First Time White Dwarf Central Density Measured By Scientists

3C 397 (also referred as G41.1-0.3) is a Galactic supernova.
X-ray: NASA/CXC/Univ of Manitoba/S.Safi-Harb et al,
Optical: DSS, Infrared: NASA/JPL-Caltech

An international collaboration recently measured the central density of white dwarf just before exploding as a so-called Type Ia supernova. Using data obtained from the astronomical satellite XMM-Newton, they made observations of the supernova remnant 3C 397 and measured its central density.

The supernovae remnant 3C 397 may be a known Type Ia supernova remnant within the Milky Way. Previous data from Suzaku had suggested that the white dwarf star progenitor of 3C 397, before the supernova explosion, must have a mass near about of the Chandrasekhar mass limit (about 1.4 solar masses).

This motivated the team to perform follow-up observations of 3C 397 with XMM-Newton, utilizing the satellite’s enhanced angular resolution compared to Suzaku.

The key to the discovery is that the first-ever detection of neutron-rich isotopes like Titanium 50 & chromium 54 within the supernova remnant or debris. Higher-the central density of the exploding white-dwarf, the more efficient the pro-duction of those isotopes.

Left: X-ray image of the supernova remnant 3C 397. Red indicates spatial distribution of iron, green indicates spatial distribution of silicon, while blue is relative abundance of chromium compared to iron. A region rich in chromium (dark blue) might be seen in the southern part of the remnant. Right: X-ray spectrum of material within white circle shown in left-hand figure. Titanium, chromium, manganese & nickel were detected in addition to iron, which is the main element formed during a Type Ia supernova
(credit: ISAS/JAXA, Ohshiro et al.).

Scientists analyzed this relationship between the mass and isotopes. They then used it to find out that the central density of 3C 397’s progenitor was about 3x higher that of a typical Type Ia supernova progenitor.

This discovery adds to the mounting evidence for diversity in Type Ia supernovae, utilized in cosmology as distance indicators through the Universe.

For the study, scientists investigated the detailed spatial distribution of the heavy synthesized elements, specifically the local mass ratios of Ti, Cr, and other elements. They found a clumpy structure within the southern a part of the remnant where the mass ratio of Ti and Cr compared thereto of iron (Fe), and nickel (Ni) was abnormally high.

This is the 1st time that Ti has been detected from a kind Ia supernova or the remnant.

When they compared their results with models supported numerical calculations of supernovae nucleosynthesis, they found that the basic mass ratios observed in 3C 397 could only be achieved within the innermost region of white dwarfs with a mass-close about of the Chandrasekhar limit that have exceptionally high central densities. The central density according to the observed elements is about 5 x 109 g cm-3, which is 2 – 3x higher than the central densities(*5) that had been previously assumed.

In the future, scientists are looking forward to investigating the mass and central density of other white dwarfs before the supernova explosion. Doing so would allow them to characterize Type Ia supernovae in order that they will be used as standard candles” to calculate distances in Universe.

The international collaboration behind this new result included Kavli Institute for the Physics and arithmetic of the Universe (Kavli IPMU) Senior Scientist Ken’ichi Nomoto and California Institute of Technology Postdoctoral Scholar Shing-Chi Leung (former Kavli IPMU Project Researcher) and was led by Yuken Ohshiro, a second-year masters student at the University of Tokyo’s Graduate school of Science, working with Professor Hiroya Yamaguchi (ISAS).

The findings were reported on Astrophysical Journal.

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