Neregėtos naujai gimusios planetos maišo dulkes aplink jauną žvaigždę

Mūsų pasaulis toks nepastovus, kad kartais mėgsta žaisti slėpynių. 2017 m. astronomus nustebino didžiulis šešėlis, apėmęs dulkių ir dujų diską, supantį netoliese esančią jauną žvaigždę TW Hydrae. Šešėlį meta vidinis dulkių ir dujų diskas, šiek tiek pasviręs į išorinio disko plokštumą. Šešėlis gali būti aiškiai matomas tik todėl, kad sistema Žemėje yra pakreipta akis į veidą, todėl astronomai gali pamatyti diską iš paukščio skrydžio, kai šešėlis skrieja aplink diską kaip laikrodžio rodyklė.

Tačiau laikrodis turi dvi rodykles (valandoms ir minutėms), kurios šluoja skirtingu greičiu. Ir pasirodo, TW Hydrae taip pat. Astronomai naudojo Hablo, kad surastų antrą šešėlį, kylantį iš kito vidinio disko, pakrypusį link dviejų išorinių diskų. Todėl sistema atrodo vis sudėtingesnė, nes bent trys persidengiantys diskai yra šiek tiek pakreipti vienas kito atžvilgiu. Diskai yra nematomų planetų aplink žvaigždę tarpiniai serveriai. Kiekviena planeta savo gravitacine jėga traukia medžiagą šalia žvaigždės ir deformuoja tai, kas būtų idealiai plokščias blyno formos diskas, jei planetų ten nebūtų. Tai nenuostabu, nes mūsų Saulės sistemos planetos turi orbitines plokštumas, kurios viena nuo kitos skiriasi keliais laipsniais. TW Hydrae suteikia astronomams galimybę pamatyti, kaip mūsų saulės sistema galėjo atrodyti jos formavimosi metais.

Palyginus Hablo kosminio teleskopo nuotraukas, kurių skirtumas yra keleri metai, paaiškėjo du baisūs šešėliai, judantys prieš laikrodžio rodyklę per jauną žvaigždę TW Hydrae supantį dujų ir dulkių diską. Diskai Žemėje pasvirę akis į akį, taip astronomams suteikiant galimybę iš paukščio skrydžio matyti, kas vyksta aplink žvaigždę. Kairėje nuotraukoje, darytoje 2016 m., matomas tik vienas šešėlis [A] Jau 11:00. Šį šešėlį meta vidinis diskas, kuris yra šiek tiek pasviręs į išorinį diską ir blokuoja žvaigždžių šviesą. Paveikslėlyje kairėje rodomas antras šešėlis, atsiradęs iš kito tarpinio disko [C] 7:00 val., nufotografuotas 2021 m. Originalus vidinis diskas pažymėtas [B] šioje vėlesnėje laidoje. Šešėliai aplink žvaigždę sukasi skirtingu greičiu, pavyzdžiui, pagal laikrodžio rodyklę. Jie liudija apie dvi nematomas planetas, kurios į savo orbitas ištraukė dulkes. Dėl to jie šiek tiek atsiremia vienas į kitą. Tai matomos šviesos vaizdas, padarytas kosminio teleskopo vaizdo spektroradiometru. Pridėta sintetinė spalva, kuri padidina detales. Autoriai: NASA, ESA, STScI, John Debes (AURA / STScI ESA), Joseph DePasquale (STScI)

Hablo kosminis teleskopas seka šešėlių žaismą aplink planetą formuojantį diską

Jauna žvaigždė TW Hydrae vaidina „šešėlių lėles“ su jį stebinčiais mokslininkais[{” attribute=””>NASA’s Hubble Space Telescope.

In 2017, astronomers reported discovering a shadow sweeping across the face of a vast pancake-shaped gas-and-dust disk surrounding the red dwarf star. The shadow isn’t from a planet, but from an inner disk slightly inclined relative to the much larger outer disk – causing it to cast a shadow. One explanation is that an unseen planet’s gravity is pulling dust and gas into the planet’s inclined orbit.

Now, a second shadow – playing a game of peek-a-boo – has emerged in just a few years between observations stored in Hubble’s MAST archive. This could be from yet another disk nestled inside the system. The two disks are likely evidence of a pair of planets under construction.

TW Hydrae is less than 10 million years old and resides about 200 light-years away. In its infancy, our solar system may have resembled the TW Hydrae system, some 4.6 billion years ago. Because the TW Hydrae system is tilted nearly face-on to our view from Earth, it is an optimum target for getting a bull’s-eye-view of a planetary construction yard. 

The second shadow was discovered in observations obtained on June 6, 2021, as part of a multi-year program designed to track the shadows in circumstellar disks. John Debes of AURA/STScI for the European Space Agency at the Space Telescope Science Institute in Baltimore, Maryland, compared the TW Hydrae disk to Hubble observations made several years ago.

“We found out that the shadow had done something completely different,” said Debes, who is principal investigator and lead author of the study published in The Astrophysical Journal. “When I first looked at the data, I thought something had gone wrong with the observation because it wasn’t what I was expecting. I was flummoxed at first, and all my collaborators were like: what is going on? We really had to scratch our heads and it took us a while to actually figure out an explanation.” 

The best solution the team came up with is that there are two misaligned disks casting shadows. They were so close to each other in the earlier observation they were missed. Over time they’ve now separated and split into two shadows. “We’ve never really seen this before on a protoplanetary disk. It makes the system much more complex than we originally thought,” he said.

The simplest explanation is that the misaligned disks are likely caused by the gravitational pull of two planets in slightly different orbital planes. Hubble is piecing together a holistic view of the architecture of the system.

The disks may be proxies for planets that are lapping each other as they whirl around the star. It’s sort of like spinning two vinyl phonograph records at slightly different speeds. Sometimes labels will match up but then one gets ahead of the other.

“It does suggest that the two planets have to be fairly close to each other. If one was moving much faster than the other, this would have been noticed in earlier observations. It’s like two race cars that are close to each other, but one slowly overtakes and laps the other,” said Debes.

The suspected planets are located in a region roughly the distance of Jupiter from our Sun. And, the shadows complete one rotation around the star about every 15 years – the orbital period that would be expected at that distance from the star. 

Also, these two inner disks are inclined about five to seven degrees relative to the plane of the outer disk. This is comparable to the range of orbital inclinations inside our solar system. “This is right in line with typical solar system style architecture,” said Debes. 

The outer disk that the shadows are falling on may extend as far as several times the radius of our solar system’s Kuiper belt. This larger disk has a curious gap at twice Pluto’s average distance from the Sun. This might be evidence for a third planet in the system.

Any inner planets would be difficult to detect because their light would be lost in the glare of the star. Also, dust in the system would dim their reflected light. ESA’s Gaia space observatory may be able to measure a wobble in the star if Jupiter-mass planets are tugging on it, but this would take years given the long orbital periods.

The TW Hydrae data are from Hubble’s Space Telescope Imaging Spectrograph. The James Webb Space Telescope’s infrared vision may also be able to show the shadows in more detail.

Reference: “The Surprising Evolution of the Shadow on the TW Hya Disk” by John Debes, Rebecca Nealon, Richard Alexander, Alycia J. Weinberger, Schuyler Grace Wolff, Dean Hines, Joel Kastner, Hannah Jang-Condell, Christophe Pinte, Peter Plavchan and Laurent Pueyo, 4 May 2023, The Astrophysical Journal.
DOI: 10.3847/1538-4357/acbdf1

The Hubble Space Telescope is a project of international cooperation between NASA and ESA. NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.