Pulsars and Supernova Remnants
Pulsars and Supernova Remnants
Goals: Discuss the end of the stellar life cycle and explore where these stellar remnants are located.
Before starting, turn on: galaxy
You will be using: snr, pul
Up to now, we've been discussing younger stars and stellar birth in the Galaxy. Now let's turn our attention to the end of the stellar life cycle. From a point of view where you see the entire Galaxy, turn on the supernova remnants.
Supernova Remnants Are the Nebulous Remains of Stellar Death
These orange points highlight the locations of the nebulous remains of a star after it has exploded. If a star is born with enough mass, it will burn through its nuclear fuel quickly and die spectacularly in the most energetic explosion in the Galaxy, called a supernova. The core of the star remains as a neutron star, while the outer layers burst out. From Earth, we see these outer layers as small nebulae or glowing gas clouds. One of the most famous examples is the Crab Nebula (M1), a remnant from the supernova of 1054.
If you've read the previous tutorials in this section, you likely know why the supernova remnants are confined to the disk of the Galaxy. If ongoing star formation is a phenomenon of the disk, then this too must be where stellar death occurs. You may also wonder why a few remnants appear to be right in the Galactic center. This is due to the large uncertainties in these data. Clouds in space are among the most difficult objects to obtain good distances for. In the case of HII regions, they are extraordinarily bright and there are chemical signatures in the radio spectrum that allow their detection. For supernova remnants, astronomers must rely on other techniques.
Supernova Remnants Glow for a Very Short Time
We see very few remnants sprinkled around the disk. The reason for this is that the remnant itself, the glowing cloud that surrounds the stellar core, has a very short lifetime. The glow lasts only about 50,000 years before the gas mixes into the ambient interstellar gas, cools, and fades from view. However, the core of the former star will be around for some time.
Pulsars Are Spinning Neutron Stars
To see these stellar cores, turn on the pulsars. A pulsar is simply a spinning neutron star, the spinning remnants of a dying star. After the star explodes, the neutron star core is spinning very rapidly. Unlike the stars that you are familiar with, like the Sun, a neutron star has been crushed by gravity to the extent that the electrons in each atom have been forced into the atomic nucleus. This makes the material extremely dense (a teaspoon of it would weigh about 100 million tons). In time, energy is lost by its rapid spinning, and after about a million years, the star is no longer visible.
The 1 million-year lifetime of the pulsar is much longer than the 50,000 years that the supernova remnant is visible, so you would expect to see more pulsars in the Atlas. For the same reason, you might also expect a wider scatter of pulsars above and below the plane of the Galaxy. The Atlas shows both these trends in addition to outlying pulsars far above the plane and even out of the Galaxy. We will talk about those in an upcoming tutorial.
© 2002-2005 American Museum of Natural History
Last Modified: 2007-12-19 by Brian Abbott