When Galileo first looked at the sky through the telescope he saw a milky band of light. He named them as galaxies. Now we know that galaxies are millions & billions of stars embedded in dust & gas that are wrapped together by gravitational attraction. Usually, they have black holes at their centres. There are about two trillion galaxies in our universe. Based on their shapes we have different kinds of galaxies: spiral barred spiral, elliptical & irregular.
If we have a concentration of massive stars at the centre with bright stars distributed as arms around the central plane, we call them as spiral galaxies. These are the most common type of galaxies. During star formation, the star-forming cloud is drawn towards the centre and the central blob of stars expands. These results in longer arms, such that they form a bar having two giant arms at the ends twisting towards the centre. Now they are called barred spiral galaxies. They can be considered as an aged population of spiral galaxies. Half of the spiral galaxies are barred spiral. The milky way galaxy where we live also has a meek central bar. If we go 60 million light-years from our milky way towards the south, we could see one special kind of giant barred spiral galaxy named as NGC 1672. It is 75000 light-years wide. NGC 1672 differs as the arms are not curled towards the centre, but they are fixed at the bar ends. As said earlier the bars serve as violent star-forming regions. The hot stars emit radiation that ionizes the hydrogen gas around them making them appear red due to Balmer Alpha emission. The beautiful image features NGC 1672 taken by Hubble Space Telescope.
-DEVIKA
Image Credit: Hubble Legacy Archive, NASA, ESA;Processing & Copyright: Daniel Nobre
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