When a star dies in a violent, fiery death, it spews its innards out across the sky, creating an expanding wave of gas and dust known as a supernova nebula. Arguably the most famous of these supernova remnants is M1, also called the Crab Nebula, a blob-like patch visible even in low-powered binoculars. Let's take a look at this viewing treasure.
Chinese astronomers watching the sky on July 4, 1054, noted the appearance of a new or "guest" star just above the southern horn of Taurus. But knowledge of star-fields was not necessary to spot this surprising visitor — according to records, the bright source was visible during the daytime for 23 days, shining six times as brightly as Venus. Those well-versed with the night sky would have been able to see it for 653 days — almost two years — with the naked eye. Other observations of the explosion were recorded by Japanese and Arab stargazers.
In 1731, British astronomer John Bevis observed a cloudy blob in the sky and added it to his star atlas. But it wasn't until French astronomer Charles Messier independently observed it 27 years later that things began to pick up for this stellar remnant.
Messier was a voracious comet hunter, but he found that the quality of telescopes at the time made it easy to confuse the fuzzy, blazing balls of ice with the hazy nebulae that dot the night sky. While searching for a comet that Edmond Halley had predicted would return in 1758, Messier discovered a hazy patch in the sky, which he would later add to his catalog as Messier 1, or M1. Studying the nebula over time revealed that, unlike a comet, it didn't move across the night sky, and thus was a completely different feature.
After a few other misidentifications, Messier was determined to put together a catalog of these objects in order to prevent other astronomers from making the same mistake. M1 became his first entry. Although he credited himself with its discovery in his first publication of the Messier catalog, he acknowledged Bevis' original finding in subsequent versions after receiving a letter from the astronomer. Messier went on to expand his list to include 110 objects, including a few other nebulae along with star clusters and galaxies.
Around 1844, British astronomer William Parsons, the third Earl of Rosse, sketched the nebula. The resemblance of that image to a crustacean led to M1's other name, the Crab Nebula.
In the early 20th century, astronomers were able to take more detailed measurements of M1 and determined that it is expanding. Working backwards, they determined its origination date, and matched the explosion up with observations from 11th-century records.
Some astronomers believed that cave paintings in the Navajo Reservation, located in the American Southwest, also depicted the nebula. But according to Scientific American, more recent research suggests that those paintings have nothing to do with the Crab Nebula.
The guts of the nebula
A supernova remnant forms when the pressure inside of a star is stronger than the gravity that holds it together, and the star explodes. As the gas rushes outward, it fills the space around it. The material ejected from the Crab Nebula is moving at more than 3 million mph (4.8 million kph). [Supernova Photos: Great Images of Star Explosions]
The nebula stretches 10 light-years across, though it continues to expand. It lies approximately 6,300 light-years from Earth, in the constellation of Taurus. M1 can be seen with the naked eye in a dark sky, but only barely. A pair of binoculars will turn up a dim patch, while more of the identifying features of the nebula become visible with a low-magnification telescope. A higher-grade, 16-inch telescope will begin to refine more of the nebula.
A bright source within
In the summer of 1967, U.S. Air Force officer Charles Schisler was on radar duty at Clear Air Force Base in Alaska when he noticed a fluctuating radio source. The source appeared over the course of several days, and Schisler noticed that its position coincided with the Crab Nebula. However, the findings weren't published by the Air Force at the time, and the discovery went unrealized until 2007.
A year later, astronomers in Puerto Rico discovered the same pulsing radio source. Determined to be a pulsar, the object is a rapidly-rotating, town-sized star that flashes about 30 times a second. Known as NP0532, or the Crab Pulsar, the neutron star is 100,000 times more energetic than the sun. Though only a few tens of miles across, it shines about as brightly as our nearest sun.
This article was corrected on Feb. 1, 2021 by Space.com Reference Editor Vicky Stein. Previously, the article stated that "Messier went on to expand his list to include 110
objects, most of them supernova remnants." In fact, most of Messier's list consisted of star clusters and galaxies.