The Nebula Theory

In the Beginning

The whole Solar System developed from a cloud of dust and gas called a nebula. Scientists believe that  all the stars in the Universe formed from a nebula that collects together through the force of gravity.

Astronomers believe that at the beginning of the Universe most of the matter that existed was in the form of hydrogen.

 

The hydrogen atom is the simplest atom that exists: it has one proton and one electron .

Element Factory

If most of the matter that existed was once hydrogen how did oxygen, nitrogen, iron, calcium and the rest of the elements develop? Good question!

Astronomers believe stars are the factories that made all of the other elements and that they use hydrogen as the fuel and the raw material to make them.

Stars may not be alive in the same way that we are, but they do have a beginning, a middle and an end to their existence. It just happens that a star’s lifetime is measured in many millions or billions of years. Since we tend to hang out around in life for less than a century, stars seem unchanging to us.

The Power of Attraction

In the beginning, the universe was a bunch of gas and dust spreading out in space. Over a very long time, this gas and dust started gathering together into clumps, or clouds through the force of gravity. In everything that exists, every atom has a gravitational pull that wants to attract something to it. As matter collects together, its gravitational pull gets stronger and it can reach out farther to grab more matter. That increases its gravitational pull even more.  This process continues until there is nothing more to grab.

A Star is Born

This image from the Hubble Telescope is of the Eagle Nebula. The large pillars are called "elephant trunks." They are light-years in length and are so dense that the gas in them contracts gravitationally and forms stars!  (Click on the image for a closer look.) Image Credit: J. Hester, P. Scowen (ASU), HST, NASA

Supernova 1987a

In February 1987, light reached Earth from a star more than 170 thousand  light yearsfrom Earth. The light was from a star that exploded in the nearby Large Magellanic Cloud galaxy. Named Supernova 1987a, it is the closest supernova since the invention of the telescope. The exlposion of the star shot huge amouts of gas, light, and neutrinos out into space. (Click on the image for a closer look.) Image Credit: C. S. J. Pun (GSFC) & R. Kirshner (CfA), WFPC2,HST, NASA

Let's Get Together

If the blob of stuff gets big enough, it forms a sphere or ball. The center of gravity of the sphere is in the middle. Everything is being pulled towards the very center of the sphere. If enough material is pulled toward the center, the weight of the outer parts crush the inner parts and cause the atoms to fuse, or join together to become newer, more complex atoms. This process is called fusion.

What About the Leftovers?

Whatever parts are not used to make the new atom are released as heat and light energy. Whenever atoms are fused or split, they release a lot of energy. That is how atom bombs work. That is also how stars works. Stars are not on fire in space, they are constantly having nuclear explosions. This is what makes them shine.

Here Comes the Sun

When our Sun formed from a nebula in this region of space, it gobbled up nearly all of the material for itself. The key word here is “nearly”, which means that some material was left over after the Sun was created. However, if the mass of the solar system was converted into one dollar, the Sun would be worth more than 99 cents, and all the planets, moons, asteroids and comets put together would total less than one penny!

Solar Winds

As the Sun shines, it generates what is called a solar wind. It is not wind as we know it where air moves around – because there is no air in space. It is a flow of energy outward from the Sun that acts like a wind and pushs things outward.

When the Sun grew large enough and started shining through nuclear fusion, the solar wind it created blew the remaining nebular material outward. The planets, moons asteroids and comets condensed from this leftover material in much the same way that the Sun formed – from gravitational attraction pulling nearby available material together. Heavier elements remained closer to the Sun and lighter elements were blown further out.

Density of the Planets

This explains why the inner planets of Mercury, Venus, Earth and Mars are dense, rocky planets and the outer planets of Jupiter, Saturn, Uranus (which, by the way, is properly pronounced ’YUR-uh-nis’) and Neptune are gas giants. Pluto, while still called a planet, resembles more closely the body of objects being classified as Kuiper Belt Objects. These distant objects are more like giant comets and are apparently made of materials light enough to be blown out past Neptune’s orbit.

