Gas bubbles reveal that this star is reaching its final stages

The star AG Carinae lives in a conflict between two forces – the internal pressure caused by nuclear fusion and the external gravity, which wants to push all the stellar material towards the center. Eventually, gravity will win, and the star will explode in a supernova, but that will still take a while to happen. At the moment, we can appreciate the transformations taking place there.

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In an image from 2020, Hubble shows how the massive blue star has evolved in recent years, compared to the photo in 2020. We can see a shell around a “small” blue circle (the color representing the dust lit by the star itself). The shell gained red colors in the Hubble palette (color that represents the gas ejected from the star, predominantly hydrogen and nitrogen).

Image from 2020 from the star AG Carinae (Image: Reproduction/ESA/Hubble/NASA/A. Note/C. Britt)

In the second image, the blue is more prominent, expanding towards the edges of the shell, in contrast to the gas distributed in the outer layers. Astronomers surmise that the dust bubbles and filaments we see in blue were shaped by a stellar wind emitted by AG Carinae.

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This wind travels through the space to about 89 thousand km/h, faster than the expansion of the shell itself. That’s why the blue dust managed to reach the external gases. When the wind increases, the gas bubbles are pushed outwards and open a cavity in the shell around the star.

All of these phenomena occur because AG Carinae is in its final stages before explode in supernova. At the end of the life of a massive blue star like this, the internal pressure of radiation begins to decrease and gravity pushes the material towards the hot core. As this occurs, this matter heats up even more and creates eruptions.


Image from 1024 from the star AG Carinae (Image: Reproduction/ESA/Hubble/NASA/A. Note/C. Britt)

These eruptions eject material out of the star, forming a shell like the one we see in the images. Although they are the outbreaks of a dying star, the eruption occurred about 40 a thousand years, and it could still be quite a while before AG Carinae finally explodes.

Before that, it is likely to run out of hydrogen and undergo successive smaller explosions, like this eruption, transforming into into a Wolf-Rayet star (a type of massive star that fuses helium or heavier elements in the core). AG Carinae is about 40 to 55 times the mass of the Sun, which makes it unstable, short-lived.

With this set of characteristics, the AG Carinae is a rare star, mainly because the others of its type “usually” to explode fast. Following these processes closely is a unique opportunity for astronomers to better understand how blue giant stars behave at the end of their lives.

Source: Science Alert, ESA/Hubble

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