as the sun ages, what will happen to life here on earth? why?

The Dominicus'due south Evolution

The Hertzsprung-Russell Diagram (aka the Main Sequence)
Nigh stars are rather simple things.  They come in a variety of sizes and temperatures, only the great bulk can exist characterized by just two parameters:  their mass and their age.  (Chemic composition besides has some effect, merely non enough to modify the overall picture of what we will be discussing hither.  All stars are about three-quarters hydrogen and one-quarter helium when they are born.)

The dependence on mass comes about because the sheer weight of the star'due south mass determines its central pressure, which in turn determines its rate of nuclear burning (higher force per unit area = more collisions = more energy), and the resulting fusion free energy is what drives the star's temperature.  In general, the more massive a star is, the brighter and hotter information technology must be.  It is likewise the case that the gas force per unit area at whatsoever depth in the star (which likewise depends on the temperature at that depth) must rest the weight of the gas to a higher place it.  And finally, of course, the total energy generated in the core must equal the full energy radiated at the surface.

This last fact generates yet another constraint, because the energy radiation of a sphere suspended in a vacuum obeys a law known as the Stefan-Boltzmann Equation:

L = C R² T^four   (Full luminosity of a hot sphere)

Here L is the luminosity of the star, C is a constant ¹ , R is the radius of the star in meters, and T is the surface temperature of the star in K°.  Note how swiftly the energy radiated past a star rises with T:  doubling the temperature causes its energy output to increment by sixteen times.

A star which meets all these constraints is said to exist in hydrostatic equilibrium.  Hydrostatic equilibrium has the fortunate effect that information technology tends to brand stars stable.  Should a star's core be compressed, the pinch causes nuclear burning to increase, which generates more heat, which forces up the force per unit area and makes the star aggrandize.  Information technology goes back to equilibrium.  As well, if a star'due south core should be decompressed, then nuclear burning decreases, which cools the star and brings the force per unit area downwardly, and thus the star contracts and again returns to equilibrium.  The energy output of the Sun has non fluctuated past more than than maybe 0.1% to 0.2% in man history – not bad for a nuclear reactor that has no regulatory committee, no engineers, and hasn't had a rubber check in about v billion years.

Navigation Menu
Introduction
Affair Nether Pressure level
The Birth Of The Sun
The Sun's Evolution
The End Of The Sun
How Large Stars Evolve
Type Ii – The Other Supernova
Afterward The Supernova

1 – Very well, if yous must know, the constant is equal to 5.67 x 10^-8 W m^-ii K^-4.

This equation is important considering it demonstrates how even small changes in the surface temperature of a star tin lead to big variations in energy output.  If the Lord's day'southward temperature was just raised from 5780 One thousand° to 5900 K°, its luminosity would rise past virtually nine%.

The tight interrelation of temperature, pressure, mass, and rate of nuclear called-for ways that a star of a given mass and age can only achieve hydrostatic equilibrium at one prepare of values.  That is, every star in our galaxy of the same mass and age every bit the Dominicus also has the same diameter, temperature, and energy output.  There is no other way for everything to balance.  If one generates a very hard-cadre astrophysics graph known as a Hertzsprung-Russell Diagram (H-R diagram for brusk), the relationship betwixt a star's mass and its other properties becomes more than articulate.  An H-R diagram is shown in Figure one.
An H-R diagram takes a set of stars and plots their luminosities (relative to the Sunday) versus their surface temperatures.  Note that the temperature calibration on the H-R diagram in Figure 1 runs backwards, right to left, and that the luminosity axis is highly compressed.  (Historically, this was how the offset H-R diagram was synthetic, so at present they all are.)  When washed for a large sample of stars, we find that the overwhelming majority of the stars fall forth a single, remarkably narrow ring that runs from the bottom-right to the top-left:  that is, from dim and red to bright and white-hot.  Astronomers phone call this ring the Main Sequence, and hence any star forth the band is chosen a primary-sequence star. ²

