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Organic Molecules in the
Interstellar Medium
Maria Hunt
School of Physics
UNSW

The Universe Started With the
Big Bang!
In the beginning there was hydrogen,
helium, and a trace of lithium…

http://www.privatehand.com/flash/elements.html

So where did all the rest come from?
What elements
are needed for
life?
Carbon (C)
Hydrogen (H)
Oxygen (O)
Nitrogen (N)
Phosphorous (P)

Galaxies are the basic “unit” of the
Universe

Stars are
arranged into
galaxies.

The Milky Way is our Galaxy
It contains around 400 billion stars.

Next come the stars…
*Stars are the basic “units” of galaxies
*Actually,
when we say
“stars” we
really mean
solar
systems.
The Jewell Box: NGC 4755

Stars “cook”
the elements
heavier than H
and He, up
until Fe

Anything heavier (e.g.
gold, uranium) is made in
a supernova explosion
Before

For Life, We Need the Atoms to
Gather Into Molecules

Chemical Evolution of the Universe
Big Bang
Atoms
Molecules
Life
Amino
Acids
Sugars
Urea
Water

What Are Molecules?
• Molecules are made of 2 or more atoms.
• The most common atoms are H, C, O, he.
• The most common molecule in the universe
is H 2.

What Are Organic Molecules?
• Organic molecules are the molecules of life
and contain carbon.
• Only carbon (and perhaps silicon) have a
chemistry complex enough to form life.

How Do We Form Molecules in
This Vast, Empty Universe?

Molecular Clouds (also know as
dark clouds) are found inbetween
the stars.
The Jewell Box: NGC 4755

Star Formation in
Molecular Clouds:
* Stellar nurseries
* Nurseries for
molecular evolution
* Nurseries for life?

SiO, SiO 2
, H 2
O
CO, CS, HCN, HNC,
HCO + , CN, C 3
H 2
,
N 2
H + , HC (2n+1)
N
NO HCO + , N 2
H +
T= 5-25 K
CH 3
OH, H 2
CO,
SO 2
, H 2
CS, OH

As the gas density increases, molecules
collide with and stick to the grain
surfaces…..
HCN
H + H +
HC 5
N
HNC
CS
HCO +
C
HNC
C
O
H +
HC 3
N
…new saturated molecules form on
the grain surfaces such as CH 3
OH,
OCS, NH 3
, H 2
CO ….

Ultracompact H
II region
Hot Molecular Core
T = 100 – 300 K
CS, SO, OCS,
CH 3
OH, SO 2
,
HCOOCH 3,
CH 3
CH 2
OH & lots
of other “life”
stuff!

What Molecules Are Out There?
• We have found 123 different molecules, with up to
11 atoms
• We see complex organic molecules in molecular
clouds, including alcohol and vinegar.
• We may also have seen the amino acid glycine.
• But, to detect these in molecular clouds with our
radio telescopes on Earth requires incredible
quantities.

How Do Planets Form
• Not all the gas collapses into the protostar.
• The “left-overs” form the planets.
• The planets (solar system) form at the same
time as the protostar.
• Planets form by accretion.
• The chemical differentiation of the planets
occurs under the influence of a stellar wind
and a temperature gradient.

After the star “turns on” the planetary
formation is controlled by falling
temperatures as we move away from the
new star.
Star
Accretion
Disk (gas
& dust)
Planetesimals and
protoplanets forming
by accretion
Stellar Wind

How do we “see” molecules?

Where does life fit into the Universe?

We need amino acids if we
want to create a living
organism.
We still don’t know the origin of
the initial amino acids on the early
Earth from which life evolved :
Space?
or
Earth?

The “Early” Earth was too hot for
molecules.

The water for the
Earth’s oceans and
the organic molecules
needed for life were
probably “delivered”
by comets

A Better Place to Look?
• Carbonaceous chondrites are meteorites that
date back to the formation of the solar
system.
• They fall to earth on a regular basis.
• They are found to contain many complex
organic molecules, including amino acids.
• Comets are also remnants of the presolar
nebula.

Murchison Meteorite
• The most studied carbonaceous chondrite.
• Found in Murchison, NW Victoria, in early
1970s.
• Contains many amino acids of
extraterrestrial origin.
• Contamination had to be ruled out before the
ET origin of these was accepted.

The amino acids are found in an almost racaemic mix
(equal numbers of left and right handedness).
It was this property that confirmed the ET origin.
However, the mix is not quite racaemic.
There is about 10% more left-handed than right handed.
This has important implications for the evolution of life on
Earth.
Equally importantly, what can be found in the Murchison
meteorite after a careful analysis (over 20 years) in an Earthbased
laboratory is almost certainly present in molecular
clouds, although very much harder to find!