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What is it anyway!?
Supernova is an explosive death of a star. Not just any star but a star that is atleast a few times massive than our Sun. The event releases an immense amount of energy which scatters it’s entire stellar matter into space. The star loses everything it has in the immense explosion of supernova. Supernovae are among the brightest and most luminous events in the universe. They can be brighter than it's entire galaxy. It marks the end of a star's life cycle with an extraordinary explosion. It is one of the biggest explosions in the cosmos. When a massive star exhausts it's nuclear fuel, it undergoes dramatic changes that ultimately drive it to a colossal explosion. Gravity fails at curtailing these powerful explosions. These ‘cosmic fireworks display’ releases an immense amount of energy and matter freely into open space. The luminosity of a supernova explosion is extreme enough to briefly outshine an entire galaxy. They can get billions of times brighter than our Sun. Such unbelievable luminosity makes them visible across vast cosmic distances of light years. They outshine everything in their vicinity for light years. Truly a nuclear bomb in the size of light years! |
| A supernova captured recently by the James Webb Space Telescope |
These cataclysmic events not only captivate astronomers but also people who able to witness it since they are extremely bright and most times. Their powerful light can tear through the daylight and make them appear in the skies as smudges of light even during the day. They play a very pivotal role in the cosmos. Yes, they are very necessary for the universe's sustenence. Supernovae enrich the interstellar space with heavy elements on the periodic table and greatly trigger the formation of new stars. Without them, you and I wouldn't exist. Supernovae are however rare events. This is because supernova befall only massive stars and most of the stars aren't massive. In a galaxy like the Milky Way, they happen roughly once every 50 years. Thus, they are remarkably a rare event. We'd be incredibly lucky to spot one.
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The life-cycle of a star
To understand supernovae, it's vital to understand the life cycle of a star. Yes, they are born and die, so they have a life cycle. Stars are born from vast clouds of gas and dust called nebulae. Nebulae have no form and they float around freely in deep space until gravity tinkers with it. In these gigantic nebulae, somewhere where there is a lot of material or density, gravity begins to coalesce the dust and gas together. Once gravity is activated, it starts getting hungry for more matter. Gravity then begins pulling nebulae matter together and the core gets denser as more and more matter fall in. As the matter becomes denser, gravity becomes more and more powerful. It begins reaching out to swallow more matter. Under the influence of gravity, these clouds collapse and become protostars. The coalesced matter becomes big as planets and keeps consuming everything around insatiably. With the core becoming very dense beyond a point, it triggers the ignition of nuclear fusion. The whole coalesced matter gets lit into a star. Thus, a new star is born. The matter begins to actively have nuclear fusion going on in it's core. From here on, it begins to release energy and producing light throughout it’s existence. With gravity now incredibly powerful, the star has the capacity to reach out farther distances to consume matter.
A star maintains a delicate balance between the outward pressure of nuclear fusion and the inward pull of gravity. It's a dance between the two or more of a fight. This fusion of hydrogen into helium releases energy that counteracts gravitational collapse and stabilizing the star. Sometimes one of them wins and immediately loses and the cycle keeps repeating throughout it's lifetime. This activity will go on for billions of years. In case of very massive stars, it can be millions of years. But as the star ages, it's core eventually runs out of it’s main fuel which happens to be hydrogen. Unless it is consuming matter, it's stock will never remain suitably forever. The end of hydrogen inside a star triggers a chain reaction that causes the star to expand and become a red giant. The star then doubles, triples, quadruples and multiplies in it's size. This is the life of a greatest number of stars in the universe. Most of the stars in our universe will meet this fate since they aren't massive enough for a supernova.
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However, there are some stars that are not your average size in mass and
volume. These stars are big dogs in the cosmos. They are either several times larger or massive than our sun. They possess unbelievable sizes or gravitational power. Our Sun is a
medium-sized star for reference. It's not a big star. These colossal stars die out in fashion. Their dramatic death is one of the most wonderful sight for our eyes. The
extinction of hydrogen in them triggers a gravitational collapse that cannot be
stopped by any process. The star will keep collapsing inwards without anything to stop. The implosion sends out explosive energy outwards in
all direction destroying the star entirely. It is sudden, it is fast and it is mercilessly titanic! The energy is so great that
unbelievable number of photons are released making it luminous than an entire
galaxy. This light will remain visible for light years and billions of years too. This explosive event is the supernova. It is one of the greatest explosions after the Big Bang itself. After the supernova, the star is
no more. The star glows no more and has died. It either becomes a variety of other cosmological bodies that we’ll
read about later on.
