Shocking news about dust grains

Jan 07, 2013
A region of star formation as seen in a false-color infrared image. The numerous extended greenish filaments are in most cases signs of shock-excited gas produced by jets from young stars in the nebula. New results find that similar fast moving shocks can evaporate water (and most other molecules) frozen onto the surfaces of dust grains in these regions. Credit: NASA and the Spitzer Space Telescope

(Phys.org)—The ubiquitous clouds of gas and dust found between stars provide the natal material for new stars and planets. These clouds are also dynamic factories that produce many complex molecules thanks to their rich environment of stellar radiation, dense gas, and dust grains. The grains (most of which are silicates, analogous to sand) act as miniature chemical laboratories. Atoms and molecules from the gas condense onto their surfaces and then interact with one another to form even more complex species. Water, a particularly abundant species, tends to form a layer of ice on the grain surfaces.

One of the outstanding set of questions in modern astrochemistry involves the processes that enable newly formed molecules to come off the frozen grains and back into the gas, where they can disperse, radiate, and can be measured with millimeter telescopes. Understanding these processes would also help scientists better characterize the physical conditions in the locations where the molecules are detected.

New stars host complex environments that including circumstellar disksand dramatic outflows of material in the form of narrow jets. The jets disrupt these environments, and where they collide with the ambient they produce shocks. Astronomers have long known that these shocks, moving at comparatively modest velocities of about ten kilometers per second (about 22,000 miles per hour) can expel from grains and prompt the molecules to radiate. In fact, shock velocities are often much faster than this. The shocks can also fracture the grains, thereby injecting molecules (SiO) into the gas. The longstanding problem has been an inability to quantify accurately the shock processes.

CfA astronomer Sven Van Loo and four colleagues have completed a series of computations that for the first time describe in a self-consistent manner how shocks disrupt grains, and that seems to agree with the observations of gas abundances in many regions. The scientists find that at speeds of 20-25 kilometers per second the grain surfaces are completely vaporized, returning all the ice to the gas as water vapor. Then, once the surface has been completely eroded, the grains begin to release SiO into the gas. Millimeter telescopes have found that SiO gas emission is a ubiquitous signal around young stars. The new research will help scientists determine the kinds of shocks responsible for these regions, in turn shedding light on the jets and young stars that produce them.

Explore further: Image: Hubble serves a slice of stars

Related Stories

Water and ammonia factories

Nov 08, 2011

(PhysOrg.com) -- Complex molecules, including many organic species, exist in a wide range of environments in the cosmos, and are especially abundant in giant molecular clouds of gas and dust where new stars ...

The anatomy of a stellar outflow

May 28, 2012

(Phys.org) -- Astronomers used to think that star formation simply involved the gradual coalescence of material under the influence of gravity. No longer. Making a new star is a complex process, among other ...

Interstellar dust and the sun

Nov 12, 2012

(Phys.org)—The space between stars is not empty. It contains copious but diffuse amounts of gas and dust; in fact about 5-10% of the total mass of our Milky Way galaxy is in interstellar gas. About 1% of ...

Water around massive young stars

Sep 16, 2010

Water is critical to human life, but also plays an important role in the life of stars and their planetary systems. As a gas, water helps to cool collapsing clouds of interstellar material so that they can ...

The earliest stages of planet formation

Mar 26, 2012

(PhysOrg.com) -- Small dust particles in a disk of gas around a young star, according to current models, gradually coagulate during the first million years until kilometer-sized objects are formed. These in ...

All about dust

Aug 28, 2012

(Phys.org)—The space between stars is not empty—it contains copious amounts of gas and dust. Astronomers estimate that about 5-10% of the total mass of our Milky Way galaxy is contained in the interstellar ...

Recommended for you

Image: Hubble serves a slice of stars

1 hour ago

The thin, glowing streak slicing across this image cuts a lonely figure, with only a few foreground stars and galaxies in the distant background for company.

Evidence of a local hot bubble carved by a supernova

21 hours ago

I spent this past weekend backpacking in Rocky Mountain National Park, where although the snow-swept peaks and the dangerously close wildlife were staggering, the night sky stood in triumph. Without a fire, ...

Astronomers measure weight of galaxies, expansion of universe

Jul 30, 2014

Astronomers at the University of British Columbia have collaborated with international researchers to calculate the precise mass of the Milky Way and Andromeda galaxies, dispelling the notion that the two galaxies have similar ...

Mysterious molecules in space

Jul 29, 2014

Over the vast, empty reaches of interstellar space, countless small molecules tumble quietly though the cold vacuum. Forged in the fusion furnaces of ancient stars and ejected into space when those stars ...

User comments : 0