Ageing stars could also be destroying their closest planets

Ageing stars could also be destroying the enormous planets orbiting closest to them, new analysis reveals – providing a glimpse into the potential destiny of the likes of Jupiter and Saturn in our personal photo voltaic system.

Once stars just like the Sun run out of hydrogen gas, they quiet down and broaden to turn out to be purple giants. In the Sun’s case this can occur in about 5 billion years.

In the brand new examine, revealed in Monthly Notices of the Royal Astronomical Society, researchers checked out practically half one million stars that had simply entered this “post-main sequence” section of their lives.

The staff of astronomers at University College London (UCL) and the University of Warwick recognized 130 planets and planet candidates (i.e., that also must be confirmed), together with 33 that had been beforehand unknown, orbiting intently round these stars.

They discovered such planets had been much less more likely to happen round stars that had expanded and cooled sufficient to be classed as purple giants (i.e. that had been additional on of their post-main sequence evolution), suggesting many of those planets might have already got been destroyed.

Lead writer Dr Edward Bryant, of Mullard Space Science Laboratory at UCL and the University of Warwick, stated: “This is strong evidence that as stars evolve off their main sequence they can quickly cause planets to spiral into them and be destroyed. This has been the subject of debate and theory for some time but now we can see the impact of this directly and measure it at the level of a large population of stars.

“We anticipated to see this impact however we had been nonetheless shocked by simply how environment friendly these stars appear to be at engulfing their shut planets.

“We think the destruction happens because of the gravitational tug-of-war between the planet and the star, called tidal interaction. As the star evolves and expands, this interaction becomes stronger.

“Just just like the Moon pulls on Earth’s oceans to create tides, the planet pulls on the star. These interactions gradual the planet down and trigger its orbit to shrink, making it spiral inwards till it both breaks aside or falls into the star.”

Co-author Dr Vincent Van Eylen, of Mullard Space Science Laboratory at UCL, said: “In a number of billion years, our personal Sun will enlarge and turn out to be a purple large. When this occurs, will the photo voltaic system planets survive? We are discovering that in some instances planets don’t.

“Earth is certainly safer than the giant planets in our study, which are much closer to their star. But we only looked at the earliest part of the post-main sequence phase, the first one or two million years of it – the stars have a lot more evolution to go.

“Unlike the lacking large planets in our examine, Earth itself would possibly survive the Sun’s purple large section. But life on Earth most likely wouldn’t.”

For their study, the researchers used data from NASA’s Transiting Exoplanet Survey Satellite (TESS). They used a computer algorithm to search for the repeated dips in brightness that indicate an orbiting planet is passing in front of the star, focusing on giant planets with short orbital periods (i.e., that took no more than 12 days to orbit their star).

The team began with more than 15,000 possible signals, and applied rigorous tests to rule out false signals, eventually whittling this number down to 130 planets and planet candidates. Of these, 48 were already known, 49 were already identified as planet candidates (i.e., they still need to be confirmed), and 33 were new candidates detected for the first time.

The team found that the more advanced a star’s evolution, the less likely it was to host a nearby giant planet.

The overall occurrence rate of such planets was measured at just 0.28%, with the youngest post-main sequence stars showing a higher rate (0.35%) similar to that of main sequence stars, and the most evolved stars, which had cooled and swelled enough to be classed as red giants, dropping to 0.11%. (For this analysis, the researchers excluded the smallest 12 of the 130 identified planets.)

From the TESS data, researchers can estimate the size (radius) of these possible planets. To confirm them as planets rather than planet candidates, astronomers must rule out the possibility of these bodies being low-mass stars or brown dwarfs (“failed stars” whose core pressure is not high enough to start nuclear fusion) by calculating their mass.

This can be done by precisely measuring the movements of their host stars and inferring the gravitational tug of the planets (and therefore their mass) from wobbles in these movements.

Dr Bryant added: “Once now we have these planets’ plenty, that may assist us perceive precisely what’s inflicting these planets to spiral in and be destroyed.”

The researchers received funding from the Science and Technology Facilities Council (STFC).

ENDS

Media contacts

Sam Tonkin

Royal Astronomical Society

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Dr Robert Massey

Royal Astronomical Society

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Mark Greaves

University College London

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Science contacts

Dr Edward Bryant

University of Warwick

[email protected]

Dr Vincent Van Eylen

University College London

[email protected]

Images & captions

Dying star engulfing a planet

Caption: This artist’s impression depicts a dying Sun-like star engulfing an exoplanet. New research published in Monthly Notices of the Royal Astronomical Society suggests that ageing stars may be destroying the giant planets orbiting closest to them.

Credit: International Gemini Observatory/NOIRLab/NSF/AURA/M. Garlick/M. Zamani

Further information

The paper ‘Determining the impact of post-main sequence stellar evolution on the transiting giant planet population’ by Edward M Bryant and Vincent Van Eylen has been published in Monthly Notices of the Royal Astronomical Society. DOI: 10.1093/mnras/staf1771.

Notes for editors

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