# why is the Crab Nebula visible? **URL:** \ **Category:** Factual Questions\ **Created:** [December 5, 2014, 1:26am UTC](https://boards.straightdope.com/t/why-is-the-crab-nebula-visible/706368 "2014-12-05T01:26:18Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![TGWATY](https://avatars.discourse-cdn.com/v4/letter/t/b5e925/32.png) [@TGWATY](https://boards.straightdope.com/u/TGWATY)\ **Post date:** [December 5, 2014, 1:26am UTC](https://boards.straightdope.com/t/why-is-the-crab-nebula-visible/706368/1 "2014-12-05T01:26:18Z")
If the crab nebula is the remnant of a supernova star, why is it that after 1000 years we can still see it? A star explodes… ok sure. But why is the residue of a star glowing afterwards? and visible from thousands of light years away? A star is visible because of nuclear fusion. What makes the diffuse gas of an exploded star glow? ---
**Author:** ![Great\_Antibob](https://avatars.discourse-cdn.com/v4/letter/g/e47c2d/32.png) [@Great\_Antibob](https://boards.straightdope.com/u/Great_Antibob)\ **Post date:** [December 5, 2014, 1:55am UTC](https://boards.straightdope.com/t/why-is-the-crab-nebula-visible/706368/2 "2014-12-05T01:55:18Z")
IIRC, there’s still a neutron star formed as a result of the supernova. That should be enough to ionize the gases. The nebula gases alone won’t account for all the mass of the supernova. The vast bulk is still where the original star was. ---
**Author:** ![Steve\_MB](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/steve_mb/32/5339_2.png) [@Steve\_MB](https://boards.straightdope.com/u/Steve_MB)\ **Post date:** [December 5, 2014, 2:01am UTC](https://boards.straightdope.com/t/why-is-the-crab-nebula-visible/706368/3 "2014-12-05T02:01:43Z")
The central pulsar (the neutron star remnant of the original stellar core) pumps energy into the surrounding nebula. ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [December 5, 2014, 2:05am UTC](https://boards.straightdope.com/t/why-is-the-crab-nebula-visible/706368/4 "2014-12-05T02:05:41Z")
At its core is a rapidly rotating neutron star - a pulsar - that is a powerful source of radiation emitting a wide range of frequencies and a total energy at least 10,000 times that of our sun. This is what continues to illuminate the expanding remnants of the supernova the created the Crab Nebula nearly 1000 years ago. ---
**Author:** ![John\_DiFool](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_difool/32/19543_2.png) [@John\_DiFool](https://boards.straightdope.com/u/John_DiFool)\ **Post date:** [December 5, 2014, 2:33am UTC](https://boards.straightdope.com/t/why-is-the-crab-nebula-visible/706368/5 "2014-12-05T02:33:08Z")
Not one but two ninjas that time… ---
**Author:** ![Duckster](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/duckster/32/1244_2.png) [@Duckster](https://boards.straightdope.com/u/Duckster)\ **Post date:** [December 5, 2014, 2:38am UTC](https://boards.straightdope.com/t/why-is-the-crab-nebula-visible/706368/6 "2014-12-05T02:38:08Z")
> [@John\_DiFool](#): > > Not one but two ninjas that time… Nebula neutron ninjas … ---
**Author:** ![TGWATY](https://avatars.discourse-cdn.com/v4/letter/t/b5e925/32.png) [@TGWATY](https://boards.straightdope.com/u/TGWATY)\ **Post date:** [December 5, 2014, 2:40am UTC](https://boards.straightdope.com/t/why-is-the-crab-nebula-visible/706368/7 "2014-12-05T02:40:39Z")
Got it. thanks. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [December 5, 2014, 3:49am UTC](https://boards.straightdope.com/t/why-is-the-crab-nebula-visible/706368/8 "2014-12-05T03:49:54Z")
Note that neutron stars are no longer burning any fuel, and so they will eventually fade out with time. That time just hasn’t come yet for the Crab Pulsar, which is still quite young. ---
