Hoag's Object (Ring Galaxy).

Our Universe is full of fascinating Objects, But the appearance of this object has interested amateur astronomers as much as its uncommon structure has fascinated professionals. This Galaxy is a type of 'RING GALAXY' because it look like a ring surrounding the bright nucleus in a circular shape. This Galaxy is named "Hoag's object" after Arthur Allen Hoag who discovered it in 1950 and identified it as either a planetary nebula or a peculiar galaxy with eight billion stars.

Hoag's Object taken by the Hubble Space Telescope.
Courtesy of NASA/ESA


 - 600 million light-years away in the constellation Serpens.


 - Redshift = 12,740

This Galaxy has a Diameter of the 6″ (seconds of arc) inner core of the galaxy is about 17±0.7 kly (5.3±0.2 kpc) while the surrounding ring has an inner 28″ diameter of 75±3 kly (24.8±1.1 kpc) and an outer 45″ diameter of 121±4 kly (39.9±1.7 kpc), which is slightly larger than the Milky Way Galaxy.

Reason behind it's Look?

When Arthur Allen Hoag  Discovered this galaxy he believed that the reason behind the shape is Gravitational Lensing. This idea was later discarded because the nucleus and the ring have the same redshift, and because more advanced telescopes revealed the knotty structure of the ring, something that would not be visible if the ring were the product of gravitational lensing.

This galaxy has remained a mystery for humans from the time when it was discovered. We still don't know how this galaxy may have formed. So-called "classic" ring galaxies are generally formed by the collision of a small galaxy with a larger disk-shaped galaxy. This collision produces a density wave in the disk that leads to a characteristic ring-like appearance. Such an event would have happened at least 2-3 billion years in the past, and may have resembled the processes that form polar-ring galaxies. However, there is no sign of any second galaxy that would have acted as the "bullet", and the core of Hoag's Object has a very low velocity relative to the ring, making the typical formation hypothesis quite unlikely.

Noah Brosch suggested that Hoag's Object might be a product of an extreme "bar instability" that occurred a few billion years ago in a barred spiral galaxy.

This Type of Galaxy are very rare but Surprisingly another more distant ring galaxy (SDSS J151713.93+213516.8) can be seen through Hoag's Object, between the nucleus and the outer ring of the galaxy, at roughly the one o'clock position in the picture to the right.