Why is there a lower end on the main sequence?

Answer 1

It's 0.08 solar masses. That's the smallest mass for a red dwarf star.

There are "brown dwarf "stars with lower masses, but they are not usually defined as "true stars" because they don't emit energy by nuclear fusion reactions.

Answer 2

The lower end of the main sequence is defined by the minimum mass needed for hydrogen fusion to occur in the core of a star. Below this threshold, there is not enough pressure and temperature for sustained nuclear fusion, so objects like brown dwarfs, with masses too low to be considered stars, form instead.

Answer 3

They must have enough gravity to burn up their hydrogen to helium. Otherwise, the object doesn't shine as a star and so that it doesn't become a star. Gravity pulls the trigger to start fusion reaction. By the way, gravity means mass.

Answer 4

It is sometimes strange to find stars on the lower end of the main sequence which are no more luminous than white dwarfs for example.

However, the explanation is to be found in the definition of main sequence stars. All stars on the main sequence stars are said to be in hydrostatic equilibrium which essentially means that the outward pressure from the nuclear reaction in the core is balanced by the inward gravitational pressure from the outer layers. The inwards pressure is actually helping to keep the energy generation going through the heat and pressure. As long as this delicate balance exists, the star is said to be on the main sequence.

Stars leave the main sequence when the balance is no longer present or otherwise interrupted. Depending on the original size and type of star, non-main sequence stars will have various sizes and luminosities

Answer 5

The smallest known star is OGLE-TR-122b, a red dwarf star which has a radius of only around 12% of our suns mass, only about 20% bigger than the planet Jupiter (although it's mass is 100 times that of Jupiter). You could get smaller stars though in theory, nuclear fusion could be supported by stars of only 0.08 solar masses.

Answer 6

Below a certain mass limit, the star won't have enough gravity, to create the combination of density and pressure required for normal fusion. This limit seems to be about 0.08 solar masses. Below that, the "star" will still be able to fuse some deuterium, and it will be called a brown dwarf.

Answer 7

.08 M Anything less falls short of the main sequence.

Answer 8

Smaller objects cannot generate enough pressure to start hydrogen fusion

Answer 9

There are black holes that have millions of solar masses.
The largest luminous stars have maybe 100 or so times the mass of our Sun. (one source has a few stars at 175 solar masses)

Answer 10

The lower mass limit for a star is thought to be 0.075 solar masses.

This is about 156 times the mass of Jupiter or 1.49*1029 kg.