An international group of researchers, led by the Australian National University, has identified a very distant galaxy (and, therefore, very old) that, despite appearing in our instruments as a small point of light, originally emits so much energy that it would be the most luminous cosmic object known.
The great energy display of this object, baptized by astronomers as J0529−4351, is explained by the existence, inside, of an active supermassive black hole. With a mass of 17 billion suns, this black hole consumes the equivalent of one Sun per day, which makes it, according to its discoverers, the most voracious of all those found to date.
Because of the similarity they present with simple stars that are much closer and located in the foreground, these types of objects, very distant galaxies with active black holes inside, are called quasars (a name derived from the expression "quasi-stellar") . With more than a million discovered, the study of quasars is especially interesting to understand what the early universe was like.
The determination of the characteristics of J0529−4351 has been possible thanks to observations made with the VLT complex, a set of four optical telescopes installed at the European Southern Observatory.
When a black hole, with its powerful gravity, attracts matter that is nearby, it rushes towards the object in a spiral trajectory, forming a so-called accretion disk. Intense friction is generated in it that is capable of raising the temperature of the material to millions of degrees and causing the emission of electromagnetic radiation (light at different wavelengths) that our instruments can capture.
From spectral analysis (the light decomposed by a prism) in the visible and near-infrared radiation range, it has been determined that the supermassive black hole that inhabits J0529−4351 (and which is 12 billion light years away) away from Earth) is capable of emitting radiation equivalent to 500 billion suns. According to Christian Wolf, principal investigator of the team that made the detection, it is “the most luminous object in the known universe.”
However, determining the precise characteristics of this type of objects is complex due to different factors, such as the viewing angle under which we view them. So, for the study of J0529−4351, astronomers have used complex computer simulations that have considered different combinations of viewing angles and masses to check which ones best fit the experimental data provided by the observations. And the results have been surprising.
The supermassive black hole that inhabits J0529−4351 would have an estimated mass of 17 billion suns and, with a 95% confidence margin, we would be seeing it at an angle of 60 degrees. It would be surrounded by an accretion disk with a diameter of 7 light years (the equivalent of 15,000 times the distance between the Sun and Neptune), which could make it “the largest accretion disk in the universe” as Samuel Lai has stated. , one of the authors of the study.
Furthermore, the enormous energy display of J0529−4351 would be possible thanks to the frenetic speed with which its black hole devours matter and which is close to the limit allowed by theoretical models. Specifically, the estimated rate indicates that between 280 and 490 solar masses disappear per year, which represents approximately one Sun per day.
To corroborate the great intrinsic luminosity of J0529−4351, researchers have had to rule out that the light, during its journey to Earth, has undergone alterations that may have increased its intensity.
One of the phenomena that can produce this type of variation is the so-called gravitational lens, which occurs when the light from very distant objects is distorted (and enlarged) when passing through regions of space, located in the foreground, in which there are large concentrations of mass, such as galaxy clusters or dark matter clumps.
The gravitational lensing effect is frequently observed in quasars, and in addition to the amplification of the light from these objects it also causes the appearance of duplicate images of them. In fact, in some of the brightest quasars detected so far it has been estimated that their original light has been magnified between 40 and 100 times due to this phenomenon.
In the case of J0529−4351, the authors of the study have resorted to additional observations, such as those made with great precision by the European space agency Gaia satellite, which have confirmed that the point of light perceived by our instruments does not show obvious signals. distortion or duplication. Likewise, the spectral analysis has ruled out the probability of gravitational lensing, reducing in any case its possible effect to a mere 1%.
In the recently published study, the authors also highlight the astonishing fact that such an extreme object has gone unnoticed until now. Indeed, although J0529−4351 already appeared in images from 1980, it could not be classified as a quasar until a few decades later. And some of the automatic algorithms used to detect this type of objects had determined that this luminous point was too bright to come from a distant object, and it had been considered a star located in the foreground.
The surprise of astronomers has been even greater considering that approximately one million quasars are known, all of them less impressive than J0529−4351. In the words of Christopher Onken, co-author of the study, this object “has literally been staring us in the face until now.”
Starting in the 1950s, astronomers began to detect intense sources of radio wave emission in the sky that, when observed with optical telescopes, did not show any visible objects. This situation changed in 1960, when it was possible to identify, for the first time, a point of light in the place from which one of these radio emissions came. The object was named 3C 48, and analysis of the spectrum of its light showed traces that baffled scientists.
Finally, in 1963, the Dutch astronomer Maarten Schmidt, studying the object 3C 273, discovered that its spectrum could be explained by considering that the origin of the emission was extraordinarily distant. Due to the expansion of the universe, light from distant bodies loses energy along its path, which results in a shift towards red (a color that is less energetic than blue). And Schmidt deduced, correctly, that this red shift had caused the dark bands that usually appear in light spectra to be so moved that, for this reason, they had not been previously recognized.
Currently, quasars are considered to be active nuclei of extremely distant galaxies that emit enormous flows of energy when the supermassive black holes that inhabit their interior attract large amounts of matter towards them (creating accretion disks). In fact, quasars are among the most luminous objects in the cosmos, typically emitting as much radiation as about a thousand galaxies like our Milky Way.
The fact that quasars are detected at enormous distances indicates that they were much more frequent in the early stages of the universe. The reason is that the activity of the supermassive black hole can be maintained as long as there is a supply of material to feed its accretion disk, so that, when all the nearby matter is consumed, the black hole becomes inactive. Thus, scientists do not rule out that, at some point in the past, the supermassive black hole at the center of our galaxy also behaved like a quasar.
