Black hole spin may create jets that control galaxy

Feb 11, 2010 by Morgan Bettex
An artist's drawing shows a large black hole pulling gas away from a nearby star. Image Credit: NASA E/PO, Sonoma State University, Aurore Simonnet

(PhysOrg.com) -- Scattered throughout every galaxy are black holes, regions that gobble up matter and energy. Although we can't see black holes, scientists can infer their size, location and other properties by using sensitive telescopes to detect the heat they generate. This heat, which we see as X-rays, is produced as material spirals around a black hole faster and faster until it reaches a point of no return -- the "event horizon" -- from which nothing, not even light, can escape.

In addition to a galaxy’s collection of black holes, which includes black holes up to 10 times the sun’s mass, there is a supermassive black hole embedded in the heart of each galaxy that is roughly one million to one billion times the mass of the sun. About 10 percent of these giant black holes feature jets of plasma, or highly ionized gas, that extend in opposite directions of the black hole. By spewing huge amounts of mostly kinetic energy, or energy created by motion, from the black holes into the universe, the jets affect how stars and other bodies form, and play a crucial role in the evolution of clusters of galaxies, the largest structures in the universe.

“This black hole in the center of the cluster is affecting everything else in that cluster,” said Dan Evans, a postdoctoral researcher at MIT Kavli Institute for Astrophysics and Space Research (MKI), who studies supermassive black holes and their jets. Because a jet gently heats the gas it carries throughout a galaxy cluster, it can slow and even prevent stars, which are created by the condensation and collapse of cool molecular gas, from forming, thereby affecting the growth of galaxies, Evans explained. “Without these jets, clusters of galaxies would look very different.”

How these jets form remains one of the most important unsolved mysteries in extragalactic astrophysics. Now Evans may be one step closer to unlocking that mystery.

The importance of spin

For two years, Evans has been comparing several dozen galaxies whose black holes host powerful jets (these galaxies are known as radio-loud , or AGN) to those galaxies with supermassive black holes that do not eject jets. All black holes — those with and without jets — feature accretion disks, the clumps of dust and gas rotating just outside the . By examining the light reflected in the accretion disk of an AGN black hole, he concluded that jets may form right outside black holes that have a retrograde spin — or which spin in the opposite direction from their accretion disk. Although Evans and a colleague recently hypothesized that the gravitational effects of black hole spin may have something to do with why some have jets, Evans now has observational results to support the theory in a paper published in the Feb. 10 issue of the .

While researchers know that the mass of a black hole is intimately linked to the galaxy in which it is located, they have, until now, known little about the role of its second fundamental property — spin. With this paper, Evans asserts that spin is crucial to understanding the dynamics of a black hole’s host galaxy because it may actually create the jet that regulates the growth of that galaxy and the universe.

“It’s the first convincing galaxy of this type seen at this angle where the result is pretty robust,” said Patrick Ogle, an assistant research scientist at the California Institute of Technology, who studies AGN. Ogle believes Evans’s theory regarding retrograde spin is among the best explanations he has heard for why some AGN contain a super-massive black hole with a jet and others don’t.

Although Evans has suspected for nearly five years that retrograde black holes with jets are missing the innermost portion of their accretion disk, it wasn’t until last year that computational advances meant that he could analyze data collected between late 2007 and early 2008 by the Suzaku observatory, a Japanese satellite launched in 2005 with collaboration from NASA, to provide an example to support the theory. With these data, Evans and colleagues from the Harvard-Smithsonian Center for Astrophysics, Yale University, Keele University and the University of Hertfordshire in the United Kingdom analyzed the spectra of a supermassive black hole with a jet located about 800 million light years away in an AGN named 3C 33.

Astrophysicists can see the signatures of X-ray emission from the inner regions of the accretion disk, which is located close to the edge of a black hole, as a result of a super hot atmospheric ring called a corona that lies above the disk and emits light that an observatory like Suzaku can detect. In addition to this direct light, a fraction of light passes down from the corona onto the black hole’s accretion disk and is reflected from the disk’s surface, resulting in a spectral signature pattern called the Compton reflection hump, also detected by Suzaku.

