Artist's conception of a shock-interacting supernova. Successive eruptions of a massive star produce ejecta with different velocities: the blue ring corresponds to slowly moving layers which are punched by fast ejecta (red-to-yellow) which shoots out. Interaction of those gas masses is via radiating shock waves which produce enormous amounts of light. This explains the phenomenon of Superluminous Supernovae with minimum requirements to the energy budget of explosions. (Credit: Kavli IPMU). Large Size jpg / Medium size jpg
Absolute u-band light curves for a fast-fading SLSN-I SN 2010gx and for a slowly fading one PTF09cnd are shown together with two calculated light curves for models N0 and B0 (from the paper by Sorokina et al.), which demonstrates that the interacting scenario can explain both narrow and broad light curves. The light curve of the typical (with “normal” luminosity) SN Ic, SN 1994I, is plotted for comparison. (Credit: Kavli IPMU). Large Size jpg / Medium size jpg
In a unique study, an international team of researchers including
members from the Kavli Institute for the Physics and Mathematics of the
Universe (Kavli IPMU) simulated the violent collisions between
supernovae and its surrounding gas— which is ejected before a supernova
explosion, thereby giving off an extreme brightness.
Many supernovae have been discovered in the last decade with peak
luminosity one-to-two orders of magnitude higher than for normal
supernovae of known types. These stellar explosions are called
Superluminous Supernovae (SLSNe).
Some of them have hydrogen in their spectra, while some others
demonstrate a lack of hydrogen. The latter are called Type I, or
hydrogen-poor, SLSNe-I. SLSNe-I challenge the theory of stellar
evolution, since even normal supernovae are not yet completely
understood from first principles.
Led by Sternberg Astronomical Institute researcher Elena Sorokina,
who was a guest investigator at Kavli IPMU, and Kavli IPMU Principal
Investigator Ken’ichi Nomoto, Scientific Associate Sergei Blinnikov, as
well as Project Researcher Alexey Tolstov, the team developed a model
that can explain a wide range of observed light curves of SLSNe-I in a
scenario which requires much less energy than other proposed models.
The models demonstrating the events with the minimum energy budget
involve multiple ejections of mass in presupernova stars. Mass loss and
buildup of envelopes around massive stars are generic features of
stellar evolution. Normally, those envelopes are rather diluted, and
they do not change significantly the light produced in the majority of
supernovae.
In some cases, large amount of mass are expelled just a few years
before the final explosion. Then, the “clouds” around supernovae may be
quite dense. The shockwaves produced in collisions of supernova ejecta
and those dense shells may provide the required power of light to make
the supernova much brighter than a “naked” supernova without pre-ejected
surrounding material.
This class of the models is referred to as “interacting” supernovae.
The authors show that the interacting scenario is able to explain both
fast and slowly fading SLSNe-I, so the large range of these intriguingly
bright objects can in reality be almost ordinary supernovae placed into
extraordinary surroundings.
Another extraordinarity is the chemical composition expected for the
circumstellar “clouds.” Normally, stellar wind consists of mostly
hydrogen, because all thermonuclear reactions happen in the center of a
star, while outer layers are hydrogenous.
In the case of SLSNe-I, the situation must be different. The
progenitor star must lose its hydrogen and a large part of helium well
before the explosion, so that a few months to a few years before the
explosion, it ejects mostly carbon and oxygen, and then explode inside
that dense CO cloud. Only this composition can explain the spectral and
photometric features of observed hydrogen-poor SLSNe in the interacting
scenario.
It is a challenge for the stellar evolution theory to explain the
origin of such hydrogen- and helium-poor progenitors and the very
intensive mass loss of CO material just before the final explosion of
the star. These results have been published in a paper accepted by The
Astrophysical Journal.
Details of the paper were published in September’s The Astrophysical Journal.
Paper Details:
Journal:
The Astrophysical Journal
Title:
Type I Super-luminous Supernovae as Explosions inside Non-Hydrogen Circumstellar Envelopes
Authors:
E.I. Sorokina (1), S.I. Blinnikov (2), K. Nomoto (3), R. Quimby (4), and A. Tolstov (5)
- Elena Sorokina, Sternberg Astronomical Institute, Moscow State University, GSP-1, Leninskie Gory, 119991 Moscow, Russia
- S. I. Blinnikov, Institute for Theoretical and Experimental Physics, 117218 Moscow, Russia
- Ken’ichi Nomoto, Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo Institutes for Advanced Study, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8583, Japan
- Robert Quimby, Cahill Center for Astrophysics, California Institute of Technology, 1200 E. California Blvd., MC 249-17 Pasedena, CA 91125
- Alexey Tolstov, Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo Institutes for Advanced Study, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8583, Japan
Paper abstract
(The Astrophysical Journal): Link
arXiv.org: 1510.00834, October 2015.
Research contact:
Ken’ichi Nomoto
Principal Investigator and Project Professor
Kavli Institute for the Physics and Mathematics of the Universe
TEL: +81-04-7136-6567
E-mail: nomoto@astron.s.u-tokyo.ac.jp
Alexey Tolstov
Project Researcher
Kavli Institute for the Physics and Mathematics of the Universe
E-mail: alexey.tolstov@ipmu.jp
Useful links: The Astrophysical Journal
Related links: Kavli IPMU press release: “Magnetar could have boosted explosion of extremely bright supernova”
All images, including those of some of the authors, can be downloaded from here.
