Almost 1 million years, it takes to reach the light on Earth, the time it
forms and travels inside the sun. Finally escapes around the photosphere.
Hello and welcome, in today's post, we'll be learning the processes and
events that photons (particles of light) experience and reach us. Let's
begin.
Introduction:
In the quantum world, various particles bear the wave nature and they are
produced, interact, and create several new entities. In this post, we'll see
how the light (photon) can take thousands to millions of years, yet
the sun's light arrives in just 8 minutes. Let's see the production
of light in the sun's core because not every single point of the sun can
produce light. Actually, the light is a kind of energy, which means it can't
be produced or destroyed. In this case, we'll know it's different
transformations that it might have gone through before reaching us.
Light is made of trillions of waves constructed by particles called
photons, which move at a speed of around 300,000 km/s in a
vacuum. Mind it, we said in a vacuum, if there is something that
alters the photonic behavior or interacts with them, it will cause a delay
in their regular movement or arrival at a specific point. Let's see first
how a photon is represented by quantum mechanics.
This is a wave result of the oscillation of the Electric and the
magnetic fields. Their wavelengths, frequencies and bound energies
are specified. We earlier said it's a wave made up of particles, so each
particle will carry some amount of energy. These photons or packets of
energy are called quanta (quantum-singular). If you wanna know more about
light, you can click
Here
we have covered all kinds and some specifications. But here we will see the
light's properties in a very brief way.
The shorter the wavelength, their energy attached will be
higher. In reality, these waves are themselves moving energies, so
there is no difference between a photon and its energy.
The Origin of Light:
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| The Interior of Sun |
In stars like our sun, their journey begins from reactions of nuclear
fusion, by either the PP chain (90%) or the CNO cycle (10%).
Once the specific steps are completed, the nuclear energy turns into light
and heat. Since they both are energy forms, if they accumulate in one
place and are never delivered to the outer environment, the core and the
Star will explode like a giant bomb. Therefore, an equal amount of
energy should be moved away before the previous reactions complete and
release energy again.
This process happens in the sun's core, even though the Sun is 99% Hydrogen
plasma, but in its outer layers, the temperature and densities are
not enough for fusion. only the central point of the core has those
properties where the temperature touches beyond 13 million K and
densities go beyond 100 grams per cubic centimeter. meaning, A 5 cm³
block of this material would weigh around half a kilogram.
In fusion, Hydrogen fuses into helium through different processes and
reactions and produces gamma rays, neutrinos,
positrons and other byproducts.
The core:
This region contains nuclear fusion and releases massive energy, while its
other ingredients at the microscopic level, like electrons, protons, Ions of
different elements, act as an obstacle to photons and contribute to local
densities. As soon as the photons are released from such a nuclear reaction,
they are immediately scattered by either Compton scattering or absorbed by
other subatomic particles and photons lose their energy and wavelength
slightly increase. Here, the energy transportation is done with Radiative
transfer, which is a series of photon absorption and scattering. only
happens in hot and dense regions of stars.
Radiative region:
This region surrounds the outer core. Energy is transferred through
processes like absorption and reemission and
Compton scattering. its bottom part starts from the temperature of
around 10-15 million Kelvin and ends beneath the convective region,
where the temperature drops to 7 million Kelvin. Of course, these
are not clear boundaries; instead, they almost blend together.
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| Compton Scattering Animation |
In Compton scattering, a photon may be stopped for some time by an
electron/proton/ or ion, it absorbs some energy from the photon, and the
obstacle particle gets excited while the actual photon gets absorbed. The
blocking particle shoots another similar photon or photons, depending on the
photon's energy, but with less energy and longer wavelength in any
direction.
In general absorption, particles like electrons or molecules absorb such a
wandering photon and assimilate their energies. Sometimes later, they reemit
another photon with slightly less energy. Since the core is the densest
region in any star, photons can't roam freely; they get absorbed or
scattered multiple times for around 600,000 years. They get trapped
there. Imagine if somebody challenges you to cross the football ground with
1 million people who are colliding with each other.
After hundreds of thousands of years, they managed to reach the outer edges
of the Radiative zone. someday, in a second, they just get kicked out of the
radiative layer and enter in the convective zone. Before they reach the
convective regions, the photons have lost a lot of their energy and become
an X-ray or a UV ray photon from a gamma ray photon.
