One of the winter sky’s more intriguing objects (at least in the Northern Hemisphere sky) is the Crab Nebula. I’ve written about it a few times here over the years. That’s because it’s a fascinating thing. When we look at the Crab Nebula (through a telescope, it’s not a naked-eye thing), we are looking at the remains of a massive star. Yes, that’s it: a star that died. Due to the vagaries of light-travel time, people on Earth didn’t see the explosion until the year 1054, but the massive star that formed the Crab actually exploded some 6,500 years earlier. It took 6,523 years for the light to reach Earth.
At that point, a relatively quiet and dark part of the sky hosted a “new star” six times brighter than Venus. It stayed bright for months before fading out to obscurity. Today, we know it as the Crab Nebula, and astronomers study it as the best example of the death of a supermassive star. It’s the current subject of a news story coming from the American Astronomical Society meeting in Hawai’i this week, and for good reason. Scientists are peering into it with everything they’ve got!
Forming the Crab Nebula
When the progenitor star that formed the Crab exploded, it sent huge clouds of material out to space. The “leftovers” of the star became a neutron star, a ball of neutrons packed together in an area about the size of our planet. Essentially, it’s the crushed core of the star. It’s spinning 30 times a second and sends bursts of radiation that we can detect here on Earth. The rhythmic pulsing of that radiation is what astronomer Jocelyn Bell measured in her ground-breaking discovery of the first pulsar in 1967. Surrounding the neutron star are filamentary remains of the star. They’re made up of gas and dust ejected from the star. Some of the remains are threaded through with magnetic fields. Interactions between the gas, dust and magnetic fields cause the clouds to glow in infrared light.
Probing the Crab
The object also gives off radio waves, x-rays, and visible light. All that light is detectable from here on Earth. So, astronomers put together an observing program using Hubble Space Telescope, the Spitzer Space Telescope, and the Chandra X-Ray Observatory. They all observed the Crab, and their data were combined to make a three-dimensional “image” of the Crab Nebula. There’s a nifty little movie that explains it all, which you can watch here.
Why We Study the Crab Nebula
Why combine all these wavelengths to look at the Crab? It’s one thing to look at this object through a telescope; a typical backyard-type instrument will show you a greyish-greenish “fog”. But, focus on it with high-resolution purpose-built telescopes tuned to different types of light, and you start to see great details.
We learn more about the actions of the material in the Crab and the distribution of gas and dust around the neutron star. And, we get a much more satisfying understanding of just what happens when a massive star dies and spreads itself out to space.
That’s why we spend time and money on astronomy research. It tells us more about our universe and the things in it. It may not show us how OUR star will die; it’s not a supermassive star, after all. But, supernovae provide the heavier elements needed to create planets like ours, and so studying them is like a look into our very distant, very ancient past.