Supernovae – Incredibly Powerful Explosions

First, an Overview^[1]

Supernovae are incredibly powerful and luminous explosions that occur when a star exhausts its nuclear fuel and collapses under its own gravitational force. The collapse triggers a massive explosion releasing enormous energy and sending shockwaves rippling through space.

Formation of a type La Supernova
Attribution: NASA, ESA and A. Feild (STScI); vectorisation by chris 論, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons
Pge URL: https://commons.wikimedia.org/wiki/File:Progenitor_IA_supernova.svg
This file is licensed under the Creative Commons Attribution 3.0 Unported license.

There are two main types of Supernovae: Type I and Type II:

Type I Supernovae occur when a white dwarf star in a binary system accumulates too much matter from its companion star and undergoes a runaway fusion reaction. The companion star must be a main-sequence or red giant star, which is transferring material to the white dwarf.
Type II Supernovae occur when a massive star (usually at least eight times the mass of the Sun) runs out of nuclear fuel and collapses under its own weight.

The study of Supernovae has led to many important discoveries, including the role of Supernovae in the synthesis of heavy elements, the connection between Supernovae and the formation of compact objects such as neutron stars and black holes, and the use of Type Ia Supernovae as standard candles^[2] for cosmological studies.

The Emergence of Supernovae
Supernovae can occur in various ways, but they are typically classified into two main types: Type I and Type II, as outlined above. The first recorded observation of a Supernova dates back to 185 AD when Chinese astronomers reported seeing a guest star^[3] visible during the day and persisting for several months. This Supernova is now known as SN 185 and is thought to have been a Type Ia Supernova^[4]. You might wonder how the observation could have occurred before modern telescopes were available: the simple explanation is that the Chinese likely observed the star’s brightening with their naked eyes and could track its movement across the sky.

Over the centuries, astronomers have observed and studied many other Supernovae. These events have played an important role in understanding the universe, providing valuable information about the composition, structure, and evolution of stars. Today, Supernovae continue to be a subject of intense scientific interest and research, as they provide important insights into the fundamental nature of the universe and the processes that drive its evolution.

Occurrence
A Supernova occurs during the last evolutionary stages of a massive star or when a white dwarf is triggered into runaway nuclear fusion. The original object, called the progenitor, either collapses into a neutron star or black hole or is completely destroyed to form a diffuse nebula. The peak optical luminosity of a Supernova can be comparable to that of an entire galaxy before fading over several weeks or months.

The last Supernova directly observed in the Milky Way was Kepler’s Supernova in 1604, appearing not long after Tycho’s Supernova in 1572. Both were visible to the naked eye. The remnants of more recent Supernovae have been found, and observations of supernovae in other galaxies suggest they occur in the Milky Way on average about two or three times every century or perhaps once in a lifetime. A Supernova in the Milky Way would almost certainly be observable through modern astronomical telescopes. The most recent naked-eye viewing of a Supernova was SN 1987A, which was the explosion of a blue supergiant star in the Large Magellanic Cloud, a satellite of the Milky Way.

Theoretical studies indicate that most supernovae are triggered by one of two basic mechanisms: the sudden re-ignition of nuclear fusion in a white dwarf or the sudden gravitational collapse of a massive star’s core.

Glossary
Recognising that some of the words and terms used in this paper may be unfamiliar, I hope the following glossary helps (it’s in alphabetical order):

