Gravitational wave detectors in Washington, Louisiana, and Italy. A Gamma-ray telescope high above Earth. An optical telescope in Chile. They all saw the same thing. The aftermath of two neutron stars smashing into one another.

NASA’s Fermi Gamma-ray Space Telescope was the first to notice August 17, 2017 was going to be a special day. A burst of high-energy gamma rays was detected. Moments before, scientists observed tiny distortions in space caused by gravitational waves sweeping through Earth.

When scientists combined the data from the two Laser Interferometer Gravitational-Wave Observatory (LIGO) facilities in Washington and Louisiana with the data from the Virgo detector in Italy, they could pinpoint where the waves were coming from in a small(ish) portion of the sky.

Their target was a patch of sky about 150 times the size of the full moon near the constellation Hydra. Like the saying goes, ‘it’s a big ass sky,’ and scientists just narrowed it down big time.

Astronomers from around the world were receiving urgent texts and emails from colleagues to point their telescopes in this spot of the sky.

telescopes observing kilonova

Telescopes from around the world observed the kilonova. Credit: ESO

Here’s Iair Arcavi, a leader on one of the studies released today, explaining what the gravitational wave signals were indicating. “Such a gravitational wave signal had never been seen before but was unmistakably generated by two neutron stars spiraling together.”

The resulting explosion from two neutron stars coming together is called a kilonova. A phenomenon that had never been definitively observed. Until now.

Kilonova as seen by Hubble

The kilonova as seen by Hubble. Credit: ESO

Telescopes around the world observed the kilonova for days afterward. You can see how quickly the explosion dimmed after just a few days.

Kilonova brightness


“This marks the first time in history that an astronomical phenomenon has been first sensed through gravitational waves and then seen with telescopes,” said Arcavi. “For years, we’ve heard theorists predict how a kilonova should look. I couldn’t believe we were finally seeing one for the first time.”

Now, scientists have the full picture of a cosmic event. Not just one half.

Here’s an artist impression of the two neutron star’s smashing into each other.

That explosion and the studies that follow support another prediction about kilonovas. They are responsible for creating chemical elements heavier than iron. Think gold and platinum. The kilonova’s spectra revealed a slew of heavy elements, including huge quantities of gold.

“The data we have so far are an amazingly close match to theory. It is a triumph for the theorists, a confirmation that the LIGO–VIRGO events are absolutely real, and an achievement for ESO to have gathered such an astonishing data set on the kilonova,” says Stefano Covino, a lead author on one of many papers released today.

Timing almost made this observation impossible. This cosmic event appeared very close to a lenticular galaxy called NGC 4993. According to the European Southern Observatory, this galaxy (and its immediate surroundings) were only observable in the evening in August. By September, it was too close to the Sun in the sky to be seen by telescopes.

Scientists are celebrating today’s discovery. Some call it the beginning of a new era of astronomy. For space fans like me, it’s just more awesome science that will only get better with technology.

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