Generic types of stars
Low-to-intermediate massive stars - These stars have up to nearly 8 times masses to that of our Sun. Our Sun falls into this category of star classification because it is relatively small. While dying, they undergo helium fusion inside them. It's when there is no more hydrogen atoms to fuse and so gravity starts fusing helium atoms. Fusing of helium atoms create heavier elements like carbon and oxygen. If you follow the periodic table, you'll be able to see the next heavier elements that follow after hydrogen. Eventually, they shed out their outer layers by enlarging themselves which continues forming into planetary nebulae. Then, the formation of new celestial bodies using these materials can start. All they leave behind are their cores which become white dwarves. That continues glowing for a long time and then dying off too.Massive stars - Stars with masses greater than 8 times that of our Sun fall into this category of stars. These stars are either extremely large in size or they are very massive with a lot of matter in them. They undergo successive stages of fusion unlike their counterparts. They burn fast and die out fast too. Their kind of fusion ends up creating elements up to iron (on the periodic table) deep within their cores. They exhaust their atoms real fast. Iron fusion is endothermic which means it absorbs energy rather than releasing it. In smaller stars, once hydrogen is over, they fuse helium atoms. But iron cannot be fused further in these cosmic cauldrons since iron is an energy drainer unlike the elements above it on the periodic table, which release energy on fusion. This leads to the core's collapse under it's own gravity which ends up triggering one of the many types of supernovae. It's one of the most fascinating end of things in the universe.
Types of supernovae
Supernovae are broadly classified into 2 main types namely Type 1 supernovae and Type 2 supernovae. These two kinds give off different information about the stars. They are based on their spectral lines and the presence or absence of hydrogen in the explosions. Based on this, scientists can decipher detailed information on the exploded star. Let's see how they are and how they differ from each other.
Type 1 supernovae
The Type 1 supernovae are characterized by the absence of hydrogen lines in their spectra. Their signature is totally different from the ones with hydrogen lines in their spectra. Type 1 novae are further subdivided into three further categories.
Type 1A - These supernovae happen as a result of thermonuclear explosion by a white dwarf in a binary star system. A binary star system is when 2 stars orbit each other in a barycenter. When the white dwarf accretes enough stellar matter from it's companion star, it crosses a critical mass called ‘The Chandrasekhar Limit’. Something extraordinary happens then. At this point, carbon fusion ignites explosively throughout the star which leads to a thermonuclear runaway reaction. The reaction won't stop at any cost. This causes it to suffer a powerful supernova explosion. Thus, the Type 1A supernovae has occured involving a white dwarf star.The fusion front propagates as a deflagration (subsonic burning) or a detonation (supersonic burning). The white dwarf has to die either way. Either of these fusion explosion is going to consume the white dwarf within a matter of seconds. The tiny star is doomed. The white dwarf is then completely disrupted and the energy release ejects all of the star's material into space. It is gone in an instant, so to say. Such supernovae from a white dwarf in a binary star system is Type 1A Supernova. The diagram below will explain better.
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Type 1B - These supernovae originate from massive stars that have lost their outer hydrogen layers. Such stars can many reasons to lose them away. They may have lost it due to strong stellar winds or from the interactions with a companion star and other cosmic bodies. The collapsing cores of these 'stripped' stars result in a powerful supernova. With no hydrogen to fuse, the resultant runaway explosion is a supernova. They are always characterized by the presence of helium lines in their spectra. This is because their hydrogen layers were stripped away, remember? So, Type 1B supernova happen with very massive stars which have lost their hydrogen envelopes because of various factors. An unexpected death for such stars.
Type 1C - These are similar to Type 1B supernovae. But, Type 1C supernovae results from the collapsing cores of massive stars that have lost both their hydrogen and helium layers. Powerful forces of the cosmos are responsible for a star in losing both hydrogen and helium layers. The massive stars matter collapse in on themselves and end up blowing itself. Their spectra lack both hydrogen and helium lines. They have to be then detected based on other parameters. Thus, these supernovae become distinct from other types of supernovae. They become unique supernovae in astronomy.
Type 2 supernovae
Type 2 supernovae are characterized by the presence of hydrogen lines in their spectra. They happen to relatively stable stars. They occur when massive stars (often more than 8 times the mass of our Sun) exhaust their nuclear fuel (which is hydrogen) and undergo uncontrolled gravitational collapse. This is the conventional supernova that we all know of. They are unable to lose enough stellar matter to become white dwarves. Hence, they have to be again classified into other types for better discretion. Type 2 supernovae are again divided based on their light curves.
