Astronomers have detected within the stellar halo that represents the Milky Approach’s outer limits a gaggle of stars extra distant from Earth than any identified 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 Approach’s halo, a spherical stellar cloud dominated by the mysterious invisible substance referred to as darkish matter that makes itself identified solely by its gravitational affect. The furthest of them is 1.08 million mild years from Earth. A lightweight yr is the space mild 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 are comparatively low mass and usually have low abundances of parts heavier than hydrogen and helium. Essentially the most distant one seems to have a mass about 70 % that of our solar. No different Milky Approach stars have been confidently measured farther away than these.
The celebs that populate the outskirts of the galactic halo could be considered as stellar orphans, most likely originating in smaller galaxies that later collided with the bigger Milky Approach.
“Our interpretation concerning the origin of those distant stars is that they’re almost certainly born within the halos of dwarf galaxies and star clusters which had been later merged – or extra straightforwardly, cannibalised — by the Milky Approach,” mentioned Yuting Feng, an astronomy doctoral scholar on the College of California, Santa Cruz, who led the examine, offered this week at an American Astronomical Society assembly in Seattle.
“Their host galaxies have been gravitationally shredded and digested, however these stars are left at that enormous distance as particles of the merger occasion,” Feng added.
The Milky Approach has grown over time by such calamities.
“The bigger galaxy grows by consuming smaller galaxies — by consuming its personal form,” mentioned examine co-author Raja GuhaThakurta, UC Santa Cruz’s chair of astronomy and astrophysics.
Containing an internal and outer layer, the Milky Approach’s halo is vastly bigger than the galaxy’s primary disk and central bulge which are teeming with stars. The galaxy, with a supermassive black gap at its middle about 26,000 mild years from Earth, accommodates maybe 100 billion–400 billion stars together with our solar, which resides in one of many 4 main spiral arms that make up the Milky Approach’s disk. The halo accommodates about 5 % of the galaxy’s stars.
Darkish matter, which dominates the halo, makes up a lot of the universe’s mass and is considered accountable 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 Approach’s neighboring Andromeda galaxy.
“We will see that the suburbs of the Andromeda halo and the Milky Approach halo are actually prolonged – and are nearly ‘back-to-back,'” Feng mentioned.
The seek for life past the Earth focuses on rocky planets akin to Earth orbiting in what is named the “liveable zone” round stars. Greater than 5,000 planets past our photo voltaic system, referred to as exoplanets, have already got been found.
“We do not know for certain, however every of those outer halo stars needs to be about as prone to have planets orbiting them because the solar and different sun-like stars within the Milky Approach,” GuhaThakurta mentioned.
© Thomson Reuters 2023
Affiliate hyperlinks could also be robotically generated – see our ethics assertion for particulars.