nrao        Yancy L. Shirley      The University of Arizona





Astro Links


M16 (credit: Travis Rector)

M64 (credit: Hubble Space Telescope)

I am interested in the physical processes involved in the incipient stages of star formation, astrochemistry, and astrobiology. My research focuses on centimeter, millimeter, and submillimeter (microwave in the figure below) imaging and spectroscopy with single-dish radio telescopes and interferometers. I have worked on a variety of projects studying low-mass and high-mass star formation and the chemical evolution of those regions within our galaxy and nearby galaxies. Please click on images to see a larger view.

Click on the image
to see the EM spectrum.

Stars form out of giant clouds of dust and gas within our galaxy named molecular clouds. The image on the right shows a portion of the Milky Way with several obscuring molecular clouds. You can easily see these clouds as opaque patches in the summer Milky Way from a dark, clear site. Astronomers study these clouds in detail to understand the conditions from which stars form.
The Milky Way (credit: Serge Brunier)

The R Corona Austrialis Molecular Cloud

How dust absorbs & re-radiates light.
Microscopic views of dust grains.
One mechanism that allows us to study forming protostars is the emission from dust grains within the cloud. Dust grains (size <~ 1 micron) absorb UV and optical light from a forming protostar, heating the grain. Since the dust grains are still very cold (T ~ 15K), they re-radiate the absorbed energy at far-infrared and submillimeter wavelengths. By imaging the submillimeter emission at different wavelengths, we can unravel the structure of the molecular cloud.

Most forming protostars are so deeply embedded within the molecular cloud that no optical light can escape. The images on the left shows an optical image of the isolated dark clouds B68 and B335. It is difficult to see that anything is happening at the center of the clouds. However, at longer wavelengths the radiation can penetrate through the cloud. B68 does not harbor a forming protostar and may be a core in the earliest phase of star formation. In the case of B335 (bottom right), observations reveal a forming protostar. The emission seen in the submillimeter image of B335 on the right is due to dust grains re-radiating the energy absorbed from the hot protostar.
B68 optical (left) and near-infrared image (right).

B335 optical image (left) and 850 um image (right).
(Shirley et al. 2000).

JCMT(left). Miranda Nordhaus with SCUBA (right).

The JCMT is atop 13,700 ft. Mauna Kea, Hawaii.
The image of B335 was observed at a wavelength of 850 microns with a submillimeter camera named SCUBA on the JCMT 15-meter radio telescope on Mauna Kea, Hawaii. This wavelength is 1500 times longer than yellow visible light; alternatively, the frequency is 3500 times higher than FM on your radio. SCUBA is a revolutionary camera that worked at submillimeter wavelengths and allowed images of protostellar clouds to be made 10,000 times quicker than previous instruments. The images on the left show the JCMT and 2003 NRAO summer student, Miranda Nordhaus (U Texas), standing next to the SCUBA dewar.

Diagram showing how CO emits radiation at
230 GHz.

Optical Image (left) and CO image (right) of the horsehead nebula (credit: NOAO & CSO).

Optical Image (left) and CO image (right) of The Whirpool Galaxy. Dark molecular clouds in the optical image are glowing in CO (credit: HST & SMA).
Another mechanism by which molecular clouds may be studied is from the radio emission from rotating molecules. Energy is quantized, therefore molecules can only rotate at discreet speeds. When molecules change the speed at which they rotate, they tend to emit energy in the radio part of the spectrum. Extremely sensitive receivers on radio telescopes can be tuned to the precise frequencies of molecular emission to study the distribution of that molecule throughout the cloud. Molecules such as carbon monoxide, water, ammonia, carbon monosulfide (a deadly gas), and formaldehyde (frog preserver) are routinely observed in molecular clouds. The example on the top left shows how carbon monoxide (CO) emits radiation at 230 GHz, 2300 times higher in frequency than FM radio. The middle images shows an optical picture of the horsehead nebula (left) with an image of the CO emission (right). Notice that the CO emission traces the shape of the dark molecular cloud observed at optical wavelengths.

Mapping protostellar cloud cores with different molecules and dust emission allow us to probe the temperature, density, velocity, and chemical structure of the cloud. Theoretical models predict how the cloud structure should evolve with time. Observations constrain those models: ruling out some while providing evidence for others. A wide variety of telescope may be used to study the dust and molecular emission from star forming regions such as the Heinrich Hertz Submillimeter Telescope, the Spitzer Space Telescope, the Very Large Array, and the Green Bank Telescope. Interferometers, such as the VLA, can observe structure on the scale of the solar system in star forming regions that 100s of light years away!

The HHSMT atop Mt. Graham, Arizona (left). The Spitzer Space Telescope before launch (right).

The VLA near Magdalena, New Mexico (left). The GBT 105m in Green Bank, West Virginia (right).

Click on images to see how complicated organic molecules form in space.
Over 150 different molecules have been detected in interstellar space with radio telescopes. Many complex organic molecules such as long carbon chains (HC11N) and simple sugars (glycolaldehyde) have been detected. Recently, very deep searches for the simplest amino acid, glycine, have been made. The basic molecular building blocks of carbon-based life are present in the raw material out of which stars and planets form! The panels to left are from the NRAO press release announcing the discovery of sugars in molecular clouds.

There are still many fundamental questions to be answered: How do molecular clouds form? Can we observe the initial stages of star formation and what are the properties of clouds at this stage? Are we observing the collapse of protostellar clouds to form stars? Why does nature prefer to form stars that are about the same mass as the sun? Are complex organic molecules present in the raw planetary/cometary material around every protostellar system? Does life exist elsewhere in the universe?
A dedicated team of researchers trying to answer some of the basic questions of star formation. Left to Right: Yancy Shirley, Jana Grcevich (Columbia), and Al Wootten (NRAO Charlottesville) at the CSO, Mauna Kea, Hawaii.