Classifying Galaxies Start of Lesson What is a galaxy? A galaxy is made of billions of stars, dust, and gas all held together by gravity. Galaxies are scattered throughout the Universe. They vary greatly in size and shape. Not all galaxies look alike. This is a galaxy. This is a galaxy. Student Lesson http://world.smv.mus.va.us/~hastings/student2.htm (1 of 6) [5/25/1999 12:33:53 PM]
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Classifying Galaxies
Start of Lesson
What is a galaxy?
A galaxy is made of billions of stars, dust, and gas all heldtogether by gravity. Galaxies are scattered throughout theUniverse. They vary greatly in size and shape. Not allgalaxies look alike.
This is a galaxy.
This is a galaxy.
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This is also a galaxy
Did you notice that these galaxy pictures don't look alike?
When telescopes led to the discovery of galaxies, astronomers observedmany differences.
In 1926, an astronomer named Edwin Hubble decided to classify the galaxies, grouping them accordingto some logical scheme.
He could have classified them according to color, because galaxies are different colors. Youcan see many different colored galaxies in the Hubble Deep Field image.
He could have classified them according to size, callingsmall galaxies "dwarf galaxies" and calling large galaxies"massive galaxies".
After considering different schemes, he decided to arrange orgroup them by shapes. He would classify them according to theway they looked. In science, the study of something according toits form or structure is called "morphology".g
galaxy galaxy galaxy galaxy galaxy galaxy galaxy galaxy galaxygalaxyLet's consider the three galaxies we saw earlier. They are
typical of the three main types of galaxies that Hubble classified.
The first type of galaxy you saw is an elliptical galaxy. The word ellipticalrefers to its degree of "roundness". Hubble used the letter "E" to stand forelliptical galaxies.To see elliptical galaxies, click on the Galaxy Guide.
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Hubble called the second type of galaxy you saw a spiral galaxy. Itreminded him of a pinwheel or whirlpool. He used the letter "S" to stand forspiral galaxies.
The third type of galaxy reminded Hubble of a spiral with asolid bar across the center. He called it a barred spiral galaxy.He used the letters "SB" to stand for barred spirals.
To see barred spiral galaxies, click on the Galaxy Guide
ga
l
Many galaxies have strange, irregualr shapes, and do not fit neatly into any of these three categories.
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To see an example of a nearby irregular galaxy, click on the Galaxy Guide.
Can you name the three main types of galaxies? Did you discover that each main typeis divided into smaller groups? Click here to review.
To show the relationship of the galactic shapes, Edwin Hubble arranged the main types ofgalaxies and the sub-types into a chart that has come to be called "The Tuning ForkDiagram".
The Hubble "Tuning Fork Diagram" is the simplest way to classify galaxies. When you lookat a picture of a galaxy, and try to classify it, you are trying to place it on the diagram whereit belongs.
You have seen some pictures of galaxies in this lesson and have looked at how they wereclassified. Now it's time for you to classify some galaxy pictures. Are you up to the
challenge? Click here.
NOTE: You must have a java-enabled browser in order for the next page to work. If yourbrowser does not work with java applets, Click here.
The Hubble Telescope has looked far into space and discovered manygalaxies. Travel to the Hubble Space Telescope Institute to look at animage of a newly discovered galaxy. See if you can classify it by itsshape.
Read the summary written below the picture to see if you were correct!Use the Back button at the top of your Web Browser to return herewhen you have finished your visit to Space Telescope Science Institute.
Space Telescope Science Institute
The Hubble Space Telescope is making frequent new
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discoveries. If you want to do more galaxy exploring at theHubble Space Telescope Institute, Click Here
Use the Back button at the top of your Web Browser toreturn here when you have finished your visit to SpaceTelescope Science Institute.
Now that you have had practice at classifying galaxies according to shape,you are ready to take the challenge of becoming a member of the HubbleDeep Field Academy.
Remember this picture?
This image was taken by the Hubble Space Telescopein December of 1995. It shows lots of previouslyunknown galaxies of different colors, shapes, andsizes.
