The coordinates from the random number generator point to a galaxy located at a distance of 114 thousand light years (35 kpc) [1] in the constellation Aires named Segue 2 (that is "segue" as in to transition uninterrupted from one thing to another and not "Segway" as in the company that once sold self-balancing two-wheeled personal transport vehicles a couple of decades ago). Segue 2 was discovered by a survery with the acronym of SEGUE [1], which stands for the Sloan Extension for Galactic Understanding and Exploration. (The people involved really worked hard on that acronym.) This survey spent time trying to identify dwarf galaxies orbiting the Milky Way by looking through data for stars observed by the Sloan Digital Sky Survey. Their strategy was to identify unusually large concentrations of stars corresponding to locations within the halo of our galaxy that could be dwarf galaxies. Segue 2 was the second galaxy found this way, and the discovery was published in 2009 [1].
Segue 2 is one of many dwarf galaxies orbiting the Milky Way. The Milky Way's brighter satellite dwarf galaxies were discovered using photographic plates [2], although the Large and Small Magellanic Clouds are so bright and so close that they can be seen without a telescope and were thus discovered before the telescope's invention. The Milky Way's fainter satellite dwarf galaxies, like Segue 2, could only be discovered using a combination of modern digital detectors and statistical methods [2], which is why Segue 2 was only discovered in 2009 [1].
In fact, Segue 2 has the distinction of being both the faintest and the smallest galaxy ever discovered. The brightness of the galaxy is equivalent to only 900 times the brightness of the Sun [1]. The mass of the galaxy, which was determined by looking at the orbits of the stars within it, is less than 150000 times the mass of the Sun [3]. Keep in mind that much of that mass is in the form of dark matter, which I'll discuss later. Because the galaxy is so faint, very few actual stars have been identified as being part of the galaxy.
So the question that comes up regarding Segue 2, which is the same question that has come up for a couple of other objects that I've featured in previous podcast episodes, is what is the difference between a very small galaxy and a very large cluster of stars. After all, the typical globular cluster orbiting the Milky Way has a mass of somewhere between 100 thousand and 1 million times the mass of the Sun, and the mass of Segue 2 falls at the low end of that range.
First of all, galaxies are expected to have stars which formed at different times, while all the stars in any given cluster should have all formed at the same time out of the same cloud of interstellar gas [4, 5]. Regarding Segue 2, it does indeed look like the very few stars found in the galaxy formed at different times. This could be determined by looking at the presence of iron in the stars' outer atmospheres. Iron is generally formed either in the centers of very massive stars just before they explode as supernovae or by nuclear processes that take place when stars die and eject their outer gas layers (and this can include big stars exploding as supernovae or smaller stars blowing off their outer gas layers to form planetary nebulae). This means that, as stars are created and then die, the amount of iron in any galaxy will increase over time. If all the stars in Segue 2 formed from the same cloud of interstellar gas at the same time, that cloud of gas would have contained a relatively uniform density of iron, and all of the stars would have the same amounts of iron in their outer atmospheres. However, the stars in Segue 2 have very different amounts of iron in their atmospheres, so some stars must have formed after others had died and ejected extra iron into the interstellar gas used to form new stars, which indicates that Segue 2 is a galaxy.
The other way to distinguish dwarf galaxies from clusters is to look for dark matter (or, technically, to look for the signs of dark matter, since it's not possible to actually see dark matter itself) [4, 5]. Anyway, as I said earlier, Segue 2 seems to have a lot of dark matter [3]. The relative amount of dark matter in a galaxy is typically quantified using the ratio of a galaxy's mass to its brightness, with the mass being determined using the orbital velocities of the stars in the object so that it's an independent measurement from the stellar brightness. If no dark matter was present in an object, like a cluster of stars, this number would be 1. For the typical large galaxy, this would be a number somewhere between 2 and 10 [6]. For Segue 2, this number has not been definitively constrained, but it has an upper limit of 360 [2], which is huge compared to spiral galaxies but actually rather typical for a few of the really weird dwarf galaxies that have been found in recent years orbiting the Milky Way.
So it looks like Segue 2 is indeed a dwarf galaxy and not a cluster of stars. This then leads to questions about how Segue 2 formed. One possibility is that it was born this way, or to be more accurate, the galaxy initially formed soon after the Big Bang with a very small concentration of dark matter that was able to gravitationally attract a small amount of primordial hydrogen gas to form a few stars [2]. The other possibility, though, is that Segue 2 may have originally been a normal-sized dwarf galaxy that gravitationally interacted with another galaxy, with the other galaxy stripping away the outer layers of Segue 2, leaving very few stars and a modest amount of dark matter [2]. Future observations as well as simulations of Segue 2 may eventually reveal which of these scenarios is correct.
Also, just before I finish up, if you do a Google search for the smallest galaxy in the universe, you might find a few webpages that mention an object called Ursa Major III, but people are still trying to figure out if that is technically a really really small galaxy or just a really small cluster of stars [7, 8]. People just haven't been able to either measure of the orbits of the stars to determine the object's mass (and whether it has dark matter) or identify the ages of the stars in Ursa Major III (to see if they formed at the same time or different times), so, as of the time I am recording this, Segue 2 is still the smallest galaxy anyone knows about.