CINXE.COM
Two Stars Collide; a New Star Is Born
<html> <head> <meta charset="utf-8"> <meta name="NYT_HEADLINE" content="Two Stars Collide; a New Star Is Born"> <meta name="BY_LINE" content="By KENNETH CHANG"> <meta name="FIRSTPAR" content=" With most of the universe being empty space, astronomers once thought the chance of stars colliding was roughly once in an eternity. "> <meta name="DISPLAYDATE" content="June 13, 2000"> <meta name="NYT_SORTDATE" content="20000613"> <title>Two Stars Collide; a New Star Is Born</title> <script id="nyt-capsule-data" type="text/json"> { "lastTransform": "2018-04-09T14:29:56.264Z" } </script> <script src="https://archive.nytimes.com/_capsule/nyt-capsule.js" type="text/javascript"></script> <meta name="Filingmethod" content="Atex"> <meta name="UnixSlug" content="../backfield/savekeep/13COLL.W01"> <meta name="Date" content="00/06/13"> <meta name="Type" content="story"> <meta name="AtexNotes" content="f1 colliding mg??? "> <meta name="AtexSlug" content="13coll "> <meta name="AtexHJ" content="w01457 "> <meta name="AtexFrom" content="copy-sci ;06/10,21:43 "> <meta name="AtexOp" content="jowils;06/11,20:59"> <meta name="AtexBy" content="babble;06/09,17:02"> <meta name="section" content=""> <meta name="subsection" content=""> <meta name="End of header" content=""> <link rel="stylesheet" type="text/css" href="https://archive.nytimes.com/_capsule/nyt-capsule.css"> </head> <body bgcolor="#ffffff" vlink="#444464" link="#000066" background="https://static01.nyt.com/images/back.c.gif"> <table border="0" cellpadding="0" cellspacing="0"> <tbody> <tr> <td align="left" width="600" valign="top"> <img src="https://static01.nyt.com/images/pixel.gif" border="0" width="600" height="1"> <table border="0" cellpadding="0" cellspacing="0"> <tbody> <tr> <td align="left" valign="top" width="60"><br></td> <td align="left" valign="top" width="480"> <img src="https://static01.nyt.com/images/1bannat-sci.gif" border="0" width="468" height="40" alt="banner"> <br clear="all"> <map name="maintoolbar2"> <area shape="rect" coords="0,0,75,16" href="https://www.nytimes.com/yr/mo/day/" onmouseover="window.status='Click to go to the Home Page';return true"> <area shape="rect" coords="76,0,154,16" href="https://www.nytimes.com/info/contents/siteindex.html" onmouseover="window.status='Click to see site contents';return true"> <area shape="rect" coords="155,0,233,16" href="https://www.nytimes.com/search/daily/" onmouseover="window.status='Click to search the current site';return true"> <area shape="rect" coords="234,0,312,16" href="https://www.nytimes.com/comment/" onmouseover="window.status='Click for discussion in the Forums';return true"> <area shape="rect" coords="313,0,391,16" href="https://www.nytimes.com/archives/" onmouseover="window.status='Click to search the archives';return true"> <area shape="rect" coords="392,0,468,16" href="https://www.nytimes.com/marketplace/" onmouseover="window.status='Click to visit the Marketplace';return true"> </map> <a href="https://www.nytimes.com/images/maintoolbar2.map"> <img src="https://static01.nyt.com/images/maintoolbar2.gif" border="0" alt="toolbar" ismap usemap="#maintoolbar2" width="468" height="16"></a> <br> </td> </tr> </tbody> </table> <blockquote> <blockquote> <h5>June 13, 2000</h5><br> <h2>Two Stars Collide; a New Star Is Born</h2> <p> </p> <p> </p> <h5>By KENNETH CHANG</h5> <p> </p> <p> </p> <table width="175" align="right" border="0" cellspacing="0"> <tbody> <tr> <td width="15" rowspan="7"> </td> <td></td> </tr> <tr> <td align="right"> <hr size="1"> <img src="https://static01.nyt.com/library/national/science/061300sci-stars.1.jpg" width="200" height="168"> <p><img src="https://static01.nyt.com/library/national/science/061300sci-stars.2.jpg" width="200" height="185"></p> <p><img src="https://static01.nyt.com/library/national/science/061300sci-stars.3.jpg" width="200" height="138"></p> <p><img src="https://static01.nyt.com/library/national/science/061300sci-stars.4.jpg" width="200" height="150"></p> <p><img src="https://static01.nyt.com/library/national/science/061300sci-stars.5.jpg" width="200" height="150"> <font size="-2"> </font> </p> </td> </tr> <tr> <td align="left"> <font size="-1"> Within the Milky Way galaxy, a collision between two stars occurs about once every 10,000 years, and astronomers have almost no chance of actually seeing one in their