(ORDO NEWS) — We all know that our Milky Way galaxy is huge. Really big. But how far does it extend? Where are the outer limits?
Astronomers aren’t exactly sure. However, a study of galaxies in the Virgo Cluster accidentally discovered a population of stars in the outer Milky Way. They can answer these questions.
The stars, called RR Lyrae variables, lie in the galaxy’s stellar halo. It is a shell of stars and dark matter that extends at least halfway to the Andromeda Galaxy. This is the nearest neighboring spiral, which is located at a distance of about 2.5 million light-years from us.
The orbit of the newly discovered RR Lyra is in the outer halo of the Milky Way at a distance of about 1 million light-years.
And because these are variables whose brightness fluctuates regularly, astronomers can use them to accurately determine distances in space. Find the distances to these ancient pulsating variables and voila! You have found the distance to their position in the halo.
The stars of RR Lyra are interesting in their own right, even apart from their role here as distance indicators. They have certain physical properties that cause them to expand and contract in a regularly repeating cycle. It’s almost like a heartbeat.
And their average brightness is the same for everyone. It is this characteristic that allows them to be used as “candles” of a standard distance through the cosmic abyss.
They are often found in globular clusters. Finding them in a stellar halo is an added bonus for astronomers who use them to determine the size of the Milky Way.
Structure of the Milky Way
Astronomer Raja GuhaThakurta of the University of California at Santa Cruz pointed out that student Yuting Feng’s research on this new population of RR Lyra studies is clearing up the “edge” of the Milky Way.
“This study redefines what makes up the outer limits of our galaxy,” he said. “[It] and Andromeda are so big that there’s almost no space between the two galaxies.”
The Milky Way has a core, arms, and a disk component that is divided into thick and thin parts. We live in a spiral arm of a disk. Our region is about 2/3 of the way from the core – often referred to as the central bulge. All this is surrounded by a stellar halo.
GuhaThakurta also explained that the galactic stellar halo is much larger than the disk. Its diameter is about 100,000 light years. The halo also contains the oldest stars in the galaxy. It spans hundreds of thousands of light years in all directions.
“The halo is the hardest part to study because the outer limits are so far away,” GuhaThakurta said. “Stars are very rare compared to the high stellar density of the disk and bulge, but the halo is dominated by dark matter and actually contains most of the galaxy’s mass.”
Looking at galaxies and finding clues about our
So, how to study this part of the galaxy if it is so hard? And what does RR Lyra have to do with it?
Yuting Feng used survey studies of galaxies in the Virgo Cluster to obtain data on the stars in our own galaxy and its halo. Computer models show that this stellar halo should extend about a million light-years from the galaxy’s core. (This is 300 kiloparsecs in the language of astronomers).
But astronomers need more data. Hence the use of survey data.
The study data Feng used is from the Virgo Next Generation Cluster Study, a comprehensive study of the cluster using optical imaging. He used the MegaCam instrument on the Canada-France-Hawaii Telescope (CFHT) on Mauna Kea.
The review was proposed to study a variety of cluster factors, including mass, intracluster environment, fossil records of star formation in the cluster, and studies of galaxy halos.
To get a deep image of M87 and other galaxies in the Virgo Cluster, the telescope also captured foreground stars in our galaxy.
“The data we used is kind of a by-product of this survey,” Feng explained. “We were able to use these variable stars as reliable indicators to determine distances,” Feng said. “Our observations confirm the theoretical estimates of halo size, so this is an important result.”
According to Feng, the discovery of RR Lyraes is of great importance. This is because astronomers have struggled to get reliable distance measurements in this region.
“This robust sample of distant RR Lyrae stars gives us a very powerful tool to study the halo and test our current size and mass models. our galaxy,” Feng said.
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