Another discovery, made by researchers from Louisiana State University, showed that the center of a nearby supernova remnant--the leftovers of an exploding star--named SNR 0509-67.5 lacks a companion star, perhaps providing another clue as to how supernovae originate.
LSU astronomers recently discovered the solution to a long-standing fundamental problem of astrophysics: what produces thermonuclear, or Type Ia, supernovae, which are tremendous explosions where the light is often brighter than a whole galaxy? LSU Professor of Physics & Astronomy Bradley Schaefer and graduate student Ashley Pagnotta have proven that these supernova are caused by a pair of white dwarf stars. Their results will appear in the Jan. 12 issue of Nature.
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“Thermonuclear stars are caused by white dwarf stars reaching a maximum mass where its carbon and oxygen constituents have a runaway explosion similar to an H-bomb,” said Schaefer. “The issue of determining their origin has been a fundamental problem in the field of astronomy.”
The LSU team’s solution represents the culmination of more than 40 years of worldwide study focused on this issue, often referred to as the “progenitor problem.” The possible types of precursor system types, called progenitors, were considered to be either a pair of white dwarfs in a close binary orbit that spiral into each other due to gravitational attraction (called the double-degenerate model) or another type of binary where the ordinary companion star in orbit around the white dwarf is feeding material onto the white dwarf until it reaches the critical mass (called the single-degenerate model). For decades the debate has raged, with no decisive evidence, and currently a roughly evenly divided opinion amongst astronomers.
“Many possible explanations have previously been suggested, and all but one of these requires that a companion star near to the exploding white dwarf be left behind after the explosion,” said Schaefer. “So, a possible way to distinguish between the various progenitor models is to look deep in the center of an old supernova remnant to find (or not find) the ex-companion star.”
The progenitor problem has increased greatly in importance over the last decade, to the point that the latest Decadal Review by the National Academy of Sciences placed the question among the top nine questions currently facing astronomy. The star system that produces the Type Ia thermonuclear supernova was previously determined to be a closely orbiting pair of white dwarf stars that spiraled inward for an explosive collision.
Schaefer and Pagnotta used images from the Hubble Space Telescope of a supernova remnant named SNR 0509-67.5 to illustrate the lack of any possible surviving companion star to the exploding white dwarf, allowing the rejection of all possible classes of progenitors except for the close pair of white dwarfs.
Any such result naturally requires extensive data processing and analysis as well as detailed theory calculations before it can be considered finalized. When finished, the central region of SNR 0509-67.5 (see Figure on attached fact sheet) was found to be starless to a very deep limit (visual magnitude 26.9). The faintest possible ex-companion star for all models (except the double degenerate) is a factor of 50 times brighter than the observed limit, and this makes for the rejection of all explanations except for the pair of white dwarf stars.
“The logic here is the same as expressed by Sherlock Holmes in ‘The Sign of the Four,’ that ‘when you have eliminated the impossible, whatever remains, however improbable, must be the truth,’” said Schaefer. “For SNR 0509-67.5, all but one model has been eliminated as impossible, so the one model remaining must be the truth.”
The finding is important because researchers theorize supernovae form when very dense, very small stars, called white dwarfs, explode. These explosions could be triggered by the merger of two white dwarfs--the so-called double-degenerate model--or by a companion star transferring mass to the white dwarf causing it to explode--the single-degenerate path.
SNR 0509-67.5 with optical and X-ray light from Hubble Space Telescope and the Chandra X-ray Observatory
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Credit: LSU
Scientists distinguish between double-degenerate and single-degenerate models by looking for the companion star that might have been near the exploding white dwarf. If the progenitor of the remnant--the exploding white dwarf--resulted from a single-degenerate model, then there should be a companion star still visible near the supernova remnant. If the progenitor resulted from a double-degenerate, then there will be no visible companion.
In the case of this discovery, researchers could not find a companion star.
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"Our NSF proposal is to help solve the Type Ia supernova progenitor problem, named one of the top nine questions in all astronomy [by the recent decadal review of the National Academy of Sciences]," said Brad Schaefer, coauthor of the study. "With this, we prove that SNR 0509-67.5 came from a double-degenerate system, where two white dwarfs in a close binary orbit slowly in-spiral until they collide and explode as a Type Ia supernova."
