Neutron star collisions give birth to heavy elements like strontium in space

Earlier, scientists believed that most of the elements in the universe heavier than helium are created in stars


                            Neutron star collisions give birth to heavy elements like strontium in space

Looking for signatures of the 2017 neutron star merger in space, scientists have detected a heavy element named strontium — found naturally in the earth's soil. The discovery provides concrete evidence that collisions between neutron stars give birth to these elements.

Earlier, scientists believed that most of the elements in the universe heavier than helium are created in stars. But the knowledge of heavy stars were hazy. They speculated that to generate elements heavier than iron, stars require even hotter environments with lots of free neutrons. And explosions, they believed, provide the perfect stage by allowing atoms to rapidly hit neutrons, thereby creating heavy elements through rapid neutron capture. 

"We know now that the processes that created the elements happened mostly in ordinary stars, in supernova explosions, or in the outer layers of old stars," said the study's lead author Darach Watson from the University of Copenhagen in Denmark. However, he added that the scientists did not understand where heavier elements were being formed for a long time.

So they specifically directed their attention towards kilonova — an explosion that happens when neutron stars collide, hoping to find signatures of heavy elements. It was here that another group of scientists spotted gold and platinum, both heavy elements, in August this year.

A team of European researchers, using data from the X-shooter instrument on ESO's Very Large Telescope, has found signatures of strontium formed in a neutron-star merger. This artist's impression shows two tiny but very dense neutron stars at the point at which they merge and explode as a kilonova. In the foreground, we see a representation of freshly created strontium. (ESO/L. Calçada/M. Kornmesser)

Using the European Southern Observatory's X-shooter spectrograph on the Very Large Telescope (VLT), they found signs of heavy elements. But they could not identify the type of heavy element. Only after they reanalyzed the 2017 data, according to Watson, they were able to identify strontium, providing proof that the collision of neutron stars creates this element in the Universe.

"This is the first time that we can directly associate newly created material formed via neutron capture with a neutron star merger, confirming that neutron stars are made of neutrons and tying the long-debated rapid neutron capture process to such mergers," said Camilla Juul Hansen from the Max Planck Institute for Astronomy in Heidelberg, who played a major role in the study.

The study was published in Nature.

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