Warwick/RAS: Dead Planets Can 'Broadcast' for Up to a Billion Years

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bystander
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Warwick/RAS: Dead Planets Can 'Broadcast' for Up to a Billion Years

Post by bystander » Thu Aug 08, 2019 8:21 pm

Dead Planets Can 'Broadcast' for Up to a Billion Years
University of Warwick, UK | Royal Astronomical Society | 2019 Aug 06

Astronomers are planning to hunt for cores of exoplanets around white dwarf stars by ‘tuning in’ to the radio waves that they emit.

In new research ... scientists have determined the best candidate white dwarfs to start their search, based upon their likelihood of hosting surviving planetary cores and the strength of the radio signal that we can ‘tune in’ to.

... the research ... assesses the survivability of planets that orbit white dwarfs, stars which have burnt all of their fuel and shed their outer layers, destroying nearby objects and removing the outer layers of planets. They have determined that the cores which result from this destruction may be detectable and could survive for long enough to be found from Earth.

The first exoplanet confirmed to exist was discovered orbiting a pulsar ... in the 1990s, using a method that detects radio waves emitted from the star. The researchers plan to observe white dwarfs in a similar part of the electromagnetic spectrum in the hope of achieving another breakthrough.

The magnetic field between a white dwarf and an orbiting planetary core can form a unipolar inductor circuit, with the core acting as a conductor due to its metallic constituents. Radiation from that circuit is emitted as radio waves which can then be detected by radio telescopes on Earth. The effect can also be detected from Jupiter and its moon Io, which form a circuit of their own.

However, the scientists needed to determine how long those cores can survive after being stripped of their outer layers. Their modelling revealed that in a number of cases, planetary cores can survive for over 100 million years and as long as a billion years. ...

Survivability of Radio-Loud Planetary Cores Orbiting White Dwarfs ~ Dimitri Veras, Alexander Wolszczan
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Re: Warwick/RAS: Dead Planets Can 'Broadcast' for Up to a Billion Years

Post by BDanielMayfield » Thu Aug 08, 2019 9:42 pm

I wondered how such a burnt out husk of a planet might be able to generate any radio signal at all so I dug deeper:
The magnetic field between a white dwarf and an orbiting planetary core can form a unipolar inductor circuit, with the core acting as a conductor due to its metallic constituents. Radiation from that circuit is emitted as radio waves which can then be detected by radio telescopes on Earth. The effect can also be detected from Jupiter and its moon Io, which form a circuit of their own.

However, the scientists needed to determine how long those cores can survive after being stripped of their outer layers. Their modelling revealed that in a number of cases, planetary cores can survive for over 100 million years and as long as a billion years.

The astronomers plan to use the results in proposals for observation time on telescopes such as Arecibo in Puerto Rico and the Green Bank Telescope in West Virginia to try to find planetary cores around white dwarfs.
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Re: Warwick/RAS: Dead Planets Can 'Broadcast' for Up to a Billion Years

Post by TheOtherBruce » Thu Aug 08, 2019 11:22 pm

Something struck me as odd in that quote. Why wouldn't a stripped planetary core last as long as any other planet? Could the release of pressure from the removed mantle layers cause the whole thing to disrupt? Is there something about the weird environment around a white dwarf that would cause a solid body to spiral in until it hits the Roche limit and then disrupts? Something even weirder?
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Re: Warwick/RAS: Dead Planets Can 'Broadcast' for Up to a Billion Years

Post by BDanielMayfield » Thu Aug 08, 2019 11:59 pm

TheOtherBruce wrote:
Thu Aug 08, 2019 11:22 pm
Something struck me as odd in that quote. Why wouldn't a stripped planetary core last as long as any other planet? Could the release of pressure from the removed mantle layers cause the whole thing to disrupt? Is there something about the weird environment around a white dwarf that would cause a solid body to spiral in until it hits the Roche limit and then disrupts? Something even weirder?
Which quote, and what specific statement are you referring to Bruce?

These "planetary cores" would be the remains of planets in orbits close enough to stars to have been engulfed by the star during its giant phase(s), but at a distance far enough from the star's center that it avoids the fate of spiraling completely in. Does this help answer your question?
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Re: Warwick/RAS: Dead Planets Can 'Broadcast' for Up to a Billion Years

Post by TheOtherBruce » Fri Aug 09, 2019 12:17 am

However, the scientists needed to determine how long those cores can survive after being stripped of their outer layers. Their modelling revealed that in a number of cases, planetary cores can survive for over 100 million years and as long as a billion years.
This bit. I was trying to visualise some mechanism where a planet big enough not to be completely destroyed by the initial white dwarf formation could still suffer a slight existence failure at a later date. None of the ideas I came up with sounded quite right.
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Re: Warwick/RAS: Dead Planets Can 'Broadcast' for Up to a Billion Years

Post by BDanielMayfield » Fri Aug 09, 2019 12:47 am

TheOtherBruce wrote:
Fri Aug 09, 2019 12:17 am
However, the scientists needed to determine how long those cores can survive after being stripped of their outer layers. Their modelling revealed that in a number of cases, planetary cores can survive for over 100 million years and as long as a billion years.
This bit. I was trying to visualise some mechanism where a planet big enough not to be completely destroyed by the initial white dwarf formation could still suffer a slight existence failure at a later date. None of the ideas I came up with sounded quite right.
Ah, see your point now. The only path to planetary destruction in such a case that I can think of would be continuing orbital decay. The same mechanism that causes black holes in tight orbits to spiral together must work on far less massive objects too.
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