What is a supernova?
The life of a star is affected by two main factors: while gravitational forces pull the gas contained in the star towards the center, pressure that is generated by the nuclear fusion which takes place in the center pushes the gas outwards. When a star runs out of fuel, gravitational forces take over and it results in the sudden collapse of the star. As a result of this sudden collapse, oversized stars get dispersed into space through a massive explosion. These explosions are called supernovas.
It may be a hard task to predict beforehand whether a particular star will be dispersed in the shape of a supernova. When explosion takes place, dispersal of the supernova happens so fast (within 2-3 minutes) that it is almost impossible for astronomers to capture the exact moment of the explosion. After the initial explosion, there is extreme brightness and this lasts for a couple of weeks. This event when observed from a distance is taken as if the birth of a new star. Later on, the brightness gets dimmer and eventually disappears. Astronomers only have to investigate the remnants of the supernova from this point on. In some supernovas, stars get completely destroyed by dispersal into space (Type 1), but in some, a neutron star is left behind (Type 2).

Type 1 supernovas
Even though supernovas are known to be explosions of oversized stars, smaller ones can also explode and still be considered as a supernova. Interestingly, supernovas of smaller stars are even brighter. Stars with a mass less than the total mass of eight suns turn into a red giant at the end of their lives. After the red giant stage, exterior layers of the star get blown into space and it turns into a white dwarf with a mass equal to 0.6 times the mass of the sun. If a hydrogen rich material from a large star nearby flows over this white dwarf, it turns the white dwarf into an explosive composition. The white dwarf reaches the brightness of a million stars by exploding. These types of explosions are called novas.

Even though we see stars in the sky as individual bodies, 60% of them are found in pairs. An amazing star bomb is generated when the two white dwarfs in a star duo join one another. These massive explosions of White Dwarfs as a result of their complete dispersal into space by thermonuclear chain reactions can even be observed from distant galaxies. They always explode at the same mass threshold and since the amount of released energy is the same, they are used as standard light sources by astronomers. When the resulting star (formed after the two dwarfs unite) exceeds the critical size of 1.4 times the mass of the sun, it starts to collapse on its own with gravitational forces. Central pressure increases during this collapse and with the start of thermonuclear reactions, it eventually builds up internal pressure.
Since the outer layer of the star is hardened, it completely disperses into space with an enormous explosion. Remnants left behind by the explosion begin to expand very rapidly (at a speed of 30,000 km/s). Brightness more powerful than a billion stars is generated during the energy release of Type 1 supernova. In other words, the energy supernova released for a couple weeks is much greater than the total lifetime energy released by the sun. The initial strength of the supernova diminishes after a few weeks. As the supernova expands, its brightness decreases proportionately.

Ultimately it becomes a gas and a dust cloud known as a nebula.

Supernovas may be observed in different levels of brightness depending on the distance of the star to the earth. Closer supernovas can be seen as big and bright as the moon however distant ones can be observed like a bright, dimmed star, or may not be visible at all.

Type 2 supernovas
Stars with a mass between 8 and 50 times the mass of the Sun go through a series of changes a lot faster than smaller stars, eventually turning into a neutron star. During these kinds of changes, all stages of nuclear fusion takes place, as first hydrogen, then in order, helium, carbon, nitrogen, oxygen, silicon, and iron are synthesized in the stars. Iron is found in the center and other elements surround it in layers. When such a star runs out of fuel, nuclear fusion ends. The finale of nuclear fusion reactions at this stage is characterized especially with iron representing a stable nuclear structure.

When the reactions are over in the center, the iron core collapses on its own with gravitational forces. Because of the intense pressure on iron, protons of this atom unite with its electrons forming neutrons. This event takes place very fast and also particles called neutrinos are emitted. These particles apply an outward pressure on the exterior layer of this star which has already turned into a super red giant, causing burst of external layers into space. This event is described as being a Type 2 supernova.

Remnants of supernovas
Supernova remnants are radioactive. In fact, a major portion of the light emitted by a supernova is derived from radioactivity. Furthermore, supernova remnants are very powerful sources of cosmic radiation. These remnants can be observed in two forms: the first form is directly observable gamma rays when high energy particles including protons and electrons interact with interstellar gasses; and the second form is indirectly observable radio waves when high speed electrons emitted via explosion get accelerated at the interstellar magnetic fields. Gases rich in heavy elements that constantly expand are left behind after supernovas. Because of abundant neutrons in the environment, elements heavier than iron are also synthesized. This richness is entirely thrown into the interstellar place. All of the heavy metals including iron are thought to have joined the solar system through a supernova explosion. “We have sent down iron” in Chapter 57 of the Holy Qur’an may refer to the dispersal of iron and other elements into the space through supernova explosions.1

Sun rising from the West
What happens when a star nearby our system explodes as a supernova? A second sun appears in the sky. Does such a supernova explosion disrupt the conditions on the earth via causing a similar or bigger impact than the sun on the planet in terms of light and heat? If such an exploding star happens to be in the west, can we consider it as the sun rising from the west? Considering that supernovas are strong light sources, a second sun appearing in the near sky for a couple of weeks will have significant impacts on planet earth.

At first, day and night would disappear. Planetary temperatures would rise to lethal degrees. Evaporation of seas and oceans may cause worldwide flooding. Local temperature rise caused by the two suns may generate severe storms. Remnants of the star as it loses brightness after a couple of weeks can color the sky blood red as described in the verse: “And finally when the heaven is rent asunder, and it becomes rosy like red hide!” (Rahman 55:37). Events pointing to doomsday as described in apocalyptic verses can take place. Surely God knows the best of everything.

Notes
1 For a similar discussion on a possible connection of this phenomenon with this Qur’anic verse, you may refer to a previously published article titled “Supernova Explosion and a Miracle of the Qur’an” by Nuh Gedik (The Fountain #54, 2006).

References
Silk, Joseph. 1997. A Short History of the Universe, W. H. Freeman.
Zeilik, Michael. 1994. Astronomy: The Evolving Universe, New York: John Wiley & Sons Inc.
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