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Images: Hubble Images a Swarm of Ancient Stars

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Hubble Images a Swarm of Ancient Stars

This stellar swarm is M80 (NGC 6093), one of the densest of the 147 known globular star clusters in the Milky Way galaxy. Located about 28,000 light-years from Earth, M80 contains hundreds of thousands of stars, all held together by their mutual gravitational attraction. Globular clusters are particularly useful for studying stellar evolution, since all of the stars in the cluster have the same age (about 15 billion years), but cover a range of stellar masses. Every star visible in this image is either more highly evolved than, or in a few rare cases more massive than, our own Sun. Especially obvious are the bright red giants, which are stars similar to the Sun in mass that are nearing the ends of their lives. By analyzing the Wide Field and Planetary Camera 2 (WFPC2) images, including images taken through an ultraviolet filter, astronomers have found a large population of "blue stragglers" in the core of the cluster. These stars appear to be unusually young and more massive than the other stars in a globular cluster. However, stellar collisions can occur in dense stellar regions like the core of M80 and, in some cases, the collisions can result in the merger of two stars. This produces an unusually massive single star, which mimics a normal, young star. M80 was previously unknown to contain blue stragglers, but is now known to contain more than twice as many as any other globular cluster surveyed with NASA's Hubble Space Telescope (HST). Based on the number of blue stragglers, the stellar collision rate in the core of M80 appears to be exceptionally high. M80 is also unusual because it was the site of a nova explosion in the year 1860. Nova outbursts occur when a close companion star transfers fresh hydrogen fuel to a burned-out white dwarf. Eventually the hydrogen ignites a thermonuclear explosion on the surface of the white dwarf, giving rise to the nova outburst. The ultraviolet Hubble observations have revealed the hot, faint remnant of this exploding star, which was named T Scorpii in the 19th century. Curiously, however, the WFPC2 observations have revealed only two other nova-like close binary stars in M80, far fewer than expected theoretically based on the stellar collision rate. So the blue stragglers in M80 seem to indicate that there are lots of collisions, yet the nova-like stars suggest only a few. Sometimes life for astronomers isn't so simple, but it is from exploring discrepancies like this that our understanding eventually deepens. This high-resolution image was created from 2 separate pointings of HST. One WFPC2 data set was obtained by Francesco R. Ferraro (ESO, Bologna Obs.), Barbara Paltrinieri (U. La Sapienza), Robert T. Rood (U. Virginia), and Ben Dorman (Raytheon/STX), who study blue stragglers. The other data set was acquired by Michael Shara (STScI, AMNH), David Zurek (STScI), and Laurent Drissen (U. Laval) to search for dwarf novae. Technical facts about this news release: About this Object Object Name: NGC 6093 (M80) Object Description: Globular Cluster in the Milky Way Galaxy Position (J2000): R.A. 16h 17m 03s Dec. -22° 58' 30" Constellation: Scorpius Distance: 8.7 kiloparsecs (28,000 light-years) Dimensions: The image is 3 arcminutes on the vertical side. About the Data Instrument: WFPC2 Exposure Dates: October 1994, August-October, 1997; January/April, 1996 Filters: F336W(U), F439(B), F555W(V), F675W(R) Principal Astronomers: 1994/1997 Image: M. Shara (STScI, AMNH), D. Zurek (STScI), L. Drissen (Laval University). 1996 Image: F. Ferraro (ESO), B. Paltrinieri (Universita La Sapienza), R. Rood (University of Virginia), B. Dorman (Raytheon STX & Laboratory for Astronomy & Solar Physics). _________________________________________ About this Image Image Credit: NASA and The Hubble Heritage Team (STScI/AURA) Release Date: July 1, 1999 12:00 noon (EDT) Orientation: North is toward the upper right of the image. What is Hubble Heritage? A monthly showcase of new and archival Hubble images. Go to the Heritage site. This stellar swarm is M80 (NGC 6093), one of the densest of the 147 known globular star clusters in the Milky Way Galaxy. Located about 28,000 light-years from Earth, M80 contains hundreds of thousands of stars, all held together by their mutual gravitational attraction. Globular clusters are particularly useful for studying stellar evolution, since all of the stars in the cluster have the same age (about 15 billion years), but cover a range of stellar masses. Every star visible in this image is either more highly evolved than, or in a few rare cases more massive than, our own Sun. Especially obvious are the bright red giants, which are stars similar to the Sun in mass that are nearing the ends of their lives. *News Release Number:*: STScI-1999-26a