Adaptive optics: Adaptive optics is a technique used in astronomy to correct for distortions caused by the Earth’s atmosphere. By measuring the distortions in real-time and adjusting the shape of a telescope’s mirrors, astronomers can obtain much clearer images of distant objects.
[A] Binary System: This is a pair of stars that orbit around a common centre of mass. Binary systems can comprise two stars of similar mass or a larger star and a smaller companion star. Binary systems are often studied to measure the masses of stars, as the properties of the system can be used to calculate the masses of both stars.
[A] Companion Star: This is a star that is part of a binary system and orbits around another star. It can influence the evolution of the other star by transferring mass or interacting gravitationally. (See further explanation below).
Cosmic Rays: These are tiny particles, mostly protons and atomic nuclei, that travel at very high speeds through space. They originate from various sources, such as exploding stars, black holes, and other cosmic phenomena. When they hit the Earth’s atmosphere, they can create a cascade of secondary particles, which can be detected by scientific instruments on the ground. Cosmic rays can provide scientists with important information about the universe, such as the properties of distant objects and the nature of high-energy phenomena. (See further explanation below).
[The] Crab Nebula is a cloud of gas and dust in space formed after a Supernova explosion. It is located in the constellation Taurus and is one of the most studied objects in the sky. (See further description below).
Diffuse Nebula: A diffuse nebula is a type of interstellar cloud composed of dust, gas, and plasma. These clouds are typically large and spread out over a relatively large area, hence the name “diffuse”. They are often illuminated by nearby stars, causing them to glow and exhibit various colours, such as pink, red, or blue. Diffuse nebulae are often the sites of active star formation, with the gas and dust within the cloud collapsing to form new stars. Some well-known examples of diffuse nebulae include the Orion Nebula, the Carina Nebula, and the North America Nebula.
Gamma-Ray Bursts (GRBs): These are incredibly energetic explosions that occur in distant galaxies. They release an intense burst of gamma-ray radiation – the highest energy form of electromagnetic radiation. GRBs are so powerful that they can outshine an entire galaxy for a brief moment. Scientists believe that GRBs are caused by massive stars collapsing or by the merging of two neutron stars. (See further explanation below).
Gravitational Waves: Gravitational waves are ripples in spacetime that are produced when massive objects, such as black holes or neutron stars, accelerate. They were first predicted by Einstein’s theory of general relativity but were only detected for the first time in 2015 by the Laser Interferometer Gravitational-Wave Observatory (LIGO). Gravitational waves provide a new way to study the universe, allowing astronomers to observe phenomena that cannot be seen with traditional telescopes.
Hertzsprung-Russell (HR) Diagram: The HR chart shows where different types of stars are located based on how hot they are and also how bright they appear from Earth. This chart helps astronomers understand how stars evolve over time and how they relate to each other. Most stars, including our Sun, are located on a diagonal line called the main sequence. As stars get older, they move away from the main sequence and become red giants or supergiants. White dwarfs are old stars that are very small and dim. The HR diagram is an important tool that helps astronomers study stars and their lifecycles. (See further explanation below).
The Large Magellanic Cloud (LMC) is a dwarf galaxy located about 160,000 light-years away from Earth in the constellation Dorado. It is one of the closest galaxies to our Milky Way and is named after the Portuguese explorer Ferdinand Magellan, who observed the galaxy during his circumnavigation of the Earth in the 16^th century. The LMC is about 14,000 light-years in diameter and contains several hundred million stars. It is classified as an irregular galaxy due to its shape, distorted by gravitational interactions with its neighbour, the Small Magellanic Cloud, and the Milky Way itself. The LMC is also an active site of star formation, with many young and hot stars present in its dense gas clouds.
Luminosity refers to the total amount of energy emitted by an object, such as a star, per unit of time. It is a measure of an object’s intrinsic brightness and is often expressed in units of watts or solar luminosities. Luminosity takes into account all of the wavelengths of electromagnetic radiation emitted by the object, from radio waves to gamma rays. It is an important quantity in astronomy, as it allows astronomers to compare the brightnesses of different stars and to study the evolution of stars and galaxies.
[A] Main-Sequence Star: This star fuses hydrogen atoms into helium atoms in its core, producing energy that makes it shine. It is the phase where most stars spend most of their lives. The term “main sequence” refers to the fact that these stars follow a particular track on the Hertzsprung-Russell diagram, a graph that plots a star’s luminosity (brightness) against its temperature.
Neutron stars: Neutron stars are the extremely dense remnants of massive stars that have undergone a Supernova explosion. They are composed almost entirely of neutrons and have a mass that is typically about 1.4 times that of the Sun but compressed into a radius of only about 10 kilometres. Neutron stars are incredibly dense, with a teaspoon of neutron star material having a mass of around 6 billion tons.
Nuclear fuel: refers to the elements used in nuclear fusion reactions in stars, such as hydrogen, helium, and heavier elements. When a star exhausts its nuclear fuel, it can no longer produce energy through fusion and begins to collapse under its own weight.
Progenitor: a progenitor star is the star that exists before it undergoes a Supernova explosion. (See further explanation below).
Pulsar astronomy: this is the study of pulsars, including their properties, behaviour, and distribution. Pulsars are used as tools for various astrophysical studies, including tests of theories of gravity, studies of the interstellar medium, and searches for gravitational waves.
Pulsars: Pulsars are highly magnetised, rotating neutron stars emitting electromagnetic radiation beams. They were first discovered in 1967 by Jocelyn Bell Burnell and Antony Hewish. Pulsars are among the most precise natural timekeepers known, and their regularity has made them useful for various astronomical studies.
[A] Red Giant: This star has exhausted the hydrogen in its core and begun fusing helium into heavier elements. It causes the star to expand and cool, turning it into a red giant. Red giants are much larger and brighter than main-sequence stars of the same mass, and they have a characteristic reddish-orange colour due to their cooler surface temperatures. Eventually, red giants will exhaust their helium fuel and undergo further changes, leading to their eventual death as a white dwarf, neutron star, or black hole, depending on their mass.
Runaway Fusion Reaction: this refers to a situation where nuclear fusion in a star’s core begins to occur at an increasingly rapid rate, leading to a catastrophic explosion.
[The] Spectra of a Supernova refers to the pattern of light emitted by the Supernova at different wavelengths. When astronomers observe the light from a Supernova, they can break it down into its component colours using a device called a spectrograph. This produces a spectrum which looks like a rainbow of colours with dark lines running through it. The dark lines in the spectrum correspond to the absorption of specific wavelengths of light by atoms and molecules in the Supernova’s outer layers.By analysing the pattern of these lines, astronomers can identify the chemical composition of the Supernova and learn about the processes that are causing it to shine.

