A brief introduction to Astrochemistry

1. Astrochemistry: Understanding
The Chemical Cosmos
Prince
IVth Year
SCS, NISER
Pillars of creation, HST
SACKLER LABORATORY

2. Today’s Astrochemistry Talk
Processes
Why different?
Growing
Interest
Detection Future
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3. Astrochemistry
Study of formation, destruction and excitation of
molecules in astronomical environments and their
influence on structure, dynamics and evolution of
astronomical objects.
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4. Interest in Astrochemistry
I. Discovery of extrasolar planets
• First exoplanet (planets revolving
around other star) - 51 Pegasi b
discovered in 1995
51 Peg b
(As seen in Celestia)
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5. II. CO at high red-shift (z)
• CO detected in z = 6.4
galaxy, chemistry is
not new to universe
@691.473 GHz
Bertoldi et al. A&A 2003
RA
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6. III. Molecules as Probes
• Chemical evolution vis-à-vis astrophysical evolution
• Chemical species are important makers of
temperature (N2H+), magnetic field (CN-) and density
(complex organic molecules) in interstellar clouds1,2,3
• Detecting habitable planets and other markers
relevant to astrobiology
1Pagani et al., A&A, 2007
2Thaddeus et al, A&A, 1972
3Ziurys et al, PNAS, 2006
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7. What we see and what actually there is
Visible Infrared
Images: Hubble Space
Telescope
● Orion nebula is nearest star-forming region
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8. ISM: A Unique Laboratory
• 99% of InterStellar Medium (ISM) is gas-phase and 1% is
solid-state
• Molecules are seen everywhere: Interstellar molecular
clouds, star forming regions, sunspots and early universe
• Typical Molecule forming environments:
Diffuse Clouds: ~80K, n(H) ~ 100 cm-3
Dense Clouds: ~10K, n(H) ~ 103-105cm-3
Vol 83 No-11, Nov-2006, J Chem Ed
•Unique Laboratory ~ Unusual Chemistry
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9. Astronomer’s Periodic Table
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10. Forming molecules is not so easy
• Remember density is ~ 10 - 104 cm-3
• on average 1 collision in 1 month at n(H) = 10000/cm3
• typical time for chemical process ~ 0.1 Myr
• star formation timescale ~ 1 Myr
• lifetime of interstellar cloud ~ 10 Myr
→ too few reactions before the clouds disperses; molecule formation not
expected
Still 160+ molecules already detected
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11. Molecules in ISM
• Some are ordinary
and some complex
(H2, CO2,H2O, NH3, HCN, NaCl, N2O,
HCOOH, CH3CH2OH)
• Fullerenes (C60,C70) and
Poly Aromatic
hydrocarbons (PAHs) also
detected
• Exotic molecules
(C5, HC9N, CH3C3N)
• Glycine detected in comet
Wild-2 by Stardust spacecraft
(Elsila et al,JMPS,2009)
Star Dust chasing
comet Wild-2
(NASA)
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12. Chemical Nurseries
• Gas phase reactions
Mostly ion-molecule reactions:
A+ + B C+ + D
H+ + H H2
+ + hv
• Shock synthesis of molecules
Mostly neutral-neutral reaction:
A + B C + D
Formation of fullerene and PAHs
(García-Hernandez et al, AJL, 2011)
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13. Chemical Nursuries:
• Chemistry on grain surfaces
“Grain surfaces are the watering
holes of astrochemistry where
species come to meet and mate.”
(Tielens, 2005)
At molecular cloud densities (104-
105 cm-3) it takes a few days for an
atom to stick to a grain
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14. In Dust We Trust!
Hydrogen atom
Oxygen atom
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15. Dust: Impacts, Growth and Our
Origin
• Size, density and velocity of projectile and density and
temperature of target decide the fate after impact
• Meteorites rich in chemicals (including nucleobase
analogs) (GSFC, NASA)
• Comet impacts on Earth brought water and seeds of life(?)
(Elsila et al., JMPS,2009)
• Hatley-2 comet has similar water content and deuterium-to-
hydrogen ratio as our oceans (Herschel Space
Observatory/HIFI)
• Rosetta Mission is to land on a comet on 12 Nov 2014
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16. Radiation From Molecules
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17. Visibility of EM waves
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18. Ground Based Telescopes
IRAM 30m telescope
SOFIA, NASA
GMRT 45m, 30 dishes
ALMA
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19. Space Based IR Telescopes
ISO
Spitzer Space Telescope
Herschel
Space
Observatory
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20. How it goes?
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21. Lets detect Ammonia!
• Nitrogen hydrides are important markers in many
astrophysical environments
• Rotational transitions are not accessible to ground
based observatories
• Remember Herschel Space Observatory??
VSRP 2014 at
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22. Spectroscopy
J=3
J=2
J=1
J=0
Rotational Energy NH3 J =1←0 572.498 GHz
levels of NH3
Rist et al , JCP, 1993
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23. Our source ~ W49N
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24. Radiative transfer
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25. Herschel/HIFI Spectra
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26. Fitted Plots
NH3
NH2
NH
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27. Results
*LTE: Local Thermodynamic Equilibrium
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28. Discussion
• NH: NH2 :NH3
NH: NH2 :NH3
Diffuse Clouds
Diffuse Clouds
LTE LTE ~ 4.3:~ 2.3:4.3:1
2.3:1
non-LTE ~ 3.2:1.9:1
non-LTE (RADEX) ~ 3.2:1.9:1
Dense Clouds
Dense Clouds~ 3:1:3
Dense (Le Clods~ Gal et 3:al, 1:A&3 (Le A, Gal 2014)
et al,
2014)
Towards IRAS 16293-2422~
3:1:19 (Hily-Blant et al., 2010a)
Protostellar Object ~ 3:1:19
(Hily-Blant et al., A&A, 2010a)
• N – Chem network still to be understood in diffuse
clouds
• These results provide a firm constraint for
upcoming modelling efforts
VSRP 2014 at
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29. Exoplanets
Astrochemistry and Life ~ Astrobiology?
Darwin & TPF will detect Biomarkers:
O3 H2O vapor.
Spectroscopic
Chemical Analysis of
Atmophere.
Courtesy: Prof. G.W. Marcy, University of California, Berkeley
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30. Burning questions
• How do complex molecules form
in space?
• Do these molecules have
anything to do with formation of
life?
• How/Which complex
species(biologically active?) can
survive extreme conditions?
• Unknown unknowns?
Image: The Cosmic Question Mark,
Hubble Space Telescope
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31. Future Missions
JWST
• Rosetta Space Probe
• Atacama Large Millimeter Array
(ALMA)
• Square Kilometer Array (SKA)
• James Webb Space Telescope (JWST) + lots more
Organic Molecules??
SKA
ALMA
Rosetta
and Philae
Astrochemistry in-situ?
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32. Thank
you!
• Astrochemistry has answers
to many of the fundamental
questions we ask. The world
is ours to explore!
RAWS 2013 & POS 2014
IISc VSRP-TIFR
NCRA
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