The Milky Way galaxy has changed a lot over the last 11 billion years – and now for the first time we can seeing images that show what it may have looked like at the beginning. Because we are part of the galaxy, we do not have the benefit of distance to see what it looked like in the past. Therefore, we have had to rely on the Hubble to look deep into space for answers. The results were described in two papers, the first of which came out over the summer and the second was made available online this week. They were published in The Astrophysical Journal Letters and The Astrophysical Journal, respectively.
The Hubble Space Telescope studied over 400 distant Milky Way-like galaxies in order to understand how they evolved to get clues about our own home. For the first time, astronomers have been able to estimate that an astonishing 90% of all the stars in the galaxy formed during the first 4 billion years. During those early years, stars were created 15 times more frequently than today.
While we currently know the Milky Way as a beautiful, glittery spiral, it’s beginnings probably looked more like a bulged disk that eventually flattened out and formed the arms of the spiral. We are located in what would have been the disk, while the oldest stars and our black hole came from the bulge in the center. It appears that the disk and bulge came about around the same time. Other galaxies appear to form the bulge first and the disk comes later, though these galaxies are usually much larger and elliptical, not spiraled. The team did not find any evidence that our galaxy was formed in two parts. Computer modeling was used to confirm that the Milky Way most likely formed all at once with the bulge and the disk appearing at the same time.
The results were obtained from a colossal collaboration of Hubble programs. Spectroscopy, visible light, and near-infrared images were combined to generate the Milky Way’s early pictures. Although the Hubble has documented over 10,000 galaxies, the 400 were chosen based on factors like distance and mass. This approach allowed the team to measure the rate at which Milky Way homologs expand and change.
More information about how galaxies are born will come from the James Webb Space Telescope, named after the NASA official who championed the Apollo program. It is currently set to launch in 2018 and will use infrared imaging to collect information about some of the earliest stages of galaxy formation.