Oxygen-Magnesium Rich Star Explosion

From supernova we know what elements a star produces at the end of its life. Astronomers find oxygen-magnesium in supernovae.

Star. We may see stars as points of light in the night sky. But the star itself is a ball of gas composed of hydrogen, the lightest gas in the universe. Stars also appear to shine in the night sky. This is different from the planets. Stars can shine because in the center of the star there is combustion or rather a nuclear fusion reaction to produce heavy elements and energy. In this case the hydrogen becomes helium. And when the hydrogen runs out, it’s the turn of helium which is then converted to become a heavy element.

In the end, even stars evolve and enter old age. If stars like the Sun end their lives as white dwarfs, then more massive stars will end in supernova events. A powerful explosion that eventually leaves the center of the star collapsing and ending up as a neutron star or black hole. When the explosion occurred, of course there is material ejected. Interestingly, the composition of the ejected material could be the last traces of material formed at the end of a star’s life before it explodes.

This is what Hanin Kuncarayakti of the University of Turku and team discovered. More precisely, Hanin and his team found supernova explosions that can add to our understanding of the final stages of a star’s life.

Circumstellar Material

Massive stars whose masses are 8 or more solar masses have an onion-like structure. So, these stars have layers with different elements in them. The further into the star, the layers we encounter actually contain elements heavier than hydrogen. There are helium, carbin, oxygen and other heavy elements that are produced by nuclear fusion reactions inside stars.

During its life, the star also loses mass. Most often this occurs through the ejection of particles that we know as stellar winds. The event of the ejection of high-energy particles from this star generally occurs due to the eruption of the star. In addition, mass loss can also occur due to interactions with partner stars.

The rate of mass loss for stars also varies. Some are slow but some are fast. The slow ones usually occur through stellar winds, but some are extraordinarily fast through star explosions. As a result, the star loses all of its hydrogen shroud and the star’s inner layers are exposed.

However, this ejected mass or material is not lost but can still be found around the star. We know it by the name of circumstellar matter.

In single stars, circumstellar material comes from material ejected from the star. However, in a double star, apart from material from a star that has lost its envelope due to an explosion, circumstellar material can also come from its partner star.

When a star explodes as a supernova, the stellar envelope is ejected leaving the center of the star which then collapses. The ejected stellar envelope is generally dominated by hydrogen gas (type IIn supernova) and helium (Ibn supernova type).

Heavy elements in circumstellar matter

In 2021, astronomers will find a supernova with circumstellar matter that is not dominated by hydrogen helium. Instead, they found heavy elements such as carbon and oxygen (type ICN supernovae) in circumstellar matter.

The discovery of heavy elements such as carbon and oxygen shows the stages of the shell being released and the accumulation of material around the star, with hydrogen as the lightest material as well as the element present in the outer layers of the star.

Survey observation with Very Large Telescope (VLT) 8.2 meters operated by ESO captures the presence of a Type I supernova that is different from what is commonly found.

Supernova SN 2021ocs.

This supernova lasts longer and does not fade immediately and is bluer in color when compared to other type Ic supernovas.

In supernova SN 2021ocs, Hanin and his colleagues found a different kind of heavy element. They found an abundance of oxygen and magnesium in the supernova spectrum. The presence of oxygen and magnesium in massive stars is not unusual because these two elements were formed before the supernova.

What’s interesting is how there can be an abundance of oxygen-magnesium in circumstellar matter.

According to Hanin, this type of supernova can occur due to circumstellar material which is dominated by oxygen-magnesium, or due to ejection of material which is dominated by oxygen-magnesium. From observations, it seems that the dominance of oxygen-magnesium in SN 2021ocs comes from ejection of oxygen-magnesium-rich gas that crashes into circumstellar material.

If so, then circumstellar matter should have collided with the ejected mass star about 1,000 days before the star exploded. Inevitably, these observations also act as time machines that track the activity of stars before the explosion and also provide information on the final stages of the life of massive stars.

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