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stronomy is not always about large-scale entities; it also has a place for supersmall subatomic particles. In this post, we'll explore each major subatomic particle type, its history, detection method, and astronomical importance. Hello and welcome to our Blog, where you learn about astronomy and astrophysics without any jargon. Like all our posts, this will avoid complex math equations and quantum theories; we'll only focus on what you need to know. Let's dive in.
Introduction:
As you know, subatomic particles are the building blocks of our world and
universe; every structure, every action, and their fate depend on these
particles. Before we jump to electrons, protons, or kaons, you must
familiarize the concept, as always, you all may not be quantum experts,
particle physicists, and so on.
How tiny are they?
Take a ruler and pen, draw a one mm line on the paper. If you can, divide
it into 1000 equal segments; each segment will be called a
micrometer or micron. Our eyes can't usually see smaller than 100
microns; an amoeba's size is about 200-300 microns. Bacteria size is about
2-8 micrometers. If you could divide this one micron again into
1000 parts, each segment would be called a nanometer or nm. That's the
ideal size range of viruses.
If we divide a nanometer into 1000 parts, it's one picometer (pm). The
Water molecule is about 275 pm or 2.75 Å (angstrom) because 100 pm = 1Å. We
use it to measure wavelengths of light, sizes of molecules, and similar
things. If you divide 1 pm into 1000 parts, we get one femtometer or fermi.
Now you can imagine how small those subatomic particles are. Today, we'll
explore them.
How can they be studied?
You see that a typical DNA molecule is thousands of times larger than an
atomic nucleus, yet it's very hard to study. The same applies to subatomic
particles; we have theories and assumptions with a handful of verified
points, and this minority of verified facts leads us to the rest of the
picture. Many Ancient philosophers believed that if we keep breaking
objects, we will reach a point where it would be unbreakable. We call this
particle an atom, but it has turned out that it's breakable if we right
tool.
The clear and successful attempt was made in the 1860s, when scientists
were using partially vacuumed tubes or jars and applied currents with
thousands of Volts. They used to see streams of glowing particles moving
from one end of the tube. One of these tubes is called Crookes' tube,
named after its developer, an English scientist, William Crookes. You
can Google it and/or watch videos.
This is a glass chamber; one end has an anode (-) from where conventional
current enters, and the other end has a cathode (+) where current leaves.
A pump is connected to remove air and create a vacuum. When its pressure
is about a thousandth of the general atmospheric pressure (atm), the
battery or whatever gives it electrical energy is turned on. At a few
1000-10,000 Volts and appropriate pressure, the gas usually glows in
yellow-green color. The direction of its beam goes from - to + or anode to
cathode.
If you just keep applying deadly voltages but with standard atm, nothing
happens. If you keep the pressure at about 1/100 of atm, the gas reveals
its type. For example, if we use Hydrogen gas, it glows blue or white in
the case of Carbon Dioxide. Whereas lower pressures like 1/1000 atm, it
glows yellow-green; if the pressure is decreased further, then the glow
disappears.
These rays are called cathode rays; they are not electromagnetic
radiations like light; instead, they are the result of electrons being
peeled away from their nuclei. These types of rays are the result of
particle streams, not of photons. They move from the anode to the cathode
side, meaning it's negatively charged and its particles are named
corpuscles by J.J. Thomson, but
G. Johnstone Stoney suggested the name electron.
When we take spectra of such rays, as we do with sunlight and reveal a
rainbow, we see tiny lines which are made by microscopic lines further,
interpretation of these lines led to the development of quantum mechanics
and atomic structure, therefore, by several experiments we have discovered
hundreds of subatomic particle classes. We'll explore them in this
article.
Basis of division:
Since we have numerous subatomic particle varieties, it becomes crucial
to know how we will recognize them from one another. Well, there are
three main characteristics of each of these particles: Mass, Charge, and
Spin. Let's see them briefly.
