Astronomers discover the most distant stars in the Milky Way

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Astronomers have detected in the stellar halo that represents the outer limits of the Milky Way a group of stars farther from Earth than any other known group within our galaxy — almost halfway to the neighboring galaxy, Andromeda.

The researchers said these 208 stars inhabit the outermost reaches of the Milky Way’s halo, a spherical stellar cloud dominated by the mysterious, invisible substance called dark matter that is only known for its gravitational influence. The most distant of them is 1.08 million light years from Earth. A light year is the distance that light travels in one year, 9.5 trillion kilometers.

These stars, as seen by the Canada-France-Hawaii Telescope on Hawaii’s Mauna Kea Mountain, are part of a category called RR Lyrae, which have relatively low mass and generally low amounts of elements heavier than hydrogen and helium.

The most distant appears to have a mass of about 70% of our Sun’s mass. No other star in the Milky Way has been reliably measured at a greater distance than these.

The stars that populate the surroundings of the galactic halo can be considered stellar orphans, probably originating from smaller galaxies that later collided with the Milky Way.

“Our interpretation of the origin of these distant stars is that they were likely born in the halos of dwarf galaxies and star clusters that were later merged — or, more directly, cannibalized — by the Milky Way,” said Yuting Feng, a doctoral candidate in astronomy at the University of California in Santa Cruz, who led the study, presented this week at a meeting of the American Astronomical Society in Seattle.

“Their host galaxies have been fragmented and gravitationally digested, but these stars are left at a great distance as debris from the merger event,” added Feng.

The Milky Way grew over time through such calamities.

“The larger galaxy grows by eating smaller galaxies — by eating its own kind,” said study co-author Raja Guha Thakurta, professor of astronomy and astrophysics at UC Santa Cruz.

Containing an inner and outer layer, the Milky Way’s halo is much larger than the galaxy’s main disk and star-studded central bulge.

The galaxy, with a supermassive black hole at its center about 26,000 light-years from Earth, contains perhaps 100 billion to 400 billion stars, including our Sun, which resides in one of the four primary spiral arms that make up the Earth’s disk. Milky Way. The halo contains about 5% of the galaxy’s stars.

Dark matter, which dominates the halo, makes up most of the universe’s mass, and is thought to be responsible for its basic structure, with its gravity influencing visible matter to come together to form stars and galaxies.

The halo’s remote outer edge is a poorly understood region of the galaxy. These newly identified stars are nearly half the distance of the neighboring Andromeda galaxy in the Milky Way.

“We can see that the suburbs of Andromeda’s halo and Milky Way’s halo are really extensive — and they’re almost ‘back to back,'” Feng said.

The search for life beyond Earth focuses on rocky Earth-like planets orbiting in what’s called the “habitable zone” around stars. More than 5,000 planets beyond our solar system have been discovered, called exoplanets.

“We don’t know for sure, but each of these stars in the outer halo should be just as likely to have planets orbiting them as the sun and other sun-like stars in the Milky Way,” said GuhaThakurta.

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