**Author:** ![Amateur\_Barbarian](https://avatars.discourse-cdn.com/v4/letter/a/59ef9b/32.png) [@Amateur\_Barbarian](https://boards.straightdope.com/u/Amateur_Barbarian)\ **Post date:** [December 5, 2014, 4:19am UTC](https://boards.straightdope.com/t/why-is-the-crab-nebula-visible/706368/9 "2014-12-05T04:19:19Z")
So the Crab Nebula… is the galaxy’s biggest CFL? 🙂 ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [December 5, 2014, 8:44am UTC](https://boards.straightdope.com/t/why-is-the-crab-nebula-visible/706368/10 "2014-12-05T08:44:49Z")
> [@TGWATY](#): > > What makes the diffuse gas of an exploded star glow? The same _basic_ principle that makes Vegas so bright. No, not [Vega](http://en.wikipedia.org/wiki/Vega), Vegas. Energy input into a gas ionizes it and makes it give off light. In the case of the Crab Nebula, because the source is [highly energetic](http://en.wikipedia.org/wiki/Pulsar_wind_nebula), a lot of that light isn’t visible - the Crab is one of the biggest X- and Gamma ray sources in the sky. ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [December 6, 2014, 6:23am UTC](https://boards.straightdope.com/t/why-is-the-crab-nebula-visible/706368/11 "2014-12-06T06:23:54Z")
That pulsar is rather impressive. It’s around 20 km in diameter, has a mass around 1.4 times that of our sun, and rotates at 1800 rpm. Some sources say its total luminosity may be 75,000 times that of the sun. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [December 6, 2014, 8:45am UTC](https://boards.straightdope.com/t/why-is-the-crab-nebula-visible/706368/12 "2014-12-06T08:45:26Z")
> [@Amateur\_Barbarian](#): > > So the Crab Nebula… is the galaxy’s biggest CFL? 🙂 😕 “CFL” ? ETA: please use the word “plerion” in future discussions of the nebula per se. Because it’s Greek and all, but different. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [December 6, 2014, 9:44am UTC](https://boards.straightdope.com/t/why-is-the-crab-nebula-visible/706368/13 "2014-12-06T09:44:24Z")
CFL > **[Compact fluorescent lamp](https://en.wikipedia.org/wiki/Compact_fluorescent_lamp)** > > A compact fluorescent lamp (CFL), also called compact fluorescent light, energy-saving light and compact fluorescent tube, is a fluorescent lamp designed to replace an incandescent light bulb; some types fit into light fixtures designed for incandescent bulbs. The lamps use a tube that is curved or folded to fit into the space of an incandescent bulb, and a compact electronic ballast in the base of the lamp. > Compared to general-service incandescent lamps giving the same amount of visible light, ... Plerion > **[Pulsar wind nebula](https://en.wikipedia.org/wiki/Pulsar_wind_nebula)** > > A pulsar wind nebula (PWN, plural PWNe), sometimes called a plerion (derived from the Greek "πλήρης", pleres, meaning "full"), is a type of nebula sometimes found inside the shell of a supernova remnant (SNR), powered by winds generated by a central pulsar. These nebulae were proposed as a class in 1976 as enhancements at radio wavelengths inside supernova remnants. They have since been found to be infrared, optical, millimetre, X-ray and gamma ray sources. > Pulsar wind nebulae evolve through var... Everything I know I learned through Google… ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [December 6, 2014, 4:00pm UTC](https://boards.straightdope.com/t/why-is-the-crab-nebula-visible/706368/14 "2014-12-06T16:00:36Z")
> [@](#): > > Quoth **Xema** : > > That pulsar is rather impressive. It’s around 20 km in diameter, has a mass around 1.4 times that of our sun, and rotates at 1800 rpm. Some sources say its total luminosity may be 75,000 times that of the sun. All of that is fairly typical of pulsars, actually, and there are some that are much more extreme.