The Anatomy of a Stellar Nursery

The Anatomy of a Stellar Nursery

Introducing the Rosette Nebula / Stellar Nursery When I first started to image stellar nurseries, I really didn’t know anything about them.  I was told that stars are being born there – that is pretty awesome, but I was curious what was it about these light generating molecular clouds (MCs) that made them prolific star builders.   Sure, stars are also created in turbulent dark molecular clouds, but stellar nurseries really churn out the stars at a much higher level – often creating whole open clusters of stars.   Many of the stellar nurseries get very large and can even be mapped from their Halpha light signal in other galaxies.   Ok, so my interest was piqued – I had to figure out

Star Nucleation Amped Up by Tidal Effects

Star Nucleation Amped Up by Tidal Effects

Spiral galaxies can vary widely in the amount of stars they are generating. It is asserted that star nucleation, via the imposition of high pressure over small volumes of molecular cloud, is the rate determining step. Turbulence of molecular clouds in galaxies is greatly increased when the chaotic, but stable, spiral galactic structure is disturbed by tidal effects of nearby galaxies. In this posting, the three main galaxies of the Leo triplet are used to illustrate and link the chain of events from tidal influence to rapid star production in the galaxies we image.

Fueling up a New Star – Gravity vs Angular Momentum

Fueling up a New Star – Gravity vs Angular Momentum

In order to grow, a nucleated (condensed), cold star core must accumulate hydrogen as future mass and fuel before igniting to fusion and becoming a full fledged shining star. But there is a problem in the way. Just as the sun cannot accumulate planets via gravity, without some mechanism to shed angular momentum, hydrogen will just orbit the baby star and not accumulate upon it. Viscous drag both dissipates angular momentum and allows hydrogen molecules to accumulate by spiraling down to the star. Unlike a planetary orbit, in a spiral gravity, angular momentum, and viscous drag (friction) are not orthogonal to one another, allowing friction to dissipate momentum as the gravitational fall increases it. Upon arrival at the star, there remains a lot of angular momentum that still need dissipating. Compressed, hot hydrogen forms a metallic core on the star where it creates an electromagnetic magneto – a sort of electric motor. The magneto converts angular momentum into linear momentum that squirts out as jets from the poles. Both mechanisms allow hydrogen to accumulate without spinning the young protostar to death. The jets also advertise to us that star formation is going on and results in beautiful images.

More than Dust in the Wind

More than Dust in the Wind

There is no deny that the dark nebula, LDN 534, makes an interesting target for astrophotography. It has all the earmarks of sky clouds being transformed by the wind. In fact it is likely a section of molecular cloud ripped out of the spiral arms, and being eroded by the winds of ISM. Unlike star fields that appear like foggy light that gets more disperse as concentration drops, the eroded molecular cloud seems to be much more wispy and reluctant to yield its integrity. Undoubtedly the hydrogen molecules do yield to the wind, disassociating to become atoms while the dust gets dispersed. We are lucky in this one, as a few stars make some nice blue reflections. In other cases, the eroded molecular cloud forms very coincidental shapes – included some naturally streamlined ones.

A Rotting Fish tells no tails

A Rotting Fish tells no tails

In this website’s second look at the Rotten Fish dark nebula, I wanted to bring home the concenpts involved in star nucleation. In case you were wondering, the answer is yes, star formation can happen in clouds not emitting Halpha light, even though we can certainly assiciate Haspha with star cluster / stellar nurseries. The answer lies in the mechanism of pressure buildup at points allowing diatomic molecular hydrogen and dust to nucleate a star. In both cases, dust provides the necessary cold temperature in addition to critical point temperature suppression. However, in the case of a dark cloud, the pressures required to nucleation is based on cloud turbulence alone, while stellar nursery clouds are aided in pressure build-up by stellar winds. It seems from images, that star formation in clouds is much more sporadic, while star clusters are more likely to be formed in stellar nurseries shining in Halpha light.

The Cave Nebula and Hydrogen’s Journey

The Cave Nebula and Hydrogen’s Journey

One cannot understand the creation of stars from molecular hydrogen clouds any more than one can understand the weather here on earth without reference to thermodynamics. The weather is largely driven by water in gaseous (vapour), liquid (rain, clouds) and solid (snow, ice and ice crystals) forms. Knowing the pressures and temperatures at which these physical phase states occur is fundamental for both water in its role of creating weather, and for hydrogen in its role of creating both stars and the galaxy itself. Every atom and molecule of hydrogen must undergo and piecewise continuous journey through its phase/space – there is no leaping allowed, and the conditions must exist somewhere in a system for phase transitions to occur.
In our description of galaxies, we discuss the atomic and molecular phase states of hydrogen, but here we illustrate and explain the rest of the phase/state journey that hydrogen, at least at the nucleus of a star, must undergo to enable star formation. This is a journey from molecular gas all the way to becoming a hot, molten, liquid metal.