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.

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.

Stars are born – Have a Cigar

Stars are born – Have a Cigar

In an everyday spiral galaxy (ho hum?), every effort is made by the galaxy itself to minimize the amount of energy wasted on forming turbulence of dust and hydrogen. As a result, areas of intense star formation in a regular spiral is usually restricted to a discrete points along the spiral arms where ISM and molecular cloud rub against each other to create the turbulence. These limited areas of star formation are seen as patches of bright red Halpha emissions. In this image of the Cigar Galaxy, it is evident that something has thrown “a wrench/spanner into the works” and created a hell of lot of turbulence, resulting in a fireworks display of red Halpha. When this occurs, stars are created at a very high rate and we reclassify such galaxies as “starburst” glaxies and the Cigar is one of them. Still, the original stars and dust lanes of this once regular spiral can be made out.

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.

Swirls, Eddies, and Star Nucleation in Molecular Clouds

Swirls, Eddies, and Star Nucleation in Molecular Clouds

The popular notion that stars are created by the spontaneous, adiabatic collapse of molecular clouds is challenged. Instead, a more physically realistic model of protostar nucleation through hydrogen/dust condensation is proposed here (and in other postings) on this website) as well as by many other astronomers and astrophyscists elsewhere. Thermodynamics dictate that such condensation requires relatively cold and places within the cloud enable such condensation coupled with possible dew/sublimation point elevation. The high pressures required is likely provides by turbulence – both viscous and electromagnetic as evidenced by independent simulations. We can also see that for ourselves in our images of molecular clouds.