Astrophysics and Cosmology

Some of the biggest ideas of the last 100 yearsOf 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