It presents about normal galaxy and how it differs to other type of galaxy. The types of galaxies are also presented like spiral galaxies, barred spiral, ellipticals, lenticulars and irregular galaxies with examples and pictures for further explanation.

2. GALAXIES
are huge collections of stars, dust and gas
 usually contain several million to over a trillion
stars and can range in size from a few thousand
to several hundred thousand light years across
 there are hundreds of billions of galaxies in the
Universe

3. EDWIN POWELL HUBBLE
 an American astronomer
Born: November 20, 1889, Marshfield,
Missouri, United States
Died: September 28, 1953, San
Marino, California, United States
Discovered the cosmos
 The HUBBLE SPACE TELESCOPE was
named after him.
Hubble classification scheme is strictly
based upon the visual appearance of
the galaxy.

4. CLASSIFICATIONOF GALAXIES
Normal Galaxy Active Galaxy

5. NORMAL GALAXIES
• make up about 90% of all galaxies in the universe.
• have luminosity and spectrum distinct to the stars
in the sky
• Have 5 basic types: Elliptical
Spirals
Barred spirals
Irregulars
Lenticulars

6. ACTIVE GALAXIES
• are galaxies which have a small core of emission
embedded in an otherwise typical galaxy
• concentrate on the possibility of a
supermassive black hole which lies at the center
of the galaxy
• Have 3 basic types: Seyferts
Quasars
Blazars

7. DIFFERENCESOF NORMAL ANDACTIVE GALAXIES
Characteristic Normal Galaxies Active Galaxies
Total Luminosity Consistent with other stars larger
Spectra Normal brightness brighter
Radiation emitted in or near the visible
portion of the electromagnetic
spectrum
do emit substantial amounts of
visible radiation, but far more
energy is emitted at longer
wavelengths

9. TYPES OF GALAXIES

10. Partsof theGalaxy

11. • Edwin Hubble was the first to develop a method to
classify the different galaxies.
• He identified five types of galaxies:
Spirals
Barred Spirals
Ellipticals
Lenticulars
Irregulars

12. SPIRAL GALAXIES
• They have flat, disk-like shapes.
• Spiral galaxies have a variety of star populations.
Mix of young and old stars in the bulge.
Young stars in the disc. (Population I)
Old stars in globular clusters in the halo. Population
II)
Vigorous star formation along the spiral arms.
• The spiral structure of these galaxies is likely
the result of past gravitation interactions with
other galaxies.

13. SPIRAL GALAXIES
• Spiral galaxies are rich in gas and dust and have
a high rate of star formation.
• Since spirals contain a high fraction of hot,
young stars, they are often among the brightest
galaxies in the universe.
• Spiral galaxies are classified by the size of
their central cores, or bulges.

14. SPIRAL GALAXIES
• 3 main types of Spirals:
Sa: have very tightly wound arms around a
larger central nucleus
Sb: are between, having moderately wound
arms around an average sized nucleus
Sc: have very loosely wound arms around a
smaller nucleus

15. The Sombrero Gallaxy, Sa

16. Sb spiral -M51

17. An Sc Galaxy, NGC 1512

18. Sc spiral - NGC 2997

19. BARREDSPIRAL GALAXIES
• characteristics are very much like spiral
galaxies except that instead of the spiral
arms emanating from spherical nucleus, the
spiral arms emanate from a bar.
• The stellar populations are predominantly
the same as those within spiral galaxies.

20. BARREDSPIRAL GALAXIES
• 3 types:
 SBa: Large core, small uniform spiral
arms
 SBb: Moderate sized core, well-formed
uniform spiral arms
 SBc: Small core, long extended and
clumpy spiral arms

21. SBa spiral - M95

22. SBb spiral - NGC 1365

23. SBc spiral - M61

24. SBb or SBc type- Milky Way Galaxy

25. ELLIPTICALS
• are elliptical in shape or egg-like shape
• resemble large globular clusters.
• exclusively old, metal-poor stars. (Population
II stars)
• do not have much gas and dust
• There are very little new star formation in
these galaxies.
• Classified by their shape.

26. ELLIPTICALS
• eight subgroups: E0 E1 E2 E3
E4 E5 E6 E7
 depend on their elongation.
 E0 : nearly circular or round spherical
shape
 E4 : somewhat elliptical, but not flat
 E7 : highly elongated or nearly a flat disk
(or So)
• Elliptical galaxies can be the largest galaxies in the known
universe (called giant elliptical) or very small galaxies (called
dwarf elliptical).

27. M87 , An E0 Galaxy

28. E1 - M49

29. E5 - M59

30. Dwarf E5 Peculiar - M110

31. LENTICULARS
• are not quite ellipticals and not quite spirals.
• These galaxies have star populations similar to
ellipticals, but show the beginnings of a disc
structure.
• There are no discernable spiral arms.
• Classified as either S0 or SB0 depending upon
whether there is any bar structure or not.

32. N G C 5 8 6 6 , A n S 0 G alax y

33. Sc NGC 7339 and S0 peculiar NGC 7332

34. IRREGULARS
• Irregular galaxies tend to be very small
compared to other galaxies.
• Has a mix of young and old stars with the
younger stars dominating.
• They have a very high rate of star
formation.
• No real coherent shape or structure.

35. IRREGULARS
• The lack of shape may be due to the gravitational tides
created by neighboring galaxies.
Types:
• Irregular I galaxies (like the Magellanic Clouds)
appear to have some spiral structure, but it appears
to have been disrupted.
• Irregular II galaxies are much more disturbed than
Irr I galaxies and look like they have been victims of
some type of explosion that has completely disrupted
their original shape.

36. Irr I- The Large Magellanic
Cloud

37. Irr II - M82

38. HUBBLE’S TUNING FORK DIAGRAM
• Edwin Hubble created the “Tuning Fork Diagram” as a
means to organize the various types of galaxies he
saw.
• Later, it was thought that this diagram may indicate
an evolutionary path for galaxies.
• Even though the diagram is suggestive, there is no
support for this.
• Spiral and barred spiral galaxies are formed through
gravitation interactions, or collisions, with other
galaxies)

39. Tu n in g F o r k Illu s tra tio n

40. GALACTIC CANNIBALISM
• Galaxies tend to form close to each other gravity will oftentimes
cause the galaxies to collide.
• These collisions may influence the rate of star formation within
the galaxies.
• This would be due to the gravitational forces causing collapse in the
gas clouds of the galaxies.
• The galaxies will be so close together that the overall shape of the
galaxies will be altered.
• In the extreme cases the galaxies will merge together as one.
• If one galaxy is much larger than neighboring galaxies, then the
large galaxy may actually consume its neighbors
This process is called GALACTIC CANNIBALISM.

41. HUBBLE’S LAW
Universal recession:
All galaxies (with a couple of
nearby exceptions) seem to be
moving away from us, with the
redshift of their motion
correlated with their distance.
• Hubble’s law relates how fast galaxies
are moving away from us at different
distances.

42. HUBBLE’S LAW
The relationship (slope of the line) is characterized by
Hubble’s constant H0:
recessional velocity = H0  distance
• The value of Hubble’s constant is currently uncertain, with
most estimates ranging from 50 to 80 km/s/Mpc (Millions of
parsecs).
• Measuring distances using Hubble’s law actually works better
the farther away the object is; random motions are
overwhelmed by the recessional velocity.

43. SOURCES:
http://coolcosmos.ipac.caltech.edu/cosmic_classroom/cosmic_reference/galaxies.html
http://wind.caspercollege.edu/~marquard/astronomy/galaxies.htm
http://gtn.sonoma.edu/resources/normal_galaxies/
http://imagine.gsfc.nasa.gov/docs/science/know_l1/active_galaxies.html

44. THANK YOU 
DAISY MAE A. VALEROSO