Stars in the Galaxy.
There are billions and billions of stars in our galaxy, the Milky Way. Estimates range from 100 billion to 400 billion [ESA – How many stars are there in the Universe? – European Space Agency]. That’s a mind-boggling number! These stars come in all different sizes and temperatures, and many have planets orbiting them. Our solar system is just one tiny speck in this vast sea of stars.
We can only see a small fraction of the stars in our galaxy with the naked eye. Most of them are too faint or too far away. But with telescopes, we can see millions of stars, and we can learn a lot about them.
Stars are born from giant clouds of gas and dust called nebulae. As the gas and dust in a nebula clump together, gravity pulls them inward. The center of the clump gets hotter and hotter, until eventually it becomes hot enough to start nuclear fusion. Nuclear fusion is the process that powers stars. In nuclear fusion, hydrogen atoms are fused together to form helium atoms, releasing a tremendous amount of energy in the process.
Once a star starts burning hydrogen, it will continue to do so for millions or even billions of years. But eventually, the star will run out of hydrogen fuel. When that happens, the star will start to die. How a star dies depends on its mass.
Small stars like our sun will eventually swell up into red giants. They will then shed their outer layers, which will form a planetary nebula, and leave behind a hot, dense core called a white dwarf.
Medium-sized stars will go through a more violent death. They will explode in a giant supernova, leaving behind a neutron star or a black hole.
Massive stars will also explode in supernovae, but they will leave behind black holes no matter what.
Black holes are regions of spacetime with such strong gravity that not even light can escape. They are invisible to us, but we can infer their presence by the way they affect the matter around them.
The biggest stars in the galaxy
While pinpointing the absolute biggest star in the Milky Way is challenging due to vast distances and limitations in measuring stellar diameters, some contenders hold the title for “biggest known star”:
- UY Scuti– This red supergiant is the current champion. Located roughly 9,500 light-years away, it has a radius estimated to be 1,708 times larger than our Sun. If placed at the center of our solar system, its surface would engulf the orbits of all the planets out to Jupiter!
- Stephenson 2-DFK 1– This red hypergiant is another strong contender, with an estimated radius of 2,150 times that of the Sun. However, measurements of its distance are uncertain, making it difficult to confirm its exact size.
- VY Canis Majoris– Previously thought to be the largest star, this red hypergiant is estimated to be around 1,420 solar radii in size. It’s located about 3,900 light-years away.
It’s important to note that these stars are incredibly vast and distant. Determining their exact sizes is difficult, and new discoveries may change the rankings in the future.
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