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
Ashley Berthelot | EurekAlert!
NASA laser communications to provide Orion faster connections
30.03.2017 | NASA/Goddard Space Flight Center
Pinball at the atomic level
30.03.2017 | Max-Planck-Institut für Struktur und Dynamik der Materie
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...
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...
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...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
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...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
30.03.2017 | Health and Medicine
30.03.2017 | Health and Medicine
30.03.2017 | Medical Engineering