| Services |
|
|
|
|
 |
|
| News |
|
|
|
|
|
|
|
|
|
| Channels |
| Home & Family |
|
|
|
|
|
|
|
| Leisure |
|
|
|
|
| Technology |
|
|
|
|
|
| Business |
|
|
|
|
| Science |
|
|
|
|
|
|
|
|
|
|
Site Search  |
|
|
|
|
| Free email |
|
|
|
|
 |
Scientists reveal how supermassive black holes bind into pairs during galaxy mergers |
| TheAllINeed.com |
(NC&T/SU) Then imagine that galaxy encountering its identical twin. The first galaxy merges with the second to produce a galaxy that's even grander and greater. Cosmologists think that's how galaxies grow—through a complex process of continuous mergers.
Now, using supercomputers to simulate galaxy mergers, scientists at Stanford and elsewhere have seen the formation of a new type of structure—a central disk of gas that can be from a hundred to a few thousand light years wide and from a few hundred million to a billion solar masses. They report the first simulated formation of a supermassive black hole (SMBH) pair in the June 7 edition of Science Express, an online version of Science magazine.
"The theory of General Relativity that Einstein developed about 90 years ago which describes the behavior of gravity has been verified in many of its predictions," says Stanford co-author Stelios Kazantzidis of the Kavli Institute for Particle Astrophysics and Cosmology. "However, there is one major consequence of this theory that has yet escaped verification, and this is the existence of gravitational waves. Due to the fact that coalescing SMBH binaries constitute the most powerful sources of gravitational-wave emission in the universe, it is of primary importance to establish the necessary conditions leading to the merger of two SMBHs."
Kazantzidis and Lucio Mayer from ETH Zurich (the Swiss Federal Institute of Technology) and the University of Zurich, the main authors, conceived the project and designed and conducted the numerical simulations. Monica Colpi from the University Milano-Bicocca and Piero Madau from the University of California-Santa Cruz helped interpret the results. Thomas Quinn from the University of Washington and James Wadsley from McMaster University wrote the code used to perform the simulations.
A SMBH binary consists of two SMBHs orbiting around their center of mass. The black holes may or may not merge depending on the existence of a mechanism that can extract angular momentum from their orbit and reduce their relative separation, Kazantzidis said.
 | | Scientists reveal how supermassive black holes bind into pairs during galaxy mergers. (Photo: Stanford U.) |
"A pair of SMBHs may interact with the stars around them or with the gas," he said. "Both the gas and the stars exert a frictional force onto the black holes. This frictional force extracts energy from the orbital motion of the SMBHs. As a result, the separation between them gradually shrinks." It is unclear whether it is the friction of the stars or that of the gas that dominates the process.
To model a galaxy merger, scientists first use a computer program that builds galaxies based on observations and theoretical predictions. For example, all galaxies are surrounded by extended, massive dark matter halos, and spiral galaxies contain a disk of stars. In all self-consistent models of disk galaxies these two components must be included.
"Once the galaxy models are constructed, we must parameterize the orbits of involved galaxies and set them on a collision course," Kazantzidis said.
The scientists found that when the merging galaxies contain some gas, their SMBHs will form a binary system in most cases. Once paired, the black holes may keep reducing their separation until they are about as far apart as our solar system's width, Kazantzidis said.
"At this point we predict that they should begin producing strong gravitational waves," he said. "Since the emission of waves extract energy from the binary black hole, the two holes will ultimately merge, less than a billion years after they had initially formed a binary."
This paper reports the first time that a galactic merger is followed through the formation of a gravitationally bound SMBH binary and down to scales of only a few light years.
While many earlier authors have investigated the formation of SMBH binaries using supercomputer simulations of galaxy collisions, Kazantzidis and his colleagues followed the processes over a wide range of spatial and temporal scales.
"With very few exceptions, earlier studies did not explore the role of gas in driving the evolution of a SMBH pair," Kazantzidis added. "Theoretical and observational evidence do suggest that the central regions of merger remnants contain significant amounts of gas. Our simulations provide new insights into how SMBHs form pairs and coalesce, and underscores the vital role of the gaseous component of galaxies in determining the fate of SMBHs."
Average galaxies such as the Milky Way do not contain such impressive gaseous nuclear disks, suggesting that mergers are important in forming these structures, Kazantzidis said. "Our simulations were the first to report the formation of such nuclear disks in galaxy mergers. It is natural to assume that the large reservoir of gas present in these nuclear disks represents the fuel that feeds the central supermassive black holes and powers the active galactic nucleus."
