Ancient stars that 'tore themselves apart' as they were dying have just been found, says new study
Astronomers now believe they have discovered ancient chemical remnants of the universe's first stars, according to new research published in The Astrophysical Journal on Sept 28.
For decades scientists have been diligently looking for direct evidence of these 'first generation' stars believed to have formed when the Earth was a modest 100 million years old. The discovery could improve our understanding of how matter in the universe evolved into what it is today, including us.
Colossally large stars 'tore themselves apart' while dying as supernovae
First-generation stars, known as 'Population III,' are thought to have been so colossally large that when they died as supernovae, they tore themselves apart, leaving a specific mixture of heavy chemicals in interstellar space.
Now, a team of astronomers from the University of Toyko claim the elements they discovered from analyzing one of the most distant known quasars could have only come from debris produced by one of these stars' all-absorbing explosion.
An innovative method deduced a distinctive interstellar mixture
The observations were made using the Gemini North telescope (GNIRS), which is one of two identical telescopes that make up NSF's NOIRLab-operated Gemini International Observatory.
Dr. Yuzuru Yoshii and colleagues used an innovative method to figure out the chemical elements in the clouds surrounding the quasar and noticed a distinctive composition. Compared to the ratio of elements in our sun, the substance had over ten times as much iron as magnesium.
The deaths of giant stars with masses 150 to 250 times that of the Sun
The explanation for this unusual composition is that it comes from a first-generation star that exploded as a pair-instability supernova. Although supernovae of this kind have yet to be observed, scientists believe they are the deaths of giant stars with masses 150 to 250 times that of the Sun.
Unlike other supernovae, these dramatic explosions leave no stellar relics, such as neutron stars or black holes. Instead, they blast all their material into their surroundings. Therefore, there are only two ways to find proof of them. This could be to witness a pair-instability supernova as it happens (highly improbable). Another way is to identify the supernova's chemical signature from the material it ejects into interstellar space — which is what the new study claims to have achieved.
There's something about 'Gemini' (the telescope)
The GNIRS splits the light emitted by cosmic entities into their associated wavelengths, each of which carries information about the elements the object is made of. The telescope is one of the few of its size with suitable equipment to achieve such observations.
Still, figuring out how much of each element is present is a challenge because a line's brightness in a spectrum depends on many other things besides the element's abundance.
The new study could be the clearest evidence of a pair-instability supernova
In the Milky Way's halo, chemical searches for a previous generation of high-mass Population III stars were conducted in the past, and at least one preliminary identification was made in 2014. Yoshii and his colleagues, however, consider that their new discovery gives the clearest signal of a pair-instability supernova based on the exceptionally low magnesium-to-iron abundance ratio displayed in this quasar.
Whatever the case, many more observations will be required to verify this theory and determine whether other objects have comparable properties.
The search for Population III stars has fascinated and eluded astrophysicists for decades. One promising place for capturing evidence of their presence must be high-redshift objects; signatures should be recorded in their characteristic chemical abundances. We deduce the Fe and Mg abundances of the broadline region (BLR) from the intensities of ultraviolet Mg ii and Fe ii emission lines in the near-infrared spectrum of UKIDSS Large Area Survey (ULAS) J1342+0928 at z = 7.54, by advancing our novel flux-to-abundance conversion method developed for quasars up to z ∼ 3. We find that the BLR of this quasar is extremely enriched, by a factor of 20 relative to the solar Fe abundance, together with a very low Mg/Fe abundance ratio: [Fe/H] = +1.36 ± 0.19 and [Mg/Fe] =−1.11 ± 0.12, only 700 million years after the Big Bang. We conclude that such an unusual abundance feature cannot be explained by the standard view of chemical evolution that considers only the contributions from canonical supernovae. While there remains uncertainty in the high-mass end of the Population III initial mass function, here we propose that the larger amount of iron in ULAS J1342+0928 was supplied by a pair-instability supernova (PISN) caused by the explosion of a massive Population III star in the high-mass end of the possible range of 150–300 M⊙ . Chemical evolution models based on initial PISN enrichment well explain the trend in [Mg/Fe]-z all the way from z < 3 to z = 7.54. We predict that stars with very low [Mg/Fe] at all metallicities are hidden in the galaxy, and they will be efficiently discovered by ongoing new-generation photometric surveys.
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