telescopes. So they turn to supercomputers to see how a collision might occur. In a simulation by Dr. Joshua E. Barnes of the University of Hawaii, two stars collide at a speed of more than 500,000 miles per hour. The smaller, denser star remains largely intact, sending up a wave of gas from the larger star as it burrows to the center. The resulting "blue straggler," will burn bluer and appear younger than it really is. </font> </td> </tr> <tr> <td> <hr size="1"> <b>Related Articles</b><br> • <a href="https://www.nytimes.com/universe">The Nature of the Universe</a> <p> <b>Video</b> <br>• <a href="https://www.nytimes.com/library/national/science/061300sci-stars.1v.ram.html">Collision of Unequal Mass Stars</a> </p> <p> <b>Forum</b><br> • <a href="http://forums.nytimes.com/webin/WebX?13@@.f03bc62">Join a Discussion on Space Exploration</a><br> </p> </td> </tr> <tr> <td align="right"> <hr size="1"> <img src="https://static01.nyt.com/library/national/science/061300sci-stars.6.jpg" width="200" height="148"> <p><img src="https://static01.nyt.com/library/national/science/061300sci-stars.7.jpg" width="200" height="201"> <font size="-2"> Adrienne Cool/ Space Telescope Science Institute </font> </p> </td> </tr> <tr> <td align="left"> <font size="-1"> The globular cluster of stars known as NGC 6397, about 7,000 light-years away, is nearly as old as the Milky Way, yet at its core are several young-looking "blue straggler" stars, which astronomers believe were formed from the collision of two or more stars. </font> </td> </tr> <tr> <td> <hr size="1"> </td> </tr> </tbody> </table> <p><img src="https://static01.nyt.com/images/w.gif" align="left" alt="W">ith most of the universe being empty space, astronomers once thought the chance of stars colliding was roughly once in an eternity. </p> <p> But in recent years, astronomers have realized that collisions are not uncommon within dense clusters of stars. </p> <p> "We believe there are several hundred every hour somewhere in the universe," said Dr. Michael Shara, curator of the astrophysics department at the American Museum of Natural History, in a symposium at the museum two weeks ago. </p> <p> At the meeting, the first devoted to interstellar collisions, astronomers said they had detected what appeared to be the aftermath of a three-star collision. Scientists are also hoping to find evidence of collisions involving ultra-dense neutron stars and black holes by detecting telltale gravitational ripples. </p> <p> The first clue of interstellar collisions came in the 1950's when astronomers looked at clusters of stars they knew to be nearly as old as the universe and saw what appeared to be large, young blue stars. Blue stars contain more hydrogen than smaller stars, but burn hotter and burn out more quickly. </p> <p> Within the star groups, known as globular clusters, the clouds of gas and dust that give birth to stars had been exhausted billions of years ago, which raised the question: where did these young blue stars come from? </p> <p> At first, some astronomers speculated that these "blue straggler" stars had somehow conserved their fuel, but with the help of the Hubble Space Telescope, astronomers have concluded that a blue straggler star is actually two small, old stars that combined to form a rejuvenated blue star. </p> <p> Collisions are more frequent in globular clusters, because there are many more stars. In the outer region of the galaxy where our solar system lies, the density of stars is about one per 10 cubic light-years. In a globular cluster, there may be several hundred thousand stars in that same space. </p> <p> Dr. Shara's estimate of several hundred collisions per hour may seem frequent, but with 100 billion galaxies in the observable universe and each galaxy containing, on average, 30 globular clusters, most of the collisions occur far away and out of view. </p> <p> According to his calculations, over the 10 billion-year lifetime of the Milky Way, Earth's home galaxy, there have been at least one million collisions within globular clusters -- or about one every 10,000 years. </p> <p> While astronomers can spot the results of the collisions, the blue straggler stars, they almost certainly will never see the collisions. </p> <p> This means that they cannot directly determine whether a particular blue straggler star originated in a binary system whose