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Presentation on theme: "-BIG.jpg During the years from 1758 to 1782 Charles Messier, a French astronomer (1730 - 1817), compiled a list."— Presentation transcript:

1 -BIG.jpg During the years from 1758 to 1782 Charles Messier, a French astronomer (1730 - 1817), compiled a list of approximately 100 diffuse objects that were difficult to distinguish from comets through the telescopes of the day. Discovering comets was the way to make a name for yourself in astronomy in the 18th century -- Messier's first aim was to catalog the objects that were often mistaken for comets.

2 What are nebulae?? 1755 Kant proposed nebulae are “island universes” Are Nebulae within or outside of our galaxy?? Nebula comes from a Greek word meaning Cloud

3 April 1920, National Academy of Sciences, Washington, DC Harlow Shapley (had determined size of Milky Way Galaxy) pushed that nebulae were relatively close by objects. Heber Curtis championed view that spiral nebulae were rotating systems of stars like our own galaxy. Debate was heated but eventually a draw as neither side could provide convincing evidence for either view

4 Edwin Hubble Oct 6, 1923 Historic Photo of M31(Andromeda Galaxy) Discovered a Cepheid variable star (thought it was a nova) Used formulas to determine the galaxy was 750 kpc (2.5 million ly) away and it was 70 kpc in diameter (recall Milky Way is only 50 kpc in diameter) Nebula was not “Near by”

5 December 30, 1924 Hubble presents his findings to American Astronomical Society Shapley-Curtis “Debate” effectively settled The Universe is a big place!!

6 Hubble Ultra-Deep Field

7 Hubble Classification of Galaxies 4 Classes of Galaxies S – Spirals SB – Barred Spirals E – Ellipticals Irr – Irregulars

8 Spirals Arched lanes of stars Spiral Arms containing young hot blue stars and associated H II regions Strong heavy elements present so lots of Population I stars in spiral arms Central bulges low star formation rate dominated by Population II stars

9 Spirals – Sub-divided Sa – Large central bulges ~4% of galactic mass in gas and dust Sb – Medium sized central bulges ~8% of galactic mass in gas and dust Sc – Small central bulges ~25% of galactic mass in gas and dust

10 Barred Spiral Galaxies Spirals originate at the end of a bar shaped region which passes through the nucleus of the galaxy rather than originating from the nucleus itself. Hubble again applied a, b, and c to rate the size of the central bulge with a being largest and c being smallest As with ordinary spirals this difference of a through c may be due to amount of gas and dust in the galaxy.

11 Bars appear to form naturally in Spirals from computer simulations Barred Spirals outnumber Spirals by about two to one Milky Way may be Barred Spiral

12 Bars appear to form naturally in Spirals from computer simulations Barred Spirals outnumber Spirals by about two to one Milky Way may be Barred Spiral A theory why all Spirals don’t have bars proposes that if a galaxy is surrounded by a large enough halo of Dark Matter bar will not form. Milky Way may have such a halo?

13 Ellipticals No Spiral Arms Further sub-divided by numbers –E0 is roundest –E7 is flattest –Category based on observation from Earth, may not be completely accurate Mostly Population II stars, little to no new star formation occurring in these galaxies

14 Hubble Tuning Fork Diagram Hubble originally proposed that it represented evolution of galaxies Ellipticals would evolve into Spirals Ellipticals have little to no rotation Modern view is diagram represents grouping by rotation Ellipticals are galaxies with little to no rotation Spirals “class c” have greatest rotations

15 Types of Irregular Galaxies Type I – Many OB associations and H II regions Type II – asymmetrical shapes implying they resulted from collisions with other galaxies or have violent activity occur within their nucleus

16 Tidal forces from Milky Way believed to be source of star formation in the two Magellanic Clouds

17 How to Determine Distances to Galaxies?? Standard Candles –Luminous to shine at great distances –Luminosity known to a great degree of precision –Light curve should be identifiable, what kind of variable star –Common enough to allow for many measurements and hence many checks Use Intensity α 1/d 2

18 “Standard” Candles?? Not all objects are “Standard” Type Ia Supernova’s – Not all have same peak luminosity. Relationship between rate of decrease in luminosity and peak luminosity

