The most spectacular nebulae in the universe
What is a nebula? Essentially, nebulae are concentrations of gas in which hydrogen, helium and stardust predominate. They are crucial structures in our universe since stars are born within them from the condensation and aggregation of matter. Some nebulae are regions where new stars are formed, but there are also other nebulae that form the remains of dead or dying stars.
How many types of nebulae are there?
Nebulae often 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 light from nearby stars that do not emit enough radiation for the nebula to be illuminated, so these dust clouds reflect light from a nearby star and appear bluer than the star because of the way the starlight is scattered by the nebula's dust particles.
Example: The Pleiades Nebula or Seven Sisters.
Emission Nebulae: These nebulae emit their own light because hydrogen atoms are excited by the powerful ultraviolet light from nearby stars; the hydrogen is ionized and generates the nebula's brightness. This is the most common type of nebula. They are visible 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, they hide the stars they contain, so they are not directly visible. 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 ejecting material into space. These outer layers of gas expand into space, forming a nebula that usually takes the shape of a ring or bubble.
Example: The Helix Nebula.
Thanks to today's powerful telescopes and long exposures we can observe beautiful and colourful images that reveal the full range of the nebula's colours, hydrogen in pink, blue, helium, nitrogen in red, blue-green oxygen...
Let's look at a sample of the most spectacular nebulae in our cosmos.
The Dumbbell Nebula, also known as Messier 27, the Haltera Nebula or Apple Nebula, pumps out infrared light in this image from NASA's Spitzer Space Telescope. It is a planetary nebula located in the constellation of Vulpecula or The Fox, about 1,360 light-years away from Earth. It's one of the largest known planetary nebulae.
The Butterfly Wings Nebula, or M2-9, is a striking example of a bipolar planetary nebula; these form 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 located 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 from the Spitzer telescope and the GALEX observatory we can contemplate this nebula as a dying star throwing a cosmic tantrum. Thus, the nebula was formed by a star similar to the Sun in the last moments of its 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), Hubble (in green), and Spitzer (in red). Located in the Large Magellanic Cloud, the Tarantula Nebula is one of the largest star-forming regions in the vicinity of the Milky Way. And also one of the most luminous.
Before us, the Veil Nebula or Swan Loop. Hot dust and gas glow brightly in this ultraviolet image taken by NASA's Galaxy Evolution Explorer -GALEX-. The nebula is about 1,500 light-years away from Earth.
In the IC 410 emission nebula, star formation is abundant, as we can see in this infrared image from NASA's Spitzer Space Telescope. With imagination towards the colossal IC 417 and the tiny NGC 1931 next to it, this pair suggests a spider and a fly, respectively. It's 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 remainder of a supernova they were able to watch in the sky for 22 months. Thus, it was observed and documented by Chinese and Arabian astronomers on July 4, 1054.
This image from the ESA Herschel Space Observatory shows part of the Rosette Nebula, a stellar nursery some 5,000 light-years from Earth in a giant molecular cloud in the constellation of Monoceros or the Unicorn. As it is located in the Milky Way band, the open star cluster inside the nebula is visible with binoculars.
Unofficially, the star cluster NGC 28 is known as the Pac-Man Nebula. The image we are looking at 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 appear to be burning (it is an emission nebula). The blazing nebula is located near the easternmost star in Orion's belt, Alnitak (one of the three 'Marys' in Orion's belt) about 1,400 light-years from Earth.
This colourful bubble is a planetary nebula called NGC 6818, also known as the Little Gem Nebula. It lies 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 outgoing material, 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.
Barnard 33 or the Horsehead Nebula is located about 1,500 light-years from Earth, near 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 Hubble's space telescope. It is about 3.5 light-years wide and is a dark absorption nebula.
In this infrared image from NASA's Spitzer telescope of the star-forming region NGC 2174 or the Monkey Head Nebula, dozens of young stars covered by cosmic dust are observed. Located in the constellation of Orion 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 dust shines brightly 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 areas of the edges not observed by Spitzer have covered with infrared observation data from NASA's Wide-field Infrared Survey Explorer (WISE) spacecraft.
Using new observations from ESO's VLT Survey Telescope, astronomers have discovered three different populations of stars within the Orion Nebula Group. They are located 1350 light-years away and, according to the data, these stars did not form at the same time (three different age sequences stand out) and, moreover, they rotate at different speeds: the youngest stars rotate faster than the oldest stars.
This surprising discovery provides valuable new information for understanding how these types of galactic clusters form.
"Although we cannot 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 form successively in less than 3 million years," explains ESO astronomer Giacomo Beccari.
Image credit: ESO/G. Beccari
The Unit 4 Telescope (Yepun) of ESO's Very Large Telescope (VLT) has now been transformed into a fully adaptive telescope. After more than a decade of planning, construction and testing, the new Adaptive Optics Facility (AOF) has managed to capture an incredibly sharp 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, scientist of the AOF project at ESO.
The new observations have shown dramatic improvements in image sharpness, revealing shell structures never before seen in IC 4406.
