APOD: GRO J1655 40: Evidence for a Black... (2010 Sep 05)

[APOD Robot]

GRO J1655 40: Evidence for a Spinning Black Hole

Explanation: In the center of a swirling whirlpool of hot gas is likely a beast that has never been seen directly: a black hole. Studies of the bright light emitted by the swirling gas frequently indicate not only that a black hole is present, but also likely attributes. The gas surrounding GRO J1655-40, for example, has been found to display an unusual flickering at a rate of 450 times a second. Given a previous mass estimate for the central object of seven times the mass of our Sun, the rate of the fast flickering can be explained by a black hole that is rotating very rapidly. What physical mechanisms actually cause the flickering -- and a slower quasi-periodic oscillation (QPO) -- in accretion disks surrounding black holes and neutron stars remains a topic of much research.

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[Guest]

I am only a fascinated onlooker of your APOD, with little astronomic knowledge.
What does GRO (as in today's APOD) stand for? Is that an acronym like NGC?
Thanks for the time you'll be dedicating to illuminate my ignorance and
best regards,
Romano

[bystander]

What does GRO (as in today's APOD) stand for?

According to Simbad: Compton Gamma Ray Observatory

http://chandra.harvard.edu/press/06_rel ... 62106.html
http://apod.nasa.gov/apod/ap060528.html

[JohnD]

Speaking of illuminating ignorance......

Is there any analogy to pulsars?
I understand that pulsars are neutron stars with polar beams (jets?) of radiation. They rotate AND precess, so that to the observer the beam flashes although it is continuous.
Black holes, being an extension of gravitational collapse, will spin faster than a neutron star. Will they precess faster too? Is this flickering a similar effect, as a beam of radiation sweeps across the observer?

JOhn

[neufer]

Speaking of illuminating ignorance......

Is there any analogy to pulsars?

I understand that pulsars are neutron stars with polar beams (jets?) of radiation.
They rotate AND precess, so that to the observer the beam flashes although it is continuous.

Black holes, being an extension of gravitational collapse, will spin faster than a neutron star.
Will they precess faster too? Is this flickering a similar effect, as a beam of radiation sweeps across the observer?

A simple neutron star pulsar does NOT "rotate AND precess" ;
rather it is a misaligned bar magnet which pulses
at the exact same (and highly variable) rate that it spins:

The observed periods of pulsars range from 1.4 milliseconds to 8.5 seconds.

Schematic view of a pulsar. The sphere in the middle represents the neutron star, the curves indicate the magnetic field lines and the protruding cones represent the emission beams.

---

However, a black hole can only have three attributes:

• 1) mass
  2) spin
  3) charge;

hence, it cannot be a bar magnet (aligned or misaligned).

GRO J1655-40 might possibly be a quark star pulsar, however:

<<In general, compact stars of less than 1.44 solar masses – the Chandrasekhar limit – are white dwarfs,

and above 2 to 3 solar masses (the Tolman-Oppenheimer-Volkoff limit),
a quark star might be created; however, this is uncertain.

Gravitational collapse will usually occur on any compact star between 10 & 25 solar masses and produce a black hole.>>

<<SN 1987A appears to be a core-collapse supernova, which should result in a neutron star. Since the supernova first became visible, astronomers have been searching for the collapsed core but have not detected it. The Hubble Space Telescope has taken images of the supernova regularly since August 1990. The images show no evidence of a neutron star. Three possibilities for the 'missing' neutron star are being considered.

• The first is that the neutron star is enshrouded in dense dust clouds so that it cannot be seen.
  
  The second is that large amounts of material fell back on the neutron star, so that it further collapsed into a black hole.
  
  The third possibility is that the collapsed core became a quark star.>>

http://antwrp.gsfc.nasa.gov/apod/ap070107.html
http://antwrp.gsfc.nasa.gov/apod/ap060125.html
-----------------------------------------------------

[Chris Peterson]

However, a black hole can only have three attributes:

• 1) mass
  2) spin
  3) charge;

hence, it cannot be a bar magnet (aligned or misaligned).

Spin is not a property of a black hole; this should properly be called angular momentum.

It is probable that what you say is true, but far from certain. Different metrics exist which also allow for a black hole to have a magnetic moment (analogous to charge). And in any case, the system formed by a black hole and its accretion disc does have a magnetic field, so the observed flickering may have some analogs with the mechanism of a pulsar.