Standard Candles: Standard candles are objects with a known intrinsic brightness that can be used to determine distances to other objects. Type Ia Supernovae are often used as standard candles because they have a consistent intrinsic brightness and are visible across vast distances.
Supergiants: These are just very big stars. They are much larger than normal stars like the Sun and can be thousands or even millions of times brighter. They are also much less common than smaller stars and tend to be quite rare and short-lived. (See further explanation below).
Supernova: A Supernova is a powerful and luminous stellar explosion that occurs when a star reaches the end of its life. A massive amount of energy is released during a supernova, creating a bright flash of light that can outshine an entire galaxy. Supernovae are important cosmic events that can provide valuable insights into the nature of the universe.
Time Domain Surveys: Time domain surveys are astronomical surveys that focus on changes in the brightness or position of objects over time. These surveys are useful for studying variable or transient phenomena, such as Supernovae, gamma-ray bursts, and asteroids.
[A] White Dwarf Star is a very dense, compact star that has exhausted all of its nuclear fuel and no longer produces energy through fusion. It is the leftover core of a star that has gone through its life cycle and shed its outer layers.

Companion Stars
A companion star is a star that is in a binary system with another star. In other words, it is a star that is gravitationally bound to another star, and both orbit around a common centre of mass. The two stars in a binary system can have different masses, sizes, and ages. They can also have different evolutionary stages, such as one being a main-sequence star and the other a red giant. The companion star can play an important role in the evolution of its partner, as it can transfer mass or influence its orbit.

Here are a few more characteristics of companion stars:

Mass transfer: In some cases, the companion star can transfer mass to the primary star, affecting its evolution and potentially triggering phenomena like Supernovae.
Binary systems: Companion stars are most commonly found in binary star systems, where two stars orbit each other and can influence each other’s evolution.
Classification: Companion stars can be classified based on their spectral type (e.g. O-type, B-type, etc.) and their distance from the primary star.
Observational importance: The presence of a companion star can affect the observable properties of a primary star, such as its brightness and spectral features. Studying these effects can provide important information about the system’s properties and evolution.

Cosmic Rays
Cosmic rays are high-energy particles that originate from outside our solar system and travel through space at nearly the speed of light. They can come from various sources, including Supernovae, gamma-ray bursts, and even distant galaxies.

Cosmic rays are high-energy particles, mainly protons and atomic nuclei, originating outside the Earth’s atmosphere. These particles can have energies many times greater than those produced by particle accelerators on Earth, making them of great interest to scientists studying the nature of the universe. They are believed to come from various sources in the universe, such as Supernovae, black holes, and other high-energy events.

When cosmic rays enter the Earth’s atmosphere, they collide with atoms and molecules in the air, creating cascades of secondary particles that can be detected by instruments on the ground. Cosmic rays can be harmful to living organisms at high intensities, so scientists study them to understand better their origins and how they interact with the Earth’s atmosphere and magnetic field.

Cosmic rays also have practical applications, such as in medical imaging and cancer treatment, as well as in the development of new technologies for space exploration.

Crab Nebula
The Crab Nebula is a Supernova remnant and pulsar wind nebula in the constellation Taurus. It results from a Supernova explosion observed by Chinese and Japanese astronomers in 1054. The explosion was so bright that it was visible in daylight for several weeks, and it left behind a rapidly expanding cloud of gas and dust.

This is a mosaic image, one of the largest ever taken by NASA’s Hubble Space Telescope, of the Crab Nebula, a six-light-year-wide expanding remnant of a star’s supernova explosion.
Attribution: NASA, ESA, J. Hester and A. Loll (Arizona State University), Public domain, via Wikimedia Commons
Page URL: https://commons.wikimedia.org/wiki/File:Crab_Nebula.jpg

The Crab Nebula is located about 6,500 light-years from Earth and has a diameter of about ten light-years. It is one of the most studied objects in the sky, and its radiation has been observed across the electromagnetic spectrum, from radio waves to gamma rays.

At the heart of the Crab Nebula is a rapidly spinning neutron star known as the Crab Pulsar. The Pulsar is the star’s collapsed core that exploded in the Supernova, and it rotates about 30 times per second, emitting a beam of radiation that sweeps across the sky like a lighthouse. This radiation powers the emission from the surrounding nebula and produces the characteristic synchrotron radiation observed in the Crab Nebula. It is an important object for astronomers because it allows them to study the physics of supernova explosions and the formation of neutron stars. It is also an important calibration source for many astronomical instruments, and its radiation has been used to test the limits of our understanding of the laws of physics.

