For the first time ever, scientists discover a heavy element born in the aftermath of a collision between two neutron stars.
Scientists have already known that a lot of heavy elements occur when a pair of neutron stars, collide and explode. But researchers have finally proved it for the first time.
On 17 August 2017, astronomers detected an event they had never seen before: the cataclysmic merger of two neutron stars (GW170817). Taking place 140 million light-years away, this event produced heavy elements such as gold, platinum, and lead. Therefore scattering them across the universe in a kilonova. The huge burst of light fades rapidly so it’s very difficult to detect one.
Neutron stars are the leftover remnants of supernovae. They have masses bigger than that of our Sun. But the average size of a neutron star is comparable to the size of a city like Chicago. This makes them incredibly dense.
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Now, astronomers have also detected strontium, a heavy element created in the aftermath of the merger. They made the observation using ESO’s X-shooter spectrograph on the Very Large Telescope (VLT).
Astronomers have been studying the physical processes that create elements since the 1950s. Over the years, they’ve determined which cosmic forces are responsible for different ones.
“By reanalyzing 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. On Earth, you can find strontium naturally in the soil and is concentrated in certain minerals. Its salts usually give fireworks a brilliant red color.
“This is the final stage of a decades-long chase to pin down the origin of the elements,” Watson said. “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. But, until now, we did not know the location of the final, undiscovered process, known as rapid neutron capture, that created the heavier elements in the periodic table.”
Rapid Neutron Capture
Rapid neutron capture is a process in which an atomic nucleus captures neutrons so it swells to an unstable size. But the whole thing happens so fast the element doesn’t have time to split apart. In addition to the speed factor, heavy elements like strontium also need incredibly hot environments full of free neutrons.
“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, study co-author at the Max Planck Institute for Astronomy in Heidelberg.
However, astronomers are still understanding what happens in this process, as well as what it produces in the aftermath.
Using the data from the X-shooter instrument on the VLT, the astronomers spotted an object with a temperature of 6,740 degrees Fahrenheit. The temperature and brightness of the object acted like a fingerprint for the element.
“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.
Researchers published their new study Wednesday in the journal Nature.