Use this link to the "Cosmic Classifier" to test yournew skill at classifying galaxies in the Hubble DeepField image.
Want to find out more about Edwin Hubble's Classification system? Click onthe obsrvatory dome!
Are you ready to go galaxy hopping on yourown? Explore these astronomy links!
What is this? Click on the image to find out!
Something mysterious at the heart of an elliptical galaxy!
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How many galaxies can you see here? Click on the image to enlarge it.
How many different galaxy classifications identify in this picture?
Click you your back-arrow to come back here when you have finished.
Click here for late-breaking galactic news!
comments to George & Jane Hastings
this page last updated November 25, 1998
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Edwin Hubble (1889-1953) guides the exposure of aphotographic plate at the Newtonian focus of the100-inch telescope in 1923. With this telescope, Hubblemeasured the distances and velocities of galaxies, workwhich led to today's concept of an expanding Universe.According to this profound idea, the Universe began tento twenty billion years ago with a Big Bang. Thereceding galaxies that Hubble observed trace theexpansion of space from that dense beginning. Thetelescope is a mechanical masterpiece and was dedicatedas an International Historical Mechanical EngineeringLandmark on June 20, 1981, by the American Society ofMechanical Engineers, only the fourth such award
granted in the United States.
Edwin Hubble grew up in Wheaton, Illinois, a suburb of Chicago.
For a complete biography, click here.
Before he went on to become a famous astronomer, Edwin Hubble taughtSpanish and physics as well as coached basketball at New Albany High School,Indiana, in 1914. The New Albany High School Yearbook "Vista" was dedicated tohim.
Look at the dedication page of the 1914 NAHS yearbook to see a picture ofCoach Hubble and the winning basketball team, then use the back arrow at the topof your browser to return here.
For more information about Edwin Hubble and his system of galaxy classificationClick Here, then use the back arrow at the top of your browser to return here.
Most galaxies are elliptical. Some elliptical galaxies are nearly circular in shape.Some elliptical galaxies are extremely stretched out, flattened,or elongated. To dealwith this variation, Hubble divided the "E" classification into 8 sub-groups, which hecalled "E0", "E1", "E2", "E3", "E4", "E5", "E6", and "E7".
E0 galaxies are nearly circular in shape. E1 galaxies are stretched out a little. E2galaxies are more elongated, E3 galaxies even more elongated or flattened, all the way up to E7galaxies, which are extremely elongated or stretched out.
Look at these examples:"E1", "E2", "E3", "E4", "E5".
When you looked at elliptical galaxies you saw that as the classification numbers progressed fromE1 toward E7, their appearance was more and more flattened or elongated. Edwin Hubbleobserved other galaxies that were elongated, but they were different from elliptical galaxiesbecause they had bright centers. He called the bright centers of galaxies "nuclei". He noted thatmany galaxies with bright nuclei also had "arms" spiraling out from the middle. He called thesegalaxies with bright nuclei "spiral galaxies".
Hubble named the galaxies that had bright nuclei but no spiral arms "S0"(S-zero) galaxies.
He classified galaxies with spiral arms into three sub-groups that described how tightlythe arms were wound around the nucleus. Hubble called spirals with their arms wound
tightly around the nucleus, type "Sa". He called spirals with their arms less tightly wound (that is,looser and looser) "Sb" and "Sc". Here are examples of these types of spiral galaxies.
In about a third of spiral galaxies, the arms spiral out, not from the center, but from astraight bar of stars, gas, and dust that extends from both sides of the bright nucleus.Hubble classified these barred spirals into sub-groups "a" to "c" in order of increasingopenness of the arms, but with a "B" for barred inserted: "SBa", "SBb", "SBc".Here are examples of these three sub-groups of barred spiral galaxies.
A new image from the Hubble telescope first posted on "Astronomy Picture of theDay" reveals a barred spiral galaxy with a starburst ring near its center, where new
Galaxies that can't be classified aseither spiral or elliptical are calledirregular galaxies. Every irregulargalaxy is unique. It doesn't look likeany other galaxy. It just isn't a spiralor an elliptical.