Gamma-Ray Bursts
Gamma-ray bursts (GRBs) are highly energetic explosions that happen in space, releasing enormous amounts of gamma-ray radiation. They are the brightest and most energetic electromagnetic events known in the universe.

GRBs are typically classified into two types based on their duration. Short gamma-ray bursts (SGRBs) last less than two seconds, while long gamma-ray bursts (LGRBs) can last up to several minutes.

LGRBs are thought to be associated with the collapse of massive stars and the formation of black holes. When a massive star runs out of fuel, it can no longer support its own weight, and its core collapses, triggering a Supernova explosion. If the core collapse is rapid and symmetric, it can lead to the formation of a black hole, which then emits a burst of gamma rays. SGRBs, on the other hand, are thought to be produced by the merger of two neutron stars or a neutron star and a black hole. During the merger, a burst of gamma rays is emitted, along with other forms of radiation such as X-rays and radio waves.

GRBs are detected by specialised instruments called gamma-ray telescopes, which are located both on Earth and in space. The most famous space-based gamma-ray telescope is NASA’s Fermi Gamma-ray Space Telescope, which has been detecting and studying GRBs since its launch in 2008.

Hertzsprung-Russell (HR) Diagram
The Hertzsprung-Russell (HR) diagram is a graphical representation of stars based on two parameters: (1) their luminosity (brightness) and (2) their surface temperature. The diagram is named after the Danish astronomer Ejnar Hertzsprung and the American astronomer Henry Norris Russell, who independently created it in the early 20^th century.

The HR diagram allows astronomers to classify stars based on their evolutionary stage by plotting them according to their temperature and luminosity. The diagram shows a clear pattern of stars, with most of them lying along a diagonal band called the main sequence. This is where stars, including our Sun, spend most of their lifetime fusing hydrogen into helium in their cores.

As stars evolve and their cores run out of hydrogen, they start to expand and cool down, eventually becoming red giants or supergiants. These evolved stars occupy different regions of the HR diagram, with red giants located above and to the right of the main sequence and supergiants located at the top of the diagram.

The HR diagram also reveals other interesting features, such as white dwarfs, which are small and extremely dense objects that are the remnants of low-mass stars that have exhausted their fuel. These objects lie in the bottom left of the diagram and are characterised by low luminosity and high temperature.

Overall, the HR diagram is a powerful tool for understanding stellar evolution, as it provides a way to visualise and categorise stars based on their observed properties.

Progenitor Stars
A progenitor star is a star that existed before a particular astronomical event, such as a Supernova or gamma-ray burst, which is believed to have given rise to that event. In the case of a supernova, the progenitor star is the star that runs out of nuclear fuel and undergoes a catastrophic explosion. The nature of the progenitor star can provide clues to the properties and behaviour of the Supernova that it produces. For example, the progenitor star of a Type II Supernova is a massive star that has exhausted its nuclear fuel and collapsed under its own gravity, whereas the progenitor star of a Type Ia Supernova is a white dwarf that has accreted material from a companion star until it reaches a critical mass and undergoes a thermonuclear explosion.

The study of progenitor stars is an important area of research in astrophysics, as it can shed light on the physical processes that lead to the formation and evolution of stars and the properties of the Supernovae that they produce.

Supergiants
Supergiants are massive stars that are much larger and brighter than main-sequence stars of the same spectral type. They have radii that are tens to hundreds of times larger than that of the Sun and luminosities that are hundreds of thousands to millions of times greater.

Supergiants are classified into two types: red and blue, based on their surface temperature:

Red supergiants have surface temperatures of about 3,500 to 4,500 Kelvin and are typically late spectral type M, K or G.
Blue supergiants have surface temperatures of about 10,000 to 50,000 Kelvin and are typically spectral type B or A.

Supergiants are very rare and have short lifetimes, as they consume their nuclear fuel much faster than smaller stars. Some of the most famous supergiants include Betelgeuse and Rigel.

Supernova Explained
The term Supernova was first used in 1934 by the astronomers Wilhelm Heinrich Walter Baade and Fritz Zwicky. Adam S. Burrows, of the Department of Astrophysical Sciences, Princeton University, New Jersey, introduced them in his excellent paper^[5] “Baade and Zwicky: ‘Supernovae,’ neutron stars, and cosmic rays“:
“In 1934, two astronomers in two of the most prescient papers in the astronomical literature coined the term “supernova,” hypothesized the existence of neutron stars, and knit them together with the origin of cosmic rays to inaugurate one of the most surprising syntheses in the annals of science.”

The word nova originally referred to a new star that appeared in the sky, but when astronomers realised that these objects were explosions, they began referring to them as Supernovae, with the -ae ending indicating it was a plural form.

