UCSB graduate student develops model explaining superluminous supernovae ‘chirps’

GOELTA, Calif. (KEYT) – A UC Santa Barbara graduate student alongside a local nonprofit research group have advanced the frontiers of physics while studying a dying star exhibiting extraordinary behavior.

"Much effort goes into designing, building, and operating astronomical facilities. While the scientific endeavor typically moves in small steps, it is enormously rewarding for everyone involved when we get to
experience something that has never been seen before being revealed," explained Dr. Lisa Storrie-Lombardi, Director of the Las Cumbres Observatory headquartered in Goleta. "I've been doing this for 30 years and the only thing with an impact close to [UCSB graduate student Joseph] Farah's result that I've been able to be a part of was the discovery nine years ago of seven earth-sized planets orbiting the star TRAPPIST-1. Farah's result is phenomenal."

Stars are fueled by a fusion reaction at their cores and throughout their existence, heat pushes outwards away from their cores and against the force of gravity pushing inward in a balance of forces that create the stars we see in the night sky.

Once the star burns through its fuel, it begins to cool and the pressure pushing back against gravity that keeps it stable, gets weaker.

When massive stars, at least eight times the size of our sun, run out of fuel, their cores collapse suddenly under the pressure of gravity and a huge explosion known as a supernova occurs.

These extremely bright celestial explosions can last for about a week and over the following several months, the gases involved cool and fade in brightness explains the Las Cumbres Observatory.

A rare class of supernova explosions discovered less than 20 years ago, known as superluminous supernovae, are ten to a hundred times brighter than a standard supernova and the power behind these recently discovered phenomena has remained a mystery.

In addition to their extreme brightness, these superluminous supernovae also often have strange bumps or observable surges in their brightness that defy our current understanding of physics.

In 2024, the ATLAS survey system discovered a supernova about a billion light-year away, referred to as SN 2024afav, and for the next 200 days, the Goleta-headquartered Las Cumbres Observatory (LCO) conducted a full suite of observations to capture the slightest surge over the course of the supernova's evolution.

SN 2024afav was discovered to have a clear series of changes to its brightness, a pattern that no random interactions could create and placed the real-time observations and testing being done at LCO at the cutting-edge of physics research.

"This is a major victory for LCO [Las Cumbres Observatory]," explained Joseph Farah, a fifth-year UC Santa Barbara graduate student at the nonprofit research organization. "The uniquely pristine and high-cadence LCO data allowed us to predict future bumps and the ability to dynamically adjust the campaign on a dime let us check our predictions in real-time. When the predictions started coming true, we
knew we were watching something special."

While the existence of a recognizable pattern of surges in luminosity challenged our current understanding of physics, another fascinating observation was also made.

The repeated changes in brightness were getting closer together, increasing in their frequency, creating what researchers dubbed a 'chirp'.

"There was just no existing model that could explain a pattern of bumps that get faster in time," shared Farah. "I started thinking about ways this could happen, because the signal seemed too structured to be due to random interactions."

Those chirps inspired Farah's model that showed what was happening and is the subject of a groundbreaking paper published in Nature this week, but before we get to his addition to our understanding of physics, we have an important part to add about what supernovae leave in their wake.

After a supernova event, a black hole or a neutron star is left behind.

Neutron stars are some of the densest objects that astronomers can directly observe, as opposed to black holes, and a rare version of them is known as a magnetar, a neutron star with a very powerful magnetic field, about 100 thousand times more than a standard neutron star.

Current theory states that when a magnetar is created after a star dies, it pumps energy from within the supernova, creating smooth surges in brightness, but that isn't what was observed with SN 2024afav.

That discrepancy is where Farah sought to fill the gaps of our understanding by developing a model to explain the observations he was gathering at LCO.

According to Farah's model, material blasted away from whats left after a supernova explosion falls back toward the magnetar and creates an accretion disk.

As the magnetar spins, it twists the fabric of space-time around it, causing the disk of material to wobble Farah's model shows.

That reality-bending effect, known as Lense-Thirring precession, occasionally blocked and reflected the light observers recorded in 2024.

As the radius of the accretion disk decreases over time, the disk moves inward and closer to the wobbling magnetar and, as a result, the surges in brightness captured on Earth get closer together, the 'chirps' that terrestrial telescopes spotted.

Farah's chirp-explaining model identified a new aspect of supernovae for scientists to investigate going forward and confirmed a mechanism explaining how superluminous supernovae are powered.

Any scientific breakthrough is immediately followed by rigorous testing and Farah's model was no exception.

"We tested several ideas, including purely Newtonian effects and precession driven by the magnetar’s magnetic fields, but only Lense-Thirring precession matched the timing perfectly," Farah noted. "It is the first time General Relativity has been needed to describe the mechanics of a supernova."

This May, Farah will defend his PhD thesis about the new model at UC Santa Barbara and will continue working alongside Professor Dan Kasen, the physicist credited with originally proposing the magnetar model as well as his advisor at LCO, Senior Scientist Dr. Andy Howell.

"I was part of the discovery of superluminous supernovae almost 20 years ago, and at first we didn’t know what they were," shared Dr. Howell. "Then the magnetar model was developed and it seemed like it could explain the astounding energies needed, but not the bumps. Now, I think Joseph has found the
smoking gun, and he’s tied the bumps into the magnetar model, and explained everything with
the best-tested theory in astrophysics – General Relativity. It is incredibly elegant."

Want to learn more about Farah's discovery?

The Las Cumbres Observatory and the Santa Barbara Museum of Natural History are cohosting a public event on March 30, at the museum's Fleischmann Auditorium starting a 7 p.m. where Farah will speak on his paper General Relativity Beats the Heart of a Dying Star detailing his discovery.

Farah expects to find more supernovae chirping in the night sky and will take advantage of the brand new astrophysics facility jointly funded by the National Science Foundation and U.S. Department of Energy, the Vera C. Rubin Observatory in Cerro Pachón, Chile.

"This is the most exciting thing I have ever had the privilege to be a part of. This is the science I dreamed of as a kid," beamed Farah. "It’s the universe telling us out loud and in our face that we don't fully understand it yet, and challenging us to explain it.