Stars collide, and UO scientists help track another cosmic first

Artist conception of neutron star collision

An epic collision that likely spewed platinum and gold into space and shook the very fabric of the universe has lit up detectors run by an international team of scientists in which the UO is a major contributor.

In another stunning first for a new kind of observatory that measures the infinitesimal throbbing of spacetime, detectors observed the cataclysmic merger of two small but incredibly massive bodies known as neutron stars. Analysis of the event could help answer the mystery of how nature’s heaviest elements are created, provide much more precise measurements of distant celestial objects and even help determine the fate of the universe itself.

And if that wasn’t enough for a team that also just won the Nobel Prize in physics, the event has confirmed Einstein’s idea, part of his theory of general relativity, that gravitational waves travel at the speed of light.

The latest news from LIGO, or Laser Interferometer Gravitational Wave Observatory, just adds to a set of accomplishments that includes the first measurements of the collision of two black holes. But the neutron star signal offers so many tantalizing new hints about the nature of the universe that even seasoned researchers were floored.

“I think we were all flabbergasted,” said the UO’s Ray Frey, head of the physics department and member of the LIGO observatory team.

Weeks later, they still are.

Physics professor Ben Farr, who’s so new at the UO he doesn’t even have office furniture, was one of the first people to get an alert about the new signal when it arrived in August and jump on the phone with a few other researchers.

“I think we were all literally shaking,” he said. “It was the birth of multimessenger astronomy.”

That refers to astronomy that uses more than just electromagnetic waves — light, radio, X-rays — to view the universe. Combining optical and gravitational wave astronomy is kind of like going from silent movies to talkies.

“We draw this analogy that with gravitational waves it’s like adding a soundtrack to the universe,” Farr said.

Signal comparison GIFWhat made the observation so groundbreaking is that, again for the first time, astronomers were able to use the signal to locate the newly formed star in space and turn dozens of conventional telescopes on it. That let them view it not only in visible light but also across a wide range of the electromagnetic spectrum, from radio to gamma radiation.

“It’s the first time that we’ve observed a cataclysmic astrophysical event in both gravitational waves and electromagnetic waves — our cosmic messengers,” said Caltech’s David H. Reitze, executive director of the LIGO Laboratory. “Gravitational wave astronomy offers new opportunities to understand the properties of neutron stars in ways that just can’t be achieved with electromagnetic astronomy alone.”

With black hole collisions, no light escapes from the ultradense object so there’s no chance of visual observations. But the smashup of neutron stars is different.

As the two bodies circle closer they first start tearing each other apart through the same force that creates the tides on Earth, then slam together with such violence they spew out and then light up a cloud of freshly created elements while also emitting powerful beams of gamma rays, known as gamma-ray bursts. The LIGO observation confirms a hypothesized association between gamma-ray bursts and neutron star mergers.

As the stars spiral together and then merge, they literally create waves in what is known as spacetime, the cosmic soup that fills the universe. These gravitational waves are what LIGO is able to detect and measure.

The collision happened 130 million years ago, meaning it took place 130 million light years from Earth in another galaxy. Traveling at the speed of light, the gravitational wave hit the LIGO detectors just 1.74 seconds ahead of the light — in the form of gamma rays — from the merger. The slight delay was how long it took for material torn loose by the collision to be blasted into space.

 

 

LIGO consists of two L-shaped observatories, one near Hanford, Washington, and the other in Louisiana. On this observation, the observatories were joined by a new facility known as VIRGO near Pisa, Italy, that provided crucial data to help locate the object in space.

LIGO research is carried out by the LIGO Scientific Collaboration, a group of more than 1,000 scientists from universities around the United States and in 14 other countries. UO researchers were among the LIGO Collaboration’s founding groups and were a key part of a recent upgrade of the Hanford observatory’s sensors, an effort known as Advanced LIGO.

Within LIGO, Frey is co-leader of a group that focuses on the gamma ray bursts that accompany stellar explosions and mergers; his research centers on gravitational-wave astrophysics. Farr is co-leader of a LIGO group that helps determine the mass, size and other characteristics of the objects that cause gravitational waves. Farr is also a member of a team of astronomers that used the Dark Energy Camera, located in Chile, to observe the counterpart in optical light.

In addition to Frey and Farr, UO research professor Robert Schofield, research associate Dipongkar Talukder and graduate students Jordan Palamos and Philippe Nguyen are members of the UO’s LIGO team who were closely involved in interpreting data from the observation. UO physics professor Jim Brau also played an important role in the development of the LIGO program and has been actively involved in research and analysis.

Neutron stars are the smallest, densest stars known to exist and are formed when massive stars explode in supernovas. The stars that collided didn’t weigh a whole lot more than our sun yet were only about 10 to 20 kilometers in diameter, making them so dense that one teaspoon of their material weighs about a billion tons.

At the moment of collision, the bulk of the two neutron stars collapsed into one ultradense object, emitting a fireball of gamma rays. Theorists have predicted that what follows the initial fireball is a “kilonova” — a phenomenon in which material left over from the stellar collision, which glows with light, is blown out of the immediate region and far out into space.

The new light-based observations show that heavy elements, such as lead and gold, are created in these collisions and subsequently distributed throughout the universe. That may answer a longstanding question about how elements heavier than iron are formed.

Another bonus from the observation is the most accurate measure yet of the distance to a celestial event. And because the event also was observed with light-based telescopes, that means researchers will be able to make better estimates of stellar distances.

Frey said it also could open new doors in cosmology by allowing astronomers to confirm recent data indicating the expansion of the universe is speeding up, and if so, by how much. The acceleration is connected with the presence of the hypothesized "dark energy" content of the universe.

By Greg Bolt, University Communications