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Life of a Star and the Elements

Stars are born when a gas and dust cloud subtracts in space by its own gravity.

Stars produce energy in fusion reaction of atomic nuclei. It is a nuclear reaction where light elements combine to heavier elements and at same time energy is released. Inside a star there is high enough temperature (about 14 million degrees) and pressure (about 200 billion atmospheres) for fusion to happen.

At the end of its life a star like our Sun produces a planetary nebula. Star has shined 5-10 billion years and the fusion reactions are ending. Now the center of star starts to subtract and the temperature of center rises to new level. At same time the center is unstable and it subtracting and expanding in cycles. The outer parts of the stars are blown to space, as a planetary nebula, in this process. The fusion reactions had produced layers of elements to the star. On top there is still hydrogen and in the core there is oxygen and carbon. At the end a white dwarf star, size of the Earth, is left in center of planetary nebula. The dwarf star fades during billions of years. This kind of end is for a star which has mass under 3 times the mass of the Sun. .

Stars which have mass over 3 times of sun produce in fusion reactions elements all the way to Iron. Iron does not combine in fusion reactions anymore, so the fusions stop, and the pressure inside the core of the star suddenly drops. Now happens a violent end. Star starts to collapse. Atomic nuclei are pushed together. Electrons combine with protons, producing neutrons. The event happens in few tens of seconds and leads to a supernova explosion. The whole outer core explodes to outer space. The supernova shines with the power of all stars in the galaxy. The energy released in explosion forces in the expanding shell the Iron to fusion to still heavier elements, producing all the elements up to Uranium. As examples of supernova explosions are Messier 1, Crab nebula and Veil nebula in Cygnus.

When mass of the star is 3 to 6 solar masses in the center there is left a neutron star, size about 30 kilometers, mass about 1 solar mass. One tee-spoon of this star weights as much as an oil tanker.

If the mass of star is over 6 solar masses, then the pressure of neutrons is not enough to stop the collapsing core in supernova explosion. The core collapses smaller than 6 kilometers limit. A black hole is born. Gravity in this 6 kilometer limit is so high that even light cannot escape.

Red dwarf stars have small mass compared to our Sun. Nuclear reactions happen slowly in them and red dwarfs will have a long lifetime, even 100 billion years. About 75% of the stars in our galaxy are red dwarfs. They are mostly so dim, that we do not see them with naked eye.

Universe was born 13.7 billion years ago in Big Bang and after it there was only the simplest elements hydrogen and helium. The heavier elements were produced by first generation of stars. In the deaths of these stars the supernovas and planetary nebulas distributed the heavy elements back to interstellar space.

Our Sun and Solar system was born 4.5 billion years ago from a gas and dust cloud, to which heavy elements, needed by life, were distributed by ancient stars.

Those atoms that are in you were produced by ancient stars: We are stardust.

Above: Supernova remnant Messier 1, Crab nebula, in constellation of Taurus. Distance 6300 light years. Angular size in sky 6 arch minutes (one fifth of angular size of Moon). Real size is 11 light years. This exploded as supernova year 1054. The extremely bright star was written to history books by Arabs, Chinese and Japanese. Visually it was four times brighter than Venus-planet and it could be easily seen even during the daytime. In the core of Crab nebula there is now a neutron star, spinning around its axis 30 times per second. It is strong roentgen and gamma ray source. Picture was taken 24.2.2020 with Helios Skyliner 200/1000 telescope. Exposures were 11 x 90 seconds, ISO 1600.

Above: Picture series of Supernova SN2011ef in galaxy Messier 101 in constellation of Big Dipper and supernova SN2014J in galaxy M82. Distance to M101 is 27 million light years. It was first found 24.8.2011. My first picture in left is 5 months after the explosion. In 3rd picture the faded supernova can still be seen as a faint bluish object. In last picture in November 2012 it cannot be seen anymore. The quality of pictures gets better from left to right in same phase as I upgraded my equipment and leaned to use it and image processing software better. same phase as I upgraded my equipment and leaned to use it and image processing software better.

Above: Veil nebula in constellation of Cygnus. It is a supernova remnant which exploded about 6000 years ago. Distance 1470 light years. The distance between arches in sky is 3 degrees. They are named as Caldwell 34 (NGC6960) and Caldwell 33(NGC6992) in catalogs. There may be a black hole here, since no neutron star has been identified in this area. This nebula was found by William Herschel year 1784. Picture was taken 8.9.2012 with EF100-400L tele zoom lens.

Planetary nebulas
M76 Little Dumbbel in Cygnus. Distance 3400 light years.
Caldwell 39 Eskimo nebula in Gemini. Distance 2870 light years.
M27 Dumbbell nebula in constellation of Fox. Distance 1250 light years.
Caldwell 6 Cat eye nebula in Kefeus. Distance 3300 light years.
M57 in Lyra. Distance 2300 light years.
M97 Owl nebula in Big Dipper. Distance 2600 light years.

Properties of the stars

It is interesting to compare the colors of the stars when they are set side by side. The color reflects the surface temperature. Cool stars are red. Hot stars are white. Telescope SkyWatcher 80/600ED. Exposures 35s, ISO1600

Black hole Cygnus X-1

Below is Black hole Cygnus X-1. In contellation of Cygnus, near star eta Cygni, there is a strong X-ray source Cygnus X-1 . It is a black hole orbiting the blue giant star HDE 226868. Distance 6070 light years. Image taken 24th of September 2017.

Double stars

Some stars are double stars which orbit each other. Below are three such cases. Albireo in constellation of Cygnus and Cor Caroli in contellation of Canes Venatici. Distance to Albireo is 430 light years and the visual separation between the componen stars is 35 arch seconds. The stars orbit each other in 100000 years. The brighter star of Albireo has 5 times the mass of the Sun and it is 1200 times brighter than the Sun. Distance to Cor Caroli is 110 light years and the visual separation between the componen stars is 20 arch seconds. The stars orbit each other in 7900 years. The double star Alya is in 132 ligth years distance.

Barnard's star moving

Barnard's star is a red dwarf in constellation of Ophiuchus. It is the second closest star to us after Alpha Centauri triple star. The mass is 14% of the Sun mass and diameter 20% of Sun. The surface temperature is 3100 degrees and its luminosity is 0.0004 times the brightness of the Sun. Barnardís star is moving in the sky fast, 10 arch seconds each year. It is moving 142 km/s relative to Sun and it will be closest to us year 11800. Then distance will be 3.75 light years. But even then it is so faint that it cannot be seen with naked eye. The age is 10 billion years, over twice the age of our Sun. Year 1998 there was a bright flare eruption in Barnardís star. In image below we see Barnard's star moving during 13 months.

Nova Delphini 2013

Below is Nova in constellation of Delphinus, 15.8.2013. Nova was found 14.8.2013. This nova can be seen with naked eyes. Nova event happens in a double star system. One of the stars is a small white dwarf and the other is a giant star in end of its life so that it has expanded. Materia if flowing from the giant star to the surface of the white dwarf. When there is enough materia on the surface of white dwarf, there happens instant fusion reaction of the surface layer. This is a nova explosion and the brigthness of the white dwarf can increase with a factor of 100000.

KIC 8462852 - Tabbys star

There is interesting observations by Kepler planet hunting satellite that around star KIC 8462852, there is 20% dimmings which are currently difficult to explain. SETI institute has started radio observations. Distance to this star is 1500 ligth years. Visual magnitude has been last years m11.88. Below are images of the star on years 2012 and 2016. It can be estimated that in these images the start is not in dimming state. See articles:
Universe Today 9.8.2016: Tabbyís Star Megastructure Mystery Continues To Intrigue
Universe Today 21.10.2015: SETI Institute Undertakes Search for Alien Signal from Kepler Star KIC 8462852
Patrick Rowan's Skywatch: Is alien megastructure blocking this star's light?

Copyright (c) for pictures, 2017 Harry Rabb. All rights reserved.

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