These coronagraphic images of a disk around the star AU Microscopii, captured by Webb’s Near-Infrared Camera (NIRCam), show compass arrows, scale bar, and color key for reference. Image Credit: SCIENCE: NASA, ESA, CSA, Kellen Lawson (NASA-GSFC), Joshua E. Schlieder (NASA-GSFC)
IMAGE PROCESSING: Alyssa Pagan (STScI)
AU Microscopii is a small red dwarf star about 32 light-years away. It’s far too dim for the unaided human eye, but that doesn’t diminish its appeal. The star has at least two exoplanets and hosts a circumstellar debris disk.
It’s also young, only about 23 million years old, and it’s the second-closest pre-main sequence star to Earth. The JWST recently imaged the star and its surroundings and found something surprising.
An MIT-led team has discovered evidence of a giant impact in the nearby HD 17255 star system, in which an Earth-sized terrestrial planet and a smaller impactor likely collided at least 200,000 years ago, stripping off part of one planet’s atmosphere.
Credits:Image: Mark A. Garlick
Titanic collisions are the norm in young solar systems. Earth’s Moon was the result of one of those collisions when the protoplanet Theia collided with Earth some 4.5 billion years ago. The collision, or series of collisions, created a swirling mass of ejecta that eventually coalesced into the Moon. It’s called the Giant Impact Hypothesis.
Astronomers think that collisions of this sort are a common part of planet formation in young solar systems, where things haven’t settled down into predictability. But seeing any of these collisions around other stars has proved difficult.
IRS 63 Circumstellar Disk C. ALMA/ Segura-Cox et al. 2020
Unless you’re reading this in an aircraft or the International Space Station, then you’re currently residing on the surface of a planet. You’re here because the planet is here. But how did the planet get here? Like a rolling snowball picking up more snow, planets form from loose dust and gas surrounding young stars. As the planets orbit, their gravity draws in more of the lose material and they grow in mass. We’re not certain when the process of planet formation begins in orbit of new stars, but we have incredible new insights from one of the youngest solar systems ever observed called IRS 63.
The Rho Ophiuchi cloud complex is a nebula of gas and dust that is located in the constellation Ophiuchus. It is one of the closest star-forming regions to the Solar System and where the young star system IRS 63 was observed
Primordial Soup
Swirling in orbit of young stars (or protostars) are massive disks of dust and gas called circumstellar disks. These disks are dense enough to be opaque hiding young solar systems from visible light. However, energy emanating from the protostar heats the dust which then glows in infrared radiation which more easily penetrates obstructions than wavelengths of visible light. In fact, the degree to which a newly forming star system is observed in either visible or infrared light determines its classification. Class 0 protostars are completely enshrouded and can only be observed in submillimeter wavelengths corresponding to far-infrared and microwave light. Class I protostars, are observable in the far-infrared, Class II in near-infrared/red, and finally a Class III protostar’s surface and solar system can be observed in visible light as the remaining dust and gas is either blown away by the increasing energy of the star AND/OR has formed into PLANETS! That’s where we came from. That leftover material orbiting newly forming stars is what accumulates to form US. The whole process from Class 0 to Class III, when the solar system leaves its cocoon of dust and joins the galaxy, is about 10 million years. But at what stage does planet formation begin? The youngest circumstellar disks we’d observed are a million years old and had shown evidence that planetary formation had already begun. The recently observed IRS 63 is less than 500,000 years old – Class I – and shows signs of possible planet formation. The excitement? We were surprised to see evidence of planetary formation so early in the life of a solar system.
The young star IRS 63 has baby planets forming around it while the star itself is still forming. Image Credit: Segura-Cox et al, 2020.
It looks like we may have to update our theories on how stars and planets form in new solar systems. A team of astronomers has discovered young planets forming in a solar system that’s only about 500,000 years old. Prior to this discovery, astronomers thought that stars are well into their adult life of fusion before planets formed from left over material in the circumstellar disk.
Now, according to a new study, it looks like planets and stars can form and grow up together.
