The death of stars

Most celestial events unfold over thousands of years or more, making it impossible to follow their evolution on human timescales. Supernovas are notable exceptions, the powerful stellar explosions that make stars as bright as an entire galaxy for several days. Although they are very rare – only a few such explosions take place every century in a typical galaxy – supernovas can be seen with the naked eye if they are reasonably nearby. In fact, when supernovas were discovered they were thought to be new stars appearing in the sky – ‘nova’ means new in Latin. Astronomers have recorded supernovas long before a theoretical understanding of these events as stellar explosions was developed in the 20th century. The most ancient documented record dates back to 185 AD, when Chinese astronomers saw a ‘guest star’ that remained visible for several months, in the vicinity of the two stars Alpha and Beta Centauri. The material ejected during these explosions sweeps up gas and dust from the surroundings, creating picturesque supernova remnants that can be observed long after the explosion. Modern astronomers believe that the object shown in this image, the supernova remnant RCW 86, is what remains of the supernova that was discovered in 185 AD. The blue and green glow at the edges of the bubble represents X-ray emission from hot gas, heated to millions of degrees by shock waves generated after the explosion. The diffuse red glow marks infrared emission from warm dust in the interstellar medium around RCW 86. Sprinkled across the image, in yellow, are young stars that shine brightly at infrared wavelengths. This image combines X-ray data from ESA’s XMM-Newton and NASA’s Chandra X-ray Observatory (combined to form the blue and green colours) with infrared observations from NASA’s Spitzer Space Telescope and Wide-Field Infrared Survey Explorer (yellow and red). The supernova remnant RCW 86 is some 8000 light-years away.

Stars inevitably run out of fuel to burn in the nuclear fusion reactions that burn in their cores and when this happen there are a number of spectacular events that occur in their death throes. As a star goes through its main sequence stage it burns hydrogen into helium through nuclear fusion. As it starts …

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What are the different types of stars?

Light Spectrum of our Sun. Credit: N.A.Sharp, NOAO/NSO/Kitt Peak FTS/AURA/NSF

In my last few posts I have talked mainly about the Sun, our closest star but what other types of star are there? Clearly by looking at the Hertzsprung-Russell diagram there are different types; cooler, dimmer smaller stars to brighter, hotter and massive stars. Astronomers class the stars according to a property called it’s Spectral …

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Where is the Sun on the H-R diagram?

The Sun on the H-R diagram

In one of my earlier posts I described a Hertzsprung Russell diagram which shows the relationship between a stars temperature and its luminosity. But where does our Sun sit on this diagram? Our sun sits squarely in the main sequence line. The main sequence makes up the majority of a stars life when it is burning …

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The Solar Eclipse

Maximum Eclipse | (C) Chris Hall 2015

Today, 20 March 2015, there was a solar eclipse in the very northern hemisphere. You could see between 85%-95% eclipse in mainland Britain but you would need to further north to the Faroe Islands or Svalbard to see a total eclipse. Here is Bristol I attempted to get some photos using a solar film cap …

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H-R Diagrams

I described stars in my last post and I talked about two that are different colours; Rigel and Betelgeuse in the constellation of Orion. Rigel is a blue super giant and Betelgeuse is a red super giant but what is the Sun, how do we classify stars as super giants and what other types of …

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What are Stars?

The constellation of Orion

Stars are all those little pin points of light in the night sky that slowly move around the sky throughout the year, but what exactly are they? Stars are the furnaces of the universe; a single star is a huge collection of matter that is gravitationally pulling itself together into a sphere and this gravitational …

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Forces of Nature – The Weak Nuclear Force

The weak nuclear force is indeed the weakest of the four forces of nature. It is responsible for the nuclear decay of atoms and there are three types of decay that take place: 1) Beta minus decay – A neutron decays into a proton and emits an electron and an electron anti neutrino. 2) Beta …

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Forces of Nature – The Strong Nuclear Force

The strong nuclear force is indeed the strongest of the Four Forces of Nature, but it only works at the heart of the atom and has a very small range, just 10-16 metres. This range is only just bigger than a proton or neutron and it comes from the gluons that hold the innards of …

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Forces of Nature – Electromagnetism

The electromagnetic force bears some resemblance to gravity in that it is infinite and obeys the inverse square law. However, this is where the similarities end. The electromagnetic force is 10^43 time stronger than gravity and, more importantly is has both a positive and negative charge. This positive and negative charge lead to important implications …

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Forces of Nature – Gravity

Plot of the inverse square law of gravitational attraction. (C) Chris Hall 2014. All rights reserved.

Gravity is the most obvious of the four forces of nature. It is what holds our feet on the ground, the atmosphere in place and keeps Earth orbiting the Sun but gravity is an attractive force only, anti gravity is the subject a science fiction. Gravity has an infinite range but is the weakest of …

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