Astronomers spot hundreds of baby stars and planet-forming disks

rod

Oct 22, 2019
1,260
411
1,060
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.
 
Jan 4, 2020
191
70
160
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.
 
Last edited:
  • Like
Reactions: rod

rod

Oct 22, 2019
1,260
411
1,060
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 :)
 
Jan 4, 2020
191
70
160
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).
 

ASK THE COMMUNITY

Latest posts