Everyone knows our galaxy, the Milky Method, is massive. Actually massive. However, precisely how far out does it lengthen? The place are the outer limits?
Astronomers aren’t precisely positive, exactly. Nevertheless, a examine of galaxies within the Virgo Cluster by chance turned up a inhabitants of stars within the outer a part of the Milky Method. They might reply these questions.
The celebrities, known as RR Lyrae variables, lie within the galaxy’s stellar halo. That is a shell of stars and darkish matter that extends not less than midway to the Andromeda Galaxy. It is our nearest neighboring spiral and lies about 2.5 million light-years away.
The newly discovered RR Lyrae’s orbit within the Milky Method’s outer halo at a distance of about 1 million light-years. And, as a result of they’re variables that pulsate commonly of their brightness, astronomers can use them to find out correct distances in house. Discover the distances to those historical pulsating variables and voila! You’ve got discovered the gap to their place within the halo.
RR Lyrae stars are attention-grabbing in their very own proper, even past their position right here as distance indicators. They’ve particular bodily properties that trigger them to broaden and contract in a commonly repeating cycle. It is virtually like a heartbeat.
And, their common brightness is similar for all of them. That is the attribute that enables them for use as normal distance “candles” throughout the gulfs of house.
They’re typically present in globular clusters. Discovering them within the stellar halo is an added plus for astronomers utilizing them to find out the extent of the Milky Method.
Milky Method construction
Astronomer Raja GuhaThakurta of the College of California Santa Cruz identified that research of this new inhabitants of RR Lyraes carried out by pupil Yuting Feng make clear the “edge” of the Milky Method.
“This examine is redefining what constitutes the outer limits of our galaxy,” he stated. “[It] and Andromeda are each so massive, there’s hardly any house between the 2 galaxies.”
The Milky Method has a core, arms, and a disk part that’s divided into thick and skinny sections. We reside in a spiral arm within the disk. Our neighborhood lies about 2/3 of the way in which out from the core – also known as the central bulge. It is all surrounded by the stellar halo.
GuhaThakurta additionally defined that the galactic stellar halo is way larger than the disk. It is about 100,000 light-years throughout. The halo additionally comprises the oldest stars within the galaxy. It extends for lots of of hundreds of sunshine years in each course.
“The halo is the toughest half to check as a result of the outer limits are so distant,” GuhaThakurta stated. “The celebrities are very sparse in comparison with the excessive stellar densities of the disk and the bulge, however the halo is dominated by darkish matter and really comprises a lot of the mass of the galaxy.”
galaxies and discovering clues about ours
So, the way to examine this a part of the galaxy if it is so powerful? And the place do the RR Lyraes are available?
Yuting Feng used survey research of galaxies in the Virgo Cluster to dig out knowledge about stars in our personal galaxy and its halo. Laptop fashions present that this stellar halo ought to stretch out about one million light-years from the core of the galaxy. (That is 300 kiloparsecs in astronomer-speak).
However, astronomers wanted extra knowledge. Therefore using survey knowledge.
The survey knowledge Feng tapped is from the Subsequent Era Virgo Cluster Survey, a complete optical imaging examine of the cluster. It used the MegaCam instrument on the Canada-France-Hawaii Telescope (CFHT) on Mauna Kea.
The survey was proposed to check a wide range of elements of the cluster, together with mass, the intracluster medium, the fossil report of star formation within the cluster, and research of galaxy haloes.
To get a deep publicity of M87 and different Virgo Cluster galaxies, the telescope additionally captured foreground stars in our galaxy.
“The information we used are type of a by-product of that survey,” Feng defined. “We have been ready to make use of these variable stars as dependable tracers to pin down the distances,” Feng stated. “Our observations verify the theoretical estimates of the dimensions of the halo, in order that’s an vital consequence.”
The invention of the RR Lyraes is important, in line with Feng. That is as a result of astronomers have struggled to get dependable distance measurements within the area.
“This strong pattern of distant RR Lyrae stars offers us a really highly effective software for learning the halo and testing our present fashions of the dimensions and mass of our galaxy,” Feng stated.