Dark Matter and Dark Energy

Most of the universe is dark matter and dark energy.

• • Most of the mass-energy, about 95%, in the universe is ‘dark’. By dark we mean that it

does not emit any form of electromagnetic

radiation. Dark energy and dark matter have not been directly observed but they have been inferred from observations of a wide variety of phenomena. There existence is vital to the Big Bang Theory.

Total Mass/Density of the Universe

Dark Energy makes up 72% of the total mass energy density of the universe. The other dominant contributor is Dark Matter, and a small amount is due to atoms or baryonic matter.

Dark Matter

• • The existence of dark matter is inferred indirectly by its gravitational effect. Inference from observations of – the motions of stars and gas in galaxies, cluster galaxy radial velocities, hot gas properties of clusters, and gravitational lensing of distant, background galaxies by foreground galaxy clusters all suggest large amounts of Dark Matter exist. – Radial velocity is the velocity of a star or other body along the line of sight of an observer.

Dark Matter

– Gravitational lensing - A gravitational lens refers to a distribution of matter between a distant source and an observer; which is capable of bending the light from the source, as it travels towards the observer.

Dark Energy

• Dark Energy is a hypothetical form of energy that exerts a negative, repulsive pressure, behaving like the opposite of gravity.

– Without dark energy, astronomers would not be able to explain why the galaxy is still increasing in size, in fact its expansion is accelerating, when gravity should make it contract.

Dark Energy

• Like Dark Matter, Dark Energy is not directly observed, but rather inferred from observations of gravitational interactions between astronomical objects.

Big Bang Nucleosynthesis

• • Big Bang Nucleosynthesis (abbreviated BBN) refers to the production of nuclei other than those of the lightest isotope of hydrogen during the early phases of the universe.

http://astro.berkeley.edu/~mwhite/darkmatte r/bbn.html

Big Bang Nucleosynthesis

• • The Universe's light-element abundance is another important criterion by which the Big Bang hypothesis is verified. It is now known that the elements observed in the Universe were created in either one of two ways. – Light elements (namely deuterium, helium, and lithium) were produced in the first few minutes of the Big Bang. – Elements heavier than helium are thought to have their origins in the interiors of stars which formed much later in the history of the Universe. – Both theory and observation lead astronomers to believe this to be the case.