Type 2P - These supernovae exhibit a plateau in their light curve. Plot them on a graph for a period of time and they become unique. This means that their luminosity keeps rising up before suddenly remaining almost constant for a long period of time. If really far away, it's difficult to tell if that was a constant supernova or a glowing star. Then, their luminosity begins to dip gradually before completely fading away. You'll never know when the constant lighting could go out. The plateau phase is caused by a recombination of hydrogen in the expanding supernova shell. That explains why it'd glow constantly for a long time.Type 2L - These supernovae show a linear decline in their light curve without a plateau phase. They glow and die down suddenly. Meaning, they rise up in luminosity and then fade away without keeping a tendency of constant shine for some time. On a graph, that would be like a rise and fall without a saturation level. They are less common than Type 2P supernovae and are theorized to happen from stars with different pre-supernova structures. Meaning, they are very rare.
Mechanics of a supernova
The core collapse of a massive star (for Type 2, 1B and 1Cc supernovae) or the thermonuclear runaway in a white dwarf (for Type 1A supernovae) are the primary mechanisms behind supernova explosions. The cores of these star collapses inwards with each collapse gathering strength and nothing able to prevent it. In core-collapse supernovae, the iron core of a massive star collapses within seconds. That takes unimaginable power known to man. The core suddenly reaches extremely high densities and temperatures possible. It keeps on collapsing even more inwards due to all this. This process leads to several key events and some of them are mentioned below.
Neutron star or a black hole formation - The core's collapse halts when it reaches nuclear densities which ends up forming a neutron star. Meaning, every atom inside the star has only neutrons now. That is because the power was too strong enough to push electrons into protons which has made the whole star full of only neutrons. In some cases, the resulting supernova might form a black hole if the core mass is sufficiently large. Black holes will happen only if the core's collapse don't even stop at sub-atomic levels. The mechanics of a black hole are not well-known at the moment due to the impossibility of finding them for analysis.Shockwave generation - As the infalling stellar matter rebounds off the dense core, there is an equally powerful shockwave that propagates outward. It is the force responsible for supernovae. It is able to fight off gravity and leave the star. This energy or shockwave will ultimately lead to the outer layers of the star to be carried away or expelled at unbelievably high velocities in seconds. As it leaves the star, it will carry away with it whatever it can hold and we see it as supernovae.
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| Actual image of a supernova shockwave of Supernova 1987A | Source : Hubble Telescope, NASA (4954621859) |
The benefits of a supernova
Supernovae play a very important role in the universe. Without them, galaxies and new stars would never form. They are responsible for creating many of the elements heavier than iron such as gold, silver, platinum, uranium etc. The fusion of hydrogen into helium and then helium and so on, is responsible for the creation of every other element on the periodic table. The more massive the stars responsible for supernovae are, the heavier-than-iron come into existence due to nuclear fusion processes. All the elements we have on Earth were once forged in the cores of other stars. These elements are scattered throughout space by supernova explosions. They then become available to us once these stars have died and their supernova sent it out. Only powerful explosions like supernovae can distribute the various elements forged in stars way into light years of space. Everything that you find on Earth came from the stars including the elements that made the Earth itself. These heavier elements go onto eventually become part of new stars, star systems, planets and even life itself. All elements on Earth and in our solar system were once part of some stars. Everything including us come from dead stars. In the words of Prof. Lawrence Krauss, the atoms of both our hands could’ve possibly come from 2 different stars. What an amazing information to know!
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| Star's shells showing what elements form when nuclear fusion intensifies upto the core |
Supernovae also have a profound impact on their surrounding environment. They alter their vicinity. The shockwaves from the explosion can trigger the formation of new stars. They carry energy which we know as power and radiation. The intense searing radiation from this cosmic destruction can ionize gas clouds and dust leading to the creation of new molecules. Planetary and star formation can then initiate because of it. Supernovae are the sources of elemental enrichment in our universe. They provide metallicity in the cosmos.
The remnants of a supernova explosion are complex structures and evolving, that continue to impact their immediate surroundings. The give life to dead floating space matter. Supernovae play a crucial role in the cosmic cycle of matter by synthesizing and dispersing heavy elements. Different elements perform different tasks in enriching the cosmos. Their birth can only happen due to supernovae. This enrichment process is essential for the formation of planets, stars and the development of life. The greatest role in all of this is that of the supernova which unlocks all the secret ingredients locked away by massive stars.