The primary sequence exists precisely considering of the inflexible nature of hydrostatic equilibrium.  Stars with very depression masses (as little as seven.v% that of the Lord's day) lie at the lower right of the H-R diagram.  They must lie at the lower right.  This part of the H-R diagram corresponds to extremely depression luminosity – as little equally a ten thousandth that of the Sun – and low surface temperature, equivalent to the dull orange-yellowish glow of molten metal.  These stars do non have plenty mass to create the pressure level necessary to make the nuclear burning in their cores go any faster.  Loftier-mass stars (upwards of 40 solar masses) reside at the upper left, every bit they must.  Contrary to the depression-mass stars, their immense masses and high key pressures give rise to giants that tin be 160,000 times more luminous than the Sunday, and then hot that they give off more than energy in the ultraviolet than they do as visible calorie-free.  The Sunday lies nearly exactly halfway between these extremes, and thus it is neither extremely dim nor extremely bright equally stars go.  It shines with a brilliant yellow-white colour.

The i-to-one nature between mass and hydrostatic equilibrium ways that every bit you vary the mass of a star, all you tin do is slide along a single, predetermined track with respect to all its other physical properties.  This track is exactly the main sequence.  But now that I've said that, a second await at the H-R diagram reveals that there is a smattering of stars well off the main sequence:  they are concentrated in "islands" at the upper correct and lower left.  Since the stars at the upper right are very luminous yet nonetheless have cool, red surfaces, astronomers phone call them red giants.  Similarly, since the stars at the lower left are very dim yet also white-hot, they are chosen white dwarfs.  We have met the white dwarfs already, in a theoretical mode.  At present let'south see where the existent ones come from.

ii – Astronomers traditionally classify chief-sequence stars with messages, like and so:
O - 30,000 to 40,000 K°
B - 10,800 to 30,000 K°
A - 7240 to ten,800 K°
F - 6000 to 7240 K°
One thousand - 5150 to 6000 K°
G - 3920 to 5150 K°
M - 2700 to 3920 K°

Within each class, numbers from 0 to 9 provide subclasses, with zero beingness the highest subclass (highest temperature).  The Sun is classified as a G2 star.

Red Giants And White Dwarfs
Red giants and white dwarfs come near because stars, similar people, change with age and eventually dice.  For people, the cause of aging is the deterioration of biological functions.  For a star, the cause is the inevitable energy crisis every bit it begins to run out of nuclear fuel.

Since its birth 4.5 billion years ago, the Sun's luminosity has very gently increased past most thirty%.

³   This is an inevitable evolution which comes about because, as the billions of years scroll by, the Sun is called-for up the hydrogen in its core.  The helium "ashes" left backside are denser than hydrogen, so the hydrogen/helium mix in the Sun's core is very slowly becoming denser, thus raising the pressure level.  This causes the nuclear reactions to run a little hotter.  The Dominicus brightens.

This brightening process moves along very slowly at first, when there is however ample hydrogen remaining to be burnt at the centre of the star.  But eventually, the core becomes and then severely depleted of fuel that its energy production starts to fall regardless of the increasing density.  When this happens, the density of the core begins to increment fifty-fifty more, because without a heat source to assist information technology resist gravity, the only possible way the core tin answer is by contracting until its internal pressure is high enough to hold up the weight of the entire star.  Bizarrely, this emptying of the primal fuel tank makes the star brighter, non dimmer, because the intense pressure at the surface of the core causes the hydrogen there to fire fifty-fifty faster.  This more takes upwards the slack from the fuel-exhausted center.  The star's brightening not only continues, it accelerates.

iii – Ane of the outstanding questions in geology is how the Sun could have steadily go brighter even as the overall temperature of the Earth has remained more-or-less constant.  We practise not know exactly, but in two words or less, the answer is: greenhouse effect.  The World's temper evidently had a much college greenhouse gas content four billion years agone, which kept it warm.  (In fact, very warm.  Average global temperatures may take been as high as 140 F°.) Various complex bio-geological feedback loops accept steadily decreased the greenhouse effect precisely because the Sun is getting brighter.
The Sun is nigh half-manner through a very long process of shifting from a way where hydrogen is burned in a kernel at its center to a manner where hydrogen volition be burned in a spherical shell wrapped around an intensely hot, very dense, but quite inert, helium core.  One time it makes the transition from core called-for to shell burning, information technology will exist entering its twilight years.  As the helium core grows, so does the hydrogen-burning shell in a higher place it, thus making the Sun always brighter fifty-fifty while ominously increasing the charge per unit at which helium is accreted onto the core.  The growing core burns the Lord's day's hydrogen nonetheless more rapidly, which in turn simply enlarges the cadre more rapidly. . . .

