This optical (blue) and NASA’s Chandra X-ray (red-orange) composite image shows Abell 2029, a cluster of galaxies where the galaxy at the center, IC 1101, is the largest known galaxy in the Universe. (OPTICAL: NOAO/KITT PEAK/J.USON, D.DALE; X-RAY: NASA/CXC/IOA/S.ALLEN ET AL.)
Compared to what we find in our Solar System, galaxies are truly enormous.
The Sun may be 109 times the diameter of Earth, but the Earth-Sun distance is over 100 times larger than the Sun’s diameter; the distance to Voyager 1 or 2 is ~100 times larger than the Earth-Sun distance; the Oort Cloud’s density peaks ~100 times farther away than Voyager 2, and the distance to the nearest stars are ~100 times farther away than even that. (NASA / JPL-CALTECH)
The smallest known galaxy is Segue 2, with only about ~1000 stars inside.
Only approximately 1000 stars are present in the entirety of the smallest dwarf galaxies such as Segue 1, 2, and 3. Gravitationally, the masses of these galaxies can be estimated at around 550,000–600,000 Suns. The stars making up the dwarf satellite Segue 1 are circled here. These galaxies have the largest dark matter-to-normal matter ratios known. (MARLA GEHA AND KECK OBSERVATORIES)
These stars are spread out over ~500 light-years: billions of times the physical size of any individual star.
Globular clusters, like Omega Centauri, have some of the highest stellar densities ever observed. Through a modest telescope, they appear like dense fuzzy balls of light. But if we take a very sharp, high-resolution photo, such as with Hubble, we can find that even in these densest regions, there are still only a few hundred stars, at most, within each cubic light year. (NASA, ESA, AND THE HUBBLE SM4 ERO TEAM)
A common image showing relative sizes (incorrectly) for a number of galaxies. Andromeda is too large for the Milky Way; M87 is too small for Andromeda; IC 1101 is way too small compared to M87. When it comes to comprehending distance scales, it’s vital to not share misleading images. (ASTRO BOB / BOB KING / DULUTH NEWS TRIBUTE)
Our own Milky Way, typical of modern spirals, is slightly over 100,000 light-years across.
The Universe is: Expanding, cooling, and dark. It starts with a bang! #Cosmology Science writer, astrophysicist, science communicator & NASA columnist.
