There are trillions of stars in the universe. Most of them we do not even see, and those that are available to our eye can be bright or very dull, depending on size and other properties. What do we know about them? Which star is the smallest? What is the hottest?
Stars and their varieties
Our Universe is filled with interesting objects: planets, stars, nebulae, asteroids, comets. Stars are massive balls of gases. Equilibrium helps them to maintain the strength of their own gravity. Like all cosmic bodies, they move in space, but due to the large distance this is difficult to notice.
Thermonuclear reactions occur inside the stars, due to which they radiate energy and light. Their brightness fluctuates significantly and is measured in magnitude. In astronomy, each quantity corresponds to a certain number, and the smaller it is, the lower the brightness of the star. The smallest star in size is called a dwarf, there are also normal stars, giants and supergiants.
In addition to brightness, they also have a temperature, due to which, stars emit a different spectrum. The hottest are blue, then (in descending order) are followed by blue, white, yellow, orange and red. Stars that do not fit into any of these parameters are called peculiar.
The hottest stars
When it comes to the temperature of stars, we mean the surface characteristics of their atmospheres. The internal temperature can only be determined by calculation. How hot a star can be judged by its color or spectral class, which is usually indicated by the letters O, B, A, F, G, K, M. Each of them is divided into ten subclasses, which are indicated by numbers from 0 to 9.
Class O is among the hottest. Their temperature ranges from 50 to 100 thousand degrees Celsius. However, recently, scientists have dubbed the hottest star Butterfly nebula, whose temperature reaches 200 thousand degrees.
Other hot stars are blue supergiants, for example, Rigel Orion, Alpha Giraffe, Gamma of the constellation Sails. Cold stars are class M dwarfs. WISE J085510.83-071442 is considered the coldest in the Universe. Star temperature reaches -48 degrees.
Dwarf stars
The dwarf is the exact opposite of super giants, the smallest star in size. They are small in size and luminosity, may even be smaller than the Earth. Dwarfs make up 90% of the stars in our galaxy. They are much smaller than the Sun, however, are larger than Jupiter. With the naked eye, it is almost impossible to see them in the night sky.
Red dwarfs are considered the smallest. They have a modest mass and are cold compared to other stars. Their spectral class is indicated by the letters M and K. The temperature can reach from 1,500 to 1,800 degrees Celsius.
Star 61 in the constellation Cygnus is the smallest star of those that can be seen without professional optics. It emits dim light and is located at a distance of 11.5 light years. A little larger in size is the orange dwarf Epsilon Eridan. Located at a distance of ten light years.
The closest to us is Proxima in the constellation Centaurus, a person could get to it only after 18 thousand years. This is a red dwarf, which is 1.5 times larger than Jupiter. From the Sun, it is located just 4.2 light years. The luminary is surrounded by other small stars, however, they have not been studied due to the small brightness.
Which star is the smallest?
We are not familiar with all the stars. In the Milky Way galaxy alone, there are hundreds of billions of them. Of course, scientists have studied only a small part of them. Known to date, the smallest star in the universe is called OGLE-TR-122b.
It refers to a binary star system, that is , it is connected by a gravitational field with another star. Their mutual rotation around the masses of each other is seven and a half days. The system was discovered in 2005 during the Optical Gravity-Lens Experiment, from the English abbreviation of which it was named.
The smallest star is a red dwarf in the constellation Kiel in the southern hemisphere of the sky. Its radius is 0.12 of the solar, and the mass is 0.09. In mass, it exceeds Jupiter by a hundred times, and in density is 50 times greater than the Sun.
The discovery of this stellar system confirmed the theory of scientists that a star can only slightly exceed the size of an average planet if its mass is at least ten times less than the solar one. Most likely, there are smaller stars in the Universe, but modern technology does not allow them to be seen.