wave astronomy is a relatively new branch of astronomy that studies
celestial objects using the submillimeter band of the electromagnetic
spectrum, which ranges from 0.1 mm to 1.0 mm (300 GHz to 3000 GHz).
This band, which lies between the far infrared and high-frequency radio
bands, contains valuable astonomical information in both continuum and
molecular spectral lines, but has been unavailable to astronomers until
recently because most of the radiation is blocked by the Earth's atmosphere.
In order to overcome this barrier, submillimeter observatories are usually
placed at high altitude.
8 (385 to 500 GHz, submillimeter-wave)
/ 108 (beads in mala) = 1157.4074
/ 3 (waves) = 385.80246
8 (385 to 500 GHz, submillimeter-wave)
submillimetre observations, astronomers examine molecular clouds and
dark cloud cores with a goal of clarifying the process of star formation
from earliest collapse to stellar birth.
our EVeryday human experience, we see that light has measurable properties.
It has intensity (brightness), and it has color. The intensity gives
an indication of the number of light "waves" or "particles"
(called photons) coming from an object. The color is a measure of the
energy contained in each photon. The colors of the rainbow (red, orange,
yellow, green, blue, violet) denote the energies of light waves that
our human eyes can see and interpret. This "color" or "energy"
range is called the visible spectrum. Red photons of light have the
least energy, violet photons carry the most energy. Until fairly recently,
all of our astronomical knowledge came from the detailed study of visible
light from astronomical objects.
visible spectrum is only a tiny portion of the total electromagnetic
(EM) spectrum, however.
that radio, TV, and microwave signals are all light waves, they simply
lie at wavelengths (energies) that your eye doesn't respond to. On the
other end of the scale, beware the high energy UV, x-ray, and gamma-ray
photons! Each one carries a lot of energy compared to their visible-
and radio-wave brethren. They're the reasons you should wear sunblock,
we look at the Universe in a different "light", i.e. at "non-visible"
wavelengths, we probe different kinds of physical conditions -- and
we can see new kinds of objects! For example, high-energy gamma-ray
and X-ray telescopes tend to see the most energetic dynamos in the cosmos,
such as active galaxies, the remnants from massive dying stars, accretion
of matter around black holes, and so forth. Visible light telescopes
best probe light produced by stars. Longer-wavelength telescopes best
probe dark, cool, obscured structures in the Universe: dusty star-forming
regions, dark cold molecular clouds, the primordial radiation emitted
by the formation of the Universe shortly after the Big Bang. Only through
studying astronomical objects at many different wavelengths are astronomers
able to piece together a coherent, comprehensive picture of how the
(0.3 - 1.0 mm) astronomy is perhaps the last wholly unexplored wavelength
frontier. Why? Submillimeter ("microwave") astronomy is technically
very difficult due to the sheer complexity of the instrumentation and
to the "opaqueness" of the atmosphere in microwave light.
Submillimeter (a.k.a. "microwave") frequency band lies between
the regions easily observed by radio telescopes and optical telescopes.
It comes as no surprise, then, that submillimeter astronomy borrows
techniques used by both optical and radio astronomers. The visual appearance
and operation of the telescope is that of a radio telescope, although
it is sheltered in an enclosure like an optical telescope. Continuum-mode
observations are done using specialized heat-sensing detectors called
bolometers, which stem from infrared techniques. Spectral-line measurements,
incorporating very high wavelength-resolution, use heterodyne receivers
somewhat resembling those found in lower-frequency radio receivers.
Such high frequency receivers (approaching 1 Terahertz, about 10,000
times higher frequency than the average FM radio!) are very difficult
to manufacture, howEVer. The recent production of sensitive receivers
for astronomical purposes (at the University of Arizona (SORAL), among
other places) has led recently to the opening of this wavelength band
for the first time.
submillimeter observations are difficult for another reason: the opaque-ness
(opacity) of the atmosphere at microwave wavelengths.
another (prettier) plot of the electromagnetic spectrum. The different
color-coded classifications reflect segments of the EM spectrum which
require different techniques for observation.
lower plot focuses on a portion of the spectrum from radio wavelengths
to x-rays. The gray-filled line demonstrates at what height in the Earth's
atmosphere incoming waves of light are blocked. Notice that the Earth's
atmosphere blocks high-energy light (UV, X-rays, Gamma rays) dozens
of miles above our heads. To observe astronomical X-ray sources, one
must therefore launch astronomical satellites above the atmosphere.
the opposite extreme, most radio- and visible- wavelength observations
are unimpeded by the atmosphere; the incoming photons can travel right
through. The atmosphere is transparent at such wavelengths. Transparency
is important since astronomers must be able to look through the atmosphere
to observe astronomical objects.
submillimeter wavelengths, ambient atmospheric water vapour will absorb
(block) incoming light. At low elevations, where most water vapour resides,
the atmosphere is very opaque at submillimeter wavelengths; the abundant
water vapour absorbs any incoming submillimeter photons before they
can reach the telescope. At higher elevations, however, the water content
decreases substantially. By minimizing the atmospheric water vapour,
one improves the transparency of the atmosphere and makes astronomical
observations possible. It is for this reason that infrared and submillimeter
observatories are built as high as possible; by being above some of
the atmosphere, the radiation from astronomical sources is much less
demonstrate how important a dry site is to a submillimeter observatory,
look at the following plot :
transparency (transmission efficiency) of the atmosphere at microwave
frequencies is plotted for two amounts of atmospheric water: 1 mm and
4 mm of precipitable water vapour. This term deserves an explanation:
4 mm of PWV means that if EVery molecule of water vapour above you could
be condensed into an ocean, it would be 4 mm deep! 4 mm of water vapour
is in fact still pretty dry, but EVen there, the atmosphere blocks all
but 2% of the light at 0.3 mm (800 GHz). Moved to a very high, dry site
under excellent conditions, you might expect to see 1 mm of PVW; and
the atmosphere would pass about 25% of the light at 0.3 mm. Lower frequency
observations (below 200 GHz, a.k.a "millimeter"-wave astronomy)
can be performed under conditions when submillimeter observations are
impractical or impossible.
astronomy promises to yield a new view upon the Universe we live in,
almost certainly shedding light upon many of the outstanding questions
in modern astronomy.
the most pressing of these questions is how stars are formed. Stars
are born from the material between other stars. In some regions of space,
the density of gas and dust is much higher than the norm, and atoms
are sufficiently shielded from destructive high-energy photons to interact
with other atoms to form simple molecules. In the highest density central
regions of such molecular clouds, material is so well shielded that
delicate, complex molecules can form. It is from these molecular cloud
cores that new stars (including our own Sun) are born. The study of
the chemistry in such regions can not only lead to an improved understanding
of the physical conditions in such a "stellar nursery", but
also can provide clues to the composition of other star-forming (and
possibly planet-forming and life-giving) solar systems. Such studies
may help astronomers understand the conditions from which life evolved
the star forming process occurs behind so much intervening dusty material,
visible-light telescopes cannot see what is happening. By moving to
the infrared, sub-millimeter and millimeter wavelength regions, where
the effects of this obscuration are nearly negligible, astronomers can
begin to directly probe regions where stars are actively being born.
the star forming process has many astronomical consequences. Knowing
what physical conditions are needed to form molecular cloud complexes
is important in understanding the star-forming EVolution of galaxies,
both in the current age and, perhaps most importantly, when galaxies
were first forming. The understanding of how a single star forms from
a molecular cloud, then, has EVen cosmological implications.