NASA Identifier: SPD-HUBBLE-STScI-1999-26a



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Date Posted:10.10.2012 12:57

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  • *Description*:  This stellar swarm is M80 (NGC 6093), one of the densest of the 147 known globular star clusters in the Milky Way galaxy. Located about 28,000 light-years from Earth, M80 contains hundreds of thousands of stars, all held together by their mutual gravitational attraction. Globular clusters are particularly useful for studying stellar evolution, since all of the stars in the cluster have the same age (about 15 billion years), but cover a range of stellar masses. Every star visible in this image is either more highly evolved than, or in a few rare cases more massive than, our own Sun. Especially obvious are the bright red giants, which are stars similar to the Sun in mass that are nearing the ends of their lives.   By analyzing the Wide Field and Planetary Camera 2 (WFPC2) images, including images taken through an ultraviolet filter, astronomers have found a large population of "blue stragglers" in the core of the cluster. These stars appear to be unusually young and more massive than the other stars in a globular cluster. However, stellar collisions can occur in dense stellar regions like the core of M80 and, in some cases, the collisions can result in the merger of two stars. This produces an unusually massive single star, which mimics a normal, young star. M80 was previously unknown to contain blue stragglers, but is now known to contain more than twice as many as any other globular cluster surveyed with NASA's Hubble Space Telescope (HST). Based on the number of blue stragglers, the stellar collision rate in the core of M80 appears to be exceptionally high.   M80 is also unusual because it was the site of a nova explosion in the year 1860. Nova outbursts occur when a close companion star transfers fresh hydrogen fuel to a burned-out white dwarf. Eventually the hydrogen ignites a thermonuclear explosion on the surface of the white dwarf, giving rise to the nova outburst. The ultraviolet Hubble observations have revealed the hot, faint remnant of this exploding star, which was named T Scorpii in the 19th century. Curiously, however, the WFPC2 observations have revealed only two other nova-like close binary stars in M80, far fewer than expected theoretically based on the stellar collision rate.   So the blue stragglers in M80 seem to indicate that there are lots of collisions, yet the nova-like stars suggest only a few. Sometimes life for astronomers isn't so simple, but it is from exploring discrepancies like this that our understanding eventually deepens.   This high-resolution image was created from 2 separate pointings of HST. One WFPC2 data set was obtained by Francesco R. Ferraro (ESO, Bologna Obs.), Barbara Paltrinieri (U. La Sapienza), Robert T. Rood (U. Virginia), and Ben Dorman (Raytheon/STX), who study blue stragglers. The other data set was acquired by Michael Shara (STScI, AMNH), David Zurek (STScI), and Laurent Drissen (U. Laval) to search for dwarf novae.      Technical facts about this news release:  About this Object Object Name: NGC 6093 (M80) Object Description: Globular Cluster in the Milky Way Galaxy Position (J2000): R.A. 16h 17m 03s  Dec. -22° 58' 30" Constellation: Scorpius Distance: 8.7 kiloparsecs (28,000 light-years) Dimensions: The image is 3 arcminutes on the vertical side. About the Data Instrument: WFPC2 Exposure Dates: October 1994, August-October, 1997; January/April, 1996 Filters: F336W(U), F439(B), F555W(V), F675W(R) Principal Astronomers: 1994/1997 Image: M. Shara (STScI, AMNH), D. Zurek (STScI), L. Drissen (Laval University).   1996 Image: F. Ferraro (ESO), B. Paltrinieri (Universita La Sapienza), R. Rood (University of Virginia), B. Dorman (Raytheon STX & Laboratory for Astronomy & Solar Physics).   _________________________________________  About this Image Image Credit: NASA and The Hubble Heritage Team (STScI/AURA) Release Date: July 1, 1999 12:00 noon (EDT) Orientation: North is toward the upper right of the image.  What is Hubble Heritage?  A monthly showcase of new and archival Hubble images. Go to the Heritage site.  This stellar swarm is M80 (NGC 6093), one of the densest of the 147 known globular star clusters in the Milky Way Galaxy. Located about 28,000 light-years from Earth, M80 contains hundreds of thousands of stars, all held together by their mutual gravitational attraction.  Globular clusters are particularly useful for studying stellar evolution, since all of the stars in the cluster have the same age (about 15 billion years), but cover a range of stellar masses. Every star visible in this image is either more highly evolved than, or in a few rare cases more massive than, our own Sun. Especially obvious are the bright red giants, which are stars similar to the Sun in mass that are nearing the ends of their lives. *News Release Number:*: STScI-1999-26a

