A recent study indicates that the top speed stars in our own galaxy may have been assimilated after being ejected from a dwarf one that merged with the Milky Way.

 

This kind of stars are dubbed “hypervelocity” stars, and were mostly believed to be originating from our galaxy's core, from where they were pushed out at enormous speeds of about 4,000 km per second by the giant black hole found there, after getting too close to it. However, 4 years ago, when the first such star was spotted, the patterns of these stars pointed that perhaps there might be actually another force behind this process of fast racing cosmic bodies, half of which (8 of the 16 known) are located within or in the near proximity of the Leo constellation.

 

Mario Abadi and his team from the Cordoba Observatory in Argentina have developed a galaxy merging computer simulation that helps them explain why this happened. According to them, when a dwarf galaxy that was orbiting our own got the closest to the Milky Way's core, it was exposed to the immense gravitational attraction of the region, which increased the energy of a part of the stars of the dwarf formation, up to the point where they escaped its gravitational force, were ejected into space and assimilated by the Milky Way.

 

Oleg Gnedin from the University of Michigan in Ann Arbor, associates the process to the spaghetti that boil in a recipient. As he explains, the dwarf galaxy nearing Milky Way's core was like increasing the heat source under an already boiling spaghetti pot, “The water gets too hot, pops the lid, and the spaghetti flies away in all directions. Some pieces are hotter and will fly a longer distance than the colder pieces that barely leave the pot.”

 

“Because each star leaves the dwarf with slightly different energy, they start separating as they drift into space,” states Julio Navarro from the University of Victoria in Canada. “The ones that gained the most energy travel the fastest and reach the farthest,” like the ones in the Leo constellation. Knowing their speed, trajectory and location, it is easy to estimate that these bodies were ejected from their original location sometimes between 100 million to 200 million years ago.

 

Nevertheless, the large mass and young age of these stars is what is puzzling researchers, since this would mean they originate from a galaxy rich in gas content. But the neighboring dwarf galaxies are low in gas levels. Future analysis will help depict the place of origin for such stars, since those in galactic cores are rich in metals, while those in dwarf galaxies are old and poor in heavy elements. Some scientists think these stars are forever trapped in our galaxy, while the measurements of others point out that some of them are fast enough in order to break free again.