Backwards Black Holes Might Make Bigger Jets

Jun 01, 2010
This artist's concept shows a galaxy with a supermassive black hole at its core. The black hole is shooting out jets of radio waves. Image credit: NASA/JPL-Caltech

(PhysOrg.com) -- Going against the grain may turn out to be a powerful move for black holes. New research suggests supermassive black holes that spin backwards might produce more ferocious jets of gas. The results have broad implications for how galaxies change over time.

"A lot of what happens in an entire galaxy depends on what's going on in the miniscule central region where the black hole lies," said theoretical astrophysicist David Garofalo of NASA's Jet Propulsion Laboratory in Pasadena, Calif. Garofalo is lead author of a new paper that appeared online May 27 in the . Other authors are Daniel A. Evans of the Massachusetts Institute of Technology, Cambridge, Mass., and Rita M. Sambruna of Goddard Space Flight Center, Greenbelt, Md.

Black holes are immense distortions of space and time with gravity that is so great, even light itself cannot escape. Astronomers have known for more than a decade that all galaxies, including our own Milky Way, are anchored by tremendous, so-called supermassive black holes, containing billions of suns' worth of mass. The black holes are surrounded and nourished by disks of gas and dust, called accretion disks. Powerful jets stream out from below and above the disks like lasers, and fierce winds blow off from the disks themselves.

The black holes can spin either in the same direction as the disks, called prograde black holes, or against the flow - the retrograde black holes. For decades, astronomers thought that the faster the spin of the black hole, the more powerful the jet. But there were problems with this "spin paradigm" model. For example, some prograde black holes had been found with no jets.

Garofalo and his colleagues have been busy flipping the model on its head. In previous papers, they proposed that the backward, or retrograde, black holes spew the most powerful jets, while the prograde black holes have weaker or no jets.

The new study links the researchers' theory with observations of galaxies across time, or at varying distances from Earth. They looked at both "radio-loud" galaxies with jets, and "radio-quiet" ones with weak or no jets. The term "radio" comes from the fact that these particular jets shoot out beams of light mostly in the form of radio waves.

The results showed that more distant radio-loud galaxies are powered by retrograde black holes, while relatively closer radio-quiet objects have prograde black holes. According to the team, the supermassive black holes evolve over time from a retrograde to a prograde state.

"This new model also solves a paradox in the old spin paradigm," said David Meier, a theoretical astrophysicist at JPL not involved in the study. "Everything now fits nicely into place."

The scientists say that the backward black holes shoot more powerful jets because there's more space between the black hole and the inner edge of the orbiting disk. This gap provides more room for the build-up of magnetic fields, which fuel the jets, an idea known as the Reynold's conjecture after the theoretical astrophysicist Chris Reynolds of the University of Maryland, College Park.

"If you picture yourself trying to get closer to a fan, you can imagine that moving in the same rotational direction as the fan would make things easier," said Garofalo. "The same principle applies to these . The material orbiting around them in a disk will get closer to the ones that are spinning in the same direction versus the ones spinning the opposite way."

Jets and winds play key roles in shaping the fate of galaxies. Some research shows that jets can slow and even prevent the formation of stars not just in a host galaxy itself, but also in other nearby galaxies.

"Jets transport huge amounts of energy to the outskirts of galaxies, displace large volumes of the intergalactic gas, and act as feedback agents between the galaxy's very center and the large-scale environment," said Sambruna. "Understanding their origin is of paramount interest in modern astrophysics."

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User comments : 20

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Caliban
2.5 / 5 (4) Jun 01, 2010
All well and good, but how is this spin-reversal supposed to be accomplished? A number of concepts are mentioned, but aren't linked together...a hopeless muddle.
omatumr
2.1 / 5 (11) Jun 01, 2010
Backward Black Holes?

ARG! If you are beneath an object doesn't it appear to spin one way; above the object doesn't it appears to spin the other?

Which is backward?

Oliver

yyz
not rated yet Jun 01, 2010
Swallowing another SMBH during a galaxy merger would be a possible mechanism.
eachus
5 / 5 (2) Jun 01, 2010
All well and good, but how is this spin-reversal supposed to be accomplished? A number of concepts are mentioned, but aren't linked together...a hopeless muddle.


Not a muddle at all. The accretion disk spins the same direction as the galaxy, not the black hole. The same effect as when a skater doing a scratch spin pulls in her arms accounts for the extremely high velocities in the accretion disk.

Now if a black hole is fed a diet of matter spinning in the opposite direction, the black hole's spin will slow, then stop and eventually reverse. That part is obvious.