There are two main types of Supernovae: Type Ia, which occur in binary systems when a white dwarf accretes matter from a companion star and explodes, and Type II, which occur when a massive star exhausts its nuclear fuel and undergoes a core collapse.

The two types of Supernovae were first identified by the German-American astronomer Rudolf (or Rudolph) Minkowski in 1941. He noticed that the spectra of different Supernovae showed different features, indicating that they might be caused by different processes. This thinking led to the classification of Supernovae into Type I and Type II based on their spectra, with further subtypes based on their light curves and other characteristics.

The first observed Supernova, which has since been referred to as SN 185, was named based on the year in which it was observed by Chinese astronomers. They recorded the event as a guest star that suddenly appeared in the sky and remained visible for several months. The Supernova was not identified until much later when astronomers analysed ancient records and compared them with modern observations. SN 185 was a transient astronomical event observed in 185 AD. The transient occurred in the direction of Alpha Centauri, between the constellations Circinus and Centaurus, centred at RA 14^h 43^m Dec −62° 30′, in Circinus.

This “guest star” was observed by Chinese astronomers in the Book of Later Han (后汉书)^[6] and might have been recorded in Roman literature.^[7] It remained visible in the night sky for eight months and is believed to be the first Supernova for which records exist. The Book of Later Han gives the following description:
“In the 2^nd year of the epoch Zhongping [中平], the 10^th month, on the day Guihai [癸亥] [December 7, Year 185], a ‘guest star‘ appeared in the middle of the Southern Gate [南門] [an asterism consisting of ε Centauri and α Centauri], The size was half a bamboo mat. It displayed various colours, both pleasing and otherwise.^[8] It gradually lessened. In the 6^th month of the succeeding year, it disappeared.^”^[9]

Type I and Type II Supernovae have different spectra because different physical processes cause them. Type I Supernovae are thought to be caused by the explosion of a white dwarf star in a binary system, and they typically have a spectrum that lacks hydrogen and shows strong lines of silicon and other elements. Type II Supernovae, on the other hand, are caused by the collapse of a massive star and typically show strong lines of hydrogen and other elements in their spectra. By studying these differences in spectra, astronomers can classify Supernovae into different types and learn more about their properties and behaviour.

Timeline of Key Observations of Supernovae in History

185 AD: Chinese astronomers observed SN 185, the first recorded observation of a Supernova.
1006 AD: Chinese, Japanese, and Korean astronomers observed SN 1006, one of the brightest Supernovae in history.
1572: Tycho Brahe observed a Supernova in the constellation Cassiopeia, which is now known as SN 1572 or Tycho’s Supernova.
1604: Johannes Kepler observed a Supernova in the constellation Ophiuchus, which is now known as Kepler’s Supernova or SN 1604.
1917: Ejnar Hertzsprung observed a Supernova in the Andromeda galaxy, the first extragalactic Supernova to be observed.
1967: Jocelyn Bell and Antony Hewish discover the first Pulsar, a type of rapidly rotating neutron star that is formed in the aftermath of a Supernova.
1987: The Supernova SN 1987A is observed in the Large Magellanic Cloud, the first Supernova to be detected by neutrino detectors.
1998: Two teams of astronomers discovered that the expansion of the universe is accelerating, a discovery that is attributed to the existence of dark energy and is based in part on observations of Type Ia Supernovae.
2011: The Supernova SN 2011fe is observed in the galaxy M101, providing new insights into the nature of Type Ia Supernovae and their use as standard candles in cosmology.

The discovery of Pulsars and the Development of New Observational Tools and Techniques
Since the discovery of pulsars and the development of new observational tools and techniques, astronomers have made many discoveries about the nature, behaviour, and evolution of Supernovae.

The Major Breakthrough
The discovery of Pulsars in the aftermath of Supernovae was a major breakthrough in our understanding of the universe. In 1967, Jocelyn Bell and Antony Hewish detected a regular, repeating pattern of radio waves coming from a source in the sky, which they dubbed LGM-1 (short for Little Green Men-1). They soon realised that the source was a rapidly rotating neutron star formed in the aftermath of a Supernova explosion. The intense magnetic field of the neutron star produced beams of radiation that swept across the sky like a lighthouse beam, causing the observed pattern of radio waves. This discovery opened up a new field of astronomy, known as pulsar astronomy, and paved the way for further discoveries about the nature and behaviour of these exotic objects.^[10]

Some of the key findings that have been made about Supernovae since the discovery of pulsars and the development of new observational tools and techniques are:

