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The SMALLEST Stars
Neutron Stars
Neutron Stars ~Manhattan Size
• The densest type of star known.
• The mass of 1 ½ Suns is packed into a
ball that is as big as Manhattan.
• One cm-cubed of neutron star material
weighs as much as one whole mountain.
Earth’s radius ~6400 km
Moon’s radius ~1740 km
The Moon is about 3 ½ times larger than the Earth
White Dwarfs
Earth’s Size; Moon is 3 ½ times smaller
(Earth drawn to Scale)
Stars as big as the Earth
No-no you cannot be serious.
Earth’s diameter ~13,000 km
Well, yes, Sirius B is a white dwarf!
Sirius A is a normal star. Sirius A and B are one
of the nearest stars (6th nearest).
Jupiter ~ 11 x larger
Sun ~ 100 x larger
Stars as big as the Earth, but as heavy as the Sun
One cm-qubed weighs as much as three cars
Planets --- Earth, Venus, and Mars (drawn to scale)
Io
Red=Earth’s Size
Europa
Jupiter is ~ 11 x Earth
Ganymede
Callisto
Moon’s Orbit ~ 400,000 km
Earth’s radius ~7,000 km
Jupiter’s radius ~ 70,000 km
Sun’s radius ~ 700,000 km
Earth’s radius ~7,000 km
Jupiter’s radius ~ 70,000 km
Sun’s radius ~ 700,000 km
Moons Orbit around Earth
Rough Size of Sun
Rough Size of Sun
Earth’s Orbit around the Sun
The Largest Stars
Jupiter’s Path around the Sun
~ 5 times Earth-Sun Distance
Earths’s Path around the Sun = 1 AU
(1 Astronomical Unit)
Betelgeuse
“Red Supergiant”
• The only star for which we have a resolved
picture since it is large and close.
• Betelgeuse 1300 times the size of the sun.
• It is ~ 6 AU; 6 times Earth–Sun distance.
Jupiter’s Path around the Sun ~5 AU
Saturn’s Path around the Sun ~10 AU
Star Birth
Picture taken
with HST from
a central region
in Orion
Size: 150 AU
Size 15 Solar Systems
Nearest Planetary Nebula
• dying star
• NOT planetary system
Star Death
Size 15 Solar Systems
Size 0.5o
(same as sun!)
One light year is the distance light travels
in one year
1 light year ~ 60,000 AU
1 light year ~ 1013 km
Distance to Sun is ~ 8 light-minutes
Greenish middle:
Oxygen
Outer Red:
Hydrogen, some Nitrogen.
Arrow is one light year
And one light years is 0.3 “parsec”
Size: 150 AU
Distance from us:
~ 24 million AU or
~ 400 light years
(parsec is the unit astronomers use for distance)
Helix Nebula
“Sun Flower Nebula”
Bok Nebulae
Distance to Vega ~ 26 light years
(arrow below is 10 light years)
Dust Clouds
• Densest & Smallest
Clouds known
• Dark – does not let
light through
• Cold – 10K – 40K
(much, much, below
freezing ~-250oC)
These clouds will
collapse to form stars
and planetary systems
Closest Star ~ 4 light years
Size ~ 20,000 Solar Systems
Horsehead Nebulae
Distance to Vega ~ 26 light years
Distance to Capella ~ 45 ly
Rigel and Betelgeuse are more
than ten times farther
Size
• 1 to 10 parsec
• 3 to 30 light years
• 200,000 AU
Molecular Clouds
(MC)
These clouds will
collapse to form stars
and planetary systems
Typical Sizes of MCs
• 30 to 300 parsec
• 100 to 1000 light
years
Size ~ 100,000 Solar Systems
One Million times Earth-Sun Distance
M16 – Eagle Nebula
(the three fingers)
Same Scale as Horsehead Nebula
“Stellar Eggs”
Stars form in these “eggs” that are dark
dense clouds (we see because they are
illuminated by nearby stars
What’s left over
are star clusters
Smallest Open
Clusters may
contain 10 stars,
while largest ones
have a few 1000
stars
Sizes
-- 25 parsec
-- 75 light years
-- ½ million AU
Larger and more
massive clouds
from globular
clusters
Globular Cluster
“47 Tucane”
Open Cluster (NGC3293)
~ 25 parsec
Distance of Rigel ~ 900 ly
Distance of Betelgeuse ~ 520 ly
Arrow is 1000 ly
Globular Clusters
have up to about
one million stars
within the same
volume
Sizes
-- 25 parsec
-- 75 light years
Start seeing some spiral structure
of our Galaxy
~ 25 parsec
Eagle Nebula M16
All these stars are in the “Solar
Neighborhood”
Spiral Structures are seen
(the three fingers)
Gas Clouds
Pink nebulae are hot
gaseous nebulae
Typical Sizes
• 100 to 1000 parsec
• 300 to 3000 light
years
Arrow is ~ 1 kilo parsec
Size corresponds to a few million
Solar Systems
(this means 1000 parsec)
Milky Way is ~100,000 light years
(It takes 100,000 years for light from the other side of
the Galaxy to reach us)
One of the nearest
galaxies to our own
This is the Small Magellanic Cloud (SMC)
(it is not a cloud but a galaxy!)
Small Irregular Galaxies
Some of the closest
galaxies are roughly
100,000 to a few
100,000 light years away
SMC has roughly one
million stars
Gravitational forces from
our own Galaxy may be
pulling the SMC apart.
Typical sizes of small
galaxies like this are
~10,000 light years
Still one of the
closest galaxies – it
belongs to the socalled Local Group
(of galaxies)
Distance from us is
~ 2.3 million light
years
So much for getting
messages from
Extra-Terrestials –
these messages must
have been send 2.3
million years ago!
Stephan’s Quintet
Scales of
“groups of
galaxies”
~ 10 million
light years
Distance ~ 100,000 light years
Size ~ 10,000 light years
Andromeda Galaxy
Hercules Cluster
Hydra Cluster
A picture of galaxies not quite at the edge of the universe
The most distant galaxies are in this
picture
There is a “rat-race” going on for the
search of the most distant one…