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Cepheid Variables in M100 Cepheid Variables in M100 Cepheid Variables in M100 Cepheid Variables in M100 Cepheid Variable Star in M100 Cepheid Brightness Changes Color Image of M100 Galaxy Animation Animations M100 Cepheids Cepheid Variables Distance Scale Press Release Text HST Measures Precise Distance to the Most Remote Galaxy Yet (PR94-49 October 26, 1994) Background Information Cosmic Yardsticks Hubble Constant http://oposite.stsci.edu/pubinfo/pr/94/49.html (1 of 2) [5/25/1999 10:39:37 AM] Cepheid Variables in M100 Links to public HST pictures Zolt Levay -- [email protected] Office of Public Outreach -- [email protected] June 14, 1995 Copyright© 1990-1999 The Association of Universities for Research in Astronomy, Inc. All Rights Reserved. http://oposite.stsci.edu/pubinfo/pr/94/49.html (2 of 2) [5/25/1999 10:39:37 AM] http://oposite.stsci.edu/pubinfo/jpeg/M100CphA.jpg http://oposite.stsci.edu/pubinfo/jpeg/M100CphA.jpg [5/25/1999 10:39:42 AM] http://oposite.stsci.edu/pubinfo/gif/M100CphA.txt PHOTO RELEASE NO.: STScI-PRC94-49a EMBARGOED UNTIL: 2:00 P.M. EDT Wednesday, October 26, 1994 CEPHEID VARIABLE STAR IN GALAXY M100 This NASA Hubble Space Telescope image of a region of the galaxy M100 shows a class of pulsating star called a Cepheid Variable. Though rare, these stars are reliable distance indicators to galaxies. Based on the Hubble observation, the distance to M100 has been measured accurately as 56 million light-years (+/- 6 million light-years), making it the farthest object where intergalactic distances have been determined precisely. Hubble's high resolution pinpoints a Cepheid, which is located in a starbirth region in one of the galaxy's spiral arms (bottom frame). The top three frames were taken on (from left to right) May 9, May 4, May 31, and they reveal that the star (in center of each box) changes brightness. Cepheids go through these changes rhythmically over a few weeks. The interval it takes for the Cepheid to complete one pulsation is a direct indication of the stars's intrinsic brightness. This value can be used to make a precise measurement of the galaxy's distance. Only Hubble Space Telescope has the required sensitivity and resolution to detect these "cosmic milepost" type stars out to great distances from Earth, according to astronomers. Typically, Cepheids in a crowded region of a distant galaxy are too faint and the resolution too poor, as seen from ground-based telescopes, to be detected clearly. Hubble was used to make twelve one-hour exposures, timed carefully in a two-month observing window, to discover 20 Cepheid variable stars in the M100 galaxy. Though M100 is the most distant galaxy in which Cepheid variables have been discovered, HST must find Cepheids in even more distant galaxies before accurate distances can be used to calculate a definitive size and age for the universe. Technical Information: The Hubble Space Telescope image was taken with the Wide Field Planetary Camera 2 (WFPC 2). This black and white picture was taken at visible light wavelengths. Target Information: M100 (100th object in the Messier catalog of non-stellar objects) is a member of the huge Virgo cluster of an estimated 2,500 galaxies. The galaxy can be seen by amateur astronomers as a faint, pinwheel-shaped object in the spring constellation Coma Berenices. Credit: Dr. Wendy L. Freedman, Observatories of the Carnegie Institution of Washington, and NASA The Wide Field and Planetary Camera 2 was developed by the Jet Propulsion Laboratory (JPL) and managed by the Goddard Space Flight Center for NASA's Office of Space Science. http://oposite.stsci.edu/pubinfo/gif/M100CphA.txt [5/25/1999 10:39:43 AM] http://oposite.stsci.edu/pubinfo/gif/M100CphA.gif http://oposite.stsci.edu/pubinfo/gif/M100CphA.gif [5/25/1999 10:39:55 AM] http://oposite.stsci.edu/pubinfo/jpeg/M100CphB.jpg http://oposite.stsci.edu/pubinfo/jpeg/M100CphB.jpg [5/25/1999 10:40:00 AM] http://oposite.stsci.edu/pubinfo/gif/M100CphB.txt PHOTO RELEASE NO.: STScI-PRC94-49b EMBARGOED UNTIL: 2:00 P.M. EDT Wednesday, October 26, 1994 HUBBLE SNAPSHOTS CAPTURE PULSATION RATE OF A "STELLAR MILEPOST" This sequence of images taken with NASA's Hubble Space Telescope chronicles the rhythmic changes in a rare class of variable star (located in the center of each image) in the spiral galaxy M100. This class of pulsating star is called a Cepheid Variable. The Cepheid in this Hubble picture doubles in brightness (24.5 to 25.3 apparent magnitude) over a period of 51.3 days. The interval it takes for the Cepheid to complete one pulsation is a direct indication of the stars's intrinsic brightness. This value can be used to make a precise measurement of the galaxy's distance, which turns out to be 56 million light-years from Earth. Cosmic distance measurements as accurate as this are needed to calculate the rate at which the universe is expanding. This value, called the Hubble Constant, is used to estimate