Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Largest collection of anomalous white dwarfs observed in new Hubble images

27.04.2009
Twenty-four unusual stars, 18 of them newly discovered, have been observed in new Hubble telescope images. The stars are white dwarfs, a common type of dead star, but they are odd because they are made of helium rather than the usual carbon and oxygen.

This is the first extensive sequence of helium-core white dwarfs to be observed in a globular cluster, a dense swarm of some of the oldest stars in our galaxy.

A study, accepted for publication in the Astrophysical Journal, suggests that these helium-core white dwarfs have had their lives cut short because of their orbital dance around a partner star.

"Helium-core white dwarfs have only about half the mass of typical white dwarfs, but they are found concentrated in the center of the cluster" said Adrienne Cool, professor of physics and astronomy at San Francisco State University, who co-authored the study with graduate student Rachel R. Strickler. "With such low masses, the helium-core white dwarfs ought to be floating all around the cluster, according to theory. The fact that we find them only in the central regions suggests that they have heavy companions -- partner stars that anchor them to the cluster center."

Being coupled with companions also helps explain the stars' atypical chemical make up. White dwarfs are stars that have reached the end of their lives and have run out of fuel. Most stars burn their fuel leaving behind a dense ball of carbon and oxygen, but these white dwarfs are made of helium. Cool suggests that a star that goes on to become a helium-core white dwarf must have a close companion so that when the star became a red giant and expanded, its outer layers spilled onto the companion. The star never had the chance to reach maturity and burn its helium into carbon and oxygen.

The study focused on star cluster NGC 6397, one of the globular clusters closest to Earth at approximately 7,200 light years away. Six helium-core white dwarfs have been observed before in this cluster. Cool and colleagues discovered the first three in 1998.

"This is the first time that helium-core white dwarf stars have been discovered in partnerships with other white dwarfs in a globular cluster," Cool said. "This large sample allows us to answer questions about the mass and nature of the partner stars, and the prevalence of these kinds of binaries in the globular cluster."

Binary stars play an important role in the evolution of star clusters. Their continual dance around each other provides energy to the cluster that astronomers believe can help prevent black holes from forming. From the data, Cool and her team are able to infer that one to five percent of stars in this globular cluster will end their lives as helium-core white dwarfs with companion stars, a finding that will help improve theoretical models of cluster dynamics. "It may not sound like a lot but it doesn't take many binaries to stir things up," Cool said.

One finding remains a mystery. Despite the Hubble camera's high level of sensitivity, the faintest helium-core white dwarfs appear to be missing.

"It's possible that these helium-core white dwarfs cool so slowly that they haven't had time to get very faint yet," Cool said. Another possibility is that the oldest binaries containing helium-core white dwarfs have been destroyed by interactions with other stars in the cluster.

Adrienne Cool is professor of physics and astronomy at San Francisco State University. Cool co-authored the paper with former SF State student Rachel R. Strickler, now a graduate student at University of California, Santa Cruz. Other collaborators include Jay Anderson, Haldan N. Cohn, Phyllis M. Lugger and Aldo M. Serenelli. The research was supported by NASA and the Space Telescope Science Institute.

"Helium-Core White Dwarfs in the Globular Cluster NGC 6397" will be published in the July 1, 2009 issue of the Astrophysical Journal.

A high-resolution image from Hubble's Advanced Camera for Surveys is available from Elaine Bible, ebible@sfsu.edu, (415) 405-3606.

Elaine Bible | EurekAlert!
Further information:
http://www.sfsu.edu

More articles from Physics and Astronomy:

nachricht NASA spacecraft investigate clues in radiation belts
28.03.2017 | NASA/Goddard Space Flight Center

nachricht Researchers create artificial materials atom-by-atom
28.03.2017 | Aalto University

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: A Challenging European Research Project to Develop New Tiny Microscopes

The Institute of Semiconductor Technology and the Institute of Physical and Theoretical Chemistry, both members of the Laboratory for Emerging Nanometrology (LENA), at Technische Universität Braunschweig are partners in a new European research project entitled ChipScope, which aims to develop a completely new and extremely small optical microscope capable of observing the interior of living cells in real time. A consortium of 7 partners from 5 countries will tackle this issue with very ambitious objectives during a four-year research program.

To demonstrate the usefulness of this new scientific tool, at the end of the project the developed chip-sized microscope will be used to observe in real-time...

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

Transport of molecular motors into cilia

28.03.2017 | Life Sciences

A novel hybrid UAV that may change the way people operate drones

28.03.2017 | Information Technology

NASA spacecraft investigate clues in radiation belts

28.03.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>