Smallest Star In The Universe

The smallest star in the universe is named EBLM J0555-57Ab. The star was detected in 2017 by a group of international astronomers. EBLM J0555-57Ab is roughly the size of Saturn. Based on other star sizes in the universe, EBLM J0555-57Ab is a very, very small star. EBLM J0555-57Ab has just enough mass to fuse hydrogen nuclei. If EBLM J0555-57Ab were any smaller in size, it would be a “brown dwarf” instead of a star!

What is a Star?

A star is a gigantic, glowing ball of hot gasses. Hydrogen atoms collide together in the core of the star. The Hydrogen atoms collide to form helium and release energy. The released energy heats the gas located in the core of the star. (AKA Nuclear fusion!) The hot gases push away from the star’s core. Gravity pulls the hot gases back in towards the center of the star. The balance between the gasses pushing outward and gravity pulling the gases back in towards the star’s core ultimately maintains a constant temperature, and overall stability, for the duration of the star’s life. 

Lifecycle of a Star

The stars in the universe have a lifecycle, just like we do! Some stars are big, some are small, and some are quite tiny. Some stars will grow larger, and others grow smaller throughout their lifecycle. Let’s look at the different types of stars.

Star TypeMass (Our sun = 1)Radius (Our sun = 1)
Main Sequence50  to .210 to 0.3
Giant 1 to 5 10 to 50
White Dwarfs<1.4<0.1
Red Dwarf0.08 to 0.6 
Super Giant10 to 70 30 to 500

Main Sequence Stars

Keeping in mind that stars have a lifecycle, most stars will spend the majority of their lives as Main Sequence stars. Main Sequence stars have a hydrogen to helium fusion occurring in the core. The pressure of the gas pushing “out” is equal to the gravity of the star’s core pulling the gases back “in.” When a star has fused all of the hydrogens in its core, the star will begin to collapse and transition away from being a Main Sequence star and into a different type of star.

There are seven classification categories for Main Sequence stars. O, B, A, F, G, K, and M. The primary differing categories identify the star’s colors, temperatures, lifetime, mass, and brightness. Our sun is a Main Sequence star.

Giant Stars

A giant star has a large radius when compared against its mass and temperature. The large radius results in very bright star that burns through its hydrogen very rapidly. 

Red Dwarf

A Red Dwarf star is among the the smallest and most prominent star groups in the Universe. Red Dwarf stars make up approximately seventy six percent of all the stars in the universe.  Red Dwarf Stars are the oppositeve of Giant Stars in terms of size, hydrogen fuel consumption, and luminosity. Whereas a Giant Star may last for millions of years before extinguishing its hydrogen supply, a Red Dwarf will burn for trillions of years. 

Star Sizes
Image Credit: NASA

White Dwarf

A White Dwarf star has consumed all of the fuel in its core. No longer able to maintain a balance between hot gasses escaping and gravity pulling the gases back in, the White Dwarf has shed its outer material. What’s left behind is a very hot (approximately 100,000 Kelvin) core. 

Super Giants

A supershort lifetime (In terms of stars!) of anywhere from a few hundred thousand years to thirty million years combined with enormous mass are the hallmark of Super Giants. Super Giants have a mass range of approximately ten to seventy times the mass of our own sun! Super Giants generally go out with a gigantic “bang” as a supernova at the end of their lives.

Smallest Star in the Universe

Image Credit: NASA

The image above is a Hetzsprung-Russell diagram. The Hetzsprung-Russel diagram allows us to classify stars based on their temperatures and luminosity. As a star’s mass increases, so too does the rate of fuel consumption. The Hetzsprung-Russel diagram allows astronomers from all around the world to use a common and unified star categorization system. Utilization of the same star categorization system allows for a “common use” system that standardizes the results.

Brown Dwarf

A Brown Dwarf is a “almost” or “failed” star. A Brown Dwarf is roughly the size of Jupiter to seventy five times the mass of Jupiter. Unable to systain hydrogen fusion, the Brown Dwarfs instead consume hydrogen-3 that was fused from duterium. Brown Dwarfs are not considered Stars or Planets. 

