Humans have the most amazing propensity to use animal “avatars” to illustrate things. A couple of entries back I wrote about cats in the sky. There are also sea creatures and even birds and bees up there! But the animalization of space isn’t limited to constellations. This deep-sky object is called the Horsehead Nebula — for the obvious reason. It’s actually a cloud of gas and dust that happens to lie in front of a bright, glowing cloud of gas and dust. The superposition of one over the other gives us the lovely vision of a horse’s head.
This high-resolution image from the European Southern Observatory takes what looks like a serene scene and shows us how very chaotic the situation is at this nebula. You can see wisps and filaments in the gases, and clouds of diffuse dust. If you look at the top of the figure you see a bright rim separating the dust from the gas cloud (also known as an H II region). Astronomers call this region an “ionization front” where the photons from the HII region are moving into the cloud. Their energy is emitted as heat, which is destroying the dust and the molecules and lighting up the gas.
Actually, the Horsehead is a short-lived object. The continual erosion of the gas and dust by the emissions from nearby stars will eventually destroy the clouds in a few thousand years. So, enjoy this deep-sky animal while we have it!
Also lurking within the confines of the constellation Taurus, the Bull, is the Crab Nebula, so named because through smaller telescopes it appears as a crab-like ghostly apparition. In reality, this thing is an expanding cloud of gas and dust marking the spot of a cataclysmic explosion called a supernova. It first shone in our skies in the year 1054 A.D. and was observed by the Chinese, Japanese, and very likely the Anasazi tribes of the American Southwest.
The Crab contains a neutron star near its center that spins 30 times per second around its axis, the remains of the original star. It flashes light pulses 30 times a second (making it a pulsar). In this picture, green light is predominantly produced by hydrogen emission from material ejected by the star that exploded. The blue light is emitted by very high-energy electrons that spiral through a huge magnetic field twisted around the pulsar.
Of course we don’t see any of this through our backyard-type telescopes — for most of us this just looks like a dim little glow in the sky, hidden more than 6,000 light-years away and unlikely to do us any harm.
