Hubble captured the surprising ‘eye’ of a huge star explosion

The death of a massive star has to be one of the universe’s finest ends.

They eject colossal amounts of matter into the space around them, sculpted by blast shock waves and stellar winds, illuminated by the star’s own light. That’s what’s happening with AG Carinae, a massive dying star 15,000 light years away, featured in new Hubble images.

In fact, AG Carinae’s agony is wilder than most. This is what we classify as a bright blue variable star, which is among the brightest and most massive stars in the galaxy.

These extremely rare stars burn hot and bright (blue), and their lifespan is much shorter than that of others – just a few million years.

AG Carinae, which is about 55 to 70 times the mass of the Sun, is a few million years old and unstable. Its brightness fluctuates quite significantly, due to warring forces: the radiation pressure pushing outward and gravity wanting to make the star collapse inward.

(ESA / Hubble and NASA, A. Nota, C. Britt)

At the end of a star’s life, as it begins to run out of fuel to merge into hydrogen, the radiation pressure begins to decrease. This causes the star to contract, with matter heating up as it nears the stellar core.

This heating then causes the star to erupt, ejecting matter outward. For AG Carinae, the surrounding shell of matter – here appearing as an iris around a pupil – is the product of such an eruption, which occurred around 10,000 years ago and contained around 15 solar masses of matter.

In Hubble images, colors represent types of materials. The red color represents the ionized gas ejected from the star, mainly hydrogen and nitrogen. The color blue is the dust around the star, illuminated by the star’s own light.

The shapes and cavities in the dust are believed to be sculpted by the star’s powerful wind, blowing at speeds of up to one million kilometers per hour (670,000 miles per hour).

(ESA / Hubble and NASA, A. Nota, C. Britt)

This wind is blowing faster than the gas nebula spreads, about 250,000 kilometers per hour; when the wind catches up with it, it hits the gas, pushes it outward and clears a cavity around the star. The stellar wind also sculpts the bubbles and filaments visible in the dust.

AG Carinae is always unstable and will probably end up becoming so depleted of hydrogen by repeated explosions that it will evolve into a Wolf-Rayet star; this process is already underway. Once this evolutionary stage in the star’s life runs out of fuel, AG Carinae will – likely – end her main sequence days in a supernova.

During this process, astronomers believe the core will collapse, leaving behind one of the Universe’s most enigmatic objects, a black hole.

You can download wallpaper versions of the composite image from the ESA Hubble website.