Mass:
It might feel funny to measure the mass of a subatomic particle due to
its extremely small size (almost nothing). It's not the same mass as the
mass of a basketball, a table, or daily life objects; it's a quantum
property. We'll see it in further sections. Actually, when subatomic
particles move in 3D space, they resist the acceleration, and this tiny
amount of resistance is provided by interactions with the Higgs field.
It's measured in eV or electron volts, it's an extremely
small amount of energy, about 1.602 x 10 ⁻¹⁹ Joules. Which is
equivalent to the energy gained by an electron, if it accelerates with a
potential difference of 1 Volt.
Of course, this energy is almost nothing to us, but electrons, quarks, or
their homies have way more mass. Therefore, we use MeV (million/mega
electron volts) and GeV (billion/giga electron volts). In convenient ways,
the mass is expressed as eV/c², which means the electron volt is divided
by light speed squared, thanks to Uncle Einstein's equation
E = mc².
It also means the more massive the particle, the more energy it will need
to push or drag. Well, who cares, our most relaxed breath becomes a storm
to them :)
Charge:
Since many of the subatomic particles are charged, meaning they tend to
interact with electromagnetic and field forces. These particles interact
with electromagnetic forces (EMF) with a certain amount of charge
measured in coulombs (C). The elementary charge is
1.602 x 10⁻¹⁹ C; this constant is denoted by e.
This charge could be either Positive or Negative; the particles with the
same polarities would repel, and the opposite would attract. For
example, two or more positives (or negatives) would repel, and the
opposite would attract.
Spin:
Like mass, it's not a classical property, as many of you who are
interested in subatomic particle physics know that Spin is a misleading
term to describe this quantum property. Let's see where the idea of
spinning particles came from.
Earlier spectroscopists noticed that in atomic spectra, there were fine
doublet lines that don't contribute to forming thick lines and can't be
explained with wave functions or the wave nature of particles alone.
These were also unexplainable by charge and mass.
Uhlenbeck and Goudsmit felt the need for another quantum property. This
was theorized as an intrinsic angular momentum, which is zero for scalar
bosons, one for gauge bosons, and half for fermions. It's a quantum
property, not a classical spin; it can't be explained in its true form,
but we can estimate it from the observations of spectroscopy. Let's try to
grasp it since you have already understood the concept of mass and charge.
In quantum mechanics, we assume every subatomic particle, whether it's a
photon, boson, electron, atom, or molecule, carries the properties of both
a particle and a wave. Every single particle, like an electron, is a
ripple or disturbance in its corresponding field.
Imagine calm water in a pond, you throw a stone in the water, and you see
concentric waves that keep expanding outward. In this case, the water acts
as a field, the waves' central point, meaning where your stone fell on the
water, acts as the electron's probable location, not exact. Because you
can't map the position and momentum of subatomic particles together, if
you know one aspect, then the other would be automatically uncertain; we
call this the uncertainty principle of Heisenberg.
That's why we call an electron a tiny ripple/disturbance in the electron
field; you can also assign wavelengths, amplitude, phase, or frequency to
electrons like a wave. Our stone's ripple doesn't have a thing like half
spin, but electrons, including all the fermions, have one. Let's see this
phenomenon more closely.
A zero spin would mean neither ripples moving outward nor inward, just
scattered without motion. Full spin would denote ripples moving outward or
inward constantly; half spin would be like waves expanding outward for a
period, then contracting, then expanding, and this cycle continues. Again,
we say this is just a way to grasp this quantum property; it's not
a true ripple, spinning ball, or anything that we've seen in this world.
Every theory and suggestion that explains the half spin is just a
metaphorical way, not the truth. It's just impossible. Actually, the spin
was coined for a property of a subatomic particle to explain its
surrounding fields like Higgs field, EM, and so forth. It's kinda phase
transition, and math does suggest it's an angular momentum, but not a
classical spin.
Quantum mechanics has successfully made us understand this
phenomenon. Like light, we can't see its photons, but our eyes see
everything through it. We can't explain what happens actually; we only map
those ripples around such a particle and have terms like spin, and people
instinctively think tiny balls twisting, turning, and rotating, but it's
far from reality. It has nothing to do with spin that we recognize; it's
just a quantum property.
