Evolution of Stars Flashcards
Demonstrate an understanding that emission nebulae, absorption nebulae and open clusters are associated with the birth of stars.
Emission nebulae
Stars inside or near the nebulae warm the gas by ultraviolet radiation. This causes electrons in the gas to ionize and then emit radiation which we see as light and radio waves. Hydrogen is the most common element and this produces a red colour.
Absorption nebulae
Stars inside or near the nebulae warm the gas by ultraviolet radiation.
This causes electrons in the gas to ionize and then emit radiation which we see as light and radio waves. Hydrogen is the most common element and this produces a red colour.
Demonstrate an understanding that planetary nebulae are associated with the death of stars.
Planetary Nebula is a misleading name. Originally they were thought to be a region around a star where planets would form. This is not the case, quite the opposite in fact.
When a red giant expels its outer layers before becoming a white dwarf or neutron star, the layers become a thin sheet of gas around the remains.
Their shape and colour depend on the size, composition of the Sun and its direction to us from Earth. Planetary Nebula can range from the width of the Solar System to more than a light year wide.
There are many good examples of planetary nebulae, some are beautiful, some are eerie and some are quite funny such as the Clownface Nebula in Gemini.
Supernova remnants are similar to planetary nebulae only caused by a supernova and usually more cataclysmic in appearance.
Demonstrate an understanding supernovae are associated with the death of stars.
A supernova is the brightest event in space. There are two types of supernova:
- Similar to a nova where a dwarf takes material from a giant. This time the explosion destroys the dwarf. Typically this takes place when the mass of the white dwarf is over 1.4 solar masses.
- When a star has a mass greater than 8 solar masses. The red giant swells so much it collapses in on itself. These are dramatic events as once they explode the core forms a neutron star or a black hole.
Describe the nature of neutron stars.
A star between 4 and 25 solar masses will grow to a red super giant and explode as a supernova, leaving a neutron star smaller than the size of Earth.
These stars are compressed so much that they are composed entirely of neutrons, parts of the atom without electrical charge.
This is the equivalent of the size of the Sun in the same area as a city or the human population on Earth fitting inside an area the size of a sugar cube.
Describe the nature of black holes.
When a very large star explodes, the mass condenses so much that is collapses in on itself. The gravity is still present.
It appears to pull in any material in the vicinity. Once matter goes past the boundary of a black hole (called the event horizon) it cannot escape back out again; not even light can escape which travels at 300,000 kilometres a second.
Describe how astronomers obtain evidence for the existence of neutron stars.
Neutron stars rotate rapidly after formation, typically spinning between fractions of a second and half a minute. We can detect this because they emit radio pulses, and the ones we detect are known as pulsars. Radio astronomy has also detected brightness and temperature from neutron stars, and astronomers have used x-ray astronomy to detect them when matter from companion stars falls onto neutron stars.
Describe how astronomers obtain evidence for the existence of black holes.
Evidence from black holes comes from binary stars that get their solar material pulled into the hole. This often forms an accretion disc of matter circling the area. It orbits so fast it is hot enough to give off x-rays which we can measure.
