For over half a century, astrophysicists worldwide have relied on a single fundamental assumption: the ratio of massive to low-mass stars at the moment of their birth remains unchanged anywhere in the Universe — from our Milky Way to the most remote corners of space. This assumption, known as the initial mass function, served as the "scales" by which scientists calculated the total mass of stellar systems. Now an international team of researchers, led by Professor Mariska Kriek of Leiden University (Netherlands), has cast serious doubt on this universality. According to the new study, early galaxies contained significantly more low-mass stars and were more massive than the standard cosmological model had assumed.
How Webb and ESO Revealed a Hidden Stellar Population
To carry out the work, the team combined two of the most powerful tools in modern astronomy: spectral data from the James Webb Space Telescope and observations from the European Southern Observatory's (ESO) large telescope in Chile. The objects of analysis were nine massive galaxies that formed in the first one and a half billion years after the Big Bang and had already ceased active star formation. It was precisely the "mature" state of these objects that allowed the scientists to assess their stellar composition without interference from the bright glow of newly born stars.
The "Skyscrapers and Houses" Effect and a New Analytical Method
The problem was that the brightest giant stars literally blinded the instruments. The researchers compare this phenomenon to a night city, where the glow of skyscrapers hides small houses from view: faint low-mass stars "sink" in the brilliance of the giants, and their signal is lost against the backdrop of the overall radiation. The traditional approach — estimating the number of bright giants and extrapolating that data to faint stars — systematically underestimated the true mass of the system. New spectral processing methods made it possible to "pierce through" the blinding light and discern a previously invisible population of small stars, radically changing the picture.
Four Times Heavier: Revising the Mass of Ancient Galaxies
The most striking result came from one of the galaxies under study, which existed just 1.5 billion years after the birth of the Universe. After recalculating with the hidden population of low-mass stars taken into account, its mass turned out to be four times greater than previously thought. This is not a one-off error but a systematic effect: if even one galaxy proved so much "heavier," then the other objects of the early Universe epoch likely require a similar upward revision.
A Challenge to the Standard Cosmological Model
Here arises a key scientific contradiction, which the authors of the study lay out openly. If the first galaxies accumulated colossal mass so rapidly, this creates significant conflicts with current theories of cosmic structure formation. The standard model assumes certain rates of galaxy growth, and the discovery of excess mass in the early Universe calls a number of its parameters into question. The scientists emphasize that this is not a refutation of cosmology as a whole, but a need to refine the mechanisms by which galaxies accumulated mass in the first billion years.
Implications for Astrobiology and the Search for Life
The shift in understanding the number of low-mass stars has direct consequences beyond pure astrophysics. As the study's lead, Professor Mariska Kriek, notes, it is precisely around low-mass stars — including red dwarfs — that rocky planetary systems most often form. If there were far more such stars in the early Universe, then the conditions for the emergence of exoplanets and potential life arose significantly earlier and on a much larger scale than previously assumed. This substantially widens the "window" for searching for traces of extraterrestrial life and redistributes priorities in astrobiology programs.
What's Next: The Path to the First Generations of Stars
In the near future, the team of astronomers plans to apply the new spectral analysis technique to even older objects, in order to get closer to the epoch of the formation of the very first generations of stars in the early cosmos. The success of this step will make it possible to definitively establish how universal the initial mass function is and whether the basic models of star formation need to be revised. For now, the main consequence of the work is that the Universe turned out to be "populated" with small stars more densely than was thought — and along with it, more habitable than the standard picture had assumed.
