Dust of Life

Dust, Interstellar Organics, and the Birth of Stars, Planets, and Life

Whether we explore the Atacama, the Sahara, or Antarctica, the chemistry of life as we know it is the chemistry of carbon and its interaction with hydrogen, nitrogen, oxygen, phosphorous, iron, sulfur plus a few dozen other elements. Our understanding of the evolution of increasingly complex carbon compounds in the Universe has been revolutionized by the collection of X-ray, visible, infrared, and radio images and spectra from the international efforts of both Earth-based and orbital observatories.

In particular mid-infrared images and spectra using 3.5 to 24 μm data from the Spitzer Space Telescope have provided stunning evidence over the past decade that large organic molecules permeate star forming regions in our galaxy as well as those of neighboring galaxies. In fact, signatures of organic material can be detected in objects at a redshift of 7 moving the appearance of carbon astrochemistry back to the first billion years following the Big Bang.

Specifically, mid-infrared signals capture the aborption and emission features of a class of organic molecules known as polycyclic aromatic hydrocarbons (PAHs). Spitzer's InfraRed Array Camera (IRAC) Channels 1 (3.6 μm center wavelength), 3 (5.8 μm). and 4 (8.0 μm) capture PAH features known to exist at 3.3, 6.2, 7.7 and 8.6 µm. Channel 2 (4.5 μm) can be used as a control channel since it does not capture a known PAH emission feature.

The Mountains of Creation

To understand the origin and evolution of star formation in stellar nurseries, Spitzer has conducted multiple observations on a massive star formation region 6500 light years from Earth in the constellation Cassiopeia known as IC 1848 or W59-11.

Spitzer’s infrared view of the region has come to be known as “The Mountains of Creation”. The famous Hubble optical image known as the “Pillars of Creation” appears in the insert properly scaled.

The composite image depicting IRAC data at 3.6 μm (blue), 4.5 μm (green), 5.8 μm (orange), and 8.0 μm (red) is dominated by the red glow of PAH emissions captured in the 8.0 μm channel. For more information see Towering Infernos.

Image credit: NASA/JPL-Caltech/L. Allen (Harvard-Smithsonian CfA)

The Large Magellanic Cloud

The Large Magellanic Cloud (LMC), 160,000 light-years from Earth, is, one of a handful of dwarf galaxies orbiting our Milky Way. The LMC is one-third as wide as the Milky Way, and, if it could be seen in its entirety, would cover the same area of sky as 480 full moons.

The composite image depicts Spitzer IRAC data at 3.6 μm in blue, 4.5 μm in green, 5.8 μm in orange and 8.0 μm in red. The signals in the 5.8 and 8.0 μm channels are predominantly due to PAH-rich dust emission stimulated by ultraviolet photons from young stars. Like our own star forming region the mid-infrared signal from this neighboring galaxy is dominated by PAH emissions captured in the 8.0 μm channel. For more information see Our Chaotic Neighbor.

Image credit: NASA/JPL-Caltech/M. Meixner (STScI) & the SAGE Legacy Team

The Antennae Galaxies

Combining data from Spitzer, Chandra, Hubble, and ALMA makes it possible to follow carbon distribution in two different molecular states - the carbon stored in large PAH molecules attached to dust grains and the carbon bound to oxygen in carbon monoxide (CO) molecules.

Approximately 62 million light-years from Earth in the constellation Corvus, two galaxies known as the Antennae Galaxies (NGC 4038/4039) are merging. The interaction of their entwined arms is generating massive star formation. The natal regions are the source of massive mid-infrared emissions.

This composite image depicts Chandra 1.5 keV x-ray data in blue pinpoints highly energetic young stars. Hubble’s 0.43 μm, 0.53 μm, and 0.83 μm wavelengths are combined for display in yellow. Spitzer’s IRAC 8.0 μm channel tracing PAH-rich dust is depicted in red. For more information see Antennae Galaxies Tangle.

Image credit for the two Antenna Galaxy images: Spitzer/Hubble/Chandra - NASA/CXC/SAO/JPL-Caltech/STScI/

J. DePasquale (Harvard-Smithsonian CfA), and B. Whitmore (STScI); ALMA (ESO/NAOJ/NRAO).

The next image depicts Hubble visible wavelength data in blue tracing newborn stars. ALMA millimeter and submillimeter observations coded red, pink and yellow trace carbon monoxide molecules in hydrogen clouds where the new stars are forming. The image shows there is a very similar, but not identical, distribution for ALMA's carbon monoxide signal (depicted in red) compared to Spitzer's map of PAH-rich dust. For more information see Alma Opens Its Eyes.

Image credit for the two Antenna Galaxy images: Spitzer/Hubble/Chandra - NASA/CXC/SAO/JPL-Caltech/STScI/

J. DePasquale (Harvard-Smithsonian CfA), and B. Whitmore (STScI); ALMA (ESO/NAOJ/NRAO).

Stellar Habitable Zones

The availability of prebiotic molecules in a nascent solar system is a critical factor in the construction of a useful "habitable zone" around the central star. Originally defined as the distance from a star permitting the existence of liquid water, such a zone is of little use if a nascent planet is devoid of the core elements needed for the appearance and evolution of life. Significant habitable zones and the associated biotic precursor elements and molecules are most likely to be found around G- and K- stellar types. For more information see Habitable Zone Photosynthetic Constraints below.

Getting to Know the Spitzer Space Telescope

For an overview of the Spitzer mission visit Spitzer.

To download pre-processed data from the mission visit the Spitzer Data Archives.

Introduction to Origins of Life and Astrobiology

The Astronomers Pocket Guide to Astrobiology (2003) Astrophysics and Space Science Library 296, 27-36 by G. D. Mcdonald and M. C. Storrie-Lombardi

Extrasolar Planets and Astrobiology (2009) University Science Books, C. Scharf.

Life in the Universe: A Beginner's Guide (2007) Oneworld Books, L. R. Dartnell.

Gravity's Engines: The Other Side of Black Holes (2012) Penguin Books, C. Scharf