Aftermath of supernovae
All the expelled matter from a supernova forms an expanding shell known as a Supernova Remnant (SNR). They form a halo from the middle where they once were. These remnants provide detailed insights into understanding the explosion mechanics and the interaction of the ejected material with the interstellar medium. They carry all the vital information on what they once were. Famous examples of SNR that we can see are the Crab Nebula (SN 1054) and Cassiopeia A (SN 1680). All our knowledge of stars come from supernovae remnants like them. When a star explodes as a supernova, it leaves behind a complex and fascinating remnant of stellar matter. They glow under different wavelengths of radiation which enable us to understand their complex past.
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| A supernova remnant | Source - NASA |
The remnants in these expanding shells of gas and debris continue to evolve for thousands or millions of years as they travel into deep space. We can trace these remnants from the radiation they emit. Thanks to modern telescope technology of our times, we can take images of these supernovae and give them colours based on accurate spectroscopy. They indeed have a lot to tell us. Their vibrant pictures give us awe and detailed visuals of such mega cosmic events. Discoveries and scientific theories can be made from studying these awesome supernovae remnants.
Types of Supernova Remnants (SNRs)
Pulsar wind nebulae - This kind of cosmic wind is formed by rapidly spinning neutron stars (pulsars) which begin emitting high-energy particles. Pulsars produce strong winds from the matter they emit due to their insanely rapid spins. These high-energy particles or pulsar winds are characterized by bright non-thermal emissions which are often in X-ray and gamma-ray wavelengths. They are easy to track today due to our various modern day instruments. Examples include the Crab Nebula and Vela Pulsar..jpg) |
| The 1st Pulsar Wind Nebular captured by astronomers around a rare ultra-magnetic neutron star |
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| Photo of a shell-type SNR |
Supernova remnant with pulsar wind nebula - This would be a combination of the two types mentioned above. Since it is possible, they exist. They are characterized by a central pulsar wind nebula surrounded by a larger shell-type remnant. You can find a puncture in the halo where the pulsar wind interacts. They show different stages in the evolution of a supernova remnant. Truly a cosmic marvel!
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| Vela Pulsar Wind Nebula and a supernova remnant image sourced from NASA |
Neutron stars - Core-collapse supernovae often leave behind compact remnants like neutron stars. The name itself is self-telling of what it is. A star made of neutrons. Neutron stars are incredibly dense entities with masses atleast 1.4 times that of our Sun. But all this mass would be packed into a sphere with a radius of about 10 to 25 kilometres only. That is a dangerously massive star. Researchers reveal that the highest mountains on neutron stars could only be a few millimeters tall!
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| NASA's rendition of a neutron star |
Black holes - Black holes are formed when the star’s core mass overcomes the limit for neutron stars. After that, there is absolutely nothing to stop the collapse and the collapse would be infinite. They are one of the most mysterious and least known cosmic bodies in the universe because they have been theorized to have infinite density. Such a density would swallow space so much indefinitely that the physics at play is currently unknowable. Their gravitational fields are so strong that not even light can escape and are only detectable from the gravitational lensing that they cause. This means, once trapped by a black hole, it's an instant eternal demise. They are the devourer of stars and eaters of worlds. With masses of millions and billions time of our Sun, there is absolutely no escaping a black hole. Their power reaches out into multiplefolds of light years. NASA says that black holes could be present in any directions of space. These bodies even devour each other and grow larger. They cannibalise each other to become supermassive and ultramassive black holes. Some of these blackholes are even several times larger than our entire solar system. Some are galaxy-sized black holes with unthinkable gravitational prowess.
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| Actual image of the black hole Messier 87 taken in the year 2018 |
Evolution of supernova remnants (SNRs)
Supernova remnants undergo several stages in their evolution. I mean, why not? They have endless time, don't they?
Free expansion phase - This is an initial phase. It kickstarts it all of in here. During this, the expanding debris encounters little resistance from the surrounding medium and almost freely travel in all directions into the void. The particles are accelerated at hypersonic speeds into everywhere in deep space.Adiabatic phase - The supernova remnants slow down because it has to interact with the interstellar medium on the way which eventually ends in heating them up. It's the only way they get slowed down. Without cosmic particles to encounter, they'd travel endlessly in hypersonic speeds. As they lose speed, they form these beautiful halos from where they left in space.
Radiative phase - The supernova remnants start cooling down and also begin to emit radiation. With no fusion heating them up, their heat dies down. They gradually begin to blend with their surrounding interstellar medium whatever that happens to be. They may form clouds, dust and other cosmic particles.