Pluto and Beyond

This image shows the newly discovered planet-like object, "Sedna," in relation to other bodies in the solar system, including Earth and its Moon; Pluto; and Quaoar, a planetoid beyond Pluto that was until now the largest known object beyond Pluto. Sedna is bigger than an asteriod, but smaller than a planet. It is three times farther away from Earth than Pluto and is the reddest object in the Solar System, after Mars.       Not in this picture is the more recently discovered "tenth planet", 2003ub313, that is estimated to be larger than Pluto, perhaps around the size of the Moon.  See the "Big Bang Theory" page for more about this discovery. (Click on the image for a closer look.) Image Credit: NASA/JPL-Caltech

Formation of the Earth

Seeing that New Hampshire is located on Earth, let’s concentrate now on our planet’s development. Earth is one of the inner planets and is made up of the denser (heavier) elements that were left over after the Sun was formed. The current accepted theory for planet development is known as theAccretion Theory. To accrete is to gather together or add on to. Sometimes it is easier for some people to think of the Accretion Theory as the ‘Snowball Theory’. Smaller lumps of planet building material were gravitationally attracted to larger chunks of planet building material and they collided; much like gathering a bunch of smaller snowballs together to make a larger snowball.

Collision Course

Very early on in our Solar System’s history, there were many more planets than there are today, though they were all smaller than today’s planets. The nine planets (and their moons) are the bodies that ‘won’ the collision contest. The collisions haven’t stopped, they have just slowed down and most of the larger planet-sized chunks have been swallowed up (thank goodness, as you will see).

Meteors

Approximately ten tons of new material enter the Earth's atmosphere every day. Most of this debris is the size of a grain of sand or a small pebble and burns up harmlessly in the atmosphere. At night the debris is often visible as shooting stars. Scientists call these pieces of planet building material that burn up in our atmosphere, meteors. After they burn up on entry into the earth’s atmosphere, their dust settles on the surface of the Earth.

Leonid Meteor Showers

The Leonid Meteor Showers happen when the Earth passes through the tail of Comet Temple-Tuttle. When the Earth passes through the comet's tail, all the dust and debris of the comet burns up in our atmosphere and is visible as meteor showers in the night sky. The Comet Tempel-Tuttle has an eliptical orbit around the sun. Most of its orbit is in the outer solar system. It enters the inner solar system and passes by Earth every 33 years. The next pass-by of the comet will occur in 2033. (Click on the image for a closer look.) Picture Credit: NASA, Hubble Space Telescope

Meteorites

Sometimes larger chunks survive the burning trip through the atmosphere and hit the surface of the Earth. These are called meteorites. Fortunately, most of our planet’s surface is ocean, so meteorites tend to land harmlessly out at sea. On rare occasions, city sized chunks of rock and/or ice slam into Earth and cause massive destruction. Scientists believe a large meteorite that hit the Yucatan Peninsula in the Gulf of Mexico 65 million years ago at the end of the Cretaceous period led to the extinction of the dinosaurs. They think that when the meteorite hit the Earth, it sent huge quantities of dust, smoke and debris into the atmosphere all over the world. The dust, smoke and debris blocked the Sun for many weeks or months.  This caused temperatures to drop all over the planet, causing winter like conditions everywhere. Plants and animals that couldn't adapt to the sudden changes in light and temperature died, and animals that depended on these organisms for food, like the dinosaurs, eventually died as well.

Friction

The friction of huge impacts creates heat. The relentless pounding the early Earth took generated so much heat that it melted the entire planet into liquid rock.  Yup, the Earth was a floating ball of lava in space!

Feel the Heat

Try the simple experiment of rubbing your hands together briskly for ten to twenty seconds and feel the heat generated from this relatively miniscule amount of friction.

Forming Layers

While the Earth was molten, it separated into layers, like oil and vinegar salad dressing does when it is undisturbed. The heavier elements settled towards the center of the planet, the lighter materials floated on top         (Click on the image for a closer look.)
and those           Image Courtesy of Windows to the Universe, at:
materials whose        http://www.windows.ucar.edu/
densities lay
between these two extremes were settled between the heaviest and lightest two layers.

The core separated into a solid inner core consisting mainly of iron and nickel. The inner core is surrounded by a liquid metal outer core that generates an electrical current as the Earth rotates. This spinning electrical current is responsible for the magnetic field that surrounds our planet. This magnetic field protects us from some of the more deadly forms of solar radiation by deflecting those harmful rays towards the North and South Magnetic Poles and in doing so, create the Northern and Southern Lights.

As the bombardment of larger chunks slowed down, the exterior of the earth had a chance to cool and harden into a crust as it was exposed to the coldness of outer space (there was no atmosphere in the early part of the Earth formation).

The mantle stayed molten because the crust served as insulation retained the heat generated from radioactive materials in the Earth’s interior.

