The Life Cycle of a Star and the development of Black Holes

Charles Sturt University SCI102

Jake Brogden 11549961

IntroductionFor most part of human history, it has beenbelieved that the earth was the centre of the ‘Celestial Sphere’, with the stars stuck to the inside of the sphere.(Strous, n.d.)

On right (Fig 1): A ‘Celestial Sphere’ model. Retrieved 2nd June 2014, from; Spaceanswers, (n.d.).

(Fig. 1)

Introduction continued…• It is now known that the brightness of a star will depend

on a number of factors. These include; the size and brightness of the star and also the distance away the sun is from the viewing point (Earth). When stars are farther away from Earth then they will appear dull. However if a star is closer to earth it will appear brighter (IPAC, n.d.).

• Stars also appear to ‘twinkle’ in the night sky. This is result of the turbulence within our atmosphere. As the atmosphere moves, the light travelling from the star will refract in all different directions, giving the illusion of a twinkling star (University, C. 2002, November 6).

Introduction Continued…

• This however is not the case for planets which can be observed from Earth. Planets do not twinkle like stars . Stars are so far away that all we can observe is a point of light in the sky. Hence light will refract once exposed to our atmosphere. Planets are closer and are actually a quantitative size (which is very small), inturn giving a more stable image because it is not affected by the Earths atmosphere (University, C. 2002, November 6).

What is a Star?

• Stars are essentially giant balls of exploding gas, which mainly consists of hydrogen and helium. The nearest star to Earth, the Sun, is constantly exploding in a nuclear reaction with the element hydrogen, which makes the explosion similar to a hydrogen bomb. These nuclear reactions are constantly releasing energy into the universe, along with solar winds and solar flares (QRG, n.d.). The only protection the earth has from the solar winds and flares is the magnetic field surrounding the Earth (Association, N. E. (n.d.).

What is a Star? Continued…

Scientists believe that the core of the sun consists of a 15 million degree Celsius plasma. This plasma contains electrons and protons which have been stripped from hydrogen atoms. These protons are constantly colliding with other protons which produces a helium nuclei in a nuclear fusion Reaction, that releases energy into the universe. The plasma makes up 90 per cent of a Star (QRG, n.d.).

Life cycle of a Star

• -Nebula• -Star• -Red Giant• -Red Dwarf• -White Dwarf• -Supernova• -Neutron Star• -Black Hole

(Fig. 2)

Above (Fig. 2): Diagram of the Life cycle of a Star. Retrieved 25th May 2014, from; NASA, forwarded by; Observatory, N. S. (n.d.).

Nebula

• A Nebula is a cloud of gas (hydrogen) and dust in space. A Star will form from the Nebula, as it is the birthplace of a Star (Telescope, n.d.).

Above (Fig. 3): The Helix Nebula, Retrieved 1st June, 2014, from; NASA, 2012.

(Fig. 3)

Star• A Star is a luminous globe of gas that produces its own heat

and light by nuclear reactions (fusion). A Star consists of hydrogen and helium which creates a surface temperature ranging between 2000°C to above 30,000 °C. The different �range of temperature will create different corresponding colours from red to blue-white (Telescope, n.d.). A cooler temperature star will radiate most of it’s energy in the form of infrared radiation. Infrared radiation lands on the red region of the electromagnetic spectrum and thus a cooler temperature Star will appear red in colour. However, a hot star will emit mostly ultra-violet wavelengths, making them appear blue or white (Mutlaq, J. n.d.).

Red Giant

• This is a large bright star with a cool surface temperature. It is formed during the later stages of the evolution of a star. At this stage of its evolution it will run out of ‘fuel’, which is in the form of hydrogen. This is situated in the star’s centre. Red Giants are very bright because they are so large, however their surface temperature is lower than that of our Sun, about 2000-3000° C (Telescope, n.d.). �Very large stars (Red Giants) are often called Super Giants.

Red Dwarf

• A Red Dwarf star is approximately one tenth the mass and diameter of our Sun. A Red Dwarf is a smaller and cooler temperature star which is not as bright as other stars. Red Dwarf Stars have an estimated lifespan of 100 billion years. This is because a Red Dwarf will burn its fuel much slower as it is much smaller and cooler than other Stars (Telescope, n.d.).

