Five remarkable stars on the other side of our galaxy promise new insight into the outer reaches of our home turf.
A single Hubble Space Telescope image can capture scores of distant galaxies, but the one galaxy we’ll never see from the outside is our own. As a result, no one knows the Milky Way’s exact size and shape. It took more than a century after the discovery of the first spiral in space before astronomers established that our galaxy is a spiral, too, and more years elapsed before they deduced that we inhabit a barred spiral — a type whose bright central region is elongated. Now, for the first time, observers have detected five stars on the far side of the galaxy that serve as outstanding yardsticks, a feat which will divulge secrets about the Milky Way’s terra incognita. “It’s a beautiful piece of classic astronomy,” says Leo Blitz, an astronomer at the University of California, Berkeley, who was not involved in the discovery.
A teacher once told me that our galaxy is on course to collide with the Andromeda galaxy in the next few million years. He said that it wouldn't do much except allow us to travel into the other Galaxy. Is this true?
We will be colliding with Andromeda, in about 4 billion years. Andromeda has 14 small galaxy companions, which Andromeda will likely interact with and accrete a lot of their matter prior to then. The Milky Was also has satellite galaxies that we will interact with – we are currently swallowing the Sagittarius Dwarf Spheroidal Galaxy, which we will pass through in about 100 million years.
Galaxy interactions lead to galaxy evolution. Andromeda and the Milky Way are both fairly massive galaxies, and their interaction will result in a giant elliptical galaxy or one disk galaxy (probably, elliptical)
Here’s a simulation showing how it might go down:
I wouldn’t say “it wouldn’t do much except allow us to travel into the other galaxy,” galaxy interactions can lead to star-formation bursts (although, by this time each galaxy may not have enough gas left to form new stars). But, the collision is an interesting step in our galaxy’s evolution!
It won’t affect life in our solar system very much other than a change in orbit around the galactic center.
Palomar 12: a globular cluster on the edge of the Milky Way that was originally born in the Sagittarius Dwarf Elliptical Galaxy, a satellite of the Milky Way Galaxy that drifted too close and lost stars due to gravitational tides.
This is the Palomar 12 globular cluster located on the outskirts of the halo within our Milky Way. Tightly bound by gravity, globular clusters are spherical collections of stars that can contain hundreds of thousands or even millions of stars. They are typically the oldest objects in a galaxy, and are among the first collections of stars to form. Yet Palomar 12 is not like other Milky Way globulars, in fact the stars are 30% younger. But why?
After astronomers dug deeper, they found that Palomar 12 was actually ripped from its initial home, the Sagittarius Dwarf Elliptical galaxy, around 1.7 billion years ago via tidal interactions between its former home and our galaxy. The dwarf galaxy that Palomar 12 once called home is a satellite galaxy to ours, and closely orbits around us — even occasionally passing through the plane of our galaxy. In fact, it is being slowly torn apart and consumed by the Milky Way. (Image credit: ESA/Hubble & NASA)
Globular cluster Terzan 7 consists of a densely packed ball of stars bound together by gravity. It lies just over 75,000 light-years away on the other side of our Milky Way galaxy. Terzan 7 used to belong to a small galaxy called the Sagittarius Dwarf Galaxy, a mini-galaxy discovered in 1994. This galaxy currently is colliding with, and being absorbed by, the much-larger Milky Way, and it seems that our own galaxy has already kidnapped this cluster from its former home. Astronomers recently discovered that all the stars in Terzan 7 formed at around the same time, about eight billion years ago, an unusually young age for such a cluster.
Image Credit: NASA, ESA, and A. Sarajedini (University of Florida); Acknowledgement: Gilles Chapdelaine