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

Gravity of a star.

  1. Mar 17, 2010 #1
    star is created from a cluster of gas. but how is this process take place? in the sense that what is driving the gas and dust to form a star? as only massive object can experience gravity. only after a star is formed, then gravity will come into play. but my question is? before gravity come into play, what causes a gas and dust to form as a star? thanks.
  2. jcsd
  3. Mar 17, 2010 #2
    Our current idea is that passing clumps of gas manipulate the each other with their gravity, therefore causing some areas in the gas to clump up on teh side nearest the passing clouds, this then keeps on collapsing to form a star.
  4. Mar 17, 2010 #3


    User Avatar
    Homework Helper

    Every object with mass experiences gravity and exerts gravity on other objects.
  5. Mar 17, 2010 #4
    but only massive object feels gravity. gas and dust is too small to exert gravity to others and feel gravity from other objects.
  6. Mar 17, 2010 #5


    User Avatar
    Gold Member

    This is not true. You are under a misapprehension.

    A volume of gas and dust of mass m will have exactly the same gravitational pull as a rocky body of mass m.
    Last edited: Mar 17, 2010
  7. Mar 17, 2010 #6
    what is the critical mass of the gas clouds in order for this to happen?
  8. Mar 17, 2010 #7
    Each little bit piles up into a bigger bit, and it just snowballs from there.
  9. Mar 17, 2010 #8
    The gravitational constant is a small number!. if the mass is small, the force it feels is small.
  10. Mar 17, 2010 #9
    what attract the small pieces to the ball of gas and dusts
  11. Mar 17, 2010 #10


    User Avatar
    Science Advisor
    Gold Member

    If a cloud of dust exceeds the Jean's mass, it will eventually collapse to form a star (or dwarf star, depending).
  12. Mar 17, 2010 #11


    User Avatar
    Gold Member

    Two microscopic particles have a gravitational force between them, even if it is very small. Clous of dust and gas though, are not merely discrete particles; they might mass as much as a whole solar system. So we're talking about each particle feeling the gravitational pull of an entire solar system's mass.

    It might take a billion years for dust and gas to form a star, but it does happen.
  13. Mar 17, 2010 #12
    Last edited by a moderator: Apr 24, 2017
  14. Mar 18, 2010 #13
    thanks, i understand it better now.
  15. Mar 18, 2010 #14
    Last edited by a moderator: Apr 24, 2017
  16. Mar 18, 2010 #15
    The additional gravity of dark matter also aided in star formation. Massive clouds of DM formed before the stars and acted as gravity wells to collect the gas and dust into stellar nurseries. Supernovae within these nurseries created shockwaves that further drove the particles together.
  17. Apr 13, 2010 #16
    ok, this is something new to me, all this while, has been taught that only gravity play the role.
  18. Apr 13, 2010 #17


    User Avatar

    Staff: Mentor

    The mass of a cloud of hydrogen is the same as (or larger than) the mass of the star created from it. Therefore the gravitational field strength is the same (or larger).

    Don't think of a star as one single object, it is a collection of individual hydrogen atoms. And a cloud of hydrogen, before collapes, is the same collection of individual hydrogen atoms - just further apart. So as long as the gravitational force pulling these particles toward the cloud's common center of mass is enough to overcome their own semi-random motion, it'll collapse.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook