The hunt for planet outside our Solar System – exoplanets – is one of the most rapidly growing fields in astronomy . Over the past few decades , more than 5,000 exoplanets have been observe and astronomer now estimate that on average there is at least one major planet per virtuoso in our galaxy .
Many current research efforts direct at detecting terra firma - alike planets suited for liveliness . These effort focalise on so - called “ main chronological succession ” wizard like our Sun – stars which are power by fusing hydrogen atoms into atomic number 2 in their cores , and remain static for billions of yr . More than 90 % of all known exoplanets so far have been detected around primary - sequence stars .
As part of an external team of astronomers , we analyse a star that looks much like our Sun will in billions of years ’ meter , and found it has a planet which by all right it should have devoured . Inresearchpublished today in Nature , we lay out the puzzle of this satellite ’s beingness – and propose some possible solutions .
Artistic depiction of a possible scenario in which Baekdu was initially a binary system consisting of a red giant star and a closely orbiting white dwarf star. The close proximity of these two stars allowed for the exchange of material between them, eventually resulting in their merger. In the foreground, we can see Planet Hella orbiting perilously close to the stellar couple, yet just far enough to withstand the impact of their explosive collision.Image: W. M. Keck Observatory/Adam Makarenko
A glimpse into our future: red giant stars
Just like man , stars undergo change as they age . Once a star has used up all its hydrogen in the core , the kernel of the star shrinks and the out envelope expands as the star cools .
In this “ red giant ” stage of phylogeny , ace can grow to more than 100 time their original sizing . When this happens to our Sun , in about 5 billion years , we anticipate it will arise so large it will engulf Mercury , Venus , and mayhap Earth .
Eventually , the gist becomes hot enough for the star to begin fusing atomic number 2 . At this stage the star flinch back to about 10 times its original sizing , and continues unchanging burning for tens of millions of days .
Sound waves inside a star can be used to determine whether it is burning helium.Image: Gabriel Perez Diaz / Instituto de Astrofisica de Canarias
We eff of hundreds of satellite orbiting red elephantine stars . One of these is called8 Ursae Minoris b , a planet with around the mass of Jupiter in an eye socket that keep it only about half as far from its whizz as Earth is from the Sun .
The planet was discover in 2015 by a team of Korean astronomers using the “ Doppler wobble ” proficiency , which measures the gravitational pull of the planet on the headliner . In 2019 , the International Astronomical Uniondubbedthe star Baekdu and the planet Halla , after the magniloquent stack on the Korean peninsula .
A planet that should not be there
Analysis of newfangled data about Baekdu collect by NASA ’s Transiting Exoplanet Survey Satellite ( TESS ) space telescope has yielded a surprising find . Unlike other red titan we have found host exoplanets on near - in orbit , Baekdu has already started fusing helium in its pith .
Using the techniques ofasteroseismology , which analyze wave inside stars , we can determine what cloth a star is burning . For Baekdu , the relative frequency of the waves unequivocally show up it has commenced burning helium in its core .
The find was puzzling : if Baekdu is burning helium , it should have been much bigger in the past times – so self-aggrandising it should have engulfed the planet Halla . How is it possible Halla pull round ?
If the star Baekdu used to be a binary, there are two scenarios which can explain the survival of the planet Halla.Graphic: Brooks G. Bays, Jr, SOEST/University of Hawai’i
As is often the case in scientific research , the first line of natural process was to rule out the most little account : that Halla never really live .
Indeed , some evident discoveries of satellite orbit red giant star using the Doppler wobble technique have later been show to be illusionscreated by longsighted - condition edition in the behavior of the star itself .
However , follow - up watching rule out such a false - positive scenario for Halla . The Doppler signaling from Baekdu has remained stable over the last 13 eld , and cheeseparing study of other indicant prove no other possible explanation for the signal . Halla is genuine – which reelect us to the question of how it survived engulfment .
Two stars become one: a possible survival scenario
Having confirmed the world of the satellite , we arrived at two scenarios which could explicate the situation we see with Baekdu and Halla .
At least half of all stars in our galaxy did not form in isolation like our Sun , but are part of binary systems . If Baekdu once was a binary star , Halla may have never faced the risk of engulfment .
A merger of these two star may have preclude the expanding upon of either star to a size of it prominent enough to engulf planet Halla . If one star became a cerise giant on its own , it would have engulfed Halla – however , if it merged with a companion lead it would jump directly to the helium - burn form without getting big enough to reach the satellite .
instead , Halla may be a relatively newborn major planet . The violent hit between the two stars may have produced a cloud of gas and dust from which the planet could have formed . In other words , the major planet Halla may be a recently born “ second coevals ” major planet .
Whichever account is right , the uncovering of a close-fitting - in major planet revolve a He - burn red gargantuan ace certify that nature finds ways for exoplanets to appear in place where we might least wait them .
This article is republished fromThe Conversationunder a Creative Commons license . translate theoriginal clause .
ExoplanetologyStar types
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