Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Basic Questions about Black hole's

  1. Jan 11, 2015 #1
    Hello, my name is Bjørnar Bergetun im somewhat new here, i've created a few posts during my stay but i tend to get warned off for not being able to scientifically formulate my questions.
    im no scientist, i lack math in school and have a job where i work with my hands but i've been thinking alot about black holes these last few months and have made a list i hope i can place here for someone to take a look at.
    help me get a better understanding about the nature of the black hole so to speak.

    here are my questions:

    1: What is the size of the magnetic field around a black hole the mass of the one in the center of the Milky Way galaxy? is it big enough to go outside the orbit the earth is in? bigger then the galaxy?

    2: If you put 2 magnets with opposing fields against eachother the smaller magnet will be pushed away by the magnetic fields interacting. could in theory the black hole's magnetic field be moving the black hole by outside forces like for instance black energy/matter pushing on the magnetic field? could this cause direction change or accelleration of a galaxy?

    *3 i've read that the size of a black hole grows 8 times more then the size of the input inserted into it. is this true?

    *4: i've also read that there are gasses coming into the galaxy from outside from the north and south position of the center from sources unknown. is this also true?

    * Sources for question 3 and 4 cannot be found, i have been searching the internet but in hindsight i think it is from a science magazine called "illustrated science" sold in norway.

    i have more questions but would like to see some kind of response to these before asking more.
    like i said, im no scientist but would apreciate it alot if you guys and gals could help me figure this out because its starting to take up alot of the idle time in my brain.
  2. jcsd
  3. Jan 11, 2015 #2


    User Avatar
    2017 Award

    Staff: Mentor

    Magnetic fields do not have a fixed size. With increasing distance, they just become weaker and weaker. For the black hole at the center of our galaxy, the magnetic field at the distance of (earth<->sun) is still quite strong. At the distance of our sun to the galactic center it is completely negligible.

    That depends on the positions and orientations of all magnets relative to each other.

    There is no "black energy/matter". I guess you mean dark matter and dark energy. Both do not interact with magnetic fields (or at least not in a relevant way). And even if they would, this would not move galaxies around.

    How do you measure size? Black holes distort spacetime so much the classical concept of a volume does not make sense inside. Their Schwarzschild radius (which is a measure of their size) grows linearly with mass, so anything volume-like would grow with the third power of mass, yes.
    Hard to tell without a source.
  4. Jan 12, 2015 #3
    Does that mean it indeed stretches as far as the position of our solar system?

    i do mean dark matter and energy. not black. im sorry.
    how can you know this though? i was under the impression we knew almost nothing about dark energy and matter besides the fact that there is alot more of it in the universe then normal matter. dark energy in particular has a bigger presence in the univers then dark matter and normal matter combined.
    how do you know that magnet fields do not interact with it? in this way or any other way?
  5. Jan 12, 2015 #4


    User Avatar
    Gold Member

    Dark energy and dark matter have unknown sources / reasons for existance, BUT ... they have very well understood effects. That is, we don't know what they are or how they came to be but we know a lot about their characteristics.

    Dark energy has NOTHING to do with magnetism. That would be like saying that the energy you exert by lifting a grapefruit is effected by magnetism. It is not.

    Dark matter is, as the name suggests, believed to be a form of matter BUT ... it does not interact with normal matter except due to gravity. Magnetism is not gravity.
  6. Jan 12, 2015 #5


    User Avatar
    2017 Award

    Staff: Mentor

    In the same way the gravitational field of a stone next to me stretches throughout the whole galaxy: completely negligible.
    If dark matter would interact with magnetic fields, it would have a charge, and then it would not be dark. The fact that it is "dark" tells us a lot about it.
    Dark energy is something completely different anyway.

    It could interact via the weak interaction. Nearly all searches for dark matter look for processes of the weak interaction.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook