Stars & our Sun

Mr. Schultz, everything with you is about gas! Why do stars shine? A star is a huge ball of hot glowing gases, called plasma. Stars twinkle because the light is distorted by Earth’s atmosphere. All stars have one thing in common, the way they produce energy. The energy comes from nuclear reactions that change hydrogen into helium. It is as if millions of atomic bombs were going off every second inside the star. Unlike bombs, where it explodes and flies apart, the enormous gravity of the star keeps the material held together. All of this energy that is produced gives off all types of electromagnetic radiation, including visible light. Mr. Schultz, everything with you is about gas!

Electromagnetic Radiation Name the seven types of Electromagnetic Radiation 1.Gamma Rays 2. X-Rays 3.Ultraviolet 4.Visible 5.Infrared 6.Microwaves 7.Radiowaves

Our Star, the Sun 11,000 degrees Fahrenheit Brighter and hotter than many of stars in Milky Way galaxy Made primarily of Hydrogen and Helium Provides heat energy for the Earth Should last about another 5 billion years, whew! Makes up 99.8% of our Solar System’s mass. That leaves only 0.2% for everything else! It takes 500 seconds or 8.3 minutes for sunlight to reach the Earth!

Betelgeuse, Proxima Centauri Colors of the stars The color of a star and the temperature at which it burns are closely linked. Star Color Temperature Examples Blue 11,000-50,000 Celsius Regulus, Rigel Blue-White 7,500-11,000 Celsius Deneb, Sirius White 6,000-7,500 Celsius Canopus, Procyon Yellow 5,000-6,000 Celsius The Sun, Alpha Centauri Orange-red 3,500-5,000 Celsius Aldebaran, Arcturus Red 2,000-3,500 Celsius Betelgeuse, Proxima Centauri

The Life of an Average Star How long does a star “live”? The main factor that determines how long a life a star will have is the star’s mass. A star of medium mass, like our Sun, will shine for billions of years. A super-giant lives a much shorter life than a smaller star. Also, based on their sizes, stars die differently. A super-giant will die very differently than a medium-sized star.

NEBULA Nebulas are huge clouds of gases and dust scattered through many regions in space that provide the materials from which stars form.

The Ant Nebula, a cloud of dust and gas whose technical name is Mz3, resembles an ant when observed using ground-based telescopes.  The nebula lies within our galaxy between 3,000 and 6,000 light years from Earth .  

Red Giant When a star’s fuel starts to run out, the star swells to many times its original size and it cools down. The outer layers of the star begin to expand far out into space. As the outer layers expand, they get farther away from the core and cool down. What color are cool stars? Yep, red! That is why, in this stage of a star’s life, it is called a “red giant”. This is what will happen to our Sun, though not for billions of years.

Now What? All stars come to this point, although from here, the path that they take changes drastically, based on their mass. Let’s take a look at what happens to a low-mass star, like our Sun.

White dwarf After a long period as a red giant, the last of the fuel will run out. The star will collapse and become a white dwarf. A white dwarf is a dead star that shines very dimly as it cools down. When our Sun turns into a white dwarf, it will shrink to about the size of Earth! The particles are very tightly packed. They are more than a million times as dense as water!

Black Dwarf Finally, the star has died completely, becoming a cool, darkened black dwarf.

Now, the high-mass stars After the red giant stage, Let the show begin…

Supernova A supernova is an exploding star that can become billions of times as bright as the Sun. As you learned before, a large-mass star lives a much shorter life. They also end their life in a much more spectacular fashion. After the red-giant stage, the massive star has two forces acting upon it. The outward push caused by the hot core, and the inward pull of gravity. When the star’s fuel is finally used up, the outward push is gone, and the inward pull of gravity takes over. The outer layers fall into the center of the star at tremendous speeds and result in a gigantic explosion known as a supernova.

After Before SN1987A before and after image from Anglo-Australian Observatory. It’s in the LMC, 160,000 light-years distant. When fusion process no longer produces energy to support the star, the core of the star collapses. With nothing to stop it, the atoms are crushed together, and the infalling material bounces off the superdense core, causing the explosion. A supernova produces 1040 erg/s (a million times more than the sun). The supernova disperses the elements it has created. In addition, the energy of the explosion creates elements heavier than iron.

Supernova black hole neutron star The life of a massive star doesn’t stop at a supernova. Some matter of the star may remain after the explosion. Depending on the mass of the star, having high mass, or very high mass, the remains can become one of two space features. A black hole or a neutron star. Very High Mass High Mass black hole neutron star

Neutron Star Neutron stars are compact objects that are created in the cores of massive stars during supernova explosions. The collapse of a massive star is so powerful, it crushes the star’s remaining matter into the most dense objects in the universe. A typical neutron star is less than 12 miles in diameter, but can weigh more than the sun! A spoonful of matter from a neutron star would weigh as much as a billion tons on earth!

Black Hole The collapse of the core of a massive star may be so powerful that it does not stop at a neutron star. A black hole is a tiny region, or point, with a very strong gravitational pull. The gravitational pull is so strong that not even light can escape!

If the neutron star or black hole is part of a binary star system, material from the normal star flows to the compact star, emitting x-rays. The system has a whole new life as an x-ray binary. Illustration from http://www.gsfc.nasa.gov/gsfc/spacesci/structure/spinningbh/spinningbh.htm Also see http://imagine.gsfc.nasa.gov/docs/features/news/30apr01.html Here you see a photograph of a black hole pulling in matter from a nearby neutron star. You cannot normally see a black hole, but you can see the x-rays given off of it with a special camera.

Star Life Cycle All Stars Low-mass Stars Massive Stars High Mass Stars Very High Mass Stars Nebula Star Red-Giant White dwarf Supernova Black dwarf Neutron star Black Hole Star Life Cycle