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Could a local black hole exists undetected?

  1. May 6, 2005 #1
    This thread asks: Can we be sure no local black hole exists? It will, I hope, focus on an effort to make at least an OOM estimate of photographic detection (visible light) by “weak quasar” radiations that may be produced as solar wind (or ISM if the BH is far away, where the solar wind density is not dominate) is converging on the event horizon. Other detection possibilities not mentioned below are welcome in this thread and those that are mention may need clarification /analysis. Please do what you can.

    Obviously, BHs could not be detected by reflected sunlight.

    Obviously, an approaching BH’s distance from sun and mass must be such that the gravitational effect on planets is not greater than small, currently unknown, perturbations that occur too frequently to reasonably be ascribed to black holes passing our solar system. (Those are possibly due to Kupper belt objects or unknown asteroids/ comets?) Note that where the BH is also has influence. For example, the differential acceleration of the planets is less (and thus less noticeable) if it is approaching the sun perpendicular to the ecliptic than if approaching in the ecliptic. One should also note that the Pioneer space craft’s position is still accurately known. It serves as a possible detector of the presence of a BH.in its sector of the heavens. There is in fact a “Pioneer anomaly,” but I lack the knowledge to know if it could be due to a local BH.

    The gravitational lens effect possibility of detection is under discussion in Nereid’s thread “Massive objects in the immediate solar neighborhood.” (He suggested that I start this new thread to consider “weak quasar” light photographic detections.) It is too early to be sure of the conclusions of that thread, but it now appears to me, that the answer is going to be: “BHs in some parts of parameter space are not clearly detectable.”

    SpaceTiger has called attention to fact that for a “local black hole“, the duration of the change in light curve from the “lensed star” is likely to be undetectable. This because of the Earth’s motion and the motion of the BH perpendicular to the line between the observing telescope and the “lensed star.” I will take this as the definition of what constitutes a “local black hole” I.e. by definition, local black holes are not detectable by gravitational lens effects.

    Initially, until more definite information is available of the parameter space in which local back holes can exist, I will consider that a BH with mass between 0.5 and 2 Solar masses located at least 100AU from the sun is a “local black hole.” I am interested in the photographic delectability of local black holes in this range, especially if two gravitationally bound ones might exist as may be the case.

    See page 6, left column of http://arxiv.org/PS_cache/astro-ph/pdf/0504/0504034.pdf [Broken]
    Primordial Black Holes - Recent Developments, Paper by B.J.Carr
    Astronomy Unit, Queen Mary, University of London

    Where it states:“…possible existence of a halo population of binary black holes. With a full halo of such objects, there could be a huge number of binaries inside 50 kpc…” Through out that paper, the author notes that the small ones (roughly solar mass) are the most common BHs.

    This interest is motivated by the history of the discovery of Pluto. - Percival Lowell, founder of the observatory at Flagstaff AZ, predicted Pluto’s existence based on observations of perturbations in Neptune’s orbit in late 1920s, but it is now known that Pluto was not the cause. - Pluto is smaller than the moon and from its orbit the perturbing mass would need to have several Earth masses to have produced Lowell’s predictions. I think it unlikely, but can not think of any likely explanation for Neptune‘s perturbations, if real, than the possibility that a BH may have passed by the solar system in the 1920s.

    Thus, the photographic delectability of small local black holes is an especially interesting question. If they are commonly formed in pairs (either as the end fate of paired stars or as B.J. Carr is suggesting above) then there is a 50/50 chance a second one will be coming along soon (instead of having passed before 1920s). If it is now approaching, it could do more that just perturb distant planets. (The passage of the first may also explain why Pluto’s orbit plane is tilted.) It only takes a very small increase in Earth’s eccentricity to throw Earth into a permanent ice age, which would rapidly drop sea levels, making oil imports impossible, etc - a rapid onset cosmic disaster without any need for the cosmic visitor to hit the Earth as usually assumed..

    In subsequent post I will seek help on many aspect of the problem of trying to estimate the photographic delectability of a local black hole. For starters:

    Can one neglect everything in the solar wind but Hydrogen? What fraction is ionic (protons), neutral, and molecular at 100 and 200AU? What is their density )(#/cc)? How much of their initial kinetic speed is thermalzed - I.e. how do the thermal and still kinetic energy compare/ what is the temperture? Are these temperature the same for electrons and the heavier components? (LTE exists?) What is the collision rate, especially for collisions that can populate the upper levels of the Balmer series lines? Etc.
    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. May 6, 2005 #2


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    Staff: Mentor

    We've discussed this before: you misunderstand the history there - or perhaps, simply the meaning of the word "perturbation". Detecting a "perturbation" in the 1920s does not imply that Neptune was "perturbed" in the 1920s in a single, isolated event. Neptune's orbit (like the orbits of all the planets) contains irregularities that if you wish, you can "discover" even today.

    Just apply the same wording to the discovery of Neptune and you'll see the English works the same way:

    -Pluto was discovered in 1930 (in part) by observing perturbations in Neptune's orbit in the 1920s.

    -Neptune was discovered in 1846 after observing perturbations in Uranus's orbit in the 50 years following it's discovery.

    Btw, Pluto was first predicted in 1915, not 1920 :wink: .
    Last edited: May 6, 2005
  4. May 6, 2005 #3
    Please elaborate, I must be dense as I don't understand that "detecting a perturbation" does NOT imply "that Neptune was perturbed."

    I don't care what it is called, but something about Neptune, especially in the late 1920, caused Lowell to spend a lot of money, hire people specifically to search for "planet X", develop new detection approaches (especially the "flicker comparator" by which Pluto was discovered on a sunny AZ afternoon.) etc.

    I also want to make more clear why I think the collisons that permit photographic detection in the 1920s would be limited to the Balmer series.
    I'm pretty sure that the ionization potential of atomic hydrogen is 13.6ev and that the principle quantum levels are below it as inverse n squared (n= 1, being 13.6ev below) but this is from memory, years old, so I could be wrong.

    If true then the n=2 level is only 3.4 ev from ionization. A Lyman alpha line, the least energetic of the lyman series, would thus have 10.2ev. Very roughly speaking, but easy to remember, is 1ev makes a 12345 Angstrom line. Thus a 10.2 ev transition would make a line of approximately 1210 A. - very much in the "vacuum ultra violet" and not detectable from the surface of the Earth or anyway in 1930 or before (unless by some very lucky ballon experiment.) (Even if my memory is wrong, and the levels go only as inverse n, Lyman alpha line still has 6.8ev and is still in the vacuum UV.)

    It really it is not important why I am interested. The detectability of a local black hole is an interesting an potentailly very important question of physics. This thread, started at Nereid's suggestion, is intended to complement his on the detectability of near by Black Holes.
    Last edited: May 6, 2005
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