The mantle doesn’t just sit there, it is in constant roiling motion due to convection of the liquid rock. The term ‘liquid’ here is slightly misleading. A more accurate description of the consistency of the earth’s mantle just below the crust is more like that of a taffy that is sticky enough to grab a hold of the rough and uneven underside of the crust and pull the crust along with it. This constant tugging at the underside of the crust by a thick, sticky substance sometimes results in separation or rupturing of the crust which might allow for the liquid rock to ooze through to the surface. But that story belongs in the  section onPlate Tectonics.

 

Creation of the Moon

Fitting right in with the Accretion Theory, the Giant Impactor Theory suggests that an object the size of Mars hit the still- forming Earth 4.5 billion years ago. When this object hit, it sent large abounts of superheated       material from          (Click on the image for a closer look.)
the outer layers       Image Credit: William K. Hartmann
of both bodies into
orbit around the Earth. This molten debris formed a ring around the Earth. The debris in the ring eventually stuck together to form the Moon. Supporting evidence for this theory includes:

• a lunar orbit that is slightly tilted in respect to Earth’s equator (An Earth and Moon that developed together side by side would most likely have had the Moon orbiting right over the earth’s equator.  Actually, this would have been cool because there would have been a lunar and a solar eclipse every month!  However, due to the slight orbital tilt of the Moon, most times the Moon travels above or below the Sun as seen from Earth – so no solar eclipses, or it travels above or below Earth's shadow in space - so no lunar eclipses each month either.  As a result, eclipses only happen once in a while when the Earth, Moon and Sun line up just right, as opposed to every month.);

• the Moon is moving away from the Earth at the rate of about an inch a year. As a result, the Moon is about a yard farther away from the Earth now than when Neil Armstrong walked on its surface;

Lunar rocks are very similar to some Earth rocks.  This is most likely the result of some material from both bodies in the collision mixing together.

H I region

An H I region is an interstellar cloud composed of neutral atomic hydrogen (H I), in addition to the local abundance of helium and other elements. These regions are non-luminous, save for emission of the 21-cm (1,420 MHz) region spectral line. This line has a very low transition probability, so requires large amounts of hydrogen gas for it to be seen. At ionization fronts, where H I regions collide with expanding ionized gas (such as an H II region), the latter glows brighter than it otherwise would. The degree of ionization in an H I region is very small at around 10^-4 (i.e. one particle in 10,000). The temperature of an H I region is about 100 K, and it is usually considered as isothermal, except near an expanding H II region. Near an expanding H II region is a dense H I region, separated from the undisturbed H I region by a shock front and from the H II region by an ionization front.

Mapping H I emissions with a radio telescope is a technique used for determining the structure of spiral galaxies. It is also used to map gravitational disruptions between galaxies. When two galaxies collide, the material is pulled out in strands, allowing astronomers to determine which way the galaxies are moving.

H II region

An H II region is a large cloud of gas and ionized gas of glowing low density in which star formation has recently taken place. Young, hot, blue stars—which have formed from the gas—emit copious amounts of ultraviolet light, ionizing and heating the gas surrounding them. H II regions—sometimes several hundred light-years across—are often associated with giant molecular clouds in which star formation takes place, and from which the stars that produce the H II region were born. The first H II known region is Orion Nebula discovered in 1610 by Nicolas-Claude Fabri de Peiresc.

H II regions are named for the large amount of ionised atomic hydrogen they contain, referred to as H II by astronomers (H I region being neutral atomic hydrogen, and H₂ being molecular hydrogen). They have extremely diverse morphologies, because the distribution of the stars and gas inside them is inhomogeneous. They often appear clumpy and filamentary, sometimes showing bizarre shapes like the Horsehead Nebula. H II regions may give birth to thousands of stars over a period of several million years. In the end, supernova explosions and strong stellar winds from the most massive stars in the resulting star cluster will disperse the gases of the H II region, leaving behind a cluster such as the Pleiades.

H II regions can be seen out to considerable distances in the universe, and the study of extragalactic H II regions is important in determining the distance and chemical composition of other galaxies. Spiral and irregular galaxies contain a lot of H II regions, while elliptical galaxies are almost devoid of them. In the spiral galaxies, including the Milky Way, H II regions are concentrated in the spiral arms, while in the irregular galaxies they are distributed chaotically. Some galaxies contain huge H II regions, which may contain tens of thousands of stars. Examples include the 30 Doradusregion in the Large Magellanic Cloud and NGC 604 in the Triangulum Galaxy.

Barnard's Loop

Barnard's Loop (catalogue designation Sh 2-276) is an emission nebula in the constellation of Orion. It is part of a giant molecular cloud which also contains the bright Horsehead and Orion nebulae. The loop takes the form of a large arc centred approximately on the Orion Nebula. The stars within the Orion Nebula are believed to be responsible for ionizing the loop.

