From CfA: “First Discovery of a Binary Companion for a Type Ia Supernova”

Harvard Smithsonian Center for Astrophysics

Center For Astrophysics

March 22, 2016
Rebecca Johnson
The University of Texas at Austin
+1 512-475-6763

Christine Pulliam
Media Relations Manager
Harvard-Smithsonian Center for Astrophysics

The blue-white dot at the center of this image is supernova 2012cg, seen by the 1.2-meter telescope at Fred Lawrence Whipple Observatory. At 50 million light-years away, this supernova is so distant that its host galaxy, the edge-on spiral NGC 4424, appears here as only an extended smear of purple light. Peter Challis/Harvard-Smithsonian CfA

Whipple 1.2 meter telescope interior Harvard, located in Amado, Arizona on Mount Hopkins
Whipple 1.2 meter telescope interior Harvard, located in Amado, Arizona on Mount Hopkins

A team of astronomers including Harvard’s Robert Kirshner and Peter Challis has detected a flash of light from the companion to an exploding star. This is the first time astronomers have witnessed the impact of an exploding star on its neighbor. It provides the best evidence on the type of binary star system that leads to Type Ia supernovae. This study reveals the circumstances for the violent death of some white dwarf stars and provides deeper understanding for their use as tools to trace the history of the expansion of the universe. These types of stellar explosions enabled the discovery of dark energy, the universe’s accelerating expansion that is one of the top problems in science today.

The subject of how Type Ia supernovae arise has long been a topic of debate among astronomers.

“We think that Type Ia supernovae come from exploding white dwarfs with a binary companion,” said Howie Marion of The University of Texas at Austin (UT Austin), the study’s lead author. “The theory goes back 50 years or so, but there hasn’t been any concrete evidence for a companion star before now.”

Astronomers have battled over competing ideas, debating whether the companion was a normal star or another white dwarf.

“This is the first time a normal Type Ia has been associated with a binary companion star,” said team member and professor of astronomy J. Craig Wheeler (UT Austin). “This is a big deal.”

The binary star progenitor theory for Type Ia supernovae starts with a burnt-out star called a white dwarf. Mass must be added to that white dwarf to trigger its explosion – mass that the dwarf pulls off of a companion star. When the influx of mass reaches the point that the dwarf is hot enough and dense enough to ignite the carbon and oxygen in its interior, a thermonuclear reaction starts that causes the dwarf to explode as a Type Ia supernova.

For a long time, the leading theory was that the companion was an old red giant star that swelled up and lost matter to the dwarf, but recent observations have virtually ruled out that notion. No red giant is seen. The new work presents evidence that the star providing the mass is still burning hydrogen at its center, that is, that this companion star is still in the prime of life.

According to team member Robert P. Kirshner of the Harvard-Smithsonian Center for Astrophysics, “If a white dwarf explodes next to an ordinary star, you ought to see a pulse of blue light that results from heating that companion. That’s what theorists predicted and that’s what we saw.

“Supernova 2012cg is the smoking — actually glowing — gun: some Type Ia supernovae come from white dwarfs doing a do-si-do with ordinary stars.”

Located 50 million light-years away in the constellation Virgo, Supernova 2012cg was discovered on May 17, 2012 by the Lick Observatory Supernova Search. Marion’s team began studying it the next day with the telescopes of the Harvard-Smithsonian Center for Astrophysics.

“It’s important to get very early observations,” Marion said, “because the interaction with the companion occurs very soon after the explosion.”

The team continued to observe the supernova’s brightening for several weeks using many different telescopes, including the 1.2-meter telescope at Fred Lawrence Whipple Observatory and its KeplerCam instrument, the Swift gamma-ray space telescope, the Hobby-Eberly Telescope at McDonald Observatory, and about half a dozen others.

NASA/SWIFT Telescope
NASA/SWIFT Telescope

U Texas McDonald Observatory Hobby-Eberle 9.1 meter Telescope
U Texas McDonald Observatory Hobby-Eberle 9.1 meter Telescope

“This is a global enterprise,” Wheeler said. Team members hail from about a dozen U.S. universities, as well as institutions in Chile, Hungary, Denmark, and Japan.

What the team found was evidence in the characteristics of the light from the supernova that indicated it could be caused by a binary companion. Specifically, they found an excess of blue light coming from the explosion. This excess matches with the widely accepted models created by U.C. Berkeley astronomer Dan Kasen for what astronomers expect to see when a star explodes in a binary system.

“The supernova is blowing up next to a companion star, and the explosion impacts the companion star,” Wheeler explained. “The side of that companion star that’s hit gets hot and bright. The excess blue light is coming from the side of the companion star that gets heated up.”

