THE
COOLER UNIVERSE
Palahalli R Vishwanath
Article in DeccanHerald 8 nov 2016
Pics are Comaprison in INR/Visible light of (1) Andromeda galaxy (2) ORION constellation
(Many
objects in the universe which are much too cool and faint to be
detected in visible light, can be detected in the infrared . Unlike X
and Gamma ray astronomies which deal with death of stars, ,Infrared
astronomy is concerned with their birth. IR studies are also
contributing significantly to the the exciting field of Exo Planets
)
The
great astronomer William Herschel who discovered Uranus also did a
simple and beautiful experiment in1800 in which white light was sent
through a prism and temperatures measured for different colors of the
ensuing spectrum. He reasoned that the unexpected excess in
temperature in the control region next to red is due to to light
which cannot be seen and was eventually named Infra Red (IR) rays.
While this was the first non visible light , whole of
electromagnetic spectrum was eventually discovered, the others
being Ultraviolet, Radio, X rays and Gamma rays . By early 1900s IR
rays had been detected from moon and several objects in the solar
system
A
piece of coal when heated produces at first heat which is due to IR
rays. In fact, any body which has any temperature is a source of IR
rays. The wavelength of IR extends from 700 nanometers (just
beyond red) to ~ 1 millimeters. The study of infrared , depending
upon the instruments, is divided into three regions , near-infrared,
mid-infrared and far-infrared.
While most big optical telescopes in sites with less moisture can
be used for studies in the near IR region, instruments above
atmosphere are needed for other regions of IR. The important
satellite IR missions have been the IRAS, the ISO , SPITZER ,
HERSCHEL, SOFIA etc. Significant results keep coming from both
SPITZER and SOFIA which are expected to function for at least 10
more years. Lyman Spitzer was the first person to propose the idea of
placing a large telescope in space and was the driving force behind
the development of the Hubble Space Telescope.
Discoveries in IR astronomy
1)
BIRTH OF STARS : IR rays give important information about birth of
stars since they are suited to study proto-stars and star formation
regions which are at of lower temperatures . Large number of stars
which are too cool to emit visible light or are hidden behind
obscuring dust have been detected by this method. Brown dwarfs
are an odd set of objects that are neither planets nor stars. The
best hope for finding brown dwarfs is in using infrared telescopes,
which can detect the heat from these objects. IR
studies seem to indicate that there is 1 brown dwarf star for every
6 stars in
our
galaxy. Also SOFIA , a
modified Boeing 747 jetliner, with a 2.5 meter IR telescope
which can cruise near the edges of the atmosphere observed very
recently (October 2016) the collapse of few interstellar clouds on
their way to becoming new stars. Detecting such infall in
proto-stars which happens very fast is very difficult to observe,
but is critical to confirm our overall understanding of star
formation. This aircraft can also
travel to almost any point on the Earth's surface, allowing
observation from the northern and southern hemispheres.
2.
GALAXIES
:The expansion of
the universe was discovered by study of the redshift of external
galaxies by Edwin Hubble in the last century. However, expansion
stretches light further and the wavelengths are shifted down into
the infrared. As a result of this Doppler effect, at large redshifts,
visible light from distant sources is shifted into the infrared part
of the spectrum. Therefore IR studies give us much information
about the very young, distant galaxies. Our Universe is about 14
billion years old, and HUBBLE/SPITZER spotted in March 2016 a galaxy
born only 400 million years after the Big Bang. This galaxy is
small , about 25 times smaller than the Milky Way galaxy . Apart from
the distant ones, many galaxies ( more than 20000) have been
detected only in the infrared. Many of these are star-burst galaxies
-with formation of enormous numbers of new stars, and are thus
extremely bright in the infrared. Also Interstellar matter radiates
strongly in the infrared. Due to all thee reasons IR pictures reveal
the structure of our galaxy much better than visible pictures can.
The center of our galaxy is one of the brightest infrared sources in
the sky. It is the IR studies which show the rapid rotation of stars
and gases near the center , thus pointing to the existence of a super
massive black hole.
3) PLANETARY STUDIES : Quite a few of the important
information about the solar system has come from IR studies like (a)
IR detection from the moon, as early as 1856 (b) the composition of
Venusian atmosphere, (c) possible internals source of energy in
Jupiter (d) the Methane atmosphere in Titan etc. An enormous
ring around Saturn that had remained hidden earlier has also been
detected . HERSCHEL telescope detected water in Comets and also
the dwarf planet Ceres giving credence to the theory that part of
water on earth has come from comets and asteroids.
4) EXO PLANETS :
The exciting field of Exo planets (Extra- Solar Planets) really
started by observation of IR emitting dust round stars. After this
initial fillip from IR astronomy, several thousands of these
exoplanets have been found by ground based telescopes and KEPLER
satellite. These detections are indirect in the sense they look for
regular dip in the in the light level given out by the system .
However SPITZER recently became the first telescope to
directly detect light of such planets outside of our Solar System, It
captured directly the warm
infrared glows of two previously detected "hot
Jupiter" planets - gas giants that zip closely around their
parent stars and shine brightly in infrared wavelengths. Since the
star-planet contrast is more favorable in IR because the planet
emits its own light, it is easier to directly detect such planets .
Further since molecules in the atmospheres of exoplanets have the
largest number of spectral features in IR wavelengths, the
temperatures, winds, and atmospheric compositions on these distant
planets can be obtained. Last year SPITZER confirmed a very close
(21 Light Years) rocky planet by finding its density . More details
on the closest exo planet, the one in Proxima Centauri, will also be
available soon from IR studies
Finally because the majority of the stars in
the Galaxy are low-mass and predominantlyIR emitters , if aliens
exist and ever do visit us, they’ll probably have infrared vision!
Our own eyes evolved to make maximum use of the Sun’s light, which
peaks in the visible. but the eyes of such aliens would have evolved
to use their home star’s infrared light !
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