Identifying the heavy element born from a neutron star

First identification of a heavy element born from a neutron star

A newly created heavy element, strontium, has been detected in space. The element was found for the first time in the aftermath of the merger of two neutron stars.

ESO’s X-shooter spectrograph observed the new discovery on the Very Large Telescope (VTL). The detection confirms that the heavier elements in the Universe can form in the merger of neutron stars. These finding provide an answer to the once mysterious question of how chemical elements are formed.

Following the detection of gravitational waves passes the Earth, in 2017, ESO utilised its telescopes in Chile, as well as the VTC, to study the source of the waves, a neutron star merger named GW170817.

Astronomers suspected that the possible production of heavier element, from the neutron star collision, could be detected in kilonovae, the explosive aftermaths of the mergers.

ESO’s team of telescopes began monitoring the emerging kilonova explosion over a vast range of wavelengths. The X-shooter took a series of spectra from the ultraviolet to the near infrared. The analysis of these spectra suggests the presence of heavy elements; however, astronomers have only just pinpointed the individual elements.

“By reanalysing the 2017 data from the merger, we have now identified the signature of one heavy element in this fireball, strontium, proving that the collision of neutron stars creates this element in the Universe,” says the study’s lead author Darach Watson from the University of Copenhagen in Denmark.

Strontium is found naturally, on Earth, in soil and other elements and is used in fireworks to give them a red colour.

“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,” says Camilla Juul Hansen from the Max Planck Institute for Astronomy in Heidelberg, who played a major role in the study.

“We actually came up with the idea that we might be seeing strontium quite quickly after the event. However, showing that this was demonstrably the case turned out to be very difficult. This difficulty was due to our highly incomplete knowledge of the spectral appearance of the heavier elements in the periodic table,” says University of Copenhagen researcher Jonatan Selsing, who was a key author on the paper.


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