PILLARS OF CREATION IN A STAR-FORMING REGION (Gas Pillars in M16 - Eagle Nebula)
Undersea corral? Enchanted castles? Space serpents? These eerie, dark pillar-like structures are actually columns of cool interstellar hydrogen gas and dust that are also incubators for new stars. The pillars protrude from the interior wall of a dark molecular cloud like stalagmites from the floor of a cavern. They are part of the "Eagle Nebula" (also called M16 -- the 16th object in Charles Messier's 18th century catalog of "fuzzy" objects that aren't comets), a nearby star-forming region 7,000 light-years away in the constellation Serpens.
The pillars are in some ways akin to buttes in the desert, where basalt and other dense rock have protected a region from erosion, while the surrounding landscape has been worn away over millennia. In this celestial case, it is especially dense clouds of molecular hydrogen gas (two atoms of hydrogen in each molecule) and dust that have survived longer than their surroundings in the face of a flood of ultraviolet light from hot, massive newborn stars (off the top edge of the picture). This process is called "photoevaporation. "This ultraviolet light is also responsible for illuminating the convoluted surfaces of the columns and the ghostly streamers of gas boiling away from their surfaces, producing the dramatic visual effects that highlight the three-dimensional nature of the clouds. The tallest pillar (left) is about a light-year long from base to tip.
As the pillars themselves are slowly eroded away by the ultraviolet light, small globules of even denser gas buried within the pillars are uncovered. These globules have been dubbed "EGGs." EGGs is an acronym for "Evaporating Gaseous Globules," but it is also a word that describes what these objects are. Forming inside at least some of the EGGs are embryonic stars -- stars that abruptly stop growing when the EGGs are uncovered and they are separated from the larger reservoir of gas from which they were drawing mass. Eventually, the stars themselves emerge from the EGGs as the EGGs themselves succumb to photoevaporation.
The picture was taken on April 1, 1995 with the Hubble Space Telescope Wide Field and Planetary Camera 2. The color image is constructed from three separate images taken in the light of emission from different types of atoms. Red shows emission from singly-ionized sulfur atoms. Green shows emission from hydrogen. Blue shows light emitted by doubly- ionized oxygen atoms.
Few pictures of the heavens have intrigued earthlings as much as a 1995 photograph of the Eagle Nebula, with its soaring star factories dubbed the Pillars of Creation. Here was star birth in action, all captured in vivid color by the Hubble Space Telescope.
Astronomers always knew it wouldn't last.
And the latest research shows that the Pillars are burning themselves out more quickly than first thought. Where the majestic structures of starlit gas and dust now soar into space, marking the architecture of a stellar womb, nothing but a few stars and black emptiness will reign in less than a million years.
Meanwhile, a mystery remains: Does the Eagle really have eggs in its nest that will become stars before the whole nursery is blown away forever? Will the Pillars of Creation live up to their name? Another new study suggests they will.able -->
Time is running out
The Eagle Nebula, also called M16, is a classic star forming region, a place roughly 7,000 light-years from Earth where gas and dust are thought to feed the birth of new stars. Several hot young stars born in the process now live just outside the Pillars, physically sculpting the colorful structures with intense ultraviolet light.
It's a scene repeated countless times in countless locations throughout the Milky Way galaxy and in other galaxies.
While the original Hubble image was revealing, in truth it raised more questions than it answered. The photograph was produced in visible light, which could not peer through the outer reaches of the nebula's dust.
Since then, astronomers have used infrared and radio telescopes to gain glimpses inside. In the late 1990s, they confirmed previous suspicions that the structures were burning out and might have only a million or so years to go.
The most recent study on the topic involves infrared views taken by Hubble in 1998 and released last month.
"The infrared images just show that this process is much further along in M16 than is evident in the optical pictures," said the University of Arizona's Rodger Thompson, who led the new study.
When seen at infrared wavelengths, which reveal heat emissions but not visible light, the Pillars "are quite transparent with only the tops being dense areas," Thompson told SPACE.com. "The tops are like capstones and are the only areas where star formation is proceeding at this time."