The existence of Type Ia Supernovae as standard candles: Type Ia Supernovae are particularly useful for cosmological studies because they have a predictable luminosity and can be used as standard candles to measure distances to other galaxies. This discovery has led to significant advances in our understanding of the large-scale structure and evolution of the universe.
The connection between Supernovae and neutron stars: Observations of Supernovae and their remnants have provided important insights into the formation of neutron stars and other exotic objects. For example, the discovery of pulsars as rapidly rotating neutron stars was made possible through observations of Supernova remnants.
The role of Supernovae in the synthesis of heavy elements: Supernovae are thought to be responsible for the synthesis of many of the heavy elements in the universe, such as gold, platinum, and uranium. By studying the chemical composition of Supernova remnants and the ejecta from Supernovae, astronomers have learned more about the processes that create these elements.
The diversity of Supernova explosions: Observations of Supernovae in different galaxies and under different conditions have revealed a wide variety of Supernova explosions, including subtypes of Type I and Type II Supernovae. These discoveries have provided new insights into the physics of Supernova explosions and the factors that influence their behaviour.
The role of Supernovae in galactic evolution: Observations of Supernovae and their remnants have shown that they play an important role in shaping the structure and evolution of galaxies. For example, Supernova explosions can trigger the formation of new stars and contribute to the chemical enrichment of the interstellar medium.
The diversity of Supernova explosions, including Type I and Type II Supernovae subtypes, and the factors that influence their behaviour, such as the mass and composition of the progenitor star and the environment in which the explosion occurs.
The role of Supernovae in the synthesis of heavy elements and the contribution of Supernovae to the chemical enrichment of the interstellar medium.
The connection between Supernovae and the formation of compact objects such as neutron stars and black holes.
The use of Type Ia Supernovae as standard candles for cosmological studies has led to significant advances in our understanding of the large-scale structure and evolution of the universe.
The discovery of Supernova remnants and their use as probes of the interstellar medium and the physics of Supernova explosions.
The detection of Supernova neutrinos has provided valuable information about the core collapse and explosion process.
The role of Supernovae in triggering the formation of new stars and shaping the structure and evolution of galaxies.
The study of the properties of Supernova shockwaves and their interaction with the surrounding medium.
The development of new observational techniques, such as time-domain surveys and adaptive optics imaging, allowing for more detailed and comprehensive studies of Supernovae.
The discovery of unusual Supernovae, such as Super-luminous Supernovae and pair-instability Supernovae, which challenge existing models of Supernova physics and offer new insights into the evolution of massive stars.

The Discovery of Gravitational Waves
The discovery of gravitational waves has opened up a new window for studying the universe, and it has also provided valuable insights into the behaviour of matter under extreme conditions – this is particularly relevant to the study of Supernovae, which involve the collapse of massive stars under their own gravity. In 2017, the detection of gravitational waves from the merger of two neutron stars provided new information about the behaviour of matter at extremely high densities and temperatures. This information can help astronomers better understand Supernovae’s core collapse and explosion process, which is still poorly understood. By combining observations of gravitational waves with other types of observations, such as electromagnetic radiation and neutrinos^[11], astronomers can better understand the complex processes involved in Supernova explosions.

The list above provides a few examples of the many discoveries made about Supernovae in recent decades. With the development of new observational tools and techniques, astronomers will likely continue making important discoveries about these powerful and fascinating objects in the future.

Observing and Studying Supernovae
Both ground-based and space-based telescopes can be used to observe and study Supernovae.

Hubble being deployed from Discovery in 1990
Attribution: NASA/IMAX, Public domain, via Wikimedia Commons
Page URL: https://commons.wikimedia.org/wiki/File:1990_s31_IMAX_view_of_HST_release.jpg

Ground-based telescopes typically have larger apertures, which allow for higher resolution and more detailed observations, but they are limited by atmospheric distortion and light pollution.

Space-based telescopes, on the other hand, are not affected by atmospheric distortion or light pollution and can observe at a wider range of wavelengths, but they have smaller apertures and are more expensive to operate.

To observe a Supernova, astronomers typically use optical telescopes that can detect visible light and other wavelengths, such as radio, X-ray, and gamma-ray telescopes. They also use time-domain surveys, which take repeated observations of the same region of the sky over time to detect any changes or transient events, such as Supernovae. Adaptive optics, which correct for atmospheric distortion in real-time, can also be used to obtain higher-resolution observations of Supernovae.

Concluding Words and Recap
Supernovae are among the most powerful and explosive events in the universe, releasing enormous amounts of energy and sending shockwaves rippling through space. The study of Supernovae has led to many important discoveries about the universe, including the role of Supernovae in the synthesis of heavy elements, the connection between Supernovae and the formation of compact objects, and the use of Type Ia Supernovae as standard candles for cosmological studies. Many key astronomers, including Tycho Brahe, Johannes Kepler, Ejnar Hertzsprung, and Jocelyn Bell, have contributed to our understanding of Supernovae throughout history.