components coalesced, or is the wreckage of two unrelated stars that happened to collide. </p> <p> In one case, however, the answer appears to be the latter. </p> <p> At the symposium, Dr. Rex Saffer, an assistant professor of astronomy and astrophysics at Villanova University, presented observations of several blue straggler stars within the globular cluster NGC 6397, located in the Milky Way about 7,000 light-years from Earth. </p> <p> Based on the age of the cluster, its surviving stars should have masses of no more than 80 percent of the mass of the Sun; more massive stars should have burnt out. </p> <p> However, four of the blue stragglers in the cluster were about 1.6 times the mass of the Sun, so they presumably represent the mergers of two stars. </p> <p> One blue straggler was a whopping 2.4 times heavier -- "so massive that it can't have formed by the merger of two stars," Dr. Saffer said. That straggler, he said, was probably born from a three-star collision, when an outsider star flew into a binary system. </p> <p> "The stars go into a chaotic dance around each other," he said, and eventually bump into one another. </p> <p> Dr. Shara described the observations as "almost certainly irrefutable proof" that this particular blue straggler formed in a collision rather than the simple coalescing of a binary system. (The latter phenomenon almost certainly occurs, astronomers have also seen binary stars so close that they are touching each other.) </p> <p> If telescopes cannot actually watch collisions, computers offer some insight into what an interstellar pileup might look like. </p> <p> Describing a simulation in which one star crashes into another about twice its size at a speed of about half a million miles per hour, "the small one actually plows through the larger one and tears a furrow," said Dr. Joshua E. Barnes, an associate professor of astronomy at the University of Hawaii. </p> <p> The crash sends a splash of gas into space while the smaller, denser star burrows to the center of the larger one. </p> <p> "There's a huge wave that gets set up in the larger one, and it's going to splash around for while," Dr. Barnes said. "The bigger one is wobbling around." </p> <p> What happens after that is not clear, because the simulation only covers the first 12 hours. </p> <p> "After that initial violence dies down, you've got an object that in many respects is not a proper star," Dr. Barnes said. "It's all swelled up, and internally, its temperature structure is not what you expect for a star. Getting through this intermediate stage where this new formed blob is sorting itself out and trying to turn back into a star, that's a long process" lasting from 100,000 years to 10 million years. </p> <p> Even near misses can leave a mark. </p> <p> The most common stars within globular clusters are red low-mass stars and white dwarfs, the cores of burned-out stars. </p> <p> Dr. Adrienne Cool, an associate professor of physics and astronomy at San Francisco State University, and her collaborators surveyed stars near the core of NGC 6397, looking for instances where a near collision between a star and a white dwarf ended up with the two in orbit around each other. The result is a "cataclysmic binary," where the white dwarf flares intermittently as gas sucked from the other star falls onto it. </p> <p> "We found a handful of them in this cluster," Dr. Cool said. </p> <p> The researchers also found the unexpected: mini-white dwarfs with half the mass of usual white dwarfs. Dr. Cool hypothesizes that these are remnants of red giant stars that had close encounters with other stars. </p> <p> As a star exhausts its hydrogen, astronomers say, it swells into a red giant, expanding, as would be the case with the Sun, past the orbit of Earth, before collapsing into a white dwarf. </p> <p> In the middle of a red giant is the seed of a white dwarf. A near miss with another star could rip away the outer layers. "If you can somehow strip off that red giant's envelope early," Dr. Cool said, "then you can lay bare this unusual core, this very low-mass white dwarf." </p> <p> Other participants at the symposium are exploring the more cataclysmic collisions of neutron stars and black holes. </p> <p> Such collisions are believed to create gravitational disturbances that may be detectable in an experiment called the Laser