Why stars fail<\/p>\n
Stars start out as huge blobs of gas in space \u2013 but how big and heavy does a blob of gas have to be before it becomes a star? It sounds like a simple question, but astronomers have debated the answer for decades.<\/p>\n
The gravitational pressure inside a star has to be great enough to fuse hydrogen atoms together into helium atoms, and to do it consistently for a long period. This is what creates the intense stream of heat and light that is a star\u2019s signature.<\/p>\n
If an object isn\u2019t quite big enough to generate that much pressure \u2013 or if fusion doesn\u2019t really kick off properly for some other reason \u2013 the gas becomes a kind of \u201cfailed star\u201d known as a brown dwarf. These objects are hot early in life, but without sustained hydrogen fusion they gradually cool, giving off a dim infrared glow.<\/p>\n
To learn more about why some blobs become stars and others become brown dwarfs, astrophysicists look for objects in the intermediate zone \u2013 the heaviest brown dwarfs and the lightest of stars.<\/p>\n
That\u2019s where TOI-2155b comes in. Weighing in at around 80.6 times the mass of Jupiter, it sits right on the theoretical boundary.<\/p>\n
Where do stars end and brown dwarfs begin?<\/p>\n
Using observations from NASA\u2019s Transiting Exoplanet Survey Satellite (TESS) together with ground-based telescopes around the world, we determined the size and mass of TOI-2155b precisely. Although it is almost the same size as Jupiter, it is around 80 times more massive.<\/p>\n
You might expect there to be a precise mass at which an object suddenly becomes a star. But as so often happens, in real life there is no clean line. <\/p>\n
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