In August 2017, humanity noticed a miracle. For the first time, we witnessed the collision of neutron stars, an event watched by telescopes around the world, alerted by the gravitational disturbances produced as the two objects spiraled towards each other to merge and form a black hole.
Right then, we knew that this explosion, a kilonova named AT2017gfo, would provide us with enough scientific data for years of study. That’s how it turned out. Now, scientists have gathered data from multiple telescopes to reconstruct the days that followed the kilonova and its violent explosion, which gave rise to a stream of heavy elements.
This event evolved, says a research team led by astrophysicist Albert Sneppen of the Niels Bohr Institute at the University of Copenhagen (Denmark), in a Big Bang-like fashion, beginning with a “hot soup” of particles that cooled and turned into matter.
“This astrophysical explosion develops dramatically from hour to hour, so no telescope can follow the whole story. The viewing angle of the telescopes is blocked by the Earth’s rotation,” explains Sneppen.
“But by combining existing measurements from Australia, South Africa and the Hubble Space Telescope, we can follow the evolution of the event in detail. The end result shows us that the whole is more than the sum of each individual data set,” says the researcher.
Colliding neutron stars help us study the Big Bang
One of the most fascinating discoveries about kilonova AT2017gfo was the creation of heavy elements. Many elements are forged inside stars, where fusion processes at the core fuse atoms together to create heavier elements, explains Science Alert.
However, there is a limit: stars cannot fuse elements heavier than iron, because the energy required for this process is greater than that produced by fusion. To produce heavier elements requires a very energetic event, such as a supernova explosion. AT2017gfo showed that kilonovae can be efficient “factories” of heavy elements; in the light emitted during the explosion, astronomers detected the presence of strontium.
Sneppen and his colleagues took the analysis further. By carefully studying several data sets, they were able to observe the hour-by-hour evolution of the kilonova and the formation of heavy elements, known as “r-process” elements, within it.
When neutron stars collide, the initial kilonova, formed from the exploding remnants of neutron stars, is extremely hot, reaching billions of degrees, compared to the heat at the beginning of the Big Bang. In this hot, plasmatic environment, elementary particles, such as electrons, move freely without being bound.
How were atoms formed at the beginning of the Universe?
As the kilonova expands and cools, the particles attract each other and turn into atoms. Researchers say this phenomenon is similar to a period in the history of the Universe known as the Epoch of Recombination. About 380,000 years after the Big Bang, the Universe cooled enough for particles in the primordial plasma “soup” to coalesce into atoms. The plasma soup scattered light instead of letting it propagate, and this “recombination” allowed light to spread throughout the Universe.
The recombination process observed in neutron star kilonova is very similar to what we think happened in the Epoch of Recombination, suggesting that kilonova could be a powerful laboratory for studying the evolution of the early Universe on a miniature scale.
The researchers also confirmed the presence of strontium and yttrium in the expanding kilonova, supporting the idea that the explosion of a kilonova is a source of heavy elements in the Universe.
“Now we can see the moment when atomic nuclei and electrons come together in the emitted light,” says astrophysicist Rasmus Damgaardfrom the Niels Bohr Institute.
“For the first time we see the creation of atoms, we can measure the temperature of matter and we can observe the micro-physics of this distant explosion. It is like admiring the cosmic background of radiation, but here we can see everything from the outside. We see before, during and after the birth of atoms,” he explains.
The research was published in the journal Astronomy & Astrophysics.
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Source: www.descopera.ro
