Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Physicists discover Crab nebula is slowly dimming

14.01.2011
Long thought to be the most stable source of high energy radiation in the sky, LSU scientists and an international team prove the Crab supernova remnant is flickering

The Crab Nebula, once considered to be a source of energy so stable that astronomers used it to calibrate their instruments, is dimming. LSU physicists Mike Cherry, Gary Case and graduate student James Rodi, together with an international team of colleagues using the Gamma-ray Burst Monitor, or GBM, on NASA's Fermi gamma-ray space telescope, discovered the anomaly. This revelation has proven astonishing for astronomers.

The Crab Nebula, one of the most studied objects in the sky, is the wreckage of a star that exploded in 1054. Considered a cornerstone of astronomical research, it even inspired its own unit of measurement, the "millicrab," which is used as a standard for measuring the intensity from other high-energy sources.

The GBM instrument was launched into orbit in summer 2008. This summer, the scientists were working on a catalog of the high energy X-ray and gamma ray signals detected mainly from sources in the galaxy powered by black holes and neutron stars. As they were preparing the catalog, which has been accepted for publication in the Astrophysical Journal, they realized that the intensity coming from the Crab Nebula was dimming.

"We were using the Crab as our calibration source and comparing the other high energy sources to it," said Case. "But as we collected more and more data, we noticed that the intensity we were measuring for the Crab was going down. This was a rather startling discovery, and it took awhile for us to believe it."

The initial suspicion was that the instrument was losing sensitivity. The team then gathered data from three other sensitive X-ray and gamma ray observatories currently in orbit – NASA's Swift and Rossi X-Ray Timing Explorer, or RXTE, and the European Space Agency's International Gamma-Ray Astrophysics Laboratory, or INTEGRAL. The result was that all four instruments were seeing the same decrease in intensity of about 7 percent since the summer of 2008.

"Nearly every other source of high energy radiation in the sky shows evidence of explosive, time-variable, transient activity. The Crab was the exception," said Cherry. "It was the only object that was bright enough and steady enough to serve as a 'standard candle.'"

Colleen Wilson-Hodge, an astrophysicist at NASA's Marshall Space Flight Center in Hunstville, Ala., recently presented the findings at the American Astronomical Society meeting in Seattle.

"Now, for the first time, we're clearly seeing how much our candle flickers," she said. The findings will be published in the Astrophysical Journal Letters.

Additional analysis showed that the Crab Nebula has brightened and dimmed several times since 1999 on approximately a three-year time scale. The current decrease is the largest so far observed, and the international team will continue to monitor the Crab Nebula to observe how much the decline continues.

The cause of the changes is not understood, but apparently involves changes in the magnetic fields close to the nebula's central neutron star. Because of this news, the scientists said that astronomers will now need to find new ways to calibrate their instruments in flight and to explore the possible effects of the inconstant Crab Nebula emissions on past findings.

About NASA's Fermi:

NASA's Fermi is an astrophysics and particle physics partnership managed by NASA's Goddard Space Flight Center in Greenbelt, Md., and developed in collaboration with the U.S. Department of Energy, with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States. For more information, visit www.nasa.gov/Fermi.

Contact Ashley Berthelot
LSU Media Relations
225-578-3870
aberth4@lsu.edu
Lynn Chandler
NASA's Goddard Space Flight Center
301-286-2806
lynn.chandler-1@nasa.gov

Ashley Berthelot | EurekAlert!
Further information:
http://www.lsu.edu

More articles from Physics and Astronomy:

nachricht From rocks in Colorado, evidence of a 'chaotic solar system'
23.02.2017 | University of Wisconsin-Madison

nachricht Prediction: More gas-giants will be found orbiting Sun-like stars
22.02.2017 | Carnegie Institution for Science

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: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

From rocks in Colorado, evidence of a 'chaotic solar system'

23.02.2017 | Physics and Astronomy

'Quartz' crystals at the Earth's core power its magnetic field

23.02.2017 | Earth Sciences

Antimicrobial substances identified in Komodo dragon blood

23.02.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>