[JohnD]

neufer,
Surprise! At your explanation, which was counter to my image of a pulsar.
So I followed the link to the Wiki article which explains that the axis of rotation and the axis of the magnetic field do not coincide, so thank you for that, as my image is better now.
But that means that, although not precessing, the beam of emitted radiation/particles DOES sweep across the observers view, and does NOT pulsate. That was my question - is the flicker a true change in time in the intensity of the radiation, or a moving beam effect, as from a pulsar. Some of the lnks from the APOD imply that the flicker is an interference effect, but then they say that it is "quasi-periodic", so it can't be that.

Chris,
Stars have a magnetic field (?). A pulsar, a collapsed star has a magnetic field, intensified by its smaller size (?) like its spin. So why does it require 'different metrics' (which sounds as if the possibility is contentious and disputed) for a black hole to have a magnetic field, or moment? Where did the original field go?

John

[León]

I solved the puzzle as my understanding of the flickering in the change of black hole's spin. I do not want to affect the rules. Those interested can view it in Spanish
http://apodando.blogspot.com/

[Chris Peterson]

Chris,
Stars have a magnetic field (?). A pulsar, a collapsed star has a magnetic field, intensified by its smaller size (?) like its spin. So why does it require 'different metrics' (which sounds as if the possibility is contentious and disputed) for a black hole to have a magnetic field, or moment? Where did the original field go?

Although it over-simplifies the situation, the basic idea is that the magnetic field ends up inside the black hole. Thus it has no influence outside the event horizon. These "metrics" that get referred to in discussions like this are different solutions to equations of GR. Because we don't fully understand all the initial conditions, different solutions exist, which must be ruled out by observation and experimentation- not all of which has been done. So there are classes of GR solutions that allow a black hole to have a magnetic field (actually, which allow a dipole to have one component inside and one component outside the event horizon).

Further complicating things is that most theory applies to stationary black holes. Moving black holes (that is, those with linear momentum) have additional parameters describing them, and can definitely have a magnetic field.

Finally, the most descriptive metrics are probably broader than really required. In practice, black holes probably carry very little charge, either. Electric charge is not generally a property of any astronomical objects (even though it is not physically excluded). Real black holes can probably be characterized by nothing more than their mass/energy and their angular momentum.

[Beyond]

....it is a misaligned bar magnet which pulses....

You mean to tell me that there is an actual Really Big GIANT bar magnet in pulsars?
well, at least we know where the iron went. Good thing there's no water there or it would rust away and after a while the pulsar would just be a sar and no-one would know its there anymore.

[Chris Peterson]

You mean to tell me that there is an actual Really Big GIANT bar magnet in pulsars?

Yes, and most amazing, it is naturally red at one end and white at the other, and has a giant "N" and "S" engraved on it. Researchers are still working on extensions to General Relativity to explain these phenomena.

[VANGELDROP]

Could it be a black hole inside a black hole?

[geoffrey.landis]

Speaking of illuminating ignorance......

...However, a black hole can only have three attributes:

• 1) mass
  2) spin
  3) charge;

Actually, that's only true in an idealized world.

In the real world, a black hole pretty much always has an additional attribute: an accretion disk.

Which can have many more aspects, such as--yes--a misaligned magnetic field.

hence, it cannot be a bar magnet (aligned or misaligned).

To the contrary: if a black hole has both charge and spin, it must have a a magnetic field (although this must be aligned).

--
Geoffrey A. Landis

[Henning Makholm]

In the real world, a black hole pretty much always has an additional attribute: an accretion disk.

That's a rather bold claim.

The ones we know of have one, because otherwise they'd be invisible, and we wouldn't know they were there. But is there any reason to think a black hole must be able to maintain an accretion disk indefinitely? One would expect all the matter in its vicinity to fall in eventually (or, more precisely, to fall far enough in that it is redshifted enough to be effectively invisible).

[neufer]

Could it be a black hole inside a black hole?

You're VERY CLEVER and it's black Holes all the way down.

[Chris Peterson]

In the real world, a black hole pretty much always has an additional attribute: an accretion disk.

I'd argue that this isn't an attribute of a black hole, merely a consequence of the behavior of things outside a black hole. A planet may or may not have a moon; that doesn't change the characterization of the planet itself. Things other than black holes can have accretion discs, too, created by the same mechanisms.

In reality, many- probably most- black holes don't even have accretion discs.

To the contrary: if a black hole has both charge and spin, it must have a a magnetic field (although this must be aligned).

That depends on how you solve the equations of GR. It is most commonly believed that black holes do not have a magnetic field, even when they have non-zero valued for both charge and angular momentum. But the question is far from being settled.

[owlice]

it's black Holes all the way down.

In the book Small Gods, the question "what does the turtle stand on?" is asked, and gets the reply "It's a turtle, for heaven's sake. It swims. That's what turtles are for."

[Beyond]

Could it be a black hole inside a black hole?

