The center of our Milky Way galaxy is a wondrous place full of huge star clusters, dust clouds, magnetic filaments and a supermassive black hole. But it can be a confusing place, too, posing challenges to astronomers trying to image these exotic features and learn more about where they are located in the galaxy.
Northwestern University's Farhad Zadeh has discovered a new tool for detecting dusty clouds and stars: simply take a picture using radio waves. He is the first to identify what he calls radio dark clouds and stars. Stars in the early and late phases of their evolution are shrouded by huge dusty envelopes in the form of dust and gas outflows.
"When you see these dark stars or clouds in radio wavelength images, it tells you something very interesting," Zadeh said. "We immediately know there is a cold gas cloud or dusty star mixing with a hot radiative medium and that an interaction is taking place. Knowing details of these clouds is important because the clouds can produce stars and also provide material for the growth of black holes."
Zadeh is a professor of physics and astronomy in the Weinberg College of Arts and Sciences and a member of Northwestern's Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA).
Unlike in the optical, X-ray and infrared wavelengths, it is unusual to see a dark feature with radio waves. Radio is a long wavelength and therefore doesn't get absorbed easily and typically passes through whatever is in its way.
Initially Zadeh thought maybe the dark features he saw on the radio images he was studying were nothing, but then he connected the features to five known dense molecular and dusty clouds located in the center of our galaxy, some near Sagittarius A* (Sgr A*), the black hole.
"This technique provides very good sensitivity of faint dusty features, and it can produce images with even higher resolution than many other telescopes," Zadeh said. "It is an initial observation that tells you something is there that needs to be studied more closely."
In addition, astronomers can measure the size of dusty stars using this new technique.
Zadeh will present his results at 11:30 a.m. PST (Pacific Standard Time) Tuesday, Jan. 8, at the 221st meeting of the American Astronomical Society in Long Beach, Calif. He also will participate in a press conference on the galactic center at 12:45 p.m. PST the same day.
The interaction of a cold dust cloud with a hot radiation field results in a loss in the continuum emission and appears as a dark feature in the radio wavelength image, Zadeh said. The dark features that trace the embedded molecular clouds provide astronomers with the size of the cloud in three dimensions.
Although not part of the work he is presenting, Zadeh said a good example of a dusty cloud that could be imaged with his technique is G2, the tiny cloud that is fast approaching Sgr A*, our galaxy's black hole.
The cloud now is too close to the black hole for Zadeh to take an image, but he is looking at earlier data to see if he can locate G2 as a radio dark cloud.
"If the cloud was farther away from the black hole than it is now, we could detect it," Zadeh said.
For his study, Zadeh used Green Bank Telescope maps and Very Large Array images from the National Radio Astronomy Observatory. The National Science Foundation (grant AST-0807400) supported the research.
The title of Zadeh's paper, which was published Nov. 1 by the Astrophysical Journal Letters, is "Imprints of Molecular Clouds in Radio Continuum Images."
Megan Fellman | EurekAlert!
What happens when we heat the atomic lattice of a magnet all of a sudden?
18.07.2018 | Forschungsverbund Berlin
Subaru Telescope helps pinpoint origin of ultra-high energy neutrino
16.07.2018 | National Institutes of Natural Sciences
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
19.07.2018 | Materials Sciences
19.07.2018 | Earth Sciences
19.07.2018 | Life Sciences