19 Tully-Fisher Relation –Use 21 cm radiation –Line is broadened due to one edge of galaxy is rotating towards us, blue-shifted, and one edge is rotating away from us, red-shifted. –Rotational velocity provides Mass –Mass provides number of stars –Number of provides luminosity *****

20 Fundamental Plane (3 points define a plane) –Relate Size, Motion, and Brightness –Measure Motion and Brightness, determine Size –Use apparent Size to Actual Size to get distance

21 Tully-Fisher relation is a correlation for spiral galaxies between their luminosity and how fast they are rotating. The idea is that the bigger the galaxy is, faster it is rotating. That means that if you know the rotation velocity of the spiral galaxy, you can tell by using this Tully-Fisher relation its intrinsic brightness (that is, how bright that galaxy really is). By comparing the intrinsic brightness with the apparent magnitude (what you actually observe -- because the further the galaxy, the dimmer it "appears"), you can calculate its distance.

22 For a cluster of galaxies where you can observe tens of galaxies, you can measure the distance to each galaxy via Tully-Fisher relation. Then take the average to calculate the distance to that cluster. (Because these clusters are so far away, you can assume that the actual size of the cluster itself can be ignored with respect to its distance from us).

23 Here, Tully-Fisher relations of two clusters at different distances are shown. The one shown in the lower part represent a cluster called Abell 1367 which is much farther than the Fornax cluster which is shown in the upper part of the diagram. The relative difference between the distances of two clusters is estimated by measuring Delta D as indicated.

24 Lasers vs. Masers LASER – Light Amplification by Stimulated Emission of Radiation LASER – Light Amplification by Stimulated Emission of Radiation MASER – Microwave Amplification by Stimulated Emission of Radiation MASER – Microwave Amplification by Stimulated Emission of Radiation

25 Stimulated Spontaneous



28 1920’s Hubble and Humanson Photographed spectra of many galaxies with the 100 inch Mt Wilson telescope They found most spectra were red-shifted (ie moving away from us) They found the amount of red-shifting was directly proportional to how close they were to us, more distant galaxies had greater red-shifts than nearby galaxies

29 Redshift (z) Doppler Shift Hubble Law H 0 is between 40 and 90 km/s/Mpc

30 Relativistic Vs Non-Relativistic Redshifts for speed Consider z = 0.32 Consider z = 2.0

31 Uncertainty in H 0 Redshifts fairly reliable Distances are not Book uses 73 km s -1 Mpc -1

32 Grouping of Galaxies Groups of Galaxies are called Clusters Rich Clusters have many galaxies Poor Clusters have few galaxies and are sometimes called groups Poor Clusters outnumber Rich Clusters Milky Way (our galaxy) is part of the Local Group ~30 galaxies (most are dwarf ellipticals)

33 Categorizing Clusters Regular – Spherical in shape obvious concentration of galaxies at its center Irregular – Not Regular! Local Group is irregular

34 Shape of Clusters Shape of Cluster is determined by which type of galaxies dominate its make-up Regular Clusters have mostly ellipticals and lenticular galaxies Irregular Clusters have a more even mixture of galaxies

35 Groupings of Clusters Clusters group to form Superclusters Typically dozens of clusters spread over a a region of space 30 Mpc across

36 1980’s mapping of clusters Use redshifts to get a 3-dimensional mapping of galaxy locations. Discovery of spherical voids which are either empty or contain Hydrogen clouds or dim galaxies Voids are about 30 to 120 Mpc in diameter Galaxies are concentrated in “Sheets” on the surfaces surrounding and between the Voids Think soapsuds in a sink with soapfilms surrounding air bubbles

37 Great Walls of Galaxies In the 3-D map we find two large structures the “Great Wall” in the northern part of the map and the “Southern Wall” in the southern part of the map. Great Wall extends ~150 Mpc along the arc and 5 Mpc perpendicular to the surface Southern Wall extends ~100 Mpc On scales above 100 Mpc, distribution of galaxies appears to be fairly uniform

38 21 cm radiation show connections of Hydrogen gas between galaxies indicating previous interactions As with the M 82, M 81 and NGC 3077, Milky Way and Large Magellanic Cloud have similar Hydrogen gas connections

39 Colliding Galaxies? Collisions produce hot intracluster gas at temperatures between 10 7 and 10 8 k Collisions unlikely to result in Star on Star collisions, too much empty space between Starburst galaxies due to compression of gas within the galaxy causing star birth

