national aeronautics and space administration · galaxies is called arp 284, after their catalog...
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Signs of a Galactic EncounterIn this Hubble Space Telescope image, the tangled shape of the spiral galaxy
NGC 7714 provides evidence of a dramatic encounter with another galaxy.Several features indicate a dynamic history. Perhaps most prominent is the
ring-like structure that arcs around the left side of the galaxy. This golden loop, composed of older, intermediate-mass stars (like our sun) appears to extend into a faint tail stretching off to the right.
The galaxy also includes two bright blue tails where vibrant star formation is occurring. One blue tail is below the galaxy’s center and leads toward the right; the other is above the center and leads off the image to the left.
Following that upper tail leads to the explanation for the distorted structures. The tail becomes part of a bridge of material connecting to the smaller galaxy, NGC 7715 (see inset image). By studying their shapes and star formation, astronomers have deduced that the two galaxies swung closely past each other about 100 million to 200 million years ago. Together, the odd-looking pair of galaxies is called Arp 284, after their catalog number in Halton Arp’s Atlas of Peculiar Galaxies.
The universe contains many examples of galaxies that are stretched, pulled, and distorted in gravitational tug-of-wars between bypassing galaxies. Such close encounters also can compress interstellar gas clouds to spark intense star formation, as seen in the blue tails.
In NGC 7714, that star formation has formed an unusually large number of a rare type of star, called a Wolf-Rayet star. These very massive stars, nearing the end of their relatively short lives, are emitting strong winds that expel their outer layers into space.
NGC 7714 resides approximately 100 million light-years from Earth, in the constellation Pisces. Other objects in the image are much nearer or much farther away. The bright object just below center is a nearby star within our own galaxy. While some of the background galaxies show spiral forms, many resemble faint smudges of light. These galaxies can be up to tens to hundreds of times more distant than NGC 7714.
Credit: NASA, ESA Acknowledgement: A. Gal-Yam (Weizmann Institute of Science, Rehovot, Israel)
VOCABULARYGalaxy: A collection of stars, gas, and dust bound together by gravity. The smallest galaxies may contain only a few hundred thousand stars, while the largest galaxies have thousands of billions of stars. The Milky Way galaxy contains our solar system. Galaxies are classified or grouped by their shape. Round or oval galaxies are elliptical galaxies, and those showing a pinwheel structure are spiral galaxies. All others are called irregular because they do not resemble elliptical or spiral galaxies.
A Tale of Two GalaxiesThe two galaxies that make up Arp 284 are shown in this wide view,
taken by a ground-based telescope. The large galaxy with the distorted spiral shape is NGC 7714 (A). A faint bridge of stars and wispy material (B) connects NGC 7714 with its partner, NGC 7715 (C). The distorted shapes and the bridge are evidence of a gravitational encounter between NGC 7714 and NGC 7715. The encounter also produced a flurry of star birth, which can be seen in the strings of young, blue stars in NGC 7714.
Credit: Sloan Digital Sky Survey
You can get images and news about the Hubble Space Telescope on our website, hubblesite.org. For images and information on the Hubble mission, go to www.nasa.gov/hubble. Follow the Hubble mission on Twitter, @NASA_Hubble.
For educational activities, go to the Amazing Space website at amazingspace.org.
National Aeronautics and Space Administration
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National Aeronautics and Space Administration
In Search of … Interacting Galaxies.
Description.The “Interacting Galaxy NGC 7714” lithograph serves as the initial
source of information to engage students in a Level One Inquiry Activ-ity. In this activity, educators will use lithograph images to help students formulate questions about interacting galaxies. Educators will suggest selected resources about interacting galaxies to help students answer their questions. Students will then conduct research and provide supporting evidence for their conclusions. This curriculum support tool is designed to be used as an introductory activity in a unit that incorporates scientific inquiry or that has an interacting galaxy theme.
About Inquiry-based Learning.The inquiry process is driven by a student’s own curiosity, wonder,
interest, or passion to understand an observation or to solve a problem. It involves a process of exploring the natural or material world. This exploration prompts students to ask questions and to make discoveries in the search for new insights. A Level One Inquiry Activity uses questions and problem-solving methods directed by an educator. The process of inquiry-based learning can help prepare students to become more independent thinkers.
Grade Level.High school, grades 11–12
Prerequisites.Students should know that galaxies are huge collections of stars, gas,
and dust held together by gravity.
Misconceptions.Educators should be aware of the following common misconceptions
and determine whether their students harbor any of them. Students may think all galaxies are the same. They also may think galaxies are static, remaining unchanged with time.
VocabularyTerms students may encounter while doing further research on
interacting galaxies include:
Elliptical galaxy: A galaxy that is shaped like a football and contains mainly old stars and little gas or dust.
