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Explore | The brightest star in the night sky and the brightest star in the universe

In the writings of ancient poets, the stars were endowed with rich symbolism. For example, "the night is like a water-soaked step, and the morning glory Vega is in sight", "the carved bow is like a full moon, shooting towards Sirius". Three bright stars are mentioned in these two verses: the Cowherd (River Drum II), Vega, and Sirius. We are familiar with the legend of the Cowherd and the Weaver Girl, and their stories are told every year during the Qixi Festival. Sirius, on the other hand, has long been regarded as a symbol of war and aggression. Today, let's delve into the mystery and charm of these two stars, and feel the charm of the stars written by the ancients.

Explore | The brightest star in the night sky and the brightest star in the universe

Summer Triangle

▏How to find Vega and Sirius?

The autumn night sky is full of twinkling stars, Jupiter shines brightly in the east, and as the brightest star, its brightness level is as high as -2.93. And to the southeast, Saturn attracts attention with its visual magnitude of 0.44. To the southwest, there is also an orange lone star, which is Arcturus, with a magnitude of -0.04, as if it is constantly blinking.

Looking up at the center of the sky, three bright stars form a huge triangle, which is known as the summer triangle. Among them, the morning glory Vega mentioned in Du Mu's poem is among them. The Cowherd, also known as the River Drum II, dominates with its apparent magnitude of 0.75, and the Vega Star, which is opposite the Milky Way, has an apparent magnitude of 0, and the two stars together weave a romantic picture of the summer night. Tianjin IV, located in the Milky Way, is the darkest of the summer triangles, with an apparent magnitude of 1.25.

Explore | The brightest star in the night sky and the brightest star in the universe

Winter Triangle

Time passes, and when the footsteps of the season step on the threshold of winter, the summer triangle will quietly disappear into the western horizon after nightfall. In its place is the beautiful Winter Triangle. This is made up of Betelgeuse in the constellation Orion (magnitude 0.45), Nanhe III in the constellation Canis Minor(magnitude 0.4), and Sirius in the constellation Canis Major (known as the first of the stars in the night sky). Sirius' apparent star rating has reached an astonishing -1.47, and as the ancients said: "Look northwest, shoot the wolf", this star carries countless meanings and yearnings.

Vega and Sirius are both jewels in the starry sky. One stands in the summer triangle with its characteristic brilliance, evoking people's romantic reverie; The other radiates a chilling glow in the Winter Triangle, evoking contemplation of its mysteries. Their peculiarity lies in the fact that they are not only symbols of light, but also carriers of culture and legends. Behind each star lies countless stories and people's yearning for the unknown.

Explore | The brightest star in the night sky and the brightest star in the universe

▏Who is bigger Vega or Sirius?

Stars have the ability to emit light on themselves, and the brilliance of massive stars is even more dazzling. Sirius is compared to Vega, and although Sirius is brighter, this does not mean that it is more massive or larger. In fact, astronomers have observed that Vega is slightly superior in mass and volume. Specifically, Vega has a mass of about 2.14 times that of the Sun, and its radius is the product of 2.26 times and 2.78 times that of the Sun. In comparison, Sirius has a mass of 2.02 times that of the Sun, but its radius is slightly smaller, only 1.71 times that of the Sun. Surprisingly, Vega's 0.12 solar masses more than Sirius are equivalent to the mass of Proxima Centauri. This subtle difference gives us a deeper understanding of the diversity of stars.

Explore | The brightest star in the night sky and the brightest star in the universe

▏ Vega and Sirius shapes

The striking feature of Vega is its unique shape. Astronomers have observed that the equatorial radius is 23% larger than the radius of the poles, giving it the appearance of an ellipsoid. The reason for this shape is the ultra-fast rotation speed of Vega, which can complete its rotation every 12.5 hours, and its rotation speed at the equator is as high as 274 kilometers per second, as if it is "flattened" by its own rotational force. Sirius, on the other hand, is milder, with a rotation speed of only 16 km/s, so its shape remains a fairly standard sphere.

