1.Astronomers estimate that a low-mass red dwarf star like Proxima Centauri will shine on the main sequence for four trillion years. Speculate why this star would last so much longer than the estimated 600 Gyr. 2.The star Mira is 1.2 times the mass of the Sun and about 10,000 times more luminous than the Sun. Would Mira fit into the table above? Why or why not? Solution 1. To understand why red dwarfs have such long lifespans, we’ll need to take a look at main sequence stars first, and see how they’re different. If you could peel back the Sun like a grapefruit, you’d see juicy layers inside. In the core, immense pressure and temperature from the mass of all that starstuff bears down and fuses atoms of hydrogen into helium, releasing gamma radiation. Outside the core is the radiative zone, not hot enough for fusion. Instead, photons of energy generated in the core are emitted and absorbed countless times, taking a random journey to the outermost layer of the star. And outside the radiative zone is the convective zone, where superheated globs of hot plasma float up to the surface, where they release their heat into space. Then they cool down enough to sink back through the Sun and pick up more heat. Over time, helium builds up in the core. Eventually, this core runs out of hydrogen and it dies. Even though the core is only a fraction of the total mass of hydrogen in the Sun, there’s no mechanism to mix it in. A red dwarf is fundamentally different than a main sequence star like the Sun. Because it has less mass, it has a core, and a convective zone, but no radiative zone. This makes all the difference. The convective zone connects directly to the core of the red dwarf, the helium byproduct created by fusion is spread throughout the star. This convection brings fresh hydrogen into the core of the star where it can continue the fusion process. By perfectly using all its hydrogen, the lowest mass red dwarf could sip away at its hydrogen fuel for 10 trillion years. 2. No , Mira does not fit in that because of high mass. .

1. 1.Astronomers estimate that a low-mass red dwarf star like Proxima Centauri will shine on the
main sequence for four trillion years. Speculate why this star would last so much longer than the
estimated 600 Gyr.
2.The star Mira is 1.2 times the mass of the Sun and about 10,000 times more luminous than the
Sun. Would Mira fit into the table above? Why or why not?
Solution
1. To understand why red dwarfs have such long lifespans, we’ll need to take a look at main
sequence stars first, and see how they’re different. If you could peel back the Sun like a
grapefruit, you’d see juicy layers inside.
In the core, immense pressure and temperature from the mass of all that starstuff bears down and
fuses atoms of hydrogen into helium, releasing gamma radiation.
Outside the core is the radiative zone, not hot enough for fusion. Instead, photons of energy
generated in the core are emitted and absorbed countless times, taking a random journey to the
outermost layer of the star.
And outside the radiative zone is the convective zone, where superheated globs of hot plasma
float up to the surface, where they release their heat into space.
Then they cool down enough to sink back through the Sun and pick up more heat. Over time,
helium builds up in the core. Eventually, this core runs out of hydrogen and it dies. Even though
the core is only a fraction of the total mass of hydrogen in the Sun, there’s no mechanism to
mix it in.
A red dwarf is fundamentally different than a main sequence star like the Sun. Because it has less
mass, it has a core, and a convective zone, but no radiative zone. This makes all the difference.
The convective zone connects directly to the core of the red dwarf, the helium byproduct created
by fusion is spread throughout the star. This convection brings fresh hydrogen into the core of
the star where it can continue the fusion process.

2. By perfectly using all its hydrogen, the lowest mass red dwarf could sip away at its hydrogen
fuel for 10 trillion years.
2. No , Mira does not fit in that because of high mass.