The study of Supernovae has led to many important discoveries, including the use of Type Ia Supernovae as standard candles for cosmological studies. Type Ia Supernovae are particularly useful because they have a predictable luminosity, allowing astronomers to use them to measure distances to other galaxies. This discovery has led to significant advances in our understanding of the large-scale structure and evolution of the universe. Another important discovery made through the study of Supernovae is the detection of Supernova neutrinos. Neutrinos are subatomic particles that are produced in the core of a Supernova when it collapses. By detecting these particles, astronomers can learn more about the core collapse and explosion process, providing valuable insights into the physics of Supernovae.

Supernovae can expel several solar masses of material at velocities up to several per cent of the speed of light, driving an expanding shock wave into the surrounding interstellar medium, sweeping up an expanding shell of gas and dust observed as a Supernova remnant. Supernovae are incredibly powerful and explosive events that occur when certain types of stars run out of fuel and collapse in on themselves. During this process, the star’s core becomes incredibly dense and hot, causing it to explode and release an enormous amount of energy and matter into space. This matter includes heavy elements formed in the star’s core during fusion. These heavy elements, which include oxygen, carbon, nitrogen, iron, rubidium and many others, are then scattered into the interstellar medium, which is the material that fills the space between stars. This material can eventually be incorporated into new stars, planets, and other objects in the universe.

Supernovae are a major source of heavy elements in the universe, and without them, the elements that make up life as we know it would not exist. The expanding shock waves of Supernovae can trigger the formation of new stars and are a major source of cosmic rays. They might also produce gravitational waves, though thus far, they have been detected only from the mergers of black holes and neutron stars.

“Finding an Elusive Star Behind a Supernova” by NASA’s Marshall Space Flight Center is licensed under CC BY-NC 2.0.

Sources and Further Reading

Books:

Supernovae: A Survey of Current Research by Alexei V. Filippenko and Dina Prialnik, published by Springer in 2017. Available for purchase on Amazon: https://www.amazon.com/Supernovae-Survey-Current-Alexei-Filippenko/dp/3319482548
Supernovae and Nucleosynthesis: An Investigation of the History of Matter from the Big Bang to the Present by David Arnett, published by Princeton University Press in 1996. Available for purchase on Amazon: https://www.amazon.com/Supernovae-Nucleosynthesis-Investigation-History-Present/dp/0691026169
The Life Cycles of Stars: From Birth to Death by Judi Kesselman-Turkel and Franklynn Peterson, published by the University of Wisconsin Press in 2005. Available for purchase on Amazon: https://www.amazon.com/Life-Cycles-Stars-Birth-Death/dp/0299213408
Supernovae: The Death of Stars by Donald D. Clayton, published by Springer in 2017. Available for purchase on Amazon: https://www.amazon.com/Supernovae-Death-Donald-D-Clayton/dp/3319502300
The Supernova Story by Laurence A. Marschall, published by Princeton University Press in 2017. Available for purchase on Amazon: https://www.amazon.com/Supernova-Story-Laurence-Marschall/dp/069117863X
Supernovae: The Explosive End of Massive Stars by R. G. McMahon, published by Springer in 2017. Available for purchase on Amazon: https://www.amazon.com/Supernovae-Explosive-Massive-Astronomy-Astrophysics/dp/3319492071
Supernovae: A Survey of Current Research by Alexei V. Filippenko (Author), B. Leibundgut (Author), Springer; 1995.
The Supernova Story by Laurence A. Marschall (Author), HarperCollins Publishers Ltd; 2003.
Supernovae and Nucleosynthesis: An Investigation of the History of Matter, from the Big Bang to the Present by David Arnett (Author), Princeton University Press; 1996.
Supernovae and Supernova Remnants: Proceedings of the International Conference by Richard A. McCray (Editor), Zdenek Stenholm (Editor), Cambridge University Press; 1991.
The Light of Supernova 1987A by Roger A. Chevalier (Author), Cambridge University Press; 1996.
Exploding Stars and Galaxies by Bruno Leibundgut (Editor), International Astronomical Union. Symposium (Editor), Springer; 2011.

YouTube Videos:

Supernovae: Explosions in Space by NASA Goddard Space Flight Center: https://www.youtube.com/watch?v=Kj447gPfhWc
What Causes a Supernova? by Seeker: https://www.youtube.com/watch?v=u5CJb5zzn8Y
The Life Cycle of a Supernova by Kurzgesagt – In a Nutshell: https://www.youtube.com/watch?v=tlTKTTt47WE
What Happens When a Supernova Explodes? by Space.com: https://www.youtube.com/watch?v=OyX1vHVP7p8
Supernovae: When Stars Die by CrashCourse Astronomy: https://www.youtube.com/watch?v=IKBb1PPniJc
The Mystery of Supernovae by The Royal Institution: https://www.youtube.com/watch?v=EDN-50FjWTc
The Science of Supernovae by Deep Astronomy: https://www.youtube.com/watch?v=htQZWOSM5_8
Supernovae: The Explosive End of a Star by National Geographic: https://www.youtube.com/watch?v=K5l_3Y1rMH0
The Biggest Explosion in the Universe – Supernova by BBC Earth: https://www.youtube.com/watch?v=cFbW1IOzuqI
The Anatomy of a Supernova by Science Channel: https://www.youtube.com/watch?v=0_tQsWq3xfg
Supernovae: The Power of a Star’s Death by Smithsonian Channel: https://www.youtube.com/watch?v=2jKusFwRiRQ
What If a Supernova Hit the Earth? by Kurzgesagt – In a Nutshell: https://www.youtube.com/watch?v=3bv-sD5B5z0

