The universe’s first stars could have formed as early as 100 million years after the universe formed. These early stars were probably big, hot, and short-lived, and probably created many of the universe’s heavy elements in their cores or in epic explosions at the end of their lives.
Now a research team published a new analysis of a distant quasar and the cloud around it in which they claim to have used a new technique to find proof of one of these early stars. Observations taken with the Gemini North telescope located near the summit of Hawaii’s Maunakea provided the data needed to produce a chemical analysis of the cloud surrounding this quasar.
The analysis found that the cloud has ten times more iron atoms for each magnesium atom as the Sun does. This unusually high iron-to-magnesium ratio could indicate that an early star that was 300 times more massive than the Sun resided there.
The analysis’ co-authors, Yuzuru Yoshii and Hiroaki Sameshima of the University of Tokyo, developed a new method for estimating the abundance of elements in and around distant objects like the target quasar. With this method, scientists could detect the cosmic “footprint” of supernovas by studying the chemical signatures left behind. They say they will continue to refine their method by taking readings of other distant objects.
Why is this a big deal?
Cosmologists gained a good grasp of the largely homogenous early universe from the cosmic microwave background radiation generated about 400,000 years after the big bang. Matter was evenly distributed. There were no “large round clumps,” like stars or planets, that had sucked up a considerable amount of the surrounding matter.
A billion years after the big bang, quasars existed. Quasars are supermassive black holes like the one at the center of the Milky Way Galaxy that can be detected by the highly energetic streams of matter that get ejected when they feed on a lot of matter. Early galaxies also existed. What changed in between these two times?
One possibility: The early “primordial soup” – the homogenous, evenly distributed matter in the universe – began to develop clumps like milk that had been left to sit out for way too long. Small clumps eventually absorbed enough matter to become bigger clumps. But they did it nearly invisibly – as the universe expanded, it cooled and the microwaves redshifted into longer waves, making it difficult for cosmologists to know exactly what happened between the start of the “primordial soup” period and the time the first stars started appearing.
Common cosmological models indicate that the clumps evolved into small systems capable of forming stars as early as 100 million years after the big bang. Most of these systems, called protogalaxies, could have consisted of mostly dark matter mixed in with the “normal” matter that scientific instruments like the Hubble Space Telescope or the twin Gemini telescopes can more easily detect.
Early stars likely formed most of the heavy elements in the universe when they died.
Hydrogen and helium already existed when the first stars formed. Population III stars – a term for the earliest stars in the universe – would have almost purely consisted of these two “lightweight” elements. Then they formed most of the heavier elements that astronomers call “metals” – a catchall term used in astronomy to indicate elements that are heavier than hydrogen and helium.
The sort-of-backwards counting scheme indicates that Population II stars were slightly metals-rich stars that came after Population III, and Population I is the most recent generation of stars that have the most metals.
A study published in The Astrophysical Journal in May 2019 indicates that the deaths of the Population III stars were brilliant, possibly asymmetrical, major sources of heavy metals that formed in the blasts, and powerful enough to possibly blow metals into other galaxies in jets of matter. As part of their research, the study’s authors studied a rare Population II star that contained a surprisingly low amount of iron and also contained a large quantity of another surprising element – zinc.
According to previous models, a lot of the iron that would have formed in the core of a Population III star probably got trapped in the black hole that it formed when it died. Most of the zinc would have, as well. However, the zinc could have escaped such a fate by getting blasted off in jets caused by an aspherical explosion. The researchers’ modeling also indicated that the supernova could have been 5 to 10 times as powerful as previously expected.
The Population III stars’ lifespans were probably short with incredibly violent deaths. Yuzuru Yoshii and Hiroaki Sameshima say they found a new method of detecting them – or at least finding evidence that a Population III star was there in clouds of dust surrounding the most distant quasars.