Astronomers spot hundreds of baby stars and planet-forming disks

Scientists using the Karl G. Jansky Very Large Array and the Atacama Large Millimeter/submillimeter Array have imaged more than 300 newborn stars and their protoplanetary disks. The material in these disks forms new planets. (Image credit: ALMA (ESO/NAOJ/NRAO), J. Tobin; NRAO/AUI/NSF, S. Dagnello)

Astronomers have imaged more than 300 newborn stars, revealing new clues about the early stages of star formation and the birth of planets.

In the new research, astronomers using the Karl G. Jansky Very Large Array (VLA) and the Atacama Large Millimeter/submillimeter Array (ALMA) studied hundreds of young stars surrounded by rings of dust and gas. These stellar infants lie in a dense star-forming region known as the Orion Molecular Cloud Complex.

The ring of dust and gas surrounding a young star, also known as a protoplanetary disk, supports the birth of new planets. Using the VLA and ALMA telescopes, the astronomers could peer through the dense clouds of dust and gas in the Orion Complex to see the protoplanetary disks forming around the infant stars, according to a statement from the National Radio Astronomy Observatory (NRAO).

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"This survey revealed the average mass and size of these very young protoplanetary disks," John Tobin, who led the survey team from the NRAO, said in the statement. "We can now compare them to older disks that have been studied intensively with ALMA as well."

The survey, called the VLA/ALMA Nascent Disk and Multiplicity (VANDAM), is the largest study of planet-forming disks around infant stars to date. Using this data, researchers identified young stars and their disks in various stages of formation.

Young stars, also known as protostars, form in dense clouds of gas and dust like the Orion Complex. When such a cloud collapses due to gravity, it forms a disk of material that continues to fuel the growth of a new star.

In turn, planets form from the leftover material in the disk surrounding the newborn star. The new images show that young protoplanetary disks tend to be more massive than older disks, because stars consume more material from their disk as they grow.

"This means that younger disks have a lot more raw material from which planets could form," Tobin said in the statement. "Possibly, bigger planets already start to form around very young stars."

Newly imaged protostars matched to their location in the Orion Molecular Clouds. (Image credit: ALMA (ESO/NAOJ/NRAO), J. Tobin; NRAO/AUI/NSF, S. Dagnello; Herschel/ESA)

Four of the young stars captured in the survey stood out from the rest, as they appeared to be "irregular or blobby," the researchers said. The strange shapes suggest that the stars are still in the very early stages of forming, because they do not yet have the flattened, rotating disk surrounding them or the strong outflow of material that are both characteristic of a protostar, the statement said.

"We rarely find more than one such irregular object in one observation," Nicole Karnath, one of the survey team members from the Stratospheric Observatory for Infrared Astronomy (SOFIA) Science Center, said in the statement. "We are not entirely sure how old they are, but they are probably younger than 10,000 years."

For an infant star, developing an outflow not only clears the surrounding dense cloud of material that would otherwise obscure it from view, but also prevents the star from spinning out of control as it grows.

However, little is known about how these outflows form. One of the four "irregular" stars surveyed, called HOPS 404, has one of the smallest outflows ever seen, shedding light on the earliest stages of star formation.

"It is a big, puffy sun that is still gathering a lot of mass but just started its outflow to lose angular momentum to be able to keep growing," Karnath said in the statement.

The findings contributed to two studies published Feb. 20 in The Astrophysical Journal.

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Samantha Mathewson joined Space.com as an intern in the summer of 2016. She received a B.A. in Journalism and Environmental Science at the University of New Haven, in Connecticut. Previously, her work has been published in Nature World News. When not writing or reading about science, Samantha enjoys traveling to new places and taking photos! You can follow her on Twitter @Sam_Ashley13.

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4 Comments Comment from the forums

rod

Admin said:
Astronomers have imaged more than 300 newborn stars, revealing new clues about the early stages of star formation and the birth of planets.

Astronomers spot hundreds of baby stars and planet-forming disks : Read more

The article stated ""This survey revealed the average mass and size of these very young protoplanetary disks," John Tobin, who led the survey team from the NRAO, said in the statement. "We can now compare them to older disks that have been studied intensively with ALMA as well."

What is the average mass and size here? The *baby stars* forming are in the Orion Molecular Cloud, a favorite for winter stargazers, e.g. M42. My telescopes show 6 stars in the Trapezium under higher power and the gas is moving away from these high mass stars as other studies show. Class O stars evaporate their surroundings quickly. The article said, "This means that younger disks have a lot more raw material from which planets could form," Tobin said in the statement. "Possibly, bigger planets already start to form around very young stars." Four of the young stars captured in the survey stood out from the rest, as they appeared to be "irregular or blobby," the researchers said. The strange shapes suggest that the stars are still in the very early stages of forming, because they do not yet have the flattened, rotating disk surrounding them or the strong outflow of material that are both characteristic of a protostar, the statement said. "We rarely find more than one such irregular object in one observation," Nicole Karnath, one of the survey team members from the Stratospheric Observatory for Infrared Astronomy (SOFIA) Science Center, said in the statement. "We are not entirely sure how old they are, but they are probably younger than 10,000 years."

