1. Nebulae &
Galaxies
B y : J a s m i n e Ta m ,
J e n n if e r L e e , &

2. What is a nebula?
A nebula is an interstellar cloud
of dust, hydrogen, helium and
other ionized gases

3. How do nebulae form stars?
Gas, dust, and other materials “clump” together
to form masses
Gravity pulls other matter to the clump
Eventually, clump will become massive enough to
form stars

4. How are nebulae formed?
Collapse of interstellar gas in space
Ultraviolet rays from surrounding
stars ionizes the surrounding gas
making the nebula visible
Supernova explosions from stars of
over 100 solar masses
When stars lose their outer layers of
gases at the end of their lives

5. Types of Nebula:
Diffuse Nebula Supernova Remnant
Emission Reflection Dark
Nebula Nebula Nebula
Planetary
H II Regions
Nebula

6. Diffuse Nebula:
Nebulae which are extended and do
not contain (visible) well-defined
boundaries
Some diffuse nebula contain enough
gas and dust to form about 100,000
stars the size of the sun
May be positioned near a bright star

7. Diffuse Nebula – Emission Nebula
Light from a nearby star energizes the gas
atoms of the nebula causing this nebula to be
able to emit light
There are 2 types of emission nebulae
Planetary Nebula
H II Regions

8. Diffuse Nebula – Emission Nebula
Planetary Nebula H II Regions
Occurs during red giant Newly formed stars emit
phase of a star when ultraviolet light which
outer layers of star is ionize the surrounding
shed gases
Ultraviolet radiation from
exposed core ionizes
shed layers
Ring Nebula “Pillars of Creation”
Eagle Nebula

9. Diffuse Nebula – Reflection Nebula
Do NOT emit light
Dust particles reflect
light from stars
Usually blue in colour
because dust grains
Witch Head Trifid Nebula
reflect more blue light
than red light Nebula

10. Supernova Remnant
Caused by the
explosion of a star
Consists of the ejected
matter from the
explosion
Crab Nebula

11. Dark Nebula

12. Dark Nebula – What is it?
Interstellar cloud that is extremely dense with
interstellar dust grains located in the
coldest, darkest places of the nebula.
It is dark enough to block out ALL light! Even
the neighbouring stars around the nebula!

13. Coal Sack Nebula
Brilliant example of a dark
nebula, as it can easily be
seen by human eyes.
On bright, starry nights, it’s
seen as a dark patch on the
night sky, clearly apparent
from the background of
Milky Way
Belongs to the constellation
Crux, and can only be seen
in the Southern Hemisphere

14. Snake Nebula
Dark Nebulae have no definite
shape and boundaries
Many twist and turn into
convulsing shapes. A good
example is the Snake Nebula
Also known as Barnard 72, it is
S-shaped and found in the
constellation Ophiuchus
Part of the Great Dark Horse
Nebula

15. Horse Head Nebula
Perhaps the most famous of the
Dark Nebulae, also known as
Barnard 33, is the Horse Head
Nebula.
Found in constellation Orion,
and it lies behind the star
Alnitak.
Categorized and found by
Edward Emerson
About 1600 light years away
More apparent because the bright
nebula, IC 434 is behind it,
casting a larger shadow.

16. Bok Globules and New Stars
Small dark nebulae are often referred to as Bok
Globules.
Cool clouds of gas and dust that are more
spherical in shape, resembling drops of
water
Named after Bart J. Bok (American astronomer)
Believed to create lower mass stars.
Dark Nebulae also site for creating new stars, as
mentioned by Jen.

17. Planetary
Nebula

18. What are they?
Type of emission nebulae
Cloud of ionized gas that emit light in various colors
Lit up by a central star
Looks like small planets through optical telescopes,
which is why they are called PLANETary nebulae
Formed when a star is dying (in red giant stage)
Outside layer of star dissipates and star shines
brighter and hotter with out outer layer
Can reach up to 25 000 to 200 000 degrees celsius
Ultraviolet radiation from the core of the star ionizes
the gas and plasma which creates the colorful
lights

19. General
Help create new stars
Info :
Star dies => metals in core sent across universe => metal
able to create new stars
Only stars that are around the same mass of our sun
(1 solar mass) can turn into a planetary nebula
8 solar masses or more will turn into a supernova instead
Generally found in the plane of the Milky Way, but are
more closely gathered in the centre of Milky Way
Not very bright compared to other nebulae, even
thought their central star are some of the hottest
known in the universe
Because the hotter a star is, the more ultraviolet rays make
it hard to see it in visible light