NASA Identifier: SPD-HUBBLE-STScI-1999-26a
  • This stellar swarm is M80 (NGC 6093), one of the densest of the 147 known globular star clusters in the Milky Way galaxy. Located about 28,000 light-years from Earth, M80 contains hundreds of thousands of stars, all held together by their mutual gravitational attraction. Globular clusters are particularly useful for studying stellar evolution, since all of the stars in the cluster have the same age (about 15 billion years), but cover a range of stellar masses. Every star visible in this image is either more highly evolved than, or in a few rare cases more massive than, our own Sun. Especially obvious are the bright red giants, which are stars similar to the Sun in mass that are nearing the ends of their lives.

NASA Identifier: GPN-2000-000930
  • *Description*:  This Hubble Space Telescope view of the core of one of the nearest globular star clusters, called NGC 6397, resembles a treasure chest of glittering jewels. The cluster is located 8,200 light-years away in the constellation Ara.  Here, the stars are jam-packed together. The stellar density is about a million times greater than in our Sun's stellar neighborhood. The stars are only a few light-weeks apart, while the nearest star to our Sun is over four light-years away.  The stars in NGC 6397 are in constant motion, like a swarm of angry bees. The ancient stars are so crowded together that a few of them inevitably collide with each other once in a while. Near misses are even more common. Even so, collisions only occur every few million years or so. That's thousands of collisions in the 14-billion-year lifetime of the cluster.  These Hubble images were taken for a research program aimed at studying what is left behind when such collisions and near misses occur. When direct collisions occur, the two stars may merge to form a new star called a "blue straggler"; these hot, bright, young stars stand out among the old stars that make up the vast majority of stars in a globular cluster. Several such bright blue stars are visible near the center of the cluster in the Hubble Heritage image.  If two stars come close enough together without actually colliding, they may "capture" each other and become gravitationally bound. One type of binary that might form this way is a "cataclysmic variable"? a pairing of a normal, hydrogen-burning star and a burned-out star called a white dwarf. In a binary system, the white dwarf will pull material off the surface of the normal star. This material encircles the white dwarf in an "accretion disk," and eventually falls onto it. The result of this accretion process is that cataclysmic variables are, as the name suggests, variable in brightness. The heat generated by the accreting material also generates unusual amounts of ultraviolet and blue light.  To search for cataclysmic variables, the program consisted of a series of 55 images of the cluster taken over a period of about 20 hours. Most of the images were taken in ultraviolet and blue filters; a few images were also taken at green and infrared wavelengths. By comparing the brightness of all the stars in all the images, the Hubble astronomers were able to identify several cataclysmic variable stars in the cluster. Comparison of their brightness in the different filters confirmed that they were emitting copious amounts of ultraviolet light. A few of these stars can be seen in the Hubble Heritage image as faint blue or violet stars.  