But Evans’ team never found a Compton reflection hump in the X-ray emission given off by 3C 33, a finding the researchers believe provides crucial evidence that the for a black hole with a jet is truncated, meaning it doesn’t extend as close to the center of the black hole with a jet as it does for a black hole that does not have a jet. The absence of this innermost portion of the disk means that nothing can reflect the light from the corona, which explains why observers only see a direct spectrum of X-ray light.

The researchers believe the absence may result from retrograde spin, which pushes out the orbit of the innermost portion of accretion material as a result of general relativity, or the gravitational pull between masses. This absence creates a gap between the disk and the center of the black hole that leads to the piling of magnetic fields that provide the force to fuel a jet.

While Ogle believes that the retrograde spin theory is a good explanation for Evans’s observations, he said it is far from being confirmed, and that it will take more examples with consistent results to convince the astrophysical community.

The field of research will expand considerably in August 2011 with the planned launch of NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) satellite, which is 10 to 50 times more sensitive to spectra and the Compton reflection hump than current technology. NuSTAR will help researchers conduct a “giant census” of supermassive black holes that “will absolutely revolutionize the way we look at X-ray spectra of AGN,” Evans explained. He plans to spend another two years comparing with and without jets, hoping to learn more about the properties of AGN. His goal over the next decade is to determine how the spin of a evolves over time.

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Birger
3 / 5 (1) Feb 11, 2010
"faster than the speed of light"

A misprint. Obviously, the intended phrase was "at nearly the speed of light".

"....analyzed spectral data collected by the Suzaku observatory, a Japanese satellite launched in 2005 "

It would be interesting to send a similar space telescope to intersect the life-of-sight to a gravity microlensing event, showing a supermassive black hole or Quasar "central engine" at extreme magnification.
Mercury_01
3 / 5 (1) Feb 11, 2010
Can anyone clarify this for me? I heard somewhere that the fast spin, or some other quality of the accretion disc of an AGN causes some kind of an outward extension of it's gravity along the equatorial plane, which is responsible for the accumulation of matter on that plane. I may have it wrong, but does anyone know anything about this?
joefarah
2.4 / 5 (5) Feb 11, 2010
The General Theory of Relativity, contrary to popular belief, does NOT imply that nothing can escape from a Black Hole. It does say, that if gravity is the only force involved, nothing can escape.

For example, consider an EMF that repels electrons at an acceleration of over c/s/s. If such a force is applied to an electron within the black hole, say, near the event horizon, the electron will escape the black hole without having to travel at the speed of light. It's net acceleration due to gravity and the EMF will cause it to move away from the black hole.

Now consider a very rapidly spinning black hole. Such forces will exist, precisely at its poles, where matter tends to be observed jetting out.

To ANYONE who is listening, for the past decade I've been trying to find someone to do the math and physics (as I'm in a completely different discipline).

Please let's stop assuming gravity is the only force at play in a black hole, as we do when we say "Nothing can escape a black hole"
CuriousNovice
4 / 5 (2) Feb 11, 2010
Wouldn't Hawking Radiation qualify as data escaping a black hole since according to the quantum mechanical uncertainty principle, rotating black holes should create and emit particles.[1] The Hawking radiation process reduces the mass of the black hole and is therefore also known as black hole evaporation.
JayK
1.7 / 5 (3) Feb 11, 2010
Yes, joefarah, go back to being an "editor" of your wildly popular and scientifically challenged World Nut Daily.

The concept of "nothing can escape a black hole" is nothing more than layman knowledge of universal phenomena.
joefarah
2.2 / 5 (5) Feb 11, 2010
JayK - You've got the wrong joefarah. The assumption is that, as nothing can travel faster than c, that, because the gravitational well has an acceleration > -c within the SS radius, not even light can escape.

Maybe light can't, but electrons and protons can. Consider the extent of fusion within the black hole creating massive plasma and iron cores. Consider these spinning cores with their mass of protons generating magnetic fields as matter/electrons accelerate in towards them. The questions are:
1) How fast a spin?
2) How many "free" electrons, not just moving through this field, but accelerating at the speed of light. The ones tangental to the core will enter a sub-orbit until they hit the pole of the rapidly changing electric and magnetic fields. The acceleration is enough to boost them. How big must the fields be to do so?
JayK
3 / 5 (3) Feb 11, 2010
Sorry, many of your previous posts in other threads have led me to believe you have the same mentality as the Joseph Farah that runs World Nut Daily. That isn't a complement.