Explore | The brightest star in the night sky and the brightest star in the universe

▏Who is brighter Vega or Sirius?

In the starry night, Vega in the summer night stands out for its dazzling brilliance, while Sirius in the winter shines equally brightly. So, which of these two stars is brighter? We can answer this question in a more precise way of measuring it – apparent magnitude. Apparent magnitude is a measure of the brightness of a star as seen by our naked eye. The smaller the value, the higher the brightness of the star.

Vega has an apparent magnitude of 0, while Sirius has an apparent magnitude as low as -1.47, which undoubtedly makes Sirius appear brighter visually. According to astronomers, each additional magnitude of the star differs in brightness by a factor of about 2.512. Based on this law, we can deduce that Sirius is about 4 times brighter than Vega.

Although both Vega and Sirius are bright stars in the night sky, by calculating the apparent magnitude, we can clearly conclude that Sirius is more visually brighter. However, in addition to the apparent magnitude, we also need to consider the actual luminosity of the star. Vega is 37 times more luminous than the Sun, while Sirius is slightly less luminous but still 25.4 times more luminous than the Sun. This also means that, in true luminosity, Vega is actually brighter.

Why do we think Vega is fainter than Sirius when we look at Earth? This is mainly due to the fact that Vega is even farther away from Earth, reaching a distance of 25 light-years. Sirius, on the other hand, is relatively recent, at only 8.6 light-years. The brightness we observe will also vary due to the difference in distance. This also reiterates that apparent magnitude does not fully reflect the true luminous ability of stars.

In order to more accurately measure the true luminous ability of stars, astronomers have come up with the concept of absolute magnitude. Absolute magnitude is the brightness measured when a star is placed 32.6 light-years away from Earth. In this way, it is as if all the stars are on the same starting line, and their true ability to emit light is clear at a glance.

In absolute magnitude, Vega shines brighter than Sirius. If we assume that the positions of Vega and Sirius are reversed so that Vega is farther away from us and Sirius is closer, how will their brightness change? By converting the apparent and absolute magnitudes, we can see that if Vega is closer, its brightness will increase greatly; Sirius's brightness decreases accordingly. Specifically, if Vega's apparent magnitude is converted to -2.3, its brightness will be similar to that of Jupiter, while Sirius's apparent magnitude will be 0.85, which will be comparable to the brightness of Cowherd.

While Sirius may appear brighter visually, Vega is much brighter in actual luminosity. The difference depends not only on the brightness of the stars themselves, but also on their distance from the Earth.

Explore | The brightest star in the night sky and the brightest star in the universe

▏ Vega and Sirius age

Although these two stars are still young, they are both "short-lived" generations. Vega is only about one-tenth the age of the Sun, and is about 450 million years old. Sirius, by contrast, hovers between 200 million and 300 million years in lifespan. Despite this, both they and the sun are reaching maturity. The reason for this is its mass, which is 2.14 times the mass of the Sun, and Sirius is 2.02 times that of the Sun. The lifetime of a star is often inversely proportional to its mass. Experts speculate that neither of them will have more than a billion years to live. In the blink of an eye, hundreds of millions of years have passed, and the two stars will swell into red giants, then towards the end of their lives, and finally into white dwarfs. Compared to the long-lived sun, their short life is particularly unfortunate.

Explore | The brightest star in the night sky and the brightest star in the universe

Spider Nebula

▏ The brightest star in the known universe

In the Great Magellanic Galaxy, located in the depths of the universe and 165,000 light-years from Earth, there is a massive Spider Nebula that spans more than a thousand light-years. The nebula is full of twinkling stars, and one particular star, R136a1, stands out.

In July 2010, astronomers discovered a stunning star here. Its brightness is astonishingly 6.16 million times that of the Sun, making it the brightest object in the universe to date. This star, R136a1, is undoubtedly a shining pearl in the universe.

