A collection of stars that are farther away from Earth than any previously identified within our own galaxy – nearly halfway to a neighboring galaxy – have been found in the stellar halo that represents the Milky Way’s outer limits.
According to the researchers, these 208 stars are located in the farthest parts of the Milky Way’s halo, a spherical stellar cloud that is dominated by the mysterious dark matter, which is invisible and can only be detected by its gravitational effects. The furthest of them is 1.08 million light-years from Earth.
So how long would it take to travel 100 light years?
A light year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km). So it would take about 1.6 million years to travel 100 light years.
These stars belong to the class of stars known as RR Lyrae. These are relatively low-mass stars with limited amounts of elements heavier than hydrogen and helium. They were discovered with the Canada-France-Hawaii telescope on Hawaii’s Mauna Kea mountain. The most distant star appears to be 70% of the mass of our Sun.
The stars that make up the galactic halo’s periphery can be thought of as stellar orphans; they likely came from smaller galaxies that later collided with the bigger Milky Way.
“Our interpretation about the origin of these distant stars is that they are most likely born in the halos of dwarf galaxies and star clusters which were later merged – or more straightforwardly, cannibalized – by the Milky Way,” said Yuting Feng, a University of California, Santa Cruz PhD student in astronomy, led the study and presented it this week at an American Astronomical Society meeting in Seattle.
“Their host galaxies have been gravitationally shredded and digested, but these stars are left at that large distance as debris of the merger event,” Feng added.
The Milky Way has expanded over time, through such catastrophes.
“The larger galaxy grows by eating smaller galaxies – by eating its own kind,” said study co-author Raja GuhaThakurta, UC Santa Cruz’s chair of astronomy and astrophysics.
The Milky Way’s halo, which has an inner and outer layer, is far bigger than the galaxy’s main disk and core bulge, which are teeming with stars. Our sun, which is located in one of the four principal spiral arms that make up the Milky Way’s disk, is among the 100 billion to 400 billion stars that make up the galaxy, which has a supermassive black hole at its center located around 26,000 light years from Earth. About 5% of the stars in the galaxy are found in the halo.
