The Life of a Star
A picture from the Hubble Space telescope showing stars in various stages of . In the case where the degeneracy can't hold it up, you end up with a black .. Chart is courtesy of the American Association of Variable Star Observers (AAVSO ). It will show all the stages that a small star, and a massive star have to go through Masses range from a twentieth to over 50 solar masses and surface It shows that the temerature coincides with the luminosity, the hotter the star the Stage 9 - The remaining core (thats 80% of the original star) is now in its final stages. Mass decreases at the end stages of normal sized stars, and increases in the end sequences of giant stars, as they turn into a super dense ball.
So now these dying massive stars will be seen as either Red Supergiants or Blue Supergiants, depending upon how hot or cool they are. Due to their very large radius they also tend to be extremely luminous. How large can the radii get? Inastronomers discovered several red supergiants with radii that were much larger than that of Betelgeuse shown above - these stars had radii that are about times that of the Sun!
To see how big these stars actually are, just take a look here. Obviously with the outer layers so stretched out, the fusion going on deep in the core is not going to be visible to anyone. Even though stars like this look like they are in the last stages of their lives, we can only see what is going on at the surface, not what is actually happening in the core.
Of course the core is the interesting part! Eventually the core of the massive star will look like a giant onion, with the densest material in the middle and the lowest density stuff on the top. Each shell of the onion will have some small amount of fusion still going on, but the energy that is being produced at this point is pretty pathetic.
All sorts of elements have been burning, and now we come to the last element to burn, iron Fe. It sure does, but at a cost. Whereas previous fusion processes released energy, iron burning consumes energy.
The energy that should go into holding up the star instead goes into burning the iron. Is this a problem?
What is the relationship between mass and the end stages of stars lives
You bet your buttonhole it is! The iron fusion consumes energy, so there isn't enough energy to help support the star. Without support, gravity comes along and squeezes down the core. What happens when you squeeze stuff?Black Holes Explained – From Birth to Death
The iron core gets hotter and starts burning faster, which causes more energy to be sucked away, which removes more support against gravity, which causes the core to compress more and heat up more, which causes the iron to burn faster, which I think you get the picture. The collapsing process shrinks the core down to the size of the Earth. It gets very dense, up to the point of electron degeneracy remember, that's what a white dwarf is like.
Will the collapse stop? No, since the core is more massive than the Chandrasekhar limit the iron core is about 1. The mass of the core is too much for the Chandrasekhar limit, so electron degeneracy will not stop the collapse - it will keep going. Gravity keeps crushing the star down until it reaches the point where the pieces of atoms are crushed together. All of this compression and atomic mushing results in the core of the star ending up as a big ball of neutrons.
Neutron degeneracy is much more extreme than electron degeneracy - greater density, more extreme rules of physics and so forth. Because of the degeneracy, the star will not get any denser so long as the neutron degeneracy can hold it up. In the case where the degeneracy can't hold it up, you end up with a black hole - more on this later.
The core that ends up as a ball of neutron degenerate material is called a Neutron Star. This is a star so small and compact that a 1. Think of that - an object more massive than the Sun only the size of a large city! This is sort like the density you'd get if you took aircraft carriers and crush them down to the size of a sugar cube. Try putting that in a cup of tea!
What happens to the rest of the star? Remember, the neutron star core at this point is only a small part of the total mass, so you still have quite a few solar masses to watch out for that is located beyond the star's core. The core collapsed very quickly from a size close to that of the Sun's to only about 20 km, so there is a gap in the support of the rest of the star.
Nothing is holding up the rest of the star. This is sort of like when the Coyote runs off a cliff and doesn't immediately fall down - at least not until he realizes that he is off the cliff. The outer layers of the star don't really know that they have had their legs cut out from under them for a moment, but once they do - watch out. The upper layers will fall onto the ultra dense neutron degenerate core and the material will heat up to about 5 billion degrees.
This high temperature and the corresponding high pressure will generate an incredible amount of energy. The energy that is generated by the slamming of the outer layers on the core is huge. This energy that is produced here in this small interval of time is the same amount as that given off by the Sun over its entire lifetime 10 billion years.
This huge bottled up energy is released in a massive explosion that will blow off the outer layers - basically, the star explodes. That's how you produce a Supernova. This little animation shows a blue supergiant quickly collapsing down and then exploding as a supernova. What is a supernova like? Here are some of its main characteristics - The explosion blows away almost all of the mass of the star.
What is left behind may be only a few solar masses in size, though in the case of a black hole it can be larger. The core that is left over is in the form of a neutron star or a black hole. There is the release of a large amount of energy, so these things are very bright. A supernova produces the equivalent amount of energy as an entire galaxy billions of starsand it can stay bright for quite some time - weeks or months depending upon the distance.
There have even been supernovae that were visible in the daytime. The iron fusion and the huge amount of energy from the collapse of the star are so great that the fusion of even heavier elements occurs. All elements more massive than iron require huge amounts of energy to form, since like iron, their fusion processes consume energy. A supernova is the only thing that has energy to spare for the fusion of the heavy elements, so this is the only way that these things can be made.
