Among the many stars in the universe, the brightness of the sun is actually not high, in fact, if you talk about the real brightness, most of the stars in the night sky of the earth that we can see with the naked eye are brighter than the sun, and in the depths of the universe, some stars can even reach millions of times the brightness of the sun, such as "R136a1" in the spider nebula in the Great Magellanic galaxy, which is as bright as about 8.7 million times the sun.
However, even "R136a1" is far from being the brightest object in the universe, so how bright is the brightest object in the known universe?
Since the 60s of the 20th century, astronomers have discovered some strange celestial objects one after another, and the observation data shows that they look very similar to stars, but they are very far away from the earth, usually reaching billions, and some even tens of billions of light years, such objects were later named "quasars".
To put it simply, according to the law of inverse square proportionality, the farther away the celestial body is, the fainter the celestial body becomes, and the brightness of "quasars" can be similar to that of stars at a distance of billions or even tens of billions of light-years, which means that their true brightness is ridiculously high, for example, there is a "quasar" called "3C 273", and its absolute magnitude reaches about -26.3.
The so-called "absolute magnitude" refers to the brightness measured by assuming that the celestial body is placed at a distance of 10 parsecs from the observer, which reflects the true brightness of the celestial body, and there is also a corresponding concept of "apparent magnitude", which describes the brightness of the star as seen by the observer with the naked eye. The values of absolute and apparent magnitudes can be negative, and for every 1 difference in value, the difference in brightness will be 2.512 times, and the smaller the value, the brighter the celestial body.
It is known that the absolute magnitude of the Sun is about 4.83 magnitude, from which it can be calculated that the true brightness of "3C 273" is about 2.83 trillion times that of the Sun.
That is, the apparent magnitude of the Sun is about -26.7 magnitude when observed on our Earth, and the "parsec" is a unit of distance commonly used by astronomers, and the 1 parsec is about 3.26 light years, that is, if we put "3C 273" at a distance of about 32.6 light years from the Earth, its brightness can be equivalent to the Sun we see on the Earth.
You must know that 32.6 light-years is almost 8 times the distance between Proxima Centauri and us, and it can be so bright at such a distance, you say that it is outrageous? However, "3C 273" is not the brightest "quasar".
According to the known observational data, the brightest "quasar" is actually "J2157-3602", which was discovered in 2018, and astronomers calculated that it is about 12 billion light-years away from us based on observational data, and its absolute magnitude reaches -32.36 magnitude, that is, its true brightness is about 266 times that of "3C 273" and 752 trillion times that of the Sun.
At this brightness, if you just put it 32.6 light-years away, the Earth would probably be dried by it, but what if you put it farther away, let's say in the center of the Milky Way?
Apparent and absolute magnitudes can be converted using the formula "m = M - 5 x lg(d0/d)" (where m, M, d0, d, represent the apparent magnitude, absolute magnitude, 10 parsecs, distance between the observer and the target object, respectively, and lg is a function, i.e., a logarithm with a base of 10).
We are known to be about 26,000 light-years away from the center of the Milky Way, and according to the above formula, we can calculate that if we put "J2157-3602" at the center of the Milky Way, then its apparent magnitude will be about -17.86 magnitude when observed on our Earth.
You must know that the full moon we see on the earth has an apparent magnitude of -12.9 at most (the earth arrives near perihelion, and the moon also reaches near perigee), that is to say, even if we put "J2157-3602" in the center of the Milky Way, its brightness in our eyes can reach about 96 times the maximum brightness of the full moon, which can easily light up the night sky of the earth, and we on the earth probably do not need to turn on the street lights at night.
In fact, "J2157-3602" is actually the brightest celestial object in the universe known at present, so the question arises, why is it so bright? As far as the current situation is concerned, there is no definite answer to this question, and astronomers can only give some reasonable speculations, among which the most agreed point is called the "black hole hypothesis".
According to astronomers' estimates, if the hypothesis is true, the black hole at the center of J2157-3602 is about 34 billion times the mass of the sun, and on average, every day, it swallows the equivalent of a solar mass.
Of course, this can only be regarded as a reasonable speculation, and whether this is really the case remains to be further explored.