Spin is not the property of the particle itself; instead, it's the field
disturbance/ripple's property that can be half, full, or zero, which is
what we've been successfully measuring for a century. Forget anything
you can imagine, anything rotating in the case of subatomic particles,
it's just a term to define a quantum property. Further, we'll meet some
more confusing terms, but let's not be confused.
As you've the basic understanding about mass, charge, and spin, we can
easily recognize the subatomic particles, and we are free to explore
this zoo.
Fermions:
|
| A Nucleus and its orbiting electron |
All the subatomic particles that have half-spin are called fermions;
they obey Pauli's exclusion principle. According to this
principle, no two identical fermions can share one state. What does that
mean? Subatomic particles are basically defined by a set of quantum
properties or numbers, like values of their energies, spin, charge,
symmetries, and others. No two fermions can have these numbers the same;
if some properties are the same, then they might share one state.
If no two fermions can share the same states, you might say, what about
many protons and neutrons living in one atomic nucleus? Well, they do
share the same house, but their energies, spins, and charges are arranged
in a way that Pauli's principle can't kick them out. For example, an s
orbital has two electrons, which are fermions. Their spins would be
alternative to each other; we call them ripples to make you understand,
but they aren't ripples actually; it's intrinsic angular momentum but not
spin.
This way, one electron's spin is denoted by an up arrow and its
partner enters down arrow spin, then first changes into down and
second into up, and this cycle continues. Protons and neutrons don't orbit
the nucleus, but their spin and other quantum numbers are defined this way
so that Pauli's rule can't be violated and threaten their existence. You
see? No two fermions can have the same quantum state.
We have two kinds of Fermions based on their interactions with fundamental
forces and other properties; they are called quarks and
leptons. Quarks are the building blocks of composite particles,
hadrons, which means when any 3 compatible kinds of quarks meet, they
create a hadron. While the leptons are fundamental, they don't have any
elementary particles. However, quarks are usually seen in groups; some
theories suggest they can also live a free life, but they lack
observational evidence.
Physicists use fractional numbers for some particles to define their
quantum traits. If you see a quark with charge 2/3e, it means it's
two-thirds of the fundamental charge 1.602 x 10⁻¹⁹ C. It becomes
more important because a lepton carries this minute charge fully, either
positive or negative, but quarks aren't found in free conditions; we cite
protons or neutrons as their true homes. Since quarks make composite
particles like mesons, protons, neutrons, etc., it's important to define
them as a denominator of 3.
In the chart, we've used some color-coded properties for clarity, for
example, white for MeV, orange for GeV, and so on. We've added
anti-fermions, their symbols, and color charges for quarks and gluons. You
can use this chart for your own purpose. If you aim to use it in online
work like YouTube or other social media, you can add a
contribution link to our blog, CosmicWisdom. You see only
the 1080p version, while the original is 8k. Prepared with high-quality
render and graphics of Ryzen 5 5600X and GTX 1660 Super, its uncompressed
Tif image to prevent any compression artifacts that can desecrate this
chart.
Displayed here is the 1080p version.
Download the 8k chart
Quark:
As you know, each subatomic particle is a ripple/disturbance in its own field. The same goes for Quarks as well; we have three generations of quarks differing in mass and lifetime. The most observable Generation is the first generation of quarks, called up and down quarks. You can see their properties in the image below. We've also added their antiparticle versions.
Quarks are a unique kind of fundamental particles; they have a quantum
property called color charge. Unlike Electric charge, which has only two
types, positive and negative, Color has three charges: red, green,
and blue. Of course, these colors have nothing to do with the colorful world
that we see because we can see due to photons (light), not quarks.
All fermions have their anti-versions as well; let's understand them.
Imagine a charm field is disturbed, but this disturbance has
-2/3 and anti-green quantum color. It's still a charm quark, but it
doesn't have the properties of Standard charm flavor, yet it's stable. We
call it anti-charm, not strange, because there is a separate opposite
version of the strange quark.
