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Neutron Star Collision Seen For the First Time Ever!

S u m m a r y :
A neutron star merger observed for the first time promises to revolutionise the world of astronomy. The findings, published in the journal Science, are hoped to educate us about neutron stars themselves, and they might also help explain the creation of elements like gold.

Neutron Stars, The Remnants of Supernovae

Neutron stars constitute collapsed cores that arise from the death of massive stars, an event called supernova which is marked by a spectacular light-show of an explosion. The destruction of these big stars, thought to be brought about by gravitational collapse, compresses their core with the resulting neutron stars ending up with a super high density, making them the smallest and densest stars. It has long been speculated as to what would happen if two neutron stars were to merge. The world of science is no more in the dark as such an event has been witnessed last month, and studied intensely ever since by scientists from the Carnegie institution for science and the University of California (UC), Santa Cruz.

“This is a huge discovery,” says Ryan Foley from UC. “We’re finally connecting these two different ways of looking at the universe, observing the same thing in light and gravitational waves, and for that alone this is a landmark event. It’s like being able to see and hear something at the same time.”

Image of the Swope Supernova Survey 2017a (or SSS17a), the neutron star merger, from the night of the discovery in August. Photo Credits: Tony Piro.

Neutron Stars & Black Holes

Carnegie’s study lead author Tony Piro compares neutron stars with black holes.

“They are as close as you can get to a black hole without actually being a black hole,” says Piro. “Just one teaspoon of a neutron star weighs as much as all the people on Earth combined.”

The collision of two neutron stars was observed by the team on August 17. The Carnegie scientists were notified of the phenomenon by the Laser Interferometer Gravitational-Wave Observatory (LIGO) where gravitational waves had been detected; these waves are indicators of distant cosmic occurrences. A LIGO team has recently been awarded the Nobel Prize in Physics for having detected gravitational waves resulting from the merging of two black holes last year. The more recent event is, however, ‘bigger’ than the first one because, while the black hole merging are not visible with telescopes because it does not emit light, the neutron star merging produces both gravitational waves and light waves.

Gravitational & Light Waves

The neutron star merger emitting light was observed using the Swope telescope at the Las Campanas Observatory; the discovery has been named Swope Supernova Survey 2017a (or SSS17a).

“The ability to study the same event with both gravitational waves and light is a real revolution in astronomy,” marvels Piro. “We can now study the universe with two completely different probes, which teach us things we could never know with only one or the other.”

The Swope telescope at Carnegie’s Las Campanas Observatory, where the neutron star collision was observed for the first time. Photo Credits: Yuri Beletsky.

A Race to Spot The Event

It is to be noted that LIGO had informed observatories all across the globe of the detection of the gravitational wave. From then on, astronomers around the world were trying to spot the source thereof. It was only the Carnegie and UC Santa Cruz astronomers who eventually made the discovery of SSS17a.

“We saw a bright blue source of light in a nearby galaxy–the first time the glowing debris from a neutron star merger had ever been observed,” says Josh Simon from the Carnegie team. “It was definitely a thrilling moment.”

Artist’s rendition of the collision of two neutron stars. Photo credits: Robin Dienel; Carnegie Institution for Science.

Neutron Stars Create Gold, Platinum, and Uranium

Being the first to spot the event, Simon and his colleagues also had the time to make further observations. They were able to obtain some of the earliest spectra of the phenomenon, which are thought to be helpful to explain the creation of gold and similar substances. The spectra allow for the separation of light from a heavenly body into its many wavelengths in a prism-like manner, and this data makes the measurement of the speed and chemical composition of cosmic sources possible. Given that neutron star mergers are thought to create elements like gold, platinum, and uranium, this theory can now be actually tested.

“I think this can prove our idea that most of these elements are made in neutron star mergers,” says Enrico Ramirez-Ruiz from UC. “We are seeing the heavy elements like gold and platinum being made in real time.”

“As we followed the glow of the explosion over the next few weeks, it showed some key characteristics ofthe radioactive decay of these heavy elements,” says Carnegie’s Maria Drout. “This strongly suggests that these elements were synthesized following the merger, solving a 70-year-old mystery.”

Further Research

The team is positive that these first spectra will shape the understanding of neutron stars further.

“These first spectra are completely unique data and will lead to a lot of science down the road,” comments Ben Shappee from Carnegie. “They will be extremely important for our understanding of neutron star mergers for years to come.”

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