White Dwarf

• This is very small star which is extremely hot. Hence the White Dwarf will appear white in colour. This is the last stage in the life cycle of a star (Telescope, n.d.).

Supernova• A Supernova is the explosive death of a star, that often results in the star obtaining

the brightness of 100 million suns for a short time. There are two main types of Supernova which will occur:-

• Type I - The fist type of Supernova will occur in binary star systems. As a result the gas from one star will fall on to a white dwarf, inturn causing it to explode (Telescope, n.d.).

• Type II The second type will occur in stars which are ten times larger than our own star. These are known as Super-Giant Stars. When the Stars nuclear fuel is exhausted the iron core will collapse and then rebound, creating a massive explosion (Mattson, D. B. 2011, January). (Fig. 4)

On right (Fig. 4): Supernova; Image captured by infrared and X-ray imaging. Retrieved 1st June, 2014, from; NASA, December, 2008

Neutron Star

The Neutron Star is produced when a Supernova explodes. The explosion will force the protons and electrons to combine and create a Neutron Star. Hence these Stars are composed mainly of neutrons (Telescope, n.d.).

(Fig. 5)

On left (Fig. 5): Neutron Star, the dense collapsed core of a massive star. Retrieved 1st June, 2014, from; NASA, August, 2008.

Black Holes• Black Holes are formed from the remnants of a larger star that dies in a

supernova explosion (NASA, 2014, May 15).• A black hole is an object so dense that nothing in the universe can escape

from it’s gravitational pull, not even light (NASA, 2014, May 15).• Black Holes are among the most violent and energetic objects in the

universe - active galactic nuclei and quasars, which shoot off jets even as they suck in surrounding gas. However, this does not apply for all Black Holes. Often older ones like the black hole at the centre of the Milky Way, are considerably more quiet (University, C. 2011, December 15).

(Fig. 6)

On left (Fig. 6): Artist’s concept illustration of a Feeding Black Hole. Retrieved 1st July, 2014, from; NASA, August, 2012.

Theory of Black Holes

• The concept of the black hole was first proposed in 1783. However it was Albert Einstein's theory of general relativity, 1915, which was first able to theoretically prove they could exist. Einstein was able to demonstrate that gravity can bend the path of light, just as it is able to bend the path of other moving objects that have a mass. By demonstrating his theory he was able to confirm the notion that Black Holes exist (University, C. 2011, December 15).

Accretion Disk• It is not possible to observe Black Holes directly, however we can observe the

effect it has on surrounding materials. The materials we can observe include: gas and dust. The Black hole will either suck the material in or will eject it away in the form of a ‘jet’. The material will eventually fall into the Black Holes abyss, however not straight away. The material will move around the black hole in an orbit, forming what is known as an Accretion Disk (University, C. 2011, December 15).

• Material orbiting in the Accretion Disk will slowly lose potential energy due to friction. The majority of this friction is due to a huge gravitational pull near the Black Hole. This gravitational pull rips apart the material whilst at the same time heating it to extreme temperatures (reaching thousands of degrees in temperature). Smaller Black Holes will heat their disks to millions of degrees. These extreme temperatures emit wavelengths equivalent to the x-ray part of the spectrum. This makes Black Holes some of the brightest objects in the Universe (University, C. 2011, December 15).

Energetic Jets• The material which is not sucked into the Black Hole is ejected by

jets that move away from the accretion disk. These jets are moving close to the speed of light. These jets have been observed in the form of: quick; enormously energetic spurts.

• The reasoning for these jets are still not well known, however it is believed that magnetic fields are required to produce these jets (University, C. 2011, December 15).

(Fig. 7)

On left (Fig. 7): Black Holes generate colossal jets that blast out twin streams of heated matter. Retrieved 1st June, 2014, from; NASA, May, 2012.

Conclusion

• Advancing technology is increasing our understanding and discovery of the Universe, in particular the formation of Stars and their life cycles. A Star will transform and develop itself over time from a: Nebula; Star; Red Giant; Red Dwarf; White Dwarf; Supernova; Neutron Star; and possibly a Black Hole.

These Black Holes are so dense that not even light can escape it’s unrelenting fury.

Thank you for taking the time to watch my

presentation.