update AGN, lepton sources, neutrinos

theory/energetic sources/AGNs.md

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 ## Active Galactic Nuclei (AGNs)
+
+### Introduction
+
+Active Galactic Nuclei or AGNs as they are known, are very powerful and bright galactic centers, powered by supermassive [black holes](../special%20stars/black%20holes.html). You can think of these black holes as cosmic vacuum cleaners of enormous size, pulling the surrounding gas and dust toward themselves.
+
+This material, as it approaches the black hole, begins to heat up due to friction and then radiates light, emitting energy across the whole spectrum-from radio waves to X-rays. This is the reason why AGNs are so bright; sometimes they outshine all the stars in their host galaxy put together. They are mostly situated at the center of the host galaxy.
+
+### Types of AGNs
+
+Varieties of [AGNs](#active-galactic-nuclei-agns) exist, and their appearance also depends on how we're looking at them. For example, quasars are AGNs that are extremely bright and can be seen from billions of light-years away. Not all AGNs are [quasars](../energetic%20sources/quasars.html). Some [quasars](../energetic%20sources/quasars.html) are so far away that the light we see today started its journey when the universe was still young.
+
+Seyfert galaxies are a kind of AGN, residing in spiral galaxies much like the Milky Way. But they are less powerful compared to quasars. [Blazars](../energetic%20sources/blazars.html) are [AGNs](#active-galactic-nuclei-agns) in which one of the two high-energy jets emanating from the [black hole](../special%20stars/black%20holes.html) happens to point directly toward Earth, which makes them exceptionally bright.
+
+### Structure of AGNs
+
+[AGNs](#active-galactic-nuclei-agns) generally have a supermassive [black hole](../special%20stars/black%20holes.html), at the core which usually hosts a mass ranging from millions to billions of times the mass of the Sun. Around the SMBH is an accretion disk, comprising gas and dust spiraling inward with the immense gravitational pull of the [black hole](../special%20stars/black%20holes.html).
+
+This material then heats up and accelerates in the accretion disk, generating massive quantities of radiation that can cover the entire electromagnetic spectrum, from radio waves to X-rays. Surrounding this accretion disk is a doughnut-shaped structure that absorbs and re-emits its energy in the infrared. Jets of relativistic particles can shoot out perpendicular to the disk and streak thousands of light-years across, emitting synchrotron radiation that is detected in radio and optical wavelengths.
+
+### How does AGNs affect the Galaxy
+
+These also play an important role in shaping galaxies. The energy and radiation from an AGN are able to push gas and dust out of a galaxy, either halting the birth of new stars or, in some cases, triggering star formation. This feedback loop is important, as it’s one of the ways that galaxies evolve over time.
+
+Additionally, they can heat up surrounding gas, creating what's known as "cooling flows." Instead of cooling and condensing into stars, the hot gas around the AGN remains too warm for [star formation](../stellar%20physics/evolution.html) to occur. This again limits the galaxy’s ability to form new stars.
+
+AGNs also play a crucial role in regulating the growth of supermassive [black holes](../special%20stars/black%20holes.html). As the [AGN](#active-galactic-nuclei-agns) feeds on surrounding matter, it sometimes ejects part of this matter outward, preventing excessive growth of both the black hole and the galaxy. This self-regulation helps keep the balance between [black hole](../special%20stars/black%20holes.html) growth and galaxy evolution.
+
+### Why are AGNs important?
+
+One of the exciting things about active galactic nuclei is that they let us glimpse far into the distant past. Light from far-away [AGNs](#active-galactic-nuclei-agns) takes billions of years to reach us, so when we observe it is as if we are seeing backward in time. By studying AGNs, we get a better understanding of what the universe was like when it was much younger. Indeed, some of the most-distant AGNs allow scientists to learn something about the early history of galaxy formation during the period after the Big Bang.
+
+![AGN](../../assets/images/theory/energetic%20sources/AGNs/AGNs.jpg)

