May 30, 2012:
Unfortunately, stars don’t have birth certificates. So, astronomers have a tough time figuring out their ages. Knowing a star’s age is critical for understanding how our Milky Way galaxy built itself up over billions of years from smaller galaxies. But Jason Kalirai of the Space Telescope Science Institute and The Johns Hopkins University’s Center for Astrophysical Sciences, both in Baltimore, Md., has found the next best thing to a star’s birth certificate.
Using a new technique, Kalirai probed the burned-out relics of Sun-like stars, called white dwarfs, in the inner region of our Milky Way galaxy’s halo. The halo is a spherical cloud of stars surrounding our galaxy’s disk. Those stars, his study reveals, are 11.5 billion years old, younger than the first generation of Milky Way stars. They formed more than 2 billion years after the birth of the universe 13.7 billion years ago. Previous age estimates, based on analyzing normal stars in the inner halo, ranged from 10 billion to 14 billion years. Kalirai’s study reinforces the emerging view that our galaxy’s halo is composed of a layer-cake structure that formed in stages over billions of years.
In a paper to be published in Astronomy and Astrophysics, available online now here, astronomers compare the Milky Way Galaxy to the Andromeda Galaxy (M31) in order to better understand the evolution of spiral galaxies. The Milky Way and the Andromeda Galaxy are the two best known galaxies of the cluster of galaxies to which we belong, simply known as the Local Group.
The European Southern Observatory (ESO) Very Large Telescope (VLT) in Chile, has produced the best ever images of a young star cluster called Arches Cluster. This cluster is estimated to be a little over 2 million years old and thus has some very young hot stars. Arches Cluster is located in the direction of the center of the Milky Way Galaxy in the direction of the constellation Sagittarius, about 25,000 light years from our Solar System. This cluster is almost completely obscured by dust in the vicinity, and can only be detailed in the near-infrared electromagnetic radiation. The ESO images detail the densest known cluster of stars, a million times more dense than the stars in our own neighborhood of the galaxy. ESO investigators have also determined that the most massive star in the group is about 120 times the mass of our Sun. Learn more about the Arches Cluster online now here.