The evidence here is not of one SMBH slowing and reversing its spin but that all retrograde black holes eventually reverse their spin.
yyz
5 / 5 (4) Jun 01, 2010
A black hole spinning in the opposite direction of its accretion disk and galactic disk. Oliver, you're slipping.
yyz
5 / 5 (2) Jun 01, 2010
eachus, they weren't suggesting that(individual) supermassive black holes reverse their direction of spin over their lifetimes. They noted that SMBHs in the distant past exhibited greater instances of retrograde spins than SMBHs found in nearby, present day galaxies.
jamey
5 / 5 (1) Jun 01, 2010
Encounters with other galaxies, especially with their black hole cores might cause a flip as well.
mlange
not rated yet Jun 01, 2010
How does a black hole form a spin in the opposite direction of the accretion disk during galaxy formation?
brant
1 / 5 (4) Jun 01, 2010
They are really reaching to fix the broken model.
Why not examine the fundamental assumption "Blackhole"?
maxcypher
5 / 5 (1) Jun 02, 2010
I like the comment that the jets effect the macro environment of the galaxy the MBH is in. I would like to see some studies exploring how these jets effect other galaxies. I can see the possibility of some sort of very long-scale feedback loop between neighboring galaxies.
yyz
not rated yet Jun 02, 2010
It is interesting to contemplate how an object only a few light-days across can affect both its host galaxy and other galaxies/intracluster medium in a galaxy cluster(feedback mechanisms do come in to play). A very visible example of a relatavistic jet directly interacting with a neighboring galaxy can be found in 3C 321 ( http://arxiv.org/abs/0712.2669 ). This radio galaxy is found to be emitting a jet that is interacting with a nearby galaxy, creating a burst of star formation and possibly acting as a trigger for AGN activity in the companion, 35kpc away.
eachus
not rated yet Jun 02, 2010
eachus, they weren't suggesting that(individual) supermassive black holes reverse their direction of spin over their lifetimes. They noted that SMBHs in the distant past exhibited greater instances of retrograde spins than SMBHs found in nearby, present day galaxies.


To-morrow, and to-morrow, and to-morrow,
Creeps in this petty pace from day to day,
To the last syllable of recorded time; -- Macbeth (Act 5, Scene 5)

I wasn't suggesting that any particular prograde SMBH was known to have been retrograde in the past, just that eventually all SMBHs will eventually rotate with the surrounding galaxy. For a given black hole, it may have already happened--or it may take two or three times the current age of the universe.

Also note that galaxy mergers may result in a (single) central black hole rotating at an angle to the merged galaxy, or a galaxy with multiple SMBHs.
in7x
5 / 5 (1) Jun 02, 2010
CSharpner
5 / 5 (1) Jun 02, 2010
omatumr,

Backward Black Holes?

ARG! If you are beneath an object doesn't it appear to spin one way; above the object doesn't it appears to spin the other?

Which is backward?


Uh, did you read the article or just the title? "Backwards" means the black hole spins in the OPPOSITE direction as the accretion disk. This is true whether you're looking at it from the north or the south (or: "above" or "beneath" as you put it).
gwrede
2.3 / 5 (3) Jun 02, 2010
Also note that galaxy mergers may result in a (single) central black hole rotating at an angle to the merged galaxy, or a galaxy with multiple SMBHs.
Yes, this is important to notice.

Since (at least) most spiral galaxies can be expected to be the result of multiple episodes of galaxy merger, it should be expected that the "central" black hole(s) is not perfectly aligned with the galaxy disk (nor that it statically occupies the exact center of gravity of the total system, either, as came up in a recent chain of comments).

I assume the momentum (as in rotation direction and speed) of a SMBH is the result of (1) its previous momentum, (2) that of the last SMBH it merged with (presumably in the last galactic merger), and (3) the momentum of their encounter. (That is, how the two spiralled each other before the merger.)

Cont'd...
gwrede
2.3 / 5 (3) Jun 02, 2010
(Continued)

This should result in most SMBHs not being perfectly aligned with the rest of the galaxy they occupy.

But with time they are pressed to settle into an alignment with their galactic disk. (Somebody with more math skills than I might tell us how long that should take.) This includes turning to prograde if it was retrograde to begin with, and later aligning the axis of rotation to that of the disk.

Now, the interesting part is, this post still doesn't explain why there is a different proportion of retrograde SMBHs in ancient galaxies compared with today. The reason for this 2-part post was to draw attention to the mechanism itself.
gwrede
1.3 / 5 (3) Jun 02, 2010
Ha!

After some thinking, it became obvious that, given two galaxies that each have a central SMBH, aligned with their galaxy, and statically in the center of mass of said galaxy:

- The only way the rotation of the resultant SMBH can be aligned with the resultant new galaxy, requires that the galaxies share a common plane of rotation, and that they approach each other in exactly this plane.

- If they have opposite rotations, then the above mentioned alignments have to be preposterously accurate.

- If the initial premise is not fulfilled, then there is no way at all which can result in a centered and aligned prograde SMBH.

(Yes, I haven't done simulations or serious math, this is only based on physical intuition. But I really challenge the formally qualified and those with computational resources to prove me wrong here.)
jsa09
not rated yet Jun 06, 2010
It seems the article IS saying that as more distant (ancient) Galaxies have a higher incidence of retrograde SMBH in their center than closer (modern) Galaxies. Implied therefore is that SMBH that have been around longer will align with the surrounding Galaxy.

@qwrede see above.

Astronomers have known for more than a decade that all galaxies, including our own Milky Way, are anchored by tremendous, so-called supermassive black holes, containing billions of suns' worth of mass.


although the word "known" should be changed to "conjectured". I find this statement then contradicts other statements that say that SMBH may be have change of vector after a merger that could cause it to be ejected from a galaxy. Should a SMBH be inside a galaxy and then at a later date it leaves the galaxy, one would have to conclude that not all Galaxies have a SMBH at or near the center. The contradiction is obvious and a problem in light of the above quote.
dsanco
5 / 5 (1) Jun 08, 2010
So close and they skirt right away from the obvious electromagnetic dynamo concept... spinning magnets and charged particles... the faster the relative spin the more powerful the resulting jets...
Skeptic_Heretic
not rated yet Jun 08, 2010
So close and they skirt right away from the obvious electromagnetic dynamo concept... spinning magnets and charged particles... the faster the relative spin the more powerful the resulting jets...

Exactly, however this was written for someone who already has that basic understanding, as you and yyz touched on, this is an aspect of BH physics that is obscure and deeply specialized.

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