In outer space, the strong gravity of large bodies irresistibly attracts smaller ones. moons become bound in orbits around planets. planets, asteroids, and comets move around larger stars, while stars gather around enormous black holes, thus creating galaxies.
Large galaxies, like the
Milky Way
, draw in smaller galaxies. The celestial vicinity of our solar system extends over 100,000 light-years and includes within it approximately
100 billion to 400 billion stars
The Milky Way is enormous, having drawn in countless dwarf galaxies with just a few billion stars each over billions of years, capturing them as satellite systems.
However, how many satellite galaxies does the Milky Way possess?
The count keeps fluctuating as advanced telescopes and extensive sky surveys uncover increasingly dim galaxies. However, let’s begin with those we can readily observe. The two most notable satellite galaxies of the Milky Way are the Large Magellanic Cloud and the Small Magellanic Cloud. These celestial bodies circle the Milky Way approximately 160,000 light-years away and are observable from the Southern Hemisphere even without a telescope, based on astronomical data.
NASA’s Goddard Space Flight Center
.
Nevertheless, these easily observable satellites are uncommon; for the most part, satellite galaxies are tiny and faint, remaining hidden from all but the strongest telescopic eyes. Researchers locate dwarf galaxies through devices equipped with an extensive viewing angle to encompass as much of the celestial expanse as feasible, noted
Or Graur
, an associate professor of astrophysics at the University of Portsmouth in the UK.
“As telescopes grow larger and our equipment improves, we can delve deeper into detecting more elusive dwarf galaxies, including those now referred to as ultra-faint dwarfs, which contain merely a few hundred thousand stars,” explained Graur to Live Science.
Related:
What is the number of galaxies in the universe?
Determining whether a neighboring dwarf galaxy is a satellite of the Milky Way requires spectroscopy — examining the light it emits — to ascertain its movement and trajectory, as mentioned.
Marla Geha
a professor of astronomy and physics at Yale University.
You can determine if the object is gravitationally tied to itself and whether this group orbits the Milky Way,” Geha explained to Live Science. “A satellite galaxy consistently—and will continue to—orbit the more massive galaxy.
A recently released census from 2020 showed
The Astrophysical Journal
It was approximated that around 60 satellites are circling the Milky Way at a distance of approximately 1.4 million light-years. However, determining the exact number of the Milky Way’s satellite galaxies remains challenging, partly due to the fact that not all suggested satellite galaxies have undergone spectroscopic confirmation to verify their orbital path around our galaxy.
“Most likely, there are between five and eight objects that lack clear spectroscopy or have uncertain spectroscopic data,” Geha stated. Additionally, she mentioned that new satellite candidates continue to be found.
When Geha embarked on her investigation into the origins and development of dwarf galaxies over twenty years ago, the Milky Way was believed to have just eleven satellite galaxies. However, this number shifted with the commencement of the Sloan Digital Sky Survey in the early 2000s, as noted by Geha. This survey created the initial digital chart spanning more than a third of the celestial sphere, and through the use of its advanced digital imaging equipment, astronomers were better positioned to detect these elusive dwarf galaxies. These small galaxies frequently struggle for visibility due to their subdued luminosity being overshadowed by larger, nearer stars.
By employing Sloan’s digital imagery, researchers managed to algorithmically remove foreground stars—a task that was significantly more challenging when working with traditional analog photos and photographic plates, according to Geha. This process uncovered dim dwarf galaxies that had been obscured until then.
Geha noted that each of the major new imaging surveys has had a transformative impact. She emphasized that technology is largely responsible for these advancements and the increase in the number of known satellites.
From Sloan in the 2000s to the Dark Energy Survey in the 2010s, every survey uncovered additional scores of satellite galaxies circling our home galaxy, the Milky Way.
Vera C. Rubin Observatory
In Chile, experts like Geha anticipate the discovery of hundreds more satellites; however, this could be prevented if the Milky Way consumes these galaxies first.
Graur stated that satellite galaxies are gravitationally tied to the Milky Way. The Milky Way continually exerts gravitational pull on these satellites. Gradually, this tug causes them to be drawn closer. As they get nearer, the Milky Way begins tearing them apart and absorbing them.
One such casualty was a dwarf galaxy currently referred to as
Gaia Enceladus
, which was torn apart and consumed by the Milky Way, with its stars now sparkling within the Milky Way’s halo, according to Graur. Ultimately, the satellite galaxies we see today will probably meet the same end, Geha noted.
If we wait for an extremely long period, say billions upon billions of years,” she explained, “the satellite galaxies will eventually be drawn into the parent galaxy and merge with it, resulting in an even larger central galaxy.
