Shane Larson gets excited about a lot of things, but the personable physicist and astronomer is really geeked when talking about anything related to a phenomenon called gravitational waves. He calls their recent confirmation "one of the emerging wonders of modern astronomy."
Larson is an Associate Professor of Physics at Northwestern University, where he is a key member of a team searching for these elusive echoes of cosmic processes that cannot be directly seen by way of radiated light or detected via other forms of electromagnetic radiation.
Larson has won awards for his communication and teaching skills, so absolutely DO NOT miss his presentation Songs from the Stellar Graveyard – Searching the Cosmos in Gravitational Waves. It is scheduled in the Meijer Theater of the Grand Rapids Public Museum at 7 pm on Thursday September 19th, presented by GRAAA in collaboration with GRPM.
"We have absolutely no previous experience in how to probe and understand the universe using this newly discovered phenomenon, but that is what makes it so exciting," Larson told me during a recent interview. He says that gravitational waves may hold the key to better understanding objects in what he terms the “stellar graveyard.”
Existing there are the collapsed remains of objects that were once prodigious energy producers, including stars like the sun, but also those far more massive which blazed hotter and brighter.
All stars go through an evolutionary cycle that ultimately brings about their demise. For our sun and similar stars, it is collapse into a tiny white dwarf that eventually cools and fades to a stellar corpse.
High mass stars have a more dramatic death throes, exploding as supernovas before collapsing under the relentless force of gravity to exotic "stellar skeletons," as Larson describes them, such as neutron stars and black holes.
Neutron stars are tiny, so they are extraordinarily difficult to pick up at great distances by way of light that can be seen, though some call attention to themselves through rapid pulses or a spray of X-rays. Black holes, by their very definition, are in such a state of collapse that not even light can escape their gravitational grip.
So how do scientists find them? Some neutron stars and black holes do not exist alone. They are part of binary systems, swinging in tandem around and interacting with an ordinary star, another neutron star, or even, in the most extreme cases, another black hole.
Way back in 1916, in his General Theory of Relativity, Einstein predicted the propagation of “gravitational waves” as a result of this interaction. He mused that these disturbances would carry so much energy that they would create a distortion in the very fabric of space as they rippled outward from their source to very great distances. He also predicted that gravitational waves would penetrate obscuring matter in a manner other forms of energy cannot.
In September of 2015, after close to a century of speculating and searching, the long theorized phenomenon was directly observed. Rippling past earth were weak gravitational waves produced by a collision of two massive black holes that occurred more than a billion years ago!
A technologically advanced detector – actually two nearly identical interceptors located almost 2,000 miles apart, one in the state of Washington and the other in Louisiana – accomplished the task after years of searching. The Laser Interferometer Gravitational Wave Observatory (LIGO) uses two detectors working in unison in order to better determine where the gravitational waves are coming from.
Shane Larson gets excited about the new era of gravitational wave astronomy because he has been interested in black holes throughout his professional career, which began in the West at Oregon State University, and then continued at Utah State in Logan, before he came to Northwestern in 2013.
Larson explains that he has been a physics geek since childhood. He was inspired by Carl Sagan’s imaginative communication skills in the original 1980s Cosmos PBS series as a teenager. "I was so impressed that he could talk about this complicated stuff and I wanted to be like him," he said during our conversation.
Larson balances his intellectual curiosity about gravitational waves and exotic objects by remaining enthusiastic amateur astronomer. Among his home-built telescopes is a 22 inch behemoth reflector he carts to regional star parties via trailer. I suspect this grounding contributes to his contagious enthusiasm and ability to communicate complex subjects effectively.
"There is nothing better than looking through a telescope at galaxies lying a gazillion light years away," he said with a laugh. I asked if that is still true after becoming absorbed in such an esoteric subject as gravity waves. "Absolutely" was the immediate response. "I think of myself as a bridge person. I have to think deeply to explain relativity and gravitational waves effectively, but I also use a telescope."
Larson reiterated that finding messages encoded in gravitational waves is like pulling back a curtain hiding processes going on in the universe that cannot tell us about themselves via conventional sources of electromagnetic energy. Gravitational waves have the potential to reveal what happened right after the big bang that ignited the entire universe.
"Gravitational waves are something our bodies were never meant to perceive, but now we are finding the means to interpret their encoded messages. How exciting is that to an astrophysicist like me?" Larson said.
Larson’s excitement extends to his involvement with a large international team working on the Laser Interferometer Space Antenna (LISA). Scheduled for launch in the early 2030s, it is a more sophisticated version of the earth-based LIGO. Because LISA is in space, a much longer baseline between the two observational points is possible, bringing about higher sensitivity and resolution of those elusive sources of gravitational waves.
"I’ve been working on LISA my whole career, and I will be sharing our excitement about it in my Grand Rapids talk," he said. "The potential is enormous."