Nebulae are vast clouds of stellar material and are generally regions where stars are forming or formed directly from the death of a star. The closest nebula to our solar system is the Helix Nebula, a planetary nebula located 650 light years away.
See the future in the past
Image of the Helix nebula taken by Hubble. Image credit: NASA/ESA
Looking at the Helix Nebula is like looking into the future. As a planetary nebula, the Helix Nebula was once a star not so different from our sun. Planetary nebulae form during the death throes of sun-like stars that have run out of hydrogen fuel. When stars with masses similar to our sun begin to run out of fuel, their own gravity causes them to collapse inward. As a star’s core compresses, temperatures and pressures shoot up, and elements heavier than hydrogen can fuse. The fusion of heavier elements releases an enormous amount of energy that counteracts the collapse of the star, causing it to expand many times its original size. As the star expands, its surface area increases and heat is spread over a larger area, causing the outer layers of the star to cool. The cooling of the outer layers causes the star to turn red and the once sun-like star to evolve into a red giant.
Although the star has increased in size, its mass has not increased. The star’s gravity is too weak to hold the star together, and the outer layers are gradually ejected. The ejected layers then form a shell of stellar material around the dying star called a planetary nebula. The Helix Nebula is an example of this process currently underway. The central star of the Helix Nebula is ejecting its outer layers, causing the entire structure to grow in size. Eventually, the central star will have exhausted all its material and a white dwarf will form. Interestingly, since the Helix Nebula is 650 light-years away, we see it as it was 650 years ago. As with much of astronomy, we are looking to the past to understand what may happen in the future.
Characteristics of the Helix Nebula
Image of cometary knots within the Helix Nebula. Image credit: NASA/ESA
As the Helix Nebula is the closest nebula to our solar system, it is also one of the most studied. The structure itself spans a distance of about 2.5 light years and is currently expanding at a rate of 19 miles per second (31 kilometers per second). The Helix Nebula is also quite young, having formed about 10,600 years ago.
The Helix Nebula is home to a series of structures called “cometary knots”. These structures get their name from the fact that they look similar to comets in our solar system, but they are far from comets. Cometary knots form as low-density material is pulled away from the nebula, causing the stellar material to stretch and elongate. Surprisingly, the cometary knots in the Helix Nebula are generally the same size as our entire solar system.
Aidan Remple October 10, 2022 in Science