The current cosmological model
According to the most widely accepted model of the Universe, Dark Energy represents 68% of the mass energy content in the Universe. This theory revived an idea that Einstein had proposed but later rejected, the existence of a cosmological constant (indicated by the scientific symbol delta) that "restrained" gravity and prevented the Universe from collapsing on itself. Energy and dark matter are now an integral part of the most widespread cosmological model, known as the Lambda-Cold Dark Matter (LCDM) model.
The theory presents some problems, not least the fact that there is no direct evidence of this mysterious energy. Moreover, while this vacuum energy is consistent with quantum mechanics, all attempts to calculate it using quantum field theory have failed. And the question remains open as to how this energy can coincide with the supermassive black holes (SMBH) present in our Universe.
Observations have shown that most galaxies have SMBH in the central region, which is why active galactic nuclei and quasars are so bright. The extremely powerful gravity of the SMBH causes the surrounding matter to fall around them, forming accretion discs and powerful relativistic jets in which matter is accelerated to almost the speed of light (and releases huge amounts of radiation into the process).
The presence of these giants at the center of the most massive galaxies would require an extremely strong force to counter them. This is especially true when it comes to the singularities theorized to exist in their nuclei, where the very laws of physics are broken and become indistinguishable. This gave rise to an exotic theory known as "cosmological coupling", which states that SMBHs may possess enormous dark energy and that they are the reason the Universe is expanding.
The need for extraordinary evidence
In their documents, the reports the first observational evidence that black holes gain mass in a manner consistent with their dark energy content. If true, the discovery eliminates the need for singularities to form in the center of black holes. This would also mean that no new forces or theory of modified gravity are needed for our cosmological models to make sense.
The team came to this conclusion by examining the evolutionary history of SMBH at the center of the giant elliptical galaxies about 9 billion years ago. It is a type of primordial galaxy that formed at the beginning of the Universe and has since ceased to form stars, a so-called "dormant galaxy".
Decades of observations have shown that black holes can increase their mass in two ways: by increasing matter or by merging with other black holes. Dormant galaxies have little material left for the accretion of their SMBH, which means that their further growth cannot be explained by the two mechanisms mentioned above.
The team then compared the observations of these elliptical galaxies - which still look young - with local galaxies dated to around 6.6 billion years ago, which have since become dormant. These findings revealed that HBMS was 7 to 20 times higher than it was nine billion years ago, much larger than predicted by the increase or possible mergers.
The theory of cosmological coupling
Artistic representation of two colliding supermassive black holes. credits: ESO
In a second article, the team also states that measurements of the relative populations of galaxies at different points in their evolution (about 7.2 billion years ago) showed a similar correlation between the mass of the SMBH and the size of the Universe. This constitutes the first proof of "cosmological coupling" by showing that the expansion of the Universe and the growth of SMBHs are correlated.
If this emerges from further observations, it could actually redefine our understanding of the Universe and the nature of black holes. This is the first observational document in which we are not adding anything new to the Universe as a source of dark energy: black holes would themselves be the dark energy we are looking for.
Of course, these claims were met with some skepticism by the astronomical/astrophysical community. In particular, the authors' claim that their observations constitute evidence of mating was contested for confusing correlation with causality. The conclusions of the authors of the study are in fact based on an important presupposition that it exists "a universal relationship between the mass of the central black hole and the mass of the stars within a galaxy, which may evolve in cosmic time but should be at the same time universal".
From this, they compared the SMBHs they chose for their sample data to determine if there exists a "coupling parameter" that maintains the same value in cosmic time. In the end, the team determined with 99.8% confidence that this parameter has a non-zero value. And although it sounds convincing, that conclusion comes down to a presumed relationship.
According to other researchers, the authors in fact assume the existence of a coupling that is not there and attribute the perceived evolution of the mass relations between black hole and star to a coupling, when what is happening is that these galaxies and their black holes are evolving. Since we measure each galaxy at a precise instant in time we have no way of knowing how a single object is evolving and that is what this research is not in any way considering.
The ability to check the results several times is one of the most important requirements for the tests to be considered valid. In other words, the results must be demonstrable over and over again and - preferably - using different methods. The research team is aware of this fact and hopes that repeated observations will confirm the extraordinary character of their statement.
References: Universe Today, The Astrophisical Journal Letters
Post a Comment