes quickly spotted the event as well, and people started recording the entire spectrum of visible light, as well as the infrared spectrum, in an attempt to capture as much information as possible.
"It went from bright blue and hot like a hot poker, to four days later it was this red dim object," Piro said.
Eventually X-ray and radio waves were monitored by scientists around the world, making it the most studied transient cosmic event ever.
According to Mansi Kasliwal, a professor of astronomy at Cal Tech, through observations of the infrared spectrum, researchers found evidence that massive amounts of heavy elements, including gold, platinum and neodymium were likely created during the merger, bringing scientists one step closer to confirming the theory of how they’re created.
It was one of the biggest discoveries in astronomy in years.