Stellar cannibalism transforms star into brown dwarf

Stellar cannibalism transforms star into brown dwarf
This image shows the white dwarf (right) stripping mass from the brown dwarf. Credit: Rene Breton, University of Manchester.

Astronomers have detected a sub-stellar object that used to be a star, after being consumed by its white dwarf companion.

An international team of astronomers made the discovery by observing a very faint binary system, J1433 which is located 730 light-years away. The system consists of a low-mass object – about 60 times the mass of Jupiter – in an extremely tight 78-minute orbit around a white dwarf (the remnant of a star like our Sun).

Due to their close proximity, the white dwarf strips mass from its low-mass companion. This process has removed about 90 per cent of the mass of the companion, turning it from a star into a brown dwarf.

Most are 'failed ', objects that were born with too little mass to shine brightly by fusing hydrogen in their cores. By contrast, the brown dwarf in this system was born as a full-fledged star, but has been stripped to its current mass by billions of years of stellar cannibalism.

The study, published in the journal Nature, used the X-Shooter instrument at the Very Large Telescope (VLT) in Cerro Paranal, Chile, in order to directly detect and characterise a system that has survived such a traumatic transition.

Lead author Juan Venancio Hernández Santisteban, a PhD student at the University of Southampton, said: "X-Shooter is a unique instrument that can observe astronomical objects simultaneously all the way from the ultraviolet to the infrared. This allowed us to dissect the light of this system and uncover the hidden signal from the faint brown dwarf.

"Our knowledge of binary evolution suggests that, if the companion star can survive the transition, brown dwarfs should be common in this type of system. However, despite several efforts, only a few candidate systems with tentative evidence for brown-dwarf companions had previously been found. Our results now confirm that the successful transformation of a star to a brown dwarf is indeed possible."

The astronomers also used their data to map the surface temperature across the brown dwarf. This turns out to be non-uniform, since this cool sub-stellar object is strongly irradiated by its much hotter white dwarf companion. The map shows a clear temperature difference between the dayside (the side facing the white dwarf) and the nightside. On average, the difference amounts to 57 degrees Celsius, but the hottest and coldest parts of the brown dwarf's surface differ by a full 200 degrees Celsius.

Professor Christian Knigge, from the University of Southampton who initiated and supervised the project, said: "The construction of this surface temperature map is a significant achievement. In many giant planets – the so-called 'hot-Jupiters' – irradiation by the host star completely overwhelms the planet's internal heat flux. By contrast, internal heat flux and external irradiation are comparable for the brown dwarf in our study. This represents an unexplored regime, making such systems valuable as laboratories for irradiated (sub-) stellar and planetary atmospheres."

The study involved astronomers from the universities of Keele, Manchester, Oxford, Sheffield, Southampton and Warwick (UK), the Instituto de Astrofísica de Canarias (Spain) and Hamburger Sternwarte (Germany). It was funded by the Royal Astronomical Society, European Union Eleventh Framework Programme, European Research Council, CONACyT (Mexico) and the University of Southampton.

Explore further

Physicists discover rare brown dwarf, essential for testing theoretical models

More information: An irradiated brown dwarf companion to an accreting white dwarf, Nature, DOI: 10.1038/nature17952
Journal information: Nature

Citation: Stellar cannibalism transforms star into brown dwarf (2016, May 18) retrieved 23 September 2019 from
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May 19, 2016
"Most brown dwarfs are 'failed stars', objects that were born with too little mass to shine brightly by fusing hydrogen in their cores."

Magma - lava on Earth clearly shows that there is no fusion, and the weight has nothing to do with "to shine brightly." Brown dwarfs are less slowly rotating body (eg. rotation lasts 500 days).
In contrast brown dwarf standing white dwarf rapidly rotating body about an axis which is confirmed by very fast orbits a brown dwarf is a star in the making that is in complete contrast with the outdated assertions and hypotheses. http://www.svemir...e-causal

May 22, 2016
I would assume that eventually the white dwarf is going to pull the brown dwarf completely unto itself, this is likely to have the results of an event somewhere between Nova and Supernova as it would be more mass than what a white dwarf would normally throw off in a nova, coming all at once, and yet it is not the same compact pass as another white dwarf so it is not the type 1a supernova either.

It may be this type of system is not all that uncommon, just harder to detect, and my be responsible for specific novae and nebulae types and configurations.

The brown dwarf in question, being tidally locked and having an orbital period of 78 minutes means that it is rotating MUCH faster than wduckss seems to think it is and so blows THAT theory clean out of the water.

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