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

Which Has A Stronger Gravitational Pull - A Black Hole or Neutron Star?

  1. Oct 24, 2014 #1
    Is this established or is it dependent on the size of the black hole?

    http://www.space.com/22180-neutron-stars.html

    Neutron stars pack their mass inside a 20-kilometer (12.4 miles) diameter. They are so dense that a single teaspoon would weigh a billion tons — assuming you somehow managed to snag a sample without being captured by the body's strong gravitational pull. On average, gravity on a neutron star is 2 billion times stronger than gravity on Earth. In fact, it's strong enough to significantly bend radiation from the star in a process known as gravitational lensing, allowing astronomers to see some of the back side of the star.


    How does that compare to a black hole's gravity?
     
  2. jcsd
  3. Oct 24, 2014 #2
    Its certainly the g-force of black hole that the greatest. In the words of Relativity, black hole not only curve the space-time like other celestial bodies(like neutron star) but also curve it so enormously the not even light could escape from it.
     
  4. Oct 24, 2014 #3

    Jorrie

    User Avatar
    Science Advisor
    Gold Member

    Further to that, if you would aim a ray of light accurately enough towards a black hole, it can bend the ray so severely that it circles around the hole and comes back to you. A neutron star cannot do that.
     
  5. Oct 24, 2014 #4

    Chronos

    User Avatar
    Science Advisor
    Gold Member

    The strength of a gravitational field is determined solely by mass and distance from the center of gravity of an object. Oddities like the bending of light are only noticeable for compact [dense] objects. In such cases a light beam can pass close enough to encounter a region of severely curved spacetime. This does not happen for a normal density object. A light beam runs into the surface before it enters a region of severe curvature. The density of a black hole is so high it has a diameter of virtually zero, whereas a neutron star diameter is a little over a dozen kilometers. The diameter of an ordinary star is many thousands of kilometers.
     
    Last edited: Oct 24, 2014
  6. Oct 24, 2014 #5

    DaveC426913

    User Avatar
    Gold Member

    Furthermore, at a fixed distance, the strength of the gravitational field is dependent ONLY on the mass.

    i.e. if you had a black hole and a neutron star and a normal star that (somehow) all massed the same, the g-force at distance X from the centre of the mass would be identical in all three cases. If you were at a million clicks distance, and your spaceship had no windows, you would have a tough time telling which of the three you were orbiting.

    mass.png
     
    Last edited: Oct 24, 2014
  7. Oct 25, 2014 #6

    Haelfix

    User Avatar
    Science Advisor

    The exterior solution of the Einstein's field equations are isomorphic in the two cases. Whether its a star, or a blackhole, the metric and hence the 'force' or deflection of light rays is the same.

    The only difference is that in the case of a stellar black hole, the actual mass of the central object is slightly greater than that of a Neutron star (its something like 3 stellar masses for a Neutron star, and greater than 4 stellar masses for a blackhole). Of course you could imagine an eternal black hole with the same mass.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Which Has A Stronger Gravitational Pull - A Black Hole or Neutron Star?
Loading...