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Thread: NGC 1365 accretion disc

  1. #1
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    NGC 1365 accretion disc

    With regards to the SMBH in NGC 1365 galaxy:

    Please see the following article:

    http://www.dailymail.co.uk/sciencete...s-history.html

    It is stated that:

    Astronomers have measured the rate of spin of a supermassive black hole for the first time.
    The sphere more than 2 million miles across - eight times the distance from Earth to the Moon - is spinning so fast that its surface is traveling at nearly the speed of light.
    Although the black hole in NGC 1365 is currently as massive as several million Suns, it wasn't born that big.
    The new measurements published in Nature help remove the mystery of what occurs in and around black holes that are so powerful that nothing - not even light - can escape.
    The immense gravitational attraction of these objects shreds and accelerates the gas and dust that has got too close.
    By exploiting NuSTAR's unprecedented accuracy the researchers discovered the spin rate of this supermassive black hole at least 84 percent of the maximum theoretically allowed in physics.
    By studying atoms in the X-ray band as they circle around the black hole before they disappear into it they could detect the effects of the incredible gravity.


    Hence, by studying atoms in the X-ray band as they circle around the SMBH, our scientists have discovered that:

    1. Those atoms are located at the accretion disc.
    2. The orbital radius of those atoms is eight times the distance from Earth to the Moon.
    3. The orbital speed of those atoms is 84% of the speed of light.

    Do you agree with that?
    Last edited by Dave Lee; 2017-Dec-29 at 04:03 PM.

  2. #2
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    Unfortunately, that's a popularized description of the research and includes many simplifications, so I'd tend to be cautious about drawing any specific conclusions.

    You probably should peruse the original publication, which is available for a fee at
    https://www.nature.com/articles/nature11938
    or its pre-print, which is available for free at
    https://arxiv.org/abs/1302.7002
    Last edited by selden; 2017-Dec-29 at 05:46 PM. Reason: added pricing comments
    Selden

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    Quote Originally Posted by Dave Lee View Post
    1. Those atoms are located at the accretion disc.
    2. The orbital radius of those atoms is eight times the distance from Earth to the Moon.
    3. The orbital speed of those atoms is 84% of the speed of light.

    Do you agree with that?
    1. As far as I can tell, they measured X-rays reflected from the inner surface of the accretion disk (not atoms at the accretion disk)

    2. The radius numbers don't seem to make much sense
    The radius of the black hole should be about 6 million kilometres (3.7 million miles).
    The distance to the inner edge of the accretion disk, where the reflection takes place, is 2.5 times that radius.
    So I don't know what the 2 million miles refers to.

    3. The spin of the black hole is 0.84. This might correspond to a speed at the event horizon of 0.84c, I'm not sure. But not necessarily the speed of any matter in the accretion disk.

    So it looks like all three statements are somewhere between very inaccurate and wrong. (Which is normal for the Daily Mail.)

    I hope someone who can understand the paper better than me adds some comments, because it looks quite interesting.

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    Quote Originally Posted by Strange View Post
    1. As far as I can tell, they measured X-rays reflected from the inner surface of the accretion disk (not atoms at the accretion disk).
    Thanks
    Quote Originally Posted by Strange View Post
    2. The radius numbers don't seem to make much sense
    The radius of the black hole should be about 6 million kilometres (3.7 million miles).
    The distance to the inner edge of the accretion disk, where the reflection takes place, is 2.5 times that radius.
    So I don't know what the 2 million miles refers to.
    Do you mean that all black holes must have a radius of 6 million kilometers regardless of their total mass?

    Please be aware that the estimated BH mass is as follow:

    "Although the black hole in NGC 1365 is currently as massive as several million Suns"
    Quote Originally Posted by Strange View Post
    3. The spin of the black hole is 0.84. This might correspond to a speed at the event horizon of 0.84c, I'm not sure. But not necessarily the speed of any matter in the accretion disk.
    We can't see a black hole.
    So if we see something , it can't be the SMBH, but some kind of real matter.
    Therefore, do you agree that this is an indication that the orbital velocity of some matter is 0.84c (even if it is at the event horizion)?
    In any case, why do we estimate that the black hole can spin?
    I thought the ultra fast spinning matter is a simple outcome of the SMBH gravity.
    Last edited by Dave Lee; 2017-Dec-30 at 05:04 PM.

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    Quote Originally Posted by Dave Lee View Post
    Do you mean that all black holes must have a radius of 6 million kilometers regardless of their total mass?
    The radius is proportional to the mass. I calculated that radius from the reported mass of the black hole (2x106 solar masses).

    We can't see a black hole.
    So if we see something , it can't be the SMBH, but some kind of real matter.
    Therefore, do you agree that this is an indication that the orbital velocity of some matter is 0.84c (even if it is at the event horizion)?
    It is not the orbital velocity of matter (if I have understood the paper correctly - I assume you haven't even looked at it). The spin of the black hole affects the spectrum of X-rays reflected from the edge of the accretion disk.So it is a measurement of the spin of the black hole.

    In any case, why do we estimate that the black hole can spin?
    Because it formed from a star that was almost certainly spinning (because t formed from a cloud of rotating disk of gas and dust). Conservation of angular momentum, in other words.

    I thought the ultra fast spinning matter is a simple outcome of the SMBH gravity.
    No, the rotation of matter in the accretion disk is due to the fact that the matter in the accretion disk is rotating (see above for the reasons). If it weren't rotating, it would fall straight towards the black hole. I suppose that frame dragging by the black hole would impart some angular momentum to the infalling matter but I don't know how large an effect that would be. Maybe someone else can comment.

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    Quote Originally Posted by Strange View Post
    The radius is proportional to the mass. I calculated that radius from the reported mass of the black hole (2x106 solar masses).
    Thanks

    Quote Originally Posted by Strange View Post

    It is not the orbital velocity of matter (if I have understood the paper correctly - I assume you haven't even looked at it). The spin of the black hole affects the spectrum of X-rays reflected from the edge of the accretion disk.So it is a measurement of the spin of the black hole.

    Because it formed from a star that was almost certainly spinning (because t formed from a cloud of rotating disk of gas and dust). Conservation of angular momentum, in other words.

    No, the rotation of matter in the accretion disk is due to the fact that the matter in the accretion disk is rotating (see above for the reasons). If it weren't rotating, it would fall straight towards the black hole. I suppose that frame dragging by the black hole would impart some angular momentum to the infalling matter but I don't know how large an effect that would be. Maybe someone else can comment.
    I'm quite confused.
    When you claim that: "the black hole affects the spectrum of X-rays reflected from the edge of the accretion disk", I assume that we actually get this spectrum from the edge of the accretion disk.
    However, in the accretion disk there is a real matter. we can see it!
    Therefore, why can't we assume that it is a reflection from a real matter from the edge of the accretion disk?

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    Quote Originally Posted by Dave Lee View Post
    When you claim that: "the black hole affects the spectrum of X-rays reflected from the edge of the accretion disk", I assume that we actually get this spectrum from the edge of the accretion disk.
    However, in the accretion disk there is a real matter. we can see it!
    Therefore, why can't we assume that it is a reflection from a real matter from the edge of the accretion disk?
    I'm not really claiming anything, just explaining what I understood from the paper. (So I may well be mistaken.)

    As I understand it, the X-rays are reflected from the edge of the accretion disk. And, yes, I assume it is reflected by the matter (plasma) in the accretion disk. Something like this, perhaps:


    So, as far as I can tell, the reflected spectrum from nearest the black hole is "distorted" by the rotation of the black hole (frame dragging, maybe) and by analysing the width of the spectral lines they can determine the spin of the black hole.

    That's about all I understood. And I may not have understood it correctly!

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    Quote Originally Posted by Strange View Post
    So, as far as I can tell, the reflected spectrum from nearest the black hole is "distorted" by the rotation of the black hole (frame dragging, maybe) and by analysing the width of the spectral lines they can determine the spin of the black hole.
    Please look at your diagram.
    A beam of light from the Corona is reflected from the accretion disc to the observer.
    It has no interaction with the SMBH.
    Therefore, I still do not understand why it can't give an indication for the orbital speed of the plasma in the accretion disc?

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    In the following article about SMBH in spiral galaxy it is stated:
    https://en.wikipedia.org/wiki/Supermassive_black_hole

    Some of the best evidence for the presence of black holes is provided by the Doppler effect whereby light from nearby orbiting matter is red-shifted when receding and blue-shifted when advancing. For matter very close to a black hole the orbital speed must be comparable with the speed of light, so receding matter will appear very faint compared with advancing matter, which means that systems with intrinsically symmetric discs and rings will acquire a highly asymmetric visual appearance.

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    Quote Originally Posted by Dave Lee View Post
    Therefore, I still do not understand why it can't give an indication for the orbital speed of the plasma in the accretion disc?
    I'm sure it can.But that is not what this paper is about. Maybe you can find another paper that looks at the doppler shift of light from the accretion disk and hence its speed, if that is what you are more interested in.

    This paper is about the broadening of lines in the spectrum caused by relativistic effects (i.e. the spin of the black hole).

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    I haven't read it, but this might give you more info: https://ned.ipac.caltech.edu/level5/...d/Lind4_2.html (it mentions Doppler and gravitational red shift as well as the subject of this thread).

    Edit: No, ignore it; lots (too much?) detail and nothing directly relevant as far as I can see.
    Last edited by Strange; 2018-Jan-02 at 11:58 AM.

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