Named after its discoverer, Arthur Hoag, is a sort of ring galaxy but not an exact one. Earlier it was thought to be either a nebula or a peculiar galaxy, but in the recent time, it has been confirmed that it is a ring galaxy with eight billion stars. One of the most peculiar objects in the cosmological world, its formation remains a puzzle till date.
During the initial days of the discovery of the HOAG’S object, the discoverer proposed that this ring was basically a product of gravitational lensing, but later this idea was discarded because the nucleus and the ring has same number of the redshifts. Numerous hypothesis have been proposed to explain the formation of Hoag’s object. Noah Brosch suggested that it might be the result of the bar instability that occurred a few billion years ago In a barred spiral galaxy, but this was further discarded because the centre of barred spiral galaxy is disc shaped, while the nucleus of this galaxy is spheroidal. Hoag’s object lies 600 million light years away from us. This object is greater than Milky Way by 25%.
“Is this one galaxy or two?” this was the first question Peter Hoag asked after discovering this unusual extragalactic object. The galaxy is dominated by bright blue stars on the outward (the ring part) and is dominated by a ball of red stars at its centre. Between the two lies a gap which appears dark, maybe formed of or due to dark matter.
Every week scientists are seen debating over this object, whether this object has one galaxy or two within it. This mystery is spreading its root deep in the world of cosmology. Well as of now, it seems next to impossible to solve this mystery.