I did review this link provided in the report, https://iopscience.iop.org/article/10.3847/1538-4357/ab6f64
"148 protostars at a resolution of ~0".08 (32 au). ", so these stars are about 400 pc distance. "mean protostellar dust disk masses" in the abstract are some 25.9 earth masses, 14.9, and 11.6 earth masses. This is small compared to computer models for protoplanetary dust disk evolution that formed our solar system, commonly >=39,000 earth masses or more. In 1999, surveys of T Tauri stars suggested 330-350 earth masses for dust disks.

The abstract also said "We use the dust continuum emission at 0.87 and 9 mm to measure the dust disk radii and masses toward the Class 0, Class I, and flat-spectrum protostars, characterizing the evolution of these disk properties in the protostellar phase. .."

Class O stars are big, massive and blow away their surroundings. Interesting observations here.
Reply
Torbjorn Larsson

rod said:
I did review this link provided in the report, https://iopscience.iop.org/article/10.3847/1538-4357/ab6f64"148 protostars at a resolution of ~0".08 (32 au). ", so these stars are about 400 pc distance. "mean protostellar dust disk masses" in the abstract are some 25.9 earth masses, 14.9, and 11.6 earth masses. This is small compared to computer models for protoplanetary dust disk evolution that formed our solar system, commonly >=39,000 earth masses or more. In 1999, surveys of T Tauri stars suggested 330-350 earth masses for dust disks.

Well, give or take the inflow from the hundreds of solar mass molecular gas clouds, each protoplanetary disk must transfer a star worth's of mass into the young star. If it is a typical star of Sun's age or younger, it has a metallicity of something like 1 %, so a Sun analog system would have 10^28 kg metal or 1,000 Earth mass worth of terrestrial planets or gas giant cores (with most of it in the star). Similarly a disk model would start out with about a star worth of mass in the dust disk, which is ~ 100,000 Earth mass.

I dunno about the survey of T Tauri stars, but a 2008 study is "Motivated by a growing concern that masses of circumstellar disks may have been systematically underestimated by conventional observational methods". It finds about 1/10 of Sun mass in the disk while mentioning older models of 10^-3 solar mass https://arxiv.org/pdf/0810.1393.pdf ]. In any case these hydrodynamic models seem like a good start for an evolutionary model, both in regards mass estimate and since they have some of the disk physics.

The paper here can observe the dust very well, and so "disk masses are given in dust mass (not scaled by an estimate of the dust-to-gas mass ratio)". Scaling the dust-to-gas ratio naively with Sun metalicity, those disks may start out at 1,000 - 10,000 Earth masses.
Reply
rod

I note that the article reporting on ALMA results in Orion on baby stars, ties the report with protoplanetary disks too that may evolve into new planets. The content contains discussions on protostellar disks that are <=26 earth masses for some of the baby stars that are <=10,000 years old. The entire subject, e.g. protostellar disk masses, protoplanetary disk masses, etc. is difficult and more studies are finding different mass measurements for disks observed now, especially when reviewing the exoplanet inventory documented today. Why do protoplanetary disks appear not massive enough to form the known exoplanet population? I find comments like this very interesting, "...Unless disk dust masses are heavily underestimated, this is a big conundrum." I like *conundrums* in disk mass estimates, measurements. Digging deeper I find "From the theoretical perspective, all models to explain the formation of planetesimals and planets are based on processes that are quite inefficient."

I will continue to dig and update my database. This is not like going to the exoplanet list I use and find a neat, clean bill presented :)
Reply
Torbjorn Larsson

rod said:
Why do protoplanetary disks appear not massive enough to form the known exoplanet population? I find comments like this very interesting, "...Unless disk dust masses are heavily underestimated, this is a big conundrum."

Yes, I remember Morbidelli's (one of the experts) recent paper on this, which is why I prefaced a comment with the incoming cloud flow - essentially we have a balance between incoming mass, mass accreting to the star(s), mass accreting to the planets, and outgoing mass (gas dispersal). The take home message to me: "This implies that either the cores of planets have formed very rapidly (<0.1-1 Myr) and a large amount of gas is expelled on the same timescales from the disk, or that disks are continuously replenished by fresh planet-forming material from the environment. These hypotheses can be tested by measuring disk masses in even younger targets and by better understanding if and how the disks are replenished by their surroundings." Which is why the ALMA(VLA dust observations will be useful when there is enough to make statistics and better models of it.

Meanwhile it certainly helps that our own system now seem to concur with rapid core + pebble rain formation on the one hand and concurrent massive disk dispersal, re the new dates for Earth and Mars formation. Meanwhile the early supernova shocks to the early system material seen in the isotope ratios (one or two) speak of environment communication (nearby giant stars formed in the same star cluster). Seems like it is more the case of making massive enough observational sets than that new planetary system formation physics is explicitly needed to make the tensions go away (but of course some new physics can be expected to show up as well).
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