The loop extends over about 600 arcminutes as seen from Earth, covering much of Orion. It is well seen in long-exposure photographs, although observers under very dark skies may be able to see it with the naked eye.

It is estimated to lie at a distance of approximately 1600 light years, giving it actual dimensions of about 300 light years across. It is thought to have originated in a supernova explosion about 2 million years ago, which may have also created several known runaway stars, including AE Aurigae, Mu Columbae and 53 Arietis, which are thought to have been part of a multiple star system in which one component exploded as a supernova.

Pelican Nebula

The Pelican Nebula (also known as IC5070 and IC5067) is an H II region associated with the North America Nebula in the constellation Cygnus. Thenebula resembles a pelican in shape, hence the name. The Pelican Nebula is a large area of emission nebula in the constellation Cygnus (the Swan), close to Deneb, and divided from its brighter, larger neighbor, the North America Nebula, by a molecular cloud filled with dark dust.

The Pelican is much studied because it has a particularly active mix of star formation and evolving gas clouds. The light from young energetic stars is slowly transforming cold gas to hot and causing an ionization front gradually to advance outward. Particularly dense filaments of cold gas are seen to still remain. Millions of years from now this nebula might no longer be known as the Pelican, as the balance and placement of stars and gas will leave something that appears completely different

Hourglass Nebula

The Engraved Hourglass Nebula (also known as MyCn 18) is a young planetary nebula situated in the southern constellation Musca about 8,000 light-years away from Earth. It was discovered by Annie Jump Cannon and Margaret W. Mayall during their work on an extended Henry Draper Catalogue (the catalogue was built between 1918 and 1924). At the time, it was designated simply as a small faint planetary nebula. Much improved telescopes and imaging techniques allowed the hourglass shape of the nebula to be discovered by Raghvendra Sahai and John Trauger of the Jet Propulsion Laboratory on January 18, 1996. It is conjectured that MyCn 18's hourglass shape is produced by the expansion of a fast stellar wind within a slowly expanding cloudwhich is denser near its equator than its poles.

The Hourglass Nebula was photographed by the Wide Field and Planetary Camera 2 of the Hubble Space Telescope.

A less-famous "Hourglass Nebula" is located inside the Lagoon Nebula.

Hourglass Nebula in popular culture

• The Hourglass Nebula was featured on the cover of the April 1997 issue of National Geographic. The nebula’s unique appearance led the magazine’s editors to comment, “Astronomers looked 8,000 light-years into the cosmos with the Hubble Space Telescope, and it seemed that the eye of God was staring back.”

• The Hourglass Nebula also serves as the front cover for Pearl Jam's 2000 album Binaural.

• The Hourglass Nebula appears in the popular game, Final Doom.

• The Hourglass Nebula appears on a poster in the CERN laboratory in the film Angels & Demons.

• The Hourglass Nebula appears extensively, and is used as a major plot point in the 2002 animated series Space Pirate Captain Herlock: The Endless Odyssey.

• The Hourglass Nebula appears in the video game titled Mass Effect 2 as one of the clusters that can be visited for missions.

• The Hourglass Effect is a 2008 album by the British band Shadowkeep.

Tarantula Nebula

The Tarantula Nebula (also known as 30 Doradus, or NGC 2070) is an H II region in the Large Magellanic Cloud (LMC). It was originally thought to be a star, but in 1751 Nicolas Louis de Lacaille recognized its nebular nature.

The Tarantula Nebula has an apparent magnitude of 8. Considering its distance of about 49 kpc (160,000 light years), this is an extremely luminous non-stellar object. Its luminosity is so great that if it were as close to Earth as the Orion Nebula, the Tarantula Nebula would cast shadows. In fact, it is the most active starburst region known in the Local Group of galaxies. It is also the largest such region in the Local Group with an estimated diameter of 200 pc. The nebula resides on the leading edge of the LMC, where ram pressure stripping, and the compression of the interstellar medium likely resulting from this, is at a maximum. At its core lies the compact star cluster R136 (approx diameter 35 light years) that produces most of the energy that makes the nebula visible. The estimated mass of the cluster is 450,000 solar masses, suggesting it will likely become a globular cluster in the future.

In addition to R136, the Tarantula Nebula also contains an older star cluster—catalogued as Hodge 301—with an age of 20–25 million years. The most massive stars of this cluster have already exploded in supernovae.

