Download Irregular galaxies

Galaxies
• Types of galaxies
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Elliptical
Lenticular
Spiral
Barred Spiral
Irregular
• Groups of galaxies
• Greeks (up to about 100 A.D.)
– Believed Earth is at the Center of the universe
– Believed that the Universe extends to the ‘orbit of
Saturn’. The largest measured distance is from Earth
to the Sun at several million miles.
• Renaissance (1500-1650)
– Believed the Sun is at the Center of the universe
– Believed the Universe extends to `distant stars’ with
an inferred distance of about 100 billion miles. The
largest measured distance is from the Sun to Saturn at
about 1 billion miles (886 million miles is actual
distance).
What are those fuzzy-looking
things out in the night sky?
• “Spiral nebulae” were identified not long after the
development of the telescope (around 1600).
• In the 1600’s, it was briefly suggested that “spiral
nebulae” are separate galaxies so far away that the
stars blur together, but most people thought they
were clouds of gas and dust.
• The question wasn’t resolved until 1923 when larger
and better telescopes were developed.
• They were still referred to as “island universes”
Classifying Galaxies
Lenticular
M100
NGC
1365
M87
NGC
3377
NGC
4449
Elliptical galaxies
• very little interstellar gas and dust
• very little star formation
• mainly old stars (red giants and red supergiants) 10
billion + years old.
• few or no young stars (main-sequence stars like our
sun)
Elliptical galaxies
Often occur in clusters
Spiral Galaxies
• It is theorized that our galaxy, the Milky Way, is a spiral
galaxy.
• Mostly young to middle-aged stars.
• Lots of gas and dust visible.
• Spiral galaxies consist of four distinct components:
– A flat, rotating disc of (mostly newly created) stars and
interstellar matter
– A central stellar bulge of mainly older stars, which
resembles an elliptical galaxy
– A near-spherical halo of stars, including many in
globular clusters
– A supermassive black hole at the very center of the
central bulge
Our Galaxy is a member of a small cluster
called the Local Group
bbb
Barred Spiral Galaxies
• The creation of the bar is generally thought
to be the result of a density wave radiating
from the center of the galaxy
• Bars are thought to be a temporary
phenomenon in the life of spiral galaxies,
the bar structure decaying over time,
transforming the galaxy from a barred spiral
to a "regular“, or “classical” spiral pattern.
• Studying the core of the Milky Way,
scientists found out that the Milky Way's
bulge was peanut-shaped.
Irregular galaxies have asymmetric
shapes and usually lots of young stars
They are often found near other galaxies. Usually much
smaller
Irregular galaxies
• The gravitational tides of other galaxies
may contribute to their irregular shape.
Irregular galaxies
• Some irregular galaxies are really spiral
galaxies that have been or are currently
being distorted by the gravitational
influence of other nearby galaxies.
Lenticular Galaxy
• A lenticular galaxy is a type of galaxy
which is intermediate between an elliptical
galaxy and a spiral galaxy
• Disk Galaxies
• Little or no new star formation
• Retain a significant amount of dust.
Lenticular
Recall what you know about the
formation of a star.
• Now imagine several hundred billion stars
forming simultaneously.
Formation of a Spiral Galaxy
Formation of an Elliptical Galaxy
Stellar Birthrate in Galaxies
Alternate thought about elliptical
galaxies:
• Current thinking is that an elliptical galaxy
may be the result of a long process where
two galaxies of comparable mass, of any
type, collide and me.rge
The “Hubble Deep Field”.
Young Universe
Young Universe
Colliding galaxies
The Mice
Cartwheel galaxy
Seyfert’s Sextet
Interacting galaxies
Interacting galaxies
Optical
Infrared
Colliding galaxies
Movie