20. Bug Nebula
Found in constellation Scorpius
Outer structure (bipolar planetary nebula)
considered to be the most complex of all known
planetary nebulae.
Central star also considered to be hottest in the
galaxy, but very faint to see on Earth -white
dwarf that burns at 200 000 K

21. Cat's Eye Nebula Found in constellation Draco
(3300 light years away)
Also contains highly
complicated structure that
contains a hot central star
that lost it’s outer layer
over 1000 years ago
Found by William Herschel
Shells that appear in the
photo are actually layers of
ionized gas from the dying
star

23. So What Happens When a Star Explodes?
As mentioned before, if the star was less than 8
solar masses, it will turn into a planetary
nebulae
If more than 8 solar masses, it will turn into a
supernova remnant!
Supernova remnant is the structure left behind
after a supernova explosion (star goes BOOM)
Heats up interstellar medium and sends out
important metals throughout universe

24. Types of Supernova Remnants (I)
2 main types: First type is the shell-type
remnant (heats up interstellar medium
during explosion)
Interstellar medium: dust and gas
between stars and galaxies (after
supernova explosion becomes
hot)
Cygnus Loop: example of a shell type
remnant (show picture)
Found in constellation Cygnus
(extremely large for a supernova
remnant)
Scientists have found 4 smaller
nebulae inside the Loop!

25. Types of Supernova Remnants (II)
Crab Nebula
Second type is crab-type found in
Famous Crab Nebula remnant.
(also called pulsar wind (show
constellation Taurus nebulae)
picture)
Contains neutron star that sends out
regular pulses of radiation Crab
Central neutron star called
Pulsar
These supernova remnants filled with
high energy electrons from the neutron
Spins 30.2 times per second
starwhile emitting radiation

26. Galaxies

27. What are Spiral Galaxies?
Thin structures similar to a disk
Have arms of stars spiralled around the galaxy’s
center.
Tightly wound spiral called “Sa” ; loose spiral is
called “Sc.”
Consist of mainly young, new stars
Have interstellar matter in galaxy disk
approximately 10,000 to almost 100,000 light
years in diameter

28. What are Spiral Galaxies?
Center of the spiral galaxy  bulge (a dense
concentration of stars)
Diameter of a few thousand light years
Extends above and below the disk.
Spiral arms & blue waves in the galaxy disk’s
density hold high proportion of huge, hot stars
Stars shine longer & have brighter light than
smaller, more common stars, eg. Sun

30. What are Barred-Spiral (SB) Galaxies?
Very similar to spiral galaxies
Have a bar of stars running through the middle
Tightly wound barred-spiral galaxy is called “SBa”
; loosely wound barred-spiral galaxy
Called “SBc.”

31. What are Barred-Spiral (SB) Galaxies?
Theories of bar fueling stars during its evolution.
Theories of bar created by density wave from the
galaxy’s center
Caused the inner stars to reshape its orbit.
Those stars orbit further out T the structure of bar

33. Milky Way (aka Earth's Galaxy)
Part of the Local Group which contains over 24 other
galaxies
Contains many beautiful and important features
Nebula in Orion’s sword.
Birthing ground where powerful stars produced.
Created from swallowing other galaxies
Stars from the Sagittarius Dwarf Galaxy
As old as the universe
Milky Way: 13.6 billion yrs ; universe 13. 7 billion yrs.
Galaxy’s disk and the bulge not created until 10-12
billion yrs ago

34. Milky Way (aka Earth's Galaxy)
Has halo of approximately 150 globular clusters
scattered around galactic center
Globular clusters = thousands of millions of old stars tightly
grouped together
Only 20-30 light years across = concentrated in a swarm
Stars so old  most less than two solar masses & glow yellow-
red.
Dusty and gassy
Only allow to see 6000 light years in visible spectrum
Deflects visible light
Infrared light can still pass through
Use infrared telescope (Spitzer Space Telescope) and clearly see
galaxy’s center and regions where stars form

35. Milky Way (aka Earth's Galaxy)
Have super massive black hole = Sagittarius A*
Diameter 15x Sun’s
Source of X-rays and radio waves from galaxy’s
center
200 + billion stars
Only 2500 seen from Earth
Low # of stars because too far from center
6000 light years closer, night sky = brighter!
Theory of having halo of dark matter
Invisible but existence believed through simulations

37. The End (: