What is radio astronomy? What is a pulsar?
Not only does our Sun provide the energy required for plants to photosynthesise, producing food and oxygen but the very atoms of carbon, oxygen and iron in our bodies were formed under the extreme conditions in the cores of earlier generations of stars. In this section we will explore the stages involved in the "lives" of stars and the physical processes that underpin them. Skip to main content. Australia Telescope National Facility. Very large, massive stars burn their fuel much faster than smaller stars and may only last a few hundred thousand years.
Smaller stars, however, will last for several billion years, because they burn their fuel much more slowly.
Eventually, however, the hydrogen fuel that powers the nuclear reactions within stars will begin to run out, and they will enter the final phases of their lifetime. Over time, they will expand, cool and change colour to become red giants. The path they follow beyond that depends on the mass of the star.
Small stars, like the Sun , will undergo a relatively peaceful and beautiful death that sees them pass through a planetary nebula phase to become a white dwarf , this eventually cools down over time leaving a brown dwarf. The Crab Nebula is a cloud created in a supernovae explosion observed by Chinese astronomers in AD. The Crab Nebula is expanding ever since. In the centre of this cloud is a pulsar, that is a Neutron Star rotating about 30 times per second. To create a Black Hole , the star core must have mass of more 2.
The matter just keeps on falling, creating a denser and denser object, until eventually it becomes a Black Hole.
However, there are other types of Black Holes. These have been found at the centre of galaxies.
Some SBHs create powerful jets called quasars. Artistic impression of a distant quasar in the early Universe. The surrounding dense gas, dust and even stars produce the brightness of the quasar when sucked into the SBH. The deposited matter at the surface of the White Dwarfs explodes.
Such an explosion is called a nova in Latin this means "new" , because it looks as if a new star appeared in the sky.
Life Cycle of a Star
About each year about tens of such novae are observed in the Milky Way alone. The star is bright for some days or weeks before it dims again. Recurrent novae were also observed, with repeat intervals of years or decades. Far away a star exploded as a type-I supernova. It is visible as the bright spot on the lower left, occurred in the outskirts of a galaxy Image source: NASA.
This is the second posibility: the White Dwarf can blow up in a gigantic explosion, called a type-I supernova. These supernovae can happen just as often and can be as bright as type-II supernovae: they can have the brightness of hundreds of billions of stars. What can remain after the death of a star? What factor makes the difference between the three outcomes above? The outcome depends on the mass of the star. When astronomers speak about the luminosity of a star, what they mean is the absolute magnitude , that is the real brightness of a star and not the apparent brightness that would depend on how far it is from us.
This is normally measured on a logarithmic scale with respect to our Sun: for example, if a star has a luminosity of 1, then it has the same brightness as our Sun. The colour of a star is related to its surface temperature: 'hotter' stars appear to be bluer than colder stars, which are reddish.
Neutron Stars consist only of neutrons and have a radii of only about 10 km. However, a Neutron Star it is so dense that just one teaspoon of their material has about 20 times the mass of the Great Pyramid of Giza. In fact, Neutron Stars are the densest objects we know of. A Black Hole is a part of space in which so much mass hence gravitation is concentrated that nothing - not even light - can escape from it. This is known as a singularity because all the matter is concentrated in one single point.
WMAP- Life and Death of Stars
As no light can escape it, black holes appear … black. However, they can be detected by observing the temperature increase of surrounding matter when it spirals and is swallowed by the Black Hole. These Black Holes usually have masses ranging from about 4 to 10 times the mass of the Sun.