There are a number of candidates for the most important star within the universe. Considered one of them, VY Canis Majoris, is over 1,500 instances the width of the solar. If it had been positioned in our photo voltaic system, it might stretch to almost the orbit of Saturn. However how can such a beast exist? The reply, as all the time, is physics.
VY Canis Majoris is a pink hypergiant star positioned about 6,000 light-years away. Though it is among the largest stars, it is not almost probably the most huge. At roughly 17 photo voltaic plenty, it is nonetheless fairly hefty. Nonetheless, it’s miles smaller than probably the most huge stars, which may attain as much as 300 photo voltaic plenty. But VY Canis Majoris completely dwarfs these behemoths when it comes to diameter. So what is going on on?
The reply is that VY Canis Majoris is close to the tip of its life, and we simply occur to be witnessing it at a really fortunate time.
All stars fuse hydrogen of their cores, changing it to helium. Because the stars age, the helium builds up like too much industrial pollution. It gets in the way of fusion reactions, which forces those reactions to occur at a faster and faster pace to maintain equilibrium.
Eventually, right before the star begins its end-of-life phase, there is so much helium built up in the core that hydrogen fusion moves into a shell around it. This fusion, now displaced from the core, emits an enormous amount of radiation. There is so much radiation that it pushes on the rest of the star, inflating it.
We call this the red giant phase of a star. In about 4.5 billion years, the sun will undergo such a transformation, swelling to reach Earth’s orbit. Because the atmosphere of a star in this stage is so far detached from the core, it cools off, causing the red color.
Another familiar star, Betelgeuse (the shoulder of Orion), is already a red giant. Astronomers estimate that it will explode as a supernova sometime within the next million years. Despite their cool temperature, red giants have enormous surface areas, making them incredibly bright. In fact, because red giants are so luminous, many of the stars visible to the naked eye are near the ends of their lives.
The same is true for UY Canis Majoris. It is highly unstable and variable, and it constantly pulses, dims and brightens again. Soon, it will explode in a supernova. In fact, it may have already done so at any point in the past 6,000 years but the light from that momentous event may not have reached us yet.
As for the most massive star, that honor goes to R136a1. Although it’s only a few times wider than the sun, it is around 300 solar masses, making it just about as massive as a star can be. That’s because of the same fusion reactions that keep a star in equilibrium. The intensity of the fusion rates is driven by a star’s mass, with higher masses increasing the pressure in the core. But higher fusion rates mean more radiation is produced, and more radiation means more energy is transferred to the star’s atmosphere.
At roughly 300 solar masses, the core of a star produces so much radiation that it simply blows away the rest of the star.
Owing to its tremendous mass, R136a1 is also the brightest known star, shining with an intensity of over 4.5 million suns. But it’s also so hot that most of that radiation is emitted in the ultraviolet region of the electromagnetic spectrum. So visibly, the star appears “only” about 167,000 times brighter than the sun to the naked eye.
But if you did want to look at R136a1, you’d better keep your distance. If this star were only 40 light-years away, it would still outshine Venus. If it were placed at the distance to our nearest stellar neighbor, Proxima Centauri, it would be brighter than the full moon.
Massive stars do not live long, however. In a few million years, R136a1 will join UV Canis Majoris and exit the cosmic scene. But star formation continues in the Milky Way, and when these giants fall, more monsters will rise to take their place.
