Star Formation | The Schools' Observatory

Stars form in huge clouds of gas and dust called nebulae. These areas of space are sometimes known as 'stellar nurseries' or 'star forming regions'.

The gravity of the gas and dust in the clouds pulls everything inwards. The clouds slowly collapse onto a number of points (or cores).

Deep in the centre of these cores, there is lots of dense material squashed together, and it is very hot. Eventually it is hot enough for nuclear fusion to start.

Nuclear fusion is the process that powers a star. This point is called stellar ignition because it is when a star starts to shine.

Stars are not true stars until they can fuse hydrogen into helium. Before that point, they are called protostars.

A wide column of red/brown cloud and gas rises upwards in the middle, splitting off into three separate vertical branches. The background is dark blue and black, though brighter around the edges of the branches. Throughout the image, there are bright red and white dots of stars scattered throughout. Three particularly large red stars are visible in the upper left quadrant of the image. — A small region of the Eagle Nebula. This structure has been named the 'Pillars of Creation'.

Star Formation Process:

Stage 1

Star formation takes place in swirling clouds of gas and dust that are many times larger than a typical solar system.

A large, circular is in the centre against a black background. The circle is seemly made of swirls of yellow, pink, and white.

Stage 2

Over time, a region within the cloud becomes denser than its surroundings. At this point, gravity kicks in and the cloud starts to collapse in on itself.

A large, circular is in the centre against a black background. The circle is seemly made of swirls of yellow, pink, and white. There are three blue diagonal arrows all pointing towards the middle of the circle.

Stage 3

As the cloud shrinks, its centre (or core) becomes very hot and dense. The cloud will start to spin a little as it collapses, forming a disk.

A flattened, enlarged oval is in the centre against a black background. The shape is seemingly made of yellow and pink swirls. In its centre, there is a darker yellow circle and four blue diagonal arrows point towards this.

Stage 4

Eventually, the star's core becomes so hot and dense that nuclear fusion begins. This is the actual birth of the star.

Stage 5

The light, heat and particles produced by the new star blow away most of the remaining cloud.

A yellow circle, ringed in white, is at the centre against a black background. Four blue arrows point out form this to each upper and lower corner. They each point at a roughly circular blob colored in pale yellow and pink.

Stage 6

The star is left alone in space to slowly use up its nuclear fuel.

A yellow circle, ringed in white, is at the centre against a black background.

After several million or billion years, it runs out of fuel and goes through the final stages of its life.

What happens after Stellar Ignition?

The sudden burst of light made by a new star blows away much of the nearby gas cloud. However, it can leave enough material behind to form a number of planets.

After stellar ignition, the star becomes relatively stable. All the energy in a star is made in its centre (its core), by a process called nuclear fusion. The star releases the energy as heat and light. This is what makes a star shine.

The outward force generated by the fusion process is balanced by the inward pull of the star's gravity. It is the balance between the two which stops the star from collapsing or expanding.

An orange and yellow circle is in the centre. Inside this, in the middle, is the word "Fusion" in red with four red arrow pointing up, down, and outwards to either side of the edges of the circle. Around the circle there are blue diagonal arrows at the top and bottom left and right. The word "Gravity" also in blue, is beside them. All the arrows are the same size. — The outward force by fusion (red arrows) is balanced by the inwards force from gravity (blue arrows). Note how all the arrows are the same size.

But what if Stellar Ignition doesn't occur?

In that case, a brown dwarf might form!

Brown dwarfs are very dim, glowing objects. We think the temperatures and pressures deep within brown dwarfs were never high enough for nuclear fusion to start. In other words, they are too big to be a planet, but not massive enough to shine like a star. We sometimes call these failed stars 'sub-stellar objects'.

A large sphere is in the centre against a black background with small, white dots of stars scatted throughout. The sphere is mostly brown in colour, though has lines like bands across its surface that are glowing yellow in some parts. — Artist's impression of a Brown Dwarf

The first brown dwarf was discovered in 1995. Like other stars, they form from a cloud of dust and gas. However, unlike the Sun and other stars, they don't release energy by nuclear fusion. Instead, their glow comes from leftover heat.

Brown dwarfs are usually bigger than gas giant planets but smaller than the lowest-mass stars. They have masses between 12 to 75 times the mass of the planet Jupiter.

Most brown dwarfs are in orbit around a parent star. However, some have been found alone in the cosmos.

Part of

Star Formation

Star

Stars

Life Cycle of Stars

Gravity

Gravitation

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