the age and size of the universe. Though M100 is the most distant galaxy in which Cepheid variables have been discovered, HST must find Cepheids in a larger sample of galaxies before a definitive number can be agreed upon for the size and age of the universe Hubble Space Telescope was used to image repeatedly a region of M100 in order to pick out the flickering Cepheid candidates from normal stars. Twelve one-hour exposures, timed carefully in a two-month observing window, resulted in the discovery of 20 Cepheid variable stars. Technical Information: The Hubble Space Telescope images were taken on (from left to right) April 23, May 4, 9, 16, 20, 31, 1994 with the Wide Field Planetary Camera 2 (WFPC 2) This black and white picture was take at visible light wavelengths. Credit: Dr. Wendy L. Freedman, Observatories of the Carnegie Institution of Washington, and NASA The Wide Field and Planetary Camera 2 was developed by the Jet Propulsion Laboratory (JPL) and managed by the Goddard Space Flight Center for NASA's Office of Space Science. http://oposite.stsci.edu/pubinfo/gif/M100CphB.txt [5/25/1999 10:40:00 AM] http://oposite.stsci.edu/pubinfo/gif/M100CphB.gif http://oposite.stsci.edu/pubinfo/gif/M100CphB.gif [5/25/1999 10:40:08 AM] http://oposite.stsci.edu/pubinfo/jpeg/M100Color.jpg http://oposite.stsci.edu/pubinfo/jpeg/M100Color.jpg [5/25/1999 10:40:14 AM] http://oposite.stsci.edu/pubinfo/gif/M100Color.txt PHOTO RELEASE NO.: STScI-PRC94-49c EMBARGOED UNTIL: 2:00 P.M. EDT Wednesday, October 26, 1994 THE SPIRAL GALAXY M100 An image of the grand design of spiral galaxy M100 obtained with NASA's Hubble Space Telescope resolves individual stars within the majestic spiral arms. (These stars typically appeared blurred together when viewed with ground-based telescopes.) Hubble has the ability to resolve individual stars in other galaxies and measure accurately the light from very faint stars. This makes space telescope invaluable for identifying a rare class of pulsating stars, called Cepheid Variable stars embedded within M100's spiral arms. Cepheids are reliable cosmic distance mileposts. The interval it takes for the Cepheid to complete one pulsation is a direct indication of the stars's intrinsic brightness. This value can be used to make a precise measurement of the galaxy's distance, which turns out to be 56 million light-years. M100 (100th object in the Messier catalog of non-stellar objects) is a majestic face-on spiral galaxy. It is a rotating system of gas and stars, similar to our own galaxy, the Milky Way. Hubble routinely can view M100 with a level of clarity and sensitivity previously possible only for the very few nearby galaxies that compose our "Local Group.'' M100 is a member of the huge Virgo cluster of an estimated 2,500 galaxies. The galaxy can be seen by amateur astronomers as a faint, pinwheel-shaped object in the spring constellation Coma Berenices. Technical Information: The Hubble Space Telescope image was taken on December 31, 1993 with the Wide Field Planetary Camera 2 (WFPC 2). This color picture is a composite of several images taken in different colors of light. Blue corresponds to regions containing hot newborn stars. The Wide Field and Planetary Camera 2 was developed by the Jet Propulsion Laboratory (JPL) and managed by the Goddard Space Flight Center for NASA's Office of Space Science. Credit: J. Trauger, JPL and NASA http://oposite.stsci.edu/pubinfo/gif/M100Color.txt [5/25/1999 10:40:15 AM] http://oposite.stsci.edu/pubinfo/gif/M100Color.gif http://oposite.stsci.edu/pubinfo/gif/M100Color.gif [5/25/1999 10:40:33 AM] http://oposite.stsci.edu/pubinfo/press-releases/94-49.txt CONTACT: Ray Villard, STScI EMBARGOED UNTIL: 2:00 P.M. EDT (410) 338-4514 Wednesday, October 26, 1994 Dr. Wendy L. Freedman PRESS RELEASE NO.: STScI-PR94-49 Carnegie Observatories (818) 304-0204 HUBBLE SPACE TELESCOPE MEASURES PRECISE DISTANCE TO THE MOST REMOTE GALAXY YET An international team of astronomers using NASA's Hubble Space Telescope announced today the most accurate measurement yet of the distance of the remote galaxy M100, located in the Virgo cluster of galaxies. This measurement will help provide a precise calculation of the expansion rate of the universe, called the Hubble Constant, which is crucial to determining the age and size of the universe. "Although this is only the first step in a major systematic program to measure accurately the scale, size, and age of the universe," noted Dr. Wendy L. Freedman, of the Observatories of the Carnegie Institution of Washington, "a firm distance to the Virgo cluster is a critical milestone for the extragalactic distance scale, and it has major implications for the Hubble Constant." HST's detection of Cepheid variable stars in the spiral galaxy M100, a member of the Virgo cluster, establishes the distance to the cluster as 56 million light-years (with an uncertainty of +/- 6 million light-years).
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