Stars form within dense molecular clouds inside galaxies.
These clouds of gas and dust obscure the first stages of stellar formation
through optical telescopes. Fortunately current advances in radio and infrared
astronomy now permit astronomers to peer within these clouds and gain a better
understanding of the processes involved in starbirth. Computationally intensive
computer simulations also permit them to model the processes and test the
results against observations.
Gravity is actually the force in charge of stellar formation
and the mass of material which forms at star mostly determines its life and
The Interstellar Medium & Nebulae
Nebulae are merely clouds of interstellar dust and gas and
show up either as dark areas blotting out background stars the so-called dark
or absorption nebulae or as brighter clouds of gas that give off or reflect
light. They are the most noticeable components of the interstellar medium.
The Interstellar Medium
Regardless of what you might think, space is not an ideal vacuum.
The room between the stars is loaded with a tenuous array of material that
gives the foundations of stars. This material is dust and gas and collectively
is called the interstellar medium (ISM). The ISM gas is mostly hydrogen whilst
the dust is approximately 1% by mass and contains carbon compounds and
silicates. Dust is in charge of the interstellar reddening and extinction of
starlight. The harder of the ISM a star's light moves through on its way to an
observer on Earth the greater it gets scattered and absorbed, reducing the
star's apparent brightness and reddening its look.
Properties of the ISM vary widely based upon its location
inside a galaxy. At its most tenuous, in hot areas between denser clouds, it
may possess a density of only 100 particles for each cubic metre, mainly
ionized hydrogen atoms. In the interior regions of shells of gas encircling
stars the density can be up to 1017 particles for each m3 although this is
still a million times less dense compared to a normal vacuum on Earth.
Stages of Star Formation
Stars are hot bodies of glowing gas that begin their life in
Nebulae. They differ in mass, size and temperature, diameters varying from 450x
smaller to over 1000x bigger than that of the Sun. Masses vary from a twentieth
to over 50 solar masses and surface temperature can vary from 3,000 degrees
Celcius to over 50,000 degrees Celcius.
The colour of a star is based on its temperature, the
coolest stars are red and the hottest stars are blue. The Sun features a
surface temperature of 5,500 degrees Celcius, its colour looks yellow.
Small stars possess a mass approximately one and a half times that of the
Stage 1: Stars
are born in an area of high density Nebula and condenses into a massive globule
of gas and dust and contracts under its own gravity.
Stage 2: An area
of condensing matter will start to heat up and begin to glow building
Protostars. If a protostar contains sufficient matter the central temperature
gets to 15 million degrees centigrade.
Stage 3: At this
temperature, nuclear reactions where hydrogen fuses to make helium can start.
Stage 4: The star
starts to release energy, preventing it from contracting even more and causes
it to shine. It is now a Primary Sequence Star.
Stage 5: A star
of a single solar mass stays in main sequence for around 10 billion years, till
all of the hydrogen has fused to make helium.
Stage 6: The
helium core now begins to contract further and reactions begin to take place in
a shell across the core.
Stage 7: The core
is hot sufficient for the helium to fuse to make carbon. The outer layers start
to expand, cool and shine less brightly. The expanding star is now referred to
as a Red Giant.
Stage 8: The
helium core runs out and the outer layers drift of far from the core as a
gaseous shell, this gas that encompasses the core is known as a Planetary
Stage 9: The rest
of the core (thats 80% of the original star) is now in its last stages. The
core turns into a White Dwarf the star at some point cools and dims. When it
stops shining, the now dead star is referred to as a Black Dwarf.
Massive stars possess a mass 3x times that of the Sun. A few are 50x that
of the Sun
Stage 1: Massive
stars evolve in a simlar way to a tiny stars until it reaces its primary
sequence stage. The stars shine steadily until the hydrogen has fused to create
helium ( it takes billions of years in a small star, however only millions in a
Stage 2: The
massive star then turns into a Red Supergiant and starts of with a helium core
encircled by a shell of cooling, expanding gas.
Stage 3: In the
next million years a number of nuclear reactions take place forming various
elements in shells across the iron core.
Stage 4: The core
collapses in less than a second, leading to an explosion known as a Supernova,
where a shock wave blows of the outer layers of the star. (The actual supernova
shines brighter than the whole galaxy for a short time).
Occasionally the core survives the explosion.
If the surviving core is between 1.5 - 3 solar masses it contracts to turn into
a tiny, very dense Neutron Star. If the core is much more than 3 solar masses,
the core contracts to become a Black Hole.