Could that possibly be a baby black hole?? if it is, I'd bet that it would be a cute little sucker

[JohnD]

Thnaks, Chris, Thanks, neufer (especially for the recursive black holes!)
I am further educated, or rather, I have better image of something I can't understand.

John

[Ann]

geoffrey.landis wrote:

In the real world, a black hole pretty much always has an additional attribute: an accretion disk.

I seem to remember a case of microlensing, when something massive but invisible passed in front of a faint background star, magnifying it considerably. I remember that astronomers speculated that the body responsible for the microlensing was most likely a stellar-mass black hole.

If this thing was a wandering stellar mass black hole, it probably didn't have an accretion disk.

Ann

[neufer]

Speaking of illuminating ignorance......

However, a black hole can only have three attributes:

• 1) mass
  2) spin
  3) charge;

Actually, that's only true in an idealized world.

In the real world, a black hole pretty much always has an additional attribute: an accretion disk.

Which can have many more aspects, such as--yes--a misaligned magnetic field.

Are you sure, G.A.L.

hence, it cannot be a bar magnet (aligned or misaligned).

To the contrary: if a black hole has both charge and spin, it must have a a magnetic field (although this must be aligned).

I stand corrected. (Newman )

<<Newman's result represents the simplest stationary, axisymmetric, asymptotically flat solution of Einstein's equations in the presence of an electromagnetic field in four dimensions. It is sometimes referred to as an "electrovacuum" solution of Einstein's equations.

Any Kerr-Newman source has its rotation axis aligned with its magnetic axis. Thus, a Kerr-Newman source is different from commonly observed astronomical bodies, for which there is a substantial angle between the rotation axis and the magnetic moment.

If the Kerr-Newman potential is considered as a model for a classical electron, it predicts an electron having not just a magnetic dipole moment, but also other multipole moments, such as an electric quadrupole moment. As of yet, an electron quadrupole moment has not been detected empirically.

Like the Kerr metric for an uncharged rotating mass, the Kerr-Newman interior solution exists mathematically but is probably not representative of the actual metric of a physically realistic rotating black hole due to stability issues. Although it represents a generalization of the Kerr metric, it is not considered as very important for astrophysical purposes since one does not expect that realistic black holes have an important electric charge.>>

[Ann]

Could it be a black hole inside a black hole?

Could that possibly be a baby black hole?? if it is, I'd bet that it would be a cute little sucker

Baby dressed in black hole.

Ann

[Beyond]

Ann, there's waayyyy tooooo much white for that to be a "Black Hole Baby!"

[neufer]

In the real world, a black hole pretty much always has an additional attribute: an accretion disk.

I'd argue that this isn't an attribute of a black hole, merely a consequence of the behavior of things outside a black hole. A planet may or may not have a moon; that doesn't change the characterization of the planet itself. Things other than black holes can have accretion discs, too, created by the same mechanisms.

In reality, many- probably most- black holes don't even have accretion discs.

Which is all pretty moot here since GRO J1655-40 clearly has an accretion disc.

However, it is not all all clear that GRO J1655-40 is a black hole.

I vote that GRO J1655-40 is more likely to be a quark star pulsar:

<<In general, compact stars of less than 1.44 solar masses – the Chandrasekhar limit – are white dwarfs,

and above 2 to 3 solar masses (the Tolman-Oppenheimer-Volkoff limit),
a quark star might be created; however, this is uncertain.

Gravitational collapse will usually occur on any compact star between 10 & 25 solar masses and produce a black hole.>>

<<SN 1987A appears to be a core-collapse supernova, which should result in a neutron star. Since the supernova first became visible, astronomers have been searching for the collapsed core but have not detected it. The Hubble Space Telescope has taken images of the supernova regularly since August 1990. The images show no evidence of a neutron star. Three possibilities for the 'missing' neutron star are being considered.

• The first is that the neutron star is enshrouded in dense dust clouds so that it cannot be seen.
  
  The second is that large amounts of material fell back on the neutron star, so that it further collapsed into a black hole.
  
  The third possibility is that the collapsed core became a quark star.>>

http://antwrp.gsfc.nasa.gov/apod/ap070107.html
http://antwrp.gsfc.nasa.gov/apod/ap060125.html

[Beyond]

You mean to tell me that there is an actual Really Big GIANT bar magnet in pulsars?

Yes, and most amazing, it is naturally red at one end and white at the other, and has a giant "N" and "S" engraved on it. Researchers are still working on extensions to General Relativity to explain these phenomena.

Chris - you wouldn't happen to have some sort of visual or infared picture of that "bar" would you? I'm feeling a tug on my pants legs.