The astronomers recently faltered upon a teeny star called 2MASS J0523-1403, and it was located just 40 light years away. As per them, it is not only the smallest star discovered so far, but it also represents the smallest possible star. By studying the stars; scientists are starting to be able to answer the questions — on where do the stars end and the brown dwarfs begin?
While the stars are the burning balls of gas held together by gravity that is powered by the fusion of hydrogen atoms to helium in their cores. They come in a variety of sizes; the smallest stars, are known as red dwarfs. These can possess as little as t% of the mass of our Sun, whereas the biggest stars or the hyper giants can be over 100 times as massive as the Sun. However, just how small can an object be and still be defined as a star? This has puzzled the astronomers for years. All that was formerly known is that objects below this limit don’t have sufficient mass to burn the fusion of hydrogen in their cores, and these objects are known as brown dwarfs. Brown dwarfs are intangible objects that are supposed to be the missing link between gas giants and low-mass stars such as red dwarfs. They’re usually around the size of Jupiter, but they don’t have enough mass to become a star. Unlike stars, brown dwarfs have no inner energy source.
However, there is another strange difference between brown dwarfs and stars; both of them have opposite relationships between mass and size. Though the more material you add to a star, in the form of hydrogen, the bigger the radius of the star. I.e. they increase their size as mass increases. Whereas, the brown dwarfs, on the other hand, actually shrink in size with increasing mass because of something called electron degeneracy pressure.
How do we find the limit that commands whether an object is a star or a brown dwarf?
To find this difference the astronomers scanned the skies and located objects that were supposed to lie around the stellar or the brown dwarf border. They then intended the light, temperatures, and radius of all of these objects and strategized them. The temperature is dependent on mass but it’s easier to measure; so they found that as temperature decreased, so did radius; this is the expected trend for stellar objects. But, they found that after temperatures of around 2100K there was a break till radius starts to increase with decreasing temperature; and this is the trend that would be expected for brown dwarfs.
Finally, the scientists can now pinpoint the specific temperature, light, and radius at which the main classification ends. However, the main classification is a relationship between luminosity and temperature and luminosity and radius; which need to be obeyed by stars throughout the majority of their lives. 2MASS J0523-1403 is located around this boundary but towards the stellar side. This star actually has a temperature of 2074K, which is the lowest described temperature so far for a main sequence of the star. It’s also the smallest and the least massive; if it had less mass then it can be a brown dwarf. This star has therefore been identified as a representative of the smallest possible star. However, it is theoretically possible that a star with a slightly smaller mass than 2MASS J0523-1403 could exist, but they still need to discover one.