When you look up at the Sun, it’ll hurt your eyes, that’s because the sun is pretty bright. In fact, the Sun is the brightest thing in the sky, by a long way.
Apparent magnitude measures how bright something is in relation to us, this takes in a few aspects like our atmosphere and how close the object we’re looking at is to us. Much like a golf score, the lower the number when looking at the magnitude, the brighter the object.
What Is The Brightest Thing In The Sky?
When we look at the apparent magnitude of the Earth’s skies, the Sun outshines everything with -26.7. This is so bright in comparison to us that during the daytime where the Sun is visible in the sky, we can’t even see the second brightest star, that second brightest star being Sirius with an apparent magnitude of -1.46.
But what if we wait until the Sun has disappeared? In the night we can see way more of our universe because the light of the Sun is depleted. However, the Sun will still ruin our view, using the second brightest object in the sky, a full moon.
A full moon has an apparent magnitude of -12.92, not even half as bright as the sun, which means you can look at the moon without injuring your eyes, but this is still bright enough to block your view of some other bright objects.
Even the third brightest object in our sky (the second brightest in the night’s sky) isn’t even a star and is still only visible due to our Sun’s reflection. Venus’ reflection has an apparent magnitude of -4.89 at only around 2 light minutes away from Earth.
It is therefore no question that the Sun has a huge influence on what we see as the brightest thing in the universe, for half of the time we can’t even see past it and the other half its reflection blocks us from seeing the rest.
However, we’ve got a bias. If you were to put a lightbulb three inches away from your eye, the light would appear as bright as our Sun. But if you put that same lightbulb next to the sun and look at them from the same distance, there wouldn’t be any competition. This is called absolute magnitude.
What Is Absolute Magnitude?
Absolute magnitude is the brightness of an object without relativity to what we can see from earth. Much like placing the light bulb and the Sun next to each other, when we stand the same distance from the light bulb and the Sun and measure their brightness, we are measuring their absolute magnitude.
Absolute magnitude changes what we think brightness is. As we’ve already established the Sun has an apparent magnitude of -26.7, but when we look at its absolute magnitude, it is a measly 4.7. In relation to this, Sirius, with an apparent magnitude of -1.46 has an absolute magnitude of 1.4, making it 70 times brighter than our sun.
In the night’s sky, the moon and Venus are now out of the question as they don’t have an absolute magnitude, as the light we see from their apparent magnitude is only the reflection of the sun. Even Sirius, which is 70 times brighter than our Sun, is nothing compared to the brightness of some other stars.
What Are The Brightest Stars?
If we travel around 150 light-years away, we’ll get to Eridani, although you don’t have to travel this distance to see it, you can see it with the naked eye. This star has an apparent magnitude of 3.55, but an absolute magnitude of -1.276, making it a staggering 255 times brighter than the Sun.
If you think that’s pretty bright, you’re probably right, you wouldn’t do too well looking right at it, but in relation to the rest of the universe, you couldn’t be more wrong.
If we travel a little further out at 864 lightyears away from Earth, we come to Rigel, a star that is very visible from Earth, more visible than Eridani even though it is 714 lightyears further away, it has an apparent magnitude of 0.12 but a blinding absolute magnitude of -8.1. Making it 120,000 times brighter than our Sun.
Now you’re getting to the big guns, and you don’t even have to travel too far to get to the brighter stars in our known universe. In fact, HD 229059 in the Berkeley 87 star system is only 3,200 lightyears away yet has an absolute magnitude of -10.3. Over 1 million times brighter than the Sun.
But all of these stars bow down to the star R136a1, a huge star that holds 256x more mass than the Sun. This gigantic star lives 163,000 lightyears away from us and it’s bright. R136a1 is the brightest star in our known universe at -12.235 absolute magnitude. That is 6,166,000 more luminous than the Sun.
If R136a1 was in place of our own Sun, the difference between the brightness of the Sun compared to R136a1 would be around the same difference of the brightness between the Sun and the moon. Not only that, its mass would pull Earth into a closer orbit, so close that a year would last around three weeks.
R136a1 is no doubt the brightest star in our known universe, but is it the brightest thing?
What Is The Brightest Thing In Our Universe?
R136a1 is not the brightest thing in our universe, stars are bright, but they aren’t the only thing that can give off light. As we’ve discussed, planets and moons can give us an apparent magnitude, but not an absolute magnitude. We still need to look at stars when we’re looking at what the brightest things in the universe are, but we’ll have to wait until one dies.
Stars are very dense and give off a lot of energy. However, this energy runs out, and when it does, the star will collapse under its own gravity. The mass of the star needs to go somewhere, however, and that somewhere is, well, everywhere. When a star dies it explodes into a supernova and ends up being dust, gas, and debris floating across lightyears of space.
This isn’t without a light show first. When the core originally collapses on itself, the star ejects bursts of gamma radiation which are arguably the brightest electromagnetic events in the universe.
A supernova can reach an absolute magnitude of -19 depending on the size of the star, these gamma-bursts release the same amount of energy in a few seconds that our sun will release in its entire 10 billion year lifetime.
However, these bursts only last a few minutes, if you want something brighter and longer-lasting, you’re going to have to look to the darkest thing in the universe, a black hole.
When a black hole eats a star, gas, and debris from the stars swirl into accretion discs. In these discs, debris and gas spin at phenomenal speeds, as it is sucked over the event horizon of the black hole, this phenomenon is called a quasar. Quasars are bright, very bright, quasars can shine brighter than entire galaxies containing billions of stars.
The first identified quasar was 3C 273, and the brightest, has an absolute magnitude of -26.7, that’s 4,000,000,000,000 times brighter than our Sun. If you put 3C 273 just 33 lightyears away from Earth it would shine just as brightly as the Sun, which is 8 light minutes away.
But from where you are standing, you aren’t going to see 3C 273, the quasar only has an apparent magnitude of 12.8 meaning that you’ll need at least a medium-size telescope to see it. So even though 3C 273 is 4 trillion times brighter than the Sun, brightness is all relative.
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