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How did COBE detect tiny variations in cosmic microwave background temperature?
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Cosmic microwave background
A full-sky map produced by the Wilkinson Microwave Anisotropy Probe (WMAP) showing cosmic background radiation, a very uniform glow of microwaves emitted by the infant universe more than 13 billion years ago. Color differences indicate tiny fluctuations in the intensity of the radiation, a result of tiny variations in the density of matter in the early universe. According to inflation theory, these irregularities were the “seeds” that became the galaxies. WMAP's data support the big bang and inflation models, and cosmic microwave background is at the farthest limits of the observable universe.
The Cosmic Background Explorer (COBE) satellite detected tiny variations in the cosmic microwave background temperature primarily through its Differential Microwave Radiometer (DMR) instrument.1
To isolate these subtle fluctuations, which represent temperature differences of only about 1 part in 100,000, the research team performed a rigorous data-processing sequence:12
- Dipole Subtraction: The team first removed the "dipole anisotropy," a temperature variation caused by the motion of the satellite, Earth, and the Milky Way relative to the cosmic background radiation field.12
- Galactic Contribution Removal: Because the Milky Way emits thermal radiation that appears as a bright strip across the sky, this signal was subtracted from the data to reveal the underlying cosmic patterns.2
- Statistical Analysis: After removing these foreground effects, the remaining intensity patterns were analyzed. The team determined that these light and dark patches were not random noise but represented genuine temperature fluctuations, providing the first evidence of the primordial density variations necessary for the formation of galaxies and large-scale structures in the universe.12