Milky Way (Photo Credit: NASA.gov.in)
Our Sun (a star) and all the planets around it are part of a galaxy known as the Milky Way Galaxy, according to NASA. A galaxy is a large group of stars, gas, and dust bound together by gravity. They come in a variety of shapes and sizes. The Milky Way is a large barred spiral galaxy. All the stars we see in the night sky are in our own Milky Way Galaxy. Our galaxy is called the Milky Way because it appears as a milky band of light in the sky when you see it in a really dark area. Do you know how the Milky Way was born?
Smaller galaxies like the Milky Way in its earlier life merge together and create larger ones. Now researchers claim to have found when our Milky Way ate one of the other galaxies that would go on to create the vast mass of swirling stars and matter that surround us.
According to a new research published on Monday, the Milky Way ate another huge galaxy 10 billion years ago in a "violent collision" that didn't fully settle for eons.
Using the Gaia space telescope, researchers from the Instituto de Astrofisica de Canarias (IAC) took the exact measurements of the position, brightness and distance of around one million stars in the Milky Way within 6,500 light years of the Sun. During the research, they identified two distinct stellar sets -- one "bluer" and containing less metal, one "redder" containing more.
After studying their composition and movement, the researchers determined that both sets of stars were equally old, but the bluer ones had been set into a "chaotic motion" -- evidence of the Milky Way swallowing a smaller galaxy in the distant recesses of time.
"The novelty of our work is that we have been able to assign precise ages to the stars that belong to the galaxies that merged and, by knowing these ages, when the merger took place," Carme Gallart, lead author of the study published in Nature Astronomy, told AFP.
She further stated that the collision, around 10 billion years ago, would have taken millions of years to unfold. "It's a very gradual process -- it's not something like a car crash -- it's something that has an effect on the galaxy as a whole. It's very massive so it happens slowly in human terms, not so slowly in cosmic time," she added.
The researchers believes that the remnants of the dwarf galaxy, known as Gaia-Enceladus, eventually formed the halo of the present-day Milky Way.
The team further determined that the collision contributed to "violent bursts" of star formation for around another four billion years, after which gas from those formations settled into the Milky Way's thin disk that runs through the centre of the galaxy.
It is to be noted that the Milky Way contains at least 100 billion stars and its centre contains an intense radio source believed to be the supermassive black hole Sagittarius A*.
However, previous studies had suggested that our home galaxy was composed of two separate sets of stars, but the precise chronology of the galactic merge remained elusive.