Irr I galaxies have lots of young stars,gas, and dust, but do not have spiralarms.
Irr II galaxies look strange. It seemslikely that Irr II galaxies have beendistorted by collisions with othergalxies at some time in their history.
South of the Equator, it is possible tosee the Large and Small Magellanic Clouds, the two irregular galaxies closest to our own Milkey WayGalaxy. Astronomers predict that they will eventually collide with the Milkey Way and be incorporatedinto our own galaxy.
This chart shows all of the classifications of different shapes of galaxies. S0 is an extra categorythat Hubble used to describe the shape of galaxies that were about halfway between ellipticalgalaxies and spiral galaxies. E = Elliptical, S = Spiral, SB = Barred Spiral.
Look at the rotating galaxy and then at the Hubble Tuning Fork Diagram next to it. Edwin Hubble wouldhave classified this galaxy as type Sa. Notice its well defined center and spiral arms.
On the next page, you will have a chance to classify some unidentified galaxies, and use your mouse toplace the galaxy images on the Hubble Tuning Fork Diagram. To move the galaxy pictures onto theHubble Tuning Fork Diagram you will:
put your mouse pointer on a galaxy image●
hold down the mouse button●
while holding down the button, move your pointer to a spot on the diagram●
release the mouse button●
When you release the mouse button, the galaxy image will move to the spot you have selected. If youwish to move it again, you can follow the same directions. When you have finished placing all the galaxyimages on the diagram, check your work by clicking on the the Galaxy Guy.
Discovery of a Nearby Spiral Galaxy Behind theMilky WayR.C. Kraan-Korteweg (Groningen), A.J. Loan (Cambridge), W.B. Burton (Leiden) O. Lahav(Cambridge), H.C. Ferguson (STScI), P.A. Henning (Univ. New Mexico), D. Lynden-Bell (Cambridge)
Color image of Dwingeloo 1 from the Isaac Newton Telescope
The full paper (100 Kb postscript file) appears in Nature, November 3 1994.
SummaryThe disk of the Milky Way contains a lot of gas and dust, which obscures about 20% of the extragalacticsky. Galaxies hidden behind the Milky Way may have an important influence on the dynamics of theLocal Group and its peculiar motion relative to the cosmic microwave background radiation. Here wereport the discovery of a large spiral galaxy, which we call Dwingeloo 1, during the course of a searchfor emission from atomic hydrogen (HI) associated with galaxies hidden by the disk of the Milky Way --such emission is not obscured by the disk if the velocity of the emission differs from that of the local gas.The new galaxy seems to be associated with the group containing IC342 and the Maffei galaxies, and asubsequent optical image suggests that it is of type SBb. The detection of Dwingeloo 1 early in thecourse of this survey suggests that many more galaxies hidden behind the Milky Way remain to bediscovered. Harry Ferguson [email protected]
The Space Telescope Science Institute is operated by the Association of Universities for Research inAstronomy, Inc. (AURA), for NASA, under contract with the Goddard Space Flight Center, Greenbelt,MD. The Hubble Space Telescope is a project of international cooperation between NASA and theEuropean Space Agency (ESA).
The Space Telescope Science Institute's Office of Public Outreach is seeking a full time teacher from anyacademic level, grades 6-12, to participate in their Internship Program. The intern will be actively involvedin the development of interactive activities for the World Wide Web; as well as, conducting pilot programsto encourage partnerships and distribution of materials nationwide.
Amazing Space is a set of web-based activities primarily designed for classroom use, butmade available for all to enjoy.
Current activities include:
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Edwin Hubble was an American astronomer who made vital contributions to the studyof galaxies, establishing the existence of galaxies outside of the Milky Way andproving that the universe is expanding. For his revolutionary contributions to ourunderstanding of galaxies and of the scope of the universe, Hubble was recognized bythe astronomical community in 1983, thirty years after his death, when the SpaceTelescope was renamed in his honor.
Early Life and Education
Edwin Powell Hubble was born on November 20, 1889 in Marshfield, Missouri before the eyes of bothhis parents and his grandparents. At a young age, Hubble had a taste for books and an interest inastronomy, unlike many of the other great astronomers portrayed in these biographies.
