James Webb might have found the mysterious population III stars!
Astronomers working with data from the James Webb Space Telescope have just made what seems to be an
exciting discovery. In a distant galaxy, far far away…they have detected light from ionized helium,
which could be evidence of the mysterious Population III stars. These stars have never
been observed before, though scientists are pretty convinced they must exist - or must have existed!
Population III stars are made up of primordial gas, primarily hydrogen,
and helium, the same primordial gas that filled the universe right after the Big Bang.
They are thought to be the very first stars to have formed.
These were big stars that, after a very short lifetime, would have gone supernova,
causing their elements to be spread throughout the cosmos, and giving birth to other stars.
The detection of light from ionized helium, which could be evidence of Population III stars,
serves as an exciting discovery by astronomers. It may give us a better
understanding of how the first stars were born, and how the universe has evolved since.
Follow me in this video to get to know exactly what James Webb
found and why it is extremely important for our understanding of the universe.
The classification Starting in 1942, the city of Los
Angeles experienced various blackouts due to the second world war. It was a dark period for most
people. Interestingly enough, though, some of them managed to turn the problem into an opportunity.
Through 1943 and 1944, Walter Baade, a german astronomer who emigrated to the US,
pushed the Mount Wilson 100-inches telescope to its very limits in order to achieve the
resolution of the nucleus of the Andromeda galaxy and of two of its elliptical companions.
He took advantage of the blackout. What he discovered was that…Andromeda
was hosting two kinds of stellar populations, which he named Population I (population one) and
Population II (population two). What Baade called population II
stars were bright yellow giants; he found no highly luminous blue or red stars. These
stars were distinct from the Population I, or “ordinary” stars near the Sun in our Galaxy.
The amazing discovery of a second stellar population made Baade like the Beyonce of
20th-century observational astronomy, outshining his more renowned colleague Edwin Hubble (who was
like a ‘One Direction’ of cosmology, showing that galaxies exist and the universe is expanding, and
thus making cosmology now a more popular science). Following the amazing work of Baade, astronomers
have been making use of this convenient classification. As of today, we know a lot of
things about the two populations. The members of these stellar populations differ from each other
in various ways, most notably in age, chemical composition, and location within galactic systems.
--- What are population I stars?
Population I is made up of the younger stars, clusters, and associations, believed to have
formed between 1 million and 1 billion years ago. These stars are often hot blue-white O and
B-type stars and are called extreme Population I objects. They are found near the arms of galaxies
such as the Milky Way and other spirals as well as irregular galaxies like the Magellanic Clouds.
It is thought that such stars originated from interstellar gas mixed with substances that
had been created through incredible supernova explosions. This in turn enriched the matter
with elements like iron, nickel, and even carbon. Approximately 90% of Population I's
makeup is hydrogen while the remaining 10% is helium, just like the composition of the Sun.
What are population II stars? Population II stars, on the other hand,
are made mostly of hydrogen and helium gas and are generally found in the halos or globular clusters
of galaxies. They are much older than Population I stars, and are generally less abundant and dimmer.
These stars tend to have lower metallicities and thus contain fewer heavy elements.
Broadly speaking, the metallicity of a star can be inferred from its spectral lines:
metal-rich stars will show on average more lines than metal-poor ones at the same temperature.
Therefore, the spectrum of a metal-rich star is quite messy.
Well, since Population II stars are in general metal-poor, they have relatively
flat spectra and low surface gravities. They only show strong hydrogen lines,
because well…they have plenty of it. They tend to be redder in color than
Population I stars and, in addition, they can be used as a tracer to calculate the age of the
universe since they have been largely unaffected by external forces for billions of years.
--- What are population III stars?
The classification made by Baade was extended later on. And this is where our
mysterious Population III stars enter the game. Population III stars are the cool kids when it
comes to astronomy - no one is quite sure if they exist, but if they do, they could bring
some amazing implications along with them! In principle, these stars could be divided
into two types. The first is made up of primordial gas leftover from the Big Bang and is the first to
create metals. The second is hypothetical but could be the dark matter of galactic halos.
These stars could have formed way back in pregalactic times, or during the earliest
phases of galaxy formation. Whatever the case, the Population III stars could be an exciting
and mysterious part of the universe. Time to dig in and find out more, don’t you think?
