Supermassive black holes appear to be present at the center of every galaxy, dating back to some of the earliest galaxies in the universe. And we have no idea how they got there. It shouldn’t be possible for them to grow from supernova remnants to supermassive sizes so quickly. And we are not aware of any other mechanism that could form something so large that extreme growth would not be necessary.
The apparent impossibility of supermassive black holes in the early universe was already a problem; the James Webb Space Telescope has only made matters worse by finding earlier and earlier instances of galaxies with supermassive black holes. In the latest example, researchers have used the Webb to characterize a quasar powered by a supermassive black hole, as it existed about 750 million years after the Big Bang. And it looks shockingly normal.
Looking back in time
Quasars are the brightest objects in the universe, powered by the active feeding of supermassive black holes. The galaxy around them feeds them enough material that they form bright accretion disks and powerful jets, both of which emit large amounts of radiation. They are often partially shrouded in dust, which glows by absorbing some of the energy emitted by the black hole. These quasars emit so much radiation that they eventually expel some of the nearby material from the Milky Way completely.
The presence of these features in the early Universe would therefore tell us that supermassive black holes were not only present in the early Universe, but were also integrated into galaxies, as is the case in more recent times. But it was very difficult to study them. To begin with, we haven’t identified many; there are only nine quasars that predate the time when the universe was 800 million years old. Because of that distance, features are difficult to resolve, and the redshift caused by the expansion of the universe takes the intense UV radiation from many elements and stretches them deep into the infrared.
However, the Webb telescope is specifically designed to detect objects in the early universe by being sensitive to the infrared wavelengths where this radiation is visible. So the new research is based on Webb pointing to the first of the nine early quasars discovered, J1120+0641.
And it looks…remarkably normal. Or at least a lot like quasars from more recent periods in the history of the universe.
Mostly normal
The researchers analyze the continuum of radiation produced by the quasar and find clear evidence that it is embedded in a hot, dusty donut of material, as seen in later quasars. This dust is slightly hotter than in some more recent quasars, but that seems to be a general feature of these objects at earlier stages of the universe’s history. Radiation from an accretion disk is also visible in the emission spectrum.
Several ways to estimate the mass produced values of the black hole in the region of 109 times the mass of the Sun, which puts it clearly in the realm of supermassive black holes. There is also evidence, from a slight blue shift in some of the radiation, that the quasar is blowing away material at a speed of about 350 kilometers per second.
There are a few quirks. One of these is that the material also appears to be falling in at about 300 kilometers per second. This may be caused by material in the accretion disk rotating away from us. But if so, it should be accompanied by material spinning toward us on the other side of the disk. This has been observed a few other times in very early quasars, but the researchers admit that “the physical origin of this effect is unknown.”
One explanation they propose is that the entire quasar is in motion, having been knocked out of its position at the center of the Milky Way by a previous merger with another supermassive black hole.
The other oddity is that there is also a very rapid outflow of highly ionized carbon, the rate being roughly twice that in quasars at later times. This has been seen before, but there is no explanation for it either.
How did this happen?
Despite its peculiarities, this object is very similar to quasars from more recent times: ‘Our observations show that the complex structures of the dusty torus and the [accretion disk] can settle around a [supermassive black hole] less than 760 million years after the Big Bang.”
And again, that’s a bit of a problem, because it indicates the presence of a supermassive black hole that integrated into its host galaxy very early in the history of the universe. To reach the sizes we see here, black holes push against what’s called the Eddington limit: the amount of material they can suck in before the radiation they produce drives out neighboring material, choking off the black hole’s food supply .
That suggests two options. One is that for most of their history, these things have been absorbing material well beyond the Eddington limit – something we haven’t observed and something that is absolutely not true of this quasar. The other option is that they started en masse (around 10am).4 times the mass of the Sun) and continued to feed at a more reasonable rate. But we don’t really know how something this big could happen.
So the early universe remains a rather confusing place.
Natural Astronomy, 2024. DOI: 10.1038/s41550-024-02273-0 (About DOIs).