When you think of a star, you probably imagine the blazing Sun or giant fireballs lighting up galaxies. But the universe doesn’t only deal in giants. It also crafts stars so small, they are barely stars at all. Earlier, we explored the smallest galaxy in the universe. Today, let’s talk about the smallest star ever discovered in the Universe.
So, what is the smallest star in the universe? How tiny can a star be and still “be a star”? And why does size matter in space?
Let’s explore the answers—and discover how even the smallest stars can teach us something huge about the universe.
What Exactly Is a Star?
To know what the smallest star is, we first need to understand what makes a star a star.
A star is not just a hot glowing ball. It’s a massive object that creates energy through nuclear fusion—a process that smashes hydrogen atoms into helium in its core. This reaction releases heat and light, and it’s what keeps stars shining for billions of years.
But for fusion to happen, a star needs enough mass. If it doesn’t, it won’t burn bright. It might become a “failed star” called a brown dwarf—a kind of object stuck between being a planet and a star.
So here’s the bottom line:
To be a true star, an object must be big enough to fuse hydrogen.
Scientists say the minimum mass needed for this is about 75–80 times the mass of Jupiter.
Meet the Smallest Known Star: EBLM J0555-57Ab
So, what’s the smallest star that fits the definition?
In 2017, astronomers discovered a fascinating object called EBLM J0555-57Ab. That name may not sound exciting, but the star certainly is.
Why Is It Special?
- Size: It’s just a bit bigger than Saturn.
- Mass: About 85 times the mass of Jupiter.
- Fusion: Yes, it performs hydrogen fusion—so it’s officially a star!
- Location: Around 600 light-years from Earth.
If this star were any smaller, it wouldn’t be able to fuse hydrogen. It would become a brown dwarf.
In fact, EBLM J0555-57Ab is right at the edge of what scientists call a star.
How Was It Found?
EBLM J0555-57Ab was discovered using a method called the transit method, where astronomers watch a star dim slightly as another object passes in front of it. This is usually how they find exoplanets, but this time, it led to something different.
Scientists originally thought they found a large planet. But after more study, they realized it was a tiny star orbiting a bigger one.
How Small Can a Star Be?
Let’s break down the numbers:
| Type | Mass (Compared to Jupiter) | Radius (Size) | Can Fuse Hydrogen? |
|---|---|---|---|
| Regular star | > 80× Jupiter | Bigger than Saturn | Yes |
| EBLM J0555-57Ab | ~85× Jupiter | Same as Saturn | Yes |
| Brown dwarf | 13–80× Jupiter | Varies | No |
| Planet (e.g., Jupiter) | 1× Jupiter | Jupiter-sized | No |
So, EBLM J0555-57Ab is the smallest known star that still fuses hydrogen. If it were even just a little lighter, it wouldn’t count as a star.
Why Are Small Stars Important?
You might wonder—why should we care about small stars?
Here’s why tiny stars are a big deal:
1. They Last Longer Than Big Stars
Small stars, like red dwarfs, burn their fuel slowly. This means they can live for trillions of years, far longer than massive stars like our Sun. Since the universe is only about 13.8 billion years old, most of these stars are still “babies.”
2. They May Host Planets
Some small stars, like TRAPPIST-1, have entire solar systems. In 2017, NASA found 7 Earth-sized planets orbiting TRAPPIST-1, and 3 of them may be in the habitable zone—where liquid water could exist.
3. They Help Us Understand Star Formation
Studying the smallest stars helps astronomers understand where stars form, how long they live, and how solar systems are built.
Other Tiny Stars You Should Know
Let’s meet a few more contenders in the “smallest star” race:
TRAPPIST-1
- Mass: About 89 times that of Jupiter
- Radius: Slightly larger than Jupiter
- Special: Hosts 7 planets
- Distance: 40 light-years away
OGLE-TR-122b
- Mass: ~97 times Jupiter
- Radius: Nearly Jupiter-sized
- Found using: Transit method
- It’s one of the smallest stars measured by radius.
These stars are small, but still manage to support entire planetary systems!
What About Brown Dwarfs?
Sometimes it’s tricky to tell where a star ends and a brown dwarf begins. Brown dwarfs are “failed stars” that don’t have enough mass to ignite fusion.
They can be:
- Big like planets
- Hotter than most planets
- Glowing faintly in infrared
NASA and other agencies use infrared telescopes to find them. Brown dwarfs help fill in the missing links between planets and stars.
The Role of Technology: How We Spot Smallest Stars
We can’t find these tiny stars just by looking through regular telescopes.
Here’s What We Use:
- Transit telescopes like Kepler and TESS
- Radial velocity instruments that detect star wobbles
- Infrared space telescopes like James Webb
- Binary star studies, where two stars orbit each other
All of these tools help astronomers find tiny, faint stars that would otherwise be invisible.
Could There Be Even Smaller Stars?
EBLM J0555-57Ab is the smallest star we’ve found—but is it the smallest that exists?
Possibly not. The universe is vast, and our telescopes can only see so far. As technology improves, we may find even tinier stars just barely big enough to light up.
| Name | Type | Mass (x Jupiter) | Radius | Notes |
|---|---|---|---|---|
| EBLM J0555-57Ab | Smallest star | 85× | Saturn-sized | Smallest known star with fusion |
| TRAPPIST-1 | Ultra-cool dwarf | 89× | Slightly larger | Hosts 7 planets |
| OGLE-TR-122b | Red dwarf | 97× | Jupiter-sized | Found using transit method |
| Brown dwarfs | Not true stars | 13–80× | Varies | Cannot fuse hydrogen |
Some scientists believe there could be stars just 78–80 Jupiter masses in hidden corners of our galaxy. They’re just waiting to be discovered.
Final Thoughts
The smallest star in the universe may be small in size, but it’s big in meaning.
Stars like EBLM J0555-57Ab teach us where the line is between a star and a brown dwarf. They help us understand how stars form, how long they live, and what kind of planets they might support.
As we build better telescopes and explore deeper into space, we’ll keep asking big questions about small stars—and learning even bigger lessons.
Source: sciencefocus.com
