The environment around a supermassive black hole is quite complex.
Sitting in the centers of the galaxies, that’s not too surprising. Crowded there, like being downtown in a big city in a hurry. But in this case it is worse, because in one city you do not have thousands of tons of material circulating in the city center at almost the speed of light that is heated to millions of degrees and explodes with enormous energy making it the most powerful source of radiation in Universe.
While the supermassive black hole is done many times. The disk is called an accretion disk, and its conditions are difficult to understand. To make matters worse, sometimes black holes and their disks somehow concentrate this energy and are important in twin beams, like a double light saber, which screams at almost the speed of light up and down, from the disk.
These beams, called astronomers by jets, contain energy across the electromagnetic spectrum from radio waves to X-rays. If that jet was pointing towards Earth, we could see all this radiation, and we would call these kinds of things quasars (or, if even too much energy is seen, blazers). They are phenomenally bright, and we can see them from billions of light years away, clearly throughout the perceptible Universe.
These jets have a profound effect on the galaxy surrounding the black hole. They can push gas away from the center of the galaxy, preventing star formation. They can also drive shock waves into the gas farther out, encouraging clouds to collapse and form stars. The growth of the black hole itself may depend on it, as it grows by feeding on the gas itself.
So astronomers try to understand them, which can be difficult, because they are so far away. But a new study, looking at a surprising 729 quasars, found a correlation between quasars in jets and those without them, and this is against the standard model of astronomers used for decades.
Astronomers looked at the high-energy X-ray emission from black holes. It is well known that quasars without jets emit a certain amount of ultraviolet light (coming from the internal disk), and X-ray emissions depend on it. If there is more UV from a quasar we see more X-rays as well, and vice versa.
The reason is thought to come from the black hole corona. It is an extremely high-energy gas that surrounds the accretion disk like a mixture. UV photons from the disk hit the electrons in this corona gas and are energized, just like how a truck can drive a car forward. The result is that UV light is amplified by X-ray energies. The more UV you emit, the more X-rays you get.
Today, jet-based quasars also emit X-rays, and more likely to be brighter (also provide more X-rays). It is thought that the X-rays came from the base of the jet, where magnetic fields were injured in a vortex of all rotating objects. It can focus energy, traveling along the lines of the magnetic field. So they focus on the jets, and the vast energies used in the jet base are the cause of the X-rays.
BUT. The new study found a similar correlation between X-rays and ultraviolet light such as jet-free quarars. That implies a similar process, meaning X-rays do not necessarily come from the jet base, but from the black hole coronae! And, these coronae have strong magnetic field lines threaded around them, which helps boost the emitted energies, which is why quarars with jets emit more X- ray than those without.
This is a big deal. The physics of the coronae is different from the jet base, so it changes the way we think the jets launched. Mind you, these jets can last millions of light years, much larger than the host galaxy of the black hole! They are massive structures, so understanding how they start is critical.
As it happens, all quarars appear to require a rapidly rotating black hole in their hearts. The rotation actually drags the spacetime fabric around them, affecting the disk. It is thought that jets depend on black hole spin, but what the new study shows is that if the black hole corona is weak, you will not get jets even if the black hole is crazy spinning.
Again, that was a big deal. This changes the way astronomers think of jets.
So the next question is, are these scientists right? So, the trends they found seem real, and compelling if not convincing. And they looked at a whole lot of quarars. I hope the theorists who study the connection between black holes, their coronae, magnetic fields, disks, and jets (phew!) Are eager for this idea, trying to figure out if they can find out all connections, and if make sense. It is interesting to see some exceptions to this rule can also be found. That really helps, because sometimes quarars can have some weird feature that sets them apart, making it easier to understand the rules by contrast (the idea of exclusion proves the rule*).
We know that the properties of entire galaxies depend on the properties of the black hole in their cores, even though the galaxy can have a million times the volume of that black hole. Obviously the black holes are small but powerful, and how they operate these jets is a big player in that game. Our own galaxy is probably a quasar, so in many ways we ourselves exist because of that fact. I think understanding how this work is an important piece of understanding how the Universe treats people. And I am human, so I take it personally.
And personally, I think it’s all incredibly cool.
*At that link you will find different meanings of this phrase, and in this case I mean it in the definition of an exception that tests the policy under different circumstances, which can help support the general rule.