What is a nebula?
In essence, nebulae are concentrations of gas in which hydrogen, helium and stellar dust predominate. They are crucial structures in our universe, since within them the stars are born from the condensation and aggregation of matter. Some nebulae are regions where new stars are formed , but there are also other nebulae that make up the remains of dead stars or that are ending their days.
With its fantastic appearance, which inevitably dazzles us, there are millions of them in our cosmos and, the name of this mass of cosmic celestial matter, diffuse and luminous, derives from its nub aspect.
How many types of nebulae are there?
Nebulae, which have different shapes and sizes, are divided into four fundamental types: reflection nebulae, emission nebulae, absorption nebulae and planetary nebulae.
- Reflection nebulae: These nebulae reflect the light of nearby stars that do not emit enough radiation for the nebula to be illuminated, so these clouds of dust reflect the light of a nearby star and appear more blue than the star because of the way that starlight is scattered by the dust particles of the nebula. Example: The Pleiades nebula or seven sisters.
- Emission Nebulae: These nebulae emit their own light as the hydrogen atoms are excited by the powerful ultraviolet light of nearby stars; the hydrogen ionizes and generates the brightness of the nebula. It is the most common type of nebula. They are visible, as we see, because they emit light thanks to the energy they receive from nearby stars. Example: The Omega or horseshoe nebula.
- Absorption nebulae: Also called dark nebulae, They are characterized by not emitting light, hide the stars it contains, so they are not visible directly. It was the astronomer William Herschel, who discovered this type of nebula. Example: the Horsehead nebula.
- Planetary nebulae: These nebulae shine because the light coming from the associated star is absorbed by the atoms of the nebula; that is, they are gas shells detached from dying stars that are expelling material into space. These outer layers of gas expand into space, forming a nebula that usually adapts to the shape of a ring or a bubble. Example: The Helix Nebula.
Thanks to today’s powerful telescopes and long exposures we can see beautiful and colorful images that reveal the whole range of colors of the nebula, hydrogen in pink, blue, helium, nitrogen in red, blue-green oxygen…
Let’s see a sample of the most spectacular nebulae in our cosmos.
The Dumbbell Nebula, also known as Messier 27, the Halter Nebula or Apple Nebula, pumps infrared light into this image from NASA’s Spitzer Space Telescope. It is a planetary nebula located in the constellation Vulpecula or The Fox, about 1,360 light-years away from Earth. It is one of the largest known planetary nebulae.
The Butterfly Wings nebula or M2-9, is a striking example of a bipolar planetary nebula; These are formed when the central object is not a single star, but a binary system. Studies have shown that the size of the nebula increases with time. The Butterfly Wings nebula is found at a distance of 2,100 light years from Earth.
It is a planetary nebula located in the constellation of Aquarius. Thanks to this image of the Spitzer telescope and the GALEX observatory we can contemplate this nebula as a dying star that throws a cosmic tantrum. Thus, the nebula was formed by a star similar to the Sun in the last moments of his life. The Helix Nebula is 694.7 light-years away from Earth.
This image of the Tarantula Nebula, 30 Doradus or NGC 207, contains data from the Chandra X-ray Observatory (in blue), the Hubble (in green), and the Spitzer (in red). Located in the Large Magellanic Cloud, the Tarantula Nebula is one of the largest regions forming stars near the Milky Way. And also of the brightest.
Before us, the Nebula of the Veil or Loop of the Swan. The hot dust and gas glow in this ultraviolet image taken by NASA’s Galaxy Evolution Explorer -GALEX-. The nebula is about 1,500 light-years away from Earth.
6Spider and Fly Nebula
In the emission nebula IC 410 abounds in star formation, as we see in this infrared image of NASA’s Spitzer space telescope. With imagination towards the colossal IC 417 and the tiny NGC 1931 at its side, this pair suggest a spider and a fly, respectively. It is about 10,000 light-years away from Earth.
