Stars: The Light of Space.

Stars: The Light of Space.

By Cody Smith, Kyle Taddeo, and Jacob Dulworth.

What is a Star?

Look up in the night sky and you'll see lots of stars. But what exactly is a star? In a scientific sense, a star is ball of hydrogen and helium with enough mass that it can sustain nuclear fusion at its core. The sun is a star, but there are many stars with all shapes and colors. The sun and most other stars are made of gas and a hot, gassy substance known as plasma. But some stars, called white dwarfs and neutron stars, consist of closely packed atoms or subatomic particles. These stars are therefore much more dense than Earth. The star is mainly composed of plasma. The star’s surface is 99.9% plasma. Plasma is highly sensitive to magnetism making it highly sensitive and unstable.

Classification of Stars StarsStar Star Type r Color

Approximate Approximate Surface TempatureTemperature

Average Mass ((Sun=1)he Sun = 1)

Average Radius ((Sun=1)un = 1)

Average Luminosity (The Sun =1) = 1)

Main Characteristics Characteristics

Examples

O Blue over 25,000 K 60 15 1,400,000

Singly ionized helium lines (H I) either in emission

or absorption. Strong UV

continuum.

10 Lacertra

B Blue 11,000 - 25,000 K 18 7 20,000 Neutral helium lines (H II) in absorption.

RigelSpica

A Blue 7,500 - 11,000 K 3.2 2.5 80Hydrogen (H) lines

strongest for A0 stars, decreasing for

other A's.Sirius, Vega

F Blue to White 6,000 - 7,500 K 1.7 1.3 6Ca II absorption.

Metallic lines become noticeable.

Canopus, Procyon

G White to Yellow 5,000 - 6,000 K 1.1 1.1 1.2

Absorption lines of neutral metallic

atoms and ions (e.g. once-ionized

calcium).

Sun, Capella

K Orange to Red 3,500 - 5,000 K 0.8 0.9 0.4 Metallic lines, some blue continuum. Arcturus, Aldebaran

M Red under 3,500 K 0.3 0.4 0.04(very faint)

Some molecular bands of titanium

oxide.Betelgeuse, Antares

Classification of Stars (cont.) • Stars are classified by their spectra (the elements that they

absorb) and their temperature. There are seven main types of stars. In order of decreasing temperature, O, B, A, F, G, K, and M.

TYPE StarIa Very luminous supergiantsIb Less luminous supergiantsII Luminous giantsIII GiantsIV Subgiants

V Main sequence stars (dwarf stars)

VI SubdwarfVII White Dwarf

Different Stages of StarsStars form in dense molecular clouds within galaxies. These clouds of dust and gas obscure the early stages of stellar formation from optical telescopes. Gravity is the force responsible for stellar formation and the mass of material that forms at star largely determines its life and fate. The most common nuclear process which is the energy force of the star is the proton- proton chain which is what keeps a star “living.” After ten billion years, a main sequence would commonly have converted about 10% of its hydrogen to helium. Outside of the range of pressures there is still mostly hydrogen, but it cannot be used because the pressures are not high enough to initiate fusion. This helium begins to contract and the outer layers begin to expand and cool glowing redder. The star is now a red giant. When a star becomes a red giant the nuclear fusion begins.

Different Stages of Stars (cont.) The star was previously unable to fuse the helium; however, now that the

core has contracted, the added pressure is enough to fuse helium into heavier elements. Simultaneously, hydrogen fusion also occurs at this point in a shell around the helium core, for pressures there have also increased enough for hydrogen to fuse. Life expectancy from here on is about 100,000,000 years. After this process occurs the red giant is know mostly composed of carbon. The outer shell of the Star then expands two times its size because of the lack of helium in the core so the hydrogen expands exponentially. The star then collapses on its self because the balance between gravity and the output and input of energy of the star is off balance. The star then collapses on itself and explodes creating a supernova. Another option is the core then remains of neutrons and collapses on it self creating a black hole.

Composition of a Star

All stars including our Sun are giant nuclear power plants! They "burn" hydrogen and helium to produce heavier elements through the process of nuclear fusion. The Sun is approximately 95% hydrogen, 5% helium, and less than 0.1% heavier elements.• 90% hydrogen (by number of atoms)•10% helium •Traces of heavy elements (everything else)