Type Ia supernova (SNe Ia) are thought to originate in the explosion of a white dwarf1. The explosion could be triggered by the merger of two white dwarfs2,3 ('double-degenerate' origin), or by mass transfer from a companion star4,5 (the 'single-degenerate' path). The identity of the progenitor is still controversial; for example, a recent argument against the single-degenerate origin6 has been widely rejected7-11. One way to distinguish between the double- and single-degenerate progenitors is to look at the center of a known SN Ia remnant to see whether any former companion star is present12,13.
A likely ex-companion star for the progenitor of Tycho's supernova has been identified14, but that claim is still controversial15-18. Here we report that the central region of the supernova remnant SNR 0509-67.5 (the site of a Type Ia supernova 400±50 years ago, based on its light echo19,20) in the Large Magellanic Cloud contains no ex-companion star to a limit of V=26.9 magnitude (MV=+8.4) within the extreme 99.73% region with radius 1.43”. The lack of any ex-companion star to deep limits rules out all published single-degenerate models. The only remaining possibility is that the progenitor for this particular SN Ia was a double-degenerate system.
Contacts and sources:
Ashley Pagnotta, Louisiana State University, Department of Physics and Astronomy
Prof. Bradley E. Schaefer, Louisiana State University, Department of Physics and Astronomy
Louisiana State University
LSU astronomers recently discovered the solution to a long-standing fundamental problem of astrophysics: what produces thermonuclear, or Type Ia, supernovae, which are tremendous explosions where the light is often brighter than a whole galaxy? LSU Professor of Physics & Astronomy Bradley Schaefer and graduate student Ashley Pagnotta have proven that these supernova are caused by a pair of white dwarf stars. Their results will appear in the Jan. 12 issue of Nature.
SNR 0509-67.5, the Type Ia supernova remnant in the Large Magellanic Cloud. This image was created using data from the Hubble Space Telescope. (HST). The large, diaphanous ellipse is the now-tenuous gas shell ejected by the supernova 400 (±50) years ago. The circle in the middle marks the site of the explosion, and the size of the circle represents the maximum allowed position for any possible ex-companion star after accounting for its motion over the 400 years since the explosion. The error circle has no stars in it. (The nebulous object is a random far-background galaxy of no connection.) The lack of any possible ex-companion stars to deep HST limits rejects all single-degenerate progenitors.
Credit: LSU
“Thermonuclear stars are caused by white dwarf stars reaching a maximum mass where its carbon and oxygen constituents have a runaway explosion similar to an H-bomb,” said Schaefer. “The issue of determining their origin has been a fundamental problem in the field of astronomy.”
The LSU team’s solution represents the culmination of more than 40 years of worldwide study focused on this issue, often referred to as the “progenitor problem.” The possible types of precursor system types, called progenitors, were considered to be either a pair of white dwarfs in a close binary orbit that spiral into each other due to gravitational attraction (called the double-degenerate model) or another type of binary where the ordinary companion star in orbit around the white dwarf is feeding material onto the white dwarf until it reaches the critical mass (called the single-degenerate model). For decades the debate has raged, with no decisive evidence, and currently a roughly evenly divided opinion amongst astronomers.
“Many possible explanations have previously been suggested, and all but one of these requires that a companion star near to the exploding white dwarf be left behind after the explosion,” said Schaefer. “So, a possible way to distinguish between the various progenitor models is to look deep in the center of an old supernova remnant to find (or not find) the ex-companion star.”
The progenitor problem has increased greatly in importance over the last decade, to the point that the latest Decadal Review by the National Academy of Sciences placed the question among the top nine questions currently facing astronomy. The star system that produces the Type Ia thermonuclear supernova was previously determined to be a closely orbiting pair of white dwarf stars that spiraled inward for an explosive collision.
Schaefer and Pagnotta used images from the Hubble Space Telescope of a supernova remnant named SNR 0509-67.5 to illustrate the lack of any possible surviving companion star to the exploding white dwarf, allowing the rejection of all possible classes of progenitors except for the close pair of white dwarfs.
