They are tackling this problem by studying the number of black holes in galaxies with different compositions. One of these galaxies, the ring galaxy NGC 922, is seen in this composite image containing X-rays from NASA's Chandra X-ray Observatory (red) and optical data from the Hubble Space Telescope (appearing as pink, yellow and blue).
X-ray: NASA/CXC/SAO/A.Prestwich et al; Optical: NASA/STScI
NGC 922 was formed by the collision between two galaxies – one seen in this composite image (where X-rays from Chandra are red and optical data from Hubble appear as pink, blue, and yellow) and another located outside the field of view. This collision triggered the formation of new stars in the shape of a ring. Some of these were massive stars that evolved and collapsed to form black holes. Astronomers are studying NGC 922 and other galaxies to determine the galactic composition that produces the biggest stellar-mass black holes.
NGC 922 was formed by the collision between two galaxies – one seen in this image and another located outside the field of view. This collision triggered the formation of new stars in the shape of a ring. Some of these were massive stars that evolved and collapsed to form black holes.
Most of the bright X-ray sources in Chandra's image of NGC 922 are black holes pulling material in from the winds of massive companion stars. Seven of these are what astronomers classify as "ultraluminous X-ray sources" (ULXs). These are thought to contain stellar-mass black holes that are at least ten times more massive than the sun, which places them in the upper range for this class of black hole. They are a different class from the supermassive black holes found at the centers of galaxies, which are millions to billions of times the mass of the sun.
Theoretical work suggests that the most massive stellar-mass black holes should form in environments containing a relatively small fraction of elements heavier than hydrogen and helium, called “metals” by astronomers. In massive stars, the processes that drive matter away from the stars in stellar winds work less efficiently if the fraction of metals is smaller. Thus, stars with fewer of these metals among their ingredients should lose less of their mass through winds as they evolve. A consequence of this reduced mass loss is that a larger proportion of massive stars will collapse to form black holes when their nuclear fuel is exhausted. This theory appeared to be supported by the detection of a large number (12) of ULXs in the Cartwheel galaxy, where stars typically contain only about 30% of the metals found in the sun.
To test this theory, scientists studied NGC 922, which contains about the same fraction of metals as the sun, meaning that this galaxy is about three times richer in metals than the Cartwheel galaxy. Perhaps surprisingly, the number of ULXs found in NGC 922 is comparable to the number seen in the Cartwheel galaxy. Rather, the ULX tally appears to depend only on the rate at which stars are forming in the two galaxies, not on the fraction of metals they contain.
One explanation for these results is that the theory predicting the most massive stellar-mass black holes should form in metal poor conditions is incorrect. Another explanation is that the metal fraction in the Cartwheel galaxy is not low enough to have a clear effect on the production of unusually massive stellar-mass black holes, and therefore will not cause an enhancement in the number of ULXs. Recent models incorporating the evolution of stars suggest that a clear enhancement in the number of ULXs might only be seen when the metal fraction falls below about 15%. Astronomers are investigating this possibility by observing galaxies with extremely low metal fractions using Chandra. The number of ULXs is being compared with the number found in galaxies with higher metal content. The results of this work will be published in a future paper.
A paper describing the results for NGC 922 was published in the March 10, 2012 issue of the Astrophysical Journal. The authors were Andrea Prestwich and Jose Luis Galache of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, MA; Tim Linden from University of Santa Cruz in Santa Cruz, CA; Vicky Kalogera from Northwestern University in Evanston, IL; Andreas Zezas from CfA and University of Crete in Crete, Greece; Tim Roberts from University of Durham in Durham, UK; Roy Kilgard from Wesleyan University in Middletown, CT; Anna Wolter and Ginevra Trinchieri from INAF in Milano, Italy.
NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge, Mass.
Megan Watzke | Newswise
SwRI-led team discovers lull in Mars' giant impact history
26.04.2017 | Southwest Research Institute
New survey hints at exotic origin for the Cold Spot
26.04.2017 | Royal Astronomical Society
More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.
Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...
Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
20.04.2017 | Event News
18.04.2017 | Event News
03.04.2017 | Event News
26.04.2017 | Materials Sciences
26.04.2017 | Agricultural and Forestry Science
26.04.2017 | Physics and Astronomy