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Giovanni Covone » 11.Stellar formation in the Orion Nebula


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).

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.

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).

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.

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.

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: M < 0.01 \, M_{\odot} Rate of mass loss: \frac{{\rm d} M}{{\rm d}t} > 10^{-7} \, M_{\odot}/{\rm year}

Therefore, proplyds should not survive longer than 10^5 years.

Proplyds population in the Orion Molecular Clouds.

HST image of the Trapezium Star Cluster. Credit: NASA.

HST image of the Trapezium Star Cluster. Credit: NASA.

Model of a proplyd. 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.

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 \sim 100 \, {\rm km/s} \,.

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.

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.

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.

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.

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)

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