Nebula: Definition, impart and variants

Nebula: Definition, impart and variants

An image of the Veil Nebula taken by the Hubble Space Telescope

(Image credit rating: ESA/Hubble & NASA, Z. Levay)

Nebula is a Latin note meaning “cloud”, but in an substantial context, it refers to any celestial object which looks cloud-relish when viewed thru a telescope.

When telescopes weren’t as principal as they’re nowadays, this time frame encompassed galaxies similar to our neighbour Andromeda, which become once continuously referred to because the “Andromeda nebula”. 

Alternatively, with the smartest thing about up to the moment telescopes we know that galaxies aren’t cloud-relish at all, but made up of billions of stars. This means astronomers now reserve the note nebula for staunch clouds — of gasoline and dirt — located inner our possess galaxy.

Connected: What is the Eagle Nebula?

The set are nebula located?

Nebula are continuously prove in the home between stars, referred to because the interstellar medium. On reasonable, this station contains handiest around one atom per cubic centimetre. Alternatively, in obvious areas the density will even be vastly bigger than this ⁠— high ample to vary into seen thru a telescope. 

The result’s what we call a nebula, and they also’re among the most spectacular sights in astronomy. In actuality an excellent deal of the most iconic Hubble telescope pictures, such because the “Pillars of Creation”, are pictures of nebula.

The central third of the image is filled with a towering structure of gas called the Eagle Nebula. In the background bright stars shine through the dust.

An image of the “Pillars of Creation” in the Eagle Nebula taken by the Hubble Residence Telescope. (Image credit rating: NASA, ESA, and the Hubble Heritage Group (STScI/AURA))

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There are several an excellent deal of styles of nebula, reckoning on how they type and their composition. Most nebula are primarily made of gasoline, which is in a station to glow with its possess gentle, constructing the shiny shows with which we’re familiar . 

But other nebula ⁠— such because the so-called “darkish nebula” ⁠— are worthy dustier in their composition, and fairly than elegant this dirt has the function of blocking off the gentle from more a ways away objects beyond it.

What are the an excellent deal of styles of nebula?

(Image credit rating: NASA/JPL-Caltech STScI)

Emission nebula: The Orion Nebula

A diffuse nebula with ongoing megastar formation, the gasoline right here is sizzling ample to glow with its possess gentle.

The relationship between nebula and stars

Nebula play a key role in the life cycle of stars, every at their delivery and demise. Stars are born in dense clumps of gasoline, dirt, and other discipline topic inner diffuse emission nebulae, also once in a while called “stellar nurseries”. 

Hubble’s Pillars of Creation is in this class, as is the well-known Orion Nebula ⁠— that you can perchance well per chance simply successfully possess seen on your self thru binoculars or a cramped telescope. 

The main power at work right here is gravity, which causes the tenuous interstellar medium to condense into a nebula, and gravity that causes clumps contained in the nebula to interrupt down down into stars.

A stellar nursery is filled with clouds of orange and yellow dust. At the center of the image is a mass of bright blue white stars.

A spectacular Hubble image showing the large “stellar nursery” in the 30 Doradus nebula. (Image credit rating: NASA, ESA, F. Paresce (INAF-IASF, Bologna, Italy), R. O’Connell (College of Virginia, Charlottesville), and the Extensive Enviornment Digicam 3 Science Oversight Committee)

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At the opposite slay of a megastar’s life, we attain upon a mumble form of emission nebula. Stars relish the sun slay their lives as highly compact white dwarfs, but as they shrink down into this share they launch clouds of gasoline which type a so-called “planetary nebula”. Here’s a fairly deceptive title, on account of such nebula possess nothing to dangle with planets.

No longer like diffuse emission nebula, these possess a more clearly defined appearance, on the overall spherical in shape, which reminded William Herschel of a planet when he first noticed them in the 1780s.

No longer all stars slay their days in the relative serenity of a planetary nebula. A megastar that’s worthy more massive than the sun will sooner or later explode as a supernova, and the debris flung out from that explosion forms yet one other more or much less nebula called a supernova remnant. Essentially the most well-known of these is the Crab Nebula, which is all that is still of a spectacular supernova that become once noticed by Chinese language astronomers in 1054.

Seeing nebulae in living color

A side by side comparison of images of the Southern Ring Nebula taken in near-infrared (left) and mid-infrared (right). The left image shows wispy orange ribbons of gas and dust surrounding an oval shape

The Southern Ring Nebula; taken by the Shut to-Infrared Digicam (NIRCam) [left] and the Mid-Infrared Instrument (MIRI) [right] aboard the JWST.  (Image credit rating: NASA, ESA, CSA, and STScI)

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To rob the spectacular nature of nebulae, telescopes — such because the Hubble Residence Telescope and the James Webb Residence Telescope ( JWST) — exhaust infrared radiation emitted by nebulae to blueprint a impart.   

The seen gentle emitted by stars forming in and around a nebula will even be blocked by the dense cosmic clouds of gasoline and dirt that dangle up a nebula. Therefore, scientists must gape to other wavelengths of gentle that are emitted from the nebula, similar to infrared radiation. 

Infrared cameras onboard the JWST possess relieved some of the most most detailed pictures of nebulae, such because the Southern Ring planetary nebula. The Southern Ring nebula — continuously referred to as NGC 3132 — is around 2,500 gentle-years a ways from Earth and residential to a demise megastar at its core. 

The utilization of its Shut to-Infrared Digicam (NIRCam) and the Mid-Infrared Instrument (MIRI), the JWST has captured some of the most detailed pictures of the nebula. Within the two pictures above, JWST has captured layers of gasoline and dirt within the Southern Ring Nebula. Every layer has been created by the expulsion of cosmic topic from the central demise megastar. 

Extra sources

For more data about nebulae, take a look at out “The Hubble Legacy: 30 Years of Discoveries and Image (opens in contemporary tab)“, by Jim Bell and “Planetary Nebulae and The style to Search Them (Astronomers’ Gazing Guides) (opens in contemporary tab)“, by Martin Griffiths. 


  • The Planets, “Nebula Info – A Manual To Nebulae (opens in contemporary tab)“, accessed July 2022. 
  • Universe Lately, “Nebulae: What Are They And The set End They Near From? (opens in contemporary tab)“, accessed July 2022. 
  • The College of Utah, “Nebula (opens in contemporary tab)“, accessed July 2022. 
  • Australia Telescope National Facility, “Celebrity Formation (opens in contemporary tab)“, July 2022. 
  • Cosmos, “Emission Nebula (opens in contemporary tab)“, accessed July 2022. 
  • James Miller, “What Are Nebulae And How Are They Fashioned? (opens in contemporary tab)“, Astronomy Traipse, December 2014. 
  • Andy Briggs, “What is a supernova (opens in contemporary tab)“, EarthSky, November 2020. 

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Andrew May

Andrew Could holds a Ph.D. in astrophysics from Manchester College, U.K. For 30 years, he worked in the educational, govt and interior most sectors, outdated to changing into a science author where he has written for Fortean Times, How It Works, All About Residence, BBC Science Level of curiosity, among others. He has also written an excellent deal of books alongside side Cosmic Impact and Astrobiology: The Spy for Existence In an excellent deal of areas in the Universe, printed by Icon Books.