The characteristics of the first stars in the universe are unknown. We have
only seen traces of them while gazing into the far reaches of the early
Universe.
But a new line of evidence found in images from the James Webb Space
Telescope appears to support a recent theory that is gaining traction:
absolute colossi with masses up to 10,000 Suns were fusion-powered balls of
heat and fury that appeared not long after the appearance of the first
stars, if not among them.
According to astronomer
Corinne Charbonnel
of the University of Geneva in Switzerland, "We believe we have found a
first clue of the presence of these extraordinary stars today, thanks to the
data collected by the James-Webb Space Telescope."
A kind of star group known as a globular cluster is the first component of
this puzzle. There are around
157 objects
classified as globular clusters in the Milky Way, making them rather common
in our neighborhood of the universe. They are spherical, very dense clusters
with between 100,000 and 1 million stars. The chemical makeup of all of
these stars is remarkably identical, indicating that they all formed from
the same cloud of gas at around the same time.
Astronomers see these ancient globular clusters as "fossils" of the early
Universe and study them to get knowledge about the chemistry of eons past.
They also frequently include very old stars on the verge of
extinction.
However, there is a really odd quality to these older globular clusters.
They show relative depletion of carbon and oxygen and enrichment of helium,
nitrogen, and sodium, chemical abundance ratios that vary from star to star
and are difficult to understand.
Hydrogen burning at extremely high temperatures is the hypothesis that best
matches these abundances. In 2013, scientists hypothesized that the cores of
big stars may be one place where very high temperatures might exist. really
large stars. possibly supermassive, with cores that are far hotter and under
much higher pressures than those of the stars we currently observe in our
vicinity, with masses of roughly 10,000 solar masses.
Then,
in 2018, Charbonnel and her colleague Mark Gieles from the University of Barcelona
in Spain came to the conclusion that it was feasible for the stellar wind
released by these stars to "pollute" the interstellar medium of globular
clusters with these elements. Gieles was formerly at the University of
Surrey. The star's mass was being restored as collisions with lesser stars
continued. The chemical abundances sown by the giant stars in the early
Universe would be inherited by any stars created from the tainted
interstellar material.
Unfortunately, the light from those old, polluted stars has long since
faded from vision; they have long since died.
Globular clusters are between 10 and 13 billion years old, whereas
superstars have a maximum life of two million years,
according to Gieles. "They consequently left the currently observed clusters extremely
quickly. There are no direct traces left.
Although everything is fairly orderly, further observational data was
needed. The JWST then focused on GN-z11, a galaxy that was discovered just
440 million years after the Big Bang and whose light has traveled for 13.3
billion years across expanding space before finally reaching us.
While JWST, the most potent space telescope ever built, was used to
investigate the spectrum of light that GN-z11 conveyed to us across space
and time, we had known about it for a
few years.
The data turned out to be somewhat strange. Nitrogen is far more abundant
than oxygen in the interstellar medium of GN-z11, with an abundance ratio
that is more than four times that of the Sun. Strange, if compatible with
how globular clusters have been observed to develop by astronomers.
After thorough analysis and modeling,
Charbonnel and her coworkers discovered that the abundance ratios in globular clusters
as well as GN-z11 can be consistently explained by giant stars between 1,000
and 10,000 solar masses that formed through runaway collisions of smaller
objects.
As demonstrated by the simulations created by Laura Ramirez-Galeano, a
Master's student on our team, the substantial nitrogen presence can only be
explained by the burning of hydrogen at extremely high temperatures, which
only the core of supermassive stars can achieve.
Although the data is far from definitive, it does point to where we might
go for further details. In order to find these early chonker stars, the
researchers aim to collect additional information about early galaxies via
JWST. This in turn could provide light on other unanswered questions, such
as how supermassive black holes developed in the early Universe and the
characteristics of the first stars.
The researchers note
that if the supermassive star scenario can be supported by further study, it
will be a significant step toward better understanding globular clusters and
supermassive star development in general.
In any case, the peculiar characteristics of GN-z11 that JWST has just
discovered demand further research in order to comprehend the physical
processes occurring in such extreme objects in the early Universe and their
potential connections to the formation of globulars, supermassive stars, and
potentially even supermassive black holes, among other things.
The research has been published in
Astronomy & Astrophysics.