Spotting these supernovae
While supernovae are incredibly bright, they are relatively rare events and very far away from us. We are unfortunately in bad luck about spotting a supernova. However, with the aid of very powerful telescopes, astronomers can detect and study these cosmic explosions happening in distant galaxies. They are the only lucky humans among us. By analyzing the light coming from distant supernovae, scientists can learn about the properties of the exploding star, the conditions in the interstellar medium and their expansion rate of the universe. They are able to capture vivid photographs and videos using various technically advanced instruments. Supernovae continue to fascinate stargazers and inspire scientists alike. They are beautiful cosmic formations. Their explosive power and all the various elements that they create are essential to our understanding of the universe and our place in the cosmos. We originate from such events.
Supernovae can be observed across different wavelengths between radio waves and gamma rays. The only requirement is expensive equipments. Modern telescopes and observatories (both ground-based and space-based) have significantly advanced our understanding of these events. They give us highly detailed data of their target. Unless a supernova happens close by, we may need our machines to spot them. We are in no such luck as of now. In the 10th century, there was one such event and there was a bright light in the sky for many days. Ancient people were in awe of it because they did not know what it was. The Chinese have written records about it. They are the only ones who recorded about a supernova. No other close by supernovae has occurred since whereby we could see them directly in the sky without any aid. Supernovaes are that rare from our Earth's perspective. The tools for observing supernovae at our disposal are as below. They are always in use all the time.Optical observations - Optical telescopes capture the visible light coming from supernovae. It gives us a view of as it is available from source. These instruments allow astronomers to study their light curves, spectra and evolution over time. These captures are published unfiltered to the public.
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| Picture of an optical observation telescope or an observatory |
Radio observations - Radio telescopes detect the synchrotron radiation produced by supernova remnants. Radio waves are large wavelengths, sometimes the size of Earth. Synchrotron data provide insights into the magnetic fields and particle acceleration within these supernova remnants. From capturing their radio waves, we can develop a radio image of the supernova which is unique and not visible in optical image.
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| The radio telescopes of CSIRO (Australia) |
X-ray and gamma-ray observations - High-energy telescopes observe the X-rays and gamma rays emitted by the hot gas and energetic particles in supernova remnants. These radiations are dangerous and short wavelengths. They unravel details about the explosion mechanics and the interaction with the particles or objects in their vicinity. Gamma ray and X-ray images show us parts of the supernovae that isn't visible in other wavelengths. They are awe-inspiring to look at.
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| Chandra X-Ray Observatory which is now orbiting the Earth in space |
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| HESS II gamma ray telescopes |
Supernovae in our own backyard
Historical records and modern observations have documented several supernovae within our Milky Way galaxy. It was very important that these records were kept since they became very useful over time. Some notable examples of these are below.
SN 1006 - Was observed in the year 1006. Back then, the Chinese recorded the event via drawings and sketches. Thanks to them, we could now trace the remnant when science was advanced. This supernova was one of the brightest events of the sky in recorded history. The nova was extremely bright. It was visible even during the brightness of daytime for many days. Many other people apart from the Chinese have mentioned of it..jpg) |
| Remnant of the SN 1006 supernova today |
SN 1054 - This supernova explosion gave birth to the Crab Nebula. The nebula is one of the most beautiful structures visible from our perspective. This nebula has become a well-studied supernova remnant that continues to provide valuable insights into supernova dynamics. Look at how incredibly beautiful it is from the actual image below.
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| The Crab Nebula sourced from James Webb Space Telescope |
SN 1604 (Kepler's supernova) - This supernova was discovered by Johannes Kepler in the year 1604. Back then, was the genesis of telescopes. This supernova is the last unaided-eye supernova observed in our Milky Way galaxy to date. A star map can tell you where to locate this SNR.
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Conclusion
Supernovae are not just spectacular astronomical events. In the bigger picture, they have vital tasks to do. They are fundamental to the evolution of our universe. They churn the universe into what it is today. By forging and scattering heavy elements, triggering star formation and leaving behind intriguing remnants like neutron stars and black holes, supernovae shape our cosmos in many profound ways. They are as beautiful too as they are useful. As our observational techniques and theoretical models continue to improve and progress, we will undoubtedly uncover even more about these cosmic explosions and their role in the grand tapestry of our observable universe. They will remain a constantly mapped and studied cosmic event.
Hope this post was able to shed brief light on supernova. Imagine what an awesome sight it'd be observe a nova for real somewhere close to our solar system. For more technical details on a supernova, read scientific papers or chat with an astrophysicist. Hope that we get to see one supernova somewhere in our lifetime. Have a super day/evening.
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