Astronomers Uncover Milky Means Galaxy’s Most-Distant Stars

Astronomers have detected within the stellar halo that represents the Milky Means’s outer limits a gaggle of stars extra distant from Earth than any identified inside our personal galaxy — virtually midway to a neighboring galaxy.

The researchers stated these 208 stars inhabit probably the most distant reaches of the Milky Means’s halo, a spherical stellar cloud dominated by the mysterious invisible substance referred to as darkish matter that makes itself identified 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 parts heavier than hydrogen and helium. Essentially the most distant one seems to have a mass about 70 p.c that of our solar. No different Milky Means stars have been confidently measured farther away than these.

The celebs that populate the outskirts of the galactic halo might be seen as stellar orphans, in all probability originating in smaller galaxies that later collided with the bigger Milky Means.

“Our interpretation in regards to the origin of those distant stars is that they’re most probably born within the halos of dwarf galaxies and star clusters which had been later merged – or extra straightforwardly, cannibalised — by the Milky Means,” stated Yuting Feng, an astronomy doctoral pupil on the College 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, however these stars are left at that enormous distance as particles of the merger occasion,” Feng added.

The Milky Means has grown over time by means of such calamities.

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

Containing an internal and outer layer, the Milky Means’s halo is vastly bigger than the galaxy’s essential disk and central bulge which might be teeming with stars. The galaxy, with a supermassive black gap at its middle about 26,000 gentle years from Earth, incorporates 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 Means’s disk. The halo incorporates about 5 p.c of the galaxy’s stars.

Darkish matter, which dominates the halo, makes up a lot of the universe’s mass and is considered 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 virtually half the space to the Milky Means’s neighboring Andromeda galaxy.

“We will see that the suburbs of the Andromeda halo and the Milky Means halo are actually prolonged – and are virtually ‘back-to-back,'” Feng stated.

The seek for life past the Earth focuses on rocky planets akin to Earth orbiting in what is 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 certain, however every of those outer halo stars needs to be about as more likely to have planets orbiting them because the solar and different sun-like stars within the Milky Means,” GuhaThakurta stated.

© Thomson Reuters 2023