We can say an antiparticle is the ripple/disturbance of its own flavor, but
many quantum properties are opposite. For example, a down quark has a 4.7
MeV mass, -1/3e charge, and any of the 3 colors and 1 baryon number. Whereas
an antidown quark will have the same mass and spin, but it would possess one
of the 3 anticolor, opposite charge, and baryon number as -1.
Also, don't be confused by the word flavor here; it has nothing to do with
taste. Suppose you see some expensive cars in a showroom, but don't know
their exact models, you only recognize the Ford Mustang, the Lamborghini,
and the Ferrari. Let's say you want to see a car that resembles a Ferrari,
you are unsure whether its Ferrari but looks like one. You'll say to the car
shop owner, Tell me about that Ferrari-looking car on the second floor.
That's how we use the word flavor to point to subatomic particles. When we
say top quark flavor, it would mean a top quark-like particle, despite it
not actually being a top, but resembling one.
Interactions:
Quarks can interact with all 4 fundamental forces: Strong, weak,
electromagnetic, and gravitational forces; however, gravitational
interaction is hypothetical. Since Quarks are mainly bound to other quarks
with appropriate charge and other quantum properties, it's because of the
strong force and gluons. A free quark can't exist; they usually appear in
groups of 3 colors of quarks that make a neutral color or white. That's
why, no matter the quark flavor, they appear red, green, and blue color
charges, because it makes the color white.
With electromagnetic force and its mediator photons, they cause repulsion
or attraction between charged particles. With Weak forces, quarks tend to
change flavor into another quark. They also cause a particle decay within
a specific period. For example, a neutron can't exist freely for a long
time; in about 15 minutes, a free neutron decays into a proton.
A proton is a famous hadron, most of you are familiar with this guy. It's
a composite particle that is made with an up (2/3), up(2/3), and down
(-1/3) quarks with RGB types. If you sum their charges, you get +1 because
2/3 and 2/3 would be 4/3, but we add -1/3, we get 3/3 or 1, which is the
charge of a proton. Another famous example is the neutron, which is made
up of two down quarks and one up quark. Proton's configuration is usually
denoted by uud, while udd denotes the neutron's structure.
In the image below, you can see some famous hadrons, their charges, and
lifetimes. We've also used their structural quarks and anti-quarks are
shown with a bar over them.
Astronomical importance:
Quarks are the building blocks of this universe; they create the most
basic particles like protons. Quarks are usually found in the interiors
of neutron stars, around black holes when Hawking radiation phenomena
occur, and in massive dying stars like pre-supernova phases. On Earth,
it's impossible to observe them without an accelerator or nuclear
reactors.
Lepton:
These are the second class of fermions; unlike quarks, they don't have
color charges. The first group of leptons has -1 charge while 1 for
their antiparticles; note this is a whole charge, not fractional like
quarks. Among these six main flavors, electrons are well known and the
hardest-working particles. We are all familiar with its daily life usage
and importance as well. Like any other fermion, the electron has an
antiparticle, which we call it Positron; it's just an electron but with
a positive charge. When the electron and positron collide, they
annihilate each other and produce gamma rays.
The second generation, meaning the muon is unstable but lives longer than
many other subatomic particles. It is usually used as a tool to experiment
with time dilation, since it decays more quickly around Earth, while in
space it lasts slightly longer. Muons behave like heavy electrons; their
average lifespan is 2.2 microseconds. Due to their larger mass, they decay
into electrons through weak force interactions. They penetrate into the
matter deeply because of electromagnetic interactions. When Muons decay,
it produces electron and an electron neutrino.
The third generation, Tau or Tauons, is the heaviest of the lepton class.
As a massive particle, it tends to decay into various other particles
depending on its charge type. A regular tau or negatively charged one
makes negatively charged hadrons like Pion- or Kaon-, tau and muon
neutrinos, and so on. While Anti-tau or positive one would make the
positive version of Pions, Kaons, and tau-muon neutrinos.