In brusque, in the end, the nuclear furnace at the eye of every star begins to overheat.  To put numbers on this, when the Sunday was formed iv.5 billion years ago it was virtually 30% dimmer than now.  At the end of the next four.8 billion years, the Sun will be about 67% brighter than it is now.  In the 1.6 billion years following that, the Sun'south luminosity will rise to a lethal 2.2 L_o.  (L_o = present Sun.)  The Earth by then will have been roasted to bare stone, its oceans and all its life boiled away past a looming Sunday that will be some 60% larger than now.

^four   The surface temperature on the Earth volition be in excess of 600 F°. But even this version of the Sunday is still stable and golden compared to what is to come.

iv – Alas, the feedback loops mentioned in footnote three cannot protect the Earth forever.  In one case its greenhouse consequence has dropped to nada, the Earth cannot do annihilation more to absurd itself.

Around the yr 7.1 billion AD, the Sun will begin evolving so speedily that it volition finish to be a main-sequence star.  Its position on the H-R diagram volition begin to shift from where information technology is now, well-nigh the center, towards the upper right where the red giants live.  This is because the Sun's helium core will eventually attain a disquisitional signal where the pressure from normal gasses cannot hold upward the crushing weight existence piled on it (not fifty-fifty gasses heated to tens of millions of degrees).  A tiny seed of electron-degenerate matter will brainstorm to abound at the eye of the Lord's day.  The details of this transition are subject to debate, but theoretical calculations indicate that it will begin when the Sun's inert helium core reaches nigh 13% of a solar mass, or nearly 140 Jupiters.
At this point in its life, the Sun will become unruly.  The machinery that has been slowly making it brighter for the past xi billion years – more core pressure level, yielding hotter nuclear burning, yielding more than helium to enlarge the core – is now accelerated to disastrous levels by the steadily increasing electron-degeneracy.  500 million years later on it hits the disquisitional point, the Sun's luminosity will airship to 34 50_o, fiery enough to create glowing lakes of molten aluminum and copper on the World's surface.  In merely 45 one thousand thousand years more than information technology will attain 105 L_o, and twoscore million years after that it will spring to an incredible two,300 L_o.
By this time the enormous free energy output of the Sun will take caused its outer layers to inflate into a vast simply very tenuous atmosphere at least the size of the orbit of Mercury, and possibly equally large every bit the orbit of Venus.  (Remember of how violently the h2o behaves in a pot of rapidly humid h2o every bit compared to that in a gently simmering pot.  This is analogous to why the Sunday'due south atmosphere "boils" outward equally its cadre becomes hotter.) ^v   The huge size of the solar atmosphere and the enormous heat output of the Dominicus mean that:  #1) the Earth will take been burnt downwards to nothing but a seared iron core by this point, if non vaporized altogether – calculations prove that information technology could go either way – and #2) the solar atmosphere will exist relatively absurd despite the Lord's day'southward tremendous energy output.  Thus, the Lord's day will be both red in color and extraordinarily luminous.  It volition have joined the ruddy giants.  (Run across Figure 2.)

5 – Just it is not a very practiced analogy.  Click here to read the full story, or click the icon.

The number of stars in the scarlet giant part of the H-R diagram is only a fraction of a percent of that on the main sequence, because no star can remain a giant for long.  When the Lord's day reaches its maximum luminosity as a red giant, information technology will exist burning more than nuclear fuel every half dozen million years than information technology did during its entire eleven-billion-year lifetime on the main sequence.  This is not sustainable.  Also, at least as importantly, cherry-red behemothic stars are never really stable in the same sense equally the Sun is now.  They are ever growing and burning their fuel ever faster, until something stops them.  In that location is no long-term equilibrium for a crimson giant. Side by side:  The Terminate Of The Sun

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