Nebula
The life of a star starts out as a cold and dense interstellar cloud or interstellar nebula. The cloud needs to be dense enough to and cold enough so that gravity will overcome pressure. Interstellar clouds are made up of mostly of hydrogen and helium, with heavy elements present in significantly smaller amounts. The dense region in the nebula begins to shrink, warm up, and become a protostar.
Main Sequence Star
When the core of a protostar becomes hot enough to initiate nuclear fusion of hydrogen to helium, it becomes a star. A star at this stage (that of fusing hydrogen to helium in its core to produce energy) is called a “main sequence” star.
Low Mass Star:
Red Giant
When hydrogen at the core of a low-mass main sequence star is consumed, the star is no longer gravitational equilibrium , and the core of the star begins to shrink and its photosphere begins to expand. The material remaining in the core is helium which requires a higher temperature to burn. In this stage, nuclear fusion is not occurring in the low-mass stars core but occurs in a hydrogen shell around the helium core. During this stage, the total luminosity of the star increases. The energy rate production of the hydrogen burning shell is higher than that of the hydrogen burning core when the star was in the main sequence. In the red giant stage, the luminosity increases even though the surface temperature decreases.
Planetary Nebula
The stage where outer layers of low-mass star are ejected is called a "Planetary Nebula". The name of the stage comes from the fact that the outer layers of stars begin to form a cloud that looks like a planet with the hot core at its center.
White Dwarf
Once the ejected outer layers of the low-mass star become part of the interstellar medium, its
hot core is left behind and the low-mass star has entered in the White Dwarf stage. A white dwarf star
is the leftover core of a low-mass star. As the white dwarf emits radiation it’s cooling down. The white dwarf star was originally the core of a low-mass star, its surface temperature will tend to be much higher than that of a brown dwarf until equilibrium is achieved.
hot core is left behind and the low-mass star has entered in the White Dwarf stage. A white dwarf star
is the leftover core of a low-mass star. As the white dwarf emits radiation it’s cooling down. The white dwarf star was originally the core of a low-mass star, its surface temperature will tend to be much higher than that of a brown dwarf until equilibrium is achieved.
White Dwarf Cooling
After the white dwarf stage, the star cools and reddens.
Black Dwarf
A black dwarf is a white dwarf that has cooled down to the temperature of the cosmic microwave background, and so is invisible. Unlike red dwarfs, brown dwarfs, and white dwarfs, black dwarfs are entirely hypothetical. When a stat has become a white dwarf, it no longer has an internal source of heat and is only shining because it is still hot. A white dwarf will cool until its the same temperature as its surroundings.
High Mass Star:
Super Giant
When the hydrogen at the core of a high-mass main sequence star is consumed, the star is no
longer at gravitational equilibrium, and the core of the star begins to shrink and its photosphere begins
to expand. The material remaining in the core is helium, which requires a higher temperature to burn. In this stage, nuclear fusion is not occurring in the high-mass stars core but occurs in a hydrogen shell around the helium core. During this stage, the total luminosity of the star increases. The energy rate production of the hydrogen burning shell is higher than that of the hydrogen burning core when the star was in the main sequence. In the red giant stage, the luminosity increases even though the surface temperature decreases.
longer at gravitational equilibrium, and the core of the star begins to shrink and its photosphere begins
to expand. The material remaining in the core is helium, which requires a higher temperature to burn. In this stage, nuclear fusion is not occurring in the high-mass stars core but occurs in a hydrogen shell around the helium core. During this stage, the total luminosity of the star increases. The energy rate production of the hydrogen burning shell is higher than that of the hydrogen burning core when the star was in the main sequence. In the red giant stage, the luminosity increases even though the surface temperature decreases.
Supernova
The collapse of the stellar core to a size of just a few kilometers liberates an enormous amount of
energy that drives the outer layer of the star into space through a titanic explosion called a supernova. For about a week a supernova can emit at an energy rate equal to 10 billion Suns (about the same as a moderate size galaxy). The ejected outer layers may remain visible for thousands of years and are called a “supernova remnant”. These outer layers of the star ejected into space contain heavy elements and will eventually become part of the interstellar medium. Depending on the amount of mass in the star’s core, once the outer layers of the high-mass star have been ejected, the leftover core will become either a neutron star or a black hole.
energy that drives the outer layer of the star into space through a titanic explosion called a supernova. For about a week a supernova can emit at an energy rate equal to 10 billion Suns (about the same as a moderate size galaxy). The ejected outer layers may remain visible for thousands of years and are called a “supernova remnant”. These outer layers of the star ejected into space contain heavy elements and will eventually become part of the interstellar medium. Depending on the amount of mass in the star’s core, once the outer layers of the high-mass star have been ejected, the leftover core will become either a neutron star or a black hole.
Neutron Star
If the leftover core of the high-mass store is stopped from collapsing by balancing gravitational
forces with neutron degeneracy pressure, the star will have become a neutron star. It will have a
mass comparable to the Sun but with a size of just a few kilometers. Most neutron stars are detected as pulsars. Pulsars emit radio pulses at fixed intervals as small as a few milliseconds. Pulsars achieve these rapid rotation rates through the conservation of angular momentum of the iron core of a high-mass star as it collapses into a neutron star.
forces with neutron degeneracy pressure, the star will have become a neutron star. It will have a
mass comparable to the Sun but with a size of just a few kilometers. Most neutron stars are detected as pulsars. Pulsars emit radio pulses at fixed intervals as small as a few milliseconds. Pulsars achieve these rapid rotation rates through the conservation of angular momentum of the iron core of a high-mass star as it collapses into a neutron star.
Black Hole
If the mass of the leftover core of a high mass star is greater than about 3 Msun, then neutron
degeneracy pressure cannot stop the gravitational collapse. Nor is there any known physical force
capable of stopping the collapse. In this case, the core would collapse into a black hole.
A black hole is an object with a gravitational field so strong that not even light can escape it,
thus the name “black hole”.
degeneracy pressure cannot stop the gravitational collapse. Nor is there any known physical force
capable of stopping the collapse. In this case, the core would collapse into a black hole.
A black hole is an object with a gravitational field so strong that not even light can escape it,
thus the name “black hole”.