The universe is filled with countless stars, ranging from incredibly bright supergiants to faint, nearly invisible celestial objects. While some stars shine brilliantly in the night sky, others are so dim that they can barely be detected. But which star is the dimmest and least bright?
To answer this question, we need to explore different categories of stars, their brightness levels, and what makes some of them nearly undetectable.
Understanding Star Brightness
What Determines a Star’s Brightness?
The brightness of a star is measured in two main ways:
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Apparent Magnitude – How bright a star appears from Earth.
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Absolute Magnitude – The true brightness of a star if all were viewed from the same distance (10 parsecs or 32.6 light-years away).
The lower the magnitude, the brighter the star. For example, the Sun has an apparent magnitude of -26.74, making it the brightest object in our sky. On the other hand, dim stars have high positive magnitudes.
Why Are Some Stars So Dim?
Several factors contribute to a star’s low brightness:
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Small size: Some stars are tiny compared to the Sun, emitting very little light.
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Low temperature: Cooler stars emit less energy, making them appear dim.
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Distance: Some stars are so far away that their light barely reaches us.
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Fading remnants: Dying stars like white dwarfs and brown dwarfs are naturally faint.
The Dimmest Star Ever Observed
1. 2MASS J09393548−2448279 (A Brown Dwarf Candidate)
One of the faintest stars ever discovered is 2MASS J09393548−2448279, a brown dwarf located about 17 light-years away. It has an apparent magnitude of about 21, making it invisible to the naked eye.
Why Is It So Dim?
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It is a brown dwarf, meaning it failed to ignite sustained nuclear fusion like normal stars.
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It emits only infrared light, which is nearly undetectable to human eyes.
This object is so faint that astronomers needed powerful infrared telescopes to detect it.
2. WISE 0855−0714 (One of the Coldest Stars Ever Found)
Another contender for the dimmest known star is WISE 0855−0714, a Y-type brown dwarf discovered in 2014.
Notable Features:
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It is 7.2 light-years away, making it one of the closest known substellar objects.
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Its surface temperature is around -13°C (8°F)-colder than some places on Earth!
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It barely emits any visible light and can only be observed in infrared wavelengths.
Because of its extreme cold and lack of fusion, WISE 0855−0714 is considered one of the faintest and least bright stars ever discovered.
Other Extremely Dim Stars
3. Van Maanen’s Star (A Faint White Dwarf)
Van Maanen’s Star is a white dwarf located 14 light-years away. Though it was once a bright main-sequence star, it has now exhausted its fuel and shrunk into a faint, dying remnant.
Key Characteristics:
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Apparent Magnitude: About 12.4, making it too dim to see without a telescope.
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Low Luminosity: As a dead star, it only shines from leftover heat.
4. OGLE-TR-122b (The Smallest Main-Sequence Star)
OGLE-TR-122b is a red dwarf and one of the smallest stars ever found-only slightly larger than Jupiter.
Why Is It So Dim?
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It is a red dwarf, the coolest and least luminous type of normal star.
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It barely emits visible light, requiring telescopes to detect it.
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Its small size (about 0.12 times the Sun’s radius) limits its energy output.
Even though it’s a fully functioning star, its dim nature makes it one of the least bright stars in the universe.
Are There Even Duller Stars?
Yes! The dimmest possible stars would be:
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Failed stars (brown dwarfs) – These never fully ignited.
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Dying white dwarfs – These are cooling and will eventually become black dwarfs (completely invisible).
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Neutron stars and black holes – These stellar remnants emit no visible light.
Since black dwarfs have never been observed (the universe isn’t old enough for one to form), the faintest known stars remain brown dwarfs like WISE 0855−0714.
How Do Astronomers Detect Such Faint Stars?
Since these stars emit little to no visible light, astronomers rely on infrared and radio telescopes to detect their faint emissions. Some of the best tools include:
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WISE (Wide-field Infrared Survey Explorer) – Used to find WISE 0855−0714.
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Hubble Space Telescope – Helps locate distant dim stars.
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GAIA Mission – Maps stars across the Milky Way, including low-luminosity ones.
Without these advanced telescopes, these dim stars would remain completely invisible to us.
The dimmest star in the universe is difficult to define, as it depends on whether we’re looking at brown dwarfs, faint red dwarfs, or dying white dwarfs.
Among the least bright stars ever detected are:
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WISE 0855−0714, an extremely cold brown dwarf.
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2MASS J09393548−2448279, another barely detectable brown dwarf.
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OGLE-TR-122b, one of the smallest and least bright main-sequence stars.
These stars are so faint that even the best telescopes struggle to detect them. As technology advances, astronomers may discover even dimmer objects, including the first black dwarf-a star that has completely cooled and no longer emits any light.