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 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 Way’s halo, a spherical stellar cloud dominated by the mysterious invisible substance referred to as darkish matter that makes itself identified solely via its gravitational affect. The furthest of them is 1.08 million mild years from Earth. A light-weight 12 months is the gap mild travels in a 12 months, 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 can be comparatively low mass and usually have low abundances of parts heavier than hydrogen and helium. Probably the most distant one seems to have a mass about 70 % that of our solar. No different Milky Way stars have been confidently measured farther away than these.

The celebrities that populate the outskirts of the galactic halo will be seen as stellar orphans, most likely originating in smaller galaxies that later collided with the bigger Milky Way.

“Our interpretation in regards to the origin of those distant stars is that they’re almost definitely born within the halos of dwarf galaxies and star clusters which have been later merged – or extra straightforwardly, cannibalised — by the Milky Way,” mentioned Yuting Feng, an astronomy doctoral pupil 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 Way has grown over time via such calamities.

“The bigger galaxy grows by consuming smaller galaxies — by consuming its personal sort,” mentioned examine co-author Raja GuhaThakurta, UC Santa Cruz’s chair of astronomy and astrophysics.

Containing an internal and outer layer, the Milky Way’s halo is vastly bigger than the galaxy’s important disk and central bulge which can be teeming with stars. The galaxy, with a supermassive black gap at its middle about 26,000 mild years from Earth, comprises 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 Way’s disk. The halo comprises about 5 % of the galaxy’s stars.

Darkish matter, which dominates the halo, makes up a lot of the universe’s mass and is regarded as answerable for its primary construction, with its gravity influencing seen matter to come back collectively and type stars and galaxies.

The halo’s distant periphery is a poorly understood area of the galaxy. These newly recognized stars are nearly half the gap to the Milky Way’s neighboring Andromeda galaxy.

“We are able to see that the suburbs of the Andromeda halo and the Milky Way 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 known as 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 positive, however every of those outer halo stars ought to be about as more likely to have planets orbiting them because the solar and different sun-like stars within the Milky Way,” GuhaThakurta mentioned.

© Thomson Reuters 2023


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