The brightest galaxies of all neither have the most stars nor the biggest black holes. Here’s how to solve the mystery.
With some 400 billion stars burning steadily, the Milky Way is just a typical galaxy in the Universe.
Many galaxies are larger, containing tens or hundreds of times as many stars.
But there are galaxies that are intrinsically brighter because they’re active, irrespective of their size.
When new stars form en masse, the most massive ones can shine up to millions of times brighter than a Sun-like star.
Galactic mergers trigger new waves of star formation, and can also activate supermassive black holes at the centers of these galaxies.
An active, supermassive black hole will accelerate nearby matter to relativistic speeds, creating bright jets of multiwavelength light.
The brightest ones, the quasars, are all thought to be housed in galaxies, though many remain unobserved.
In 2015, a new record was set for the brightest known galaxy, thanks to observations with the WISE telescope.
Supermassive black holes power Extremely Luminous Infrared Galaxies.
The brightest ones shine 10,000+ times as bright as our Milky Way.
Although the Universe is just 10% of its current age and the galaxy is even smaller than ours, it outshines them all.
Some ultra-distant quasars may even surpass it, although their galaxies have yet to be seen.
Mostly Mute Monday tells the astronomical story of an object, class, or phenomenon in the Universe in visuals, images, and no more than 200 words. Talk less, smile more.Ethan Siegel is the author of Beyond the Galaxy and Treknology. You can pre-order his third book, currently in development: the Encyclopaedia Cosmologica.