Billions and billions of stars

Billions and billions of stars

The Trifid Nebula Distance ~5200 lyrs

Star forming regions include the famous Orion nebula About 1500 light years away.

The belt of Orion

The Flame Nebula can you spot the horses head? Image obtained with the new ground based VISTA telescope

N44 globule gemini telescope

At ~60 light years

Understanding how energy is generated inside the Sun and Stars A long standing problem in astrophysics. Early ideas: If the sun were a huge spherical lump of coal it would only last 1 million years. Heat from the contraction of the gas cloud that made the sun - lifetime only ~30x10 6 years (Kelvin 1860s). Geologists age of the earth ~4 billion years - the sun must be older than this. Solution (1920s and 30s via Einstein s 1905 special relativity) - Nuclear Fusion Energy - this could easily keep the sun shining for billions of years. The sun is a gravitationally bound fusion reactor! As are all of the stars.

Inside the Sun The high temperature gives the protons enough kinetic energy to overcome their electrical repulsion and fusion can take place. L sun =3.8x10 26 W M sun =2x10 30 kg L/c 2 =4x10 9 kg/s!! D sun = 1.4 million km = 109D earth

The Proton-Proton Chain - the basic energy generation process overall 4p 4 He p + p D +e + + v e the positron annihilates with an electron to produce gamma rays = energy, the neutrino also takes away some energy. p + D 3 He +γ the gamma ray = energy 3 He + 3 He 6 Be 4 He + 2p

Each of these reactions produces 0.0287amu of mass loss which is equivalent to 26.72MeV of energy (4x10-12 J)- not a lot compared to the sun s luminosity! However there are a lot of these reactions occurring every second - about 10 38 of them! This adds up to the required 4 million tonnes per second that the sun looses in mass! The neutrinos produced in these reactions are important and will be discussed later.

Life cycle of lightweight stars (most stars in the universe) timescales depends on mass consider a solar type star lower masses take longer. Equilibrium between pressure out and gravity in. Shell burning Eventually the core is just inert Carbon, the H/He shell burning becomes unstable leading to stellar winds and pulsations that drive off outer envelope of star leading to a planetary nebula. 10 10 yrs on the main sequence moves onto the asymptotic giant branch heated due to contraction of core star becomes redder and larger Red giant phase triple α process 10 8 yrs on the horizontal branch

The Ring Nebula M57 ~2300 lyrs, 1.4 arcmin

The Helix Nebula D ~ 450 lyrs, 0.5 degrees

Ground based 8m Subaru telescope Hawaii

The cat s eye nebula D~3000 lyrs, 6 arc min

Large area image from the NOT LaPalma

Eta Carina supernova in the making?

Massive stars towards the end of their lives many more shells building up heavier elements all the way to Fe.

Supernova explosions. Type Characteristics Type I explosion of white dwarf in binary star Type Ia Lacks hydrogen and presents a singly ionized silicon (Si II) line at 615.0 nm (nanometers), near peak light. Type Ib Non-ionized helium (He I) line at 587.6 nm and no strong silicon absorption feature near 615 nm. Type Ic Weak or no helium lines and no strong silicon absorption feature near 615 nm. Type II explosion of massive star core collapse Type IIP Reaches a "plateau" in its light curve Type IIL Displays a "linear" decrease in its light curve (linear in magnitude versus time)

Supernovae build up all of the elements heavier than iron during the explosion. via the r-process of n absorption and following decays to stable nuclei. The Cygnus Loop

SN RCW86 seen 185AD in China X-ray image XMM/Chandra

SN1006 in Scorpio, d~7000lyrs X-ray image by Chandra (also a radio sourcepks1459-41) Possibly brightest of the historical supernovae, m~-9, recorded across Europe and Asia.

The crab nebula type II D ~ 6300 lyrs 6x4 arc min new star seen in 1054 recorded in China.

The First Pulsar

Pulsars

SN1572 Tycho s supernova m~-4, 7000 lyrs, also recorded in China. Radio source 3C10, faint in optical in Cass. Light echo seen in 2008. Spitzer IR image + X-ray

Kepler s SN1604, Ophiuchus, m~-3, Type II, 3C358, 15,000 lyrs, also obs in China. HST vis Spitzer IR (also observed echo)

Cass A Radio source supernova remnant explosion 1680 unobserved except maybe by Flamsteed, m~6. Radio map IR vis X-ray

Supernova 1987A

Light curve of SN1987A The first supernova and the second object ever (after the Sun) to be observed as a source of neutrinos.

SN1987A Light Echos

Light rays leaving the surface of a very dense star because of the immense G field the light leaving the star does not necessarily travel in straight lines a prediction of Einstein s general relativity theory. From a point on the surface some light escapes (a cone shape exit beam) some gets dragged into orbit around the star and some is dragged back into the star. Collapsing neutron star Eventually if the mass is a few times the mass of the Sun all of the light gets dragged in! A black hole is formed.

Cygnus X-1

Implies small size Observations only possible by satellites (rockets and balloons in the 60s 70s) because X rays are absorbed by the atmosphere.

Distance ~6000 lyrs Stars separated by 0.2 AU (~0.0001 )