Among the ten most important discoveries of the last decade, at the 10th place we find SN 1000+0216
In November 2012, the results of a research signed by Jeff Cooke and collaborators, which would have attracted the attention of the scientific community, were published in Nature. The most distant supernova ever observed, named SN 1000 + 0216, had just been discovered.
It was immediately noted that the spectral lines of this supernova showed a visible shift towards lower frequencies due to the expansion of the universe, a phenomenon known as “cosmological redshift”. Basically, the light emitted by a star very distant from the Earth (even several billion light years), along its path to our planet is “stretched” by the expansion of the space in which it is traveling. In other words, the wavelengths emitted by these distant objects are increased. In this way, the light reaches the observers on Earth at lower frequencies than the emitted ones. Given our daily experience with visible light, and given the fact that red occupies the lowest frequency portion of the visible spectrum, astronomers calls this phenomenon “redshift”. However, it should be kept in mind that this phenomenon affects the entire electromagnetic spectrum, from radio waves to gamma rays.
A record-breaking redshift
The more a celestial body is distant from us in the universe, the more its light will spend time in space before reaching our telescopes, the more it will be subject to the expansion of the universe, and therefore more it will be shifted to lower frequencies. This shift is quantified by the parameter e z, defined as the ratio
z = (observed wavelength – emitted wavelength) / emitted wavelength
In short, it is a parameter that quantifies the relative variation of the wavelength of a radiation.
SN 1000 + 0216 presented a redshift z = 3.9, corresponding to an enormous distance from the Earth, equal to 12 billion light years. That is, astronomers have actually observed a supernova that exploded 12 billion years ago, when the Universe was just over a billion and a half years old!
But how is it possible to observe an astronomical event at that distance? It would seem almost impossible! The observation of this supernova was in fact made possible only because it was about 10 times more powerful than a standard core-collapse supernova. But not only … the researchers, through a careful analysis of the light curve, were able to establish that the progenitor of this enormous explosion was an incredibly massive star, with a mass about 200 times greater than the Sun! However, this was not a total surprise, as astronomers are aware that the early Universe was much poorer in heavy elements than today. As a consequence, the opacity of the interstellar clouds was very small, making a possible fragmentation during their collapse, from which the first stellar generations were formed, less likely. This lack of fragmentation therefore favored the birth of a few extremely massive stars from these clouds, at the expense of stars of smaller mass.
Why was it important?
SN 1000 + 0216 therefore offered the great opportunity to observe and study the death of a star during the primordial phases of the universe. However, it appears that it would hardly have been part of the very first stellar generation, which is expected to have lived a few hundred million years earlier. But despite this, it has actually allowed us to push ourselves towards new temporal horizons, ever closer to the supreme moment in which the very first stars were born and lived for their very short and powerful life. In fact, they will be one of the main scientific objectives of various research projects in the coming years, first of all the gigantic “Extremely Large Telescope” (ELT, 39 meters in diameter, in Chile) and the “James Webb Space Telescope”. The the first light of ELT is scheduled in 2025, while the launch of the second is scheduled for 31st October 2021. Exciting times are coming up!
References:
- Cooke et al.; NATURE VOL 491 8 November 2012
