Small, faint galaxies, like the Draco dwarf spheroidal galaxy shown here, have much more dark matter in them relative to the normal matter found inside than larger galaxies. For the smallest galaxies of all, this is the most extreme example of dark matter. (BERNHARD HUBL / ASTROPHOTON.COM)

The Smallest Galaxy Ever Discovered Demonstrates The Unequivocal Need For Dark Matter

It’s not the only one of its kind, but it’s definitely makes no sense without dark matter.

Throughout the Universe, galaxies and star clusters come in all different sizes and masses.

This NASA/ESA Hubble Space Telescope image shows a massive galaxy cluster, PLCK_G308.3–20.2, glowing brightly in the darkness. Although the largest, brightest galaxies in this cluster are the easiest to see, they are vastly outnumbered by smaller, fainter structures with much lower luminosities, and cannot be seen in this image. All told, even with the limits of the Hubble Space Telescope, we’re seeing fewer than 10% of the total galaxies expected to be out there. (ESA/HUBBLE & NASA, RELICS; ACKNOWLEDGEMENT: D. COE ET AL.)

While the brightest ones are always the easiest to see, the faint ones are far greater in number.

The dwarf galaxy UGC 5340 is forming stars irregularly, likely due to a gravitational interaction with a companion galaxy that is not pictured here. Many other galaxies, much more massive but also more distant, can be seen off in the background. (NASA, ESA, AND THE LEGUS TEAM)

Even within our Local Group, with just 2 or 3 large galaxies, some 60 dwarf galaxies and hundreds of globular clusters abound.

Our Local Group of galaxies is dominated by Andromeda and the Milky Way, but there’s no denying that Andromeda is the biggest, the Milky Way is #2, Triangulum is #3, and the LMC is #4. Perhaps 60 other smaller dwarf galaxies abound, and hundreds if not thousands of globular clusters and other even smaller structures make up our corner of the Universe. (ANDREW Z. COLVIN)

Only the stars emit visible light, but all forms of matter exert their gravity.