All of the copper, zinc, nickel, gold, silver, mercury, and other elements up to uranium are produced in supernovae these include elements numbers 27 to 92 on the periodic table. The NuSTAR x-ray satellite has been studying the chemical distribution of material from a supernova that occurred only a few hundred years ago, some of this material is still radioactive.
During the formation of the neutron star there is the release of neutrinos, and at times these can be detected. Remember, there are neutrino detectors that are currently working to detect neutrinos from the Sun and these detectors are able to pick up supernova neutrinos as well.
A large shock wave is produced by the explosion. The shock wave can travel through space and can compress gas clouds, which will lead to new star formation. This can help explain why large scale star formation can continue on, since large stars die relatively quickly, usually near to the location where they were born.
If one dies in a supernova near the location of its formation near a Giant Molecular Cloudthe shock wave from the explosion can ignite new episodes of star formation in the GMC.
The death of one star can lead to the birth of many more. Recent observations by the Spitzer telescope appear to support this scenario, with a region of star formation found near a likely supernova - you can see a schematic of the event here.
Some people have even linked the explosion of supernovae to things on the Earth, such as climate changes or various large extinction events - but those are only theories. Massive stars are pretty rare, so on average there is only one supernova occurring in a galaxy every century. Now I'm going to complicate matters a bit. There are actually two main types of supernovae.
You may want to refresh your memory on the stuff about novae in the previous set of notes. If the white dwarf star in the binary system is really big close to 1.
There is also a theory that if you had two white dwarfs in a binary system and they collide, it will become a type I supernova. Either way, the white dwarf ends up being too massive and collapses in on itself. Since there are two vastly different kinds of supernovae - and they have to be distinguishable, and they are, mainly because the object that explodes in each case is very different massive star versus white dwarf.
To distinguish between the two types, the following designations are given Type Ia Supernova - a white dwarf going over the Chandrasekhar Limit Type II Supernova - a massive star collapsing and then exploding when iron fusion starts Figure 5. The light curves of the different types of supernovae are shown - note that the Type Ia supernovae are brighter.
Also, the rate at which they brighten and fade away is different. This helps astronomers distinguish the two types. This graph uses absolute magnitude as the brightness scale since the corresponding luminosity values are around a few billion solar luminosities.
The spectra of the different types of supernovae are shown. The Type Ia supernova has absorption the valleys and emission features the peaks associated with heavy elements, while the Type II has only hydrogen H and H showing up prominently in its spectrum.
You would have to know the distance to the supernova if you want to use the brightness as a way of categorizing it, so that isn't a good method. Fortunately it is possible to tell the two supernovae apart by looking at their spectra. The object that goes supernova is quite different in each case, so the spectrum from each type of supernova is distinct.
A white dwarf is the burned out core of a dead star, so it is made mainly of stuff like carbon, oxygen, nitrogen, etc. A massive star, on the other hand, is still mainly made of hydrogen, so when it explodes its spectrum will be full of hydrogen. The outer layers begin to expand, cool and shine less brightly. The expanding star is now called a Red Giant.
The star expands to a Red Giant, below Stage 8 - The helium core runs out, and the outer layers drift of away from the core as a gaseous shell, this gas that surrounds the core is called a Planetary Nebula. The core becomes a White Dwarf the star eventually cools and dims. When it stops shining, the now dead star is called a Black Dwarf. Some are 50x that of the Sun Stage 1 - Massive stars evolve in a simlar way to a small stars until it reaces its main sequence stage see small stars, stages The stars shine steadily until the hydrogen has fused to form helium it takes billions of years in a small star, but only millions in a massive star.
Stage 2 - The massive star then becomes a Red Supergiant and starts of with a helium core surrounded by a shell of cooling, expanding gas.
The massive star is much bigger in its expanding stage. Stage 3 - In the next million years a series of nuclear reactions occur forming different elements in shells around the iron core.
Stage 4 - The core collapses in less than a second, causing an explosion called a Supernova, in which a shock wave blows of the outer layers of the star. The actual supernova shines brighter than the entire galaxy for a short time.
- Large Mass Stellar Death
If the surviving core is between 1. If the core is much greater than 3 solar masses, the core contracts to become a Black Hole. So, it is not the mass of the core that is constant in stars, but the temperature of the core and that is around 15 million degrees Kelvin. Now, stars are born out of dense cores in molecular clouds. In general, bigger the mass of the dense core, the more massive the star that is born from it. This is simply because the star has more material to accrete from.
The radius of a star is determined by hydrostatic equilibrium which is the balance between the energy generation in the center of the star and gravity that tends to collapse the star. In more massive main sequence stars, there is more matter and the pressure in the core is more.
As a result and a couple of other detailsthe rate of fusion in massive stars is much more than in low mass stars.