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Okay… So you’re finally home after a long sunny day at the park. You open the door, enter, and realize that no one told your eyes that they were leaving the sunshine. They are still accustomed to the brightness outside and you’re left there squinting like a blind bat.
We all know that the sun is rather bright (understatement of the year), and while it is certainly the brightest thing in the visible sky, is certainly isn’t the brightest thing in the universe? Before we try to figure out what is, let’s just clarify what the term ‘brightness’ actually means.
What is ‘Brightness’ really?
Brightness is a measure of how much light from a glowing object actually reaches the receptors – our eyes. Brightness is relative to the distance between the observer and the object, and this fact is what makes everything a bit more confusing. The sun is bright, but so is a 100-watt light bulb if you hold it close to your face. Actually, it’s almost exactly as bright. Therefore, we’re not going to concern ourselves with apparent brightness, but rather ‘absolute’ brightness. To put things into perspective and to really compare the brightness level of things, we first need a scale of measurement. This can be easily be done, assuming that we’re looking at them from the same distance.
Our Sun is far from the brightest thing in the universe, something that you’ll begin to realize as you continue reading. The Sun’s close proximity to Earth is why it looks like the brightest thing in our sky.
This unceremoniously named star is 256 times more massive than our sun. It might not be the biggest star by volume, but it is extremely massive and also the brightest star out there. This behemoth is 8.6 million times brighter than our Sun.
If something that bright was as close to us as the Sun, the Earth would be a thousand times hotter than it is now, and we would never have had a shot at life . The phrase ‘brighter than the Sun’ doesn’t have the same ring to it now, does it?
When stars die, having run out of hydrogen to fuel the nuclear reactions inside, some of them explode violently, resulting in supernovas. Supernovas can emit flashes of radiation called Gamma Ray Bursts that are so grandiose in scale that they put R136a1 to shame.
A single gamma ray burst can emit as much energy in a few seconds as our Sun does in its whole lifetime of 10 billion years. If such a beam were to strike Earth, even from a distance of a million light years, astronomers predict that it could deplete our ozone layer by 25%, causing mass extinction. However, these events are very brief, lasting for only a few minutes, and in some cases, just some milliseconds. Although brighter than the brightest stars, these still aren’t the heavyweights of the universe.
Paradoxically, the brightest things in the universe exist only because of the darkest things in the universe – black holes. By definition, a black hole is dark, but it also is unimaginably massive. Owing to its huge mass, its gravitational force is also huge – so huge, in fact, that even light cannot escape its field. This makes them impossible to see, because in order to see something, light needs to be reflected from it. This is why black holes are so dark by nature. This gravitational field does not let anything nearby escape; sometimes, stars in close proximity to black holes are inexorably pulled towards them. The tremendous amounts of energy generated in the process of black holes swallowing stars is anything but dark.
Initially, the gas and debris from the stars swirls around the black hole, forming cosmic circular shapes called ‘accretion discs’. Friction in these discs generates so much energy that even galaxies pale in comparison. Next up is the spectacular event in which the black hole swallows the stars whole, forming something called a QUASAR. These quasars shine thousands of times more brightly than entire galaxies that contain billions of stars. They lie in areas that are also home to other galaxies, but these galaxies are easily drowned out by the quasar’s luminescence.
To put the brightness of quasars in still another perspective, let’s look at a picture captured by the Hubble telescope.
The bright spot on the right is a star just a few hundred light years away, while the left one is a quasar 9 billion light years away.
If you’re wondering why these quasars so far away, then think about what being a light year from something actually means. The light from a star that is one light year away would, by definition, take one year to reach you, so whatever you’re actually seeing is in fact what the star looked like a year ago. Technically, this means that you can see into the past! Now, let’s look at how far the nearest quasar is… 9 billion light years! Quasars do not last forever, so whatever we know about them is through 9 billion-year-old photographs. They are actually remnants of the early universe, when things were more chaotic, for lack of a better word.
It’s quite interesting that the things considered to be the darkest things out there have turned out to be the reason why the brightest things exist. Neil Degrasse Tyson, a renowned astrophysicist, says that in order for a black hole to be able to produce a quasar, it needs to swallow an average of 10 stars every year (roughly 30 million times the mass of Earth). Talk about being hungry, huh?
However, since we know that one of our neighboring galaxies, Andromeda, is on a collision course with the Milky Way, scientist believe that this collision might induce the conditions required for a quasar to be formed. No worries, this won’t happen for 4 billion years.