A Space & astronomy forum. SpaceBanter.com

Go Back   Home » SpaceBanter.com forum » Astronomy and Astrophysics » Astronomy Misc
Site Map Home Authors List Search Today's Posts Mark Forums Read Web Partners

Cosmic Weight Loss: The Lowest Mass White Dwarf (Forwarded)



 
 
Thread Tools Display Modes
  #1  
Old April 18th 07, 10:17 PM posted to sci.astro
Andrew Yee
external usenet poster
 
Posts: 667
Default Cosmic Weight Loss: The Lowest Mass White Dwarf (Forwarded)

Public Affairs Office
Harvard-Smithsonian Center for Astrophysics
Cambridge, Massachusetts

For more information, contact:

David A. Aguilar, Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462

Christine Pulliam, Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
617-495-7463

For Release: Tuesday, April 17, 2007

Release No.: 2007-08

Cosmic Weight Loss: The Lowest Mass White Dwarf

Cambridge, MA -- Astronomers have found the lowest mass white dwarf known
in our galaxy: a Saturn-sized ball of helium containing only about
one-fifth the mass of the Sun. In addition, they have spotted the source
of the white dwarf's radical weight-loss plan. An unseen companion, likely
another white dwarf, has sucked away much of the tiny white dwarf's
material, leaving it a shadow of its former self.

"This star is bizarre," said Warren Brown of the Harvard-Smithsonian
Center for Astrophysics. "It takes extraordinary circumstances to make
such a low mass white dwarf."

When a Sun-like star ages and dies, it becomes a white dwarf. The newfound
white dwarf, with the unwieldy designation of SDSS J091709.55+463821.8
(hereafter J0917+46) lies about 7,400 light-years from Earth near the
border of the constellations Lynx and Ursa Major. Where a typical white
dwarf holds about half a Sun's worth of material, the newfound white dwarf
contains only a fraction of that mass.

"Our white dwarf is skinny in terms of mass, yet it looks fat in terms of
its physical size," stated first author Mukremin Kilic of Ohio State
University. "It's about nine times bigger than a typical white dwarf in
diameter."

When the astronomers first found J0917+46, they predicted that it must
have an unseen companion that had aided its weight loss. A subsequent
radial velocity search, which looked for signs that the white dwarf
wobbled when tugged by a companion's gravity, confirmed the prediction.
The astronomers ruled out the possibility that the companion is either a
low-mass main sequence star or a black hole. It must be either another
white dwarf or a neutron star, with a white dwarf being the more likely
candidate.

"No star is old enough to produce such an extremely low-mass white dwarf
by itself," explained Brown. "Therefore, we knew that mass must have been
stripped from the white dwarf by a companion."

"Finding the companion means that stellar evolution theories have passed a
major test," added co-author Scott Kenyon of the Smithsonian Astrophysical
Observatory. "The fact that the companion is a more massive white dwarf or
neutron star is also consistent with theory."

The team also described the oddball pair's history. This binary system
began with one star about twice the mass of the Sun and a second star
slightly less massive than the Sun. The more massive star was the first to
evolve, becoming a white dwarf weighing perhaps one-third as much as the
Sun. Ten billion years later, its companion became another white dwarf. In
each step, the puffed-up outer layers of the evolving star enveloped the
companion, causing friction that moved the two stars closer together. They
now orbit each other every 7.6 hours at a distance of about 650,000 miles
and a stunning speed of 335,000 miles per hour.

"The relation between our white dwarf and its companion is like a cosmic
marriage in which both people have to give a lot," said Kilic. "Two stars
start out close to each other. One of them engulfs the other (like a hug)
and gives continuously (losing mass), and they get closer. Then the other
star evolves and becomes a giant and engulfs the first star (hugging back)
and now it has to give a lot, or lose a lot of mass. They get closer and
closer and end up dancing continuously."

The astronomers predict that the two white dwarfs eventually will merge.
However, that merger will not take place for 10 billion years or more.

Key observations were made with the MMT Observatory in Arizona, which is
operated jointly by the Smithsonian Astrophysical Observatory and the
University of Arizona.

These findings are reported online at
http://arxiv.org/abs/0704.1813
and
http://arxiv.org/abs/astro-ph/0611498

Note to editors: Images to accompany this release are online at
http://cfa-www.harvard.edu/press/200...08_images.html


 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Cosmic Weight Loss: The Lowest Mass White Dwarf (Forwarded) Andrew Yee[_1_] News 0 April 18th 07 10:18 PM
Scientists compute death throes of white dwarf star in 3D (Forwarded) Andrew Yee[_1_] News 0 March 23rd 07 05:10 PM
Some Rare Abnormal Stars may have White Dwarf Parents to Blame (Forwarded) Andrew Yee News 0 January 11th 07 06:33 PM
Pre-Supernova White Dwarf Uncovered by Hubble Team (Forwarded) Andrew Yee Astronomy Misc 0 January 14th 06 07:25 AM
Pre-Supernova White Dwarf Uncovered by Hubble Team (Forwarded) Andrew Yee News 0 January 14th 06 06:56 AM


All times are GMT +1. The time now is 06:15 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 SpaceBanter.com.
The comments are property of their posters.