From molecular clouds to stars

Amaury Thiabaud – M2 A2P – 14/11/2011

From molecular clouds to stars Amaury Thiabaud - English M2 A2P 2

In this talk…IntroductionRequirements : molecular clouds

CollapseNuclear fire : a star is born

Conclusion

1) Requirements : molecular clouds

2) Collapse

3) Nuclear Fire : a star is born

In this talk…

From molecular clouds to stars Amaury Thiabaud - English M2 A2P 3

What’s needed to form a star ?Why do molecular clouds fulfill these requirements ?

IntroductionRequirements : molecular clouds

CollapseNuclear fire : a star is born

Conclusion

What’s needed to form a star ?

abundant matter : H2, H, He

dense regions

compact regions

What’s needed to form a star ?Why do molecular clouds fulfill these requirements ?

IntroductionRequirements : molecular clouds

CollapseNuclear fire : a star is born

Conclusion

Why do molecular clouds fulfill these requirements ?

From molecular clouds to stars Amaury Thiabaud - English M2 A2P 4

Enough hydrogen : nH ~ 1000 cm-3

One of the most dense object in the Universe

Can be compacted if something breaks its equilibrium :

• shock waves

• encounters with another MC

Formation of a gaseous ringInfluence of magnetic fieldGas fragmentation

IntroductionRequirements : molecular clouds

CollapseNuclear fire : a star is born

Conclusion

Formation of a gaseous ring

From molecular clouds to stars Amaury Thiabaud - English M2 A2P 5

Basic principle : conservation of angular momentum

• rotating object must adjust its speed to its dimensions

• collapsing causes an acceleration centrifugal force spread

Doughnut formation

Formation of a gaseous ringInfluence of magnetic fieldGas fragmentation

IntroductionRequirements : molecular clouds

CollapseNuclear fire : a star is born

Conclusion

Influence of magnetic field

From molecular clouds to stars Amaury Thiabaud - English M2 A2P 6

Everywhere in the Galaxy, but weak

Trapped in the clouds

Contraction increases the magnetic field :

• acts on the ions

• decelerates the gaseous ring

Formation of a gaseous ringInfluence of magnetic fieldGas fragmentation

IntroductionRequirements : molecular clouds

CollapseNuclear fire : a star is born

Conclusion

Gas fragmentation

From molecular clouds to stars Amaury Thiabaud - English M2 A2P 7

Sufficient speed to « explode »

Each resulting fragment takes some angular momentum

A new collapse can happen in this « core »

And so on, until the angular momentum is no longer an obstacle

Proto-starT. Tauri starA new star

IntroductionRequirements : molecular clouds

CollapseNuclear fire : a star is born

Conclusion

Proto-star

From molecular clouds to stars Amaury Thiabaud - English M2 A2P 8

Matter goes in the center of the doughnut, center is growing

This forms a proto-star :

• compression high pressure high temperatures

Around proto-star : proto-planetary disk, « eaten » by energy released

Transparency light can be seen

Proto-starT. Tauri starA new star

IntroductionRequirements : molecular clouds

CollapseNuclear fire : a star is born

Conclusion

T. Tauri star

From molecular clouds to stars Amaury Thiabaud - English M2 A2P 9

Such a star is known as T. Tauri star

Gas contraction : only energy source

Unstable object. Eventually stabilises when contraction ceases

Proto-starT. Tauri starA new star

IntroductionRequirements : molecular clouds

CollapseNuclear fire : a star is born

Conclusion

A new star

From molecular clouds to stars Amaury Thiabaud - English M2 A2P 10

When gravitation = pressure

No more production of energy from the collapse

H fusion prevents the star from cooling too fast

Proto-planetary disk can form planets planetary system

IntroductionRequirements : molecular clouds

CollapseNuclear fire : a star is born

Conclusion

Conclusion

From molecular clouds to stars Amaury Thiabaud - English M2 A2P 11

Thank you for your attention !