Gargantuan black hole challenges theories about early universe

Gargantuan black hole challenges theories about early universe
Gargantuan black hole challenges theories about early universe

The James Webb has added yet another spectacular sighting to its collection. In a press release spotted by ScienceAlertresearchers have announced that the king of telescopes has allowed them to document a black hole like no other, and for good reason: it is so heavy and so ancient that it defies all current cosmological models.

The discovery of this object, named J1120+0641dates back to 2011. For several years, it was the oldest black hole ever documented. Although astronomers could not extract much information from it, it was still known that it formed a little over 13 billion years ago, about 770 million years after the Big Bang. But since then, technology has progressed greatly with the arrival of new cutting-edge instruments, such as those of the James Webb Space Telescope. This opened the way for much further observations, and the status of this black hole completely changed in light of this new information.

Today, his age no longer constitutes a record. In recent years, JWST has focused its lens on even older black holes like the one in the GN-z11 galaxy, which formed about 13.4 billion years ago — just 400 million years ago. after the Big Bang. To understand what makes it so intriguing to researchers, his age is not enough; its mass must also be taken into account.

An object too massive for its age

In fact, this has been estimated between one and two billion times that of the Sun. It therefore falls very largely within the closed circle of so-called supermassive black holes, these true titans so imposing that their gravitational influence can structure entire galaxies. And even when compared to other members of this category, this one is particularly huge. For reference, Sagittarius A*, the supermassive black hole that occupies the center of the Milky Way, is “only” about 4 million solar masses.

However, this is not an absolute record. Astronauts have already spotted several others that are even more massive. We can cite M87, the supermassive black hole that was the first to be directly photographed in 2019, with 6.5 billion solar masses, or NGC 4889, with 21 billion solar masses. At the top of this scale, we find TON 618, the most imposing black hole discovered to date with a mind-boggling 66 billion solar masses on the counter.

J1120+0641 does not box at all in the same category as the latter. Compared to them, he would almost look like a weakling. But when you factor both its mass and its age into the equation, you get an object that seems completely aberrant.

An artist’s impression of an active supermassive black hole like J1120+0641. © T. Müller / MPIA

Indeed, his age places him in an era called theCosmic Dawn, the pivotal period when the very first stars began to form and illuminate the cosmos. However, in theory, supermassive black holes appearing this early (relatively speaking) in the history of the Universe should be significantly less imposing. For reference, the black hole of GN-z11 is limited to “only” 2 million solar masses, or 500 times smaller than J1120+0641! And for the moment, astronomers have great difficulty explaining how such a behemoth could have emerged during the Cosmic Dawn.

To estimate the theoretical mass of a black hole, researchers rely largely on the Eddington Limit. It depends on the balance between the gravitational forcesdirected towards the center of the object, and the radiation pressure which works in the opposite direction. Beyond this limit, the material superheated by the Dantesque forces emanating from the black hole would become so luminous that the radiation pressure would overcome gravity, preventing the object from growing. Now, to exceed the billion solar mass mark so early in the history of the Universe, J1120+0641 would have had to pulverize the Eddington limit.

Alternative tracks collapse

To try to explain this decidedly disturbing inconsistency, astronomers explored another avenue: that ofsupra-Eddington accretion. The idea is that if a supermassive black hole suddenly activates at a time when it has a huge amount of material available, it could swallow a gigantic amount of material before the radiation pressure starts to take effect. And thus temporarily exceed the Eddington limit.

For this scenario to hold water, however, it was necessary to confirm that J1120+0641 has a buffet of gas and dust sufficiently stocked to allow it to gorge itself at a maddening rate. Researchers therefore pointed the JWST and its high-performance infrared sensors at the black hole last year. They hoped to find traces of such a banquet. But after analyzing the data for more than a year, they finally came up empty-handed. Everything indicates that the black hole perfectly respects the Eddington limit, and that it absorbs matter at a normal rate for a behemoth of this kind.

In other words, the JWST observations cut short the supra-Eddington accretion trail. Now orphaned of their best hypothesis, the study’s authors wondered whether they might have misinterpreted the data. According to ScienceAlert, an excess of dust could, for example, have gone unnoticed, thus leading the team to overestimate the mass of the object. But no matter how much the researchers dissected the images in all the wavelengths at their disposal, they found no trace of such a cluster. The mystery therefore remains complete.

« Ultimately, these new observations only reinforce the mystery: this early quasar is surprisingly normal, no matter what wavelength we observe “, explains Sarah Bosman, postdoctoral fellow at the prestigious Max Planck Institute and lead author of the study, in a press release.

The ball is in Webb’s court

But this is not a disappointment. By showing that primordial black holes follow the same rules as the most recent ones, the researchers have above all shown that there are probably still lots of things to learn about the formation of black holes and galaxies. A very exciting prospect that will push astronomers to explore new avenues. For example, the authors have identified another possibility that could help explain this combination of mass and age: J1120+0641 could have been obese at birth.

© ESO/M. Kornmesser / NASA / ESA / Hubble Heritage Team (STScI/AURA)

Indeed, the results could be consistent if the black hole had formed with a initial mass of at least 100,000 solar masses, compared to 5 to 10 for a typical black hole. But again, the mechanisms at play are not clear. According to the team, J1120+0641 may have originated fromgravitational collapse of a huge cloud of primordial gas, as opposed to the more classic black holes that emerge when an isolated massive star dies. But whatever happens, we will have to wait to discover other titans of this kind at Cosmic Dawn to hope to confirm this scenario.

It will therefore be appropriate to carefully follow the observations of the James Webb Space Telescope, which has continued to push the limits of the observable Universe since its commissioning.

The text of the study is available here.

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