ALMA images of the planet-forming disk with misaligned rings around triple star system GW Orionis. The image on the right is made with ALMA data taken in 2017 from Bi et al. The image on the left is made with ALMA data taken in 2018 from Kraus et al.
Credit: ALMA (ESO/NAOJ/NRAO), S. Kraus & J. Bi; NRAO/AUI/NSF, S. Dagnello
Whatever we grow up with, we think of as normal. Our single solitary yellow star seems normal to us, with planets orbiting on the same, aligned ecliptic. But most stars aren’t alone; most are in binary relationships. And some are in triple-star systems.
And the planet-forming disks around those three-star systems can exhibit some misshapen orbits.
Artist's conceptualization of the dusty TYC 8241 2652 system as it might have appeared several years ago when it was emitting large amounts of excess infrared radiation. Credit: Gemini Observatory/AURA artwork by Lynette Cook. https://www.gemini.edu/node/11836
Astronomers like to observe young planets forming in circumstellar debris disks, the rotating rings of material around young stars. But when they measure the amount of material in those disks, they don’t contain enough material to form large planets. That discrepancy has puzzled astronomers.
The answer might come down to timing.
A new study suggests that planets form much quicker than astronomers think.
The brilliant tapestry of young stars flaring to life resembles a glittering fireworks display in this Hubble Space Telescope image. The sparkling centerpiece of this fireworks show is a giant cluster of thousands of stars called Westerlund 2. The cluster resides in a raucous stellar breeding ground known as Gum 29, located 20,000 light-years away from Earth in the constellation Carina. Hubble's Wide Field Camera 3 pierced through the dusty veil shrouding the stellar nursery in near-infrared light, giving astronomers a clear view of the nebula and the dense concentration of stars in the central cluster. The cluster measures between six light-years and 13 light-years across.
Credits: NASA, ESA, the Hubble Heritage Team (STScI/AURA), A. Nota (ESA/STScI) and the Westerlund 2 Science Team
Westerlund 2 is a star cluster about 20,000 light years away. It’s young—only about one or two million years old—and its core contains some of the brightest and hottest stars we know of. Also some of the most massive ones.
There’s something unusual going on around the massive hot stars at the heart of Westerlund 2. There should be huge, churning clouds of gas and dust around those stars, and their neighbours, in the form of circumstellar disks.
But in Westerlund 2’s case, some of the stars have no disks.
There’s an iconic scene in the original Star Wars movie where Luke Skywalker looks out over the desert landscape of Tatooine at the amazing spectacle of a double sunset. Now, a new study out of the National Radio Astronomy Observatory (NRAO) suggests that such exotic exoplanet worlds orbiting multiple stars may exist in misaligned orbits, far out of the primary orbital plane.
This is an artist’s impression of a white dwarf (burned-out) star accreting rocky debris left behind by the star’s surviving planetary system. It was observed by Hubble in the Hyades star cluster. At lower right, an asteroid can be seen falling toward a Saturn-like disk of dust that is encircling the dead star. Infalling asteroids pollute the white dwarf’s atmosphere with silicon. Credit: NASA, ESA, and G. Bacon (STScI)
About 570 light years from Earth lies WD 1145+017, a white dwarf star. In many respects it’s a typical white dwarf star. Its mass is about 0.6 solar masses, and its temperature is about 15,900 Kelvin. But five years ago, a team of astronomers wrote a paper on the white dwarf, showing that something unusual was going on.
Are baby planets responsible for the gaps and rings we’ve spotted in the disks that surround distant, young stars? Image Credit: C. Pinte et al, 2020
Astronomers like observing distant young stars as they form. Stars are born out of a molecular cloud, and once enough of the matter in that cloud clumps together, fusion ignites and a star begins its life. The leftover material from the formation of the star is called a circumstellar disk.
As the material in the circumstellar disk swirls around the now-rotating star, it clumps up into individual planets. As planets form in it, they leave gaps in that disk. Or so we think.
