Anne’s Image of the Day: Dust Pillar the “Spire”

 

March 21, 2014

The Spire, a dust pillar in the Eagle Nebula

The Spire, a dust pillar in the Eagle Nebul

Image Credit: NASA, ESA, and The Hubble Heritage Team STScI/AURA)

The Spire is a pillar of cold gas and dust – looking like a winged fairy-tale creature poised on a pedestal – of about 9.5 light-years high within the Eagle Nebula (Messier 16), located some 7,000 light-years away from Earth in the northern constellation of Serpens Cauda (Serpent’s Tail).

The Eagle Nebula contains several evaporating dust sculptures, such as this “Spire” and the “Pillars of Creation”. In fact, the Eagle Nebula is a giant evaporating shell of gas and dust inside of which is a growing cavity filled with a spectacular stellar nursery currently forming an open cluster of stars.

Stars in the Eagle Nebula are born in clouds of cold hydrogen gas that reside in chaotic neighborhoods, where energy from young stars sculpts fantasy-like landscapes in the gas. This tower may be a giant incubator for those newborn stars. A torrent of ultraviolet light from a band of massive, hot, young stars (off the top of the image) is eroding the pillar.

The starlight also is responsible for illuminating the tower’s rough surface. Streamers of gas can be seen boiling off this surface, creating the haze around the structure and highlighting its three-dimensional shape. The pillar is silhouetted against the background glow of more distant gas.

The edge of the dark hydrogen cloud at the top of the tower is resisting erosion; thick clouds of hydrogen gas and dust have survived longer than their surroundings in the face of a blast of ultraviolet light from the hot, young stars.

Inside the gaseous tower, stars may be forming. Some of those stars may have been created by dense gas collapsing under gravity. Other stars may be forming due to pressure from gas that has been heated by the neighboring hot stars.

The first wave of stars may have started forming before the massive star cluster began venting its scorching light. The star birth may have begun when denser regions of cold gas within the tower started collapsing under their own weight to make stars.

The bumps and fingers of material in the center of the tower are examples of these star-forming areas. These regions may look small but they are roughly the size of our Solar System. The fledgling stars continued to grow as they fed off the surrounding gas cloud. They abruptly stopped growing when light from the star cluster uncovered their gaseous cradles, separating them from their gas supply.

Ironically, the young cluster’s intense starlight may be inducing star formation in some regions of the tower. Examples can be seen in the large, glowing clumps and finger-shaped protrusions at the top of the structure. The stars may be heating the gas at the top of the tower and creating a shock front, as seen by the bright rim of material tracing the edge of the nebula at top, left. As the heated gas expands, it acts like a battering ram, pushing against the darker cold gas. The intense pressure compresses the gas, making it easier for stars to form. This scenario may continue as the shock front moves slowly down the tower.

This image was taken in November 2004 with the Advanced Camera for Surveys aboard the NASA/ESA Hubble Space Telescope, and was in scientifically re-assigned colors released in 2005 as part of the fifteenth anniversary celebration of the launch of the Hubble Space Telescope. The dominant colors in the image were produced by gas energized by the star cluster’s powerful ultraviolet light. The blue color at the top is from glowing oxygen. The red colon in the lower region is from glowing hydrogen. (The text is partly acquired from Spacetelescope.org.)

“Old Young” Stars in the Eagle Nebula

 

The early stages of a star’s life are critical both for the star and for any future planets that might develop around it. The process of star formation, once thought to involve just the simple coalescence of material under the influence of gravity, actually entails a complex series of stages, with the youngest stars assembling circumstellar disks of material, possibly preplanetary in nature. 

Messier 16, M16, NGC 6611, IC 4703

A composite infrared/optical image of the Eagle Nebula. The so-called “Pillars of Creation” can be seen at the center. Astronomers have discovered that the cluster of hot stars to the upper right contains many “old young” stars – stars that are still in their pre-main-sequence stage of life hosting circumstellar disks of material, but yet are about 16 million years old, many millions of years older than most other young stars in this first phase of life. Image Credit: ESO

In the current models, conservation of angular momentum during the collapse of cloud cores leads to the formation of these disks. The presence and evolution of these circumstellar disks is important both for the planets that form from them and for the star itself.

Stars start their lives by burning deuterium, an easier fuel to ignite than hydrogen (although it is less abundant). Stars that burn hydrogen are called main-sequence stars (the Sun is one), and they can continue in this stage of life for ten billion years or more depending on their mass (at least for stars of the Sun’s mass or less). Stars young enough to still primarily burn deuterium are called pre main-sequence stars, and this stage of their life typically lasts a few hundreds of thousands of years or less (also depending sensitively on the initial mass of the star).

The reason that circumstellar disks are so important for young stars (and not just for its planets) is because during the pre-main-sequence phase the star continues to grow in mass, and its growth comes from accreting gas from this disk. The time-scale of disk dissipation therefore sets crucial constraints for models of both star and planet development.

Understanding these early stages has been difficult for astronomers, in part because they take place in nurseries heavily obscured by dust, but they are critically important to an understanding of how our young Solar System and its planets were born and evolved.

CfA astronomer Mario Guarcello and three colleagues examined 110 stars located in the Eagle Nebula (associated with the so-called “Pillars of Creation,” a star forming region made famous by its dramatic Hubble portrait). These stars were red in color, typical of pre main-sequence stars, and like young stars they also showed evidence for accretion, but they were peculiar in being considerably less red than expected. The team analyzed the X-ray emission of the stars, their red color, total luminosity, and the abundance of certain elements.

The astronomers found convincingly that these pre main-sequence stars are old – in fact, around sixteen million years old and possibly as much as thirty million years old, making them the largest sample of such “old young” stars known. Besides improving our understanding of how stars develop, the team also determined the characteristic lifetime for the protoplanetary disks in these systems: it can last for about six million years, giving planets around such stars a longer time to form than had been imagined.

More information:

Pre-main-sequence Stars Older Than 8 Myr in the Eagle nebula,” Guido De Marchi, Nino Panagia, M. G. Guarcello, and Rosaria Bonito, MNRAS, 435, 3058, 2013

Source: Harvard-Smithsonian Center for Astrophysics (CfA)