40 The Antennae Galaxies

41 M64: The Sleeping Beauty Galaxy -Gas rotates opposite direction of the stars!!

42 Warped Spiral Galaxy ESO 510-13 (150 Million ly)

43 Warped Spiral Galaxy ESO510-13 (150 Million ly)

44 NGC 1410/1409: Intergalactic Pipeline

45 Cluster is 8 Billion ly away

46 Sagittarius Dwarf to Collide with Milky Way

47 Colliding Galaxies Galactic deformations due to tidal forces Stars may be ejected from galaxy Often the colliding galaxies repeatedly collide until they merge and form one new galaxy – Galactic Cannibalism!! Milky Way on track to collide with Andromeda (M 31) in ~ 6 billion years *****

48 Third Method to form Spiral Arms? Close encounters between galaxies may provide another way to form spiral arms in addition to Density Wave model or Self-Propagating Star Formation spiral-galaxies-arms.html

49 Why do clusters stay together? Observed measurements of galactic speeds from Doppler shift measurements indicate that galaxies are moving too fast to remain in a cluster. The amount of mass required to keep them gravitationally bound is not present in the visible mass Answer is of course Dark Matter

50 Where is the Dark Matter? 1970’s found hot x-ray emitting gas within clusters Measuring amount of x-ray radiation provides for about 10% of the needed missing mass

51 Where is Dark Matter? Shape of rotation curves for different galaxies tell us that the edge of the galaxy is not where the visible part ends as the rotation should drop back down like Kepler’s law predicts Dark Matter must extend out past the visible edges of galaxies ew-clues-to-the-mystery-of-dark-matter.html?_r=2&

52 Where is Dark Matter? No evidence for Dark Matter in Intergalactic Space Dark Matter appears to be within and in the immediate space surrounding galaxies The visible components appear to trace the locations of Dark Matter

53 Looking at distant objects (galaxies, clusters, quasars, etc) is looking back in time Galaxies were bluer in the past More vigorous star birth and lots of hot short-lived O and B stars

54 Rich clusters with redshifts of z=0.4 correspond to ~4 billion years ago had 30% spiral galaxies, while nearby rich clusters (today) have ~ 5% spiral galaxies

55 Where did the Spirals Go? Galactic collisions and mergers Collisions often repeated would increase star formation, possibly using up available gas. Spirals no longer seen as they are not making new stars along spiral arms Tidal forces among galaxies could have disrupted spiral arm patterns

56 Events listed previously while they do destroy Spirals, they do not create Ellipticals or Lenticular Galaxies. Ellipticals are mostly composed of Pop II stars that appear to have formed over 4 billion years ago in a burst of star formation. Spirals seem to have a more steadier approach to star formation

57 Theories of Galaxy Creation 1960’s One Huge Primordial Gas Cloud Condenses Type of Galaxy depends on Star Formation rate –Slow rate  Disk shaped galaxy probably Spiral –Fast rate  Elliptical shaped galaxy formed This would account for distribution of Pop II stars in Halo and Pop I stars in main disk Also accounts for highly elliptical orbits of Halo objects

58 Theories of Galaxy Creation 1977 Galaxies formed from the merging of several smaller clouds instead of one large isolated cloud Third theory speculates a large number of fairly small clouds merge to form a Galaxy

59 Open Questions on Galaxy Formation Where did subgalactic gas clouds come from? What happened in early Universe to cause primordial Hydrogen and Helium to clump into the size clouds they did? Why not bigger or smaller? What about the 90% of the Universe’s mass that is Dark Matter? What is it?

60 help-solve-mystery-of-ultra-compact-burned-out/#.U0fwLFcXKSo The research, supported by several ground-based telescopes, solves a 10-year-old mystery about the growth of the most massive elliptical galaxies we see today. It provides a clear picture of the formation of the most massive galaxies in the universe, from their initial burst of star formation through their development of dense stellar cores to their ultimate reality as giant ellipticals. January 2014

61 Through the research, astronomers have determined the compact ellipticals voraciously consumed the gas available for star formation, to the point they could not create new stars, and then merged with smaller galaxies to form giant ellipticals. The stars in the burned-out galaxies were packed 10 to 100 times more densely than in equally massive elliptical galaxies seen in the nearby universe today, and that surprised astronomers, according to Toft. help-solve-mystery-of-ultra-compact-burned-out/#.U0fwLFcXKSo

