A rare galaxy that challenges our understanding of the universe
Day 22 / 365
The number of galaxies in the universe is estimated to be anywhere between 200 billion and 2 trillion. When first discovered, the most common criteria for classifying them was their shape. We know these shapes fall under 4 known categories, with Spiral being the majority. Our own galaxy, the Milky way is spiral as well.
The reason why more than a third of the galaxies are spiral is that they are spinning, and because of something called density waves. You can think of density waves like compression waves that cause piling up of stars, much like how sound waves through the air would have piling up of air molecules.
We have strong theories about the formation and evolution of such common galaxies, but we don’t know much about some rare irregular shapes. An especially rare case of this is Hoag type galaxies.
Hoag type galaxies have a dense spherical center surrounded by a circular ring of stars, with nothing in the middle to connect them. These galaxies are extremely rare, less than 1 in 1000.
While the case of a Hoag type galaxy is mysterious enough, Burçin Mutlu-Pakdil — the speaker of this Ted talk, discovered something even rare.
Burçin’s team thought they had discovered another case of a Hoag’s object. But on analyzing it further they discovered that in addition to an outer ring, it had an additional inner ring of stars. This was never observed before, and this type is now commonly known as Burçin’s Galaxy.
The scale at which the universe works it hard to comprehend, let alone theorize and predict. One explanation given for these circular rings is a smaller galaxy going through another larger disc-shaped galaxy like a bullet. Imagine that!
Cases like this highlight the gaps in our knowledge about the universe, and we can rest assured that the field of astronomical research is not going to get boring any time soon.
This story is part of my 365 Day Project for 2019. Read about it here
Yesterday’s blog — What would the world be without us?