"Long before it's in the papers"
May 06, 2015

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Image said to show planets forming

May 6, 2015
Courtesy of the University of Toronto
and World Science staff

A re­cent and fa­mous im­age from deep space is the first that shows plan­ets form­ing, ac­cord­ing to a stu­dy.

As­t­ro­phys­i­cists led by Dan­iel Ta­ma­yo of the Uni­vers­ity of To­ron­to con­clud­ed that fledg­ling plan­ets ex­plain cir­cu­lar gaps in a disk of dust and gas swirling around a young star called HL Tau.

This im­age sparked sci­en­tif­ic de­bate when it was re­leased last year, with re­search­ers ar­gu­ing over wheth­er new­ly form­ing plan­ets were re­spon­si­ble for gaps in the dust and gas swirling around the young star. (Cred­it At­a­cama Large Mil­lime­ter/­sub& Ar­ray (ALMA))


It “likely rep­re­sents the first im­age tak­en of the in­i­tial loca­t­ions of plan­ets dur­ing their forma­t­ion,” said Ta­ma­yo. “This could be an enor­mous step for­ward in our abil­ity to un­der­stand how plan­ets for­m.”

The im­age, tak­en last Oc­to­ber by the At­a­cama Large Mil­lime­ter/­sub­mil­lime­ter Ar­ray in Chile’s At­a­cama Des­ert, sparked a de­bate from the be­gin­ning over wheth­er it showed plan­ets form­ing.

If planets are there, they’re too small to be made out dir­ectly. Rat­her, their effects are vi­sible as they clear out ob­jects in the gaps through their gra­vity. 

Some sug­gested that the gaps, es­pe­cially the out­er three, could­n’t rep­re­sent plan­ets be­cause they are too close to­geth­er. Some al­so ar­gued that plan­ets mas­sive enough to carve such gaps should be scat­tered by the force of gra­vity and tossed out of the sys­tem.

Ta­ma­yo’s study in­stead sug­gests the gaps are ev­i­dence of plan­e­tary forma­t­ion be­cause the dis­tances be­tween them are con­sist­ent with what’s called a spe­cial res­o­nant con­figura­t­ion. In oth­er words, these plan­ets avoid crash­ing in­to each oth­er by hav­ing spe­cif­ic or­bit­al pe­ri­ods, or lengths of time per or­bit, so that they miss each oth­er. This is si­m­i­lar to how Plu­to has avoided Nep­tune for bil­lions of years even though their or­bits cross.

Ta­ma­yo cre­at­ed two videos to show how HL Tau would look in both “res­o­nant” and “non-res­o­nant” con­figura­t­ions. The sys­tem can be much more sta­ble in a res­o­nant con­figura­t­ion and it’s a nat­u­ral state to which plan­ets in the HL Tau sys­tem can mi­grate, said Ta­ma­yo. 

The sys­tem is es­ti­mat­ed as less than a mil­lion years old and about 36 bil­lion km (22 bil­lion miles) wide. It re­sides in the di­rec­tion of the con­stella­t­ion Tau­rus 450 light-years from Earth. A light-year is the dis­tance light trav­els in a year.

Since a thick shroud of dust and gas en­velops young sys­tems like HL Tau, they can’t be seen us­ing vis­i­ble light. AL­MA solves that by us­ing a se­ries of tele­scopes that pick up lower-energy light, which gets through the fog.

“We’ve disco­vered thou­sands of plan­ets around oth­er stars and a big sur­prise is that many of the or­bits are much more el­lip­ti­cal than those found in our so­lar sys­tem,” said Ta­ma­yo. This and fu­ture AL­MA disco­veries may be the key to con­nect­ing these new­found plan­ets to their orig­i­nal birth loca­t­ions, he added.

While the HL Tau sys­tem re­mains sta­ble in its rel­a­tively young age, Ta­ma­yo said over bil­lions of years it will act as a “tick­ing time bom­b.” Even­tu­ally the plan­ets will scat­ter, eject­ing some and leav­ing the re­main­ing bod­ies on el­lip­ti­cal or­bits like the ones found around old­er stars.

Our so­lar sys­tem does­n’t seem to have un­der­gone such a dra­mat­ic scat­tering, said Ta­ma­yo, but might be un­usu­al in that re­spect. “If fur­ther ob­serva­t­ions show these to be the typ­i­cal start­ing con­di­tions around oth­er stars, it would re­veal our so­lar sys­tem to be a re­markably spe­cial place,” he added.

The find­ings are to be pub­lished in the up­com­ing edi­tion of As­t­ro­phys­i­cal Jour­nal.


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A recent and famous image from deep space is the first that shows planets forming, according to a study. Astrophysicists led by Daniel Tamayo of the University of Toronto concluded that fledgling planets explain circular gaps in a disk of dust and gas swirling around a young star called HL Tau. It “likely represents the first image taken of the initial locations of planets during their formation,” said Tamayo. “This could be an enormous step forward in our ability to understand how planets form.” The image, taken last October by the Atacama Large Millimeter/submillimeter Array in Chile’s Atacama Desert, sparked a debate from the beginning over whether it showed planets forming. Some suggested that the gaps, especially the outer three, couldn’t represent planets because they are too close together. Some also argued that planets massive enough to carve such gaps should be scattered by the force of gravity and tossed out of the system. Tamayo’s study instead suggests the gaps are evidence of planetary formation because the distances between them are consistent with what’s called a special resonant configuration. In other words, these planets avoid crashing into each other by having specific orbital periods, or lengths of time per orbit, so that they miss each other. This is similar to how Pluto has avoided Neptune for billions of years even though their orbits cross. Tamayo created two videos to show how HL Tau would appear in both “resonant” and “non-resonant” configurations. The system can be much more stable in a resonant configuration and it’s a natural state to which planets in the HL Tau system can migrate, said Tamayo. The system is estimated as less than a million years old and about 36 billion km (22 billion miles) wide. It resides in the direction of the constellation Taurus 450 light-years from Earth. A light-year is the distance light travels in a year. Since a thick shroud of dust and gas envelops young systems like HL Tau, they can’t be seen using visible light. ALMA solves that by using a series of telescopes that pick up lower-energy light, which gets through the fog. “We’ve discovered thousands of planets around other stars and a big surprise is that many of the orbits are much more elliptical than those found in our solar system,” said Tamayo. This and future ALMA discoveries may be the key to connecting these newfound planets to their original birth locations, he added. While the HL Tau system remains stable in its relatively young age, Tamayo said over billions of years it will act as a “ticking time bomb.” Eventually the planets will scatter, ejecting some and leaving the remaining bodies on elliptical orbits like the ones found around older stars. Our solar system doesn’t seem to have undergone such a dramatic scattering, said Tamayo, but might be unusual in that respect. “If further observations show these to be the typical starting conditions around other stars, it would reveal our solar system to be a remarkably special place,” he added. The findings are to be published in the upcoming edition of Astrophysical Journal.