Travel the universe with Dr. Ethan Siegel as he answers the biggest questions of all
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.
The SDSS view in the infrared — with APOGEE — of the Milky Way galaxy as viewed towards the center. Containing some 400 billion stars, infrared wavelengths are the best for viewing as many as possible due to its transparency to light-blocking dust. (Sloan Digital Sky Survey)
Many galaxies are larger, containing tens or hundreds of times as many stars.
The giant elliptical near the center of the Coma Cluster, NGC 4874 (at right), is typical of the largest, brightest galaxies found at the centers of the most massive galaxy clusters. Its stars are primarily older and redder, with only a few populations of bluer stars found sparsely inside. (ESA/Hubble & NASA)
But there are galaxies that are intrinsically brighter because they’re active, irrespective of their size.
Galaxies undergoing massive bursts of star formation can outshine even much larger, typical galaxies. M82, the Cigar Galaxy, is gravitationally interacting with its neighbor (not pictured), causing this burst of active, new star formation, making it much brighter than a typical galaxy of its size and mass. (NASA, ESA, and The Hubble Heritage Team (STScI/AURA))
When new stars form en masse, the most massive ones can shine up to millions of times brighter than a Sun-like star.
The largest group of newborn stars in our Local Group of galaxies, cluster R136, contains the most massive stars we’ve ever discovered: over 250 times the mass of our Sun for the largest. The brightest of the stars found here are more than 8,000,000 times as luminous as our Sun. (NASA, ESA, and F. Paresce, INAF-IASF, Bologna, R. O’Connell, University of Virginia, Charlottesville, and the Wide Field Camera 3 Science Oversight Committee)
Galactic mergers trigger new waves of star formation, and can also activate supermassive black holes at the centers of these galaxies.
The most distant X-ray jet in the Universe, from quasar GB 1428, is approximately the same distance and age, as viewed from Earth, as quasar S5 0014+81, which houses possibly the largest known black hole in the Universe. These distant behemoths are thought to be activated by mergers or other gravitational interactions. (X-ray: NASA/CXC/NRC/C.Cheung et al; Optical: NASA/STScI; Radio: NSF/NRAO/VLA)
An active, supermassive black hole will accelerate nearby matter to relativistic speeds, creating bright jets of multiwavelength light.
An illustration of an active black hole, one that accretes matter and accelerates a portion of it outwards in two perpendicular jets, is an outstanding descriptor of how quasars work. (Mark A. Garlick)
The brightest ones, the quasars, are all thought to be housed in galaxies, though many remain unobserved.
This artist’s rendering shows a galaxy being cleared of interstellar gas, the building blocks of new stars. Winds driven by a central black hole are responsible for this, and may be at the heart of what’s driving a number of active, ultra-distant galaxies. (ESA/ATG Medialab)
This artist’s concept depicts the current record holder for the most luminous galaxy in the universe. The galaxy, named WISE J224607.57–052635.0, is erupting with light equal to more than 300 trillion suns. It was discovered by NASA’s Wide-Field Infrared Survey Explorer, or WISE. The galaxy is smaller than the Milky Way, yet puts out 10,000 times more energy. (NASA / JPL-Caltech)
Many galaxies, particularly young and dusty ones, emit most of their energy in the infrared portion of the spectrum. If we want to find the brightest galaxies of all, we’ll need a next-generation infrared space telescope. The Fireworks galaxy, from NASA’s Spitzer space telescope, is a local example of a predominantly infrared galaxy.(NASA / JPL-Caltech / SSC / R. Kennicutt et al.)
This artist’s rendering shows a galaxy called W2246–0526, the most luminous galaxy known. New research suggests there is turbulent gas across its entirety, much of which is being expelled. This is the first example of its kind. (NRAO/AUI/NSF; Dana Berry / SkyWorks; ALMA (ESO/NAOJ/NRAO))
Although the Universe is just 10% of its current age and the galaxy is even smaller than ours, it outshines them all.
An ultra-distant quasar showing plenty of evidence for a supermassive black hole at its center. How that black hole got so massive so quickly is a topic of contentious scientific debate, but mergers of smaller black holes formed in early generations of stars might create the necessary seeds. Many quasars even outshine the most luminous galaxies of all. (X-ray: NASA/CXC/Univ of Michigan/R.C.Reis et al; Optical: NASA/STScI)
This image shows SDSS J0100+2802 (center), the brightest quasar in the early Universe. It’s light comes to us from when the Universe was only 0.9 billion years old, versus the 13.8 billion year age we have today. (Sloan Digital Sky Survey)
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.
