Astrochemistry basicsAstrochemistry basics

How we detect elements and How we detect elements and molecular compounds in spacemolecular compounds in space

BeginBegin

Background photograph - NASA - http://hubblesite.org/gallery/album/galaxy_collection/pr1999041a/ Background photograph - NASA - http://hubblesite.org/gallery/album/galaxy_collection/pr1999041a/

Whoa!! I don’t understand Whoa!! I don’t understand the term Astrochemistry???the term Astrochemistry???

Astrochemistry is the Astrochemistry is the (relatively)(relatively) new branch of new branch of Astronomy that deals with Astronomy that deals with how/where how/where elements elements and compounds come from that are found in:and compounds come from that are found in:

• The Milky Way (The Milky Way (ourour very own Galaxy) very own Galaxy) learn morelearn more

• Nebulae (clouds of gas within our galaxy) learn Nebulae (clouds of gas within our galaxy) learn moremore

• Other galaxies learn moreOther galaxies learn more

• Any other place in the universe INCLUDING our Any other place in the universe INCLUDING our Solar SystemSolar System

Some useful conceptsSome useful concepts

Spectral linesSpectral lines

Absorption / Emission linesAbsorption / Emission lines

Radio TelescopesRadio Telescopes

Detection Detection

We detect these chemicals in We detect these chemicals in space by at least two methods:space by at least two methods:

Atomic SpectroscopyAtomic Spectroscopy – – Useful forUseful for Visible, Infrared, and Ultraviolet LightVisible, Infrared, and Ultraviolet Light

Molecular Spectroscopy Molecular Spectroscopy – Useful for – Useful for Radio Waves, and Microwaves Radio Waves, and Microwaves (type of (type of

Radio Wave),Radio Wave),

Atomic SpectroscopyAtomic Spectroscopy

Atoms of a specific Atoms of a specific element emit a element emit a specific specific wavelength of light wavelength of light when an electron when an electron undergoes a undergoes a transition between transition between energy levels energy levels (Bohr (Bohr model of the Atom)model of the Atom)

Molecular SpectroscopyMolecular Spectroscopy Molecules of a compound Molecules of a compound

have rotation energy. have rotation energy. When they change When they change rotation energy states, rotation energy states, they emit a photon at a they emit a photon at a specific wavelength (specific wavelength (λλ).).

Different molecules emit Different molecules emit photons of unique photons of unique wavelengths for that wavelengths for that rotation energy state.rotation energy state.

Diatomic molecule rotationDiatomic molecule rotation

Absorption / Emission Absorption / Emission lineslines

Electrons making an energy transition is Electrons making an energy transition is the key to the key to either either emission of light or radio emission of light or radio waves.waves.

AbsorptionAbsorption is the process where energy is is the process where energy is taken in by an electron to change it’s taken in by an electron to change it’s energy level to a “non-rest” state.energy level to a “non-rest” state.

EmissionEmission is the process where energy is is the process where energy is given off by the electron as it returns to its given off by the electron as it returns to its “rest” state.“rest” state.

Absorption SpectraAbsorption Spectra Happens when waves Happens when waves

of an electromagnetic of an electromagnetic wave wave (shown in visible light)(shown in visible light) passes through a cool passes through a cool gas. The gas “robsgas. The gas “robs” ”

(absorbs)(absorbs) photons at photons at specific wavelengths specific wavelengths to energize its to energize its electrons.electrons.

Result – Specific Result – Specific wavelengths “drop wavelengths “drop out” of the otherwise out” of the otherwise continuous spectrum.continuous spectrum.

Absorption Spectra Examples:Absorption Spectra Examples:

The absorption of these specific wavelengths of light The absorption of these specific wavelengths of light prove the presence of Hydrogen gas in the outer prove the presence of Hydrogen gas in the outer atmosphere of the star.atmosphere of the star.

Absorption Spectra Examples:Absorption Spectra Examples:Yup, another example…Yup, another example…

Psst!, This is how we identify Spectral Psst!, This is how we identify Spectral types!!!types!!!

Emission SpectraEmission Spectra Happens when Happens when

photons are created photons are created by an energized gas. by an energized gas. The gas “createsThe gas “creates” ” (emits)(emits) photons at photons at wavelengths wavelengths corresponding to the corresponding to the energy change of its energy change of its electrons.electrons.

