The ISM systems in Orion
The Giant Molecular Cloud in Orion.
The whole system includes:
- emission nebulae M42 and M43,
- dark nebula Horsehead,
- reflection nebula NGC 1977,
- the Trapezium Star Cluster,
- The Barnard Loop.
The complex structure of ISM systems in Orion. Credit: Rogelio Bernal Andreo (DeepSkyColors.com).
Orion seen by IRAS
The complex structure of ISM systems in Orion seen by IRAS. Credit: The Infrared Legacy Gallery.
Barnard’ Loop
Orion GMC is dominated by the Barnard’s Loop, an emission nebula centered approximately on the Orion Nebula.
Distance: 1600 light years.
Size: 600 arcminutes (about 300 light years).
Likely originated in a supernova explosion (about 2 million years ago).
Alternative hypothesis: the winds from bright Orion stars.
A wide view of the Barnard's Loop. Credit: Hunter Wilson (Wikimedia Commons).
M42 in the optical and near-infrared light
Infrared/visible comparison of the Orion Nebula. Credit: ESO/J. Emerson/VISTA & R. Gendler.
Inside the Orion Nebula: Trapezium Cluster
High-resolution images of the region around the Trapezium Star Cluster. Credit: NASA/ESO.
“Proplyds” in the Trapezium Cluster
What is a “proplyd”.
A protoplanetary: is a rotating circumstellar disk of dense gas surrounding a young newly formed star.
Formation of “proplyds”.
Typical mass: 
Rate of mass loss: 
Therefore, proplyds should not survive longer than 
years.
Proplyds population in the Orion Molecular Clouds.
HST image of the Trapezium Star Cluster. Credit: NASA.
Model of a proplyd. Credit: NASA.
Proplyds in the Orion Nebula
Distribution of proplyds in the central region of M42. Credit: NASA/HST.
Herbig-Haro objects
Small emission regions located near the end of high velocity jet-like outflows from young stellar objects.
Formed when gas ejected by young stars collides with clouds of gas and dust nearby at speeds of 
Shocked gas: the material in the jet is stopped by the ISM.
They are found in star-forming regions, usually seen around a single star, aligned along its rotational axis.
Mass and temperature.
Diagram of an Herbig-Haro objects, showin the accrredtion disk and the polar jets. Credit: Wikimedia Commons.
The Herbig-Haro object 47
Hubble Space Telescope image of the Herbig-Haro object 47. Credit: NASA/HST.
Time evolution of HH 47
Movie obtained by combing Hubble Space Telescope images since 1994. Credit: NASA.
Herbig-Haro object 901
High-resolution images of the HH 901 in the Carina Nebula. Credit: NASA/HST.
What we learned from Orion
Best studied star-forming region in the sky.
- On the detailed structure of molecular clouds.
- Propagation of star-formation.
- Accretion disk around new stars.
- Universal Inital Mass Function.
- Transient clusters of young stars.
- Superbubbles created by massive stars.
- On the formation of massive stars.
- On the formation time-scale of stars and associations.
- Measurements of star-formation efficiency.
Le lezioni del Corso
1. Introduction to the study of the physics of the interstellar medium
2. A census of systems in the Interstellar Medium
3. A census of systems in the Interstellar Medium, part 2
4. Matter components of the ISM
5. Equilibrium configurations the ISM
9. Properties of the interstellar dust
10. Ionized systems in the ISM: Warm ionized medium and …
11. Stellar formation in the Orion Nebula
12. Introduction to the study of the intracluster medium
I materiali di supporto della lezione
C.F. McKee & E. C. Ostriker, “Theory of Star Formation”, in Annual Review of Astronomy & Astrophysics (2007)
E.M. Huff & S.W. Stahler, “Star formation in space and time: the Orion Nebula Cluster”, The Astrophysical Journal 644, 355 (2006)
Il Podcast della lezione
Le altre lezioni del corso con podcast
1. Introduction to the study of the physics of the interstellar medium
2. A census of systems in the Interstellar Medium
3. A census of systems in the Interstellar Medium, part 2
4. Matter components of the ISM
5. Equilibrium configurations the ISM
9. Properties of the interstellar dust
10. Ionized systems in the ISM: Warm ionized medium and …
11. Stellar formation in the Orion Nebula
12. Introduction to the study of the intracluster medium
13. The intergalactic medium - first part
14. The intergalactic medium - part second
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