New low-mass objects could help refine planetary evolution

September 26, 2016
Artist’s conception courtesy of Robin Dienel. 

When a star is young, it is often still surrounded by a primordial rotating disk of gas and dust, from which planets can form. Astronomers like to find such disks because they might be able to catch the star partway through the planet formation process, but it's highly unusual to find such disks around brown dwarfs or stars with very low masses. New work from a team led by Anne Boucher of Université de Montréal, and including Carnegie's Jonathan Gagné and Jacqueline Faherty, has discovered four new low-mass objects surrounded by disks. The results will be published by The Astrophysical Journal.

Three of the four objects discovered by these researchers are quite small, somewhere between only 13 and 18 times the mass of Jupiter. The fourth has about 120 times Jupiter's mass. (For comparison the Sun is just over 1,000 times more massive than Jupiter.)

"Finding disks in low-mass systems is really interesting to us, because objects that exist at the lower limit of what defines a star and that still have disks that indicate can tell us a lot about both stellar and planetary evolution," said first author Boucher, who works at her university's Institute for Research on Exoplanets (iREx).

In a planet-forming disk, the dust grains collide and aggregate to form pebbles, which grow into boulders, and so on, increasing in size through planetesimals, planetary embryos, and finally rocky terrestrial planets (some of which then become the cores for ). Astronomers are able to identify these types of planet-birthing disks, because the star heats up the surrounding dust, which affects the way it looks using a telescope with an infrared camera.

However, some disks indicate that planet formation isn't ongoing, but has already finished. These disks are made up of the debris left behind by all the collisions during planet formation and by subsequent collisions of the newly formed planets. Eventually these dusty remains are swept away. But until that happens, a cooler, thinner ring of dust surrounds the star.

Some disks even represent an intermediate stage between the planet-forming and dusty remnant phases.

It's important for astronomers to try to distinguish between these different types of disks, because then they can better chart the way planetary systems, including our own Solar System, are born and change over time.

The research team was able to determine that the disks surrounding their four newly discovered low-mass objects were all likely in a phase of planet forming. None were in the dusty aftermath phase.

Even more interesting, two of the objects are possibly between 42 and 45 million years old. This would make them the oldest objects surrounded by active disk systems ever found.

"There is still so much to learn about disks around low-mass objects such as these four," concluded Gagné, who is also a iREx collaborator. "Hopefully, we can conduct further research on them and be able to narrow down what kind of activity is happening in them and whether or not they would be good targets for future planet hunters."

The other co-authors are: David Lafrenière and René Doyon of Université de Montréal, and Lison Malo of the Canada-France-Hawaii Telescope.

This work was supported by Fonds de Recherche du Québec - Nature et Technologies, the Natural Science and Engineering Research Council of Canada, and the Centre de Recherche en Astrophysique du Québec.

Explore further: The minimum mass of a proto-solar system disk

More information: BANYAN. VIII. New Low-Mass Stars and Brown Dwarfs with Candidate Circumstellar Disks, arXiv:1608.08259 [astro-ph.SR] arxiv.org/abs/1608.08259

Related Stories

The minimum mass of a proto-solar system disk

October 19, 2015

Astronomers estimate that at the time the Solar system formed, its proto-planetary disk contained the equivalent of about twenty Jupiter-masses of gas and dust. This so-called "minimum mass solar nebula (MMSN)" is derived ...

Smaller stars pack big X-ray punch for would-be planets

June 14, 2016

Young stars much less massive than the Sun can unleash a torrent of X-ray radiation that can significantly shorten the lifetime of planet-forming disks surrounding these stars. This result comes from a new study of a group ...

Resolving the planetesimal belt around HR8799

August 15, 2016

Planets develop from the dusty placental disk of material that surrounds a star after it begins to shine. The dust in that disk, according to most models, starts to stick to itself until clumps develop large enough to attract ...

Hubble images three debris disks around G-type stars

September 14, 2016

A team using the Hubble Space Telescope has imaged circumstellar disk structures (CDSs) around three stars similar to the sun. The stars are all G-type solar analogs, and the disks themselves share similarities with our Solar ...

ALMA finds unexpected trove of gas around larger stars

August 25, 2016

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) surveyed dozens of young stars—some Sun-like and others approximately double that size—and discovered that the larger variety have surprisingly ...

Recommended for you

A catalog of habitable zone exoplanets

January 18, 2017

The last two decades have seen an explosion of detections of exoplanets, as the sensitivity to smaller planets has dramatically improved thanks especially to the Kepler mission. These discoveries have found that the frequency ...

Galaxy murder mystery

January 17, 2017

It's the big astrophysical whodunnit. Across the Universe, galaxies are being killed and the question scientists want answered is, what's killing them?

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.