Densest Galaxies Ever Found Will Forever Haunt Your Nights
Two undergraduate astronomy students have identified the densest galaxies ever found. They are called UCDs or Ultra-Compact Dwarf galaxies.
Michael Sandoval and Richard Vo from San José University were looking through databases of archived galaxies when they came across two galactic gems that were hiding in plain sight.
Here’s some vital statistics about the two galaxies
- 1/200th the width of the Milky way
- 10,000 times the stellar density near our sun
- also about 1/200th the size of the Milky Way
- A whopping 1 million times the density of our sun’s stellar neighborhood
Think about that for a minute. If you were on a planet in one of those galaxies, your night-sky view would be beyond breathtaking. You would potentially see a million stars or more from your alien backyard. Compare that to the paltry 3,000 or so stars you can see from your earth backyard on a clear night.
Such a density means that the closest star to you would be, on average, quite close. The closest star to us, Proxima Centauri, is about 4 light years away. In galaxy M85-HCC1, it would be 1/80th that distance. That’s so close that it would actually be well within our Oort cloud of comets thought to orbit the sun about 2 light years away. My guess is that such a cloud of comets couldn’t even form with so many stars nearby.
So why do they have such a high average density? Such galaxies could be the cores of larger galaxies that have had their less-dense outer regions stripped away by tidal interactions with a nearby galaxy. This theory is based on two fairly compelling lines of evidence. One is that the supermassive black holes at the very center of these galaxies are larger than expected. They’d be more at home in a larger galaxy. Second, these UCDs are quite rich in heavy metals like iron which are most efficiently produced in galactic centers.
When I realized that these UCDs were essentially just galactic cores, I was actually a little disappointed. All galactic cores are pretty dense after all. If we lived near the core of the Milky Way, our night skies would be pretty amazing too. Yet these are even more amazing since their density is somewhere near 3 times the density of stars in our core.
As much as I love looking at our night sky, I can’t help but feel like I’m going to be disappointed for a while.
Image Credits: NASA, ESA, G. BACON (STSCI) AND P. VAN DOKKUM (YALE UNIVERSITY)
A. ROMANOWSKY (SJSU), SUBARU, HUBBLE LEGACY ARCHIVE