Space is basically the coolest, coldest, biggest, all-around awesomest… so many superlatives. But what’re the brightest and darkest things out there? When we’re talking about the brightest and darkest things in space, there are a few things to consider, but let’s start off with what we experience here on Earth.
We know that the brightest thing in our sky is the Sun. It’s a star, but it’s so close to the Earth that it dominates the daytime sky, outshining other stars. After the Sun sets and we can see the other stars, it’s easy to see that they vary in brightness.
Astronomers have observed this for millennia and used it as a way to catalogue stars. More than 2,000 years ago, the Greek astronomer Hipparchus catalogued the brightness of stars saying that the brightest was a magnitude 1 star and the dimmest was a magnitude 6 star. He classified stars based on their apparent or visual magnitude. But this isn’t a perfect method. Not only is it measuring stars with the imperfect human eye, it’s making measurements relative to our Earthly perspective.
Two stars that look to be equally bright might only appear to be so. In reality, one could be much brighter but further way, so it appears dimmer. If we want to know what the brightest is, we need to talk about absolute magnitude, which is measuring bright things against each other irrespective of our Earthly vantage point. The solution astronomers came up with was to implement an absolute magnitude scale similar to, but more complete than Hipparchus’ scale. A star’s absolute magnitude is determined by calculating its brightness as it would appear if it was 32.6 light-years (which is a nice round 10 parsecs) from the Earth.
Astronomers can also use luminosity as a measure, looking at the amount of light energy that a star puts out. So let’s look at the Sun again as an example. Its visual magnitude, its brightness from here on Earth, is -26.74, but its absolute magnitude, what it would be from 32.6 light years away, is 4.83.
The brightest known star is called R136a1. It lies about 165,000 light years from Earth and has a visual magnitude of 12.77. But looking at it away from our Earthly vantage point, R136a1 is about 10 million more luminous than our Sun. But even the brightest star isn’t the brightest thing.
When stars die, they explode brilliantly in what is called a supernova, expelling huge amounts of energy as x-rays and gamma rays. So how bright are supernovas? They can shine as bright as 10 billion suns, one was even recorded as being 600 billion times brighter than the Sun, releasing more energy in an instant than our Sun will over its whole lifetime. So they’re bright, but they don’t last and they’re still not the brightest. To understand the brightest sustained thing in the Universe, we have to look at the darkest thing in the Universe. To consider something dark, we have to consider how it interacts with light, because properly speaking darkness is the absence of light. This means we can’t really look at dark matter as something dark because it doesn’t interact with light at all.
But black holes do, and true to their name, they are the darkest things in the universe. A black holes is a highly concentrated, densely packed gravitational point in space from which nothing can escape. Any material that strays too close to a black hole will be devoured, and that generally means stars, gases, and dust. This cosmic material swirls around the black hole, which is what astronomers see when they detect a black hole, but ultimately the pull of gravity is so strong that even light can’t escape. So this is what makes black holes the darkest thing in the universe.
But the process of a black hole devouring all that material is the opposite of dark. Black holes rotating at the centre of galaxies devouring material is a hugely energetic process. Some material is sucked into the hole, but some is sent streaming away from it in giant jets above and below it, essentially “turning on” what’s called a quasar.
Quasars are part of a class of objects known as active galactic nuclei, and they release far more energy than normal stellar production does alone. And that energy is bright. Quasars can shine between 10 to 100,000 times brighter than our own Milky Way galaxy — a quasar called W2246-0526 emits as much light as 350 billion suns. It’s the brightest object ever found in the universe. So black holes are the darkest and quasars are the brightest, but what about other superlatives in space? Like, who has traveled the furthest from the Earth? It was the crew of Apollo 13 in 1970. And speaking of Apollo 13, how exactly did NASA make sure there wasn’t a repeat performance of the explosion that crippled the mission?