A strong athlete in high school, Hubble received a scholarship from the University of Chicago but had towork hard nonetheless to pay the balance of his expenses. Perhaps his most interesting job during thistime was as a lab assistant to Robert Millikan -- well known for determining the charge of an electron inhis Nobel prize-winning oil drop experiment.
Hubble received his B.S. degree from the University of Chicago and was offered a Rhodes Scholarship tostudy law at Queens College in Oxford. Though Hubble started a law practice after returning to theUnited States, he abandoned his practice and returned to Chicago to study for his doctorate in astronomy,which he received the day before joining the army in 1917.
Hubble and the Observatory
It is difficult to find a photograph in which Edwin Hubble is not seen poised on a mammoth telescope inan observatory. From the time he began his doctorate work at the University of Chicago's YerkesObservatory in 1914 to his death, Hubble worked with many observatories and was influential in theconstruction of the largest ground-based telescope in the world.
Mount Wilson. After the First World War, Hubble was married to Grace Burke and began work at theMount Wilson Observatory with its 100-inch telescope. Above all, his research there demonstrated theneed for a larger telescope that could see farther. Hubble left Mount Wilson in 1942, off again to war,where he would be awarded a Medal of Merit in 1946, and returned again after the war to continue hisresearch.
Mount Palomar. Most of Hubble's work was done at the Mount Wilson Observatory, but he wasintimately involved with the Mount Palomar Observatory, part of the committee that oversaw its
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construction. Even more importantly, he advised and assisted in the construction of the Mount Palomar200-inch Hale telescope, where he can be seen perched in photos.
Hubble's "Island Universe" Theory
In the early 20th century, before Hubble began his extensive work, there was an intense debate raging inthe field of astronomy over great clusters of stars, called "nebulae." At the time, there was no evidencethat there were galaxies in the universe that lay beyond the Milky Way. At issue, then, was whether these"nebulae" were a part of the Milky Way or some other star formations beyond our galaxy. In some ways,it is more difficult to comprehend that the existence of other galaxies was uncertain in such recent yearsthan to believe that Copernicus was doubted in the 16th century for proposing the idea of a solar system.
Finally, Hubble determined that these "nebulae" are indeed other galaxies because they are moving awayfrom the earth. In fact, he concluded that these star systems are each "island universes," not part of ourown galaxy. This was an enormously important discovery, for it opened up a great new realm of researchand provided an important base for the theory of the expanding universe.
The Expanding Universe
When Hubble observed other galaxies moving away from Earth, he was lookingat the wavelengths of their light. If the wavelengths are longer and towards thered end of the spectrum, then the galaxy is going away from us; but if thewavelengths are shorter and bluish, then the galaxy is coming towards us. Laterin the Guided Tour, we will expand on the concepts of "redshifting" and"blueshifting." For now, it is enough to understand that he could prove that thesegalaxies were moving away from Earth.
Diagram. Red shift and Blue shift. Hubble used the wavelengths of light to determine whether galaxies were movingtowards or away from us. Galaxies with wavelengths in the red regions are moving away while those with wavelengths inthe blue regions are coming towards us. Original diagram by The Online Planetarium Show.
Another interesting aspect of Hubble's research was his discovery that more distant galaxies move awaymore quickly than those closer to us. The very notion that these galaxies were actually receding is animportant one because it is a central tenant of the Big Bang theory, in which a powerful explosioninitiates the inflation of the universe. Incredibly, Albert Einstein referred to Hubble's work as "beautiful"and adjusted his relativity equations to account for the fact that the universe is expanding!
Classification of Galaxies
Hubble's work classifying galaxies is hardly unimportant, yet it pales in comparison with his far-reachingdiscoveries. Hubble grouped galaxies into three main categories:
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Spirals -- with arms winding around a central nucleus; our Milky Way, for instance, is a spiral●
Ellipticals -- found in a variety of rounded shapes●
Irregulars -- come in plenty of peculiar forms●
Ever since, astronomers have been identifying galaxies as either spiral, elliptical or irregular. Though weregularly use these terms to describe galaxies and though this terminology is exceedingly important toastronomy, Hubble's name is only rarely mentioned, much less associated with these classifications.
