On Sept. 14, 2015, detectors at the Laser Interferometer Gravitational-Wave Observatory facility in Livingston, Louisiana picked up a curious signal from the background noise of the universe. 10 milliseconds later, detectors at the facility in Hanford, Washington picked up the same signal. Phone calls were made; teams were assembled; and, in the Louisiana facility’s control room, Allegheny College was represented by alumnus Alex Urban, ’10.
“It was like being at Mission Control in a science-fiction movie where everyone is yelling all these science terms,” said Urban. “It was pretty cool.”
The forces that LIGO’s facilities are designed to detect are generated by interstellar impacts between high-density objects. These could be neutron stars or, in the case of the Sept. 14 discovery, black holes. When two objects collide—“coalesce” was Urban’s preferred term—they let out an explosion of visible light as well as an explosion of gravitational waves. The findings were officially announced to the public on Thursday, Feb. 11, according to multiple news outlets.
“We want to detect these waves quickly so we can get word out to astronomers,” said Urban. “And this was the very first detection of gravitational waves. It was game-changing, and I don’t think that’s a hyperbole. LIGO is opening a new sense for us to explore the universe.”
Urban, a graduate student at the University of Wisconsin in Milwaukee, originally joined the LIGO project in January 2013 at the recommendation of his adviser, Patrick Brady, professor of physics. Urban was known for his coding expertise, and Brady knew that LIGO needed data-analysis.
“My thesis is about joining the detection work that LIGO does with follow-ups by other telescopes and observatories around the world and in space,” said Urban. “LIGO will detect a source—two things colliding. My role is trying to compute where that signal is found in the sky, and give that information to astronomers. By doing that, we get a complete picture of what is happening—the anatomy of the explosions, if you will.”
The LIGO project was conceived, according to Urban, in 1992. Construction on the facilities began in 1995. Brady, Urban’s future adviser became involved with the project in 1998. LIGO began officially recording data in 2002. Eleven years later Urban joined the team as a research assistant to Brady.
In 2010, the team took the detectors offline and began a five-year upgrading project known as “Advanced LIGO.” The goal was to improve the sensitivity of the detectors tenfold from what it had been in 2010. In 2015, the detectors were turned on, and almost immediately, detected a signal.
“Strictly speaking, it happened before we turned it on,” said Urban. “The ‘observing run’ was going to start Sept. 18 but the detectors were already online doing basic testing. The signal happened on Sept. 14, and surprised everybody. I was there in Louisiana when it happened.”
One challenge in detecting these waves involves interference, or “noise:” LIGO detectors sift through things like earthquakes, solar radiation and quantum noise from individual photons, according to Urban.
“We require a signal to show up in both detectors just to be confident that it is a real signal,” said Urban. “The same signal showed up in the same shape in both detectors within about 10 milliseconds of each other—and that’s about the time light takes to travel the distance between detectors.”
This confirms that the signal was genuine, and it also supports one of the hypotheses regarding gravitational waves: that they are able to travel at the speed of light.
According to James Lombardi Jr., associate professor of physics at Allegheny, this discovery is vital to physicists’ understanding the limits of general relativity.
“What [the team at LIGO] saw was amazing, but it did not defy our current laws or theoretical models,” said Lombardi.
The implications are still huge, according to Lombardi, so much so that the discovery is only matched in the history of physics research by the observations that Galileo Galilei made 400 years ago through a telescope.
“You can only see so far back in time in the visible universe,” said Lombardi. “We can currently only see to 380,000 years after the Big Bang. Before that, everything was too opaque. But gravitational waves can travel through opaque objects, so we’re hoping that now we will be able to see further back in time.”
One of the perks of being on the front lines of interstellar discovery included meeting with renown astrophysicist and science communicator Neil deGrasse Tyson. In early November, while Urban was working at the Louisiana facility, Tyson paid an unexpected visit and chatted with some of the staff.
“He asked us about outreach—things like, how would we describe our research and this discovery to our friends and family?” said Urban. “On television, [Tyson] seems like such a neat, humble guy, and it turns out it’s not an act, it’s all genuine.”
Urban graduated from Allegheny with a Bachelor of Science in physics and two minors, in math and political science. Shafiqur Rahman, professor of physics at Allegheny, served as Urban’s academic adviser for Urban’s senior comprehensive project.
Urban met Rahman as a sophomore at Allegheny, and later helped the professor develop worksheets on a theoretical model of statistical mechanics.
“[Urban] was quite an intelligent student,” said Rahman. “But he was unlike the typical student.”
Daniel Willey, professor of physics at Allegheny, was Urban’s second reader. According to Willey, Urban’s senior project involved solid state physics, a branch far more theoretical than the analytical work Urban now finds himself undertaking.
“I was impressed by his ability to communicate,” said Willey. “I wrote a letter of recommendation for him for graduate school…. I commented in my recommendation that Alex’s presentation for his senior project was one of the few that I’ve been to that I could say that I’ve actually learned something from.”