Stars on and off the Main Sequence Just a history of a star’s birth, life and death

Main Sequence Stars Where are they on the H-R Diagram? How long is their life compared to other stars? What is their dying process? What do they ultimately become? Why?

A Look at the Non-Main Sequence Stars: Birth and Death of Stars Protostars T-Tauri stars Brown Dwarfs Red dwarfs Neutron stars White dwarfs Red Giants Super Giants

Protostars A protostar is what you have before a star forms If it has enough mass and begins to fuse, it becomes a T-Tauri star If it does not have enough mass it becomes a Brown Dwarf (not red)

T-Tauri Stars Star's formation and evolution right before it becomes a main sequence star Occurs at the end of the protostar phase Gravitational pressure holding the star together is the source of all its energy

T-Tauri Stars Continued Don't have enough pressure and temperature at their cores to generate nuclear fusion Same temperature as MS stars but brighter because they're a larger

T-Tauri Stars Have large areas of sunspot coverage Have intense X-ray flares Extremely powerful stellar winds Remain in the T Tauri stage for about 100 million years

Main Sequence Stars, Again The majority of all stars are main sequence stars Our nearest neighbors, Proxima Centauri, Sirius and Alpha Centauri are main sequence stars Stars can vary in size, mass and brightness

Main Sequence Continued All doing the same thing Converting hydrogen into helium in their cores Releasing a tremendous amount of energy

Main Sequence Continued In a state of hydrostatic equilibrium Gravity is pulling the star inward Pressure from all the fusion reactions in the star are pushing outward

Main Sequence Continued Lower mass limit for a main sequence star is about 0.08 times the mass of the Sun (ex: Red Dwarf) To more than 100 times the mass of the Sun

Red Giant Star When an average star like our Sun consumes all hydrogen in its’ core, fusion stops No longer generates outward pressure to counteract inward pressure Outer shell of H around core ignites, prolonging life of star

Red Giants Continued But the shell of ignited H causes it to increase in size dramatically Can be 100 times larger than it was in its main sequence phase

Red Giants Continued When hydrogen fuel is used up, further shells of helium and heavier elements can be consumed in fusion reactions Will only last a few hundred million years before it runs out of fuel completely and becomes a white dwarf.

White Dwarf Stars An average star has completely run out of hydrogen fuel in its core It lacks the mass to force higher elements into fusion reaction It becomes a white dwarf star

White Dwarf Stars Continued Outward light pressure from the fusion reaction stops Star collapses inward under its own gravity No fusion reactions happening and cools down Process takes hundreds of billions of years

Red Dwarf Stars Most common kind of MS stars Low mass Much cooler than stars like our Sun Able to keep the hydrogen fuel mixing into their core for a longer time

Red Dwarf Stars Continued Can conserve their fuel for much longer than other stars Some red dwarf stars will burn for up to 10 trillion years The smallest red dwarfs are 0.075 times the mass of the Sun and largest up to ½ our Sun

Neutron Stars If a stars has between 1.35 and 2.1 times the mass of the Sun the star dies in a catastrophic supernova explosion The remaining core becomes a neutron star

Neutron Stars Continued It is an exotic type of star that is composed entirely of neutrons How? The intense gravity of the neutron star crushes protons and electrons together to form neutrons

Neutron Stars Continued More massive stars do not become neutron stars What do they become? What do we know about these structures created by the death of super massive stars?

Supergiant Stars The largest stars in the Universe are supergiant stars Dozens of times the mass of the Sun Consuming hydrogen fuel at an enormous rate

Supergiant Stars Continued Will consume all the fuel in their cores within just a few million years Live fast and die young Detonating as supernovae Disintegrating themselves in the process Betelgeuse is a prominent example of a red supergiant star. It is located at the shoulder of Orion

Nova and Other Things to Consider Nova means "new star" They are actually "newly visible" stars One model of novae suggests that they occur in binary systems

Nova Continued One is a white dwarf The other is on its way to becoming a red giant The red giant can lose mass which would trigger hydrogen fusion as it falls on the white dwarf

Nova Continued This would blow the gas off and the process could repeat itself. A notable nova example is Nova Cygni 1975.

Pulsars Evidence: precisely repeated radio pulses Attributed to rotating neutron stars which emit lighthouse type sweeping beams as they rotate

Pulsars Continued Variations in the normal periodic rate are interpreted as energy loss mechanisms or, in one case, taken as evidence of planets around the pulsar

Quasars These objects were named Quasistellar Radio Sources Quasars are closely related to the active galaxies The quasars have very large redshifts

Quasars Continued Quasars are extremely luminous at all wavelengths and exhibit variability on timescales as little as hours, indicating that their enormous energy output originates in a very compact source

Black Holes What are they? How do they form? What do we know about them? What don’t we know? How does time operate at a black hole? How does time operate inside the black hole?

Black Holes Continued What is singularity? What is the event horizon? Do black holes rotate? What are the only emissions from a black hole?

We will add more to the Hertzsprung-Russell Diagram As we look at more information As we look at mass As we look at cycles As we look at nebulae