2. The Hubble Ultra Deep Field, or HUDF, catalogs thousands of galaxies in a small section of space in the southern constellation Fornax.
Previous versions of the HUDF covered the range of wavelengths stretching from near-infrared through the visible spectrum, plus the far ultraviolet.
But the near-ultraviolet part of the spectrum wasn't covered nearly as well, until

3. Galaxies

4. The Milky Way Galaxy
We live on the quiet outskirts of a galaxy of approximately ____ ____________.
The Milky Way, is roughly __________ and is about _______ ________ in diameter.
Named for the band of faint whiteness that stretches across the night sky
400
billion stars
disk-shaped
100,000
light yrs
Our galaxy seen from the inside!

6. Our galaxy probably looks like this: A Barred Spiral

7. The Milky Way Galaxy
Our galaxy seen edge-on…

9. Parts of Our Galaxy Ours is a __________________. It is composed of:
a ____________ with a bar of stars
a ________ containing the _____ ____
a ____ of globular clusters
Possible halo of unknown material commonly known as “__________”.
Barred Spiral Galaxy
central bulge
flat disk
spiral
arms
halo
dark matter

10. Galactic Terminologies
Central Bulge – The central portion of a spiral galaxy that is roughly spherical (or football shaped) and bulges above and below the plane of the galactic disk.
Disk – The portion of a spiral galaxy that looks like a disk and contains an interstellar medium with cool gas and dust; contains stars of many ages.

11. The disk All types/ages of stars, nebulae, etc. Spiral arms
____ “where the stars are”
Rather, where ____________ stars are
Luminous stars are ___________
Massive stars are young (they don’t live long)
Spiral arms show ______ star formation
Not
most luminous
massive stars
recent

12. Galactic Terminologies
Spiral Arms – The bright, prominent arms, usually in a spiral pattern, found in most spiral galaxies
Halo – The spherical region surrounding the disk of a spiral galaxy
Globular Clusters – A spherically shaped cluster of up to a million or more stars; globular clusters are found primarily in the halos of galaxies and contain only very old stars

13. Spiral Arms - Density Waves
The arms are traced out by ____________, __________. Arms are regions of higher _______ that stars and gas pass through.
Gravity of mass in the arm pulls in clouds that collapse and form stars.
massive bright
young stars
density

14. The halo Stars in the halo are mostly ___ Therefore mostly ________
Many are found in globular clusters
old
low mass

15. Globular clusters

16. Parts of Our Galaxy
In addition to the stars, star clusters, dead ‘stars’, failed stars, planetary nebulae, black holes, planets, moons, comets, and asteroids, the disk is filled with _________________ (IM).
IM is composed primarily of ________ (70%) and _______ (28%).
_______________ produced by the star-gas-star cycle account for about 2% of the materials.
interstellar medium
hydrogen
helium
Heavier elements

17. Our place in the galaxy Lots of gas and dust
____ = individual atoms/molecules
____ = larger (microscopic) specks
Using visible light, you can’t see very far through our galaxy
Question: How do we know how our galaxy is laid out?
Other kinds of light (______________ _______) are not effected by gas & dust
Gas
Dust
electromagnetic
radiation

18. Our galaxy, seen from the inside

19. What is Lurking in the Center of Our Galaxy?
Near the center of our galaxy there are roughly __ million stars packed into one cubic light year.
In the center is an object smaller than the __________________ but several mill. times the mass of the Sun.
Little light is visible from object, thought to be a ______________. 10
size of Jupiter’s orbit
This is called a supermassive
black hole - about 2.5 million
solar masses. Most other
Galaxies are also thought to
have these huge black holes
in their centers.
large black hole

20. Globular Clusters and the Center of the Galaxy
Globular clusters tended to be distributed in an ________ region of space.
Used to find ______ of the galaxy.
_____ not at the center of the galaxy.
elliptical
center
Globular
Clusters
contain some
of the oldest
stars in the
galaxy.
Sun

21. Where are we? The Sun is about _______ light years from the center
About 2/3 of the way out
The stars all ‘_____’ around the center
In the direction of ___________
Our orbit = the solar circle
The Sun orbits at __________.
Takes ~ ___________ years per orbit
28,000
orbit
Sagittarius
220 km/sec
240 million

23. Orbits of Stars in Our Galaxy
Disk Stars
orbit the center of the galaxy in the same direction.
Orbits bobs up and down like the horses of the merry-go-round
Halo Stars
Orbit the galaxy in a more or less elliptical orbit.
The orientation of these orbits are random
Bulge Stars
Bulge stars also orbit the galactic center in elliptical orbits and in a random fashion.

