Astronomers have detected within the stellar halo that represents the Milky Way’s outer limits a bunch of stars extra distant from Earth than any recognized inside our personal galaxy — nearly midway to a neighboring galaxy.
The researchers mentioned these 208 stars inhabit probably the most distant reaches of the Milky Way‘s halo, a spherical stellar cloud dominated by the mysterious invisible substance referred to as darkish matter that makes itself recognized solely by means of its gravitational affect. The furthest of them is 1.08 million gentle years from Earth. A lightweight yr is the space gentle travels in a yr, 5.9 trillion miles (9.5 trillion km).
These stars, noticed utilizing the Canada-France-Hawaii Telescope on Hawaii’s Mauna Kea mountain, are a part of a class of stars referred to as RR Lyrae which might be comparatively low mass and usually have low abundances of components heavier than hydrogen and helium. The most distant one seems to have a mass about 70 p.c that of our solar. No different Milky Way stars have been confidently measured farther away than these.
The stars that populate the outskirts of the galactic halo could be considered as stellar orphans, in all probability originating in 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, cannibalised — by the Milky Way,” mentioned Yuting Feng, an astronomy doctoral scholar on the University of California, Santa Cruz, who led the examine, introduced this week at an American Astronomical Society assembly 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 grown over time by means of such calamities.
“The larger galaxy grows by eating smaller galaxies — by eating its own kind,” mentioned examine co-author Raja GuhaThakurta, UC Santa Cruz’s chair of astronomy and astrophysics.
Containing an interior and outer layer, the Milky Way’s halo is vastly bigger than the galaxy’s primary disk and central bulge which might be teeming with stars. The galaxy, with a supermassive black gap at its heart about 26,000 gentle years from Earth, accommodates maybe 100 billion–400 billion stars together with our solar, which resides in one of many 4 major spiral arms that make up the Milky Way’s disk. The halo accommodates about 5 p.c of the galaxy’s stars.
Dark matter, which dominates the halo, makes up many of the universe’s mass and is regarded as chargeable for its fundamental construction, with its gravity influencing seen matter to come back collectively and kind stars and galaxies.
The halo’s distant periphery is a poorly understood area of the galaxy. These newly recognized stars are nearly half the space to the Milky Way’s neighboring Andromeda galaxy.
“We can see that the suburbs of the Andromeda halo and the Milky Way halo are really extended – and are almost ‘back-to-back,'” Feng mentioned.
The seek for life past the Earth focuses on rocky planets akin to Earth orbiting in what known as the “habitable zone” round stars. More than 5,000 planets past our photo voltaic system, referred to as exoplanets, have already got been found.
“We don’t know for sure, but each of these outer halo stars should be about as likely to have planets orbiting them as the sun and other sun-like stars in the Milky Way,” GuhaThakurta mentioned.
© Thomson Reuters 2023