The stars we see on a clear night have been burning for millions or billions of years. But how did they come to be?
Stars, like our sun, are created from vast interstellar clouds of gas and dust called nebulae. These stellar objects can measure more than 100 light years across. (A light year is the distance light travels in one year; because light moves at a speed of approximately 300,000 kilometres per second, a light year is almost 9.5 trillion kilometres.) Over time, smaller clouds in the nebula might rub against each other, or the shockwave of a nearby supernova might disturb the cloud to start a slight spinning motion.
As the cloud rotates, it picks up speed as more gas starts condensing and collapsing toward the middle, and as gravity accelerates the process. The core continually gets hotter and grows, much like the snowball effect. Over time, the star grows to a critical mass, temperatures in the core reach about 15,000,000 °C, and the star lights up. It took our sun about 50 million years to grow.
These regions of starbirth are also called “stellar nurseries”, and you can easily see one tonight. It is called the Orion Nebula, or M42. The constellation Orion the Hunter now rises in the east a couple of hours after sunset. Locate the iconic three stars in a row that form his belt. Look down the imaginary sword hanging off the belt and you will see a hazy patch of light. This is where thousands of stars will eventually be born, but the process will still take millions of years.
The Orion Nebula is located about 1,500 light years from us and measures about 30 light years across. The Hubble Space Telescope has imaged small cocoons of material showing the baby stars forming in the swirling cloud of dust and gas. As with many stars, possible exoplanets will be born from the leftover dusty material. This is the same process our solar system followed in the early stages of its birth.
Our Milky Way contains hundreds of these emission nebulae, but a telescope is required to locate and observe them. M42 is an easy target for the unaided eye or binoculars. It is also well placed on the celestial equator, allowing both the northern and southern hemispheres to see it.
Till next time, clear skies.