Stars, The Universe and Galaxies Image at

What are we going to cover?  Classifying Stars  History of the Universe  Classifying Galaxies

Different types of stars Image from

Types of Stars  Big  Small  Red  Blue  Yellow  In groups

What is a “nebula”?  A cloud in space made of gas and dust, where stars are born  Most of the ones we see are inside our Milky Way Galaxy Orion image at

Life Cycle of a star Low mass star Main Sequence Red Giant Planetary Nebula White dwarf Stellar Nebula- Protostar High-mass star main sequence red supergiant supernova Neutron star or black hole (Depending on mass) (Depending on mass)

Magnitude of stars  Absolute Magnitude- a measure of the amount of light a star gives off (luminosity- how bright)  Apparent Magnitude- amount of light received on Earth (the way it appears to us)

Large, massive, bright nebulae Emission Nebula The hot gas is emitting lightThe hot gas is emitting light Orion image at

Colder, darker nebulae Dark dust blocking the hot gas behind it NOAO/AURA/NSF Image from

Young stars and some planets form in nebular cloud from Small Magellanic Cloud Image at

Star-forming region in the Large Magellanic Cloud:

Orion image at

Neutron Star or Pulsar Image at

Supernova—Massive Star Explodes Images at

Leftovers from an Explosion Supernova remnant (smaller, less gas) Image at

H-R Diagram  Indicates differences and relationships between stars  Horizontal axis (X) = surface temp  Vertical axis (Y) = Luminosity-absolute magnitude (brightness)  Sun rests in the middle-we use for comparison

Using a Star’s Spectrum  We can use a star’s spectrum to classify it. NOAO/AURA/NSF image at

Hertzsprung-Russell Diagram Images from and

Black Hole  A black hole is a dense well thought to have zero volume but infinite density  Its gravity is so strong that not even light is fast enough to escape it  Scientists hypothesize that black holes are remnants of supernova explosions. (When a star uses up all its fuel and explodes, the gases and dust that remain collapse to form the black hole.)

Our Sun Image at Regular/medium sized starRegular/medium sized star Average temp and brightnessAverage temp and brightness On an outer arm and far away from the center of the Milky WayOn an outer arm and far away from the center of the Milky Way

Our Sun   Main Sequence stage of life   Nuclear Fusion reactions (2 atoms jammed together- energy emitted as light and heat)- converts 600,000,000 tons of hydrogen into helium every second   93 million miles or 150 million km from Earth (closer than any other star)   A planet’s characteristics are often determined by distance from the Sun (ex- rocky, gaseous, temperature)

In a few Billion years… Red Giant Image at

By 5 billion years… White Dwarf Image at Small, but very hot

Building a Universe  Instantaneous filling of space with all matter

What is our Universe made of?  Stars and planets  Gas and dust  Organized into star clusters  Organized into nebulae  Organized into galaxies  Other things:  Black holes  Dark matter  Dark energy Image from

When Did the Universe Form?  ~13.7 billion years ago  How do we know?  Spreading (Red Shift) - know distances, rates of retreat, relative positions  Pervasive background radiation of 2.7°C above absolute zero - afterglow of the Big Bang Cosmic background radiation temperature on celestial sphere

History of the Universe seconds - gravity separates from other forces to seconds - fundamental particles - quarks and electrons seconds - quarks combine into protons and neutrons 1 second - electromagnetic and weak nuclear forces separate 3 minutes - protons and neutrons combine into atomic nuclei 10 5 years - electrons join nuclei to make atoms; light is emitted years - matter collapses into clouds, making galaxies and stars Orion Nebula -

History of the Universe Image from Image from

Later History Image at

Big Bang Theory Image at Image at  dded a "cosmological constant" to the theory of relativity because astronomers assured him that the universe was static  In 1915, Albert Einstein concluded that the universe could not be static based on his recently-discovered theory of relativity and added a "cosmological constant" to the theory of relativity because astronomers assured him that the universe was static  Aleksandr Friedmann and Abbe George LeMaitre are credited with developing the basics of the Big Bang model between 1922 and 1927; their calculations suggested that universe is expanding, not static.  Years later, Einstein called his cosmological constant the biggest mistake of his career