Hubble's . . . Legacy?
When we speak of the telescope, Galileo's name frequently surfaces, for he popularized the instrumentfor astronomical purposes. For all of Edwin Hubble's incredible discoveries that are discussed in thisbiography -- particularly his proof of the very existence of galaxies outside of the Milky Way -- it wouldseem that the leaps in astronomy's understanding of the universe made by his work are comparable tothose made by the studies Galileo or Copernicus.
Yet for all of his accomplishments, Hubble's name is relatively obscure; even when we hear about theSpace Telescope that was named in his honor, we rarely learn about his contributions or life. Accordingto several biographers, he should be looked upon as an astronomer who "revolutionized" ourunderstanding of the universe -- much like Galileo or Copernicus. Perhaps in several hundred years wewill.
Return to "The Entrancing Mysteries of Space"...
Browse the Table of Contents...
Return to The Online Planetarium Show Homepage...
The Online Planetarium Show: The Life of Hubble
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Looking for more astronomy information?Try these links!
Project Ceres - Classifying Galaxies
Astronomy resources - this is excellent!
Galaxies and Quasars
Hands On Universe: Galaxy Types
Space Telescope Science Institute - These are links to information of generalinterest regarding the Hubble Space Telescope (HST) and the Space TelescopeScience Institute (ST ScI). This includes information or interest to educators,students, the media and the general public; pictures resulting from observations byHST instruments.
young galaxies - Single image - part of the famous Hubble "Deep Field"
THE SCIENCE EDUCATION GATE-WAY! - Learning adventures in Earth and Space science from aNASA-sponsored partnership of museums, researchers and educators. SEG-way is the public userinterface of the Science Information Infrastructure (SII), funded by NASA's Information Infrastructure
Galaxy Hot Links to other Astronomy Resources
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Technology and Applications (IITA), a component of the Federal High Performance Computing andCommunications program (HPCC).
What is a galaxy? - To continue your study of galaxies, visit this site. It is a service of the HighEnergy Astrophysics Science Archive Research Center (HEASARC) at the NASA GoddardSpace Flight Center in Maryland.
StarChild: A learning center for young astronomers a COOL site for kids, includes Level I andLevel II sections on "The Solar System", "The Universe", "Space Stuff", and a Glossary.
Harvard Atlas of Galaxies - galaxy images in multiple wavelengths.
Links to Telescope Sites - Almost 300 observatories all over the world now maintain links on the worldwide web. Many of them have more information about galaxies.
Students for the Exploration and Development of Space - Internet Space ArchiveLPL/Arizona. A large internet resource of Space related images, information and software.
The Interactive NGC Catalog Online - This is the interactive NGC (and IC, and Messier) catalog atSEDS (Students for the Exploration & Development of Space). It contains open and globular starclusters, diffuse and planetary nebulae, supernova remnants, galaxies of all types.
Astronomical Society of the Pacific
List of NGC Images
NGC 5 through NGC 1982
NGC 2023 through NGC 3995
NGC 4027 through NGC 5904
NGC 6093 through NGC 7793
Appendix: NGC Additions
Information Infrastructure Technology and Applications - Multimedia libraries at your fingertips.Remote sensing databases of the earth and the universe easily accessible to everyone. Classrooms on theInternet allowing students to interact with scientists and engineers while they work. A project of theNational Aeronautics and Space Administration (NASA), IITA is working on all of this and more byfunding fifty different programs. Explore this site and learn what the future holds for you!
Multiwavelength Atlas of Galaxies - Education and Outreach - This atlas of spiral and elliptical galaxiescontains images that span the optical, X-ray, Radio and Infrared regions of the electromagnetic spectrum.These images of galaxies provide important information about the stars, cold, warm and hot gas, dust andcharged particles that exist in each galaxy. If you are interested in background information about types ofgalaxies, or the origin of the radiation, links will give you this information at a high school orundergraduate level. Another link will lead you to web sites of the telescopes that took these images.