24. Motion in the Galaxy
Most of the _____ of our galaxy is ____ visible to us!
This invisible mass is called _____ ______
No one knows what it is at this time
Makes up as much as ____ of the Milky Way’s mass!
One of the most important questions in modern astronomy
mass
not
dark
matter
90%

25. Other Galaxies

26. Types of Galaxies
1920’s Hubble classified galaxies based on __________.
______
______ Spirals
________
__________ (Lenticular)
_________
appearance
Spirals
Barred
Ellipticals
Transitional
Irregulars

27. The Hubble Tuning-Fork Diagram
The traditional way of classifying galaxies is though …

28. Types of galaxies Spiral galaxies -75 - 85% of large galaxies
____________ and halo
Arched lanes of stars + gas and dust
Vary in __________ and how _____ _____ the arms are
Sa _____ bulge, ____ arms
Sb _______ bulge, _________ arms
Sc ______ bulge, ______ arms
Nuclear bulge
size of bulge
tightly
wound
Large
tight
Medium
moderate
Small
loose

29. Sa Galaxies
Sa galaxies have a large (dominant) bulge, and a very smooth disk with only a trace of spiral arms.

30. Sb Galaxies
In Sb galaxies, the bulge and disk components are comparable. Spiral structure is becoming visible in the disk.

31. Sc Galaxies
Sc galaxies have little or no bulge and a prominent disk with clearly defined spiral arms. These arms appear knotty.

32. Types of galaxies Same classification as spirals
Barred spiral galaxies
Have a distinct ‘___’ through the middle
_____ (2) extend from ___, not bulge
Same classification as spirals
____ Large bulge, tight arms
____ Medium bulge, moderate arms
____ Small bulge, loose arms
bar
Arms
bar
SBa
SBb
SBc
The Milky Way is and SBc

33. SBa Galaxies
SBa galaxies have a large (dominant) bulge, and a very smooth disk with only a trace of spiral arms.

34. SBb Galaxies
In SBb galaxies, the bulge and disk components are comparable. Spiral structure is becoming visible in the disk.

35. SBc Galaxies
SBc galaxies have little or no bulge and a prominent disk with clearly defined spiral arms. These arms appear knotty.

36. Types of galaxies Elliptical galaxies ________ component (no arms)
Categorized base on shape - ______
E0 = ______ - E7 = Most _________
Includes a __________ of sizes
Giant ellipticals - the ______ galaxies in the Universe
Dwarf ellipticals - Amongst the ________ galaxies
No disk
ellipse
Circle
Elongated
wide range
largest
smallest

37. Elliptical Galaxies
They are classified E0 (round) through E7 (very elliptical).

40. ___________ (S0 and SB0) Galaxies
Transitional
Transition objects. No star formation, no spiral arms, and very little cold gas/dust.

41. Types of galaxies Irregular galaxies
______ ‘spiral’ shaped nor ‘elliptical’
Often associated with galaxy-to-galaxy interactions
Neither

42. Irregular Galaxies
Irregular galaxies have a _____ amount of ____, ___, and __________, but no spiral structure.
large
dust
gas
young stars

45. Galaxy Evolution How are galaxies formed?
What phases do they go through?
Do they ‘die’?
All are unanswered questions
There is no ‘HR diagram’ for galaxies!

46. Galaxy formation Four Hypotheses Rotation
Fast rotating clouds --> spirals
Slowly rotating clouds --> ellipticals
Collapse speed
Fast collapse --> ellipticals
Slow collapse --> spirals

47. Galaxy Formation 3) Collisions 2 colliding spirals --> 1 elliptical
4) Irregular galaxies
Many are associated with colliding galaxies

51. Galaxy Clusters and Superclusters
Galaxies are grouped into _________
Gravitationally bound, orbit each other and collide
Pass through, merge, hurl stars into space
Milky Way and Andromeda Galaxies are part of the __________ (Cluster)
Clusters of galaxies are grouped into ___________ (Virgo)
Contain dozens of individual clusters
clusters
Local Group
Superclusters

52. http://academic.pgcc.edu/~lgarcia/256,1,The Milky Way Galaxy9
evolution
14, Our Galaxy
Galaxy: The Population I Component