The Eagle Nebula created its first stars about 3 million years ago -- very recent by astronomical standards. Ever since, radiation from the hottest of those stars, a cluster of which are near the Pillars, has been breaking apart the dust and molecules that formed their cocoon. It's a little like the Sun evaporating water on a wet street, Thompson explained.
So how long do the Pillars have?
"It is hard to estimate the end point," he said, "but it will probably be in less than a million years, since most of the material has already been dissipated."
And then what will the region look like?
"There will just be the stars that formed before the Pillars dissipated," Thompson said. "The density of stars will be higher than average, but otherwise it will look just like any other place in the galaxy."
Thompson worked with Bradford A. Smith of the University of Hawaii and Jeff Hester of Arizona State, producing a paper that will be published in an upcoming issue of the Astrophysical Journal.
Cracking the EGGs
Another research team recently examined stars inside the Pillars at infrared wavelengths using a ground-based telescope. Mark McCaughrean and Morten Andersen, both of the Astrophysical Institute Potsdam, Germany, looked into M16 with the 27-foot (8.2-meter) Very Large Telescope at the European Southern Observatory's Paranal Observatory in Chile.
Their results, which were released in December and will be published in the European journal Astronomy & Astrophysics, similarly confirm the short life span of the nursery, though McCaughrean reiterated that predicting a specific time of death is difficult.
In an e-mail interview, McCaughrean discussed one of the great remaining mysteries of the Pillars and their fate inside the Eagle Nebula.
"The important question is whether the famous Pillars of Creation will manage to live up to their name, and actually form any stars before being obliterated, or are they just tattered remnants of the molecular clouds that formed the big cluster, blowing prettily in the wind before being ionized off into the sunset?"
To answer this question, McCaughrean and Andersen made some of the most detailed observations ever of globs of material inside the nebula, called evaporating gaseous globules, or EGGs.
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Jeff Hester first proposed that these structures were, almost literally, eggs -- cocoons in which young stars are incubating. Dozens of them cling to the edges of the Pillars, protruding like warts. Each is about to unveil its contents as it breaks away from the main structure.
But what will be inside? Proof has been lacking that the EGGs have star-stuff in them; the visible-light Hubble images could not see inside the globules. Astronomers want to know, because M16 is thought to be representative of many star-forming regions and its dynamics could bear on the prevalence of planets in our galaxy.
The new infrared pictures reveal that out of 73 EGGs, at least 11 appear to have something inside. Equally important, McCaughrean says, there is evidence for several other newborn stars unassociated with the EGGs, still obscured within very dense dust shells.
Some of the embryos are rather wimpy, however, and will not do well. They'll be born, but then they will linger as giant yet dim gaseous objects, much bigger than planets but just shy of stardom. Brown dwarfs, they'll be called.
"If there are stars in those EGGs, then they're going to have a very rough ride as their cocoons get blasted away," McCaughrean said. "They'll have less material to gather up, making them smaller in mass than expected, and if they have circumstellar disks around them, they might find it hard to form planets."
Circumstellar disks are flat, rotating seas of gas and dust, the remains of star formation. One such disk provided the raw material for planets, asteroids and comets in our solar system. Other studies are seeking to learn how common the process is elsewhere.
More study needed
Further study of the Eagle Nebula should reveal additional details about what's going on inside, near the top of the Pillars, where the dust is densest. That, however, will require other and more powerful telescopes.
"To wring out even the most embedded, youngest sources lurking deep in the dust beyond the reach of near-infrared wavelengths, we need a combination of the Next Generation Space Telescope (NGST) and the Atacama Large Millimeter Array (ALMA), to make detailed images of the pillars at mid-infrared and millimeter wavelengths," McCaughrean said.
The NGST, tentatively slated for launch in 2009, would be a cooperation between NASA, the European Space Agency and the Canadian Space Agency. ALMA is to go online at about the same time, and will be built in Chile by a European, American, and Japanese consortium.