The James Webb Space Telescope (JWST) may have found some of the first stars in the universe. These stars are called Population III stars and are thought to have formed when the universe was very young
The JWST was built to help us understand the early universe. In June 2023, scientists reported that the JWST may have found three bright objects that could be supermassive “dark stars”. Until now, dark stars have only been theoretical.
The JWST can see 13.6 billion years into the past, while the universe is 13.7 billion years old. However, the early universe was so compressed that light was immediately absorbed by other things. It took 380,000 years for the universe to cool and thin enough for light to travel through it. This first light is called the cosmic microwave background and can still be detected today.
We are tantalisingly close to seeing the beginning of the cosmic dawn, the time when the first stars and galaxies formed, with the James Webb Space Telescope (JWST)
Population III stars are hypothetical stars that are thought to have formed in the early universe. They are believed to have formed before the first metal-rich stars, and are thought to have played a key role in the formation of the first galaxies.
Population III stars are predicted to be extremely massive and short-lived, with masses of 100 to 300 solar masses and a lifespan of less than one million years. They are thought to have formed from the primordial gas left over after the Big Bang, and to consist almost entirely of hydrogen and helium, with very little to no heavy elements (metals).
Over time, these stars exhausted their fuel and exploded in supernovae, forming the heavier elements found in stars today.
The term “Population III stars” was first introduced by Neville J. Woolf in 1965.
Population II stars are thought to have formed earlier than Population I stars because they have lower metallicity. This means they contain fewer heavy elements, which indicates that they formed earlier in the history of the universe.
Population II stars are typically found in the halo and globular clusters of galaxies, while Population I stars are found in the disk and spiral arms of galaxies.
Population II stars are older, less bright and cooler than Population I stars, with fewer heavy elements. They are formed from gas that has been enriched with heavy elements from previous generations of stars. However, the disk of a galaxy is continually being enriched with heavy elements from ongoing star formation.
Population II stars formed when the abundance of elements heavier than hydrogen and helium was low.
Hydrogen and helium are the two lightest elements created in the Big Bang. During the early stages of the universe, the intense heat and pressure allowed these elements to fuse together and form the first stars.
Stars shine by the fusion of hydrogen and helium in their cores. Stars are primarily made of very hot gases, which are mostly hydrogen and helium.
Population II stars are relatively rich in hydrogen and helium but poor in elements heavier than helium. They contain 10 to 100 times less of these elements than Population I stars.
Population II stars can form elements such as carbon, oxygen, calcium, and iron. These elements were dredged up from the core of stars and ejected by means of stellar winds to the interstellar medium.
Population I stars have more heavy elements than Population II stars.
Population I stars are young stars that contain roughly 2% heavy elements and 98% hydrogen and helium. Population II stars are older stars that contain little heavy metals in their atmosphere.
Population I stars are usually blue in color, while Population II stars are usually red in color like the sun.
Population I stars include the brightest stars in the Milky Way’s disk, which are predominantly blue. The brightest Population I stars are hot blue giants and supergiants, which are much more massive than the Sun.
Population II stars are found throughout the galaxy, including some in the disk and others in the halo. The brightest stars in the Milky Way’s globular clusters, which are predominantly red, are Population II stars.
The Sun is a Population I star. Population I stars are young and luminous, and are found in the spiral arms and disks of spiral galaxies. Population I stars include bright supergiant stars, main-sequence stars, and members of young open star clusters.
Population I stars are metal-rich, with heavy elements making up 1–4% of their total stellar mass. This includes elements like carbon, nitrogen, and oxygen. Population I stars are younger than Population II stars, and some are as old as 10 billion years, while others are still forming today. The Sun is about 5 billion years old.
No Population III stars have been directly observed yet. However, indirect evidence of their existence has been found in a gravitationally lensed galaxy in a distant part of the universe.
Some say that Population III stars may not have been observed because they were all high-mass stars that ended their lives as stellar remnants like black holes and neutron stars.
However, recent observations of GN-z11 by the James Webb Space Telescope (JWST) have revealed hints that this galaxy may harbor Population III stars. The JWST was built to transform our understanding of the early universe.
The James Webb Space Telescope (JWST) may be able to detect Population III stars in distant galaxies. However, direct detection of Population III stars remains elusive.
The JWST may be able to detect stars in the relevant magnitude range if gravitational lensing is favorable. However, some say that it’s unlikely that the JWST will detect individual Population III stars at these redshifts.
The JWST may have detected one of the first stars to exist in the universe. However, this discovery doesn’t provide direct evidence or observation, only emissions coming from a very distant place in the universe.
Population III stars are thought to be massive for a few reasons:
- More gas available
- Gas fragments less
- Stars don’t lose as much mass
- Lack of efficient coolants in the primordial gas
- Central helium burning
The first stars could have been smaller than present stars because of the enhanced formation of molecular hydrogen at early epochs. However, the lack of metals or the effects of the microwave background could have increased the fragment mass.
The star expands and the stellar radius becomes more than 10 times larger at the end of helium burning than that on the main sequence.
Theories place an upper limit of 1000 solar masses on Population III stars. Any more mass would have caused the nebula to collapse into a blackhole before nuclear fusion took place
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