Types of Galaxies
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Transcript of Types of Galaxies
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Types of Galaxies
Barred Spiral
Elliptical Irregular
LenticularSpiral
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Deep Sky Catalogs• Messier Catalog
• Charles Messier, 1781• 110 objects (40 galaxies)
• New General Catalog (NGC)• JLE Dreyer, 1888• 7840 objects
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Messier Objects
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Spiral Galaxies(face on)
NGC 1357 M81Bode’s Galaxy NGC 4321
Sa ScSb
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Spiral Galaxies(edge on)
M104Sombrero Galaxy NGC 891 NGC 4631
Herring Galaxy
Sa ScSb
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Spiral Galaxiesvariety of spiral arms
M74
Poorly defined spiral arms
M33Triangulum Galaxy
Well defined spiral arms
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The Winding Dilemma
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Density Waves
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Barred Spiral Galaxies
NGC 4650 M83Southern Pinwheel
Galaxy
NGC 1365
SBa SBcSBb
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Lenticular Galaxieslack spiral arms
M102
S0
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Elliptical Galaxies
M105 M49
E1 E5E4
M59
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Elliptical Galaxies
Virgo clusterM84 (right) and M86 (left)over 2 million ly diameter
Giant Elliptical Galaxies Dwarf Elliptical Galaxy
Leo I(type E4)
3000 ly diameter
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Hubble’s Classification Scheme
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Irregular Galaxies
Large Magellanic Cloud(LMC)
NGC 4485 (top)NGC 4490 (bottom)
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Structure in the Universe
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Galaxy Clusters
Virgo cluster Fornax cluster
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Galaxy Clusters
Hercules cluster
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The Local Group
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Galactic Collisions
NGC 4676“The Mice” BGC 2207 and IC 2163
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Galactic Collisions
M81
M82
NGC 3077
visible radio
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Simulated collisions
animation
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The redshifts of remote superclusters indicate that the
universe is expanding• During the 1920s, Edwin Hubble and Milton
Humanson were studying galaxy spectra• They found that galaxy spectral lines were
redshifted• They measured the distance to galaxies by
finding Cepheid variables and using the period-luminosity relationship
• They found that the most distant galaxies had the largest redshifts
• This is called the HUBBLE FLOW.
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Hubble’s Law
slope = 75 km/s/Mpc called Hubble’s
Constant
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Astronomers measure distances to distant galaxies using supernovae
and the Tully-Fisher relation• Standard candle method
• If you know how bright something really is and compare that to how bright it looks, then the distance can be determined
• Supernovae• All Type Ia supernovae have the same luminosity (M=-
19)• Tully-Fischer Relation
• The broader the spectral line, the faster it is rotating and the more luminous the galaxy.
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Methods of estimating distance
• Parallax (up to 150 pc)• Spectroscopic Parallax (40pc-10kpc)• RR Lyrae variable stars (5-100 kpc)• Cepheid variables (1kpc-30Mpc)• Tully-Fisher relation (700kpc-150Mpc)• Type Ia supernovae (1 to 1000 Mpc)
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Quasars look like stars but have huge redshifts• object with a spectrum
much like a dim star• highly red shifted• enormous recessional
velocity• huge distance (ala Hubble’s
Law)• must be enormously bright
to be visible at such a great distance
• Quasi-stellar object• QSO or Quasar
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Active Galaxies bridge the energy gap between ordinary galaxies and
quasars• peculiar galaxies (pec)
• appear to be blowing themselves apart• Seyfert galaxies
• luminous, star-like nuclei with strong emission lines
• BL Lacertae objects (BL Lacs)• featureless spectrum with a brightness
that can vary by a factor of 15 times in a few months.
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Radio image of Cygnus A showing a small but very bright radio galaxy in the
middle of the 320,000 ly wide lobes
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Active galaxies lie at the center of double radio sources
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Supermassive black holes lurk at the centers of some
galaxies• High resolution spectroscopy allows
astronomers to peak at the motion of gas near centers of galaxies
• Some galaxies exhibit high-velocity jets of material leaving the center
• Observations suggest that the centers of some galaxies are incredibly massive
• All of this suggests the existence of supermassive black holes
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Galaxy (which is
actually quite large)
Intergalactic gas jet
Giant Gas Clouds
(surrounding the galaxy)
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Jets of matter ejected from around a black hole may explain quasars and
active galaxies
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Jets of matter ejected from around a black hole may explain quasars and
active galaxies
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From where you observe it might make all the difference ...
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TONIGHT:Telescope observations
• 8:45 pm Tuesday, May 20, after night class (telescopes on the roof)
• Weather permitting (looks good!)• Attendance not required, but
strongly recommended and will be for credit
• If you can’t make it, see me for an alternate assignment
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Class Websitehttp://www.hartnell.edu/faculty/kjordahl
All lectures from the semester will be available by next week (as HTML and PowerPoint)
Catch up on your reading in the textbook!