When Neutron Stars Collide: Spot Scientists Kilonova Explosion from Epic 2016 Crash


Scientists recently spotted a gold-and-platinum factory in space, the remains of a massive collision of stellar bodies.

The precious elements were formed in a "kilonova, "or an epic explosion that is likely to happen when two very dense stars (called neutron stars) slammed into each other. (A kilonova is an even stronger type of explosion than the typical supernova that happens when wide stars blow up.)

The kilonova's power comes from superdense colliding neutron stars, where weird physics reigns. These objects are the remnants of a wide range of stars – once many times the mass of our sun – that exploded, leaving behind a dense core. Although neutron stars are only the size of a city, their mass is about 1.4 times that of our sun. Because they are so dense, when these neutron stars collide, their echoes are visible across a large stretch of space.

Related: First Glimpse of Colliding Stars Neutron Yields Stunning Pics

Now, scientists think they have been stuck at the time. Astronomers spotted a burst of ultrabright gamma-rays in the sky in August 2016, but they did not understand initially what was going on.

Then a little thing called LIGO happened. The incredibly productive Laser Interferometer Gravitational-Wave Observatory (whose founding scientists had already won a Nobel Prize for a discovery made by the observatory in 2015) made a historic observation in 2017 when it recorded first observation of two neutron stars merging. Scientists tracked the event in every imaginable wavelength, as well as the gravitational waves.

Inspired by LIGO, scientists revisited their strange 2016 data and had a pleasant surprise. Initially, the observations in 2016 did not match what models of the day predicted for a kilonova event; that was because "barely any signal remained" after 10 days, lead author Eleonora Troja, an astronomer and research scientist at the University of Maryland, said in a statement.

"We were so disappointed," Troja recalled their initial observations of the 2016 event. But LIGO's detection is helping them to look at the old data with new understanding. "[We] We have indeed caught a kilonova in 2016, "Troja added." It was a nearly perfect match. "

In infrared wavelengths, both the 2016 and 2017 events had similar luminosities (or intrinsic brightness) happening at exactly the same time. While scientists observed the latter 2016 event, what sets the future is that there is information about the first few hours of the kilanova explosion. That's because NASA's Neil Gehrels Swift Observatory tracked the 2016 gamma-ray burst just minutes after it was detected, while the observations of the 2017 burst were delayed by about 12 hours.

By comparing the two events, the researchers concluded that the 2016 observations were likely also of a kilonova formed by two colliding neutron stars. That said, scientists are not sure yet or such an explosion would also form when a black hole and a neutron star merge, and if so what it would look like.

Troja and her colleagues plan to examine other past explosions by this finding, and to create a fresh approach to future observations. In particular, they will focus on events that are strong in infrared light, which suggests that the explosion is gold and platinum.

A paper based on the new research was published on Aug. 27 in the journal Monthly Notices of the Royal Astronomical Society.

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