The closest supernova observed since the invention of the telescope, Supernova 1987A, occurred in the outskirts of the Tarantula Nebula.

Carina Nebula

The Carina Nebula (also known as the Great Nebula in Carina, the Eta Carina Nebula, or NGC 3372) is a large bright nebula that surrounds several open clusters of stars. Eta Carinae and HD 93129A, two of the most massive and luminous stars in our Milky Way galaxy, are among them. The nebula lies at an estimated distance between 6,500 and 10,000 light years from Earth. It is located in the constellation of Carina. The nebula contains multiple O-type stars.

The nebula is one of the largest diffuse nebulae in our skies. Although it is some four times as large and even brighter than the famous Orion Nebula, the Carina Nebula is much less well known, due to its location far in the Southern Hemisphere. It was discovered by Nicolas Louis de Lacaille in 1751–52 from the Cape of Good Hope.

Within the large bright nebula is a much smaller feature, immediately surrounding Eta Carinae itself. This small nebula is known as the Homunculus Nebula (from the Latin meaning Little Man), and is believed to have been ejected in an enormous outburst in 1841 which briefly made Eta Carinae the second-brightest star in the sky.

Red Square Nebula

The Red Square Nebula is a celestial object located in the area of the sky occupied by star MWC 922. The first images of this bipolar nebula, taken using the Mt Palomar Hale telescope in California, were released in April 2007. It is notable for its square shape, which according to Sydney University astrophysicist Peter Tuthill, makes it one of the most symmetrical celestial objects ever discovered.

The explanation proposed by Tuthill and his collaborator James Lloyd of Cornell University claims that the shape arises from two cone shapes placed tip-to-tip. This also explains the "double-ring" structure seen in SN 1987A.

Towards the end of their lives, many low-mass stars, like the Sun, slough off their outer layers to produce striking 'planetary' nebulae. But the hot star at the heart of the Red Square nebula, called MWC 922, appears to be relatively massive, suggesting another process formed its signature shape.

In 2007, a finalist team in the Australian Sharemarket game was named after the renowned nebula. Due to the teams great performance and success, the nebula has been labeled a bringer of success and good luck. "We believed that from the Red Square Nebula's striking shape and rare display of symmetry that it would bring us good luck, and it did!" Quoted by one of members of the Red Square Team. Since the impressive performance of the team, many others have used the legendary nebula as a good luck charm including the newly formed "Red Square Wildlife Protection Agency" and a recently constructed yacht named "Red Square I".

Eskimo Nebula

The Eskimo Nebula (NGC 2392), also known as the Clownface Nebula or Caldwell 39, is a bipolar double-shell planetary nebula (PN). It was discovered by astronomer William Herschel in 1787. The formation resembles a person's head surrounded by a parka hood. It is surrounded by gas that composed the outer layers of a Sun-like star. The visible inner filaments are ejected by strong wind of particles from the central star. The outer disk contains unusual light-year long orange filaments.

NGC 2392 lies more than 2,870 light-years away and is visible with a small telescope in the constellation of Gemini.

Rosette Nebula

The Rosette Nebula (also known as Caldwell 49) is a large, circular H II region located near one end of a giant molecular cloud in theMonoceros region of the Milky Way Galaxy. The open cluster NGC 2244 (Caldwell 50) is closely associated with the nebulosity, the stars of the cluster having been formed from the nebula's matter.

The complex has the following NGC designations:

• NGC 2237 – Part of the nebulous region (Also used to denote whole nebula)
• NGC 2238 – Part of the nebulous region
• NGC 2239 – Part of the nebulous region (Discovered by John Herschel)
• NGC 2244 – The open cluster within the nebula (Discovered by John Flamsteed in 1690)
• NGC 2246 – Part of the nebulous region

The cluster and nebula lie at a distance of some 5,200 light years from Earth (although estimates of the distance vary considerably) and measure roughly 130 light years in diameter. The radiation from the young stars excite the atoms in the nebula, causing them to emit radiation themselves producing the emission nebula we see. The mass of the nebula is estimated to be around 10,000 solar masses.

It is believed that stellar winds from a group of O and B stars are exerting pressure on interstellar clouds to cause compression, followed by star formation in the nebula. This star formation is currently still ongoing.

A survey of the nebula with the Chandra X-ray Observatory in 2001 has revealed the presence of very hot, young stars at the core of the Rosette Nebula. These stars have heated the surrounding gas to a temperature in the order of 6 million kelvins causing them to emit copious amounts ofX-rays.