Carnegie: New Technique Reveals Supernova Progenitor

[bystander]

Carnegie: New Technique Reveals Supernova Progenitor

[url=https://carnegiescience.edu/sn_2013cu][b][i]SN 2013cu[/i][/b][/url] [b][i](Courtesy of Avishay Gal-Yam of the Weizmann Institute of Science)[/i][/b]

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Wolf-Rayet stars are very large and very hot. Astronomers have long wondered whether Wolf-Rayet stars are the progenitors of certain types of supernovae. New work from the Palomar Transient Factory team, including Carnegie’s Mansi Kasliwal, is homing in on the answer. They have identified a Wolf-Rayet star as the likely progenitor of a recently exploded supernova. This work is published by Nature.

Wolf-Rayet stars are notable for having strong stellar winds and being deficient in hydrogen when compared with other stars. Taken together, these two factors give Wolf-Rayet stars easily recognizable stellar signatures.

It is thought that Wolf-Rayet stars explode as type IIb, Ib or Ic supernovae. Yet, direct evidence linking these types of supernovae to their progenitor stars has heretofore been missing. ...

A Wolf–Rayet-like progenitor of SN 2013cu from spectral observations of a stellar wind - Avishay Gal-Yam et al

• Nature 509(7501) 471 (22 May 2014) DOI: 10.1038/nature13304

[Ann]

The news about finding out about the supernova progenitor is really very interesting. Thank you, bystander!

I was, however, surprised at this:

Wolf-Rayet stars are very large and very hot.

Wolf-Rayet stars are indeed very hot. They have blown off their outer layers, revealing parts of their even hotter interiors. All stars that blow off parts of their outer layers and reveal parts of their interiors are hot.

Credit:B.J. Mochejska, J. Kaluzny (CAMK),
1m Swope Telescope

Consider the HR diagram of globular cluster M55. In this diagram, the stars are hotter the farther to the left they are, and they are redder the farther to the right they are. They are also brighter the higher up they are, and fainter the lower down they are. Note that the red giants get brighter the redder they are. That is because the reddest, coolest red giants are also the largest by far. Note, however, that the horizontal branch stars get fainter the bluer they are. That is because the horizontal branch stars are comparatively small, and the hotter they get, the more they have shrunk. The very hottest stars in this diagram are some of the white dwarfs, however, and they are very, very small indeed.

A Wolf-Rayet star is like a gigantic version of a star turning into a white dwarf. Both are losing huge amounts of mass. Both are revealing their inner layers. Both are hotter than they were before the tremendous mass-loss started. The star turning into a white dwarf is most certainly smaller than it was. I would be most surprised if the same thing was not true about the Wolf-Rayet star.

Of course, the expelled outer layers must go somewhere. As can be seen in today's APOD, the expelled gases may form a tremendous halo around the star losing mass. If a similar enormous halo somehow gets involved in the supernova explosion of a Wolf-Rayet star, then I can certainly imagine that the explosion might be titanic.

Ann