Hubble Sees Stellar Block Party Rip-Up Neighborhood
All good parties, no matter how good-natured, will inevitably leave behind some damage -- and this also rings true for young stars letting off some steam in a star-forming nebula.
All good parties, no matter how good-natured, will inevitably leave behind some damage - and this also rings true for young stars letting off some steam in a star-forming nebula.
In this dazzling image from the NASA/ESA Hubble Space Telescope, stunning detail of an open cluster, called Trumpler 14, can be seen. Sparkling bright like diamonds are 2,000 young, massive stars that are pumping out incredible quantities of energy. The cluster is located around 8,000 light-years from Earth.
By cosmic standards, these stars are crazy-young, only 500,000 years old, but many are also very massive. Their mass dictates that the party for this young cluster will be short; quickly burning through their supply of hydrogen fuel and going out with a bang (supernova).
The brightest star in this Hubble observation is HD 93129Aa and holds the record as the hottest star in the Milky Way.
As the young stars party hard, they produce savagely-powerful stellar winds that slam into the surrounding cloud of dust and gas, generating shock waves and bursts of X-rays. These winds rip through the interstellar medium, carving out vast cavities in the nebula. This also has the effect of compressing gas clouds to spark the formation of more young stars.
These stars may be living fast and dying young, ripping their stellar nursery to shreds, but they also spawn the birth of more stars in their wake.
, this week, astronomers using data from NASA's Spitzer Space Telescope and Wide-field Infrared Survey Explorer (WISE) missions presented their findings of a special class of star and their associated "bow shocks." Here are a few of the stunning examples of "runaway stars" and their impact on interstellar gases.
Image: As seen by Spitzer, the star Kappa Cassiopeiae (HD 2905) is generating a dazzling infrared bow shock. The star's stellar wind and magnetic field are hitting the thin interstellar gases, highlighting the star's direction of travel (toward the lower right of the image).
As a boat cruises through the ocean, water at the bow of the vessel will be pushed against water flowing in the opposite direction. The resulting wave is descriptively known as a "bow wave," which trails away from the boat as it continues on its way. Now imagine a star, powering through the interstellar medium. That star is itself pumping out stellar gases. In the direction the star is travelling, the stellar winds buffer against the interstellar gases and a huge bow shock -- not too dissimilar to our boat analogy -- is generated. Depending on the conditions in the interstellar medium and the speed at which the star is moving, these shocks can be detected from Earth -- the heated gases are spotted via their infrared signature. This stunning Spitzer observation shows the striking detail that can be revealed in the bow shocks of some of the speediest stars. This particular example shows the star Zeta Ophiuchi (Zeta Oph) traveling at around 54,000 mph (24 kilometers
) relative to its surroundings. Runaways are a special type of star that is alone and the nature of their bow shock can reveal some information about their origins.
This observation is also of Zeta Oph but imaged by the WISE mission. The infrared signature as seen by WISE is more diffuse than the Spitzer view as cooler dust and gas is being detected by the space telescope's filters. The size and shape of a particular star's bow shock also reveals some information about the star's mass and speed. Zeta Oph is around 20 times more massive than our sun, generating more powerful stellar winds and is traveling faster. Its bow shock will therefore be more dramatic than anything our sun can generate. "Some stars get the boot when their companion star explodes in a supernova, and others can get kicked out of crowded star clusters," said William Chick from the University of Wyoming in Laramie, at the AAS meeting. "The gravitational boost increases a star's speed relative to other stars."
Interestingly, the researchers used archival data from both WISE and Spitzer to identify the presence of bow shocks throughout the galaxy, finding 200 candidate signals. Although some of the signals were in fact glowing star-formation nebulae, ground observatories confirmed that most were indeed caused by runaway stars. "We are using the bow shocks to find massive and/or runaway stars," said Henry "Chip" Kobulnicky, also from the University of Wyoming. "The bow shocks are new laboratories for studying massive stars and answering questions about the fate and evolution of these stars."
Another group of researchers, who also presented their results this week, are going about the "bow shock hunt" in a different way. "WISE and Spitzer have given us the best images of bow shocks so far," said Cintia Peri of the Argentine Institute of Radio Astronomy. "In many cases, bow shocks that looked very diffuse before, can now be resolved, and, moreover, we can see some new details of the structures." Peri's team is seeking out the speedy stars first and then finding their associate bow shocks after.
The diffuse glow of a star's bow shock can also be seen in this Spitzer observation. Of all the runaway stars identified in this new study, all ranged in mass from 8 to 30 solar masses.
Bow shocks haven't only been detected by WISE and Spitzer. WISE's predecessor, NASA's Infrared Astronomical Satellite (IRAS), scanned the whole sky in 1983 and identified the first glowing bow shocks emanating from runaway stars. Other missions, including the Hubble Space Telescope, have also spied the phenomenon, but not just from the speedy stars. In this stunning observation by Hubble, a very young star called LL Ori was spied with a very pronounced bow shock. As young stars evolve furiously, they generate very powerful stellar winds that ram into the surrounding gases inside their star forming nebulae -- in this case inside the star factory in the heart of the Orion nebula. The result of the collision of supersonic gases powering through the nebula can also create bow shocks, sans runaway star.