How does gravitational equilibrium work

April 01 Nonisothermal Gravitational Equilibrium Model K. This Site. Google Scholar. Society of Petroleum Engineers. You can access this article if you purchase or spend a download. View full article. Sign in Don't already have an account? Personal Account. You could not be signed in. Please check your username and password and try again. Sign In Reset password.

Sign in via OpenAthens. Pay-Per-View Access. Buy This Article. Annual Article Package — Buy Downloads. View Your Downloads. View Metrics. Cited By Web Of Science 6. Email Alerts Article Activity Alert. Articles in press Alert. Could these unresolved discrepancies in G hide some new physics?

This seems unlikely. I believe undiscovered systematic errors in all or some of these new experiments is the answer — G is difficult to measure but it should not be too difficult! Quinn, T. A , Gibney, E. Cavendish, H. Google Scholar. Cohen, E. Speake, C. Physics Today 67 , 27—33 July Download references. You can also search for this author in PubMed Google Scholar. Correspondence to Terry Quinn. Reprints and Permissions.

Gravity on the balance. Nature Phys 12, Download citation. Published : 02 February Turbulence within the cloud causes knots to form which can then collapse under it's own gravitational attraction. As the knot collapses, the material at the center begins to heat up.

That hot core is called a protostar and will eventually become a star. The cloud doesn't collapse into just one large star, but different knots of material will each become it's own protostar. As the protostar gains mass, its core gets hotter and more dense. At some point, it will be hot enough and dense enough for hydrogen to start fusing into helium. It needs to be 15 million Kelvin in the core for fusion to begin.

When the protostar starts fusing hydrogen, it enters the "main sequence" phase of its life. Stars on the main sequence are those that are fusing hydrogen into helium in their cores. The radiation and heat from this reaction keep the force of gravity from collapsing the star during this phase of the star's life. This is also the longest phase of a star's life.

Our sun will spend about 10 billion years on the main sequence. However, a more massive star uses its fuel faster, and may only be on the main sequence for millions of years.

Eventually the core of the star runs out of hydrogen. When that happens, the star can no longer hold up against gravity. Its inner layers start to collapse, which squishes the core, increasing the pressure and temperature in the core of the star.

While the core collapses, the outer layers of material in the star to expand outward. At this point the star is called a red giant. When a medium-sized star up to about 7 times the mass of the Sun reaches the red giant phase of its life, the core will have enough heat and pressure to cause helium to fuse into carbon, giving the core a brief reprieve from its collapse.

Once the helium in the core is gone, the star will shed most of its mass, forming a cloud of material called a planetary nebula. The core of the star will cool and shrink, leaving behind a small, hot ball called a white dwarf. A white dwarf doesn't collapse against gravity because of the pressure of electrons repelling each other in its core. A red giant star with more than 7 times the mass of the Sun is fated for a more spectacular ending.