Astrophysics and Cosmology

Some of the biggest ideas of the last 100 years

Of the Stars, the Universe and Everything!!! (the answer is 42. . . )

Star Life Cycle: Birth

• Stars are born out of a cloud of dust

• Dust Collapses together due to gravity

• When sufficient heat and pressure, nuclear fusion starts– Atoms combine – Releasing lots of Energy– Star shines

Star Life Cycle: Life

• Our sun is a typical star• Typical lifetime is 10

billion years for sun-sized star

• Combines Hydrogen into Helium

• Hotter stars burn brighter, Blue

• Colder stars burn Red

Star Life Cycle: Deaththe form star-death takes depends on star’s size

Star Life Cycle: Supernova

• Heavy stars can collapse in a Supernova

• Two types of Supernova– Small star eats bigger star

(Ia)– Massive star collapse (IIa)

Some History

• Supernovae observed by Chinese and Arab astronomers (1006 ACE, possibly others)

• Tycho observed a supernova in 1572– Convinced him that stars change– A nail in the coffin of Aristotelian “spheres”

• Most recent in Milky Way observed by Kepler in 1604• Nova means “new”• Supernovae are “new” stars – they appear suddenly

– Are brightest in sky for a month– Visible during daytime– Visible at night for a year or two– Leave behind a Nebula

Supernova Part of Cycle

• Shockwave drives nebular gas together

• Creating more dense clumps of gas

• Igniting new stars• Supernovae produce

and spread heavy elements– So we are “star stuff”

Star Life Cycle: Black Hole

• Large enough star collapses

• So dense, that light’s path is bent by gravity as it travels – Gravity so strong– Light can’t escape:

• Black Hole

Black Holes – Very Weird• Center – Singularity• Edge: “Event Horizon”– Anything falling in is gone

forever• Time slows to a stop

inside• Inside event horizon,

forces rip matter apart• “Rip” in Space-Time• Gravity can swallow other

stars or planets– Making Black Hole bigger

Cosmology: The Big Bang

Cosmology: The Big Bang

• Edwin Hubble (of Hubble telescope) big name• Saw galaxies moving away from each other– Tracing backwards, then. . .

• All matter in the universe starts off at one point -- “singularity”

• Expands outward rapidly – “Inflation”• Matter at first “hot soup” of particles

The Process

• Expands, cools into atoms

• Atoms clump up into gas• Gas clumps up into stars

and galaxies• Process currently

theorized to take place over 13.75 billion years

Cosmology: Evidence – Universe Expanding

Arno Penzias and Robert Wilson 1965: Cosmic Microwave Background

• Had Antenna to measure microwaves

• Looking for point sources (Stars!)• Found constant buzz through all

of sky• Thought there was a problem

– Cleaned out bird poo– Buzz still there

• Evidence for: the Big Bang

What does it mean?

• Radiation released when matter first formed

• Went in all directions• Universe expanded• This light is only getting to

us now– 13.75 billion years later!– From the edge of the

Universe • Uneven parts are clumps

– That later became galaxies

Dark Matter

• The Galaxies are rotating faster than predicted– What force causes the galaxies to rotate?– What does it mean if they rotate fast?– And what does that imply?

• Dark Matter– Acts like matter in terms of gravitational pull– Unlike normal matter (stars, dust), emits no

radiation– Hence “Dark”, we can’t see it

• It’s a “Conceptual Placeholder”

Dark Matter is a “Conceptual Placeholder”

• If we stick with Newton’s Theory of Gravity, we need it

• Might be made of new particles• Or just lots of planets we can’t see– According to Newton/Einstein theory, 83% of

matter in the Universe is Dark Matter• Or maybe the Theory’s just insufficient as it is . . . We don’t really know