Molecular clouds contain abundant hydrogen and helium and can become dense enough to collapse under gravity. The collapse forms a rotating gas disk and fragments into cores that further collapse to form protostars. Protostars heat up and stabilize as new stars once hydrogen fusion counters gravitational pressure to form a long-lasting star. The star is then surrounded by a proto-planetary disk that may form planets, completing the process from molecular cloud to star system.

1. From molecular clouds to stars Amaury Thiabaud – M2 A2P – 14/11/2011

2. 1) Requirements : molecular clouds 2) Collapse 3) Nuclear Fire : a star is born From molecular clouds to stars Amaury Thiabaud - English M2 A2P 2 In this talk… Introduction Requirements : molecular clouds Collapse Nuclear fire : a star is born Conclusion In this talk…

3. 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 ? Introduction Requirements : molecular clouds Collapse Nuclear fire : a star is born Conclusion What’s needed to form a star ? abundant matter : H 2 , H, He dense regions compact regions

4. What’s needed to form a star ? Why do molecular clouds fulfill these requirements ? Introduction Requirements : molecular clouds Collapse Nuclear 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 : n H ~ 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

5. Formation of a gaseous ring Influence of magnetic field Gas fragmentation Introduction Requirements : molecular clouds Collapse Nuclear 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

6. Formation of a gaseous ring Influence of magnetic field Gas fragmentation Introduction Requirements : molecular clouds Collapse Nuclear 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

7. Formation of a gaseous ring Influence of magnetic field Gas fragmentation Introduction Requirements : molecular clouds Collapse Nuclear 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

8. Proto-star T. Tauri star A new star Introduction Requirements : molecular clouds Collapse Nuclear 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

9. Proto-star T. Tauri star A new star Introduction Requirements : molecular clouds Collapse Nuclear 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

10. Proto-star T. Tauri star A new star Introduction Requirements : molecular clouds Collapse Nuclear 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

11. Introduction Requirements : molecular clouds Collapse Nuclear fire : a star is born Conclusion Conclusion From molecular clouds to stars Amaury Thiabaud - English M2 A2P 11

12. Thank you for your a ttention !