Our galaxy, the Milky Way, is a heartless thief. Findings of a new study have revealed that some of its most distant stars may have been stolen from another smaller galaxy.
Sagittarius Dwarf Galaxy
The Sagittarius Dwarf Elliptical Galaxy is an elliptical loop-shaped galaxy spanning about 10,000 light-years in diameter.
Officially discovered in 1994, the galaxy is recognized as one of the nearest known neighbors of the Milky Way. It is among dozens of mini-galaxies surrounding the Milky Way. The Sagittarius dwarf is about 70,000 light-years away from Earth traveling in a polar orbit at a distance of about 50,000 light-years from the center of the Milky Way.
Second Closest Galaxy To The Milky Way
Because of its proximity to the Milky Way, being the second closest galaxy to our own, the Sagittarius dwarf appears to be the perfect victim for the celestial crime perpetrated by our thieving galaxy.
Involved are some of the 11 farthest known stars in the Milky Way located about 300,000 light-years away from Earth well and outside our galaxy's spiral disk.
Distant Milky Way Stars May Have Been Ripped From Sagittarius Dwarf
In a new research, Harvard astronomers showed that half of these distant stars may have been ripped from another galaxy, which is highly likely one of the Milky Way's closest celestial companions, the Sagittarius dwarf.
The Sagittarius dwarf has passed through the plane of the Milky Way several times in the past. With each passage, our galaxy's gravitational tides tugged on the smaller galaxy pulling it apart.
Study researchers Marion Dierickx and Avi Loeb, from the Harvard-Smithsonian Center for Astrophysics (CfA), used computer models to simulate Sagittarius dwarf's movement over the past 8 billion years.
Sagittarius Dwarf Has Lost About A Third Of Its Stars
At the beginning of the simulation, the weight of the Sagittarius dwarf was equivalent to about 10 billion times of the sun, which is about 1 percent of the mass of the Milky Way. Calculations revealed that over time, the dwarf has lost about a third of its stars and 90 percent of its dark matter, which resulted in three distinct streams of stars plunging into as far as 1 million light-years away from the center of the Milky Way.
"We simulate the full infall trajectory of the Sgr progenitor from the time it first crossed the Milky Way virial radius 8 Gyr ago," the researchers wrote in their study, which was accepted for publication in the Astrophysical Journal. "An exploration of the parameter space of initial phase-space conditions yields tight constraints on the angular momentum of the Sgr progenitor."
The researchers also found that five of the 11 most distant stars in our galaxy have velocities and positions that match what would be expected of stars that were stripped from its smaller neighbor. The other six of the stars do not appear to have come from Sagittarius but it is possible that they may have also been removed from a different dwarf galaxy.
"More interlopers from Sagittarius are out there just waiting to be found," Dierickx said.
