Day 6

When stars collide: How 4,000 scientists converged for an epic kilonova cram session

The never-before-seen collision of two dead stars led to an unprecedented astronomical collaboration and interrupted a day at the spa.
Vicky Kalogera (right) is among the many astronomers involved in studying the collision of the two stars depicted in an illustration on the left. (A. Simonnet/National Science Foundation/LIGO/Sonoma State University and Northwestern/YouTube)

Millions of years ago, two dead stars collided, setting in motion a chain of events that would interrupt Vicky Kalogera's vacation and consume two months of her life.

This illustration depicts the merger of two neutron stars and the rippling of spacetime as gravitational waves ripple outward from the explosion. (A. Simonnet/National Science Foundation/LIGO/Sonoma State University)
On the morning of Aug. 17, Kalogera — an astronomer and professor at Northwestern University — had planned the perfect "spa relaxation day."

But when she checked her email, she found exciting news: astronomers had detected gravitational waves followed by a gamma ray burst.

Together, these indicated the existence of a kilonova (a collision of two super-dense neutron stars) 130 million light-years away. Two months later, on Oct. 16, astronomers revealed their findings to the public.

Kalogera tells Day 6 that after she saw the news, she emailed her colleagues, telling them: "This is life-changing. We're dropping everything and this is what we're working on."


Never-before-seen collision

For Kalogera and astronomers all over the world, this was a thrilling discovery they'd waited a decade for.

LIGO, or the Laser Interferometer Gravitational-Wave Observatory, detected gravitational waves in 2015 by recording the sound of two black holes colliding.

This is life-changing. We're dropping everything and this is what we're working on.- Vicky Kalogera

But unlike LIGO's previous discoveries, which involved impossible-to-see black holes, this one could be directly observed by astronomers.

Within hours of the alert, 70 teams of astronomers, following a set plan, trained their telescopes on the kilonova, recording observations across the electromagnetic spectrum — which includes X-rays, radio waves, gamma rays, microwaves and visible light.

Concrete and stainless steel tubes house and protect the four-kilometer long laser apparatuses at the LIGO Hanford Observatory in Hanford, Washington, January 9, 2002. (Anthony P. Bolante/Reuters)


Unprecedented report a "major, major challenge"

Kalogera was one of 10 writers across five time zones who documented the process in what they call "the multi-messenger astronomy publication."

It details how astronomers "started with the first alert in gravitational waves then mobilized the entire astronomy community to discover the same source across the entire electromagnetic spectrum," Kalogera says.

Writing it "was a major, major challenge."

The report is unprecedented in scale.


"Normally when you write scientific publications, a group of people is involved," Kalogera says.

"Sometimes they are all at the same institution, maybe they're spread around a couple of institutions. And you communicate over email, you pass back and forth the manuscript in different versions."

But in this case, that wasn't possible. Paper writers were responsible for representing the work of about 4,000 co-authors.

"That is definitely the highest-authorship paper ever written for an astronomy discovery," Kalogera says.


Exhausting, "but needed"

Writers drafted the report, responding to thousands of comments from authors as they worked.

Once the paper was nearly complete, Kalogera and the other writers spent nearly two weeks holding daily teleconferences.

For 12 to 14 hours, they would stay connected on a voice channel. If they had questions, they would ask the right person or team to get answers.

Vicky Kalogera, a professor and astronomer at Northwestern University, was one of 10 co-writers who worked on a paper with about 4,000 co-authors. (Northwestern University/YouTube)

"We would discuss. Sometimes we would argue. Sometimes we needed to take votes and make a decision. How would we write one paragraph? How would we write one sentence? It was exhausting, but it was needed. Because this story had to be told," Kalogera says.

Kalogera says this "revolutionary" experience helped show astronomers how important collaboration is.

"Juicy, exciting science is going to keep happening more and more as we move forward. So we're going to become more and more accustomed to working this way."

To hear Vicky Kalogera tell her story, download our podcast or click the 'Listen' button at the top of this page.