By Barbara Kennedy, Penn State
According to a wealth of new data from NASA’s X-ray Observatory, what scientists are calling a “supernova factory” has come to life in the Carnia Nebula, located a mere 7,500 light years from Earth. This discovery may help astronomers to better understand how some of the Milky Way Galaxy’s heaviest and youngest stars race through their lives and release newly-forged elements into their surroundings.
“The Carina Nebula is one of the best places we know about to study how young massive stars live and die,” said Leisa Townsley of Penn State, who led the large Chandra campaign to observe Carina. “Now, we have a compelling case that a supernova show in Carina has already begun.”
For example, it appears that some of the massive stars in Trumpler 15, a star cluster in Carina, already have been destroyed in supernova explosions. These explosions would explain the deficit of bright X-ray sources in Trumpler 15, one of the ten star clusters that make up the Carina complex. The discovery is being presented today at the 218th American Astronomical Society meeting in Boston, and it will be published in a special Astrophysical Journal Supplement issue devoted to the new Chandra observations of Carina.
Another outcome from the new Chandra survey of Carina is a new population of young massive stars. These stars had not been seen before because of obscuration, or because they are located outside well-studied clusters.
“We may have doubled the number of known young and massive stars in Carina by looking this long with Chandra,” said Matthew Povich of Penn State, first author of a paper on this new population. “Nearly all of these stars are destined to self-destruct in supernova explosions.”
Carina Nebula lies in the Sagittarius-Carina arm of the Milky Way. Long studied by telescopes in many wavelengths, this new view of Carina in X-rays from Chandra shows the massive star-forming region like never before. Chandra’s extraordinarily sharp vision has pinpointed over 14,000 young stars in this region, and a diffuse X-ray glow.
“There are fewer of the heaviest stars in Trumpler 15 than we would expect,” said Junfeng Wang of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., first author of a paper on this cluster. “These stars were likely between 20 and 40 times the mass of the Sun and would have exploded in the last few million years, which is very recent in cosmic terms.”
The detection of six possible neutron stars, the dense cores often left behind after stars explode in supernovas, is another clue indicating a supernova bonanza in Carina. One neutron star in Carina previously had been confirmed using XMM-Newton, Chandra, and other X-ray data. Neutron stars in star-forming regions are very difficult to spot because they are characterized by low-energy X-rays, which are easily absorbed by dust and gas. Therefore, any true neutron stars probably represent only a small fraction of the complete population. The diffuse emission observed by Chandra also supports the idea that supernovas already have erupted in Carina. Some of the diffuse X-ray emission almost certainly comes from the winds of massive stars, but some also may come from the remains of supernova explosions.
Undoubtedly the most famous constituent of the Carina Nebula is Eta Carinae, a massive, unstable star that may be on the verge of exploding as a supernova. When it does explode, it likely will be a spectacular — yet still safe — light in the Earth’s sky. These latest results suggest Eta Carinae is not alone in its volatility. “Supernovas aren’t just eye-catching events, but they release newly-forged elements like carbon, oxygen, and iron into their surroundings so they can join in the formation of new objects, like stars and planets,” said Townsley.
The Chandra survey has a large field of 1.4 square degrees, made of a mosaic of 22 individual Chandra pointings. A great deal of multiwavelength data have been used in this campaign including infrared observations from the Spitzer Space Telescope and the Very Large Telescope (VLT).
NASA’s Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA’s Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra’s science and flight operations from Cambridge, Mass.