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.
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.
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.
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.
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)
Progetto "Campus Virtuale" dell'Università degli Studi di Napoli Federico II, realizzato con il cofinanziamento dell'Unione europea. Asse V - Società dell'informazione - Obiettivo Operativo 5.1 e-Government ed e-Inclusion
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