Astronomy Education Resources - AstroEd: K-12 Outreach Project, University of Washington
Galaxy Hot Links to other Astronomy Resources
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What's New Curriculum materials and on-line courses. Newsletters and magazines, Images andAnimations, History of Astronomy, Views of the Sky, Additional Astronomy Resources, Mirror Sites,NASA, Physics Resources, and Other Science Resources.
HEASARC/GSFC Home Page - High Energy Astrophysics Science Archive Research Center
Mount Wilson Observatory - Includes a "Virtual Tour" and sections on Science, Education, What's New,History, Services, and Requesting time on the 100" telescope.
Space Telescope Electronic Information Service - Search for Hubble Space Telescope images of nearbygalaxies or distant galaxies
Space Hotlist at NASA.
Lots of space links
STAR HUSTLER Home Page
More Astronomy Links
The WWW Virtual Library: Astronomy and Astrophysics
Astronomy (Science)
Astronomy Information Systems
The Galaxy Page
Harvard-Smithsonian Center for Astrophysics
Harvard-Smithsonian Theoretical Astrophysics Group
International Journal of Solar System Exploration
Archive-name: astronomy/ftp-sites
The sci.astro FAQ
Galaxy Hot Links to other Astronomy Resources
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Astronomy Picture of the DayDiscover the cosmos! Each day a different image or photograph of our fascinating universe is featured,
along with a brief explanation written by a professional astronomer.
March 26, 1998
Galaxies AwayCredit: W. Keel and R. White (U. Alabama), NASA
Explanation: This striking pair of galaxies is far, far away ... about 350 million light-years from Earth.Cataloged as AM0500-620, the pair is located in the southern constellation Dorado. The backgroundelliptical and foreground spiral galaxy are representative of two of the three major classes of galaxieswhich inhabit our Universe. Within the disks of spiral galaxies, like our own Milky Way, gas, dust, and
APOD: March 26, 1998 - Galaxies Away
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young blue star clusters trace out grand spiral "arms". The dust lanes along the arms of this particularspiral stand out dramatically in this Hubble Space Telescope image as they obligingly sweep in front ofthe background elliptical. Like the central bulges of spiral galaxies, elliptical galaxies tend towardspherical shapes resulting from more random motions of their stars. But while spirals produce new stars,star formation in ellipticals which lack gas and dust seems to have stopped. How do galaxies evolve withcosmic time? Evidence is growing that graceful galaxy shapes can hide a violent history.
< Archive | Index | Search | Calendar | Glossary | Education | About APOD >
Back to Classifying Galaxies
Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)NASA Technical Rep.: Jay Norris. Specific rights apply.
A service of: LHEA at NASA/ GSFC&: Michigan Tech. U.
APOD: March 26, 1998 - Galaxies Away
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Astronomy Picture of the DayDiscover the cosmos! Each day a different image or photograph of our fascinating universe is featured,
along with a brief explanation written by a professional astronomer.
April 9, 1998
Quasar in an Elliptical GalaxyCredit: J. S. Dunlop, R. J. McLure (U. Edinburgh), HST, NASA
Explanation: Where do quasars live? Quasars are the brightest objects in the universe, so bright they canbe seen from across the universe. Observations continue to show that most quasars are surrounded by arelatively faint nebulous patch. Astronomers are trying to identify the nature of these patches. The abovefalse-color picture shows a central quasar embedded in an unusual elliptical galaxy. The galaxy is beinggravitationally distorted by a neighboring galaxy. Recent evidence indicates that most quasars live nearthe centers of large, elliptical galaxies - even those quasars where no host galaxy could be found before.Quasars themselves are thought to result from matter falling toward supermassive black-holes.
Tomorrow's picture: Comet Atmosphere
APOD: April 9, 1998 - Quasar in an Elliptical Galaxy
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Astronomy Picture of the DayDiscover the cosmos! Each day a different image or photograph of our fascinating universe is featured,
along with a brief explanation written by a professional astronomer.
