what are the different types of it?
Type Ia supernovae
Dark matter
Type Ia supernovae 
what is the galaxy? It is a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter. where does the name come from? It is derived from the Greek word literally "milky". when was the last component mentioned above studied? 1884 who studied it? Lord Kelvin
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Dark matter [SEP] Type Ia supernova distance measurements
Type Ia supernovae can be used as standard candles to measure extragalactic distances, which can in turn be used to measure how fast the universe has expanded in the past. Data indicates the universe is expanding at an accelerating rate, the cause of which is usually ascribed to dark energy. Since observations indicate the universe is almost flat, it is expected the total energy density of everything in the universe should sum to 1 (). The measured dark energy density is ; the observed ordinary (baryonic) matter energy density is and the energy density of radiation is negligible. This leaves a missing which nonetheless behaves like matter (see technical definition section above) dark matter.