Combined with the models, the observations indicate that the binary companion star has a minimum mass of six suns.

“This is an interpretation that is consistent with the data,” said team member Jeffrey Silverman, stressing that it is not concrete proof of the exact size of the companion, like would come from a photograph of the binary star system. Silverman is a postdoctoral researcher at UT Austin.

Only a few other Type Ia supernovae have been observed as early as this one, Marion said, but they have not shown an excess of blue light. More examples are needed.

“We need to study a hundred events like this and then we’ll be able to know what the statistics are,” Wheeler said.

The work is published today in The Astrophysical Journal.

This press release is being issued jointly with The University of Texas at Austin.

Other scientific institutions involved in this study:

University of Texas at Austin, 1 University Station C1400,
Austin, TX, 78712-0259, USA
2 Harvard-Smithsonian Center for Astrophysics, 60 Garden
St., Cambridge, MA 02138, USA;
3 George P. and Cynthia Woods Mitchell Institute for Fun-
damental Physics & Astronomy, Texas A. & M. University,
Department of Physics and Astronomy, 4242 TAMU, College
Station, TX 77843, USA
4 Department of Optics and Quantum Electronics, University
of Szeged, Domter 9, 6720, Szeged, Hungary
5 NSF Astronomy and Astrophysics Postdoctoral Fellow
6 Physics Department, Texas Tech University, Lubbock, TX ,
79409, USA
7 Department of Physics and Astronomy, Rutgers the State
University of New Jersey, 136 Frelinghuysen Road, Piscataway,
NJ 08854 USA
8 Department of Physics, Lehigh University, 16 Memorial
Drive East, Bethlehem, Pennsylvania 18015, USA
9 Department of Physics, Southern Methodist University,
Dallas, TX 75275, USA
10 Astronomy Department, University of Illinois at Urbana-
Champaign,1002 W. Green Street, Urbana, IL 61801 USA
11 Department of Physics, University of Illinois Urbana-
Champaign, 1110 W. Green Street, Urbana, IL 61801 USA
12 Center for Theoretical Physics and Department of Physics,
Massachusetts Institute of Technology, Cambridge, MA 02139
13 Department of Astronomy, University of California, Berke-
ley, CA 94720-3411, USA
14 Las Cumbres Observatory Global Telescope Network, 6740
Cortona Dr., Suite 102, Goleta, CA 93117, USA
15 Department of Physics, University of California, Santa
Barbara, Broida Hall, Mail Code 9530, Santa Barbara,CA
93106, USA
16 Carnegie Observatories, Las Campanas Observatory,
Colina El Pino, Casilla 601, Chile
17 Department of Physics and Astronomy, Aarhus University,
Ny Munkegade 120, DK-8000 Aarhus C, Denmark
18 Department of Astronomy, Kyoto University,
Kitashirakawa-Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan
19 Kavli Institute for the Physics and Mathematics of the
Universe (WPI), University of Tokyo, 5-1-5 Kashiwanoha,
Kashiwa, Chiba 277-8583, Japan
20 Department of Astrophysical Sciences, Peyton Hall, Prince-
ton University, Princeton, NJ 08544, USA
21 Department of Physics & Astronomy, Western Washington
University, 516 High Street, Bellingham, WA 98225

The science team (numbers refer to above institutions):

G. H. Marion1,2, Peter J. Brown3, Jozsef Vink´o1,4, Jeffrey M. Silverman1,5, David J. Sand6, Peter Challis2,
Robert P. Kirshner2, J. Craig Wheeler1, Perry Berlind2, Warren R. Brown2, Michael L. Calkins2,
Yssavo Camacho7,8, Govinda Dhungana9, Ryan J. Foley10,11, Andrew S. Friedman12,2, Melissa L. Graham13,
D. Andrew Howell14,15, Eric Y. Hsiao16,17, Jonathan M. Irwin2, Saurabh W. Jha7, Robert Kehoe9,
Lucas M. Macri3, Keiichi Maeda18,19, Kaisey Mandel2, Curtis McCully14, Viraj Pandya7,20, Kenneth J. Rines21,
Steven Wilhelmy21 and Weikang Zheng13

Other observatories included:
Las Cumbres Observatory Global Telescope Network
LCOGT Las Cumbres Observatory Global Telescope Network

Piszk´estet˝o Mountain Station of the Konkoly Observatory

Magellan Observatory
Magellan 6.5 meter telescopes
Baade and Clay telescopes

Caltech Palomar 1.5 meter 60 inch telescope interior

CfA Whipple 1.5 meter Tillinghast telescope
CfA Whipple 1.5 meter Tillinghast telescope

South African Large Telescope
SALT South African Large Telescope

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

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