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Post Info TOPIC: J0923+3028
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Title: The ELM Survey. I. A Complete Sample of Extremely Low Mass White Dwarfs
Authors: Warren R. Brown, Mukremin Kilic, Carlos Allende Prieto, Scott J. Kenyon

We analyse radial velocity observations of the 12 extremely low-mass <0.25 Msol white dwarfs (WDs) in the MMT Hypervelocity Star Survey. Eleven of the 12 WDs are binaries with orbital periods shorter than 14 hours; the one non-variable WD is possibly a pole-on system among our non-kinematically selected targets. Our sample is unique: it is complete in a well-defined range of apparent magnitude and colour. The orbital mass functions imply that the unseen companions are most likely other WDs, although neutron star companions cannot be excluded. Six of the 11 systems with orbital solutions will merge within a Hubble time due to the loss of angular momentum through gravitational wave radiation. The quickest merger is J0923+3028, a g=15.7 ELM WD binary with a 1.08 hr orbital period and a <130 Myr merger time. The chance of a supernova Ia event among our ELM WDs is only 1%-7%, however. Three binary systems (J0755+4906, J1233+1602, and J2119-0018) have extreme mass ratios and will most likely form stable mass-transfer AM CVn systems. Two of these objects, SDSS J1233+1602 and J2119-0018, are the lowest surface gravity WDs ever found; both show Ca II absorption likely from accretion of circumbinary material. We predict that at least one of our WDs is an eclipsing detached double WD system, important for constraining helium core WD models.

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Blobrana


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The binary star system J0923+3028 consists of two white dwarfs that are gradually spiraling in toward each other. In about 100 million years they will merge. Since their combined mass is too low to result in a supernova (i.e. less than the Chandrasekhar limit), a single, more massive white dwarf will be left after the merger. Nuclear fusion of a shell of material on the surface will result in a flash of light like a supernova but fainter.
(Credit: Clayton Ellis, Harvard-Smithsonian Centre for Astrophysics)

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Blobrana


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Astronomers Discover Merging Star Systems that Might Explode

Sometimes when you're looking for one thing, you find something completely different and unexpected. In the scientific endeavor, such serendipity can lead to new discoveries. Today, researchers who found the first hypervelocity stars escaping the Milky Way announced that their search also turned up a dozen double-star systems. Half of those are merging and might explode as supernovae in the astronomically near future.
All of the newfound binary stars consist of two white dwarfs. A white dwarf is the hot, dead core left over when a sun-like star gently puffs off its outer layers as it dies. A white dwarf is incredibly dense, packing as much as a sun's worth of material into a sphere the size of Earth. A teaspoon of it would weigh more than a ton.
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