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End Notes and Explanations

Source: Compiled from research using information at the sources stated throughout the text, together with information provided by machine-generated artificial intelligence at: bing.com [chat] and https://chat.openai.com ↑
Explanation: In astronomy, the term “standard candle” refers to an astronomical object or phenomenon that has a known, fixed luminosity or brightness. Because the intrinsic brightness of a standard candle is known, astronomers can use it as a reference to measure the distances to other objects in space.
For example, Type Ia supernovae are often used as standard candles in cosmology because they have a predictable luminosity. By observing the apparent brightness of a Type Ia supernova in a distant galaxy and comparing it to its known intrinsic brightness, astronomers can calculate the distance to that galaxy. Other examples of standard candles include Cepheid variable stars and certain types of galaxies with a known luminosity. ↑
Explanation: In ancient times, a “guest star” was a term used to describe a new star that appeared in the sky, particularly one that was not seen before. This was before the invention of telescopes and modern astronomy, and it was not yet understood that these objects were actually exploding stars, now known as supernovae. Today, the term “guest star” is still occasionally used to refer to supernovae that are discovered by amateur astronomers or other non-professionals. ↑
Explanation: A Type Ia Supernova is a subcategory of Type I supernovae, which occur in binary star systems where a white dwarf star accretes (accumulates) matter from a companion star until it reaches a critical mass, causing a runaway fusion reaction that triggers an explosion. Type Ia Supernovae are particularly useful for cosmological studies because they have a predictable luminosity and can be used as “standard candles” to measure distances to other galaxies. This means that by studying the brightness of a Type Ia Supernova, astronomers can determine its distance from Earth and use this information to calculate the distance to the galaxy in which it occurred. ↑
Source: Adam S. Burrows’ paper “Baade and Zwicky: ‘Super-novae,’ neutron stars, and cosmic rays”, at: https://www.astro.princeton.edu/~burrows/papers/pnas201422666_7rt2gl.pdf. see also: Baade W, Zwicky F (1934) On super-novae. Proceedings of the National Academy of Science USA 20(5):254–259, and Baade W, Zwicky F (1934) Cosmic rays from super-novae. Proceedings of the National Academy of Science USA 20(5):259–263. ↑
Source: Zhao FY; Strom RG; Jiang SY (2006). “The Guest Star of AD185 Must Have Been a Supernova”. Chinese Journal of Astronomy and Astrophysics. 6 (5): 635–40. Bibcode:2006ChJAA…6..635Z. doi:10.1088/1009-9271/6/5/17. Cited at: https://en.wikipedia.org/wiki/SN_185 ↑
Source: Stothers, Richard (1977). “Is the Supernova of A.D. 185 Recorded in Ancient Roman Literature?”. Isis. 68 (3): 443–447. doi:10.1086/351822. JSTOR 231322. S2CID 145250371. Cited at: https://en.wikipedia.org/wiki/SN_185 ↑
Source: Ye, Fan. Book of the Later Han http://chinesenotes.com/houhanshu/houhanshu113.html Cited at: https://en.wikipedia.org/wiki/SN_185 ↑
Source: In Chinese. Cited as Reference 5, at: https://en.wikipedia.org/wiki/SN_185 ↑
Source: Original scientific paper published in Nature in February 1968, titled “Observation of a Rapidly Pulsating Radio Source.” PDF at: https://www.researchgate.net/profile/P-Scott/publication/32005350_Observation_of_a_Rapidly_Pulsating_Radio_Source/links/0deec51a72db0aaca3000000/Observation-of-a-Rapidly-Pulsating-Radio-Source.pdf ↑
Explanation: A Neutrino is a tiny subatomic particle that has almost no mass and no electric charge. It is one of the most abundant particles in the universe and is produced in many natural processes, including nuclear reactions in stars and the decay of radioactive isotopes. Neutrinos are very difficult to detect because they rarely interact with matter, passing through most materials, including the Earth, with very little effect. However, they are important to study because they can provide information about the processes that create them and about the fundamental properties of matter and energy in the universe. ↑

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Supernovae – Incredibly Powerful Explosions

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Supernovae – Incredibly Powerful Explosions

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