Population III stars are really old stars, they are like the grandparents of all the stars in
the universe - or, as astronomers would say: they are the progenitors of all the stars we know of!
Having formed right after the big bang, starting from the primordial gas at their disposal,
these stars - if they exist - must be characterized by some interesting features.
First of all, they are expected to be composed entirely of primordial gas - namely hydrogen
and helium. That’s all! Maybe just a really tiny amount of lithium and beryllium, but nothing else!
If we could find a Population III star,
its spectrum would be basically flat - except for the hydrogen and helium lines.
In fact, the primordial gas had not been recycled yet from previous generations of stars and was
pristine material from the Big Bang. No metals can be found in the Population III stars!
Astronomers think these stars were short-lived, and most of them exploded into supernovae that
eventually spread the metals created by the nuclear burning processes during the lifetime
of these huge stars, and contributed to the birth of the Population II stars.
Do population III stars even exist? The real problem with the Population
III stars is that…even though we have a nice theoretical background that seems
to fit everything and explain what we observed today, we have never seen one!
Among the millions of stars they studied, astronomers have never been able to find a
perfectly flat spectrum. Some of them got actually tricked because they thought they had found one,
but then they discovered their star actually showed some presence of metals…so they had to
exclude it from the possible candidates. The thing is…it is extremely hard to find a star with an
almost flat spectrum, especially because all the measurements are affected by instrumental errors,
and this makes everything much more complicated. Nevertheless, astronomers know where to look at.
In fact, if the theory is correct, we expect Population III stars to be characterized
by two specific and narrow emission lines, which come from ionized helium.
Basically, if we ever managed to find some stars that have a really flat spectrum and two strong
emission lines of ionized helium, we might be facing a Population III star, one of the first
stars in the universe. ---
Unfortunately, until now, no one discovered anything. If I was an astronomer, I would ask
myself if it is actually worth trying anymore. But luckily, we have JAMES WEBB. This amazing
telescope, this incredible piece of art, is taking us closer to the solution to this mystery.
JWST discovery
We all know how images from the James Webb space telescope
constitute a precious treasure for science. In December 2022, scientists published a paper
analyzing approximately 2,000 different targets within JWST images, looking for specific helium
emissions. The same helium emissions they expect to find in Population III stars.
From their research, they discovered a galaxy with a redshift of 8.16 which appeared only
620 million years after the Big Bang, when the universe was still a baby.
Interestingly, the galaxy seemed to be split into two parts with one half
possessing helium signatures, as well as many other elemental signatures.
At first, it was assumed that the population III stars in the galaxy had already created
a lot of younger stars and caused the production of other emissions, however,
the intensity of the helium emissions implied that this may be a region rich in population 3 stars.
It was also noted that the emissions did not include oxygen, nitrogen, or carbon signatures,
which excludes the presence of a black hole, and therefore this is quite an intriguing discovery:
James Webb might have found a region in the universe, rich in population III stars!
The research in December of 2022 has opened up a wealth of possibilities as to the origin
of the emissions from the galaxy. It will be interesting to see what further studies uncover
and to learn more about this unique discovery. Unfortunately, this discovery doesn’t really tell
us anything about the existence of Population III stars, because what we see is a mixture of
multiple emission lines. It could be that this galaxy is made up of population III stars and
other types of objects, but there’s no way to split the components to verify this hypothesis.
What scientists are hoping to find is the light of the population III stars that gets magnified by an
effect known as “gravitational lensing”. This is a relativistic effect that takes into consideration
the fact that light gets bent when it gets close to a massive object. For example, the light from
a Population III star could get bent - and therefore, magnified - just like it happens
with a lens, by a massive cluster of galaxies that lies between us and the Population III star.
A bunch of stars has already been discovered with this method, but it is quite a rare event,
because of the geometry of the problem: you would need the lens (for instance,
a cluster) to be aligned with the emitter (in our case, the Population III star); and you
also need to be lucky enough to be observed that specific region of the sky when this happens.
So, what can we say? Based on the current evidence, it appears that
Population III stars are likely to remain elusive in the future. While the possibility of finding
some Population III stars in the distant universe can't be completely ruled out, the probability of
this happening is still very low. Continued observations and research will be required to
further advance our understanding of the formation and evolution of these mysterious stars, thereby
providing insight into the early history of our universe. And James Webb will surely help us.