theory/particle physics/lepton sources.md

@@ -7,3 +7,34 @@ nav_order: 2
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 ## Lepton Sources
+
+### What are Leptons?
+
+[Leptons](#lepton-sources) are elementary particles, the fundamental building blocks of the universe, alongside quarks. Unlike quarks, leptons don't form larger particles but exist independently, playing a key role in shaping the world around us. There are six types of leptons: three carry a negative charge (electron, muon, and tau), while the other three are neutral (the corresponding neutrinos). Electrons, the most familiar, are integral to the structure of atoms, while [neutrinos](../particle%20physics/neutrinos.html), though nearly invisible to us, flood through space and matter, interacting so rarely that billions pass through your body every second without a trace.
+
+### What are Lepton Sources?
+
+[Lepton sources](#lepton-sources) are regions in the universe or human-made facilities where these particles are created. Natural sources include stars, [supernovae](../energetic%20sources/supernovae.html), and [cosmic rays](../particle%20physics/cosmic%20rays.html) that bombard Earth from space. For instance, the Sun produces an incredible number of [neutrinos](../particle%20physics/neutrinos.html) as a byproduct of the nuclear fusion that powers it.
+
+{: .fun }
+> Do you know that particle accelerators like the Large Hadron Collider generate leptons by smashing particles together at nearly the speed of light, recreating conditions of the early universe!!
+
+### Different Kinds of Leptons
+
+There are six lepton types, but probably the most well-known are electrons and [neutrinos](../particle%20physics/neutrinos.html). Electrons are negatively charged and important in the making of atoms, composing all that surrounds us. [Neutrinos](../particle%20physics/neutrinos.html) are extremely elusive particles that seldom interact with the rest of the matter.
+
+Unlike quarks, leptons are unique in that they do not come together in order to make more massive particles. They come independently or within simple couples; that is, as a product of beta decay (a process within both stars and radioactive materials).
+
+![Leptons](../../assets/images/theory/particle%20physics/lepton%20sources/neutrinos/lepton.jpg)
+
+### How Are Leptons Produced?
+
+Leptons are produced in many high-energy processes. For example, electrons are produced whenever atoms are ionized. This is as common as in a normal lightning bolt, which actually involves very high-energy discharges. [Neutrinos](../particle%20physics/neutrinos.html) are produced in nuclear reactions, such as those taking place in the Sun.
+
+[Supernovae](../energetic%20sources/supernovae.html), or exploding stars, are also high-energy environments that produce leptons. Then there are the man-made sources for this subatomic particle: particle accelerators, such as the Large Hadron Collider, which can smash particles at near light speed into one another and create conditions similar to those of the early universe.
+
+### Why Are Sources of Leptons Important?
+
+[Lepton sources](#lepton-sources) have, therefore, facilitated the understanding by scientists of some of the most basic processes in the universe. For instance, neutrinos are thought to hold the key to certain key mysteries, such as why there is more matter than antimatter in the universe. The Standard Model, describing all known forces and particles and their interaction, also includes leptons in a very important position.
+
+As a matter of fact, it is the behavior of electrons (a type of lepton) which makes electronics, electricity, and even chemistry work. Life as we know it would not be possible without leptons.

theory/particle physics/neutrinos.md

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 ## Neutrinos
+
+### What are Neutrinos?
+
+[Neutrinos](#neutrinos) are ultrasmall, electrically neutral elementary particles. By being electrically neutral, neutrinos join the family of fundamental particles called [leptons](../particle%20physics/lepton%20sources.html), which include other members like electrons and muons. Neutrinos form that group of particles present in space in abundance but very hard to detect, since they interact very rarely with matter.
+
+### Properties of Neutrinos
+
+[Neutrinos](#neutrinos) come in three flavors or types: neutrino electron, neutrino muon, and neutrino tau. Each is associated with a charged lepton-electron, muon, and tau. Neutrinos have very negligible mass, probably zero mass. They also travel at almost the speed of light.
+
+The mass of the neutrino, as related to its energy, E, momentum, p, and speed, v, is given by the expression below:
+
+$$E^2 = (pc)^2 + (mc^2)^2$$
+
+where,
+
+$$E$$ = energy of the neutrino
+
+$$p$$ = momentum of the neutrino
+
+$$c$$ = the velocity of light
+
+$$m$$ = mass of the neutrino
+
+### How Do We Detect Neutrinos?
+
+By their very nature, [neutrinos](#neutrinos) can be detected only indirectly, by observing the particles they produce when interacting with matter. Really big neutrino detectors are constructed deep underground  to protect them from background radiation from [cosmic rays](../particle%20physics/cosmic%20rays.html). When a neutrino interacts with an atomic nucleus in the detector, it produces a secondary particle that may be observable.
+
+![Neutrino](../../assets/images/theory/particle%20physics/lepton%20sources/neutrinos/neutrinos.jpg)
+
+### What Do We Know About Neutrinos?
+
+These are always streaming through us from the Sun and from other parts of the universe and are similarly produced in nuclear reactions on Earth, for instance, those that happen in nuclear power plants. [Neutrinos](#neutrinos) can change their type while traveling in space-a phenomenon called neutrino oscillation-this means neutrinos have a small but nonzero mass.
+
+The neutrino oscillation probability between one type and another would have been given by the following formula:
+
+$$P(ν_α → ν_β) = sin^2(2θ) * sin^2(1.27 Δm^2 L / E)$$
+
+where,
+
+$$P(ν_α → ν_β)$$ is the probability of neutrino type α oscillating to β
+
+$$θ$$ is the mixing angle between the two neutrino flavours
+
+$$Δm^2$$ is the difference in squared masses of the two neutrino types
+
+$$L$$ = distance of neutrino travel
+
+$$E$$ = neutrino energy
+
+### Why Study Neutrinos?
+
+[Neutrinos](#neutrinos) play a major role in many astrophysical processes, including the [evolution of stars](../stellar%20physics/evolution.html) and [supernovae](../energetic%20sources/supernovae.html). The study of [neutrinos](#neutrinos) can help in understanding those processes and enlightening us further about the universe. Neutrinos could also hold the key to understanding [dark matter](../cosmology/dark%20matter.html) of which they are fundamental blocks, assumed to constitute the greater part of the matter in the universe.