62 One group of galaxies is the compact ellipticals. The other group contains galaxies that are highly obscured with dust and undergoing rapid star formation at rates thousands of times faster than observed in the Milky Way. Starbursts in these dusty galaxies likely were ignited when two gas-rich galaxies collided. These galaxies are so dusty that they are almost invisible at optical wavelengths, but they shine bright at submillimeter wavelengths, where they were first identified nearly two decades ago by the Submillimeter Common-User Bolometer Array (SCUBA) camera on the James Clerk Maxwell Telescope in Hawaii. help-solve-mystery-of-ultra-compact-burned-out/#.U0fwLFcXKSo

63 When Toft's team compared the samples of the two galaxy populations, it discovered an evolutionary link between the compact elliptical galaxies and the submillimeter galaxies. The observations show that the violent starbursts in the dusty galaxies had the same characteristics that would have been predicted for progenitors to the compact elliptical galaxies. Toft's team also calculated the intense starburst activity inside the submillimeter galaxies lasted only about 40 million years before the interstellar gas supply was exhausted. help-solve-mystery-of-ultra-compact-burned-out/#.U0fwLFcXKSo


65 By 1944 Sagittarius A – Galactic nucleus Cassiopeia A – Supernova Remnant –Both inside of Milky Way Cygnus A - Where ??

66 Cygnus A First Photographed by Baade and Minkowski in 1951 Spectrum showed strong emission lines Normally galaxies show absorption lines as light gets absorbed by star atmospheres. Emission lines were strongly redshifted by 5.6% ( z = 0.056)

67 Amount of Luminosity for Cygnus A is 10 7 times the amount of luminosity for an ordinary galaxy 1960 Sandage discovered a star at the location of a strong radio source 3C 48 Also contained Strong Emission lines Unable to identify chemical composition

68 1962 3C 273 Discovered Has a jet coming off one side Again Chemical Composition could not be figured out

69 1963 – Break Through!! Schmidt took another look at 3C 273 ‘s Spectrum He realized there were four emission lines with the same pattern as four lines in the Balmer portion of the Hydrogen spectrum Lines were Red-Shifted!!! Recognizing that, distances could be determined and these objects are outside of Milky Way

70 3C 273 was determined to have a redshift of z = 0.158 3C 48 was determined to have even larger redshift of z = 0.367 Because of their strong Radio emission and star like appearance, these objects were called Quasi-Stellar Radio Sources and later this was shortened to Quasars

71 Later there were discovered High Redshift objects that were quiet in Radio Emissions These were called initially Quasi-stellar Objects - QSO’s Now Quasars apply to both ~10% of Quasars are Radio-loud More than 10,000 Quasars are known today, all have star like appearances All have large Redshifts 0.06 < z < 5.8, Most are at least z = 0.3 (fairly far away)

72 Where have Quasars gone? Nearest Quasar is ~250 Mpc (~800 Million ly) No new Quasars in almost a billion years Quasars initially quite prevalent, peaked about 10 Billion years ago and the numbers have been declining since

73 Quasars are Incredibly Luminous Quasar Luminosities range from 10 38 to 10 42 W Milky Way’s Luminosity is 10 37 W Radiation from Galaxies is mostly a mixture of normal star light, hence blackbody radiation usually from star temps of 2500 to 50,000 K Quasars have radiation stronger in the x-rays and gamma rays implying temps of 100,000 K

74 Spikes due to emission lines Width of emission lines is broadened due to some gas clouds move towards us while others move away

75 Redshift Debate 1960’s Arp suggested that the Hubble Law might not apply to Quasars Quasars might actually be closer to us therefore their luminosity may not be so large and thus not so unexplainable Debate ends in 1970’s when galaxies seen near quasars have same redshifts

76 Redshift Debate Debate further ended when host galaxies were able to be imaged Difficult to image host galaxy due to galaxy’s relative dimness compared to quasar Redshift of host galaxy matches quasar’s redshift

77 Relatively nearby Radio quiet Quasars tend to be in Spiral Galaxies (z<0.2) Radio Loud and more distant Quasars tend to be in Ellipticals Often though host galaxies tend to be distorted and often have nearby companion galaxies Possible connection between Quasars and galactic collisions or mergers??

