The James Webb Space Telescope (JWST) is the most powerful telescope ever launched by humanity. It is designed to observe the early universe and the formation of galaxies, which are some of the most mysterious and fascinating topics in astronomy. However, the JWST is not only capable of revealing the secrets of the distant past, but also of discovering new and unexpected objects in our own galaxy. In fact, the JWST has recently found 21 brown dwarfs, which are objects that are too big to be planets but not big enough to be stars. They are sometimes called “failed stars” because they never started nuclear fusion in their cores, which is the process that makes stars shine. In this article, we will explain how the JWST detected these brown dwarfs, what are their properties, and why they are important for astronomy and cosmology.

How the JWST Detected the Brown Dwarfs

The JWST was not looking for brown dwarfs, but for distant and ancient galaxies, which are its main scientific goal. To do so, it used its infrared sensors, which can penetrate through dust and gas that block visible light. The JWST performed two surveys: JADES and CEERS, which covered different regions of the sky and different wavelengths of infrared light. The JADES survey focused on the deep field, which is a small area of the sky that contains many faint and faraway galaxies. The CEERS survey scanned a larger area of the sky that contains more nearby and bright galaxies.

However, among the data from these surveys, there were some sources that did not match the expected characteristics of galaxies. They were too red, too variable, and too isolated. These sources turned out to be brown dwarfs, which were hidden in the data from both surveys. The JWST found 21 brown dwarfs in total, which is a surprising number considering that it was not looking for them. Finding brown dwarfs with the JWST is not easy, because they are very faint and hard to distinguish from other infrared sources. Moreover, they can change their brightness over time due to weather patterns in their atmospheres or eclipses by their companions. Therefore, finding these brown dwarfs required careful analysis and verification of the data from the JWST.

What are the Properties of the Brown Dwarfs

The 21 brown dwarfs that the JWST found have different properties, such as their temperatures, masses, and distances from Earth. They range from very cold (about 300 degrees Celsius) to very hot (about 3000 degrees Celsius), which means that they span different spectral types: T, Y, and L. The spectral type of a brown dwarf indicates its temperature and color: T-type brown dwarfs are cooler and redder than L-type brown dwarfs, which are cooler and redder than Y-type brown dwarfs. The Y-type brown dwarfs are the coldest and rarest type of brown dwarfs known so far.

The masses of the brown dwarfs are also different: some of them are as massive as 80 times Jupiter’s mass, while others are as light as 10 times Jupiter’s mass. The mass of a brown dwarf determines whether it can start nuclear fusion in its core or not: if it is more than 75 times Jupiter’s mass, it can fuse deuterium (a heavy form of hydrogen), but if it is less than that, it cannot fuse anything at all. The 21 brown dwarfs that the JWST found are all below this threshold, which means that they never ignited nuclear fusion in their cores.

The distances of the brown dwarfs from Earth are also different: some of them are as close as 50 light-years away, while others are as far as 500 light-years away. The distance of a brown dwarf affects how bright it appears in the sky: the closer it is, the brighter it is. However, even the closest brown dwarfs are very dim compared to stars or planets: they are about a million times fainter than the Sun or about a thousand times fainter than Jupiter.

Why the Brown Dwarfs are Important for Astronomy and Cosmology

Finding these 21 brown dwarfs with the JWST is not only a remarkable achievement, but also a valuable contribution to astronomy and cosmology. Brown dwarfs can help us understand the structure and history of our galaxy, especially the thick disk and halo regions where most of them are located. These regions contain very old stars and objects that formed when our galaxy was young and had different chemical compositions than today. By studying these regions with the JWST, we can learn more about how our galaxy evolved over time.

Brown dwarfs can also provide clues about the formation and evolution of stars and planets. Brown dwarfs are thought to form in a similar way as stars: by collapsing from clouds of gas and dust under gravity. However, some brown dwarfs may also form in a similar way as planets: by accreting material from a disk around a star. By comparing the properties of brown dwarfs with those of stars and planets, we can test different theories and models of how these objects form and change over time.

Brown dwarfs can also serve as benchmarks for future observations with the JWST. The JWST is expected to find many more brown dwarfs in the coming years, as well as other exotic objects such as rogue planets, which are planets that do not orbit any star. By using the 21 brown dwarfs that it already found as references, the JWST can calibrate its instruments and improve its data quality and accuracy. Moreover, the JWST can also study the atmospheres and chemistry of these brown dwarfs, and search for planets around them, which could reveal new and exciting phenomena.

Conclusion

The JWST is a remarkable telescope that can explore the wonders of the universe, from the earliest galaxies to the nearest brown dwarfs. The JWST has already found 21 brown dwarfs by accident, which are fascinating objects that are too big to be planets but not big enough to be stars. These brown dwarfs have different properties, such as their temperatures, masses, and distances from Earth. They are also important for astronomy and cosmology, because they can help us understand the structure and history of our galaxy, the formation and evolution of stars and planets, and the potential for future discoveries with the JWST. The JWST is a powerful tool that can reveal new and unexpected things in the sky, and we are eager to see what else it will find in the coming years.