This image shows a composite view of the Crab Nebula, an iconic remnant of the supernova in our galaxy, the Milky Way, according to observations from the Herschel telescope and the Hubble Space Telescope. This nebula is 6,523 light years away from Earth and forms the rest of a supernova that could be seen in the sky for 22 months. Thus, it was observed and documented by Chinese and Arab astronomers on July 4, 1054.
This image from the ESA Herschel Space Observatory shows a part of the Rosette nebula, a stellar nursery some 5,000 light years from Earth in a giant molecular cloud in the constellation Monoceros or the Unicorn. As it is located in the band of the Milky Way, the star cluster opened within the nebula is visible with binoculars.
Unofficially, the star cluster NGC 28, is known as the Pac-Man nebula. The image we see contains X-ray data from the Chandra observatory in purple, with infrared observations from the Spitzer telescope, in red, green, blue. The similarity with the famous arcade video game is palpable. It is located in the constellation of Cassiopeia.
NGC 2024 or the Flame Nebula takes its name because the clusters of the nebula seem to burn in flames (it is an emission nebula). The flaming nebula is located near the easternmost star of the Orion belt, Alnitak (one of the three ‘Marys’ of the Orion belt) about 1,400 light-years from Earth.
11Little Gem Nebula
This colorful bubble is a planetary nebula called NGC 6818, also known as the Little Gem Nebula. It is found in the constellation of Sagittarius about 6,000 light years away from Earth. Scientists believe that the stellar wind from the central star propels the material that comes out, sculpting the elongated shape of NGC 6818. The image was captured by the Hubble telescope, using different filters to reveal a different view of the nebula.
12Horse Head Nebula
Barnard 33 or Horsehead Nebula is located about 1,500 light-years away from Earth, close to the Orion belt. The backlit rays along the upper ridge of the horsehead nebula are being illuminated by Sigma Orionis, a system of five young stars captured by the Hubble Space Telescope. It measures approximately 3.5 light years wide and is a dark absorption nebula.
13Monkey Head Nebula
In this infrared image of the NASA Spitzer telescope of the star formation region NGC 2174 or Monkey Head Nebula,dozens of young stars covered by cosmic dust are observed. Located in the Orion constellation about 6,400 light-years away from Earth, some of its clouds resemble the head of a monkey in visible light images (hence its nickname). The hot powder glows at infrared wavelengths (light with a wavelength of 3.5 microns is shown in blue, with 8.0 microns in green, and 24 microns in red). The edge areas not observed by Spitzer were covered with infrared observations data from the Wide-field Infrared Survey Explorer (WISE) spacecraft.NASA.
14The Orion Nebula
Using new observations from ESO’s VLT Survey Telescope, astronomers have discovered three different star populations within the Orion Nebula Group. They are located at 1,350 light-years and, according to the data, these stars were not formed at the same time (they highlight three different age sequences) and, in addition, they rotate at different speeds: the younger ones rotate faster than the older stars.
This surprising discovery provides new and valuable information to understand how these types of galaxy clusters are formed.
“Although we can not yet formally refute the possibility that these stars are binary, it seems much more natural to accept that what we see are three generations of stars that are formed in a period of less than 3 million years,” explains Giacomo Beccari, astronomer of that.
15The planetary nebula IC 4406
The Unit Telescope 4 (Yepun) of ESO’s Very Large Telescope (VLT) has now been transformed into a fully adaptable telescope. After more than a decade of planning, construction and testing, the new Adaptive Optics Facility (AOF) has managed to capture an incredibly clear view of the planetary nebula IC 4406 . All thanks to the adaptive optics that work to compensate for the blurring effect of the Earth’s atmosphere, allowing MUSE to obtain much sharper images.
“Now, even when the weather conditions are not perfect, astronomers can obtain excellent image quality thanks to the AOF,” explains Harald Kuntschner, AOF project scientist at ESO.
The new observations have shown dramatic improvements in the sharpness of the images, revealing shell structures never seen before in IC 4406.