Neutrinos are leptons with zero charge and interact only when a particle
decays; we call it a weak interaction. This unique trait of neutrinos
makes them extremely hard to detect since most of our machines and
detectors work on the principles of electromagnetic interactions, like
atoms, molecules, electrical, or chemical reactions. That's why neutrinos
were theorized much earlier but were detected in the late 20th century.
Neutrinos are among the most abundant particles in our universe, but their
interaction and behavior make them extremely difficult to study.
Fusion
cycles like CNO, PP chain, Alpha processes, and others produce neutrinos;
their main sources are stars, neutron stars, dying both massive and
intermediate stars, etc. To detect these ghostly particles, it requires a
special kind of detector and must be built underground to filter the
cosmic rays and other radiation.
Boson:
Now you know that when quarks meet together, they form composite
particles like protons and neutrons, and when these meet, they form
atomic nuclei. Now let's consider what binds them. If you come from a
non-scientific background or just heard that our world is made up of
three small particles, protons, neutrons, and electrons, then you have
only got the drops instead of the sea.
Just as several kinds of nuts and bolts are needed to combine two or
more mechanical parts, bosons work exactly like that. If you assemble or
disassemble a machine, you'll need the right kind of screwdrivers,
pliers and other tools. In the subatomic world, if Fermions and their
composite particles are mechanical mini assemblies, then bosons are the
carriers of forces that hold, form, and destroy.
Bosons are the particles or energy carriers, and they usually have one or
zero spin. If you look at our subatomic chart, you have pieces and
elementary blocks on the left side, and nuts, bolts and pliers or cutters
on the right side. That's how our universe's Lego kit has been classified.
Let's see them in depth, because not all those screws would fit into all
holes or work for all kinds of fermions.
Gluon:
These are closely connected with quarks of all generations; remember
that quarks have a unique property, color. This color or quantum
property, designated as color, is mediated by gluons. Based on all
colors, anticolors, and their interactions, there are eight types of
gluons. The first 6 are combinations, whereas the last two are linear
combinations that make the result neutral or white. In math or theory,
you can choose any color combination, but these selective colors are
proven by experiments, which is why we can't choose any colors.
Gluons act like glue among quarks; we call this force the strong force. As
you know, baryons are the combinations of 3 colored quarks that achieve
white or color neutrality, whereas mesons are quark-antiquark pairs.
Strong force not only combines quarks, but also baryons such as the proton
and neutron. That's why protons and neutrons are bound inside the atom.
You might also ask, you didn't mention electrons, atoms, and molecules
because they are the components of matter's structure. The strong force is
short ranged powerful force; it has done its job by binding nucleons
(proton-neutron together.
Remember that there are other kinds of bosons in our chart, let's see if
any of them can be used to bind such a larger structure, larger? Yes,
atoms become larger since they've got quarks, protons, and neutrons.
Photon:
|
| Two Photons travelling in space |
Just as all subatomic particles are disturbance/ripples in their
corresponding fields, photons are ripples in the electromagnetic field.
They are not only particles of light, but they are also a very useful
tool in the subatomic world. They are the carriers of the
electromagnetic energy or radiation. A photon is a fascinating particle
because it's considered not only stable but invincible. Let's see what
their secret of immortality is.
If an electron accelerates, it also disturbs the electromagnetic field
because of its charge. If any ripple occurs in the electric field, the
magnetic field will respond with disturbance or oscillations, or if the
magnetic field gets disturbed first, the electric field will respond. Then
the photon comes into existence, the direction a photon travels, its
perpendicular electric field will oscillate, while ripples in the
perpendicular electric field will occur at the same time in the magnetic
field. This kind of disturbance keeps the photon alive because they power
each other, and the photon flies at its speed, about 300,000 km/s.
It's considered massless, and it can't stop; that's why a resting photon
is just imagination.
Energy doesn't continuously splash like a fountain, but it emits as
droplets or bundles of energy, which we call quanta (quantum in singular).
If the strong force is a kind of energy in a strong field, then its quanta
will be gluons; if the same happens to the Electromagnetic field, the
photons will be its quanta.
