The New Largest Star in the Universe 2024

The New Largest Star in the Universe 2024

On a clear, moonless night, above our heads, we can observe thousands of glistening stars. But that's just what we can see with the unaided eye. Observe the galaxy with powerful telescopes, and billions more are revealed. In fact, the Milky Way galaxy alone is estimated to have between 100 to 400 billion stars. And looking even further to our neighboring galaxies and beyond, there are unaccountable amounts more.

The closest star to us, the Sun, appears enormous, the largest body in the solar system, as it rises and sets every day. And although it dwarfs most things that come close to it, in reality, the Sun is just average-sized. The universe boasts far larger stars that aren't just a little bit bigger; they are stunningly bigger.

So, how big is the largest star we have observed so far? How big can stars theoretically grow? And whatever happened to UI Scooty?

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When it comes to the largest stars in the known universe, it depends on whether we are talking about mass or total volume. Mass can be thought of as how much matter a star contains, whereas volume is how much space it takes up. The most massive stars tend to be quite unremarkable when it comes to sheer size, and the most voluminous stars often contain a lot less matter considering their physical size.

As stars get older, they tend to lose their mass. This is something that is happening to the Sun as it ages. Until eventually, in an estimated 5 billion years from now, after it has exhausted all of its nuclear fuel, it will evolve into a bloated red giant, engulfing the orbits of Mercury, Venus, and possibly even Earth. And although this process will make our sun enormous, there are stars out there that come a lot bigger.

Before we look at the largest by physical size, let's look at the current largest by mass, named Bat 99 to 98. This star is estimated to be 226 times the mass of the Sun. That's 226 Suns' worth of matter all crammed into one. How this star became so massive isn't fully understood, but it may be the result of two stars that once merged together. Scientific models suggest that Bat 99 to 98 is only 7.5 million years old, making it extremely young compared to the age of the Sun, which is 4.6 billion years old. It is also shedding its mass at a rapid rate since its birth; models suggest it has already lost 20 Suns' worth of mass. Because of how active it is, it is thought that it will inevitably end its life in a catastrophic way, most likely as a supernova that leaves behind a black hole.

But although Bat 99 to 98 is extremely massive, it is nowhere near the largest by physical size. With an estimated radius of 37.5 times that of the Sun, it doesn't even come close. If you type into Google, "What is the largest star in the universe?" you will receive pages of websites telling you it is UI Scooty, a red supergiant that just a few years ago was considered the largest star by physical size ever observed. It was originally measured to be around 1,700 times the size of the Sun. However, it turns out that the distance of UI Scooty from Earth had been measured incorrectly, significantly altering its estimated radius to 775 times the size of the Sun, knocking it well and truly off that top spot. This new measurement actually puts UI Scooty closer in size to popular stars like Betelgeuse, still unbelievably enormous, but nowhere near the largest. In fact, it currently doesn't even make it into the top 80.

So, what about another star that was also believed to be the largest just a couple of years ago, named Stevenson 2-8? A possible red hypergiant star that was estimated to be so big, if it was placed in our solar system, it would engulf the orbit of Saturn. And if you could travel around it at the speed of light, it would take almost 9 hours to complete one loop. In comparison, making the same trip around the Sun would take only 14.5 seconds. Some estimates put Stevenson 2-8 at being 2,150 times the radius of the Sun. But according to the stellar evolutionary theory, that might be problematic because there could also be a theoretical limit to how big stars can apparently grow. According to the theory, the limit a star can grow is around 1,500 times the radius of the Sun. This could mean that Stevenson 2-8 has been overestimated, possibly due to its distance from Earth being uncertain by as much as 50%, which, like UI Scooty, would significantly alter its estimated size.

But then again, as far as I could find, there is no clear-cut equation that determines how big a star can grow since it depends not only on mass but composition, evolutionary history, and the strength of its stellar wind. For potential giant stars such as Stevenson 2-8, the outer atmosphere can, in theory, continue to puff up and grow essentially without limit. However, at some point, the diffused gas of its outer layers becomes merged with the interstellar medium and cannot really be regarded as the stellar surface. So when it comes to measuring the size of a gigantic star, it turns out that it's no easy task. These objects are, of course, extremely big, thousands to millions of times the volume of the Sun, extremely far away, and extremely luminous. And as I just mentioned, they also tend to have far-extending atmospheres and photospheres that are ever-changing and are often shrouded in enormous clouds of dust, making their true size very difficult to discover.

Nonetheless, astronomers attempt this by using a range of different factors such as the distance and the environment around a star. By discovering these measurements among other things, they can more or less get estimates that fall within a smaller or larger area of confidence.

So, based on our best measurements, what is the current largest star in the known universe? Well, according to the list of largest stars known, the title is currently held by a red supergiant called W26. W26 is located around 160,000 light-years away in a neighboring satellite galaxy called the Large Magellanic Cloud. W26 has an estimated radius of 1,540 times that of the Sun, meaning that if it took the place of the Sun in the solar system, it would engulf the orbits of Mercury, Venus, Earth, Mars, and even Jupiter. This measured radius also fits in nicely with that theoretical growth limit and is consistent with many other large red supergiants found elsewhere. W26 is likely in the latter stages of its stellar evolution. These types of stars have exhausted their nuclear fuel, leading to the expansion of their outer layers, transforming them into true cosmic giants. The enormous star is also shrouded in a torus-shaped cloud of dust about a light-year in diameter, which consists of material it has expelled. Incredibly, it is estimated that if all the material in the torus cloud were collected, it would be enough to make our entire solar system nine

times over.

So, have we discovered the largest star in the universe? It's hard to say definitively, as our understanding of the cosmos is continually evolving, and new discoveries are made regularly. However, as of the latest information available, W26 is currently regarded as the largest star known to us based on its estimated radius. It's a red supergiant located in the Large Magellanic Cloud, a neighboring satellite galaxy of the Milky Way.

But who knows what the future holds? With advancements in technology and our ever-expanding quest to understand the universe, there may be even larger stars waiting to be discovered, hidden in the vast expanse of space, just waiting for us to find them.