Fast Facts About Star-Forming Regions of the Universe

Orion Nebula

 

Stars are born in nurseries with a collection of siblings that range in mass but share chemical compositions and dynamic histories. The natal environment containing a large number of “just-born” celestial objects is called a “Star Forming Region”. We find them scattered across the Milky Way primarily in the disk of the Galaxy.  In this article I review four fast facts of these critical components to propagating new generations of stars in the Universe.

Jackie Faherty, astrophysicist at the American Museum of Natural History and Editor at The Daily Galaxy.

 

Fast fact #1: Stars are born in families within star forming regions

A star forming region is created when a giant molecular cloud fragments into pre-stellar cores which ultimately become stars.   In order to make a star, you need an accumulation of gas and dust.  You can look around the plane of the Milky Way and find numerous spots of “dark nebula” or giant molecular clouds which are cold places that have accumulated thousands to upward of a million solar masses of gas and dust (see the molecular clouds post for details on this).  However you need energy to pass through those regions, causing a compression or heating that ultimately will ignite pockets into stars.  Galaxies are actually massive working machines, with things constantly in motion.  Shockwaves from volatile events (like Supernova explosions) will move through space and as they run into giant molecular clouds, they compress material which in turn heats up.  When fragments collapse under the force of gravity, their cores become hotter and hotter as you are pushing material closer and closer together.  Eventually the central regions of these protostars will arrive at a temperature that allows for nuclear burning.  At this point,  Hydrogen is converted into Helium and “a star is born” onto the stellar main sequence.  Within a star forming region, you don’t just get one star.  Depending on the size of the original molecular cloud and the amount of gas and dust, you will get hundreds to thousands of stars all anchored to each other by the same natal chemical environment.  Those stars can be considered family members and they will share a dynamic kinematic history as they move through the Galaxy.

Fast fact #2 The constellation Orion contains one of the closest and brightest star forming regions

The constellation of Orion is famous for its shape in the sky.  Three stars — named Mintaka, Alnilam and Alnita — map out the belt of the larger shape which many attribute looks like a Greek Huntsman named Orion.  At the north (the elbow of the Huntsman) is a red star named Betelgeuse and at the south (the knee of the Huntsman) is a blue star named Rigel.  When it comes to star formation, everything is centered around the belt.  That is where we find one of the closest and brightest molecular cloud complexes with star formation well underway.  The most famous portion of that complex is called the Oriona nebula cluster (ONC or also commonly known as Messier 42).  It is located more than 1300 light years away and can be spotted as a fuzzy colorful structure just south of the belt. Our best estimate of the age places it at just ~3 Myr which means it would not have been around when the dinosaurs roamed the Earth.   Scientists have focused on the ONC with every major astronomical observatory: the Hubble space telescope, the Spitzer space telescope, the Chandra observatory  in order to fully understand the process of star formation (see Proplyds discussion below).  

Fast fact #3 “Proplyds” — which are the precursors to planetary systems — are ionized protoplanetary disks around newborn stars and they have been mapped in exquisite detail in star forming regions

Newly born stars are compact and hot fragments of the gas and dust that was originally accumulating in a giant molecular cloud.  An important component of newly formed stars is that they are spinning (sometimes rapidly) and as such accumulate a disk of material around them called a protoplanetary disk.  Within that disk, planets, planetesimals, comets, and asteroids will all form.  Staring at a young stellar nursery like the Orion Nebula Cluster means we can catch that disk and the surrounding material in its infancy.  The Hubble Space Telescope has famously resolved numerous young stars in the ONC and mapped — in beautiful detail — tens of objects with their ionized protoplanetary disks or what we call proplyds.  While the material in the disks is relatively “dark”, the light from nearby and newly forming stars illuminates portions of them and allows astronomers to study the properties of the dust grains.  Given that these proplyds give way to solar systems, understanding their composition and relationship with the surrounding material is critical to theories of planetary formation.  

Fast fact #4 While star forming regions are beautiful to look at, they are sites of violent radiation from massive stars

Star forming regions are the source of Astronomy’s most brilliant imagery.  Massive structures of gas and dust are illuminated by bright and brilliant stars.  Rich colors can be used to showcase the excitation of elements like Hydrogen and Oxygen which are abundant in the stellar nursery.  However what is hidden in the beauty of the imagery is the massively violent state that these nurseries must take on in their youth.  Within the Orion Nebula for instance is a star called Theta 1 Orionis C.  This massive star (estimated at more than 30 times the mass of our Sun) has strong stellar winds and emits a large amount of ultraviolet radiation which spreads throughout the cluster.  Consequently it is “blowtorching” the more fragile environments that are forming around sibling, less massive stars.  For instance, the proplyds — which are described above as surrounding material around newly formed stars that ultimately lead to planetary systems — are captured in various states of destruction from the stellar winds of Theta 1 Orionis C.  It appears that it’s a matter of racing against the clock for these systems to build up enough structure so planets can form before the violent winds and radiation from massive stars evaporate all the material away.

Image credit: The Orion Nebula, located only 1,500 light years away from the solar system, is the brightest diffuse nebula is the night sky. This Canada-France-Hawaii Telescope image shows the 3-dimensional structure of this star formation region: a large cavity, created by the radiation pressure from new-born stars located in the brightest area of the image, lies within a huge cloud of dust and gas. Identified as an independent star cluster, NGC 1980 is associated with this well-studied star formation region, around the brightest star seen at the bottom of this image, iota Ori. The disks around the star are the result of internal light reflection in the camera optics. © CFHT/Coelum (J.-C. Cuillandre & G. Anselmi)

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