Whether you call it a mail slot, coin slot or a light sabre, the Hubble space telescope has captured a rare image of a galaxy, according to astronomers.
The galaxy, labeled NGC 4452, provides a near perfect side on view of a spiral galaxy.
Associate Professor Peter Tuthill, research astrophysicist at the University of Sydney, says although very thin galaxies are relatively common, photographs like this one are quite rare.
"It's no more than just a freaky chance to see it in this alignment; but that of itself doesn't tell you anything amazing about the physics," says Tuthill.
Bad Astronomy blogger, Phil Plait says the chances of photographing a galaxy like this as similar to flinging a handful of loose change into the air and taking a flash photograph. If you fling enough coins up, eventually one of them will be snapped edge-on.
William Herschel first trained his telescope on NGC 4452 in 1784. He described the object as a bright nebula, small and very much elongated.
NGC 4452, a 35,000 light year wide galaxy in the Virgo cluster, is unusual because of its almost uniform thickness. Spiral galaxies, like the Milky Way, usually bulge noticeably at the centre. NGC4452 maintains a width to thickness ratio of about 100:1, compared to the Milky Way's 40:1 ratio.
Our side-on view of NGC4452 makes it difficult to tell what kind of galaxy it really is. NASA speculates that a view from above would reveal a classic spiral structure.
Galactic structure pure guesswork
"It's a mystery", says Tuthill, "because you're only seeing it from side on and you don't really know what it looks like. But if it's a spiral you would think that it should have a bigger bulge."
The fact that it doesn't show the usual clouds of dark dust indicates that it might be a low-dust lenticular galaxy, NASA says, but it's also possible that infrared filtering has hidden a dust lane.
"Normally when you see these things side on you see these dramatic dust lanes; there's this gunk in the galactic plane which blocks out some of the light from the stars", acccording to Tuthill.
He says working out the structure of a galaxy always involves a bit of guesswork.
"If you actually knew what it looked like from the top at the same time, that would give you quite a powerful data set because it is hard to unravel both pieces of the puzzle for any galaxy."
"That's the problem we're confronted with in our own galaxy in a way. All we see of our own galaxy is this thin band of light.
"It's a fairly new finding that the Milky Way is a galaxy called a barred spiral, not a simple spiral.
"Nobody really knows how many arms there are in our galaxy. It's kind of this problem that we can't see the forest because we're in amongst the trees. I guess that is well illustrated by this particular galaxy."