Hubble Reveals the Final Stages of a Dying Star

Hubble's 31st-anniversary photo was released in April 2021. It's a portrait o AG Carinae. This star is one of the most brilliant in the Milky Way. AG Carinae is constantly in a constant struggle with itself and periodically releases matter to ensure that it eventually reaches stability.
We can now see the amazing struggle thanks to Hubble.

The Hubble team has released another image or images of AG Carinae. It is composed of Hubble observations from the star as far back as 1994, 2020, and 2014. AG Carinae (Light Blue Variable) is a luminous variable (LBV). Its appearance changes with time. These changes are brought to life by the images.

AG Carinaes struggles between the outward pressure of fusion and the inward pressure gravity. Stars struggle when these two forces are out-of-balance. Stars seek equilibrium.

At this point in its life, the star is losing mass continuously. Outward radiation pressure drops as the star runs out fuel for fusion. This is where gravity can win. Gravity pulls some stars' mass inward towards the center. The matter is propelled into space by heat as it moves inward. This will continue until AG Carinae loses sufficient mass to reach equilibrium.

Two Hubble views showing the luminous blue variable AG Carinae. These images show dust bubbles as well as a gas shell that is made of material periodically ejected by the star. Image credit: NASA/ESA/Hubble, A. Nota, C. Britt

The image to the left depicts ionized nitrogen and hydrogen emissions. These are part of the expanding emission nucleus surrounding the star. Because the star is extremely hot, high-energy ultraviolet photons emitted from it energize hydrogen and nitrogen and cause them to emit light.

The right image shows dust in blue lit by reflected starlight. It's a reflection Nebula, which is a cloud of dust reflecting the starlight. AG Carinae can be described as a combination of two nebulae: an emission and reflection nebula. Astronomers believe powerful stellar winds are responsible for the formation of the filaments and bubbles made up of gas and dust around the star. This gives them their diaphanous appearance. AG Carinaes Nebula measures approximately five light-years across.

AG Carinae lies approximately 20,000 light years away in the constellation Carinae. It is difficult to see due to its distance and the fact that it is obscured by visible light. Its apparent brightness swings between 5.7 to 9, making it difficult to see. The Hubble can handle it though.

The material in the nebula itself is approximately 15 solar masses. About 10,000 years ago, some of this material was ejected by the star. Humanity was at the beginning of its neolithic phase and nearing the end its paleolithic periods. The caves and simple structures of primitive human settlements provided basic tools and shelter. If you ever wondered what your ancestors did at that time, here are some answers.

The star is approximately 0.4 to 1.2 Parsecs away from the nebula. Outside of that cavity, there's an 8.8 Parsec wide interstellar medium cavity. It was created by AG Carinaes strong stellar winds.

The speed of the gas in the nebula's nebula is fast, at a rate of 69 km (43 mile per second). Even faster are the stellar winds that blow from the star. They travel at around 200km (124 miles per second).

AG Carinae likely experienced multiple outbursts. The largest amount of gas is nitrogen and hydrogen, as seen in red. There are multiple rings that indicate multiple outbursts. Individual rings from different outbursts could have collided. The blue dust does not have the form of rings, but is made into clumps and filaments by the stellar winds. The stellar winds of AG Carinaes are extremely powerful. It is possible for massive stars to have winds one billion times stronger than our Suns stellar wind.

Although AG Carinae has been well studied, there are still many things that astronomers don't know. The nebula is non-spherical, and instead displays bipolar symmetry. This could indicate that the binary companion of the massive star is not yet known. It could also mean that the massive star rotates extremely fast, as other massive stars.

Future prospects for the massive stars are uncertain. There is evidence that it will eventually explode as supernova. Its stellar spectrum is similar to that of stars nearing core collapse. However, the models that can predict this are only applicable to stars with 20-25 stellar masses. AG Carinae has between 55 to 70 solar masses after having about 100 solar masses at its beginning. Its potential supernova ending is therefore uncertain.

Whatever AG Carinaes fate may be, we still have the Hubble to gaze at and wonder.

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