ting from a neutron star collision
• A neutron star is an extremely compact star consisting mainly of neutrons. It is typically only about 20 km in diameter, but can weigh up to two times more than the Sun.
• When two neutron stars collide, a phenomenon known as a kilonova occurs. Darach Watson and his colleagues realized that the kilonova spectrum could be overall approximated using a so-called ‘blackbody spectrum’, which is the simplest radiation emitted by any hot material. However there were deviations from a pure blackbody which the researchers could then identify as being due to the presence of the heavy element strontium.
• When neutron stars merge, a huge mass of heavy elements is produced. A minimum of 10 Earth masses of strontium is required to explain the observed features, and the amount of strontium produced was likely larger.
• The element strontium is a metal, number 38 in the periodic table. It appears in solid form at room temperature. Its main practical application is in the production of cathode ray tubes for television screens.
The figure shows four spectra of a kilonova indicationg the presence of strontium. Here the light is decomposed into its spectral components (split wavelength by wavelength).
From left to right is shown (in angstroms) how much light there is in the blue, in the visible, and in the near-infrared spectre. At all epochs, the spectra show a departure from the simple, thermal kilonova spectrum, due to the presence of the element strontium, which both absorbs and re-emits some of the light.
These deviations are indicated by the red shaded areas. These areas highlight the difference between the observed data (the grey line) and the kilonova model without strontium (the dotted blue line). The kilonova model including the effect of strontium is indicated by the red line.
(Figure: Niels Bohr Institute/DTU Space)
In addition to scientists from the University of Copenhagen (Niels Bohr Institute) and DTU Space, researchers from institutions in Iceland, Italy, England, The Netherlands, Germany and USA have participated in the discovery.