BOAT

Brightest Of All Time

You’ve heard of the abbreviation GOAT, right?

No, not that sort of goat. I’m talking about “Greatest Of All Time”, something that might be attributed to Michael Jordan or The Beatles, but it also might be attributed to Lebron James or Led Zeppelin. In other words, GOAT is subjective, and it depends on human interpretation.

BOAT, on the other hand, is very much cut-and-dried. It stands for Brightest Of All Time, but it only stands for that because I just now made it up. Still, it’s something we can measure and agree on, so there can be only one.

Well… even then, we have to be a little cautious. There are two things astronomers can mean when they talk about how bright something is.

One means how much of the light we can see. This one is called flux, and if you ask the average person on the street which star in the night sky is brightest, they’ll probably point to Sirius, the Dog Star. If you look up there, more light from Sirius will reach your eye than any other star.

You can probably see where this is going. Sirius is way, way closer than stars that throw much more light off, so it appears brighter from our perspective. That doesn’t mean it blasts the most light out there, though! It just means it looks that way from our perspective.

By “looks that way”, I really mean to say that all of our measurements indicate this to be the case. It’s not just the visible light that flux measures, but all photons that reach us.

Luminosity, by contrast, describes how much energy a star throws off, period.

I mentioned Sirius as the brightest star in the night sky, so we already have two caveats. First, we’re not just after stars, and Sirius doesn’t hold a metaphorical candle to the Moon’s brightness, overwhelming any nearby stars with its incredible apparent brightness.

Of course, the Moon doesn’t make me want to sneeze whenever I catch a glimpse of it from the top of my eyes, but the Sun sure does. That’s because it’s about 450,000 times brighter, flux-wise, than the Moon. Meanwhile the luminosity of the Moon is pretty close to zero—the Sun pumps out nonstop energy from fusion, but the Moon only reflects a minuscule fraction of that light back out into space.

So, the Sun is like the BOAD—the Brightest Of All Day, maybe—but what about of all time? And we should probably ignore the flux aspect—that only covers how bright it appears to an arbitrary observer, whereas luminosity measures total energy output. We’ll use luminosity.

If we’re ranking these in terms of peak luminosity, then there’s really not much of a contest: Gamma-Ray Bursts (GRBs) take the cake. One way to describe just how powerful these directional blasts can be is by putting into terms of our Sun. GRBs can be literal quadrillions of times more luminous than our Sun.

If you added up all of the stars that make up a typical galaxy, GRBs can be much brighter. Hundreds of billions of stars can be less bright than one single burst, like when an unimaginably enormous star finally collapses under its incredible gravitational pressure, or when two neutron stars smash into one another.