The Mystery of Dark Matter.
                     The Mystery of Dark 
Matter
INTRODUCTION
• Matter as we know it—atoms, stars, planets, 
trees, rocks and us—account for less than 5% 
of the known universe. 
• The rest remains somewhat of a mystery. 
Source: www.science.org.au
DARK ENERGY
• Astronomers and cosmologists think around 25 
per cent of our universe is made of something 
called dark matter, and the remainder around 
70 per cent is what’s known as dark energy.
Source: www.science.org.au
INTERACTION WITH 
GRAVITY
• Dark matter doesn’t interact with l ight, so we 
can’t see it.  
• The only reason we know there’s something 
out there beyond what we can directly see is 
because it interacts with gravity.
Source: www.science.org.au
EXTRA GRAVITY
• Essential ly, the gravity exerted by the visible 
mass of galaxies and clusters is insuffi cient to 
hold them together there’s got to be some 
additional mass there to create the extra 
gravity needed.
Source: www.science.org.au
UNIVERSE WITHOUT 
DARK MATTER
• Without dark matter, stars would l ikely be 
scattered all  throughout the universe. 
• Galaxies, including our Milky Way, and 
therefore us, would not exist.
Source: www.science.org.au
UNDERSTANDING OF 
DARK MATTER
• In 1933, the astronomer Fritz Zwicky observed 
that galaxies within the Coma cluster were 
moving faster than expected.
• Speeds which should have caused them to 
leave the cluster rather than being held in by 
its gravitational pull .  
Source: www.science.org.au
AUSTRALIAN 
ASTRONOMER
• Australian astronomer Ken Freeman noticed 
gas was moving around galaxies at greater and 
greater distances at the same speed, despite 
there being l ittle material at these large 
distances. 
Source: www.science.org.au
OBSERVATIONS BY 
ASTRONOMERS
• These observations indicated that the 
gravitational fi elds in the galaxies were 
greater than expected based on their amount 
of visible mass—the large gravitational pull  
they were exerting could only be explained by 
the presence of some sort of additional mass. 
Source: www.science.org.au
MYSTERY 
• No one knows much about this particle, except 
to be pretty sure it’s something we’ve never 
encountered here on Earth. 
Source: www.science.org.au
MEANING OF DARK 
MATTER
• I t  doesn’t interact with l ight, hence the name 
‘dark’ matter, which means that it’s neutral,  
with no electrical  charge. 
Source: www.science.org.au