September 29, 1998
A Peculiar Cluster of GalaxiesCredit: FORS1, 8.2-meter VLT, ESO
Explanation: Far across the universe, an unusual cluster of galaxies has been evolving. A diverse groupof galaxies populate this cluster, including, on the left, an unusual galaxy showing an equatorial polarring and a large spiral. Above looms a large elliptical galaxy. The reason for the small size of galaxies onthe right is not yet known - these galaxies might be smaller or might just lie even further in the distance.Almost every spot in this picture is a galaxy. Studying distant clusters like this may help astronomersbetter understand when and how these cosmic giants formed.
APOD: September 29, 1998 - A Peculiar Cluster of Galaxies
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THE UNIVERSE "DOWN UNDER" IS THE TARGET OF HUBBLE'S LATEST DEEP-VIEW
Turning its penetrating vision toward southern skies, NASA's Hubble Space Telescope has peered down a 12 billion light- yearlong corridor loaded with a dazzling assortment of thousands of never-before seen galaxies. The observation, called the HubbleDeep Field South (HDF-S), doubles the number of far-flung galaxies available to astronomers for deciphering the history of theuniverse.
See more details below the image.
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This new far-look complements the original Hubble "deep field" taken in late 1995, when Hubble was aimed at a small patch ofspace near the Big Dipper. The new region is in the constellation Tucana, near the south celestial pole.
The 10-day-long observation was carried out in October 1998 by a team of astronomers at the Space Telescope Science Institute(STScI), Baltimore, MD, and NASA's Goddard Space Flight Center, Greenbelt, MD. It is being made available today to theworldwide astronomy community for further research, and to the general public interested in the most distant reaches of thecosmos.
"The southern field promises to be the most studied area of the sky over the next five years," says STScI astronomer RobertWilliams, when as STScI Director, he used his discretionary time to undertake the first deep field campaign, and has overseenthe latest observation.
"We have eagerly awaited this new set of images ever since the first HDF, which had a dramatic impact on the entire science ofastronomy. Hubble's deep field views revealed a large, heretofore unseen fraction of the universe and opened it up tointerpretation and understanding."
It will take months for astronomers to digest what new secrets of the universe are within this latest look. At first glance theHDF-S appears to validate the common assumption that the universe should look largely the same in any direction.
The two deep fields now give astronomers two "core samples" of the universe for better understanding the history of thecosmos. The pair of observations can be compared to more confidently infer the state of the cosmos as a whole. It would takeastronomers 900,000 years to use Hubble to survey the entire sky to the depths of the HDF. So, they must rely on a thin,"looking-through-soda straw" view across the cosmos and infer the history of star and galaxy formation.
The new deep field also provides an astronomical gold mine for powerful new ground-based telescopes located in the southernhemisphere to undertake follow-up observations of galaxies and precisely measure their distances.
All of Hubble's new cameras and other instruments were trained on the sky simultaneously for the observation. The SpaceTelescope Imaging Spectrograph was used to dissect light from a quasar (bright, active core of a distant galaxy) in its field ofview. The light from the quasar has traveled nearly three- quarters of the way across the universe, and provides a powerfulthree-dimensional probe of the universe's hidden structure. Invisible clouds of primeval hydrogen gas strung along billions oflight-years between us and the quasar will be detectable in the signature of the quasar's light. The quasar is so brilliant it is like asearchlight shining through haze.
The original HDF engaged hundreds of astronomers around the world. Broad conclusions were drawn based on meticulousfollow-up studies of the myriad galaxies along Hubble's extremely narrow line-of-sight. To date, conclusions about the rate ofstar formation and evolution of galaxy shapes have been based on this one narrow "core-sample" of the universe. Because theoriginal HDF was picked as a seeming bland example of what the universe at large probably looks like, astronomers haveassumed it was a representative sample. But they needed a second sample to validate early assumptions, and they needed a fieldthat contained a distant quasar to give them important additional information that the northern field did not contain.
The Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy, Inc. (AURA)for NASA, under contract with NASA's Goddard Space Flight Center. The Hubble Space Telescope is a project of internationalcooperation between NASA and the European Space Agency.
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