78 Why Skeptical that Quasars exist?? Quasars are so much more luminous than other objects (such as normal Galaxies) that it just seemed impossible. Active Galaxies discovered that bridge the energy gap between normal Galaxies and Quasars 1943 Seyfert discovered a series of very luminous Spiral Galaxies. These are now known as Seyfert Galaxies

79 Why Skeptical that Quasars exist?? Quasars are so much more luminous than other objects (such as normal Galaxies) that it just seemed impossible. Active Galaxies discovered that bridge the energy gap between normal Galaxies and Quasars 1943 Seyfert discovered a series of very luminous Spiral Galaxies. These are now known as Seyfert Galaxies

80 Seyfert Galaxies About as luminous as a weak Quasar Little to no radio activity Seyfert’s appear to often be the result of colliding galaxies or are seen in pairs of galaxies which are interacting NGC 1275 is actually a colliding Spiral galaxy with an Elliptical galaxy

81 Radio Galaxies Radio Galaxies are Elliptical Galaxies They are Strong in Radio Radiation Have similar Luminosities as Seyfert Galaxies First one discovered in1918 by Curtis, M 87

82 Types of Radiation from M 87 Thermal Radiation (Black Body Radiation) is very prominent in the Central region of M 87 Non-Thermal Radiation (Synchrotron Radiation) is more pronounced in the Jet Radiation of M 87 Jet radiation is Polarized, Black Body is unpolarized but Synchrotron is usually Polarized

83 Radio Galaxies Radio Galaxies usually have two Radio Lobes that span 5 to 10 times the size of the parent galaxy usually a Giant Elliptical Galaxy which sits in between the lobes These galaxies are often referred to as double radio sources

84 Radio Galaxies Often found near center of Rich Clusters Probably subject to collisions and mergers as Seyfert’s are Energy output is on par with Seyfert’s

85 Recently Quasars have been discovered in between radio lobes (both lobes and Quasar are highly redshifted) Speculation exists that Seyfert Galaxies may be former Radio Quiet Quasars Radio Galaxies are former Radio Loud Quasars

86 Blazars 1929 BL Lacertae was discovered and thought to be a variable star due to the variability of its brightness However, the light from the central part had no features, no emission lines, no absorption lines 1970’s the central light was blocked and the remainder of the light (fuzz) around the center showed normal spectral evidence of an elliptical galaxy

87 Blazars The Light from the center appears to be polarized synchrotron radiation Objects were originally known as BL Lac objects but now, they are just called Blazars It is now believed that they are double radio sources (elliptical galaxies) which are oriented so one of the two jets is towards us Further Evidence of this idea that Jets are aimed at us comes from apparent Faster Than Light motion!!

88 Quasars Vs Blazars Quasars generally exhibit lower superluminal speeds typically (1 to 5) x c Blazars typically (5 to 10) x c Blazar jets are assumed to be aimed more directly towards us than Quasar jets are

89 Active Galaxies Seyfert Galaxies – Spirals Radio Galaxies – Ellipticals Quasars –Radio Quiet – Spirals –Radio Loud – Ellipticals Blazars All have active Galactic Nuclei !!

90 Limit on Size of Active Objects Variations in the intensity of an object can place a limit on how big it is Consider an active object 1 ly in diameter It suddenly “Flashes” Near side emitted photons reach us Middle photons reach us 6 months later Far side photons reach us 1 year later Intensity increase lasts a full year

91 Some Active galaxies flicker in such a way their volume is ~ 1 light day across Energy of a Thousand galaxies being emitted from a volume the size of our Solar System !! Obvious candidate  Black Hole

92 Supermassive Black Holes at Galaxy Centers As early as 1968, Lynden-Bell proposed that Black Holes were responsible for Active Galaxies Gravitational energy of gases falling into Black Holes would provide power for the immense radiation being seen from these galaxies However these Black Holes are much larger than the 5 to 10 M (  ) Black Holes in binary systems

93 Limits on Luminosity by a Black Hole Amount of Radiation from an Accretion disk is known as the Eddington Limit If the Luminosity exceeds this limit, there is too much radiation pressure present to allow additional gas to fall inward towards the Black Hole The gases would be pushed outward instead With gas pushed away, the luminosity fades and the pressure is reduced, so gas begins to fall inward again