The results are good news for LISA, or the Laser Interferometer Space Antenna experiment, a space-based observatory designed to detect gravitational waves using laser interferometry over astronomical distances. The LISA detector is ideal for probing merging supermassive black holes such as those simulated by Kazantzidis and colleagues. A joint venture of NASA and the European Space Agency, LISA is expected to begin observations around 2015.
"Detecting the gravitational waves from the merging supermassive black holes will not only be the strongest confirmation of one of the most fundamental theories of physics (General Relativity) but also a confirmation of our general scenario for galaxy formation and evolution," Kazantzidis says. "This is one of the most beautiful examples of the deep connections between fundamental physics and astrophysics."
Simulations were performed on supercomputers at the Pittsburgh Supercomputing Center, the University of Zurich and ETH Zurich. "The numbers of calculations needing to be computed is astronomical," Kazantzidis said. "This is why we resort to powerful supercomputers capable of performing very large numbers of calculations per second. Supercomputer simulations allow us to effectively compress the vast cosmological timescales that apply to the largest structures in our universe down to weeks of virtual time. This gives us a completely new view of the universe from what is available to us by observation alone."
What's more, the supercomputers provide the closest thing to a physics lab that is available to the astrophysicist. "The numerical simulations we conducted constitute the most extensive calculations ever performed on this topic, consuming several months of supercomputing time each at various supercomputer centers around the world," he said.
While the merger that the scientists simulated—one where both galaxies have equal mass—is less probable than a merger of unequal galaxies, it's not at all improbable, Kazantzidis said. In fact, it's the fate of our own Milky Way.
"Our galaxy is in a collision course with its largest neighbor, Andromeda, due to take place in approximately three billion years time," Kazantzidis said. "The result of this collision will be the destruction of the disks and the formation of an elliptical galaxy."
Support for the work came from the U.S. Department of Energy, NASA and the Alexander von Humboldt Foundation.
How to make your home heating and cooling system cost effective? By: Ophelia Smith
Did your heating bill again knock your socks off? Why not mine? I have a 2100 plus square foot house but my heating system costs only $200 per month. As compared to me, your bill may be even more than $500. Why is there such a big difference? Let's know the basics to minimize this intolerable difference.
When it comes to my house, its visage is southern and obtains a good heat in winter seasons which turns into shade in summer. Most importantly, it is earth sheltered and on ground floor it is heated by propane heater. Additionally I have a wood stove for wintry days and even it is used for cooking whenever power is off. Higher altitude of mountainous location gives my home an appreciable air conditioning for free.
Now let's look on possible problems in your house. First of all your house may be in city where it gets little sun heat. Even though your house might be new and expensive but still I think insulation may be poor. Additionally you may have conventional gas heating and electric cooling system, both of which are expensive. In this way your house is sucking some extra money from your pocket. Obviously most of the houses in US are power controlled. So what you should do to save money? Here are three valuable strategies to do it efficiently.
1. Make sure to use less gas and power in extra efficient systems like air conditioners, hot water heaters and thermostats.
2. Insulation makes a big difference. You should try to increase insulation in structures which are not properly insulated. Cover all cabinets and shelves in the wall with doors. Also build a porch to shade the windows which will serve to save your home from hot sun. Investment in new sheet rock and insulation is required only once but your bill will come every month. Surely these are old ideas but we need to bring these ideas back to save some useful money.
3. While building your house you should ensure good science. Many builders avoid learning and doing something new so they use conventional ideas which are surely sucking our resources. Also poor quality systems are embedded in these extra large and too fragile houses. For this you need to learn all the basics so you become able to ask your builder for a higher quality.
Always remember houses built on small footprints have proved more energy efficient. Experiences have proved that smaller houses are cheaper to have proper heating and cooling system. Another way of proper heating and cooling is to stack the floors over each other. This way they work more efficiently and save some extra money. Similarly, earth sheltering is another useful approach. By this approach the under ground temperature remains 55 degree and it requires only a small amount of heating and dehumidifying. However some of these structures my not need any cooling or heating but still best thing about them is storm and fire resistance capability. Another option can be the addition of solar collectors to your yard and house. The idea of fireplace can be excellent in cold climates to have good heating environment in your house.
Does all this sounds good for you? Surely, if we go for good science rather than fashion, valuable money can be saved to invest some where else!
|
|
|
| Quotes | Barman, three German beers-said Tom drily.
Be an optimist, at least until they start moving animals in pairs to Cape Kennedy.
Anonymous.
A smart man covers his butt, a wise man simply leaves his pants on.
C.D. Bailey
|
| Writers | | If you are a writer and want to see your article published at Theallineed.com, just click here to submit. |
|
Fabulous Fremantle: Western Australia's shoppers paradise