Stars are categorized by their temperature, color, mass, and life stage. Here are the main types of stars:
1. Spectral Types (O–M Classification)
Stars are grouped by surface temperature and color using the Morgan–Keenan (MK) system, from hottest to coolest:
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O-type: Blue, extremely hot (>30,000 K), very rare, short-lived (e.g., Zeta Puppis)
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B-type: Blue-white, hot (10,000–30,000 K), luminous (e.g., Rigel)
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A-type: White, 7,500–10,000 K (e.g., Sirius)
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F-type: Yellow-white, 6,000–7,500 K (e.g., Procyon)
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G-type: Yellow, 5,200–6,000 K (e.g., our Sun, G2V)
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K-type: Orange, 3,700–5,200 K (e.g., Arcturus)
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M-type: Red, <3,700 K, most common (e.g., Proxima Centauri)
2. By Size and Brightness
These categories apply to different phases and masses:
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Main Sequence Stars: Like the Sun, fuse hydrogen in their cores.
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Giants: Stars that have expanded late in life, cooler but very large.
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Supergiants: Massive stars, extremely bright, often end as supernovae.
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White Dwarfs: Hot, dense remnants of stars like the Sun.
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Neutron Stars: Ultra-dense cores left after supernovae; often pulsars.
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Black Holes: Collapsed remnants of very massive stars.
3. Special Types
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Brown Dwarfs: "Failed stars" too small to sustain hydrogen fusion.
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Variable Stars: Change brightness due to internal or external factors (e.g., Cepheid variables).
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Binary and Multiple Star Systems: Stars that orbit a common center of mass.