The numbers
- Where they are born
- In clouds of gas and dustBetween one star and the next
- Who does the work
- GravityWhich gathers and squeezes the gas
- When it lights up
- When the heart is hot enoughAnd fusion begins
How it happens, step by step
A cold cloud
In the space between the stars there is a cloud of gas and dust, dark and freezing, many light-years across.
Something stirs it
A shock wave or a passing arm of the galaxy makes it ripple, and in some places the gas gets thicker.
The clumps grow
Each thicker spot pulls in more gas, and the more gas it pulls in, the thicker it gets. It feeds itself.
The center heats
At the center of the clump the matter is squeezed, and a squeezed gas heats up. The ball gets hotter and hotter.
It lights up
At the right temperature the nuclei fuse, the push outward stops the collapse, and it is a star.
To get an idea
The thicker a clump of gas gets, the more gas it pulls in: once it has started, the process feeds itself.
The star lights up when its heart gets hot enough for the nuclei to fuse.
Fun facts
These are not in the book: there was no room on paper.
A gas that gets squeezed heats up, and that is why the heart of the clump gets scorching hot.
Before it lights up, the future star glows faintly with the heat of its own fall.
From the same cloud, many stars are almost always born together, not just one.
The material left over around the new star can form its planets.
Molecular clouds are exactly the nebulae where stars are forming right now.
The biggest stars form faster than the small ones, and they die much sooner.
Test yourself
The first question is the one printed under the QR code, with the answer the book did not give. The other four only exist here.
Question 1 of 5★ is the one from your book
Where are stars born?
Question 2 of 5
What starts the process?
Question 3 of 5
Why does the center of the clump heat up?
Question 4 of 5
When does the clump really become a star?
Question 5 of 5
Are stars still being born?
Riddles
Before I really shine, I shine for pretend, with the heat of my own fall. I become real only when my heart reaches the right temperature. What am I?
The thicker I get, the more I pull in, and the more I pull in, the thicker I get: once I have started there is no way to stop me. What am I?
Try it yourself
Pump air into a bike tire and touch the pump: it has warmed up. Squeezing a gas heats it, and that is the engine that lights up stars.
Pour metal pellets onto a stretched sheet: they gather in the dip, and the more gather, the deeper the dip gets. That is gravity making clumps.
The words
- shock wave
- A front of squeezed gas that travels fast after an explosion.
Sources: Wikidata (Q1069303), Wikipedia (Formazione stellare).