One of the more intriguing results of this study was completely unexpected. Three faint blue stars can be seen near the center of the cluster ? in the Hubble Heritage image they appear turquoise. These three stars don't vary in brightness at all, and were clearly not cataclysmic variables. These stars may be very-low-mass white dwarfs, formed in the cores of giant stars whose evolution is somehow interrupted before a full-fledged white dwarf has time to form.   Such an interruption might occur as the result of a stellar collision or an interaction with a binary companion. When a giant star interacts with another star, it can lose its outer layers prematurely, compared to its normal evolution, exposing its hot, blue core. The end result will be a white dwarf of a smaller mass than would have otherwise ensued. In any case, these unusual stars are yet more evidence that the center of a dense globular cluster is a perilous place to reside.  A large number of normal white dwarfs were also identified and studied. These stars appear throughout the cluster, since they form through normal stellar evolution processes and don't involve any stellar interactions, which occur predominantly near the cluster center. Nearly 100 such burned-out stars were identified in these images, the brightest of which can be seen here as faint blue stars.  This Hubble image is a mosaic of two sets of images taken several years apart by the Wide Field Planetary Camera 2. Archival data from science teams led by Jonathan Grindlay (Harvard University) and Ivan King (University of California, Berkeley), taken in 1997 and 1999, were combined with Hubble Heritage data taken in 2001. Adrienne Cool (San Francisco State University), who was also on both archival science teams, worked with the Hubble Heritage team to acquire the new observations.     Technical facts about this news release:  About the Object Object Name: NGC 6397 Object Description: Globular Cluster Position (J2000): R.A. 17h 40m 41s.36 Dec. -53° 40' 25".3 Constellation: Ara Distance: 8,200 light-years (2.5 kiloparsecs) Dimensions: This image is roughly 2 arcminutes (3.8 light-years or 1.2 parsecs) wide. About the Data Data Description: These images were created from HST data from the following proposals: 9313: K. Noll (STScI), A. Cool (SFSU), J. Anderson (Rice), I. King (U. Washington), L. Frattare, H. Bond, C. Christian, F. Hamilton, Z. Levay, T. Royle (STScI); 7335: J. Grindlay (Harvard U.), A. Cool (SFSU), C. Bailyn (Yale U.), H. Cohn and P. Lugger (Indiana U.); and 5929: I. King (U. Washington), A. Cool (SFSU), C. Sosin (UCB), H. Cohn and P. Lugger (Indiana U.), J. Grindlay (Harvard U.), P. Callanan (UCC), and C. Bailyn (Yale U.). Significant contributions to the science were also made by A. Bolton (MIT), J. Taylor (Harvard U.), and P. Edmonds (CfA). Instrument: WFPC2 Exposure Date(s): March 6/7, 1996; April 3/4 1999; November 4, 2001 Exposure Time: 7 hours Filters: F336W("I"), F439("B"), F814W("U") About the Image Image Credit: NASA and the Hubble Heritage Team (STScI/AURA) Release Date: August 7, 2003 Orientation: Too Close for Comfort [ http://imgsrc.hubblesite.org/hu/db/2003/21/images/a/formats/compass_large_web.jpg ]  What is Hubble Heritage?  A monthly showcase of new and archival Hubble images. Go to the Heritage site.   Back to top [ #top ] *News Release Number:*: STScI-2003-21a