Could Jupiter Turn into a Star?

Jupiter, while quite large to us, is woefully small for a Brown Dwarf. Jupiter would need to add approximately thirteen additional Jupiters to its mass to qualify for Brown Dwarf (duterium fusion) status. Jupiter would need to add about eighty three additional Jupiters to its mass to reach a point where hydrogen fusion begins. 

If Jupiter were able to add eighty five additional Jupiters to it’s mass, it would have the approximate mass of EBLM J0555-57Ab, the smallest star in the Universe. 

The Smallest Star in the Universe

The discovery of the smallest star in the universe occurred when astronomers were searching for planets! 

Who Discovered EBLM J0555-57Ab

A group of astronomers from the Universites of Warwick, Leicester, Keele and St Andrews, led by astronomers from the University of Cambridge are involved in the Wide Angle Search for Planets (WASP.) 

WASP is a ground based searh for exoplanets in transit. A charge coupled device (CCD) array of eight cameras captures images of the night sky each night (weather permitting.) There’s a WASP camera configuration in Observatorio del Roque de los Muchachos that covers the Northern Hemisphere skies. The Southern Hemisphere night time skies are imaged by a similar CCD camera array in at the South African Astronomical Observatory (SAAO) located in  Sutherland in South Africa .

The WASP astronomers discovered EBLM J0555-57Ab during their search for exoplanets by utlizing the transit method.

Exoplanet Discovery with the Transit Method

The transit discover methodology is based on the observation of a known object. The light intensity is observed and cataloged for] the object. The transit method is based on calculating the known illumintensity variation and then looking for system variations that ‘transit’ across the object.  

Example: You’ve collected data on the sun.  You know the intensity of the sun. During the time your collecting data (this is key!), another objects, like Venus or Mercury, pass between us (Earth) and the sun.  The new data (containing the Venus or Mercury transit) will be compared to the old data when Venus or Mercury were not between the Earth and the Sun.  The data will show that something moved across the sky. We may not be able to “see” the object, but mathematically, we can learn of its existence. 

Base on transit data astronomers can learn the size of the object (usually a exolplanet) and the size of the exoplanets orbit. The light that’s emitted from the exoplanet is analyzed to determine the atmosphere to better understand potential habitability. 

Image Credit: NASA

The image above represents the transit method. Once a variation is detected, astronomers will “zero in” on the particular object that’s of interest and collect additional. The additional data will be primarily based on the expoplanet and not the star, or exoplanet, that its transitioning between. 

EBLM J0555–57A was being studied as a potential exoplanet against the (very bright) backdrop of EBLM J0555–57A, a much larger star, when it was discovered in 2017.

EBLM J0555-57Ab Star Classification

EBLM J0555-57Ab, the smallest star in the universe, is classified as a Red Dwarf on the Hetzsprung-Russell diagram. Look for it in the lower right hand corner of the diagram. EBLM J0555-57Ab is just barely big enough that Hydrogen fusion is able to occur. 

5 Must Know Facts about The Smallest Star in the Universe

  • The smallest star in the universe is located approximately 632 light years away in the Pictor Constellation. 
  • The size of EBLM J0555-57Ab is slightly larger than Saturn.
  • Initially EBLM J0555-57Ab was thought to be a exoplanet. Data analysis revelated that its a star and not a exoplanet.
  • The gravitational pull on the surface of EBLM J0555-57Ab is about 300 times stronger than what we feel on earth.
  • The star is 2,000 to 3,000 times dimmer than our own sun. 

Wrap up: Smallest Star in the Universe

The discovery of EBLM J0555-57Ab has astronomers excited! Smaller Red Dwarf Stars, like EBLM J0555-57Ab, have the highest possibility of explanets with conditions that would have habitable conditions. 

EBLM J0555-57Ab is orbiting a much larger primary star named EBLM J0555-57A. The high illumination of the primary star made EBLM J0555-57Ab very difficult to detect. Astronomers believe that EBLM J0555-57Ab may be the smallest star possible in the universe. 

Astronomers are excited by the detection of the smallest star in the universe and with the awareness than future exoplanet data analysis may lead to new star discoveries. 

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