Ring of the Week: Arp 147

“Then take me disappearin’ through the smoke rings of my mind
Down the foggy ruins of time…

Yes, to dance beneath the diamond sky with one hand waving free,
Silhouetted by the sea, circled by the circus sands,
With all memory and fate driven deep beneath the waves,
Let me forget about today until tomorrow.”
– Bob Dylan, “Mr Tambourine Man”

After last week’s leisurely cruise through 450 million light years to Mayall’s Object, this week I take you on a flying tour across the local Universe to view the spectacular galactic jewels known as “Smoke Rings”.

Smoke Rings, like all collisional ring galaxies, are formed when a smaller galaxy hits bull’s-eye into the centre of a larger disk galaxy. The impact creates a density wave, throwing matter out into a ring shape. With the help of the Zooites I’ve found just 12 Smoke Rings in the Galaxy Zoo and so these amazing objects are very rare indeed. You can see 4 of them below:

There are two things you’ll notice about these galaxies:

Firstly, all of the smoke rings we’ve found are blue in colour. This is because as the shock wave expands into the disk, it triggers the birth of large numbers of high mass stars. Massive, young stars are extremely hot and so the light that they radiate is bright blue.

Secondly smoke rings, by definition, have no central nucleus. Answering the question of why smoke rings have no obvious nucleus is not as simple as it may sound but we believe that smoke rings are created in one of the following situations:

1. The original target galaxy had no substantial nucleus to start with
2. Or the angle and position of impact was such that the nucleus was thrown out into the ring
3. Or the nucleus was destroyed by the impact

Smoke rings are incredibly important as they are shining blue clues as to how galaxies collide. My Ring of the Week this week is Arp 147 – a perfect example of the way that smoke rings allow us to turn back the clock and stare deep into the Universe’s distant past.

Arp 147 is located in the constellation Cetus over 400 million light years from Earth. The image on the left is the Galaxy Zoo Arp 147 image and on the right is an image taken by the Hubble Space Telescope. We can clearly see the “bullet” galaxy on the left and, on the right, the bright blue ruins of the original “target” galaxy. What makes Arp 147 so special is the unusual reddish-brown spot at the bottom of the ring and we believe that this marks the exact position of the original nucleus of the “target” galaxy. From the positions of the bullet, the smoke ring and the red spot we can rewind time over millions of years and simulate exactly how these two galaxies collided.

So as we “dance beneath the diamond sky” it is the smoke rings, beautiful in their simplicity, that make the “foggy ruins of time” crystal clear.

The Hubble image is part of a collection of 59 images of merging galaxies released on the occasion of its 18th anniversary on April 24, 2008. (NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University))