Expanding Universe  In 1929, Edwin Hubble showed that most galaxies are red-shifted (moving away from us), and that a galaxy’s velocity is proportional to its distance (galaxies that are twice as far from us move twice as fast) Image from

Hubble’s Evidence  Doppler shifting - wavelength emitted by something moving away from us is shifted to a lower frequency  Sound of a fire truck siren - pitch of the siren is higher as the fire truck moves towards you, and lower as it moves away from you  Visible wavelengths emitted by objects moving away from us are shifted towards the red part of the visible spectrum  The faster they move away from us, the more they are redshifted. Thus, redshift is a reasonable way to measure the speed of an object.  When we observe the redshift of galaxies, almost every galaxy appears to be moving away from us – the Universe is expanding.

Origin of the Universe  Data collected (from Hubble Telescope) is used as evidence to help develop scientific theories  Big Bang  Dominant scientific theory about the origin of the universe  Occurred ~13.7 billion years ago

What is the Big Bang?  Infinitely dense point not governed by our physical laws or time  All matter and energy contained in one point Image from Image from antimatter-factory-spark-brightest-supernova.htmlhttp:// antimatter-factory-spark-brightest-supernova.html

Predictions for the Big Bang Model The expansion of the Universe  Edwin Hubble's 1929 observation that galaxies were generally receding from us provided the first clue that the Big Bang theory might be right. The abundance of the light elements H, He, Li  The Big Bang theory predicts that these light elements should have been fused from protons and neutrons in the first few minutes after the Big Bang. The cosmic microwave background (CMB) radiation  The early universe should have been very hot. The cosmic microwave background radiation is the remnant heat leftover from the Big Bang.

Evidence for Big Bang  Red shift - as light from distant galaxies approach earth there is an increase of space between earth and the galaxy, which leads to wavelengths being stretched  In 1964, Arno Penzias and Robert Wilson, discovered a noise of extraterrestrial origin that came from all directions at once - radiation left over from the Big Bang  In June 1995, scientists detected helium in the far reaches of the universe - consistent with an important aspect of the Big Bang theory that a mixture of hydrogen (75%) and helium (25%) was created at the beginning of the universe

Measuring Distances  What is a Light Year?  A light year is the distance light travels in a year. Light moves at a velocity of about 300,000 kilometers (km) each second;  ~ 6 trillion miles or ~ 10 trillion km  Astronomical Unit:150 million Kilometers  Why do we use light years?  We need numbers that make sense to us in relationship to objects; we scale up and use meters and kilometers for large numbers.  Distances between stars and galaxies  Different wavelengths of Electromagnetic spectrum are used to gain information about distances and properties of components in the universe

What is a “galaxy”? Image at

Galaxies  System of stars, dust, and gases that are held together by gravity and categorized by shape   come in different shapes and classifications   Spirals   Ellipticals   Irregulars   are fairly close together, relative to their sizes

Elliptical Galaxies Images at and

Elliptical galaxies   range from spherical to football shaped   range from very small to giant   have very little gas or dust   mostly old stars

Spiral galaxy--Andromeda NOAO/AURA/NSF Images at and

Spiral Galaxies   have flat disk, spiral arms, central bulge, and a surrounding halo   some have a “barred” bulge   are fairly large (no dwarf spirals)   have lots of gas and dust and younger stars in their arms, but older stars and little gas or dust in their halos and central bulges   EX: Our Galaxy… The Milky Way

Spiral Galaxy on Edge Image at

Our Galaxy: the Milky Way   has about 200 billion stars, and lots of gas and dust   is a barred-spiral (we think)   about 100,000 light-years wide   our Sun is halfway to the edge, revolving at half a million miles per hour around the center of the Galaxy   takes our Solar System about 200 million years to revolve once around our galaxy

Mapping the Milky Way We can see stars  star clusters  nebulae  Galaxies  Let’s try to Map our Galaxy How do we know what our Galaxy looks like?

The Milky Way Image at

Irregular Galaxies NASA and NOAO/AURA/NSF Images at and

Irregular Galaxies   No distinct shape or size   usually have lots of gas and dust and young stars   may have a distorted shape from interaction with another galaxy

Active galaxy Image at

at the center of a large galaxy Image at andhttp://hubblesite.org/newscenter/archive/releases/exotic/black-hole/1998/22/results/20/