Result – Specific Result – Specific wavelengths of light wavelengths of light are created where are created where there was no light there was no light before.before. Emission lines of specific gassesEmission lines of specific gasses

Tools of the Radio AstronomerTools of the Radio Astronomer

Radio Telescopes – Similar in Radio Telescopes – Similar in many ways to Optical many ways to Optical telescopes telescopes

Focus configurations: Focus configurations: • A. Prime Focus – radio receiver A. Prime Focus – radio receiver

at the prime focusat the prime focus• B. Cassegrain – secondary B. Cassegrain – secondary

convex reflector at prime focusconvex reflector at prime focus How do you make a radio How do you make a radio

telescope (almost) the size of telescope (almost) the size of the Earth??the Earth??• Ans: VLBAAns: VLBA

Very Long Baseline ArrayVery Long Baseline Array

What is a VLBA?? What is a VLBA?? Answer: a Very Long Baseline Array – Answer: a Very Long Baseline Array –

A grouping of A grouping of identicalidentical radio telescopes at radio telescopes at different places on the earth that act as one different places on the earth that act as one large radio telescopelarge radio telescope

Combining the signals from more Combining the signals from more than one telescope is called than one telescope is called interferometry. (learn more)interferometry. (learn more)

Telescopes of the VLBATelescopes of the VLBA

The National Science Foundation's VLBA The National Science Foundation's VLBA (learn more) is a system of ten identical (learn more) is a system of ten identical radio-telescopes controlled from a radio-telescopes controlled from a common headquarters in New Mexico, and common headquarters in New Mexico, and working together as a single instrument. working together as a single instrument. The radio signals received by each The radio signals received by each individual antenna contribute part of the individual antenna contribute part of the information used to produce images of information used to produce images of celestial objects with hundreds of times celestial objects with hundreds of times more detail than Hubble Space Telescope more detail than Hubble Space Telescope images.images.

Telescopes of the Telescopes of the VVery ery LLong ong BBaseline aseline AArray (VLBA)rray (VLBA)

NRAO / AUI / NSFNRAO / AUI / NSF

Radio TelescopesRadio Telescopes

How big is the world’s How big is the world’s largest Radio Telescopelargest Radio Telescope, and where is it?, and where is it?

NRAO / AUI / NSFNRAO / AUI / NSF

How Big: > 100 m (> 300 ft.)How Big: > 100 m (> 300 ft.)

Where: Green Bank, West VirginiaWhere: Green Bank, West Virginia

BeginningsBeginnings

In the ‘50s & ’60s, Radio telescopes first In the ‘50s & ’60s, Radio telescopes first discovered the “signature” line of discovered the “signature” line of Hydrogen at 21 cm wavelength Hydrogen at 21 cm wavelength betweenbetween stars. stars. • The hydrogen gas was found (in abundance) in the The hydrogen gas was found (in abundance) in the

“empty” space between stars.“empty” space between stars.• Note: Domestic microwave ovens use a signal of Note: Domestic microwave ovens use a signal of

~ 12 cm wavelength to cook food ~ 12 cm wavelength to cook food

This gas was “dark” in optical wavelengths This gas was “dark” in optical wavelengths but “bright” in radio wavelengths.but “bright” in radio wavelengths.

Keeping scoreKeeping score

What molecules have been discovered and What molecules have been discovered and at which wavelengths?at which wavelengths?Ans: Well over 100 molecules of compounds Ans: Well over 100 molecules of compounds

have been found in Interstellar space. have been found in Interstellar space. Here are just a few of them showing where Here are just a few of them showing where

they were discovered and at the they were discovered and at the corresponding “signature” frequencies and corresponding “signature” frequencies and wavelengthswavelengths

Familiar Compounds in Familiar Compounds in SpaceSpace

NameName

(Popular (Popular Name)Name)

FormulaFormula

(Chemical (Chemical formula)formula)

WavelengthWavelength

( ( λλ - in cm) - in cm)FrequencyFrequency

(MHz)(MHz)Found In:Found In:

Suphur Suphur MonoxideMonoxide

SOSO 8.28 8.28 3620236202 OrionOrion

MethanolMethanol CHCH33OHOH 8.298.29 3616936169 SagittariusSagittarius

FormaldehydeFormaldehyde HH22CC1818O O 6.836.83 4388 4388 SagittariusSagittarius

Carbon Oxide Carbon Oxide SulfideSulfide

OCSOCS 8.228.22 3648836488 TaurusTaurus

Silicon MonoxideSilicon Monoxide SiOSiO 7.057.05 4251942519 SagittariusSagittarius(Var. Supergiant)(Var. Supergiant)

Silicon Silicon Tetracarbide Tetracarbide

SiCSiC446.986.98 4294442944 TaurusTaurus

AmmoniaAmmonia NHNH33 16.6516.65 1801718017 Giant Giant Molecular Molecular CloudCloud

How can we find Molecules How can we find Molecules with a Radio Telescopewith a Radio Telescope

Check out this website. It relates many compounds found Check out this website. It relates many compounds found in the universe and at which frequency they are detected.in the universe and at which frequency they are detected.

http://physics.nist.gov/cgi-bin/micro/table5/start.plhttp://physics.nist.gov/cgi-bin/micro/table5/start.pl

Hints: Hints: • Start the frequency range at about 1200 Hz. You can type in Start the frequency range at about 1200 Hz. You can type in

the upper frequency range at about 44,000 Hz.the upper frequency range at about 44,000 Hz.• Check the “Name” field at the bottom. This will add the Check the “Name” field at the bottom. This will add the

familiar chemical formula name to the table which the web site familiar chemical formula name to the table which the web site creates for you.creates for you.