This is a very slow yet microscopically violent process.
Convective region:
This region transfers energy (light/heat) by the convection method.
Imagine you're boiling water in a bowl with a burner. Here, the bowl's
basal part is the hottest, whereas upper parts, have lower temperatures.
Water is being boiled at a certain temperature. You will notice that some
bubbles form in the base and they gradually rise in the water and come to
the upper side. If they don't pop, they will reach the top area of the
water and disappear. Let's see what's actually happening, then we'll come
to the sun's convective region.
The water particles on the bottom get heat from the base of the bowl,
which is getting heat from the burner. Some particles carry the heat and
start to rise; in their way, some similar warm particles also join this
group and they rise together. As they gradually move up, they lose their
heat. If they carry enough heat, they will reach the top part of the water
and dump their heat energy to the local particles and that's how the
burner's heat energy flows in the water and after some time, the entire
water becomes hot.
This method is called convection, in which fluids like gas or
liquid particles get the heat energy and rise together, reach the top and
dump their heat in the local zone. particles descend and get the heat
again and rise, this cycle continues until the entire system's temperature
reaches optimal conditions.
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| The Convective region of the Sun |
In the sun's convective layer, this fluid is plasma, and it gets the heat
from the radiative region and creates a similar heat-carrying current like
water. Among these plasma particles, like electrons, protons or neutrons,
the photon gets stuck and move with them. at a certain point in the cooler
areas, the particles dump the energy, including heat and light. that's how
the sun's convective zone works. It also mixes the fusion products like
helium, Nitrogen, oxygen or others.
The convective region starts from a temperature of around
7 million Kelvin outside the Radiative region. it ends around the
inner part of the photosphere, with a temperature of around
2 million Kelvin.
Photons lose their energy in this process too; they become UV or visible
light. Depending on local densities and energy flow, they spend some days,
months, or a few years before reaching the photosphere.
Photosphere:
 |
| Cross section of the sun: Emission of Photons and solar wind particles |
This is the true outer surface of Stars, where the light comes from. At
the time of sunrise, sunset and other appropriate conditions, you see
the sun as a glowing sphere, that's the photosphere. This area is known
for shooting photons in all directions. It also hosts events like
Flares,
CMEs, and
solar spots. most of these
regulate the energy flow in the sun or any other star. Photons that have
spent hundreds to several hundred thousand years in the deeper zones.
escape at a speed of around 300,000 km/s. If you want to know more about
flares, CMEs and other stellar phenomena, please refer to this
Post.
Sometimes, when lines of the Magnetic field reconnect, arrange or twist and interact with other lines, this causes flares. Numerous unprocessed photons, like Gamma rays and X-ray photons, which didn't lose energy like common photons in the interior yet or to escape after hundreds of years, can be ejected directly into space immediately without weakening or being trapped by other subatomic particles.
If the sun were to release gamma rays or X-rays without trapping them, it would be a nightmare for the solar system. Planets will lose their atmospheres, basic chemical structures. Life on Earth will be impossible in such conditions. Therefore, those high-energy photons lose their energy by scattering, being absorbed by other particles. After 10,000-1,000,000 years, they become the normal photon as we know them and when they reach earth, they provide universal food, aka Carbohydrate, through Photosynthesis done by green plants.
The photons usually have a 500 nm wavelength; these photons are abundantly emitted from the photosphere of the sun at a speed of around 300,000 km/s. They reach Earth in 8 minutes. In the 43rd minute, they fly near Jupiter's orbit, and they can cross Neptune's orbit in just 4 hours. In around 16 hours, they cross the Kuyper Belt and enter in Heliopause where incoming cosmic material and outgoing solar wind stop each other. In one day and night, the photons leave the solar system and enter the Interstellar medium, and their journey through the universe begins, which will never stop unless an obstacle comes.
In the End:
We hope you enjoy this brief post. Next time, when you wake up from your bed and the sun is glowing in an orange-yellow color near the horizon. Don't forget to say welcome and best of luck for their happy journey in space.
Let's meet in another exciting post. Until then, stay safe and strong.
Goodbye.