NASA Identifier: SPD-HUBBLE-STScI-2003-21a
  • *Description*:  This Hubble Space Telescope view of the core of one of the nearest globular star clusters, called NGC 6397, resembles a treasure chest of glittering jewels. The cluster is located 8,200 light-years away in the constellation Ara.  Here, the stars are jam-packed together. The stellar density is about a million times greater than in our Sun's stellar neighborhood. The stars are only a few light-weeks apart, while the nearest star to our Sun is over four light-years away.  The stars in NGC 6397 are in constant motion, like a swarm of angry bees. The ancient stars are so crowded together that a few of them inevitably collide with each other once in a while. Near misses are even more common. Even so, collisions only occur every few million years or so. That's thousands of collisions in the 14-billion-year lifetime of the cluster.  These Hubble images were taken for a research program aimed at studying what is left behind when such collisions and near misses occur. When direct collisions occur, the two stars may merge to form a new star called a "blue straggler"; these hot, bright, young stars stand out among the old stars that make up the vast majority of stars in a globular cluster. Several such bright blue stars are visible near the center of the cluster in the Hubble Heritage image.  If two stars come close enough together without actually colliding, they may "capture" each other and become gravitationally bound. One type of binary that might form this way is a "cataclysmic variable"? a pairing of a normal, hydrogen-burning star and a burned-out star called a white dwarf. In a binary system, the white dwarf will pull material off the surface of the normal star. This material encircles the white dwarf in an "accretion disk," and eventually falls onto it. The result of this accretion process is that cataclysmic variables are, as the name suggests, variable in brightness. The heat generated by the accreting material also generates unusual amounts of ultraviolet and blue light.  To search for cataclysmic variables, the program consisted of a series of 55 images of the cluster taken over a period of about 20 hours. Most of the images were taken in ultraviolet and blue filters; a few images were also taken at green and infrared wavelengths. By comparing the brightness of all the stars in all the images, the Hubble astronomers were able to identify several cataclysmic variable stars in the cluster. Comparison of their brightness in the different filters confirmed that they were emitting copious amounts of ultraviolet light. A few of these stars can be seen in the Hubble Heritage image as faint blue or violet stars.  One of the more intriguing results of this study was completely unexpected. Three faint blue stars can be seen near the center of the cluster ? in the Hubble Heritage image they appear turquoise. These three stars don't vary in brightness at all, and were clearly not cataclysmic variables. These stars may be very-low-mass white dwarfs, formed in the cores of giant stars whose evolution is somehow interrupted before a full-fledged white dwarf has time to form.   Such an interruption might occur as the result of a stellar collision or an interaction with a binary companion. When a giant star interacts with another star, it can lose its outer layers prematurely, compared to its normal evolution, exposing its hot, blue core. The end result will be a white dwarf of a smaller mass than would have otherwise ensued. In any case, these unusual stars are yet more evidence that the center of a dense globular cluster is a perilous place to reside.  A large number of normal white dwarfs were also identified and studied. These stars appear throughout the cluster, since they form through normal stellar evolution processes and don't involve any stellar interactions, which occur predominantly near the cluster center. Nearly 100 such burned-out stars were identified in these images, the brightest of which can be seen here as faint blue stars.  This Hubble image is a mosaic of two sets of images taken several years apart by the Wide Field Planetary Camera 2. Archival data from science teams led by Jonathan Grindlay (Harvard University) and Ivan King (University of California, Berkeley), taken in 1997 and 1999, were combined with Hubble Heritage data taken in 2001. Adrienne Cool (San Francisco State University), who was also on both archival science teams, worked with the Hubble Heritage team to acquire the new observations.     Technical facts about this news release:  About the Object Object Name: NGC 6397 Object Description: Globular Cluster Position (J2000): R.A. 17h 40m 41s.36 Dec. -53° 40' 25".3 Constellation: Ara Distance: 8,200 light-years (2.5 kiloparsecs) Dimensions: This image is roughly 2 arcminutes (3.8 light-years or 1.2 parsecs) wide. About the Data Data Description: These images were created from HST data from the following proposals: 9313: K. Noll (STScI), A. Cool (SFSU), J. Anderson (Rice), I. King (U. Washington), L. Frattare, H. Bond, C. Christian, F. Hamilton, Z. Levay, T. Royle (STScI); 7335: J. Grindlay (Harvard U.), A. Cool (SFSU), C. Bailyn (Yale U.), H. Cohn and P. Lugger (Indiana U.); and 5929: I. King (U. Washington), A. Cool (SFSU), C. Sosin (UCB), H. Cohn and P. Lugger (Indiana U.), J. Grindlay (Harvard U.), P. Callanan (UCC), and C. Bailyn (Yale U.). Significant contributions to the science were also made by A. Bolton (MIT), J. Taylor (Harvard U.), and P. Edmonds (CfA). Instrument: WFPC2 Exposure Date(s): March 6/7, 1996; April 3/4 1999; November 4, 2001 Exposure Time: 7 hours Filters: F336W("I"), F439("B"), F814W("U") About the Image Image Credit: NASA and the Hubble Heritage Team (STScI/AURA) Release Date: August 7, 2003 Orientation: Too Close for Comfort [ http://imgsrc.hubblesite.org/hu/db/2003/21/images/a/formats/compass_large_web.jpg ]  What is Hubble Heritage?  A monthly showcase of new and archival Hubble images. Go to the Heritage site.   Back to top [ #top ] *News Release Number:*: STScI-2003-21a

NASA Identifier: SPD-HUBBLE-STScI-2003-21a

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