Interferometer Gravitational Wave Observatory, or LIGO. Initial observations should begin next spring with full operations in 2002. </p> <p> According to Einstein's general theory of relativity, as gravitational waves pass, the distance between any two points contracts and expands. LIGO's two detectors -- one in Hanford, Wash., the other in Livingston, La. -- will be able to spot a change as slight as half the width of an atom along the 2.5-mile-long paths traveled by the detectors' laser beams. </p> <p> That should be sensitive enough to pick out ripples emanating from the crash of two neutron stars up to 100 million light-years away or a collision of black holes up to 500 million light-years away. </p> <p> Theorists have been trying to determine whether these collisions occur often enough and close enough for LIGO to spot. </p> <p> If recent calculations are right, probably not. "We don't have any comfortable predictions to expect a detection with LIGO I," said Dr. Vassiliki Kalogera, a post-doctoral fellow at the Harvard-Smithsonian Center for Astrophysics. </p> <p> At best, Dr. Kalogera said, LIGO will detect one collision of black holes in a year. </p> <p> The predictions are more optimistic for an upgraded LIGO, scheduled for 2006, that will be able to detect waves from collisions 10 times farther away. </p> <p> Then, Dr. Kalogera said, a "conservative lower limit" would be the detection of 1 or 2 neutron star collisions and 10 black hole collisions per year. </p> <p> "We could have a couple of hundred events per year if our most optimistic predictions are correct," Dr. Kalogera said. </p> <p> </p> <p> </p> </blockquote> </blockquote> <br> <table border="0" cellpadding="0" cellspacing="0"> <tbody> <tr> <td align="left" valign="top" width="60"><br></td> <td align="center" valign="top" width="468"> <hr size="1"> <p> <font size="-1"> <a href="https://www.nytimes.com/"><b>Home</b></a> | <a href="https://www.nytimes.com/info/contents/siteindex.html"><b>Site Index</b></a> | <a href="https://www.nytimes.com/search/daily/"><b>Site Search</b></a> | <a href="https://www.nytimes.com/comment/"><b>Forums</b></a> | <a href="https://www.nytimes.com/archives/"><b>Archives</b></a> | <a href="https://www.nytimes.com/marketplace/"><b>Marketplace</b></a> </font> </p> <p> <font size="-1"> <a href="https://www.nytimes.com/yr/mo/day/late/">Quick News</a> | <a href="https://www.nytimes.com/yr/mo/day/front/">Page One Plus</a> | <a href="https://www.nytimes.com/yr/mo/day/world/">International</a> | <a href="https://www.nytimes.com/yr/mo/day/national/">National/N.Y.</a> | <a href="https://www.nytimes.com/yr/mo/day/business/">Business</a> | <a href="https://www.nytimes.com/yr/mo/day/tech/">Technology</a> | <a href="https://www.nytimes.com/yr/mo/day/science/">Science</a> | <a href="https://www.nytimes.com/yr/mo/day/sports/">Sports</a> | <a href="https://www.nytimes.com/weather/">Weather</a> | <a href="https://www.nytimes.com/yr/mo/day/editorial/">Editorial</a> | <a href="https://www.nytimes.com/yr/mo/day/oped/">Op-Ed</a> | <a href="https://www.nytimes.com/yr/mo/day/artleisure/">Arts</a> | <a href="https://www.nytimes.com/yr/mo/day/auto/">Automobiles</a> | <a href="https://www.nytimes.com/books/yr/mo/day/home/">Books</a> | <a href="https://www.nytimes.com/diversions/">Diversions</a> | <a href="https://www.nytimes.com/yr/mo/day/jobmarket/">Job Market</a> | <a href="https://www.nytimes.com/yr/mo/day/realestate/">Real Estate</a> | <a href="https://www.nytimes.com/yr/mo/day/travel/">Travel</a> </font> </p> <p> <font size="-1"> <a href="https://www.nytimes.com/subscribe/help/">Help/Feedback</a> | <a href="https://www.nytimes.com/classified/">Classifieds</a> | <a href="https://www.nytimes.com/info/contents/services.html">Services</a> | <a href="http://www.nytoday.com/">New York Today</a> </font> </p> <p> <font size="-1"> <a href="https://www.nytimes.com/subscribe/help/copyright.html"><b>Copyright 2000 The New York Times Company</b></a> </font> </p> <p> <font size="-1"> </font> </p> </td> </tr> </tbody> </table> </td> <td align="left" width="14" valign="top"> <img src="https://static01.nyt.com/images/pixel.gif" border="0" width="14" height="1"></td> <td align="center" width="140" valign="top"> <img src="https://static01.nyt.com/images/pixel.gif" border="0" width="140" height="2"> </td> </tr> </tbody> </table> </body> </html>