You do realize that electrons and protons have mass and are still bound by the same universal laws that govern everything else, right? Unless you want to claim electron spin propagation is actually what you're talking about, your second question has little merit. An answer to your first question can be found in the journal article and its corresponding citations.
baudrunner
4 / 5 (2) Feb 11, 2010
Birger: I see no place in the article which says "faster than light".

I am tired of reading "faster than light". That should read "faster than the rate of propagation of the visible wave lengths in the optical spectrum", or something to that effect. The narrow band of the visible frequency oscillations in the optical spectrum requires stable atomic configurations, complete with electron orbitals. When an atom passes through the event horizon of a black hole, its electrons are stripped from the nucleus. That is why we can't see the black hole, but we can detect X-rays and beyond, because they originate out of the oscillations of atomic nuclei.

The article is very interesting indeed. There is not enough space here to explain just why so.
PinkElephant
5 / 5 (4) Feb 11, 2010
Consider the extent of fusion within the black hole creating massive plasma and iron cores...

Way to misconstrue the whole situation, joefarah. The very reason we have black holes, as opposed to neutron stars or ordinary stars with fusion and cores, is because the gravity is too great for any repulsive force to resist. At the singularity there are no atoms, no electrons, no protons or neutrons, no quarks, no particles we know of or have ever experienced.
The acceleration is enough to boost them. How big must the fields be to do so?

Beyond infinite. Matter literally cannot exceed light speed: as it approaches light speed, it gains up to infinite momentum and infinite mass. Even light can't escape a black hole, so no field of any strength can push anything out of the black hole, because that would amount to accelerating matter to faster than lightspeed within the local volume of the spacetime manifold.
Sazzle
4.5 / 5 (2) Feb 12, 2010
@ Baudrunner(& All): the article has been edited since it was first posted yeaterday (Quite Correctly). Birger quoted part of a sentence in the first paragraph that read "from the black holes into the universe faster than the speed of Light". When I read it yesterday I nearly fell of my seat! & had to re-read the paragraph a few times to make sure I had read it properly. Then Birger posted his comment before I got a chance to say something similar.
antialias_physorg
5 / 5 (3) Feb 12, 2010
CuriousNovic:

The particles that make up Hawking radiation are created outside the event horizon (they only _apparently_ come from the direction of the black hole)
Hawking radiation is not thermal radiation - it carries no information about the inside of the black hole.
mysticshakra
2.3 / 5 (4) Feb 14, 2010
None of this debate even matters since haven't made much of a case for black holes existing in the first place. The evidence does not require fantasy inventions to explain it. Simpler explanations exist without dreaming up mythical objects.
denijane
not rated yet Feb 20, 2010
I don't quite get something - aren't accreation disks supposed to follow the direction of the spin of the ergo region? At least it makes sense they do. In which case there won't be retrograde spinning.

As for nothing can escape the black hole - maybe you guys should consider the black hole defined only outside of the outer horizon. Because inside the outer horizon, the physics is complicated and ugly (and unstable).
frajo
not rated yet Feb 21, 2010
Because inside the outer horizon, the physics is complicated and ugly (and unstable).
Until now I thought the physics "inside" to be simply unknown. Could you please give me a link to the complicated, ugly, and unstable physics "inside"?
denijane
not rated yet Feb 22, 2010
"Gravitational instability of the inner static region of a Reissner-Nordstrom black hole"
http://arxiv.org/abs/1001.0152
"Gravitational instabilities in Kerr space-times "
http://arxiv.org/abs/0805.4306
But these are only for the most inner regions.

I'm under the impression somebody proved that Kerr BH's are linearly unstable for r_-< r < r_+ as well, but I'll have to check a lot of references before I find exactly who did it. If you really want it, I'll search for it, but otherwise, I won't bother.
frajo
not rated yet Feb 22, 2010
I'm under the impression somebody proved that Kerr BH's are linearly unstable for r_-< r < r_+ as well, but I'll have to check a lot of references before I find exactly who did it. If you really want it, I'll search for it, but otherwise, I won't bother.
You don't need to bother as your links provide the first glimps I was looking for and will keep me busy for some time. Thanks.