Spiral galaxy: A large pinwheel-shaped system of stars, dust, and gas clouds.See the lithograph for additional vocabulary terms.
Purpose.The purpose of this activity is to engage students in a Level One Inquiry
Activity with astronomical images and information. Students will gain experience using the Internet to search for information. They will practice the process skills of observing and analyzing. Students also will organize their material, present their findings, and reflect on what they have learned.
Materials. • “Interacting Galaxy NGC 7714” lithograph• Computer with Internet connection for conducting research.
Instructions for the Teacher.Preparation. • Obtain a lithograph for each student. The “Interacting Galaxy NGC 7714” lithograph PDF can be found at http://amazingspace.org/resource_page/516/galaxies/type• View the litho’s “Overview” page at http://amazingspace.org/resource_page/516/galaxies/type#educator_tab• Bookmark or identify as favorites the following suggested websites:
– STScI: “Hubble Spies a Loopy Galaxy” http://hubblesite.org/newscenter/archive/releases/2015/04/
– STScI: “Infant Galaxies Merging Near ‘Cosmic Dawn’” http://hubblesite.org/newscenter/archive/releases/galaxy/interacting/2013/53/
– STScI: “Tales of … A history of colliding galaxies: From oddballs to galaxy building blocks” http://amazingspace.org/resource_page/203/galaxies/type
– STScI: “Telescopes From the Ground Up: Edwin Hubble’s discovery that other galaxies exist” http://amazingspace.org/resources/explorations/groundup/lesson/scopes/mt_wilson/discovery.php
– STScI: The Star Witness news: “Close Encounters of the Galactic Kind” http://amazingspace.org/news/archive/2008/02
In Search of … Interacting Galaxies (cont’d)
– STScI: HubbleSite: “Interacting Galaxies” news releases http://hubblesite.org/newscenter/archive/releases/galaxy/interacting/
– Halton Arp’s “Atlas of Peculiar Galaxies” http://nedwww.ipac.caltech.edu/level5/Arp/frames.html
Procedure. Identify your students’ misconceptions about galaxies by having them
write down anything they know and understand about this topic. Have students volunteer their ideas about galaxies. From those ideas, identify their misconceptions and discuss them with the class. An alternative method is to collect your students’ written ideas about galaxies. From those ideas, compile a list of their misconceptions and discuss them with the class.
Ask students to study the images on both the front and back of the lithograph. Then have students write as many questions as they can about the features visible in the images. Collect the questions and group them by common themes. Ask students to read the information on the back of the lithograph. Then ask them if they found the answers to any of their questions. Have students use the Internet to research their questions. The Internet sites listed in the “Preparation” section provide a starting point for their research. Tell students how to access other websites.
Have students prepare presentations or written reports that include the answers to their questions. Their presentations also should address the evidence astronomers use to determine that galaxies are interacting. The presentation can be in the form of a skit, a story, a graphic organizer, or a PowerPoint show — any method that conveys a student’s understand-ing of the topic to another student, to a group of students, or to the entire class. Students may work individually or in groups. Ask students to check whether their original questions were answered during their research or from talking with other students. Then ask if they have any additional questions.
Instructions for the Student.Your teacher will ask you to write down what you know and understand
about galaxies. You may be asked to share this information with the rest of the class. Study the image of the interacting galaxy NGC 7714 on the front of the lithograph, and then look at the image on the back. Write down as many questions as you can about what you see in the images. When instructed by your teacher, read the back of the lithograph to find answers to your questions.
Using your questions as a guide, conduct research on the Internet to find the answers to your questions. Your teacher will provide websites to use for your research. Your teacher will ask you to create a presentation or a writ-ten report to demonstrate your understanding of the material you collected through your research. Your presentation also should address the evidence astronomers use to determine that galaxies are interacting. The presentation could be a skit, a story, a graphic organizer, a PowerPoint show, or whatever format that will communicate the information you learned about interact-ing galaxies. Your teacher will direct you to work individually or in small groups. You may be instructed to make your presentation to another student, to a group of students, or to the entire class.
Education Standards.AAAS Benchmarks: Project 2061.http://www.project2061.org/publications/bsl/online/index.php 1. The Nature of Science
B. Scientific InquiryBy the end of the 12th grade, students should know that:• Sometimes, scientists can control conditions in order to obtain evidence. When that is not possible, practical, or ethical, they try to observe as wide a range of natural occurrences as possible to discern patterns.
4. The Physical SettingG. Forces of Nature
By the end of the 12th grade, students should know that:• Gravitational force is an attraction between masses. The strength of the force is proportional to the masses and weakens rapidly with increasing distance between them.
National Aeronautics and Space Administration
Goddard Space Flight Center8800 Greenbelt RoadGreenbelt, Maryland 20771
www.nasa.gov
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