The making of dust

The making of dust
An optical image of the globular cluster 47 Tucanae. Astronomers studying the production of dust in evolved stars analyzed the optical and infrared properties of the stars in this cluster. Credit: Thomas V. Davis

( -- On the Earth, dust particles are everywhere - under beds, on bookshelves, even floating in the air. We take dust for granted. Dust is also common in space, and it is found for example in the cold, dark molecular clouds where stars are born. Dust is a critical ingredient of the cosmos for several reasons. It is a repository for many chemical elements (carbon and silicon, for example). It also acts as a catalyst for the chemical reactions that produce the many complex molecules observed in space, molecules which in turn play a key role in the heating and cooling of the clouds that leads to the formation of the next generation of stars (and their planets).

Astronomers are not certain where where all of this dust comes from. Most of it is produced in the winds of stars that have finished the nuclear fusion of hydrogen and helium in their cores. These stars have made copious amounts of carbon and oxygen, begun to swell in size, and blown off material that condenses into . But numerous puzzles remain, including the nature of the grains (composition, size, shape), precisely when the process begins and ends in stars of different masses, and how formation depends on element enrichment in the .

One way to address many of these problems is by looking at evolved stars in a single globular cluster; all of the stars in a globular cluster are about the same age and composition, and differ primarily in their masses. CfA astronomer Joe Hora and Tom Robitaille have joined with thirteen colleagues to analyze the dust production in 47 Tucanae, the nearest (about fifteen thousand light-years away) and one of the most massive (almost a million solar masses) globular clusters. The scientists combined optical data with infrared measurements from the to model the of 47,727 stars in the inner part of the cluster. Since the team was concentrating on the issue of dust and its infrared contribution to a star's radiation, they narrowed the full list to 258 stars with clear signs of dust emission.

The astronomers reach several important conclusions in their study. First, in disagreement with some earlier work, they find that only the brightest few percent of the stars produce dust, and virtually all stars brighter than about 2000 solar luminosities make dust. They also find that the initial stellar composition does not appear to be an important factor in dust production, an important conclusion when considering dust production in the early epochs of the universe. Not least, they refine the age of the cluster as 12 +-1 billion years, and its distance as 15,032 +- 650 light-years.

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Jul 06, 2011
Astronomers are not certain where where all of this dust comes from."

1. Most stars, including the Sun, routinely give off

a.) Hydrogen: A neutron-decay product, and
b.) Helium: A product of H-fusion.

2. In a deep-seated explosion, they eject elements from the interior of the star that condense into grains of dust, like those that comprise the rocky planets and ordinary meteorites.

Fe, O, Ni, Si, S, Mg and Ca

3. In a less violent ejections, lightweight elements like C and N are released and may form carbonaceous, graphite-like material.

With kind regards,
Oliver K. Manuel
Former NASA Principal
Investigator for Apollo

Jul 07, 2011
Can someone answer: moving through the interstellar medium, at what speed might the "dust" become a problem? Let's assume an interstellar density found in some of the less dense regions between our sun and stars about 50ly distant. Let's also assume some sort of conventional physical spacecraft and conventional movement through space(no magical scifi stuff please).

Is 3% to 5% of light speed even possible?

Jul 07, 2011
The impact energy is the kinetic energy (at those speeds I think we can assume we are dealing with non-elastic impacts).

Asteroids (and presumably other space objects like dust) travel on average with about 25km/s. But let's say our spaceship is travelling at 1% of c (30000km/s). We can neglect the dust's own speed by comparison.

A grain of sand (which has somewhere around 0.1mg of mass - depending on what source you look at) will hit you with an impact energy of 45 MegaJoules at that speed (I couldn't find the values for the mass of 'dust', but we should assume that occasionally we'll hit something slightly bigger along the way.)

For comparison: a car (mass 1000kg) crashing into a wall at 100km/h will have an impact energy of around 400 kJ

So picture your spaceship running into 100 cars at 100km/h at once distributed over the area of a grain of sand. Not a pretty picture.

Oh yeah: No way we can look ahead far enough to evade/destroy a grain of sand at those speeds.

Jul 08, 2011
"2. In a deep-seated explosion, they eject elements from the interior of the star that condense into grains of dust, like those that comprise the rocky planets and ordinary meteorites.

Fe, O, Ni, Si, S, Mg and Ca"

If this were the case, why do we see no (x-ray) evidence for Ni-56 or Ti-44 in the newly discovered *cold* dust cloud at the center of SN1987A: http://www.physor...mic.html

Jul 09, 2011
Two papers recently were posted on arXiv detailing observations of SN 1987A at far infrared(FIR) and submillimeter wavelengths for the first time:



The central object in the SNR has NOT been detected at x-ray wavelengths as would be expected if heavy (radioactive) elements like Co-60, Ti-44, Ni-56 are to be found in the dust cloud surrounding the central object in SN 1987A (according to Oliver, anyway). Surely, the SN was not deficient in these isotopes, as they are seen, by both Chandra X-ray Observatory and the XMM-Newton X-ray satellite, in the collisional ring over one l.y. distant from the central remnant.

Back to reality, these new observations are intriguing and will help us to better understand the evolution of young SN into SNRs.

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