Image credit: ESO
The Flaming Star Nebula, also known as IC 405, is an emission/reflection nebula located about 1,500 light-years away in the constellation of Auriga. AE Aurigae is the bright star we can see on the left side, it is a massive and very hot O-type star that is moving fast through space probably after being ejected from a collision of multiple stellar systems in the vicinity of the Orion nebula millions of years ago. This bright nebula spans about 5 light-years, so it is also visible with a small telescope if we look at the right constellation.
Here we see the Trifid nebula in visible light, in an image obtained from the ground with a small telescope. This nebula, also known as Messier 20, is located in the constellation of Sagittarius about 5,500 light-years away from Earth and its name means "divided into three lobes", as it has three bright lobes separated by dark lines of dust. It is a nebula of both emission and reflection and quite young: about 300,000 years.
In this image we see only two different colours because it is not an image obtained with a large telescope, but by an amateur telescope.
Image credit: ESO/Gabor Tót
The Pencil Nebula or NGC 2736 is a small part of the Sailing Supernova remnant, located near the Sailing Pulsar in the constellation of the same name. This huge remnant in which the Pencil Nebula is located is the product of a supernova explosion that took place some 11,000 years ago. The linear appearance of this nebula gave rise to its popular name. It lies 815 light-years away from Earth and moves at 644,000 kilometres per hour.
The Keel Nebula, also called the Carina Nebula, is a vast emission nebula that surrounds several open clusters of stars. Located in the Sagittarius Arm of the constellation Carina, it is about 7,500 light-years away from Earth. It contains numerous O-type stars (with temperatures above 33,000 K), such as the well-known Eta Carinae, one of the brightest stars in the Milky Way, or HD 93129A, another incredibly massive and luminous star. It is 4 times larger and brighter than the Orion nebula but is less well known due to its location in the southern hemisphere.
5,500 light-years away from Earth is NGC 6334, also known as the Cat's Paw Nebula. It was discovered in 1837 by English astronomer John Herschel. It is an emission nebula that covers an area of the sky slightly larger than that of the Moon in its full phase. The characteristic red colour of the image is due to the incandescent hydrogen gas in this 50 light-year-long cloud, as it is a huge star-forming nursery and the hot young stars make the surrounding hydrogen gas shine in these intense reddish tones.
This image taken by the NASA / ESA Hubble Space Telescope resembles the fog illuminated by a lamppost swirling around a curiously shaped hole and there is certainly some truth in this resemblance. What we see is the NGC 1999 reflection nebula where the "fog" is dust and gas illuminated by the star and the "hole" is actually empty space in the sky, as discovered by ESA's Herschel Space Observatory.
The bright star that stands out in this snapshot is V380 Orionis, a young star with 3.5 times the mass of our star, the Sun. It appears white due to its high surface temperature of approximately 10,000°C, almost twice that of the Sun.
Copyright: NASA and The Hubble Heritage Team (STScI)
ESO 378-1 or the Southern Owl Nebula, is a planetary nebula located in the constellation of Hydra, 3,500 light-years away from the Earth. In this image captured by ESO's VLT (Very Large Telescope), we observe an extraordinary bubble, which glows like the ghost of a star in the absolute darkness of space. Planetary nebulae (the remains of a dying star) play a crucial role in the chemical enrichment and evolution of the universe, as new stars and planets can emerge from them.
Image credit: THAT
A square nebula? The Red Square or Red Square Nebula is located in the constellation Serpens (the Snake) and is very recognizable thanks to its square shape, which makes it one of the most symmetrical celestial objects ever discovered. Why does it have this square shape? The main hypothesis is that the central star expelled cones of gas during a late stage of development that forms right angles from the Earth's point of view.
Image credit: Peter Tuthill, Palomar and Keck Observatories
IC 1805, better known as the Heart Nebula because of its peculiar heart shape in long exposure photographs, is located 7,500 light-years away from Earth in the constellation of Cassiopeia. It has a size of almost 300 light-years (radius 100 light-years) and represents a mixture of bright interstellar gas and dark dust clouds. In the image, it appears in these reddish shades due to the emission of a specific colour of the light emitted by hydrogen gas.
This Hubble image captures a small region within M17, also known as the Omega Nebula or Swan Nebula. This hotbed of star formation is coloured according to the chemical elements present. Red represents sulfur, green indicates hydrogen and blue oxygen. It is one of the largest star-forming regions in the Milky Way. It is located 5,500 light-years from Earth in the constellation of Sagittarius and has an apparent magnitude of 6, so it can be seen with a pair of binoculars. The best time to observe it is in August.
Image credit: ESA, NASA and J. Hester (Arizona State University)
This image shows a nebula, specifically NGC 604, located in one of the spiral arms of the Messier 33 galaxy, better known as the Triangle Galaxy, which is 2.723 million light-years away from Earth. More than 200 immensely hot stars heat the nebula's ionized hydrogen gas, making it fluoresce, as we see in this image from NASA/ESA's Hubble Space Telescope.
This image of dust, gas and bright young stars, gravitationally bound in the shape of a smiling skull, was captured with ESO's Very Large Telescope (VLT). This is the NGC 2467 nebula and it is an active star-forming region as dark as it is beautiful. Can you identify the skull?