Any such result naturally requires extensive data processing and analysis as well as detailed theory calculations before it can be considered finalized. When finished, the central region of SNR 0509-67.5 (see Figure on attached fact sheet) was found to be starless to a very deep limit (visual magnitude 26.9). The faintest possible ex-companion star for all models (except the double degenerate) is a factor of 50 times brighter than the observed limit, and this makes for the rejection of all explanations except for the pair of white dwarf stars.
“The logic here is the same as expressed by Sherlock Holmes in ‘The Sign of the Four,’ that ‘when you have eliminated the impossible, whatever remains, however improbable, must be the truth,’” said Schaefer. “For SNR 0509-67.5, all but one model has been eliminated as impossible, so the one model remaining must be the truth.”
The finding is important because researchers theorize supernovae form when very dense, very small stars, called white dwarfs, explode. These explosions could be triggered by the merger of two white dwarfs--the so-called double-degenerate model--or by a companion star transferring mass to the white dwarf causing it to explode--the single-degenerate path.
Credit: LSU
Scientists distinguish between double-degenerate and single-degenerate models by looking for the companion star that might have been near the exploding white dwarf. If the progenitor of the remnant--the exploding white dwarf--resulted from a single-degenerate model, then there should be a companion star still visible near the supernova remnant. If the progenitor resulted from a double-degenerate, then there will be no visible companion.
In the case of this discovery, researchers could not find a companion star.
SNR 0519-69.0, the Type Ia supernova remnant in the Large Magellanic Cloud. This image was created using data from the Hubble Space Telescope (HST). The large, diaphanous ellipse is the now-tenuous gas shell ejected by the supernova 600 (±200) years ago. The circle in the middle marks the site of the explosion, and the size of the circle represents the maximum allowed position for any possible ex-companion star after accounting for its motion over the 600 years since the explosion. This circle has many stars in it. Any of the brighter stars inside this circle (all of which are main sequence stars) could be an ex-companion star as predicted by the supersoft source progenitor model. Alternatively, maybe none of these stars is the ex-companion star, because there is no ex-companion as predicted by the double degenerate progenitor model. Importantly, none of the stars in the circle are red giant or subgiant stars, as required by most of the single-degenerate progenitor models (including the symbiotic stars, recurrent novae, helium stars, and spin-up/spin-down systems). The nearest red giant and sub giant stars are marked by "RG" and "SG" in the picture. Thus, out of the many possible ideas for progenitors, only two remain possible for SNR 0519-69.0; the double degenerate model and the supersoft system progenitor model.
Credit: LSU
"Our NSF proposal is to help solve the Type Ia supernova progenitor problem, named one of the top nine questions in all astronomy [by the recent decadal review of the National Academy of Sciences]," said Brad Schaefer, coauthor of the study. "With this, we prove that SNR 0509-67.5 came from a double-degenerate system, where two white dwarfs in a close binary orbit slowly in-spiral until they collide and explode as a Type Ia supernova."
Type Ia supernova (SNe Ia) are thought to originate in the explosion of a white dwarf1. The explosion could be triggered by the merger of two white dwarfs2,3 ('double-degenerate' origin), or by mass transfer from a companion star4,5 (the 'single-degenerate' path). The identity of the progenitor is still controversial; for example, a recent argument against the single-degenerate origin6 has been widely rejected7-11. One way to distinguish between the double- and single-degenerate progenitors is to look at the center of a known SN Ia remnant to see whether any former companion star is present12,13.
A likely ex-companion star for the progenitor of Tycho's supernova has been identified14, but that claim is still controversial15-18. Here we report that the central region of the supernova remnant SNR 0509-67.5 (the site of a Type Ia supernova 400±50 years ago, based on its light echo19,20) in the Large Magellanic Cloud contains no ex-companion star to a limit of V=26.9 magnitude (MV=+8.4) within the extreme 99.73% region with radius 1.43”. The lack of any ex-companion star to deep limits rules out all published single-degenerate models. The only remaining possibility is that the progenitor for this particular SN Ia was a double-degenerate system.
Contacts and sources:
Ashley Pagnotta, Louisiana State University, Department of Physics and Astronomy
Prof. Bradley E. Schaefer, Louisiana State University, Department of Physics and Astronomy
Louisiana State University
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