As we've talked about earlier, electrons feel this electromagnetic force,
mediated by photons. This is stronger than the strong force. It binds and
forces electrons to orbit the nuclei and ties atoms and molecules. You
could say photons are the hardest-working bosons, working in stars, atoms,
molecules, space, and daily life objects. Every time charged particles
accelerate, a photon must be emitted; every time electrons change their
orbit, photons must be absorbed or released.
Note that you can't see all kinds of photons, since a photon is just a
quantum world entity with wave-particle duality, it also has frequencies,
wavelengths, and phase that you can find in a typical wave. You could only
see photons with wavelengths about 380-780 nm.
We've made a specific
article
about photons because they are the most important entities in astronomy,
subatomic studies and many other scientific and daily life fields.
W and Z boson:
If you've looked at our baryon-meson chart carefully, you might have noticed most of those entities were dying faster than a sandcastle. Let's consider the transformation and lifetime of subatomic particles, which is done via weak forces and their quanta W⁻, W⁺ and Z⁰ bosons. Weak forces are mainly destructive to particle assemblies; if they don't like a combination, they'll terminate. It feels comic, but it's true.
Only electrons and protons are stable and long-lived, while others are surprisingly unstable. Their instability comes from charges, mass or other quantum properties' imbalances, but there is no rule of thumb for how and when a particle decays.
One of the famous decays is beta decay, when a particle decays into another particle or species with the same mass and other properties, we call it beta decay. In about 15 minutes, A free neutron transforms into a proton, releasing an electron and an anti-neutrino. When a proton decays into a neutron, it releases a positron and a neutrino. As you can see, neutrinos only interact when a particle decays through weak interactions. It's a kind of adaptation to a more stable formation.
The W⁺ boson has a positive electric charge, whereas its antiparticle W⁻ has the same charge but negative. Z⁰ is the neutral weak boson. W bosons can change quark flavors like up to down, charm to strange, and so on. They connect charged leptons: electron, muon and tauon with their neutrinos. The W⁻ decays into an electron and an electron antineutrino because of their mass. W bosons are massive particles about 80 GeV/c², so they are unstable.
Z⁰ bosons connect leptons and their neutrinos. As a neutral particle, quarks can be scattered off, but it doesn't change their flavor or charge through Z⁰ exchange, transferring momentum only. With charged leptons, it causes neutrino and electron scattering but doesn't change their property. The Z⁰ is the only way that neutrinos interact. You can understand how difficult it is to detect neutrinos, since Z⁰ bosons are already neutral, our modern scientific studies are based on energy, charge, and changes of various properties; it can't easily detect such a neutral interaction.
At this point, we've seen the gauge bosons, which have spin one; now, let's move to the spin-zero or scalar boson, or the Higgs boson.
Higgs Boson:
As you know, these subatomic particles are supersmall, yet they have slight mass, but it's not the mass we experience or know. At the start of this post, we talked about resistance when particles accelerate. This tiny resistance is granted by the Higgs fields and their interaction; its quanta are called Higgs bosons. It's actually an omnipresent field that allows subatomic particles their mass or resistance. Higgs boson is too massive and very unstable, but its contribution to subatomic physics makes it an important thing.
It's also a mystery because, despite our universe being filled with those subatomic particles, the abundance of this boson is too low. This doesn't have any electric or color charge, and photons and gluons don't interact with it.
Conclusion:
Now you've the idea of all the fundamental particles and their basic features. The knowledge of photons and subatomic particles makes our universe's picture clearer and easier.
The current understanding of subatomic particles mainly focuses on lab and accelerator-based evidence while, so many entities aren't understood such as gravity and its hypothetical graviton, Dark matter and other interstellar reactions.
But don't be disappointed, we often avoid theories and focus on well-established points. So that's all for today's post. Notice that this is our last post based on quantum mechanics, it was too important to make you familiar with fundamental particles and their roles in our universe.
We'll meet you again in another fascinating post.
Have a Wonderful day.