Astronomers have revealed the farthest reaches of our galaxy

Not only is trying to visualize the size of the universe a daunting task — and somewhat unsettling — but it’s also a paradoxical one. In a sense, our cosmic vastness is finite because it hasn’t existed forever… and infinite because it’s constantly expanding in every direction. The most manageable thing, in terms of cosmic mapping, is to quantify all things inside Our universe seems to be.

And what better place to start than our own Milky Way? This week, at the annual meeting of the American Astronomical Society in Seattle, astronomers announced that they may have finally determined the boundaries of the outermost Milky Way galaxy.

In short, they estimate that our universe extends more than a million light-years from the galactic center, which lies about halfway to our neighboring galaxy, Andromeda.

“This study redefines what constitutes the outer boundary of our galaxy,” Raja Guathakurta, professor of astronomy and astrophysics at UC Santa Cruz and co-author of the findings study, said in a statement. “Our galaxy and Andromeda are both very big, and there is no space between the two.”

For context, a light-year is about 5.88 trillion miles (9.46 trillion km) and at 3,000 mph — close to the speeds of the Orion spacecraft Artemis I that circled the moon and returned last year — it’d take you over a billion hours to cover that distance. .

I don’t even want to write how long it will take to travel not just one, but a Million light years.

The clues were in the stars

Basically, you can think of the territory of the Milky Way divided into three sections.

First, there are the iconic spiral arms (one of which holds our solar system) wedged inside what’s known as a “thin disk,” which is pretty much a flat disk dotted with stars, planets, and moons about 100,000 light-years across.

This illustration shows what we think the Milky Way looks like, with two large spiral arms.


The bulging central region of this disk is surrounded by an inner halo containing some of the oldest stars in our galaxy and extending hundreds of thousands of light-years in each direction.

Finally, there is the outer aura.

This elusive area, floating around his inner aura, he controlled dark matter (nervous music) It makes up most of the mass of our galaxy. However, it is “the hardest part to study because the outer limits are so far away,” GuhaThakurta said. “The stars are very sparse compared to the high stellar density of the disk and bulge.”

However, GuhaThakurta and his fellow researchers came up with an idea for how to tell where the Milky Way’s outer halo ends.

The three distinct parts of the Milky Way.

This illustration shows the inner and outer halos of the Milky Way. The halo is a spherical cloud of stars surrounding a galaxy.

NASA, ESA and A. Field (STScI)

They track what is known as RR Lyrae stars living in its hazy glow. In short, RR Lyrae stars are special stellar objects of the type that pulsate in their brightness. They regularly expand and contract, appearing to astronomy instruments on Earth as glowing a little more powerfully, then fading gently — over and over again.

“The way it varies its brightness looks like an EKG — it’s like the heartbeat of a galaxy — so brightness goes up quickly and goes down slowly, and the cycle repeats perfectly with this very distinctive shape,” GuhaThakurta said. “In addition, if you measure their average brightness, it’s the same from star to star. This combination is great for studying galactic structure.”

In other words, RR Lyrae stars are better at measuring distance because it is possible to get average brightness on them. Other types of stars, for example, might be really bright because they’re close or because they’re…really bright. RR Lyrae’s stars are less questionable. Their brightness is easily related to their distance, so they help scientists calibrate the structure of the entire universe.

“Only astronomers know how painful it is to have reliable trackers at these distances,” Yuting Feng, a UCLA doctoral student and lead author of the study, said in a statement.

Feng and GuhaThakurta hit the jackpot when they reallocated data collected by the Next Generation Virgo Cluster Survey, which imaged a large cluster of galaxies near the Milky Way. During its existence, this program also happened to capture a group of foreground stars in the same field – 208 of them were RR Lyrae stars.

“The data we used is kind of a by-product of this survey,” Feng explained. “This powerful sample of distant RR Lyrae stars gives us a very powerful tool for studying the halo and testing our current models of the size and mass of our galaxy.”

In addition, according to Feng, the team’s observations confirmed ancient theoretical estimates of the corona’s outer limits.

Those estimates suggest the halo lies roughly 300 kiloparsecs, or 1 million light-years, from the galactic center — and the team’s study found that RR Lyrae stars live at distances from 20 to 320 kiloparsecs, their last term just over A million light-years away from the center of the galaxy.

This is pretty darn close.

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