94 Eddington Limit L Edd is the maximum luminosity that can be radiated by accretion on a compact object M is the mass of the compact object M (  ) and L (  ) are the Standard Solar Mass and Solar Luminosity respectively

95 Quasar 3C 273 L 3C 273 = 3 x 10 13 L (  ) Assume that this is the Eddington Limit Mass of Black Hole in 3C 273 ~ 1 Billion Solar Masses

96 Milky Way Galaxy probably has a Black Hole in its center of about 3 Million Solar Masses

97 Rotational Speeds are not constant in the core of the galaxy as other models have predicted Nor do they tend toward zero, but rather there are steep peaks on either side of the exact center These peaks indicate extremely large mass contained within ~ 5 arcseconds of galaxy center

98 Measurements on M 31 indicate a Black Hole at its center of 30 Million M (  ) in a volume of 5 pc New Techniques using better resolving telescopes (such as the X-ray Chandra Scope) have indicated a number of galactic black holes as they can resolve down to about 0.5 arcseconds Quasars not so useful as they are so far away they have too small an angular size. However no other source of energy seems plausible to create Quasar’s energy output

99 How Does a Black Hole Explain Active Galaxies?? Good Model should explain all facets of Active Galaxies –Large Luminosity –Unusual Spectra –Variable Light Output –Strong Energetic Jets Unified Model Proposes all Active Galaxies are different views of same type of object Supermassive Black Hole with an Accretion Disk

100 Gasses in Accretion Disk follow Kepler’s third law (conservation of Angular Momentum) – Gasses on inner orbits travel faster than gasses on outer orbits Faster inner gasses have friction with slower outer gasses cause outer gasses to lose kinetic energy and thus fall inward As gasses fall inward they are gravitationally compressed to high temperatures causing them to glow (Luminosity)

101 Variations in gas density will cause variations in gravitational compression which will cause variations in temperatures and hence variations in Luminosity (Variations in Active Galaxy Luminosity)

102 Inward motion towards center of Accretion disk is stopped abruptly near hole due to conservation of Angular Momentum Inertia wants rotating objects to move outward as their rotational speed increases (pizza dough) The point at which the inward force due to gravity of Black Hole is balanced by this outward movement due to inertia creates the inner edge of the Accretion disk

103 This inner edge is also where a shockwave is created due to this sudden stopping of inward flow To relieve the pressure created by this shockwave outward flows develop as shown perpendicular to the Accretion disk The particles leaving are traveling at high rates of speed and are thus Relativistic particles These Relativistic Particles are also charged, hence they create and drag Magnetic Fields with them

104 Forming Jets Recall with our Sun, differential rotation rates between the equator and the poles and the fact that magnetic fields are anchored somewhat to plasma, caused twisting of the Sun’s magnetic field eventually creating sunspots In the Accretion Disk Outflows, again recall the inner part of the accretion disk is moving more rapidly than the outer parts thus the magnetic field of the accretion disk is being distorted into a helix shape

105 Recent Evidence for Unified Theory Hubble Space Telescope views of NGC 4261 Shows two radio lobes extending 15 kpc from the nucleus of the galaxy A magnified view shows a disk ~250 pc in diameter at center of galactic nucleus Doppler measured speed of gas and dust indicate a mass of 1.2 x 10 9 M (  ) must exist

106 Types of Seyfert Galaxies Type 1 have both broad and narrow emission lines, usually with narrow weak emission lines superimposed over the broad lines Type 2 have only narrow emission lines

107 Type 1 Seyfert galaxy, NGC 5548 (to the left) normal spiral galaxy of similar distance and type, NGC 3277 (on the right).

108 NGC 3393 Type 2 Seyfert Galaxy

109 Type 2 Seyfert due to looking at the accretion disk more edge on so that only a small amount of the gas spiraling inward is seen Type 1 Seyfert due to looking at the accretion disk more along a pole which would allow more of the turbulent gasses to be observed

110 Why No New Quasars? Over time the available gas and dust that could be accreted to a Black Hole is used up. The acretion disk is used up. Unless new material comes near the black hole, no more fuel. The rest of galaxy is not gone. The material is just not close to the black hole. Galactic Collisions and mergers could provide new fuel sources

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