Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Zoom-up star photos poke holes in century-old astronomical theory

19.04.2011
The hottest stars in the universe spin so fast that they get a bit squished at their poles and dimmer around their middle. The 90-year-old theory that predicts the extent of this "gravity darkening" phenomenon has major flaws, according to a new study led by University of Michigan astronomers.

The von Zeipel law, named for its creator, Swedish astronomer Edvard Hugo von Zeipel, has been used for the better part of a century to predict the difference in surface gravity, brightness and temperature between a rapidly rotating star's poles and its equator.

Using a technique called interferometry the researchers essentially zoomed in to take close-up pictures and measurements of the winter star Regulus. It's the brightest star in the constellation Leonis and if it were spinning just a few percent faster, it would fly apart.

The astronomers found that the actual difference in temperature between its equator and poles is much less than the old theory predicts.

"Our model fitting of interferometry data shows that while the law correctly describes the trend of surface temperature variation, it deviates quantitively," said Xiao Che, a doctoral student in the Department of Astronomy who is first author of a paper on the findings to be published in Astrophysical Journal on April 20.

"It is surprising to me that von Zeipel's law has been adopted in astronomy for such a long time with so little solid observational evidence."

It's important to get this number right, says John Monnier, an associate professor in the U-M Department of Astronomy.

"In some cases, we found a 5,000-degree Fahrenheit difference between what the theory predicts and what our actual measurements show," Monnier said. "That has a big effect on total luminosity. If we don't take this into account, we get the star's mass and age and total energy output wrong."

Monnier led the creation of the Michigan Infra-Red Combiner (MIRC) instrument that was used to take the measurements that led to this discovery. MIRC uses interferometry to combine the light entering four telescopes at the CHARA array at Georgia State University so that it seems to be coming through a device 100 times larger than the Hubble Space Telescope. The technique lets astronomers see the shape and surface characteristics of stars. Previously, stars were mere points of light even with the largest telescopes.

In this case, zooming in on Regulus let the researchers measure its poles and equator temperatures separately.

"Normally, you would just be able to get an average temperature," Monnier said.

So where did von Zeipel go wrong? Monnier believes his Swedish predecessor didn't take into account circulation on stars that's not unlike wind patterns on Earth.

"The Earth has a hot equator and cold poles and that causes air circulation," Monnier said. "The hot air wants to flow toward the poles and equilibrate, bringing the temperatures closer together. This is a source of some weather patterns on Earth."

The paper is titled "Colder and Hotter: Interferometric imaging of â Cassiopeiae and á Leonis." The CHARA Array is funded by the National Science Foundation and Georgia State University. Funding for the MIRC combiner came from the University of Michigan and observations were supported through National Science Foundation and NASA.

Nicole Casal Moore | EurekAlert!
Further information:
http://ns.umich.edu/htdocs/releases/story.php?id=8374

Further reports about: Astronomy Earth's magnetic field Interferometry Regulus Science TV poke holes

More articles from Physics and Astronomy:

nachricht Magnetic nano-imaging on a table top
20.04.2018 | Georg-August-Universität Göttingen

nachricht New record on squeezing light to one atom: Atomic Lego guides light below one nanometer
20.04.2018 | ICFO-The Institute of Photonic Sciences

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: Spider silk key to new bone-fixing composite

University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.

Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.

Im Focus: Writing and deleting magnets with lasers

Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.

Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...

Im Focus: Gamma-ray flashes from plasma filaments

Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.

The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...

Im Focus: Basel researchers succeed in cultivating cartilage from stem cells

Stable joint cartilage can be produced from adult stem cells originating from bone marrow. This is made possible by inducing specific molecular processes occurring during embryonic cartilage formation, as researchers from the University and University Hospital of Basel report in the scientific journal PNAS.

Certain mesenchymal stem/stromal cells from the bone marrow of adults are considered extremely promising for skeletal tissue regeneration. These adult stem...

Im Focus: Like a wedge in a hinge

Researchers lay groundwork to tailor drugs for new targets in cancer therapy

In the fight against cancer, scientists are developing new drugs to hit tumor cells at so far unused weak points. Such a “sore spot” is the protein complex...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Invitation to the upcoming "Current Topics in Bioinformatics: Big Data in Genomics and Medicine"

13.04.2018 | Event News

Unique scope of UV LED technologies and applications presented in Berlin: ICULTA-2018

12.04.2018 | Event News

IWOLIA: A conference bringing together German Industrie 4.0 and French Industrie du Futur

09.04.2018 | Event News

 
Latest News

Magnetic nano-imaging on a table top

20.04.2018 | Physics and Astronomy

Start of work for the world's largest electric truck

20.04.2018 | Interdisciplinary Research

Atoms may hum a tune from grand cosmic symphony

20.04.2018 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>