* Astronomy

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RE: Blue straggler stars

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Title: Detection of white dwarf companions to blue stragglers in the open cluster NGC 188: direct evidence for recent mass transfer
Author: Natalie M. Gosnell, Robert D. Mathieu, Aaron M. Geller, Alison Sills, Nathan Leigh, Christian Knigge

Several possible formation pathways for blue straggler stars have been developed recently, but no one pathway has yet been observationally confirmed for a specific blue straggler. Here we report the first findings from a Hubble Space Telescope ACS/SBC far-UV photometric program to search for white dwarf companions to blue straggler stars. We find three hot and young white dwarf companions to blue straggler stars in the 7-Gyr open cluster NGC 188, indicating that mass transfer in these systems ended less than 300 Myr ago. These companions are direct and secure observational evidence that these blue straggler stars were formed through mass transfer in binary stars. Their existence in a well-studied cluster environment allows for observational constraints of both the current binary system and the progenitor binary system, mapping the entire mass transfer history.

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Astronomers discover how mysterious blue straggler stars stay young

Mysterious "blue stragglers" are old stars that appear younger than they should be: they burn hot and blue. Several theories have attempted to explain why they don't show their age, but, until now, scientists have lacked the crucial observations with which to test each hypothesis.
Armed with such observational data, two astronomers from Northwestern University and the University of Wisconsin-Madison report that a mechanism known as mass transfer explains the origins of the blue stragglers. Essentially, a blue straggler eats up the mass, or outer envelope, of its giant-star companion. This extra fuel allows the straggler to continue to burn and live longer while the companion star is stripped bare, leaving only its white dwarf core.
The astronomers studied the NGC 188 open cluster, which is in the constellation Cepheus, situated in the sky near Polaris, the North Star. This cluster is one of the most ancient open star clusters, but it features these mysterious young blue stragglers.
The scientists report their evidence in a study to be published Oct. 20 by the journal Nature.
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"Vampire" Stars Found in Heart of Our Galaxy

The stellar version of vampires - stars that drain life away from other stars - have been discovered for the first time in the heart of our Milky Way galaxy.
Called blue stragglers, these cannibal stars have been spotted in other parts of the Milky Way. They seem to lag in age next to the other stars with which they formed - appearing hotter, and thus younger and bluer.
Astronomers suspect blue stragglers look so youthful because they've stolen hydrogen fuel from other stars, perhaps after colliding into their victims.
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NASA'S Hubble Finds Rare 'Blue Straggler' Stars In Milky Way's Hub

NASA's Hubble Space Telescope has found a rare class of oddball stars called blue stragglers in the hub of our Milky Way, the first detected within our galaxy's bulge.
Blue stragglers are so named because they seemingly lag behind in the aging process, appearing younger than the population from which they formed. While they have been detected in many distant star clusters, and among nearby stars, they never have been seen inside the core of our galaxy.
It is not clear how blue stragglers form. A common theory is that they emerge from binary pairs. As the more massive star evolves and expands, the smaller star gains material from its companion. This stirs up hydrogen fuel and causes the growing star to undergo nuclear fusion at a faster rate. It burns hotter and bluer, like a massive young star.
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Blue stragglers

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RE: Blue straggler stars

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For almost 50 years, astronomers have puzzled over the youthful appearance of stars known as blue stragglers.
Blue stragglers are the timeworn Bollywood starlets of the cosmos: They shine brightly, they are older than they appear, and they have, disconcertingly, gained mass at a late stage of life.

"These blue, luminous stars should have used up their hydrogen fuel and flamed out long ago. Yet they are still here. By some means or another, they have recently increased their mass, their fuel supply" - Robert Mathieu, a University of Wisconsin-Madison astronomer.

Now, Mathieu and Wisconsin colleague Aaron Geller, writing Dec. 24 in the journal Nature, show that blue stragglers, in most if not all cases, steal that mass from companion stars and that they sometimes do so by crashing into their neighbours, a scenario once thought far-fetched by astronomers.

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WIYN 3.5-m telescope rounds up "Blue Stragglers"

Astronomers have reported new observations of a remarkable binary star population in a well-known star cluster. In a press release, Nature features two interesting studies of a class of atypical stars known as "Blue Stragglers". One paper was written by Robert Mathieu and Aaron Geller, University of Wisconsin-Madison, who used the WIYN telescope at Kitt Peak National Observatory for their observations. Mathieu and Geller found that the blue stragglers in NGC188 (Caldwell 1), an open cluster in our galaxy, have a binary fraction of 76%, which is three times the frequency for normal stars of this type. They conclude that possibly all of these stars originate in multiple star systems, and that several formation mechanisms could be operating. Geller, a PhD candidate at the University of Wisconsin-Madison, has been granted long term observing status for this project, which is part of the WIYN Open Cluster Study.
Source

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Blue straggler stars (BSSs)