Despite being over 20 times the mass of the Sun and at least five times hotter, Wolf-Rayet stars are poorly understood. They are rare and often shrouded by other interstellar bodies, and their lifecycle has been enigmatic. Now, new data gathered by the intermediate Palomar Transient Factory survey has revealed that Wolf-Rayet stars meet their demise as Type IIb supernovae.
The survey scans the skies for supernovae and is carried out by the National Energy Research Scientific Computing Center and Energy Sciences Network at the U.S. Department of Energy's Lawrence Berkeley National Laboratory.
According to a Berkeley Lab statement, astronomers led by Gal-Yam of the Weizmann Institute of Science in Isreal observed supernova SN 2013cu mere hours after the explosion. They instructed telescopes on the ground and in space to gather further observations 5.7 and 15 hours after the explosion. SN 2013cu is located in the galaxy UGC 9379, 360 million light-years from Earth in the Bootes constellation. The supernova appeared as a new and very bright source of flue light in UGC 9379, indicating the demise of an enormous star.
"For the first time, we can directly point to an observation and say that this type of Wolf-Rayet star leads to this kind of Type IIb supernova," said Peter Nugent, head of the Berkeley Lab's Computational Cosmology Center.
Type 11b supernovae were first recognized in 1987, though their stellar progenitors remained elusive; now, the new findings show that at least some of them mark the deaths of massive Wolf-Rayet stars. Some supermassive stars change into Wolf-Rayet stars near the end of their lives. Such a star has long exhausted its supply of hydrogen and is fusing helium, carbon, oxygen, neon, sodium, magnesium, and other heavier elements to form iron and still heavier elements. Once its core becomes too massive, the star collapses and releases huge quantities of energy and neutrinos that drive a shockwave through the dying star, ejecting its outer layers into space in the event known as a supernova.
The Wolf-Rayet stage immediately precedes the supernova. The heavier elements created in the star's core bubble to the surface and generate strong winds that push material into space, blocking the view from telescopes. In the case of SN 2013cu, the astronomers happened to observe the supernova before the explosion had totally overtaken the winds; the winds were illuminated and heated by an ultraviolet flash from the shockwave moving through the star.
The identity of the dying star as a Wolf-Rayet was confirmed with light spectra obtained by the Keck Telescope in Hawaii. Over the following days, the astronomers called in other telescopes, which helped reveal the weak hydrogen signature and strong helium signature characteristic of a Type IIb supernova.
The new discovery has been published in the journal Nature.
Have something to say? Let us know in the comments section or send an email to the author. You can share ideas for stories by contacting us here.
Source : http://thespacereporter.com/2014/05/mysterious-stars-linked-to-supernova-death/