Not only is the brightness of the R136a1 amazing, but its quality is also breathtaking. It is estimated to be 230 to 345 times more massive than the Sun, making it one of the most massive stars known. In addition, its surface temperature is as high as 52,000 ° C, which is almost ten times that of the sun.

In the grand universe, the volume of R136a1 is also quite large. Its radius is about 35.4 times that of the Sun, which is equivalent to about 24,638,400 kilometers. Amazingly, this star is capable of holding 44,000 suns. Although R136a1 is not very large compared to other obese red giants, in the universe, mass is the measure of celestial value.

R136a1 is also a Wolf-Layet star, and its internal nuclear fusion reaction is unusually rapid, creating a delicate balance between its gravitational pull and the pressure of the star's outward radiation. This equilibrium causes stellar winds of up to several thousand kilometers per second to be generated on the surface of the star, causing it to lose about 50 suns of mass in just one million years. This also means that the R136a1 used to be even more massive. Compared to the mild sun, R136a1 is undoubtedly a terrifying monster in the universe.

Explore | The brightest star in the night sky and the brightest star in the universe

R136a1 vs. Sun

▏Can R136a1 illuminate the entire solar system?

If R136a1 were placed at the core of the solar system, would it be able to illuminate the entire solar system? First, let's explore the sun's illumination capabilities. How amazing is the brightness of the Sun, the brightest object in the solar system?

Scientists tell us that the total radiated power of the sun is as high as 3.86×10^26 watts. In comparison, the power of the electric lights we use on a daily basis is usually between 10 and 100 watts. The more powerful the lamp, the brighter it will be. From this, we can imagine how amazing the brightness of the sun is. Even on Earth, we are separated by a distance of 150 million kilometers, and we still do not dare to look directly at the strong rays of the sun. Here on Earth, the Sun's apparent magnitude reaches a staggering minus 26.74.

Explore | The brightest star in the night sky and the brightest star in the universe

However, as we head towards the edge of the solar system, we will find that the sun's rays gradually dim. Scientists estimate that the radius of the solar system is about 1 light-year. So, how much brightness will the Sun dim when we reach the edge of the solar system? Using the formula for converting apparent and absolute magnitudes, we find that its brightness is comparable to that of Venus in the sky at its faintest. This suggests that although the Sun is so bright, it cannot illuminate the entire solar system on its own.

So, what about the R136a1 star? It is 6.16 million times brighter than the Sun. What kind of concept is this? The absolute magnitude of R136a1 determined by scientists is minus 12.24. This means that if R136a1 were 32.6 light-years away from Earth, its apparent magnitude would be about the same as that of a Full Moon. Just imagine, on a full moon night, you can deeply appreciate the powerful glowing ability of R136a1.

If we place R136a1 in the position of the Sun, its apparent magnitude will be extremely bright from Earth, reaching minus 43.71. This brightness is equivalent to what we could expect to see when we look at the Sun 60,000 kilometers off its surface. However, to achieve the same brightness as the Sun, we must observe it at a distance of about 0.4 light-years from R136a1 – which equates to a distance of 378.4 billion kilometers. This is enough to prove how powerful the brightness of R136a1 is.

So what would be the brightness of R136a1 at a light-year distance from the edge of the solar system? After calculations, we know that its apparent magnitude is minus 19.8. This brightness is similar to or brighter than the sun we see on Neptune, or it is similar to the sky shortly after the sun sets in the evening. However, it is important to note that if the brightest star in the universe is located in the center of the solar system, the Earth may be instantly scorched by its intense heat.

Thus, we can conclude that R136a1, the brightest known star in the universe, is fully capable of illuminating the entire solar system. However, this does not mean that we should place it at the center of the solar system. Despite its brilliance, too close to a star also means great risks and unknown implications.

(Picture from the Internet)

Author | Kiwi graduated from the University of Lincoln, New Zealand. He has a strong interest in popular science knowledge, and has published popular science articles in many popular science journals. Pay attention to the facts and actively explore cutting-edge technology.