<blockquote>
  <p>We know that stellar radiation pressure balances the gravitational compressive forced of a star.</p>
</blockquote>

<p>We do not know that. Degeneracy pressure, thermal pressure, and radiation pressure are what collectively balance gravitation in a star. Degeneracy pressure dominates over the other two in white dwarfs and neutron stars. Thermal pressure dominates in low mass stars such as the Sun. It's only in very massive stars where radiation pressure dominates.</p>

<blockquote>
  <p>Shouldn't the process of shrinking be a quasistatic process making stars (Eternally Collapsing Objects)?</p>
</blockquote>

<p>You are forgetting about fusion. A star is more or less in equilibrium thanks to a number of negative feedbacks. (Negative feedback in a control system is good. Positive feedback is very bad. The "screech!" sound you occasionally hear from microphones is positive feedback.)</p>

<p>Suppose the fusion rate increases slightly in a region near the center of a star. This increases the temperature and thereby the pressure, which in turn causes the core to expand, which in turn causes the density and temperature in the core to fall, which in turn decreases the fusion rate. The reverse applies for a slight decrease in the fusion rate. Similar negative feedbacks apply for changes in temperature, pressure, and density. A main sequence star is self regulating.</p>

<p>Things get a bit trickier when a star leaves the main sequence, but that is a different question. </p>

CC BY-SA 3.0
2016-07-07T19:42:05.630Z
Engineers and scientists use feedback as a noun and write about multiple feedbacks when more than one feedback mechanism is present. Please do not re-edit the answer.
David Hammen
CC BY-SA 3.0
2016-07-07T16:30:47.197Z
2016-07-07T19:11:40.673Z
2016-07-07T19:11:40.673Z
David Hammen
<p>We know that stellar radiation pressure balances the gravitational compressive forced of a star. Are there other factors which resist such a collapse? Also, if radiation pressure balances gravitational compression, shouldn't the process of shrinking be a quasistatic process making stars Eternally Collapsing Objects (ECOs)?</p>

CC BY-SA 3.0
2016-07-07T15:47:05.183Z
Are you talking about things like the electron degeneracy pressure?
Dean
CC BY-SA 3.0
2016-07-07T16:18:51.973Z
Yes. But does the electron / neutron degeneracy pressures come into play significantly for normal stars? (Not neutron stars).if not, then is thete anything other than radiation pressure which counters the forced of gravity?
Lelouch
<radiation><stellar-dynamics>
Why aren't stars like Eternally Collapsing Objects?
Lelouch
# Why aren't stars like Eternally Collapsing Objects?

(Asked by: username_0 on 2016-07-07)

We know that stellar radiation pressure balances the gravitational compressive forced of a star. Are there other factors which resist such a collapse? Also, if radiation pressure balances gravitational compression, shouldn't the process of shrinking be a quasistatic process making stars Eternally Collapsing Objects (ECOs)?

**Tags:** radiation, stellar-dynamics

> **Comments:**
> **username_1**: Are you talking about things like the electron degeneracy pressure?  
> **username_0**: Yes. But does the electron / neutron degeneracy pressures come into play significantly for normal stars? (Not neutron stars).if not, then is thete anything other than radiation pressure which counters the forced of gravity?  

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## 1 answers

### Answer by username_2 on 2016-07-07. Score: 5 | Accepted answer

> We know that stellar radiation pressure balances the gravitational compressive forced of a star.

We do not know that. Degeneracy pressure, thermal pressure, and radiation pressure are what collectively balance gravitation in a star. Degeneracy pressure dominates over the other two in white dwarfs and neutron stars. Thermal pressure dominates in low mass stars such as the Sun. It's only in very massive stars where radiation pressure dominates.

> Shouldn't the process of shrinking be a quasistatic process making stars (Eternally Collapsing Objects)?

You are forgetting about fusion. A star is more or less in equilibrium thanks to a number of negative feedbacks. (Negative feedback in a control system is good. Positive feedback is very bad. The "screech!" sound you occasionally hear from microphones is positive feedback.)

Suppose the fusion rate increases slightly in a region near the center of a star. This increases the temperature and thereby the pressure, which in turn causes the core to expand, which in turn causes the density and temperature in the core to fall, which in turn decreases the fusion rate. The reverse applies for a slight decrease in the fusion rate. Similar negative feedbacks apply for changes in temperature, pressure, and density. A main sequence star is self regulating.

Things get a bit trickier when a star leaves the main sequence, but that is a different question.

> **Comments:**
> **username_2**: Engineers and scientists use feedback as a noun and write about multiple feedbacks when more than one feedback mechanism is present. Please do not re-edit the answer.  

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