# Min./Max. Mass of Stars?

Why is there a minimum and a maximum mass that a star can have? Roughly what

are the minimum and maximum masses?

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• 8 months ago

A star becomes a star by fusing material within it's mass.  To do that, you need a minimum amount of heat and pressure to maintain the fusion reaction.  So, the minimum is about 80 times the mass of Jupiter, or about 8% of the mass of the sun.  ( https://hypertextbook.com/facts/2001/KellyMaurelus... )

The largest stars thought possible for years were greater than 150 solar masses, but there have been some discovered that are estimated at twice this amount, and perhaps larger.   The larger stars may be the result of collisions between two smaller stars.  The largest stars formed without the result of a collision is limited by how much material the proto-star can collect prior to fusion ignition, because once fusion begins, solar wind will tend to blow away additional material.

• 7 months ago

The minimum mass for a main sequence star is about 0.075 solar masses. The maximum stable mass is about 60 solar masses, but you can find stars with more mass that are busy throwing off their own outer layers.

• Anonymous
8 months ago

The minimum mass is the easy one, it's the mass at which hydrogen fusion can occur inside the star due to its gravity. That's about 10% of the Solar mass.

The maximum size is a bit harder to determine, because it depends on which generation of stars, among other factors. Current estimates are that they can get around 300 solar masses in the modern generation. But the first stars (known as Pop III stars) could have theoretically been upto 10's of thousands of solar masses.

• 8 months ago

The minimum mass is a mass at which the probability protons will quantum tunnel being so low that nuclear fusion won’t happen within in a star. The higher the mass, the more particles a star has and the higher chance particles will quantum tunnel.

• 8 months ago

There is absolutely no limit at all

• 8 months ago

An object with too little mass doesn't have the pressure at its core to fuse hydrogen to helium.

That minimum mass is around 13 Jupiter masses.

An object with too much mass so that gravity is stronger than the outward pressure at the core due to heat production will collapse into a black hole.

That maximum mass is around 8 solar masses.

• 8 months ago

The more mass you pile up in the same place (a planet, a star...) the more each bit will attract each other through gravity. As the mass increases, the pressure (and temperature*) increases at the centre. As long as the mass is below a certain threshold, the natural repulsion of each atom for every other atom (because of the electron clouds around each atom) is sufficient to keep them apart, and the pressure and temperature provides an outwards pressure to counteract the inward pressure of gravity.

At some point, the above is no longer sufficient. Atoms are forced too hard against each other and they begin to fuse, for example, two hydrogen atoms fuse together to form a deuterium atom (plus a positron and a neutrino), and, in a two step process, 4 atoms of hydrogen become one atom of helium plus two positrons - and two neutrinos. In each case, the mass of 4 hydrogen atoms is more than the resulting one atom of helium (plus the stuff); the "lost mass" is transformed into energy that adds to the outward pressure against gravity.

This is how most normal stars exist during their "Main sequence" life.

Most stars are relatively stable because if the inward pressure increases, then the rate of fusion increases (atoms are pressed together with more force, making them fuse together more easily), which creates more energy to combat the inward pressure. If this energy increases, the outward pressure wins and the gravity stops increasing the pressure at the centre.

The higher the mass, the more energy is needed to combat the inward pressure of gravity. That is why massive stars live shorter lives: they must fuse their hydrogen a lot faster to combat gravity. The idea of a maximum is that there should be a maximum mass where the radiative pressure (outward) is so strong that it causes the star's outer layers to evaporate back into space, thus reducing the total mass. For a while (over 50 years ago), it was thought that this maximum was around 200 times the mass of our Sun. However, we have since observed more massive stars. We still think there must be a maximum (because the inward pressure of gravity grows faster than the outward radiative energy), but we are no longer sure of the exact number.

• 8 months ago

minimum because below the minimum there is not enough mass to cause the pressure and temperature in the interior to be enough to initiate fusion.

The smallest stars around are the tiny red dwarfs. These are stars with 50% the mass of the Sun and smaller. In fact, the least massive red dwarf has 7.5% the mass of the Sun. Even at this smallest size, a star has the temperature and pressures in its core so that nuclear fusion reactions can take place.

Maximum:

A limit on stellar mass arises because of light-pressure: For a sufficiently massive star the outward pressure of radiant energy generated by nuclear fusion in the star's core exceeds the inward pull of its own gravity. This effect is called the Eddington limit.Stars of greater mass have a higher rate of core energy generation, and heavier stars' luminosities increase far out of proportion to the increase in their masses. The Eddington limit is the point beyond which a star ought to push itself apart, or at least shed enough mass to reduce its internal energy generation to a lower, maintainable rate. The actual limit-point mass depends on how opaque the gas in the star is, and metal-rich Population I stars have lower mass limits than metal-poor Population II stars, with the hypothetical metal-free Population III stars having the highest allowed mass, somewhere around 300 x mass of our sun.

In theory, a more massive star could not hold itself together because of the mass loss resulting from the outflow of stellar material. In practice the theoretical Eddington Limit must be modified for high luminosity stars and the empirical Humphreys–Davidson limit is used instead.