admin Supermassive black holes (SMBHs) – black holes with a mass one million times the mass of the sun – are known to dominate the universe today. However, it remains unclear when, where and how they formed during the 13.8 billion years of cosmic history.
Observations over the past few decades have revealed that every galaxy contains an SMBH at its center, and that the mass of the black hole is almost always one thousandth of the mass of the host galaxy. This close relationship implies that galaxies and SMBHs grow together.Therefore, revealing the origin of the SMBH is crucial not only for understanding the SMBH itself, but also for shedding light on the processes that form galaxies, the main component of the visible universe.
The key to solving this problem lies in the early universe, where the time elapsed since the Big Bang (i.e. the beginning of the universe) is less than a billion years. Thanks to the limited speed of light, we can go back in time by observing the distant universe.Did SMBH exist when the universe was a billion years old or less? Can a black hole achieve such a massive mass (in excess of a million solar masses and sometimes billions of solar masses) in such a short time? If so, what are the underlying physical mechanisms and conditions?
To better understand the origins of SMBH, we need to observe them and compare their properties with those predicted by theoretical models. And to do that, we first need to figure out where they are in the sky.
The large number of quasars we have detected has allowed us to define the most basic measurement called the “luminance function”, which describes the quasar’s spatial density as a function of radiant energy. We found that quasars formed very quickly in the early Universe, while the overall shape of the luminosity function (apart from magnitude) remained unchanged over time.
This characteristic behavior of the luminosity function provides strong constraints on theoretical models, which can ultimately reproduce all observables and describe the origin of the SMBH. Our research is published in the Astrophysical Journal.
On the other hand, the universe is known to have undergone a massive phase transition called “cosmic reionization” in its early stages.Previous observations suggest that the entire intergalactic space was ionized during this event. The ionization energy source is still being debated, of which quasar radiation is considered a promising candidate.
By integrating the luminosity function above, we find that quasars emitted 1028 photons per second per unit volume 1 light-year apart in the early universe. This represents less than 1% of the photons needed to maintain the ionized state of intergalactic space at the time, suggesting that quasars contribute only a small part to cosmic re-ionization pillar. Other sources of energy are needed and, according to other recent observations, may be radiation from hot giant stars during the formation of galaxies.
Provided by Ehime University
